Advanced Networking

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CS-260 ADVANCED NETWORKING

Table of Contents

CHAPTER 1 : FUNDAMENTALS OF NETWORKING I 1.1 1.2 1.3 1.4 1.# 1.% 1.( 1.) 1.* 1.1+ 1.11 1.12

1!1

Introduction................................................................................................................... 1-2 Functional Components of a Computer Network...................................................1-2 Major Tansmission Function.......................................................................................1-3 i!nal "ower.................................................................................................................... 1-4 i!nallin! $ate................................................................................................................ 1-4 &it $ate 's. &aud........................................................................................................... 1-% erial Transmission....................................................................................................... 1-% "arallel Transmission.................................................................................................... 1-( erial 's. "arallel Transmission.................................................................................1-( imple,- .alf-/uple, and Full-/uple, Transmission............................................1-) 0s1nc2ronous and 1nc2ronous Tansmission..........................................................1-) 0snc2ronous 's 1nc2ronous Tansmission..............................................................1-* 1.12.1 0s1c2ronous C2aracter Format.....................................................................1-* 1.12.2 1nc2ronous Messa!e Format......................................................................1-1+

1.13 1.14

Interfacin!.................................................................................................................... 1-11 $e3iew 4uestions......................................................................................................... 1-13 "!1

CHAPTER " : FUNDAMENTALS OF NETWORKING II 2.1 2.2

Modulation...................................................................................................................... 2-2 /i!ital i!nals and 0nalo! 1stems.........................................................................2-4 2.2.1 0mplitude 2ift 5e1in! 60 57......................................................................2-4 2.2.2 Fre8uenc1 2ift 5e1in! 6F 57.......................................................................2-# 2.2.3 "lase 2ift 5e1in! 6" 57.................................................................................2-#

2.3 2.4

T2e $ole of a Modem in /ata Communication........................................................2-% Communications $esource 2arin!............................................................................2-% 2.4.1 Multiple,in!....................................................................................................... 2-( 2.4.2 "ollin!.................................................................................................................. 2-*

2.# 2.%

Contention..................................................................................................................... 2-11 $e3iew 4uestions........................................................................................................ 2-12 #!1

CHAPTER # : TRANSMISSION MEDIA AND SWITCHING TECHNI$UES 3.1

Transmission Media...................................................................................................... 3-2 3.1.1 Twisted "air....................................................................................................... 3-2

3.1.2 Coa,ial Ca9le...................................................................................................... 3-3 3.1.3 :a3e ;uides...................................................................................................... 3-4

3.1.4 <ptical Fi9re..................................................................................................... 3-4 3.1.# Terrestrial Microwa3e....................................................................................3-% 3.1.% 3.2 atellite Microwa3e.........................................................................................3-( witc2in! Tec2ni8ues.................................................................................................. 3-) 3.2.1 Circuit witc2in!.............................................................................................. 3-* 3.2.2 Messa!e witc2in!.........................................................................................3-1+ 3.2.3 "acket witc2in!............................................................................................. 3-11 3.3 $e3iew 4uestions........................................................................................................ 3-14 %!1

CHAPTER % : NETWORK SECURIT& 4.1 4.2

Introduction................................................................................................................... 4-2 Network Faults.............................................................................................................. 4-2 4.2.1 0ttenuation........................................................................................................ 4-2 4.2.2 /ela1 /istortion................................................................................................ 4-3 4.2.3 Noise.................................................................................................................... 4-3

4.3

=rror /etection and Correction Tec2ni8ues..........................................................4-3 4.3.1 =3en > <dd "arit1............................................................................................. 4-4 4.3.2 ?on!itudinal $edundanc1 C2eck 6?$C7 and 'ertical $edundanc1 C2eck 6'$C7.................................................................................................................... 4-#

4.4 4.# 4.% 4.(

0ssurin! =rror-free data Communication...............................................................4-% T2e 0utomatic $epeat > $e8uest 60$47 1stem.................................................4-% Flow Control................................................................................................................... 4-( 4.%.1 0$4 lidin! :indow "rotocol.......................................................................4-( .uman Interference.................................................................................................... 4-) 4.(.1 0ut2entication.................................................................................................. 4-) 4.(.2 =ncr1ption.......................................................................................................... 4-) 4.(.3 /ata Compression........................................................................................... 4-1+

4.)

$e3iew 4uestions........................................................................................................ 4-1+ '!1

CHAPTER ' : OSI MODEL AND TCP ( IP #.1 #.2 #.3 #.4 #.#

<pen 1stems Interconnection.................................................................................#-2 ?a1ered 0rc2itecture Concept..................................................................................#-3 ?a1ers- er3ices and Functions.................................................................................#-4 =ntities- "rotocol and Interfaces.............................................................................#-# < I $eference Model................................................................................................. #-% #.#.1 "21sical ?a1er.................................................................................................... #-( #.#.2 /ata ?ink ?a1er................................................................................................. #-) #.#.3 Network ?a1er.................................................................................................. #-*

#.#.4 Transport ?a1er............................................................................................... #-11 #.#.# ession ?a1er............................................................................................................... #-12

CHAPTER 1 : FUNDAMENTALS OF NETWORKING I
C)a*te+ Ob,e-t./es @pon completion of t2is c2apter- 1ou will 9e a9le toA

⇒ descri9e w2at is data communicationB ⇒ descri9e t2e functional components of a data communication networkB ⇒ descri9e major transmission functionsB ⇒ differentiate 9etween serial and parallel transmissionB ⇒ differentiate 9etween s1nc2ronous and as1nc2ronous transmissionB ⇒ descri9e 9it rate and 9aud rateB ⇒ descri9e simple,- 2alf duple, and full duple, transmissionB ⇒ descri9e Interface standard $ -232C. 1 1 Int+o01-t.on 0 computer network is defined as an interconnection of network components t2at allow mo3ement of information 9etween t2e users. T2e users ma1 9e t2e end-users or ser3ice pro3iders. T2e t1pes of information t2at are carried 91 a computer network 2as si!nificantl1 c2an!ed o3er t2e 1ears. In t2e 1*(+Cs t2is information was mostl1 3oice wit2 3er1 small amount of data. T2is 2as c2an!ed in present decade and will keep on c2an!in! in t2e 1ears to come. Now t2e information includes 3oice- te,t- data- 3ideo and ima!es. =ac2 of t2ese t1pes of information places different re8uirements on t2e network. T2e speed at w2ic2 t2is information needs to 9e mo3ed 3aries from 1++ 9its>sec 6for telemetr1 t1pes of application7 to 1++ m 9its>sec 6for 2i!2 resolution T' application7. 1 " F1n-t.onal Co2*onents of a Co2*1te+ Net3o+4 Network components can 9e an1 piece of 2ardware or software t2at 2elps in t2e mo3ement of information. T2e fi!ure 9elow s2ows some of t2e possi9le candidates of network components.

1-6

CS260

CHAPTER 1: FUNDAMENTALS OF NETWORKING I

Customer premises components Telephones Data terminals Workstations LAN

Network components

Transmission Switching Signalling Network Management



Figure 1-1

er3ices pro3ided 91 a data communication network are pro3ided 91 two major cate!ories of componentsB customer premises component and t2e network components. T2e customer premises components include all t2e terminals and ot2er communication e8uipment t2at reside in customer premises. T2e most common one is- of course- t2e telep2one set. It also includes "CCs and work stations etc. <n t2e ot2er 2and network components will pro3ide connecti3it1 functions so t2at t2e terminals can communicate effecti3el1. Network components include transmission links- switc2in! nodessi!nallin! links etc. Network components pro3ide four major ser3ices and t2e1 areA ♦ ♦ ♦ ♦ Transmission witc2in! i!nallin! Network Mana!ement

In t2is particular su9ject we will 9e concentratin! on customer premises e8uipment and t2e tec2nolo!1 9e2ind t2em. ome of t2e underl1in! tec2nolo!ies 9e2ind transmission will 9e discussed in t2is and su9se8uent c2apters for a 9etter understandin!. 1 # Ma,o+ T+ans2.ss.on F1n-t.on T2e major transmission functions include t2e followin! A ♦ Transmittin! > $ecei3in! • T2e 9asic function of transmission is to transmit information o3er a media to t2e recei3in! side. 0n e,ample will 9e a telep2one set w2ic2 includes a transmitter and recei3er. ♦ Modulation > /emodulation • Modulation con3erts a si!nal from one form to anot2er formsuita9le for transmission. /emodulation restores t2e si!nal 9ack to its ori!inal form. 0n e,ample will 9e t2e use of modem to con3ert di!ital si!nal to analo! and 3ice-3ersa.

1-7

CS260

CHAPTER 1: FUNDAMENTALS OF NETWORKING I

Transmitting terminal Transmitting Modulation Coding Multiple"ing

Medium

Intermediatede vice Signal Ampli ication S!nchronisation

Medium

Receiving terminal Receiving Demodulation Decoding Demultiple"ing

Figure 1-2
♦ Codin! > /ecodin! • Codin! is a tec2ni8ue t2at defines 8uantiDed si!nals into a predetermined 9inar1 se8uence for transmission on a di!ital s1stem. 0t t2e recei3in! end t2e si!nal is decoded. T2is tec2ni8ue is used for 9etter s1nc2ronisation and error detection. ♦ Multiple,in! > /emultiple,in! • Multiple,in! is a tec2ni8ue t2at ena9les a num9er of communication c2annels to 9e com9ined and transmitted o3er a common 9road9and c2annel. 0t t2e recei3in! end- demultiple,in! of t2e 9road9and c2annel separates and reco3ers t2e ori!inal c2annels. T2e primar1 purpose of multiple,in! is to make efficient use of transmission facilities 9andwidt2 capa9ilit1 to ac2ie3e a low transmission cost. ♦ i!nal amplification or re!eneration • 0s si!nals tra3el t2rou!2 t2e transmission media- t2e stren!t2 of t2e si!nal decreases wit2 distance 9ecause of losses. T2ese si!nals must 9e amplified 6analo!7 or re!enerated 6di!ital7 in order to 2a3e accepta9le le3els at t2e recei3in! end. ♦ 1nc2ronisation • 1nc2ronisation is re8uired in a network for accurate fre8uenc1 and sta9le time si!nals to co-ordinate numerous analo! and di!ital transmission. In a di!ital s1stem- s1nc2ronisation is especiall1 important. 1 % S.5nal Po3e+ i!nal power is a 3er1 important parameter in a transmission s1stem. :2en si!nal tra3els t2rou!2 t2e transmission media- t2e stren!t2 of a si!nal attenuates wit2 distance. It is important to know t2e si!nal power at 3arious points alon! t2e transmission pat2. =ac2 si!nal possesses a uni8ue power w2ic2 is con3entionall1 e,pressed in terms of watts- mw- uw- nw and pw. &ut t2ere are times t2at si!nal power at 3arious points of a transmission network are too small to 9e e,pressed in con3entional units. T2e unit d&m 9ecomes 2and1. ♦ ♦ =,pression of d&m from mw to d&9

1-8

CS260

CHAPTER 1: FUNDAMENTALS OF NETWORKING I " 6d&m7 E 1+ lo! "6mw7

• ♦

from d&m to mw • " 6mw7 E 1+ "6d&m7>1+

=,ampleA =,press t2e transmitted and t2e recei3ed si!nal powers in d&m. tudents s2ould 9e aware of t2e numerical distinction 9etween t2e con3entional power unit and d&m. Tanjon! "a!ar 1 watt olutionA Transmitted power E 1 watt E 1+lo!1+3 $ecei3ed power E 1 mw E 1+ lo! 1++ 1 ' S.5nall.n5 Rate T2e rate of transmission in data communication s1stems is e,pressed in terms of num9er of 9its sent per second or t2e num9er of si!nallin! elements sent per second. /ependin! on t2e application- 9ot2 measures are important. E +d&m E 1+
3

/2o91 ;2aut 1 mw

E 3+d&m E 1++ mw

T2e si!nallin! rate is e,pressed as t2e num9er of si!nallin! elements per second or 9aud. 0 1%++ 9aud transmission t2en- is one t2at sends 1%++ si!nallin! elements per second.

Amplitude

Time # second
Signaling rate $ % &aud

Figure 1-3
T2e definition of a si!nallin! element will depend on t2e transmission sc2eme used. In t2e e,ample s2own a9o3e- pulses are defined as si!nallin! elements. /ifferent si!nallin! elements wit2in a transmission mi!2t 2a3e different

1-9

CS260

CHAPTER 1: FUNDAMENTALS OF NETWORKING I duration. T1picall1 9aud is calculated 9ased upon t2e si!nallin! element of t2e s2ortest len!t2. T2us if t2e s2ortest si!nallin! element last 1 secondst2e 9and is 1>1.

1 6

7.t Rate 8s 7a10 &aud and 9it rates are not alwa1s t2e same. T2is is 9ecause of t2e reason t2at a si!nallin! element can carr1 more t2an a sin!le 9it of data. T2e relations2ip 9etween 9aud and 9it rate isA

9it rate6in 9its>sec7 E 6si!nallin! rate in 9and7 F 6num9er of 9its per si!nal element7. T2e 9it rate is !i3en as t2e num9er of 9its per second 69ps7. If eac2 si!nallin! element carr1 one 9it of data t2en 9ps E 9aud. =,ampleA

'olta!e ?e3el Information content

+ 3olts

++

2 3olts

+1

4 3olts

1+

% 3olts

11

T2en +1 11 ++ +1 1+ 11 ++ will 9e transmitted asA

Amplitude

% * + ,

Time
'()) milliseconds
i!nallin! $ate E 1>6.)33 F 1+ -37 E 1-2++ 9aud

1 - 10

CS260

CHAPTER 1: FUNDAMENTALS OF NETWORKING I

&it $ate E 1-2++ F 2 E 24++ 9its per second 1 9 Se+.al T+ans2.ss.on In serial transmission- data 9its of a c2aracter are transmitted seriall1 one 9it after anot2er. T1picall1 t2e least si!nificant 9it of a c2aracter is transmitted first. erial transmission is slow as t2e 9its are sent one at a time on a sin!le pat2. Conse8uentl1 to transmit a c2aracter w2ic2 consists of ) 9its- ) 9it-times is re8uired for transmission.

Signal

# , , # , , # , # , # ,, # , # ,,, # , # ,, # LSLSLS-

Figure 1-4
1 : Pa+allel T+ans2.ss.on In parallel transmission a dedicated pat2 is allocated to eac2 9it position in t2e c2aracter. Conse8uentl1 ) pat2s need to 9e a3aila9le to transmit a ) 9it c2aracter. In t2e e,ample s2own 9elow t2e most si!nificant 9it is transmitted on t2e top pat2 w2ere as t2e least si!nificant 9it is transmitted on t2e 9ottom pat2.

Receiver

Transmitter ms&

ls& clock

Figure 1-

For parallel transmission an e,plicit clock si!nal is re8uired w2ic2 is critical. It is a re8uirements t2at all 9its of a c2aracter are transmitted at t2e same time so t2at t2e1 can 9e correctl1 recei3ed 91 t2e recei3er. T2e rate of transmission is controlled 91 t2e clock. T2e clock si!nal informs t2e recei3er w2en it s2ould record or sample all of its inputs simultaneousl1.

1 - 11

CS260

CHAPTER 1: FUNDAMENTALS OF NETWORKING I <ne major pro9lem in parallel transmission is skew. T2e transmitter to send all 9its of a c2aracter at t2e same time uses t2e clock si!nal. <3er lar!e distances 6a9o3e 1++ feet7- t2e 9its can lose t2e relati3e timin! relations2ip. T2e arri3al of t2e 9its from t2e same c2aracter at different times at t2e recei3er is called skew. kew occurs 9ecause t2e propa!ation dela1 is not identical for all transmission pat2s. Increase in distance will cause increase in skew impl1in! a proportional relations2ip. i!nificant skew will cause t2e 9its to 9e recei3ed wron!l1 at t2e recei3in! end w2ic2 will mean recei3in! wron! c2aracter. <ne wa1 to reduce skew is to reduce t2e transmission distance. $ecommended transmission distance ran!es from fift1 to se3ent1 fi3e feet.

1 ;

Se+.al 8s Pa+allel T+ans2.ss.on T1pical usa!e of parallel transmission is 9etween central processin! unit and its perip2erals suc2 as disk dri3es- printers and tape dri3ers. "arallel nature of connection is

1 - 12

CS260

CHAPTER 1: FUNDAMENTALS OF NETWORKING I consistent wit2 mac2ines internal arc2itecture and it pro3ides 2i!2 speed data transmission. <ne disad3anta!es of parallel transmission is t2at it is e,pensi3e 9ecause of t2e num9er of transmission pat2s. It also re8uires transmission and recei3in! e8uipment to 2a3e )-9it internal arc2itecture. T2e cost increases wit2 t2e distance of transmission.

<n t2e ot2er 2and serial transmission is t1picall1 used for lon! distancecomputer to computer communication. erial connections can co3er lar!e distances at a comparati3el1 low cost and are relati3el1 eas1 to 9uild. erial communication 2as a low data t2rou!2put compared to its parallel counterpart. Furt2ermore- t2ere is an additional o3er2ead due to serial>parallel con3ersion t2at needs to 9e performed. 1 1< S.2*le=> Half !D1*le= an0 F1ll !D1*le= T+ans2.ss.on imple, transmission means t2at t2e flow of information is onl1 in one direction. For e,ample an input de3ice 6card reader or remote sensor7 attac2ed to a computer could 9e confi!ured in suc2 a wa1 so t2at it can onl1 transmit and can ne3er recei3e. <n t2e ot2er 2and- output de3ices 6printer or monitor7 can 9e confi!ured to recei3e data onl1. Normall1 imple, kind of transmission is not used !enerall1 9ecause of lack of 2and s2akin!.

.alf duple, 6./F7 transmission means t2at t2e connection is 9idirectional9ut information can onl1 flow in one direction at a time. Two- wa1 radios are e,ample of t2e 2alf-duple, s1stem.

Full /uple, 6F/F7 transmission means t2at 9ot2 stations ma1 transmit to eac2 ot2er at t2e same time. Full duple, transmission usuall1 re8uires two separate transmission pat2s. "eople talkin! to eac2 ot2er o3er t2e p2one is an instance of full duple, communication. 1 11 As?n-)+ono1s an0 S?n-)+ono1s T+ans2.ss.on erial transmission can 9e accomplis2ed usin! eit2er 1nc2ronous or 0s1nc2ronous tec2ni8ues. In as1nc2ronous transmission eac2 c2aracter in a messa!e is transmitted as an indi3idual entit1 irrespecti3e of w2en t2e pre3ious c2aracter was transmitted. 0t least two framin! 9its are associated wit2 eac2 c2aracterB one framin! 9it indicates t2e 9e!innin! of t2e c2aracter 6start 9it7 and at least one framin! 9it indicates t2e end of t2e c2aracter 6stop 9it7. T2e ratio of framin! 9its to data 9its is 2i!2. 0t least ten 9its need to 9e transmitted in order to transmit an )-9it c2aracter accountin! for )+G utilisation. 0s1nc2ronous transmission is commonl1 used 9etween terminals and computers. T2is is 9ecause t2e terminal users are relati3el1 slow in enterin! data. ♦ 0s1nc2ronousA

1 - 13

CS260

CHAPTER 1: FUNDAMENTALS OF NETWORKING I

#,,##,# , #

,#,, # # ,

.raming ls&

ms& .raming

Figure 1-!

1 - 14

CS260 1nc2ronousA

CHAPTER 1: FUNDAMENTALS OF NETWORKING I



#,,##,#,#,#,,##,

ls&

ms&

Figure 1-"
1nc2ronous transmission means t2at all c2aracters in a messa!e are transmitted one after anot2er conti!uousl1. Framin! c2aracters indicate t2e 9e!innin! and end of t2e messa!e 9lock. T2e ratio of framin! c2aracters to data c2aracters is low. Conse8uentl1 line efficienc1 in e,cess of ** percent can 9e maintained. 1nc2ronous transmission is commonl1 used for computer communication. Computers can take ad3anta!e of t2e 2i!2 line efficienc1 since t2e1 t1picall1 maintain a 2i!2 transmission speed and send 9locks of c2aracters at a time. 1 1" As?n-)+ono1s 8s S?n-)+ono1s T+ans2.ss.on 0s1nc2ronous transmission 2as a lower cost and is eas1 to implement. 1nc2ronisation 9etween t2e transmitter and recei3er is relati3el1 simple as indi3idual c2aracters are sent independentl1 wit2 itCs own framin! information. 0s1nc2ronous transmission is less efficient and t2e 9est utilisation t2at can 9e ac2ie3ed is )+G.

1nc2ronous transmission on t2e ot2er 2and is used for interconnection of 2i!2 speed de3ices. &ecause of t2e 2i!2 speed- a met2od for automatic error detection and correction is re8uired. 1nc2ronous transmission re8uires sop2isticated timin! met2od. In addition to determinin! t2e 9e!innin! and end of 9lock of c2aracters- t2e recei3er must also determine t2e duration of eac2 9it. &ot2 steps are re8uired to successfull1 recei3e a 9lock. ince s1nc2ronous transmission speeds ma1 9e se3eral million 9its per secondeit2er an e,tremel1 accurate clock must 9e present at all transmitters or recei3ers- or else a si!nal transmission tec2ni8ue is re8uired t2at pro3ides timin! information. T2e latter is t2e preferred solution.

/ue to re8uired automatic error-reco3er1 procedure- timin! consideration and comple, si!nallin! tec2ni8ues- 1nc2ronous transmission is more e,pensi3e t2an its 0s1nc2ronous counterpart. 1 1" 1 As?n-)+ono1s C)a+a-te+ Fo+2at T2e dia!ram 9elow s2ows t2e format of an as1nc2ronous c2aracter. <9ser3e t2at t2e line state ma1 9e eit2er 2i!2 6M0$57 or low 6 "0C=7. .istoricall1- t2e presence of a 3olta!e on t2e line indicates t2e M0$5 state- and t2e a9sence of a 3olta!e indicates a "0C= state.

1 - 15

CS260

CHAPTER 1: FUNDAMENTALS OF NETWORKING I :2en t2e transmitter is not sendin! an1 si!nal- t2e line is idle. 0n idle line is kept in t2e M0$5 state to distin!uis2 lack of transmission from a cut wireB a cut wire would lose power and present itself in t2e "0C= state.

T2e as1nc2ronous c2aracter- is preceded 91 a framin! 9it called t2e T0$T 9it. T2e T0$T 9it is alwa1s in t2e "0C= statusB t2us- t2e recei3er knows t2at a c2aracter is arri3in! w2en it detects t2e M0$5-to- "0C= transition. T2is transition also s1nc2ronises t2e recei3erCs clock.

T2e ne,t HNH 9it-times will 9e comprised off t2e data 9its- w2ere t2ere are HNH 9its in eac2 c2aracter. In practice- t2e most common 3alue for N is ei!2t. Note t2at t2e ? & of t2e c2aracter is most commonl1 sent first. If parit1 is used- it will 9e t1picall1 placed in t2e most si!nificant 6M &7 position.

Start -its MAR/ S0AC1 ls& Data -its

Stop Interval

Idle Line

Figure 1-#
T2e c2aracter is followed 91 a T<" inter3al- w2ic2 must last for at least 1- 1.# or 2 9it times. T2e T<" inter3al alwa1s returns t2e line to t2e M0$5 state. T2is ensures t2at if two as1nc2ronous c2aracters are sent conti!uousl1- t2e M0$5-to- "0C= transition will still occur w2en t2e T0$T 9it presents itself. 0 lon! T<" inter3al is re8uired for t2ose de3ices t2at need additional time to reset after recei3in! a c2aracter. T2e transmitter and recei3er must a!ree upon a num9er of parameters in order to 2a3e successful communication. T2ese parameters include t2e num9er of 9its per c2aracter- t2e len!t2 of a 9it time 6i.e. t2e transmission speed7- t2e num9er of T<" 9its- electrical si!nal le3els- t2e order of 9it transmission- and t2e c2aracter code. 1 1" " S?n-)+ono1s Messa5e Fo+2at T2e followin! dia!ram s2ows t2e format of a !eneric s1nc2ronous messa!e. 0 s1nc2ronous messa!e is t1picall1 referred to as a 9lock or a frame. 0 s1nc2ronous messa!e is sent as a conti!uous 9it stream- wit2 no 9reak 9etween c2aracters.

0 s1nc2ronous messa!e !enerall1 comprises t2e followin! fieldsA

1 - 16

CS260

CHAPTER 1: FUNDAMENTALS OF NETWORKING I

S2NC char

Message 3eader

Data

Message Trailer

Figure 1-$

1 - 17

CS260

CHAPTER 1: FUNDAMENTALS OF NETWORKING I



1nc2ronous C2aracters • T2ese c2aracters indicate to t2e recei3er t2at a messa!e is a9out to 9e recei3ed. Furt2er more- t2e1 define ei!2t-9it 9locks so t2at t2e indi3idual c2aracters can 9e correctl1 interpreted



Messa!e .eader • &e!innin!-of-messa!e framin!- w2ic2 ma1 include t2e se8uence num9er of t2e 9lock 6or frame7



/ata • @se information



Messa!e Trailer • =nd-of-messa!e framin!- w2ic2 ma1 include error detection information

♦ uccessful s1nc2ronisation transmission will depend upon t2e a!reement of se3eral parameters in as1nc2ronous transmission. T2ese parameters include • • • • 1 1# Inte+fa-.n5 /i!ital de3ices !enerate di!ital si!nals and t2e1 are not capa9le of transmittin! t2is di!ital data to a lon!er distance. o t1picall1 di!ital de3ices are not tied to t2e transmission facilit1 directl1. Computers and terminals are termed as /ata Terminal =8uipment 6/T=7. T2e de3ice w2ic2 2elps /T= for data communication is known as /ata circuit-terminatin! e8uipment 6/C=7 and it sits 9etween t2e /T= and t2e transmission media. Modem is one e,ample of /C=. <n t2e transmission side- /C= recei3es data from /T= and transmits data o3er t2e transmission media. <n t2e recei3er end- t2e /C= recei3es data from transmission media and passes it to t2e /T=.
RS4+)+C 0C Modem Modem 0C

?en!t2 of a 9it time 6data rate7 i!nal le3els INC c2aracters iDe and content of t2e messa!e 2eader and trailer

DT1

DC1

DC1

DT1

Figure 1-1%

1 - 18

CS260

CHAPTER 1: FUNDAMENTALS OF NETWORKING I In order to standardise t2e interface 9etween /T= and /C=- t2e =lectronics Industries 0ssociation in t2e @nited tates 2as come out wit2 a interface standard known as $ -232C. T2is $ -232 interface standard is descri9ed 91 means of mec2anical- electrical- functional and procedural specifications. Mec2anical specification deals wit2 t2e p21sical connection of /T= and /C= w2ereas t2e electrical specification deals wit2 3olta!e le3els and timin! of 3olta!e c2an!es. Functional specifications specif1 t2e functions t2at are performed 91 different circuits. "rocedural specification specifies t2e protocol 9etween /T= and /C= .

$ 232-C ♦ $ 232-C standard is specified in terms of t2e four specifications mentioned a9o3e and t2e1 areA • Mec2anical pecification

$ 232-C is a 2# pin connector w2ere t2e pins are or!anised into two rows. "ins num9ered 1-13 are in t2e top row w2ere as t2e pins num9ered 14-2# are in t2e 9ottom row. 0ll ot2er mec2anical dimensions are specified in t2is specification. =lectrical pecification In $ -232C standard- 3olta!e !reater t2an J4 3olt is considered as lo!ical + and 3olta!e smaller t2an -3 3olt is considered as lo!ical 1. T2e ca9le len!t2 9etween two $ -232C connector can ran!e a ma,imum of 1# meters and it can support a data rate of 2+ k9ps. Functional pecification 0lt2ou!2 $ -232C is a 2# pins connector- onl1 * of t2e pins are alwa1s used in practice. Functional specification sa1s t2at t2e circuits connected to t2e pins can 9e !rouped into four !roups i.e. data- control- !round and timin!. /ata !roups include transmit and recei3e si!nals w2ic2 are connected to pin 2 and 3 respecti3el1. :2ene3er t2e "C wants to transmit data to t2e modem- it uses t2e transmit line and it uses t2e recei3e line to !et data from modem. Control !roup include control si!nals like $e8uest To end 6$T 7 and Clear To end 6CT 7 lines w2ic2 are connected to pin 4 and # respecti3el1. "C uses $T si!nal to inform t2e modem t2at it wants to transmit data. T2e modem sends CT si!nal to t2e "C to inform t2at t2e modem is read1 to recei3e data from t2e "C. Timin! !roup includes clock si!nals w2ic2 are used for s1nc2ronous transmission. ;round !roup is t2e set of circuits used for !roundin!. "rocedural pecification

• -

• -



1 - 19

CS260

CHAPTER 1: FUNDAMENTALS OF NETWORKING I T2e procedural specification for $ -232C specifies t2e se8uence of e3ents t2at occur 9etween /C= and /T= in order to transmit

-

Computer

5+,6 Data terminal read! 5(6 Carrier Detect 576 Signal 8round 5%6 Data Set Read! 596 Clear To Send 5*6 Re:uest To Send 5)6 Receive 5+6 Transmit 5#6 Shield

Modem

data. T2e se8uence of e3ents t2at occur 9etween computer and modem durin! communication are listed 9elowA 1. :2en t2e computer is powered up- it sends a /ata Terminal $ead1 si!nal to t2e modem. 2. :2ene3er t2e modem powers up- it sends a /ata et $ead1 si!nal to t2e "C. ♦ Transmit

3. :2ene3er t2e "C wants to transmits data- it sends $e8uest To end si!nal to t2e modem. 4. In response- t2e modem transmit a carrier fre8uenc1 on telep2one line and sends Clear To end si!nal to t2e "C to indicate t2at it is read1 to recei3e data from t2e computer. #. In response to /C= si!nal- t2e computer transmits data o3er t2e transmit line. ♦ i7 $ecei3e

:2ene3er t2e modem detects a carrier fre8uenc1 on t2e transmission line- it means t2at t2e remote modem is transmittin!. o- modem sends a carrier detect si!nal to t2e computer. ii7 line. In response "C recei3es t2e incomin! data o3er t2e $ecei3e

1 1%

Re/.e3 $1est.ons 1. /escri9e in detail- t2e major functions in transmission.

2. :2at is parallel transmissionK @nder w2at condition will 1ou c2oose parallel transmission o3er serial transmissionK 3. /escri9e simple,- 2alf-duple, and full duple, transmission. 4. :2at is 9aud rateK :2at is t2e difference 9etween 9aud and 9it rateK

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CS260

CHAPTER 1: FUNDAMENTALS OF NETWORKING I #. <utline t2e difference 9etween s1nc2ronous and as1nc2ronous transmission. %. :2at will 9e t2e o3er2ead of transmission if ( 9it 0 CII c2aracter is transmitted usin! as1nc2ronous transmission. 0ssume 1 T0$T- 1 T<" and 1 parit1 9it. (. /escri9e t2e 2and s2akin! si!nals t2at are e,c2an!ed 9etween a "C and a modem durin! data transmission usin! $ -232C link. ). :2at is $ -232CK :rite down t1pical applications of $ -232C. *. :2at are standardsK :21 do we need standardK ?ist down a few of t2e standard 9odies and t2eir functions. 1+. :2at are t2e different functional components of a computer networkK

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CHAPTER 2: FUNDAMENTALS OF NETWORKING II
C)a*te+ Ob,e-t./es @pon completion of t2is c2apter- 1ou will 9e a9le toA ⇒ descri9e 3arious modulation tec2ni8uesB ⇒ descri9e t2e role of t2e modem in data communicationB ⇒ descri9e communications resource s2arin! concepts suc2 as multiple,in!pollin! and contention. " 1 Mo01lat.on Modulation is a si!nal process w2ic2 s2ifts t2e si!nal from one fre8uenc1 ran!e to anot2er so t2at t2e si!nal can 9e transmitted properl1. T2e si!nal is encoded into a carrier si!nal wit2 fre8uenc1 t2at is compati9le wit2 t2e transmission medium 9ein! used.

Input signal

;
carrier signal

Modulated signal

Figure 2-1
T2e input si!nal is called t2e modulatin! si!nal or 9ase9and si!nal w2ic2 can 9e eit2er analo! or di!ital. T2e output si!nal is called t2e modulated si!nal. ♦ T2ere are 3 t1pes of modulationA • 0mplitude Modulation 60M7 T2e amplitude of t2e carrier si!nal c2an!es accordin! to t2e 3ariation of t2e input si!nal.

Figure 2-2

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CS260

CHAPTER 2: FUNDAMENTALS OF NETWORKING II Fre8uenc1 Modulation6FM7 • T2e fre8uenc1 of t2e carrier si!nal c2an!es accordin! to t2e 3ariation of t2e input si!nal



Figure 2-3
♦ "2ase Modulation 6"M7 • T2e p2ase of t2e carrier si!nal c2an!es accordin! to t2e 3ariation of t2e input si!nal.

Figure 2-4

2 - 23

CS260 " "

CHAPTER 2: FUNDAMENTALS OF NETWORKING II D.5.tal S.5nals an0 Analo5 S?ste2s :2en di!ital si!nals are transmitted on an analo! s1stem- t2e discrete elements are transmitted as continuous si!nals. Normall1 di!ital data is transmitted o3er analo! network usin! t2is tec2ni8ue. T2is t1pe of data t1picall1 re8uires t2e use of Modem 6Modulator>/emodulator7. T2e modem modulates t2e di!ital data into an e8ui3alent analo! form at t2e transmission end and at t2e recei3in! end it reconstructs t2e di!ital data from t2e analo! si!nal recei3ed.

In most of t2e applications- data is represented as a di!ital si!nal 91 t2e /T= 6/ata Terminal =8uipment e.!. "C7. T2is di!ital si!nal is t2en supplied to t2e modem for modulation or recei3ed from t2e modem as a demodulated si!nal. ♦ 0 few of t2e modulation tec2ni8ues areA • • • 0mplitude 2ift 5e1in!60 57

Fre8uenc1 2ift 5e1in!6F 57 "2ase 2ift 5e1in!6" 57 " " 1 A2*l.t10e S).ft Ke?.n5 @ASKA In amplitude s2ift ke1in!- t2e di!ital input is con3erted to analo! si!nals w2ere t2e amplitude of t2e si!nal represents t2e di!ital input.

Figure 2In t2e dia!ram a9o3e two-le3el codin! 2as 9een demonstrated w2ere t2e analo! si!nal 2as two different amplitude le3els representin! eit2er a L1C or a L+C. In t2e fi!ure a9o3e 2i!2er amplitude si!nal represents a L1C and low amplitude represents a L+C. T2e fre8uenc1 and p2ase of t2e si!nal remains unc2an!ed. 0 5 can 9e e,panded to carr1 additional 9its 91 definin! additional amplitude le3els. &ecause of t2e suscepti9ilit1 to interference from noise- 0 5 tec2ni8ues are rarel1 used in modems.

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CS260

CHAPTER 2: FUNDAMENTALS OF NETWORKING II

" " " F+eB1en-? S).ft Ke?.n5 @FSKA In fre8uenc1 s2ift ke1in!- t2e di!ital input is con3erted to analo! si!nal w2ere t2e fre8uenc1 of t2e analo! si!nal represents t2e di!ital

Figure 2-!
input. T2e a9o3e dia!ram s2ows two-le3el codin! w2ere t2e 2i!2er fre8uenc1 represents a L1C and lower fre8uenc1 represents L+C. T2e amplitude and p2ase of t2e analo! si!nal remains unc2an!ed. imilar to 0 5- F 5 can 9e e,panded to carr1 additional fre8uenc1 le3els. F 5 tec2ni8ues are commonl1 used in ine,pensi3e- low speed modems 612++ 9ps and 9elow7. " " # P)ase S).ft Ke?.n5 @PSKA In p2ase s2ift ke1in!- t2e amplitude and fre8uenc1 of t2e si!nal remains unc2an!ed. 0t t2e 9e!innin! of a 9it time- t2e p2ase of t2e

Figure 2-"
si!nal is c2an!ed.

" 5 tec2ni8ues is commonl1 used in modems.

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CS260

CHAPTER 2: FUNDAMENTALS OF NETWORKING II

" #

T)e Role of a Mo0e2 .n Data Co221n.-at.on T2e /T= 6/ata Terminal =8uipment e.!. "C7 !enerates or recei3es di!ital si!nals. T2e modem transforms t2e di!ital si!nal into an e8ui3alent analo! si!nal and send t2rou!2 t2e analo! network 6suc2 as t2e analo! Telep2one network7. <n t2e recei3in! end- t2e analo! si!nal is recei3ed 91 t2e recei3in! modem w2ic2 transforms t2e si!nal into di!ital si!nals and deli3ers t2ese to t2e /T=.

T2e network supplies t2e user wit2 a 9and-limited c2annel. For e,ample t2e filter in t2e analo! telep2one network supplies t2e user wit2 a c2annel w2ic2 2as a pass 9and of appro,imatel1 3++.D to 33++.D. If we transmit 2i!2speed di!ital data t2rou!2 t2is c2annel- t2e output will !et distorted 9ecause of t2e remo3al of 2i!2 fre8uenc1 si!nal components. T2e modem 2owe3er con3erts t2e di!ital si!nal to an analo! si!nal 2a3in! onl1 fre8uenc1 components t2at can pass t2rou!2 t2e pass9and of t2e c2annel. T2is allows all t2e fre8uenc1 components of t2e analo! si!nal to pass t2rou!2 t2e analo! network undistorted. " % Co221n.-at.ons Reso1+-e S)a+.n5 $esource 2arin! in communications means allocation of a common 2i!2 capacit1 transmission facilit1 to more t2an one user. ?on! distance transmission facilities 2a3e a lar!e 9andwidt2 for communication and are usuall1 e,pensi3e. 0 sin!le user !enerall1 does not re8uire suc2 a 2i!2 capacit1 for transmission and it also 9ecomes 8uite e,pensi3e for a sin!le user to afford. For e,ample- a twisted pair media 2as a 9andwidt2 of 1+M.Dmuc2 more t2an t2e t1pical 2ome computer can utilise. o we need to pro3ide a capa9ilit1 so t2at a num9er of low speed de3ices can s2are a sin!le 2i!2speed c2annel. T2is tec2ni8ue is known as multiple,in! w2ic2 pro3ides a cost efficient wa1 to allow 5 de3ices to s2are a sin!le communications facilit1 91 creatin! 5 c2annels o3er t2at facilit1. T2ere are different multiple,in! sc2emes used in t2e analo! and di!ital en3ironments. :e will 9riefl1 discuss t2e analo! tec2ni8ues 9ut t2e focus will 9e on di!ital tec2ni8ues. :e will also take a look into 9roadcast network and two main sc2emes to ac2ie3e resource s2arin! in t2ose networks- i.e. pollin! and contention.

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CS260

CHAPTER 2: FUNDAMENTALS OF NETWORKING II

" % 1 M1lt.*le=.n5 In multiple,in! se3eral low speed lines are com9ined into a 2i!2 speed line for lon! distance- 2i!2 speed transmission. ;enerall1 t2ere is a point at w2ic2 a lon! distance 2i!2-speed transmission facilit1 is c2eaper t2an some num9er of lower speed lines w2ose com9ined capacit1 is e8ui3alent to t2e 2i!2 speed link. o it is sensi9le to use multiple,ers in certain telecommunication networks.

Figure 2-#
" % 1 1 F+eB1en-? D./.s.on M1lt.*le=.n5 @FDMA

In t2is multiple,in! sc2eme- t2e total fre8uenc1 of t2e communication c2annel is di3ided amon! 5 users- w2ere eac2 user is !i3en a fi,ed portion of t2e fre8uenc1 spectrum. In t2e fi!ure 9eloweac2 of t2e four de3ices are assi!ned a free fi,ed fre8uenc1 c2annel. ome 9andwidt2 9etween eac2 c2annel is allocated to pro3ide a !uard 9and. T2e !uard 9and pro3ides ade8uate separation 9etween t2e fre8uenc1 allocation of eac2 c2annel. T' and radio stations s2are t2e fre8uenc1 spectrum on t2e air usin! F/M.

" % 1 "

T.2e D./.s.on M1lt.*le=.n5

Figure 2-$
In di!ital en3ironment- time on t2e c2annel is s2ared rat2er t2an t2e fre8uenc1. T2is tec2ni8ue is known as Time /i3ision Multiple,in!6T/M7. In t2is sc2eme- a station !ets access to all of t2e c2annels 9andwidt2 for some period of time. T2ere are two t1pes of T/M sc2eme and t2e1 areA

2 - 27

CS260

CHAPTER 2: FUNDAMENTALS OF NETWORKING II S?n-)+ono1s TDM In t2is t1pe of T/M- e3er1 user is !i3en a time slot on a sc2eduled 9asis. In t2e e,ample 9elow- four stations are connected to a multiple,er t2at samples eac2 station in turn. =ac2 station is allocated a fi,ed time slot on a sc2eduled 9asis i.e. a station is !ranted a time slice w2et2er it 2as an1t2in! to transmit or not. T2e composite line data will 9e at least e8ual to t2e sum of all of t2e input lines.

Figure 2-1%
T2us t2e composite link will 2a3e data rate of at least 4-)++9ps. 1nc2ronous T/M is a fair al!orit2m and eas1 to implement. .ow e3er t2is tec2ni8ue will 9e inefficient if t2e stations 2a3e low utilisation due to t2e fact t2at man1 time slots will !o unused. In t2e case of 9urst1 transmission- one station ma1 2a3e man1 transmission 8ueued up waitin! for its time slot w2ile all ot2er de3ices are idle and t2eir time slots will !o to waste. Stat.st.-al T.2e D./.s.on M1lt.*le=.n5 ♦ In s1nc2ronous T/M- time slices ma1 9e wasted w2en a !i3en station 2as not2in! to transmit durin! its time slice- t2us makin! t2e sc2eme inefficient. T2ese unused time slices could 9e assi!ned to acti3e stations to increase t2e efficienc1 of line usa!e. ome 2eader information must now 9e included in t2e data stream to identif1 a particular station t2at owns t2e time slice. T2is tec2ni8ue is called tatistical Time /i3ision multiple,in! or statistical multiple,er and tatmu, is t2e de3ice used for t2e purpose. • • S?n-)+ono1s TDM Stat.st.-al TDM

2 - 28

CS260

CHAPTER 2: FUNDAMENTALS OF NETWORKING II

Idle time slots

T# T+ T) T# T+ T) T# T+ T) T#

Figure 2-12

T# T+ T) T# T+ T) T# T+ T) T#

Figure 2-11
T2e performance of a tatmu, ma1 9e 9elow t2at of an ordinar1 time di3ision multiple,er if all t2e attac2ed stations use t2e line fre8uentl1. .owe3er data transmission is t1picall1 9urst1 and so- in t2e usual case- t2e statistical approac2 is superior. tatmu, assi!ns a time slot to a station onl1 w2en t2e station 2as somet2in! to transmit. <lder statmu,es assi!ns a fi,ed time slot if a time slot is needed w2ere as newer statmu,es assi!n a 3aria9le len!t2 time slot to user. T2e data rate of t2e composite link out from a statmu, ma1 9e less t2an t2e sum of all of t2e input data rates. T2is is possi9le since eac2 station will not usuall1 9e transmittin! at a rate t2at uses t2e entire a3aila9le capacit1 of its line to statmu,. Conse8uentl1 it is possi9le t2at twel3e 12++9ps terminal could s2are a stamu, t2at 2as a composite line rate of onl1 4)++9ps. :2ere as 1nc2ronous T/M multiple,er will re8uire a composite link rate of 14-4++9ps. tatmu,es are more efficient t2an s1nc2ronous T/M sc2eme alt2ou!2 t2ere are some o3er2eads of addressin!. In s1nc2ronous T/M sc2eme- if t2ere are 5 c2annelssome station j owns e3er1 kt2 time slot. Conse8uentl1 a time slot onl1 needs to contain dataB t2e relati3e position of t2e slot in time implies t2e station address. &ut t2is concept does not appl1 to tatmu,. .ence address must 9e e,plicitl1 included as part of t2e transmission.

" % " Poll.n5 In 9roadcast t1pe of network allocation of s2ared communication facilit1 is ac2ie3ed 91 means of pollin!. In pollin! t2ere is a central controller w2ic2 !i3es eac2 of t2e stations control of t2e communication facilit1 accordin! to t2e same strate!1. .owe3er t2e

2 - 29

CS260

CHAPTER 2: FUNDAMENTALS OF NETWORKING II 9urst1 nature of most computer communications makes t2is tec2ni8ue inappropriate. Most of t2e stations polled will 2a3e not2in! to transmit. T2ose stations w2o want to transmit will 2a3e a !reat deal of data to transmit and 9e un2app1 if t2e1 2a3e to wait for t2e entire pollin! c1cle 9etween transmission.

T2e desi!n of a HlocalH 9roadcast network is an issue w2en more t2an two mac2ines s2are a link. T2is is called a multipoint- or multidropen3ironment. :2en multiple mac2ines s2are t2e link- some al!orit2m must e,ist so t2at t2e mac2ine can all 2a3e orderl1 access to t2e c2annel. T2ere are two approac2es to t2is - t2e 9alanced and un9alanced approac2.

2 - 30

CS260 Case 1

CHAPTER 2: FUNDAMENTALS OF NETWORKING II





Case 2

C

C

C

C

Figure 13

Case 1 s2ows an un9alanced confi!uration- w2ic2 is an e,ample of centralised pollin!. <n an un9alanced link- one mac2ine is desi!nated as t2e primar1 6"7 stationB all ot2er stations are called secondar1 6 7. It is t2e primar1Ms responsi9ilit1 to poll eac2 secondar1 to determine if t2e secondar1 wis2es to transmit or is read1 to recei3e. For t2e case e,amined 2ere- all communication on t2e link is 9etween some secondaries and t2e primar1. Control of t2is s1stem is centralised since one station controls t2e access to t2e link for all ot2er stations. 0s an e,ample- I&MCs &I INC is t1picall1 used in un9alanced confi!uration.

Case 2 s2ows t2e 9alanced approac2. <n a 9alanced link- eac2 station is called a com9ined 6C7 station. T2e reason for usin! t2is term is t2at all stations are peers and ma1 communicate wit2 eac2 ot2ert2us 2a3in! attri9utes in common wit2 Hprimar1H and Hsecondar1H de3ices. Control of t2is communication link is distri9uted since e3er1 station 2as an e8ual role in determinin! w2ic2 station !ains access to t2e line. 0ll ?0Ns use a 9alanced approac2. " % " 1 D.st+.b1te0 Poll.n5: To4en Pass.n5

Token passin! networks utilise two t1pes of tokens. 0 9us1 token is placed at t2e 9e!innin! of a data frameB user data immediatel1

2 - 31

CS260

CHAPTER 2: FUNDAMENTALS OF NETWORKING II follows a 9us1 token. :2en a station sees a free token- it is allowed to c2an!e it to a 9us1 token and transmit data. :2en t2e data returns- t2e transmitter must reissue a free token. T2e ke1 2ere is t2at taps are acti3e- rat2er t2an passi3e de3ices- and introduce a 19it dela1 91 remo3in! and t2en re!eneratin! a 9it.

2 - 32

CS260

CHAPTER 2: FUNDAMENTALS OF NETWORKING II T2e followin! dia!ram s2ows an e,ample of c2an!in! a free token to a 9us1 token. In t2is e,ample- w2en t2e station sees t2e incomin! free token- it can c2an!e it into a 9us1 token merel1 91 in3ertin! t2e last 9it. I== )+2.4 token 9us standard uses t2is pollin! mec2anism.

Figure 2-14
" ' Content.on 0not2er approac2 for s2arin! communication facilit1 in a 9roadcast en3ironment is Contention. In t2is sc2eme stations will transmit w2ene3er t2e1 want to. If a collision occurs- t2e stations 2a3e to 9ack off and tr1 later a!ain. ome mec2anism must 9e pro3ided to randomise t2e 9ack off period or else an infinite strin! of collisions will occur.

Most 9us- or s2ared media networks control access 3ia some form of contention. :2en people talk to eac2 ot2er- t2e1 s2are a mediumB namel1 t2e air. :2en one person wants to speak- 2e or s2e speaks. If two or more people want to speak- some al!orit2m is used so t2at onl1 one does so. If more t2an one person talks at t2e same time- HcollisionsH occur t2at destro1 all of t2e words. T2e al!orit2ms t2at people use can not 9e easil1 adopted 91 computer. "eople ma1 defer to eac2 ot2er utilisin! politeness or seniorit1B optionall1- t2e loudest 3oice ma1 win 6utilisin! a rudeness protocol7. In an1 case- t2e people standin! around talkin! to eac2 ot2er 2a3e more information a9out t2eir network t2an t2e stations on t2e 9us.

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CS260

CHAPTER 2: FUNDAMENTALS OF NETWORKING II T2e followin! dia!ram illustrates a pure contention- a station starts to transmit its frame as soon as it is read1. 0s s2own- station 1 9ecomes read1 and transmits. ome time after 1 is finis2ed- station 2 9ecomes read1 and it transmits. :2ile station 2 is transmittin!- station 3 9ecomes read1 and it too- starts to transmit. ince t2e end of station 2Cs frame collides wit2 t2e 9e!innin! of station 3Cs frame- 9ot2 t2e frames are destro1ed. T2e collision

Figure 2-1
sc2eme descri9ed 2ere is called "ure 0lo2a- named for 0?<.0N=T.

" 6

Re/.e3 $1est.ons 11. :21 do we need to modulate a si!nalK 12. :2at is modulationK /escri9e different tec2ni8ues used to modulate an analo! si!nal into a analo! s1stem. 13. :2at are t2e different modulation tec2ni8ues used to modulate a di!ital si!nal into an analo! s1stemK 14. :2at is t2e role of modem in data communicationK 1#. :2at is multiple,in!K /escri9e different t1pes of multiple,in! sc2eme. 1%. :2en would 1ou use tatmu, in place of s1nc2ronous time di3ision multiple,in!. 1(. /escri9e 2ow a communication facilit1 is s2ared in 9roadcast t1pe of en3ironmentK :21 do we need to s2are a communication facilit1K

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CHAPTER 3 : TRANSMISSION MEDIA AND SWITCHING TECHNI&UES
C)a*te+ Ob,e-t./es @pon completion of t2is c2apter- 1ou will 9e a9le toA ⇒ descri9e t2e ad3anta!es and disad3anta!es of different transmission mediaB ⇒ descri9e w21 a particular transmission media is used for a certain applicationB ⇒ descri9e different t1pes of switc2in! networksB ⇒ descri9e 2ow information flows t2rou!2 different nodes of a computer networkB ⇒ descri9e t2e ad3anta!es and disad3anta!es of different t1pes of switc2in! networks. # 1 T+ans2.ss.on Me0.a T2e nature of transmission media determines t2e 8ualit1 and c2aracteristics of data transmission. For !uided transmission media- t2e medium itself pla1s an important role in determinin! t2e transmission limitation. .owe3er for un!uided media- t2e medium itself does not 2a3e a 3er1 9i! impact in determinin! transmission c2aracteristics. In t2is case t2e fre8uenc1 9and of t2e si!nal produced 91 t2e transmittin! de3ice pla1s an important role. In t2is c2apter- we will take a look into different t1pes of !uided and un!uided media. # 1 1 T3.ste0 Pa.+ Twisted pair is composed of wood-pulp or plastic insulated wires twisted to!et2er into pairs. In some ca9les- man1 twisted pairs are stranded into a rope-like form called a 9inder !roup. e3eral 9inder !roups are- in turn- twisted to!et2er around a common a,is to form t2e ca9le core and a protecti3e s2eat2 is wrapped around t2e core. Twisted pair is manufactured in a num9er of standard siDes and ma1 contain from si, to 3-%++ wire pairs. T2e electroma!netic interference 9etween t2e indi3idual pairs are minimised 91 twistin! t2em to!et2er. Twisted pair can 9e used to transmit 9ot2 analo! or di!ital si!nals. $epeater distance for analo! si!nals is #-% km w2ere as for di!ital si!nals- t2e repeater distance is 2-3 kms. Twisted pair is t2e least e,pensi3e media for a num9er of reasons. It uses t2e minimum amount of raw ca9le material- it is eas1 to make- and is readil1 a3aila9le. <ne of t2e pro9lems of twisted pair is t2at it acts like an antenna- it 2as 2i!2 suscepti9ilit1 to =lectroma!netic Interference

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6=MI7 and $adio Fre8uenc1 Interference 6$FI7. Twisted pair 2as a lar!e 9andwidt2. 0 !ood estimate will 9e 2#+ 5.D . 0t distances of 1.# km- 9it rates of 2.+4) M9ps can 9e maintainedB #% k9ps can 9e maintained up to distances of # km. @nfortunatel1 its error rate is 2i!2 and securit1 of transmission is low. T2e main application of twisted pair is in local loop 6transmission link 9etween user telep2one local e,c2an!e7 and e,c2an!e areas. # 1 " Coa=.al Cable Coa,ial ca9les contain a num9er of 6t1picall1 from 4 to 247 coa,ial units called tu9es. =ac2 tu9e consists of an inner conductor and a c1lindrical outer conductor separated 91 insulatin! disks. In addition to coa,ial tu9es- coa,ial ca9le contains a small num9er of twisted pair wire pairs and sin!le pairs for maintenance and alarm functions. imilar to twisted pair- coa,ial ca9le can transmit 9ot2 analo! and di!ital si!nals. $epeaters needs to 9e used e3er1 few kilometres for a lon! distance analo! si!nal transmission. In case of lon! distance di!ital transmission- repeaters are re8uired e3er1 kilometre or so. 0lt2ou!2 coa,ial ca9le pro3ides s2ieldin! a!ainst =MI and $FI due to t2e arran!ement of its conductors- it still 2as low transmission securit1. T2e s2ieldin! and ca9le structure adds to t2e cost of material and manufacturin!. T2e coa,ial ca9le can 1ield data rates of 1+ to 1# M9ps. ?ar!e diameter coa,ial ca9le can 1ield lar!er data rates. 0 !ood estimate for t2e 9andwidt2 of a coa,ial ca9le is 3#+ M.D . Coa,ial ca9le is enjo1in! increasin! utilisation in a wide 3ariet1 of applications and it is per2aps t2e most 3ersatile transmission media. Coa,ial ca9les are used primaril1 on intercit1 routes in t2e lon!-2aul network or in undersea ca9le s1stems. <t2er applications include tele3ision transmission and distri9ution- ?ocal area networks and 2ort-run s1stem links.

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Figure 3-1

# 1 # Wa/e G1.0es 0 wa3e !uide is a rectan!ular or circular copper pipe t2at confines and !uides radio wa3es 9etween two locations. ItCs main ad3anta!e is low attenuation at microwa3e fre8uencies. T2e application of wa3e !uide is limited 9ecause it must 9e manufactured to e,treme uniformit1 and e,treme care is re8uired durin! installation to minimise s2arp 9ends. # 1 % O*t.-al F.b+e /ue to t2e ad3anta!es of optical fi9re tec2nolo!1 suc2 as wide 9andwidt2 interference immunit1 and so on- Fi9re is o93iousl1 t2e transmission medium of c2oice. T2e constantl1 !rowin! need for lar!e 9andwidt2 ser3ices lead to t2e ad3anced de3elopment of optical fi9re s1stem. Interference to optical

Figure 3-2

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fi9re s1stem is ne!li!i9le- compared wit2 ot2er s1stems suc2 as coa,ialradio or satellite. 0 t1pical <ptical Fi9re link is s2own 9elow.

T2e si!nal source can 9e 3oice- data or 3ideo and t2e si!nal can 9e analo! or di!ital. In ot2er words- an optical fi9re s1stem can 9e used to transmit analo! or di!ital si!nals. T2e dri3er is re8uired 9ecause optical de3ices- suc2 as li!2t source- re8uire different 3olta!es and currents from t2e con3entional electronic de3ices. T2e structure of an optical fi9re 3aries from one manufacturer to

Figure 3-3
anot2er. &ut- t2e four-la1er structure !raduall1 9ecame t2e industr1 standard.

Functions of A • Fi9re core A si!nal transmission- t2at is- it ser3es as t2e transmission medium. • • Fi9re claddin! A to !uide t2e li!2t so t2at it will tra3el wit2in t2e fi9re core to ser3e as a protection la1er for t2e core. "rotection la1ers "rotect t2e fi9re from e,tra forces. "rotect from moisture tren!t2en t2e fi9re "re3ent t2e penetration of outside material.

<ptical fi9re !uides a 9eam of li!2t 6si!nal encoded7 91 means of total internal reflection. 0n1 transparent medium t2at 2as a 2i!2er inde, of refraction t2an t2e surroundin! medium can 2a3e total internal reflection. Conse8uentl1 optical fi9re acts as a wa3e !uide

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for fre8uencies. /ependin! on t2e siDe of t2e fi9re- t2ere are two different kinds of optical fi9re i.e. sin!lemode fi9re and multimedia fi9re. For a multimedia fi9re w2en li!2t from a source enters t2e plastic core- ra1s at s2allow an!les are reflected and propa!ated alon! t2e fi9re and ot2er ra1s are a9sor9ed 91 t2e surroundin! material. For multimode fi9re- t2e ma,imum data rate t2at can 9e ac2ie3ed is limited. T2is is 9ecause multiple propa!ation pat2s e,ist in a multimode transmission causin! t2e si!nal elements to take different pat2s and 2ence different time. T2is pro9lem 2owe3er does not e,ist in a sin!le mode fi9re w2ere t2e fi9re core radius is reduced to t2e order of a wa3elen!t2. Conse8uentl1 onl1 a sin!le an!le or mode can pass- t2e a,ial ra1. ince t2ere is a sin!le transmission pat2- si!nal elements can not spread out in time like multimode fi9re. in!lemode fi9re 2as superior performance t2an multimode fi9re and t2e data rate can reac2 up to 1.% ;9ps. T1picall1 standard multimode fi9res 2a3e a core diameter of #+ um w2ere as sin!le mode fi9re 2as a core diameter of # um or less.

Figure 3-4

i!nals tra3ellin! in optical fi9re can 9e attenuated 9ecause of t2e followin! reasonsA • T2e li!2t couplin! from t2e li!2t source to t2e fi9re is not 1++G. • T2e splicin! of t2e fi9re causes reflection of li!2t and misali!nment of fi9res. ♦ T2e si!nal will alternate due to t2e splicin!. • ;lass a9sor9s li!2t

• =,ternal > !eometric effects of t2e followin! can cause si!nal attenuation • • 09sorption 91 impurit1 or <. ions Micro9endin! from surface distortion

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• •

/iameter 3ariation. &u99le penetratin! t2e core.

T2ere are t2ree t1pes of li!2t source t2at is used for optical fi9re transmission and t2e1 are i. ?i!2t emittin! diode 6?=/7

ii. ?aser diode 6?/7 iii. in!le mode or sin!le fre8uenc1 laser diode 6?/7

T2ese are semiconductor de3ices t2at emits li!2t w2en a 3olta!e is applied. ?/Cs can sustain lar!er data rates t2an ?=/. # 1 ' Te++est+.al M.-+o3a/e Microwa3e radio transmission is widel1 used as an alternati3e to coa,ial ca9le for lon! distance communication. Microwa3e antennas are para9olic and t2e diameter is t1picall1 1+ ft. Transmittin! antenna focuses a narrow 9eam to ac2ie3e line-of-si!2t transmission to t2e recei3in! antenna. Microwa3e antennas are mounted on towers w2ic2 2a3e a su9stantial 2ei!2t. T2e tower 2ei!2t is re8uired to e,tend t2e ran!e 9etween antennas and to 9e a9le to transmit o3er inter3enin! o9stacles. T2e 2i!2er t2e tower- t2e !reater t2e ran!e. 0 su9stantial portion of t2e fre8uenc1 spectrum is co3ered 91 microwa3e. Transmission fre8uencies ran!e from 2 to 4+ ;.D resultin! in 2i!2er potential data rate for transmission. 0ttenuation in microwa3e transmission is caused 91 rainfall. 0not2er source of impairment for microwa3e is interference w2ic2 is caused 91 o3erlap transmission areas. Terrestrial microwa3e is used for lon!-2aul telecommunication ser3ice. Compared to coa,ial ca9le- microwa3e facilit1 re8uires fewer repeaters. 0not2er application of microwa3e includes 3oice and tele3ision transmission. # 1 6 Satell.te M.-+o3a/e :it2in t2e last 2# 1ears- communication satellites 2a3e 9ecome t2e dominant carrier of international communication. T2e first commercial satellite INT= 0T 6or =arl1 &ird7 was launc2ed on 0pril #- 1*%#. T2e International Telecommunication atellite <r!anisation 6Intelsat7 2as !rown at a rate of 2+ percent per 1ear since 1*%#. atellite communications are more effecti3e t2an an1 ot2er means of communicationA ♦ ♦ :2en t2e nodes or sites- w2ic2 re8uire ser3ices- are scattered o3er a wide area :2en t2e nodes are in motion or porta9le. &esides radio s1stemsatellite communication 9ecomes t2e onl1 solution for ade8uate ser3ices.

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:2en a !reat man1 recei3ers are at one location- to keep t2e cost of communication low. atellite communications are t2e ultimate means of ser3ice pro3isions.

T2e customer to a satellite communication can 9e 3oice fre8uenc1 si!nal- data- 3ideo or fa,. atellite communications can 9e 3iewed as a microwa3e radio tower in t2e sk1. 0 satellite is used to link to two or more !round 9ased microwa3e transmitter >recei3er- known as eart2 stations. T2e satellite recei3es transmission on one fre8uenc1 9and called uplink- amplifies or repeats t2e si!nal- and transmits it on anot2er fre8uenc1 called downlink. T2ere are two common uses of

Figure 3communication satellite and t2e1 are depicted in t2e fi!ure 9elow

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Figure 3-!
In t2e first fi!ure- satellite pro3ides a point-to-point link 9etween two distant !round-9ased antennas w2ereas in t2e second fi!ure t2e satellite pro3ides a transmission link 9etween one !round-9ased transmitter and a num9er of !round 9ased recei3ers. 0 satellite needs to 9e wit2in t2e line-of-si!2t of its eart2 stations at all times. T2is re8uires t2e satellite to remain stationar1 wit2 respect to its position o3er eart2. In order to remain stationar1- t2e satellite must 2a3e a period of rotation e8ual to t2e eart2Cs period of rotation. T2is matc2 occurs at a 2ei!2t of 3#-()4 km. For satellite transmission- optimum fre8uenc1 ran!es from 1 to 1+ ;.D. &elow 1;.D- t2ere is si!nificant noise from natural sourcesincludin! solar- atmosp2eric and 2uman-made interference from 3arious electric de3ices. 09o3e 1+ ;.D t2e si!nal is se3erel1 attenuated 91 atmosp2eric a9sorption. For most satellites pro3idin! point to point communication- uplink fre8uenc1 ran!es from #.*2# to %.42# ;.D w2ere as down link fre8uenc1 ran!es from 3.( to 4.2 ;.D. T2is com9ination is referred to as C 9and or 4>% ;.D 9and. 0mon! t2e most important applications for satellites are Tele3ision distri9ution- ?on! distance transmission and pri3ate 9usiness network. # " S3.t-).n5 Te-)n.B1es T2ere are t2ree 9asic t1pes of switc2in! networks for transmittin! information and t2e1 areA i. Circuit switc2in!

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ii. Messa!e switc2in! and iii. "acket switc2in! Fi!ure 9elow s2ows a !eneric switc2in! network w2ic2 consists of a set of nodes connected 91 transmission media. T2e nodes can 9e computerstelep2ones- terminals or ot2er data communicatin! de3ices. /ata enterin! t2e network from a station are routed to t2e destination 91 9ein! switc2ed from node to node. For e,ample- data from station 9- intended for station d- can 9e sent 91 routes 2-3-# or 2-4-3-#. T2e classification as to w2et2er t2e network is circuit- messa!e or packet depends on t2e wa1 nodes switc2 data from one link 9etween t2e source and destination. # " 1 C.+-1.t S3.t-).n5 In t2is kind of switc2in!- a sin!le pat2 9etween two nodes is e,clusi3el1 dedicated to customers. For e,ample if customer wit2 access to station 9 wants to transmit > recei3e data to>from anot2er customer attac2ed to station d- 2e 2as to do t2e followin!A i. Call set up Customer wit2 access to station 9 dials up customer wit2 access to station d. If customer at station d is read1 to communicate- a dedicated pat2 will 9e esta9lis2ed 9etween customer at 9 and customer at d. ii7 /ata transfer

Figure 3-"
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<nce t2e dedicated pat2 is esta9lis2ed- data transfer 9etween customer at 9 and customer at d can continue. iii7 Call termination <nce t2e data transmission is o3er and 9ot2 t2e parties a!ree to terminate t2e session- t2e call will 9e terminated. <nce t2e call is terminated- t2e dedicated pat2 will 9e released and can 9e used 91 some9od1 else. Telep2one con3ersation can 9e one !ood e,ample of circuit switc2in!. Circuit switc2in! can 9e inefficient- since t2e pat2 is dedicated to t2e customers e3en w2en no information is 9ein! transmitted. For a 3oice connection- utilisation is 2i!2 alt2ou!2 not 1++G 6con3ersations- in !eneral- do not 2a3e lon! periods of silence7. 0lso note t2at w2ile sendin! data- error control can 9e performed onl1 on an end-to-end 9asis- after t2e complete messa!e 2as 9een sent. In t2is kind of switc2in!- after t2e connection is esta9lis2ed- t2e network is transparent to t2e customer. T2at is- t2e network 9ecomes a conduit for w2ate3er kind of information t2e customer wants to send. 0s a result of t2is transparent conduit- t2e network and t2e customer do not 2a3e to a!ree on a common format w2en data is 9ein! transmitted. For messa!e and packet switc2in! 2owe3er- customer and network must a!ree on formats. # " " Messa5e S3.t-).n5 Messa!e switc2in! is !enerall1 used for e,c2an!e of di!ital data suc2 as computer to computer communications or sendin! a tele!ram. T2is tec2ni8ue 2owe3er does not re8uire a dedicated pat2 9etween two communicatin! nodes. T2e switc2in! node is desi!ned to 2a3e t2e capa9ilit1 to store t2e messa!e in a 9uffer until a link to t2e ne,t node 9etween t2e two customers is a3aila9le. $eferrin! to fi!ure 3-(assume t2at station 9 corresponds to a computer t2at is sendin! information to anot2er computer at station d. Node 1 is accessed and information is stored in a 9uffer until a line from eit2er 1 to 3 or 1 to 2 9ecomes a3aila9le. 0ssumin! t2at messa!e switc2in! node 2 9ecomes a3aila9le first- t2e information is t2en transferred o3er t2e 1-2 link. T2en it is stored in a 9uffer at node 2- w2ere it will 9e transferred to node 4 and t2en to t2e computer at station d. T2ust2e computer at d will recei3e t2e information from t2e computer at station 9. 0n1 ensuin! dela1 depends on t2e messa!e len!t2 and t2e time it takes for t2e inter3enin! switc2es to 9ecome a3aila9le. In a messa!e-switc2ed network- t2e messa!e in a !i3en switc2 is stored and su9se8uentl1 forwarded to t2e ne,t switc2 w2en a link 9ecomes a3aila9le. T2us- t2e messa!e-switc2ed network is also referred to as a store-and-forward network. imilarl1- a packet-

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switc2ed network is also a store-and-forward network. T2e messa!e stora!e capa9ilit1 at t2e switc2es makes t2e network appear to 9e non-9lockin!- since if t2e pat2 to t2e ne,t node is 9us1- t2e messa!e switc2 ma1 still accept t2e messa!e- dependin! on t2e switc2 9uffer siDe. "otential 9lockin! at t2e switc2 is translated into a potential dela1. .owe3er- 9ein! dela1ed is far less serious t2an 9ein! 9locked. Messa!es can 9e statisticall1 multiple,ed and transmitted w2en t2e pat2 to t2e ne,t node 9ecomes a3aila9le. T2e tendenc1 to fill in t2e !aps 9etween messa!es on t2e pat2 leads to e,tremel1 2i!2 efficienc1 of network resources as well as 2i!2 utilisation of t2e inter-switc2 connection c2annels. =3en w2en no messa!e is 9locked- t2e dela1 t2rou!2 t2e network can 9e lon! wit2 a 2i!2 3ariance 6dependin! on t2e messa!e len!t27. T2is dela1 is a major disad3anta!e- and messa!e switc2in! is not well suited for real-time traffic 6e.!. di!ital 3oice7 and speciall1 interacti3e communication 6e.!. airline reser3ation7. 0not2er disad3anta!e is t2at t2e messa!e switc2 re8uires lar!e 9uffers for lon! messa!es. T2e 2ardware in t2ese 9uffers is wasted w2en s2ort messa!es are recei3ed. =3en if a pat2 to t2e ne,t node is a3aila9le- a switc2 node can not 9e!in to rela1 t2e messa!e until t2e entire messa!e 2as 9een recei3ed. Finall1- 9ecause complete messa!es are stored in full at t2e messa!e switc2es- securit1 can 9e a pro9lem. "ersonnel workin! at t2ese switc2in! centres would 2a3e access to t2is information. T2e network and t2e customer now need to a!ree on a common messa!e format. T2is 9rin!s up t2e need for a!reements 9etween t2e network pro3ider and t2e manufacturer of customer e8uipment. uc2 a!reements are called rules or protocols.

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# " # Pa-4et S3.t-).n5 /ata transmission- includin! di!ital 3oice- is 9urst1- since t2ere are periods of time w2en no transmission occurs. T2e packet switc2in! tec2ni8ue uses t2is 9urstiness to com9ine t2e ad3anta!es of messa!e and circuit switc2in! w2ile minimisin! t2e disad3anta!es associated wit2 t2ose approac2es. In t2is switc2in! sc2eme network dela1 is reduced and line efficienc1 is increased. Information is 9roken into packets- and t2ese small messa!es are transmitted packet 91 packet. 0s in messa!e switc2in!- descri9ed a9o3e- eac2 packet must 9e stored in 9uffers at t2e switc2in! nodes. /ifferent packets of t2e same messa!e ma1 follow different pat2s durin! t2e same time period. /ela1 is reduced- since packets are s2ort in len!t2- 2a3e a s2ort transmission time- and re8uire a small amount of 9uffer space. $eferrin! to fi!ure 3-(- assume t2at station 9 corresponds to a computer t2at is transmittin! data to anot2er computer at station d. 0ssume- furt2er- t2at t2e messa!e consists of t2ree packets- ,- 1and D. T2e 9asic transmission operation will 9e descri9ed for packet switc2in! usin! fi!ure 3-(. 0n actual transmission in3ol3es packetscomposed of 9its- inserted into frames t2at contain additional control information 9its. In t2is simple description- we do not distin!uis2 9etween 9its- frames- and packets. T2e flow of t2e messa!e is initiated 91 t2e transmission of packet , to switc2in! node 1. 0fter t2e packet is completel1 stored in t2e 9uffer of node 1- t2e switc2 6followin! a set of routin! rules7 will transmit packet , toward its destination 91 sendin! it- in t2is caseto packet switc2 3. 6It is assumed for t2e moment t2at switc2 2 is not a3aila9le7. In t2e mean time- packet 1 is mo3in! into t2e 9uffer in switc2 1. /urin! t2is time- t2e conditions in t2e network c2an!e 6for instance- a lar!e amount of traffic from end office c arri3es at switc2 37- so t2e second packet- 1- of t2e messa!e is routed from 9 to d 3ia switc2 2. T2e t2ird packet of t2e messa!e- D - arri3in! at switc2 1 soon after t2e second packet- 1- is similarl1 routed 3ia switc2 2. 0n1 information t2at is properl1 recei3ed is acknowled!ed 91 t2e recei3in! switc2. T2us- in fi!ure 3-(- switc2 3 2as sent a s2ort acknowled!ement- desi!nated as 0C5,- 9ack to switc2 1- informin! t2e ori!inal sender t2at t2e packet was recei3ed wit2out error 91 t2e ne,t switc2. T2e acknowled!ement is t2e ke1 to t2e error mec2anism- w2ic2 ensures t2e inte!rit1 and accurac1 of t2e transmitted data packet. If an acknowled!ement is not recei3ed wit2in a certain predefined time period- t2e time out period- t2e sendin! switc2 presumes t2at t2e packet was recei3ed erroneousl1 and re-transmits t2at packet. $eturnin! to our e,ample- packet , is successfull1 transmitted to switc2 4. 0fter 9ein! recei3ed correctl1 91 switc2 2- packet 1 is

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transmitted to t2e destination switc2- switc2 4. &ut durin! t2at transmission- an error occurs. :2en switc2 4 recei3es packet 1- t2e error mec2anism determines t2e e,istence of t2e error. T2is error can 9e eit2er wit2in t2e packet or wit2in t2e control 9its sent alon! wit2 t2e packet. ince- switc2 4 does not know w2ere t2e error ist2e packet is discarded. T2e error mec2anism detects onl1 t2e presence of errors- not t2e location of errors wit2in t2e packet or control 9its. witc2 4 can not re8uest retransmission of t2e dama!ed packet- 1- since t2e control 9its could 9e in error. .owe3er- switc2 4 knows t2e num9er called a se8uence num9er- of t2e ne,t e,pected packet from switc2 2. T2is se8uence num9er is contained wit2in t2e control 9its t2at are sent alon! wit2 eac2 packet. T2e error mec2anism re8uests a retransmission w2en t2e ne,t error-free frame from switc2 2 arri3es. T2is procedure is illustrated in fi!ure 3-( w2ere t2e packet D is s2own arri3in! at switc2 4- 9e2ind packet 1- wit2 no errors. 6If packet D contained errors- it would appear t2at switc2 4 2as no wa1 of communicatin! to switc2 2 t2at packet D contains errors. T2e time out mec2anism a3oids an1 pro9lem. witc2 2 would retransmit packet 1 after t2e timeout period etc.7. <nce it is determined t2at packet D contains no errors- switc2 4 e,amines t2e se8uence num9er wit2in t2e control 9its sent alon! wit2 packet D. ince t2is num9er does not e8ual t2e e,pected se8uence num9er stored wit2in t2e memor1 of switc2 4packet D is also discarded. .owe3er- a ne!ati3e acknowled!ement is sent to switc2 2 re8uestin! a retransmission of all packets startin! wit2 t2e se8uence num9er of packet 1. T2is procedure is illustrated in fi!ure 3-( 91 t2e ne!ati3e acknowled!ement N0C51. witc2es keep copies of all transmitted packets until packets are successfull1 acknowled!ed. T2e 9uffer wit2in switc2 4 is s2own. T2ese packets are deli3ered to t2e computer at d in t2e correct se8uence - ,- 1- D. 0s noted earlier- packet switc2in! is also store-and-forward s1stem9ecause it permits different packets from a sin!le messa!e to arri3e at t2e destination 91 different routes and wit2 different dela1s. 6<f course- t2is met2od does not preclude packets arri3in! 91 t2e same route7. It also permits t2e recei3ed packets to 9e in different order t2an t2e ori!inal transmission. T2e process of se8uencin! t2e packets ma1 9e performed at t2e recei3in! switc2 6packet switc2 4 in fi!ure 3-( 7 usin! packet se8uence information t2at accompanies t2e user data t2rou!2 t2e network. <r it ma1 9e done 91 t2e customer at station d- dependin! on t2e kind of ser3ice pro3ided to t2e customer. =ac2 messa!e in a circuit switc2in!- messa!e switc2in!- or packet switc2in! must include not onl1 t2e information 9its- 9ut additional 9its referred to as o3er2ead information. <3er2ead information contains 9ot2 packet - specific information 6a packet 2eader7 and link - specific information 6t2e frame 9its w2ic2 surround t2e packet

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2eader and packet data 9its7. Frame 9its contain t2e control information necessar1 for error-free transmission 9etween t2e communicatin! switc2es 6refer to fi!ure 3-( 7. :it2in t2e packet 2eader- t2e o3er2ead 9its can identif1 t2e destination of a messa!eor packet- so t2at eac2 switc2in! centre will know 2ow to furt2er route t2e information. <3er2ead 9its also can specif1 t2e source of t2e messa!e or packet- so t2at acknowled!ement is possi9le- and t2e user identification- so t2at t2e user can 9e c2ar!ed for ser3ices. 1nc2ronisation 9its are part of t2e switc2 o3er2ead and must 9e included to identif1 t2e 9e!innin! and end of a frame containin! t2e messa!e or packet. T2e packet 2eader also can contain num9ers to allow reassem9l1 in proper se8uence. In a messa!e-switc2ed s1stem- t2e o3er2ead information is appended to eac2 messa!e- w2ere as in packet switc2in!- eac2 packet is accompanied 91 o3er2ead 9its. T2us- if t2ere is more t2an one packet > messa!e- t2e packetiDed messa!e 2as more o3er2ead. 0ccordin!l1- wit2 respect to messa!e switc2in!- packet switc2in! 2as two disad3anta!esA 1). To transmit a !i3en amount of information per unit time- packet switc2in! re8uires t2at 9its 9e transmitted at a more rapid rate t2an is re8uired in messa!e switc2in!. 1*. T2e switc2in! 2ardware needed to packetiDe- add o3er2eaddepacketiDe- and reassem9le is more complicated and must operate more rapidl1 t2an t2e correspondin! 2ardware needed in messa!e switc2in!. =3en t2ou!2 packet switc2in! re8uires more o3er2ead 9its- a packet switc2in! s1stem will transmit a !i3e amount of information wit2 less dela1 t2an messa!e switc2in!. T2is feature results from t2e fact t2at a switc2in! computer can not 9e!in to retransmit a messa!e 6relati3el1 lon!7 or a packet 6relati3el1 s2ort7 until t2e entire messa!e or packet 2as 9een recei3ed. :it2 packet switc2in!- t2e lon! messa!e is 9roken into smaller packets so t2at t2e 9ufferin! dela1 at t2e switc2es is reduced.

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Note a!ain- in a manner similar to messa!e switc2in!- t2at t2e packet-switc2in! network and t2e customer must a!ree on a common packet format. 0!reements 6rules or protocols7 must 9e met 9etween t2e packet network pro3ider and t2e manufacturer of customer e8uipment. T2e F.2# protocol is an e,ample of suc2 an a!reement. # " # 1 Pa-4et S3.t-).n5 Con-e*ts



T2ere are two kinds of rules- or protocols- for transmittin! packets. <ne is 9ased on t2e processin! rules wit2in t2e network and is referred to as internal processin!B t2e ot2er is 9ased on t2e processin! rules 9etween t2e customers and t2e network and is called e,ternal processin!. T2e tec2ni8ues for internal processin! are called data!ram and 3irtual circuit. /ata!ram Tec2ni8ue • In t2e data!ram approac2- t2e internal packet switc2in! network treats eac2 packet independentl1- just as t2e post office treats t2e mailin! of letters. <ccasional packets will 9e lost- and t2e customer ma1 or ma1 not know t2is unless t2ere is some acknowled!ement from t2e recipient. For e,ample- if a 9ill is paid and !ets lost in t2e mail- 1ou can 9e sure t2at t2e part1 owed t2e mone1 will 9e in touc2. <n t2e ot2er 2and- if 1ou re8uest information a9out a product 91 filin! out an information post card w2ic2 is su9se8uentl1 mailed and lost- 1ou pro9a9l1 will not 9e notified since t2e mailin! was not e,pected 6t2ere is also no economic impact from t2is loss7. T2us- in t2is approac2- packets from a sin!le messa!e can arri3e at t2e customer 91 different routes- wit2 different dela1s- and out of order. T2e customer 2as t2e responsi9ilit1 to determine t2at t2e packets are out of se8uence and to reorder t2em.



'irtual-Circuit Tec2ni8ue • In t2e 3irtual-circuit approac2- a lo!ical connection is esta9lis2ed 9efore an1 packets are sent. It is similar to t2e call setup- suc2 as makin! a telep2one call w2ere a route must 9e selected and e8uipment is dedicated to t2e call. T2e set-up procedure for t2e 3irtual-circuit approac2 esta9lis2es t2e route 9etween t2e caller and t2e recei3er. It uses software to make entries into ta9les stored wit2in eac2 switc2in! node alon! t2e route. 0 ta9le specifies t2e addresses of adjacent switc2es for t2e call. <nce t2e set-up is complete- information is directed o3er t2e same route 91 t2e appropriate ta9le wit2in eac2 packet-switc2in! node. T2e packet format after call set-up does not re8uire complete addressin! information since t2e 3irtual circuit directs t2e packets to t2eir destination. T2e 3irtual-circuit is Hp2one-likeH 9ecause t2ere is a specific route 9etween t2e caller and recei3er t2rou!2 t2e networks for t2e

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duration of t2e call. :it2 data!rams- routin! ma1 9e different for eac2 piece of data. .owe3er- it does not mean t2at t2ere is

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dedicated pat2- as in circuit switc2in!. /ata frames will 9e 9uffered if t2e flow of traffic at a switc2 9ecomes too 2i!2 and 8ueued for transmission o3er t2e esta9lis2ed route. Transmission 9e!ins w2en lines 9ecome a3aila9le. :2en two stations e,c2an!e lar!e files- w2ic2 can take a lon! time- t2ere are certain ad3anta!es for emplo1in! t2e 3irtualcircuit approac2- all related to relie3in! t2e stations of unnecessar1 communications-processin! function. 0ll packets for a specified 3irtual circuit follow t2e same route and arri3e in se8uence. # # Re/.e3 $1est.ons 2+. :2at is a co-a,ial ca9leK :2at is t2e difference 9etween &ase9and and &road9and co-a,ial ca9leK 21. H<ptical Fi9re is t2e medium of c2oiceH- Comment on t2is statement. 22. :2at is t2e ad3anta!e of usin! satellite microwa3e transmissionK 23. :2ere would 1ou use terrestrial microwa3e as a transmission mediaK 24. :2at is circuit switc2in!K :2at are t2e disad3anta!es of circuit switc2in!K 2#. :21 packet switc2in! is more efficient t2an messa!e switc2in!K :2at are t2e t1pical applications of messa!e switc2in!K 2%. /escri9e in detail- t2e difference 9etween t2e data!ram and 3irtual circuit tec2ni8ues 2(.

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CHAPTER 4 : NETWORK SECURIT'
C)a*te+ Ob,e-t./es @pon completion of t2is c2apter- 1ou s2ould 9e a9le to A ⇒ descri9e w2at network securit1 isB ⇒ descri9e some of t2e main reasons of network faultsB ⇒ descri9e 2ow errors are detected and corrected durin! data transmissionB ⇒ descri9e w2at is flow control and some of t2e protocols related to flow controlB ⇒ descri9e different measures t2at are adopted to pre3ent 2uman interference in data communication. % 1 Int+o01-t.on For a computer network- securit1 is of utmost importance. T2is is 9ecause t2e network is used as a 2i!2wa1 of information mo3ement. T2e failure and success of man1 companies depend on t2e inte!rit1 of t2e information transmitted. &ecause of t2is securit1 is one of t2e prime considerations of network desi!n. Network securit1 is concerned wit2 protectin! t2e network from faults or from 2uman interference wit2 t2e network. Faults mi!2t occur wit2in t2e network itself or it ma1 9e caused 91 natural disaster or 2uman error. <n t2e ot2er 2and- 2uman can interfere wit2 t2e network to corrupt t2e data or retrie3e 3alua9le information. Network faults are minimiDed 91 desi!nin! t2e network in suc2 a wa1 so t2at it can o3ercome t2e pro9lem in2erent into a computer network. <n t2e ot2er 2and- different protecti3e measures are taken to pre3ent 2uman 9ein!s from interferin! t2e network. T2e tec2ni8ue and measures for network securit1 is discussed 2ere in detail. % " Net3o+4 Fa1lts Most of t2e network faults are caused 91 transmission impairment- w2ic2 means t2at t2e recei3ed si!nal differs si!nificantl1 from t2e transmitted si!nal 9ecause of some random 3ariations and de!radation of si!nal 8ualit1. T2ere are essentiall1 t2ree parameters t2at is attri9uted to t2is impairment and t2e1 areA ♦ 0ttenuation ♦ ♦ /ela1 /istortion Noise

% " 1 Atten1at.on 0s t2e transmission distance increases- t2e si!nal stren!t2 decreases. T2ere are mainl1 t2ree aspects of attenuation and t2e1 areA

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CHAPTER 4 : NETWORK SECURITY ♦ $ecei3ed si!nal s2ould 9e stron! enou!2 so t2at t2e recei3in! end can detect and interpret t2e si!nal. ♦ T2e si!nal le3el s2ould 9e a9o3e t2e noise le3el so t2at t2e transmitted si!nal can 9e recei3ed wit2out error. ♦ Increase in fre8uenc1 increases attenuation.

T2e first and second issue is addressed 91 usin! amplifier or re!enerators. 0mplifiers or re!enerators are used on t2e transmission links to 9oost up t2e weak si!nal. T2e num9er of amplifiers or re!enerators to 9e used for a particular transmission link depends on t2e transmission media. T2e t2ird issue is caused 9ecause of imperfect amplitude fre8uenc1 response. T2is can 9e a3oided if all fre8uencies wit2in t2e pass 9and are su9jected to e,actl1 same loss or !ain. % " " Dela? D.sto+t.on "ropa!ation 3elocit1 of a si!nal t2rou!2 a !uided medium 3aries wit2 fre8uenc1. T2e 3elocit1 tends to 9e !reater near t2e centre fre8uenc1 of a 9and limited si!nal and 3elocit1 decreases towards t2e ed!es of t2e 9and. T2is causes different components of a si!nal to arri3e at t2e destination at different times causin! dela1 distortion. T2is p2enomenon is 3er1 critical for di!ital transmission. T2is t1pe of distortion can 9e a3oided 91 e8ualisin! t2e 3elocit1 of si!nal across t2e 9and. % " # No.se Noise consists of an1 undesired si!nal in a communication circuit. Noise 2appens to 9e t2e major limitin! factor in s1stem performance. T2ere are four major cate!ories of noise and t2e1 areA % " # 1 T)e+2al no.se

T2ermal noise occurs in all transmissions media and all communication e8uipment. It arises from random electron motion- and is a function of temperature. T2is is also referred to as w2ite noise and is uniforml1 distri9uted across t2e fre8uenc1 9and. T2ermal noise places an upper 9ound on an1 communication s1stem performance and it cannot 9e eliminated. % " # " Inte+!2o01lat.on No.se

If two si!nals wit2 fre8uencies F1 and F2 as passed t2rou!2 a non linear de3ice or medium- t2e result will 9e intermodulation product t2at are spurious fre8uenc1 components 6F1JF27. T2ese components ma1 9e present eit2er inside or outside of t2e 9and of interest for t2e de3ice. T2ese components interfere wit2 a si!nal at t2e fre8uenc1 F1JF2.

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CHAPTER 4 : NETWORK SECURITY

Cross talk occurs w2en t2ere is electrical couplin! 9etween near91 twisted pair or coa,ial ca9le carr1in! multiple si!nals. 0not2er kind of cross talk 2appens w2en microwa3e antennas pickup unwanted si!nal. :2ile usin! telep2one- one can e,perience crosstalk w2en 2e can listen to anot2er con3ersation. % " # % I2*1lse no.se

Impulse noise is non-continuous- consistin! of irre!ular pulses or noise spikes of s2ort and of relati3el1 2i!2 amplitude. T2ese spikes are often called H2itsH. Impulse noise de!rades 3oice telep2on1 onl1 mar!inall1. .owe3er it ma1 seriousl1 de!rade error rate on data or ot2er di!ital circuits. % # E++o+ Dete-t.on an0 Co++e-t.on Te-)n.B1es 1nc2ronous and 0s1nc2ronous transmissions are suscepti9le to noise. T2e speed of s1nc2ronous transmissions is often 2i!2er- and t2erefore t2e conse8uence of noise is more se3ere. 0s1nc2ronous transmission contain a !reat deal of idle time- w2ere as s1nc2ronous data are conti!uous- addin! furt2er reason for concern. Transmission line noise is 91 nature 9urst1. $elati3el1 lon! period of time will elapse wit2out a serious noise and t2en a click will occur t2at will destro1 a tent2 of a second wort2 of data. In a *%++ 9it>second transmission- t2is click will destro1 a %+ 9its or 12+ consecuti3e c2aracters. T2is leads to t2e conclusion t2at error detection and correction tec2ni8ues are of prime importance. ♦ T2e 9asic principle of error control code is to add redundanc1 to information 9it stream. T2e error control codes can 9e classified as A • • • error detection code error correction code error detection and correction code.

T2ere are man1 error control codes 9ut onl1 few of t2em are discussed 9elowA % # 1 E/en( o00 Pa+.t? T2is is t2e simplest error control code w2ere one e,tra 9it is added to t2e c2aracter 9ein! transmitted. For e3en parit1 t2is 9it is set suc2 t2at t2e total num9er of 1Cs in eac2 c2aracter is alwa1s e3en. <n t2e ot2er 2andfor odd parit1 t2is 9it is set so t2at t2e total num9er of 1Cs in eac2 c2aracter is alwa1s odd. =3en >odd parit1 sc2eme can onl1 detect error 9ut cannot correct t2em. =,ampleA

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CS260

CHAPTER 4 : NETWORK SECURITY 0ppl1 e3en parit1 to e3er1 two namesA /ole- &aer- Fan- &us2- C2enCole- .art- kin!. 0lso discuss error detection>correction capa9ilit1usin! t2e !i3en recei3ed 9it stream +++++11 +1++11+ 1++1+11 11+1111. InformationA +++++1 I "arit1 insertionA 1 Transmitted si!nalA +1++11 I 1 1++1+1 I 1 11+111 I 1

+++++11 +1++111 1++1+11 11+1111

=rror detection>correction capa9ilit1A $ecei3ed si!nalA +++++1 1 +1++11 + 1++1+1 1 11+111 1 "arit1 C2eckin!A First nameA 1 J 1 E =3en num9er of 1Cs econd nameA 1 J 1 J 1 J + E <dd num9er of 1Cs T2ird name A 1 J 1 J 1 J 1 E =3en num9er of 1Cs Fourt2 name A 1 J 1 J 1 J 1 J 1 J 1 E =3en num9er of 1Cs o from parit1 c2eckin!- we can see t2at second name is in error. % # " Lon5.t10.nal Re01n0an-? C)e-4 @LRCA an0 8e+t.-al Re01n0an-? C)e-4 @8RCA T2e simplest error detectin! sc2eme is one dimensional parit1 c2eckin! w2ere an e,tra 9it is added to eac2 c2aracter to make t2e total num9er of 1 9its in t2e c2aracter e3en 6for e3en parit17 or odd 6for odd parit17. T2e one-dimensional procedure is known as 'ertical $edundanc1 C2eckin! 6'$C7. T2is tec2ni8ue is effecti3e if a su9stantial num9er of t2e errors t2at occur in transmission are sin!le 9it errors. '$C is clearl1 defeated 91 an error t2at affects an1 e3en num9er of 9its. 0n additional parit1 c2eck can 9e performed on t2e columns- called lon!itudinal redundanc1 c2eck 6?$C7. T2e terms 3ertical and lon!itudinal refer to paper tape s1stems in w2ic2 t2ese tec2ni8ues w2ere de3eloped. T2e '$C>?$C com9ination is an effecti3e errordetectin! sc2eme. &ut t2is sc2eme can 9e defeated 91 certain t1pes of multiple 9it errors. 0n important t2in! to note is t2at '$C is also applied to t2e parit1 c2eck c2aracter.

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CS260

CHAPTER 4 : NETWORK SECURITY T2e followin! e,ample illustrates t2e met2ods- and notes some situation in w2ic2 t2e1 fail to detect an error. =,ample 0ppl1 odd parit1- ?$C and '$C to t2e 0 CII HItCs a 9irdNH. /iscuss error detection > correction capa9ilit1 if t2e recei3ed si!nal is !i3en as s2own. 0 CII code 6in octal7 I E 111B t E 1%4B C E 4(B s E 1%3B pace E 4+B a E141B 9 E 142B I E 1#1B r E 1%2d E 144B N E 41 $ecei3ed si!nal 6eac2 c2aracter plus its '$C is transmitted followin! anot2er c2aracter plus its '$C .7 11+1++1+ 111+1++1 +1++1111 111++11+ +1++++++ 11++++1+ +1++++++ 11+++1++11+1++11 111++1+1 11++1+++ +1++++11 1++1+1++ olutionA Transmitted si!nal I 1++1++1+ tA 111+1++1 CA +1++1111 sA 111++11+ paceA +1++++++ aA 11++++1+ paceA +1++++++ 9A 11+++1++ iA 11+1++11 rA 111++1+1 dA 11++1+++ NA +1++++11 C2eck c2arA 1++1+1++ 1++1+1++ OOOOOOOOO ?$C 3erification k!kkkkkk '$C onoooooo n! E no !ood <5 $ecei3ed si!nal 11+1++1+ 111+1++1 +1++1111 111++11+ +1++++++ 11++++1+ +1++++++ 11+++1++ 11+1++11 111++1+1 11++1+++ +1++++11 "arit1 3erification '$C N; '$C <5 '$C <5 '$C <5 '$C <5 '$C <5 '$C <5 '$C <5 '$C <5 '$C <5 '$C <5 '$C <5

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CS260 '$C 3erification • • ♦ <5 N;

CHAPTER 4 : NETWORK SECURITY



No error or e3en erroneous 9its in one c2aracter <dd erroneous 9its in one c2aracter

?$C 3erification • <5 A No error or e3en erroneous 9its amon! all t2e 1st- t2e 2nd- t2e 3rd- P - 9its of all c2aracters 6parit1 c2eck c2aracter included7 • N; A <dd erroneous 9its- instead

If t2e c2annel 2as a !ood performance record- t2at is- one 9it in error in t2ousands of 9its transmitted- we can assume t2at one error in at most ma1 occur in transmittin! t2is sentenceA HItCs a 9irdNH. T2en from t2e matri,- one can conclude t2at t2e first recei3ed 11+1++1+ E i will 9e detected as an erroneous c2aracter and corrected as 1++1++1+ E I % % Ass1+.n5 E++o+!f+ee Data Co221n.-at.on =rrors in a communication facilit1 can occur 9ecause of man1 reasons. 0 met2od of detectin! and correctin! errors in transmission must 9e de3eloped to assure error-free data communication. T2ere are two different approac2es to t2e pro9lem and t2e1 areA ♦ Transmit enou!2 e,tra 9its wit2 t2e actual data to allow detection of errors 91 t2e recei3er. <nce an error is detected- t2e recei3er re8uests a retransmission of t2e messa!e. <r ♦ Transmit sufficient e,tra 9its wit2 t2e messa!e so t2at t2e recei3er can detect and correct most errors wit2 2i!2 pro9a9ilit1. T2is mi!2t lower t2e efficienc1 of transmission 9ecause a relati3el1 lar!e num9er of non-information 9its are sent wit2 e3er1 transmission. T2e c2aracteristic of t2e communication facilit1 determines t2e efficienc1 of t2e first approac2. If t2e pro9a9ilit1 of error is low enou!2- t2e efficienc1 of t2is met2od e,ceeds t2at of t2e Herror correctin!H met2od 9ecause relati3el1 few non-information 9its are sent. If t2e pro9a9ilit1 of error is 2i!2 t2en efficienc1 will 9e low. =rror detection is t2e preferred c2oice since t2e communication c2annels are reasona9l1 error-free and t2e 9andwidt2 costs for t2e correction o3er2ead are not alwa1s economical. % ' T)e A1to2at.- Re*eat( ReB1est @AR$A S?ste2 For detect onl1 approac2- t2e recei3er will t1picall1 si!nal t2e acceptance or rejection of a 9lock of user information. If a 9lock is rejected- t2e transmitter is to re- transmit t2e 9lock in 8uestion. T2us an automatic repeat re8uest is !enerated 91 a reject si!nal. T2is t1pe of error control s1stem is referred to as an automatic repeat re8uest s1stem.

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CHAPTER 4 : NETWORK SECURITY 0$4 s1stems can 9e eit2er stop-and-wait or continuous. In stop-and-wait 0$4- t2e transmitter waits after eac2 transmitted 9lock for an acknowled!ement or reject si!nal 60C5 and N057. In continuous 0$4- t2e transmitter continues to send 9locks w2ile acknowled!ements arri3e on a return c2annel. ome means of identif1in! t2e 9lock 9ein! acknowled!ed or rejected must 9e pro3ided.

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% 6

Flo3 Cont+ol In a transmission scenario- t2e transmittin! and recei3in! end ma1 not operate at t2e same speed and t2e transmitter can transmit data faster t2an t2e recei3er can recei3e. T1picall1 t2e recei3er 2as a 9uffer area w2ere data is stored and processed 9efore t2e 9uffer area is cleared. Conse8uentl1- if t2e recei3er is not fast enou!2 to clear t2e data 9uffer- t2e 9uffer will 9e o3erwritten 91 t2e incomin! data causin! o3erflow pro9lem. ome sort of flow control mec2anism must 9e in place 9etween t2e transmitter and recei3er. ♦ implest kind of flow control mec2anism is known as flow control mec2anism. T2is sc2eme works as followsA top-and-wait

• transmitter transmits one frame and waits for and acknowled!ement from t2e recei3erB • once t2e recei3er recei3es t2e frame successfull1 assumin! error free transmission- it sends 9ack an acknowled!ementB • upon recei3in! t2e acknowled!ement- transmitter transmits t2e ne,t frame. T2is sc2eme works fine w2en messa!es are transmitted in few lar!e frames. T2is is 9ecause t2ere will 9e fewer re-transmissions re8uired if necessar1makin! an efficient use of t2e transmission 9andwidt2. &ut in practice messa!es are not transmitted in lar!e frames- as t2e1 are more suscepti9le to error. <t2er reasons include limited 9uffer siDe at t2e recei3in! end and lar!e frames monopolise t2e transmission links. o in practice- messa!e is transmitted in smaller frames. o if we use t2is sc2eme for flow control- it ma1 not 9e efficient 9ecause of t2e num9er of re-transmissions. 0not2er more efficient sc2eme is known as lidin! :indow "rotocol. In t2is sc2eme t2e transmitter and t2e recei3er is considered to 2a3e a window. T2e ma,imum allowa9le siDe of t2e transmitter window is t2e num9er of 9locks t2e recei3er is prepared to accept at an1 time. =ac2 time t2e recei3er acknowled!es a 9lock- t2e transmitter window rotates 91 one and t2e transmitter is permitted to send one more 9lock. 6T2is rotatin! of t2e window results in t2e concept of t2e Hslidin! windowH7. % 6 1 AR$ Sl.0.n5 W.n0o3 P+oto-ol ?et us assume t2at e3er1 out 9ound 9lock contains a se8uence num9er in t2e ran!e 6+- 2n -17. 2n is called t2e modulus of t2e protocol. T2e sender is re8uired to keep a list of all 9locks t2at 2a3e 9een sent 9ut not 1et acknowled!ed. T2is structure is called transmitter window. ?ikewise t2e recei3er keeps a list of 9locks t2at it can accept. T2e recei3erCs window- as it is called- is of constant siDe- w2ile t2e transmitters window ma1 !row to a ma,imum siDe a!reed to 91 9ot2 parties. Note t2at t2e window siDe is a flow control parameter. If for e,ample- t2e transmitter window siDe is restricted to 1- we 2a3e a

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CHAPTER 4 : NETWORK SECURITY stop-and-wait protocol- w2ile if t2e transmitter window siDe is lar!ea su9stantial num9er of 9locks can 9e sent in s2ort order. T2us 91 adjustin! t2is window siDe- t2e recei3er can protect itself from 9ein! o3errun 91 a Dealous transmitter. If t2e recei3er !ets a 9lock t2at is not in its window- t2e 9lock is discarded wit2out comment. If t2e 9lock is t2e one at lower ed!e of t2e window- it is acknowled!ed and t2e window is rotated. T2e followin! dia!ram illustrates t2e idea wit2 a transmitter window siDe of 2 and a recei3er window siDe of 1.

Figure 4-1
Normal slidin! window interc2an!e. Transmitter 6top row7 2as window siDe E 2- recei3er window siDeE1 617 ender transmits 9lock +- recei3er waits +.

627 ender transmits 9lock 1. It must now wait until an acknowled!ement is recei3ed- $ecei3er !ets +- sends 0C5 and ad3ances window. 637 ender !ets 0C56+7- sends 9lock 2. $ecei3er !ets 9lock 1- sends 0C5 617 and ad3ances window. 647 6#7 &locks sent and recei3ed normall1. % 9 H12an Inte+fe+en-e It is 3er1 important to protect t2e network from 2ackers w2o ma1 cop1 or corrupt t2e information. some of t2e tec2ni8ues t2at can 9e used to pre3ent 2umans from doin! so are discussed 9elow. % 9 1 A1t)ent.-at.on T1picall1 aut2entication is ac2ie3ed 91 means of identif1in! t2e useruser terminal and t2e le3el of aut2orisation. &ut t2ese tec2ni8ues cannot !uarantee t2at t2is aut2entication information will not 9e tapped 91 a 2acker. T2is pro9lem can 9e a3oided 91 introducin! a pu9lic ke1 w2ic2 will 9e known to t2e user and t2e 2ost s1stem onl1. :2ene3er t2e user tries to esta9lis2 a session wit2 t2e 2ost s1stem-

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CS260

CHAPTER 4 : NETWORK SECURITY t2e 2ost picks a random num9er- encr1pts it wit2 t2e pu9lic ke1 and sends it to t2e user. T2e user is suppose to decr1pt t2e data usin! t2e pu9lic ke1 and send it 9ack to t2e 2ost. 0s t2e user is t2e onl1 person w2o knows t2e pu9lic ke1- t2e user can 9e 8uite safe. T2e 2acker ma1 tr1 to record t2e data traffic and retransmit durin! anot2er session. &ut 2e will 9e unsuccessful as t2e random num9er will 9e different. &esides t2e pu9lic ke1- t2e 2ost mi!2t re8uire t2e user to attac2 additional aut2entication information wit2 t2e messa!e. T2is aut2entication information could 9e a se8uence num9er- secret password or time information of transmission. 0ll t2ese additional aut2entication information makes it difficult for t2e 2acker to record t2e data traffic and pla1 it 9ack at a later time durin! anot2er session. % 9 " En-+?*t.on =ncr1ption in3ol3es t2e use of a ke1 to process t2e ori!inal c2aracter strin! to produce a cr1pto!ram w2ic2 is transmitted o3er t2e medium. T2e recei3er- knowin! t2e ke1- can decr1pt t2e messa!e to !et 9ack ori!inal c2aracter strin!.

Figure 4-2
T2e messa!e to 9e encr1pted is known as Hte,tH. =ncr1ption process output is known as Cip2er te,t or Cr1pto!ram w2ic2 is transmitted o3er t2e medium. 5e1 5 is a parameter to t2e function w2ic2 con3ert t2e te,t to Cip2er te,t. <nce t2e messa!e is encr1pted- it 9ecomes difficult for t2e 2acker to decr1pt it as t2e1 donCt 2a3e t2e ke1. T2ere are two standard cate!ories of encr1ption tec2ni8ues and t2e1 are u9stitution Cip2er In t2is kind of encr1ption- a letter or a !roup of letters is su9stituted 91 anot2er letter or !roup of letters. <ne e,ample of su9stitution cip2er is s2own 9elow Te,t A Informatics =ac2 c2aracter in t2e te,t is su9stituted 91 a c2aracter w2ic2 is s2ifted 91 n E# letters t2en t2e c1p2erte,t 9ecomes C1p2erte,t A Nsktwrf1n2,





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CHAPTER 4 : NETWORK SECURITY ;enerall1 it is eas1 to 9reak su9stitution cip2er. Transposition Cip2er In transposition cip2er t2e order of letters is c2an!ed 9ut t2e letters remain unc2an!ed. T2is is unlike su9stitution cip2er w2ere t2e order of plain te,t s1m9ols are preser3ed. For t2is kind of cip2er- t2ere will a ke1 w2ic2 will t1picall1 9e a word wit2out containin! an1 repeated letters. 0ll t2e letters in t2e ke1 are assi!ned num9ers accordin! to t2eir alp2a9etical order. T2e letter closer to t2e 9e!innin! of alp2a9et is assi!ned num9er 1. T2ese num9ers are used to num9er t2e columns. T2e te,t to 9e encr1pted is written down 2a3in! as man1 columns as t2ere are num9ers in t2e ke1. T2en all t2e columns are written down 2oriDontall1 startin! wit2 column 1.



=,ampleA

Te,tA t2issentenceis!oin!to9eencr1ptedusin!su9stitutioncip2er 5e1A 5=I:<$/ 5 3 t t ! 9 p n i c = 2 2 e o e t ! t i I ( i n i e e s u p : % s c n n d u t 2 < 4 s e ! c u 9 i e $ # e i t r s s o r / 1 n s o 1 i t n a

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CS260 Cip2erte,tA

CHAPTER 4 : NETWORK SECURITY



nso1itna2eoet!titt!9pnicse!cu9ieeitrssorscnndut2inieesup T1picall1 t2e transposition cip2er is more difficult to 9reak t2an su9stitution cip2er. % 9 # Data Co2*+ess.on In data communication- data compression tec2ni8ue is used to utilise t2e communication c2annel efficientl1. T2is compression tec2ni8ue also acts as a form of encr1ption a!ainst 2ackers. T2ere are different wa1s of ac2ie3in! data compression dependin! on t2e application. For e,ample t2ink a9out a scenario w2ere a departmental store communicates to its 2ead office usin! a communication software. 0t t2e end of t2e da1- t2e departmental store needs to send a report to t2e 2ead office listin! all t2e items t2at are in demand. 0ssumin! t2ere are 1+++ items wit2 eac2 item name 9ein! 1+ c2aracters lon!- 1+++Q1+E1+-+++ c2aracters needs to 9e transmitted for t2e item names onl1. T2e situation can 9e impro3ed if we represent t2e items 91 a se8uence num9er. o we can ac2ie3e data compression 91 transmittin! se8uence num9er instead of names. 0not2er wa1 to ac2ie3e data compression is 91 encodin! t2e s1m9ols in te,t dependin! on t2eir fre8uenc1 of occurrence. It is 8uite apparent t2at some s1m9ols occur more fre8uentl1 t2an consonants. 5eepin! t2is fact in mind- more fre8uentl1 occurrin! s1m9ols are encoded usin! smaller num9er of 9its compared to ot2er s1m9ols. Num9er of 9its t2at will 9e used to encode a s1m9ol depends on t2e pro9a9ilit1 of occurrence. ;reater pro9a9ilit1 of occurrence will mean lesser num9er of 9its to encode t2e s1m9ol. =ncodin! s1m9ols t2is wa1 2elps in ac2ie3in! data compression compared to t2e sc2eme w2ere eac2 s1m9ol is represented usin! same num9er of 9its. % : Re/.e3 $1est.ons 2). :2at is noiseK /escri9e different t1pes of noise. 2*. .ow error is detected durin! data transmissionK <nce error is detected- w2at are t2e different wa1s in w2ic2 t2e error can 9e correctedK 3+. :21 is flow control is re8uired in data communicationK /escri9e different tec2ni8ues used to control t2e flow of data transmission. 31. /escri9e w2at is slidin! window protocol. 32. :2at is encr1ptionK :21 is encr1ption re8uiredK 33. /escri9e w2at computer crime is. 34. :21 do we need aut2enticationK :2at are t2e different t1pes of aut2enticationK

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CHAPTER
C)a*te+ Ob,e-t./es

: OSI MODEL AND TCP(IP

0fter completion of t2is c2apter- 1ou will 9e a9le toA ⇒ learn a9out < I model and t2e different la1ers in3ol3edB ⇒ learn and appl1 t2e followin! conceptsB • • • • • • t2e function of "21sical ?a1er and t2e ser3ices it pro3ides to /ata ?ink ?a1er t2e function of /ata ?ink ?a1er and t2e ser3ices it pro3ides to Network ?a1er t2e function of Network ?a1er and t2e ser3ices it pro3ides to Transport ?a1er t2e function of Transport ?a1er and t2e ser3ices it pro3ides to ession ?a1er t2e function of ession ?a1er and t2e ser3ices it pro3ides to "resentation ?a1er t2e function of "resentation ?a1er and t2e ser3ices it pro3ides to 0pplication ?a1er t2e function of 0pplication ?a1er and t2e ser3ices it pro3ides to user application process



⇒ learn a9out TC">I"B ⇒ learn a9out FT" and MT". ' 1 O*en S?ste2s Inte+-onne-t.on $apid proliferation of protocols- modems- si!nallin! met2ods- and network arc2itectures created man1 pro9lems. @sers were o9li!ed to support e,pensi3e redundant e8uipment. T2e standards or!anisation decided to define common structure of data processin! mac2ines to alle3iate some of t2e pro9lem. In 1*() t2e International tandards <r!anisation 6I <7proposed a la1ered network arc2itecture- called t2e <pen 1stems Interconnection $eference Model 6< I $M7. T2is model makes it possi9le for data processin! mac2ines from different 3endors to freel1 communicate and interc2an!e data. In t2e < I en3ironment t2e complicated communication task is di3ided into a set of mana!ea9le functions called la1ers. =ac2 la1er performs a su9set of task re8uired to communicate wit2 ot2er s1stem. <pen 1stem Interconnection 6< I7 is concerned wit2 t2e e,c2an!e of information 9etween s1stems- in fact- HopenH s1stems. :it2in < I- a distinction is made 9etween HrealH s1stems and HopenH s1stems. 0 real s1stem is a computer s1stem to!et2er wit2 t2e associated softwareperip2erals- and terminals. :2ereas- open s1stem is onl1 a representation of real s1stem t2at is known to compl1 wit2 t2e arc2itecture and protocols as defined 91 < I. In fact- an open s1stem is t2at portion of a real s1stem t2at is 3isi9le to ot2er open s1stem in t2eir attempts to transfer and process

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CS260

CHAPTER 5: OSI MODEL AND TCP/IP information jointl1. It s2ould 9e mentioned t2at < I is not onl1 concerned wit2 interconnection and e,c2an!e of information 9etween open s1stems- 9ut also wit2 interconnection aspects of co-operation 9etween s1stems w2ic2 includes acti3ities suc2 as inter-process communication.

Figure -1

' "

La?e+e0 A+-).te-t1+e Con-e*t Fi!ure #-2 s2ows a collection of real s1stems t2at are interconnected 91 usin! p21sical media. T2e o3erall o9jecti3e of all software or 2ardware t2at forms t2e open s1stem is to ena9le interconnection 9etween application processes. 0pplication processes are an a9straction of user pro!rams t2at implement certain user applications. .owe3er onl1 certain aspects of application pro!rams are of interest- t2ose t2at concern communication 9etween users. To desi!n and implement comple, mec2anisms for information transfer and co-operation- t2e entire network must 9e 3iewed as a series of la1ers. =ac2 open s1stem is lo!icall1 di3ided into a collection of su9s1stemseac2 implementin! a certain function. 0 la1er is a collection of all su9s1stems from different open s1stems t2at perform similar function.

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CHAPTER 5: OSI MODEL AND TCP/IP

Figure -2

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CS260

CHAPTER 5: OSI MODEL AND TCP/IP

' #

La?e+s> Se+/.-es an0 F1n-t.ons 0 network of computers ma1 9e 3iewed as a series of la1ers. =ac2 la1er pro3ides a collection of ser3ices to t2e su9s1stems in t2e 2i!2er la1er - t2e a9ilit1 to ena9le users to e,c2an!e data wit2out concern for its representation. 0s we !o up t2e la1ers- t2e kind of ser3ices made a3aila9le at eac2 la1er c2an!es. =ac2 la1er must implement certain functions o3er and a9o3e t2e ser3ice made a3aila9le to it 91 t2e lower la1ers- t2ere91 enlar!in! t2e ser3ice. T2e concept of la1erin! is similar to sol3in! a lar!er pro9lem as a series of smaller mana!ea9le pro9lems. 0s an e,ample- one 2as to pro3ide a ser3ice wit2 w2ic2 a user ma1 transfer relia9l1 across network wit2out concern for representation of information. T2is pro9lem is sol3ed 91 implementin! specific functions in different la1ers to sol3e eac2 aspect of t2e pro9lem. T2e desi!n of a la1er ma1 9e c2an!ed to incorporate new tec2nolo!1 wit2out 2a3in! to c2an!e t2e ot2er la1ers. In some wa1s t2e la1ered arc2itecture approac2 is similar to a top-down desi!n of a 2ardware>software s1stem. <ne 9reaks down t2e pro9lem of interconnection 9etween s1stems into a num9er of smaller pro9lems- eac2 pro9lem 9ein! sol3ed wit2in la1er. T2is approac2 2as a num9er of ad3anta!es like modular construction- independence from implementation of t2e underl1in! la1er- maintenance- and standardisation. <nce t2e ser3ice made a3aila9le 91 eac2 la1er is defined- t2en it is eas1 to see w2at t2e function of eac2 la1er is. 0 la1er 9rid!e t2e !ap 9etween t2e ser3ices made a3aila9le 91 it and t2ose a3aila9le to it.

Figure -3

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CHAPTER 5: OSI MODEL AND TCP/IP

' %

Ent.t.es> P+oto-ols an0 Inte+fa-es 0 su9s1stem consists of one or more entities. 0n entit1 is a 2ardware or a software module. <nl1 t2at aspect of a module- w2ic2 is 3isi9le from t2e 3iewpoint of communication 9etween entities- is considered part of t2e entit1. For e,ample- t2ree entities are re8uired to 2andle t2ree transmission lines in eac2 s1stem. T2e t2ree entities to!et2er form t2e su9s1stem t2at uses t2e transmission media. 0 network ma1 9e 3iewed as a collection of entities. Two entities in two different s1stems ma1 interact or communicate wit2 eac2 ot2er- pro3ided t2e1 9elon! to t2e same la1er. uc2 entities are called peer entities- and t2e interaction 9etween t2em is !o3erned 91 w2at is known as a protocol. 0 protocol specifies t2e nature of information t2at ma1 9e e,c2an!ed 91 two peer entities- 9ot2 in respect of semantics and s1nta,. It also specifies under w2at conditions- entit1 ma1 send or recei3e information. imilarl1- two entities wit2in a real s1stem ma1 interact wit2 eac2 ot2er pro3ided t2e1 9elon! to two adjacent la1ers. T2is form of interaction across a la1er is consistent wit2 t2e ser3ice made a3aila9le 91 an entit1 to t2e entit1 in t2e ne,t 2i!2er la1er. Its specification is in terms of t2e collection of primiti3e operations called primiti3es t2at eit2er entit1 is allowed or capa9le of supportin!. T2ese are primiti3e in t2e sense t2at t2e1 ma1 not 9e 9roken down an1 furt2er. 0ssociated wit2 eac2 primiti3e is a collection of parameters t2at ma1 9e e,c2an!ed. In aspects pertainin! to t2e implementation of t2e ser3ice- primiti3es are not part of t2e arc2itecture specification. Neit2er is t2e representation of t2e parameters. 0n implementation of t2e ser3ice is referred to as interface.

Figure -4
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CS260 ' ' OSI Refe+en-e Mo0el

CHAPTER 5: OSI MODEL AND TCP/IP

T2e dia!ram 9elow s2ows t2e < I reference model allowin! application pro!ram 0 in 2ost F to communicate wit2 application pro!ram & in 2ost I. T2e connection 9etween 0 and & is s2own 91 t2e dotted line. T2e model includes se3en la1ers as s2own. T2e lower la1ers- one t2rou!2 t2ree e,ists in 9ot2 t2e nodes and t2e 2ost computer and are responsi9le to transport data packet across t2e su9net. ?a1ers four t2rou!2 se3en are called end-to-end la1ers and e,ist in t2e 2osts onl1. T2e upper la1ers- fi3e t2rou!2 se3en- deal wit2 t2e wa1 t2e application pro!ram communicates. T2e transport la1er is a liaison 9etween t2e lower la1ers and t2e upper la1ers and pro3ides an end-toend relia9le pat2 9etween t2e applications. =ac2 la1er pro3ides ser3ices to t2e la1er a9o3e it and recei3es some ser3ices from t2e la1er 9elow. 0 la1er re8uests t2e ser3ices of t2e la1er 9elow it t2rou!2 an interface s2own 91 3ertical arrows. =ac2 entit1 talks wit2 its peer entit1- w2ic2 resides in a network node or anot2er data station. T2e peer communication is !o3erned 91 a protocol s2owed 91 dotted 2oriDontal arrows. T2e ser3ices and protocols at eac2 la1er are specified 91 t2e I <. T2e peer entities communicate wit2 one anot2er o3er a lo!ical connection. "21sical connection e,ists at t2e p21sical la1er w2ic2 t2e actual p21sical mo3ement of information occurs.

Figure -

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CHAPTER 5: OSI MODEL AND TCP/IP

' ' 1 P)?s.-al La?e+ "21sical la1er is responsi9le for t2e transparent transmission of information across t2e p21sical medium. T2e data unit at t2e p21sical la1er is a 9it. T2e standards of t2is la1er include =I0-232-C- =I0232-/ and F.21. T2e attri9utes of t2e p21sical la1er interfaces can 9e !rouped as followsA ♦ =lectricalA T2is is concerned wit2 electrical c2aracteristics. e.!. 3olta!e le3els- impedances- and t2e timin! of t2e electrical c2an!es to represent a 9inar1 + or 1. FunctionalA T2is is concerned wit2 t2e meanin! of t2e 3olta!e le3els on certain pins of t2e connector. =,amples of t2is functions are control- timin!- data and !round- t2e interc2an!e circuits 9etween two stations 6functional c2aracteristics of $ -232-C7 Mec2anicalA T2is deal wit2 wires- t1pes of connectors- p21sical dimensionsallocation of pins and so on 6p21sical c2aracteristics of $ -232C7. "roceduralA T2e procedural specification define t2e rules appl1in! to 3arious function- t2e se8uence in w2ic2 certain e3ents ma1 occur i.e. t2e1 descri9e w2at t2e pins on t2e connectors must do and t2e se8uence of e3ents re8uired to effect actual data transfer across t2e interface. =,ample of procedural specification of $ 232-C can 9e found in c2apter one.







' ' 1 1

Se+/.-es P+o/.0e0 to t)e Data L.n4 La?e+

Followin! are some of t2e ser3ices pro3ided 91 t2e "21sical ?a1er to t2e /ata link la1erA ♦ "21sical connectionA 0 p21sical connection effecti3el1 sets up a H/ata Circuit 9etween p21sical connections end points. ♦ "21sical connection end pointsA T2e p21sical la1ers pro3ide identifiers of p21sical connection end-points w2ic2 ma1 9e used 91 t2e /ata ?ink ?a1er. ♦ e8uencin!A T2e p21sical la1ers deli3ers 9its in t2e same order in w2ic2 t2e1 were su9mitted. ♦ /ata circuit identificationA T2e p21sical la1er pro3ides identifiers w2ic2 uni8uel1 specif1 t2e data circuits 9etween two s1stems.

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CS260

CHAPTER 5: OSI MODEL AND TCP/IP ♦ Fault condition notificationA T2e data link la1er is informed of fault conditions detected wit2in t2e p21sical la1er.

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CS260

CHAPTER 5: OSI MODEL AND TCP/IP

' ' 1 "

F1n-t.ons Pe+fo+2e0 b? t)e P)?s.-al La?e+

T2e followin! functions are performed 91 t2e "21sical ?a1er w2ic2 are independent of t2e actual p21sical medium used. ♦ =sta9lis2ment- maintenance and release of connectionsA 0cti3atesmaintains and deacti3ates p21sical connections for 9it transmission 9etween /ata ?ink entities possi9l1 t2rou!2 intermediate s1stem- eac2 rela1in! 9it transmission wit2in t2e p21sical la1er. ♦ TransmissionA T2e transmission of 9it streams- w2ic2 can 9e in full duple, or 2alf-duple,- s1nc2ronous or as1nc2ronous. ♦ Mana!ementA T2e "21sical ?a1er protocol deals wit2 some aspects of t2e mana!ement acti3ities in t2e la1er.

' ' " Data L.n4 La?e+ T2e data link la1er s2ields t2e 2i!2er la1er from t2e c2aracteristics of t2e p21sical transmission medium and pro3ides a relia9le and error free data link connection. :it2in t2e data link la1er- t2e p21sical la1er data streams are arran!ed into 9locks of data called HframesH. 1nc2roniDation of t2e 9its wit2in t2e frame- error detection- error correction 691 re-transmission of frame7- and flow control are all data link la1er functions. ome of t2e e,istin! standards of t2is la1er areA ♦ I < ./?C- w2ic2 is a superset of se3eral classes of data link protocols ♦ I=== )+2.2- for local area network

' ' " 1

Se+/.-es P+o/.0e0 to t)e Net3o+4 La?e+



T2e followin! are some of t2e ser3ices pro3ided 91 t2e /ata ?ink ?a1er to t2e Network la1erA /ata link connectionA T2e pro3ision of one or more data link connection 9etween two network entities e8uencin!A Maintainin! t2e frames of data in t2e correct se8uence =rror notificationA ♦ If an unreco3era9le error is detected- t2e Network la1er is notified Flow controlA T2e Network ?a1er can d1namicall1 control t2e rate at w2ic2 it recei3es frames of data.





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CHAPTER 5: OSI MODEL AND TCP/IP

' ' " "

F1n-t.ons Pe+fo+2e0 b? t)e Data L.n4 La?e+

♦ ♦

T2e followin! are some of t2e functions performed 91 t2e /ata ?ink ?a1erA =sta9lis2ment and releaseA et up and release of data link connections. /elimitin! and s1nc2ronisationA T2is is essentiall1 t2e framin! function w2ic2 or!anises 9its into frames. :it2in t2e /ata ?ink ?a1er- t2e "21sical ?a1er 9it streams are arran!ed into 9locks of data called HframesH. 1nc2ronisation of t2e 9its wit2in t2e frame is maintained. e8uence controlA Maintains t2e se8uential order of frames transmitted o3er a data link. =rror detectionA T2is function detects transmission- format and operational errors- usuall1 91 re-transmission of frames. =rror reco3er1A T2is function attempts to reco3er from errors- usuall1 91 re-transmission of frames. Flow controlA T2e flow control function is done 91 turnin! frame transmission on and off accordin! to t2e state of t2e recei3in! s1stem. Control of data circuit interconnectionA T2is function con3e1s to t2e Network ?a1er t2e information necessar1 to control t2e interconnection of data circuits wit2in t2e p21sical la1er. Mana!ementA T2e /ata ?ink ?a1er protocols deal wit2 some mana!ement acti3ities of t2e la1er.













' ' # Net3o+4 La?e+ 0 practical re8uirement for a network is to allow multiple users to 2a3e access to multiple applications. T2e essential functions of t2e Network ?a1er is to pro3ide t2e transparent transmission of data from a Transport ?a1er in one s1stem 6e.!. in a user terminal7 to a transport la1er in anot2er s1stem 6e.!. an application 2ost computer7. In comple, network- t2e transport la1er communicatin! entities need not 9e adjacent to eac2 ot2er 9ut are connected 3ia one or more intermediate s1stems w2ic2 perform a rela1in! function. In some cases t2e network la1er pro3ides

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CHAPTER 5: OSI MODEL AND TCP/IP routin! functions. =ac2 intermediate s1stem ma1 9e a network- and a set of one or more intermediate s1stem used for a connection is termed a Hsu9-networkH. 0 practical e,ample mi!2t 9e t2e interconnection of a pu9lic data network- a pri3ate data network and a local area network. Network addresses are used to identif1 Transport la1er entities to t2e network la1er. T2e data unit in t2e Network la1er is known as packet. <ne e,ample of network la1er protocol is CCITT F.2#- t2e packet la1er protocol. ' ' # 1 Se+/.-es P+o/.0e0 to t)e T+ans*o+t La?e+

Followin! are some of t2e ser3ices pro3ided 91 t2e Network ?a1erA ♦ Network 0ddresses. Network addresses are pro3ided 91 t2e network la1er and are used 91 transport entities to uni8uel1 identif1 ot2er transport entities. ♦ Network connectionsA Network connections pro3ide t2e means of transferrin! data 9etween transport entities. ♦ Network connection end-point identifiersA T2e network la1er pro3ides to t2e transport entities an identifier w2ic2 identifies t2e network connection end-point uni8uel1 wit2 t2e associated network address. ♦ =rror notificationA @nreco3era9le errors detected 91 t2e network la1er are reported to t2e transport la1er. ♦ e8uencin!A T2e network la1er ma1 pro3ide se8uenced deli3er1 of packets o3er a !i3en network connection. ♦ Flow controlA 0 transport entit1 w2ic2 is recei3in! at one end of a network connection can cause t2e network ser3ice to stop sendin! data units. T2is flow control condition ma1 or ma1 not 9e propa!ated to t2e ot2er end of t2e network connection. ♦ $eleaseA 0 transport entit1 ma1 re8uest release of a network connection. ' ' # " F1n-t.ons Pe+fo+2e0 b? t)e Net3o+4 La?e+

Network la1er functions pro3ide a wide 3ariet1 of confi!uration from point-to-point connections to comple, com9inations of su9-network wit2 different c2aracteristics. Followin! are some of t2e functions performedA ♦ $outin! and rela1in!A Network connections are pro3ided 91 network entities in end s1stems 9ut ma1 in3ol3e intermediate s1stems w2ic2 pro3ide rela1in!. $outin! functions determine an appropriate route 9etween network addresses. ♦ Con!estion controlA T2e o9jecti3e of t2is function is to maintain t2e num9er of packets wit2 t2e network 9elow t2e le3el at w2ic2 performance falls off dramaticall1.

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CHAPTER 5: OSI MODEL AND TCP/IP ♦ Network connectionsA T2is function pro3ides network connection 9etween transport entities- makin! use of data link connections pro3ided 91 t2e data link la1er. ♦ e!mentin! and 9lockin!A T2e network la1er ma1 se!ment and>or form into 9locks t2e Network ser3ice data units for t2e purpose of facilitatin! t2e transfer. ♦ =rror detectionA T2is function is used to c2eck t2at t2e 8ualit1 of ser3ice pro3ided o3er a network connection is maintained. =rror detection in t2e network la1er uses error notification from t2e data link la1er. ♦ =rror reco3er1A T2is function pro3ides for reco3er1 from detected errors and ma1 3ar1 dependin! on t2e 8ualit1 of t2e network ser3ice pro3ided. ♦ e8uence deli3er1A e8uencin! pro3ides for t2e se8uenced deli3er1 of packets o3er a !i3en network connection. ♦ Flow controlA 0 transport entit1 w2ic2 is recei3in! at end of a network connection can cause t2e network ser3ice to stop sendin! data units. T2is flow control condition ma1 or ma1 not 9e propa!ated to t2e ot2er end of t2e network connection. ' ' % T+ans*o+t La?e+ T2e transport la1er pro3ides t2e functions necessar1 to 9rid!e t2e !ap 9etween t2e ser3ices a3aila9le from t2e network la1er and t2ose re8uired 91 t2e la1ers a9o3e. T2e four lower la1ers pro3ide t2e user wit2 a transport ser3ice- t2e transport la1er role is to complement t2e underl1in! network so as to ensure t2at t2e re8uired 8ualit1 of ser3ice is made a3aila9le to t2e user. Transport functions are concerned wit2 cost optimisation- error control- flow control- se8uencin! and multiple,in!. T2e transport la1er can also c2eck for lost or duplicated information. If t2e network connection is temporaril1 9roken- t2e transport connection ma1 9e 2eld until t2e network connection is restored. Transport la1er protocols are desi!ned to cope wit2 a 3ariet1 of different networks of 3ar1in! 8ualit1 of ser3ice. T2e data unit at t2e transport la1ers and t2e la1ers a9o3e it are a messa!e. <ne e,ample of Transport ?a1er protocol is @nited tates /epartment of /efence 6/</7 Transmission control "rotocol6TC"7 used in 0$ "0N=T. ' ' % 1 Se+/.-es P+o/.0e0 to t)e Sess.on La?e+

T2e transport la1er uni8uel1 identifies eac2 session entit1 91 its transport address. T2e transport ser3ice pro3ides t2e means to esta9lis2- maintain and release transport connections 9etween a pair of transport addresses. T2e connections are full duple, and more t2at one connection can

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CHAPTER 5: OSI MODEL AND TCP/IP 9e esta9lis2ed 9etween t2e same pair of addresses. Followin! ser3ices are pro3ided 91 t2e transport la1erA ♦ Transport connection esta9lis2mentA Transport connections are esta9lis2ed 9etween session entities identified 91 transport addresses. T2e 8ualit1 of ser3ice of t2e connection is ne!otiated 9etween t2e session entities and t2e Transport er3ice. ♦ /ata transferA "ro3ides data transfer in accordance wit2 t2e a!reed 8ualit1 of ser3ice. ♦ Transport connection releaseA "ro3ides t2e means 91 w2ic2 eit2er session entit1 can release a transport connection. ' ' % " ♦ F1n-t.ons Pe+fo+2e0 b? T+ans*o+t La?e+

Transport ?a1er performs t2e followin! functionsA • • =sta9lis2ment p2aseA /urin! t2is p2ase t2e followin! functions are performed <9tains a network connection w2ic2 matc2es t2e re8uirements of t2e session entit1 takin! into account cost and 8ualit1 of ser3ice =sta9lis2 as optimum transport packet siDe elects t2e function w2ic2 will 9e operational durin! data transfer Maps transport addresses onto network addresses "ro3ides identification of transport addresses Transfers data

• • • • •

♦ /ata transfer p2aseA T2is is ac2ie3ed 91 t2e transmission of packets and t2e followin! ser3ices A • • • • • • • • • ♦ e8uencin! &lockin! Concatenation e!mentin! Flow control =rror detection =rror reco3er1 =,pedited data transfer Transport connection identification

$elease p2aseA $elease p2ase includes t2e followin! functions. • • • Notification of reason for release Identification of transport connection released Transfer of data

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CHAPTER 5: OSI MODEL AND TCP/IP

?ower four la1ers of t2e < I model are concerned wit2 pro3idin! end-to-end connection. T2e upper t2ree la1ers deal wit2 useroriented ser3ices. More specificall1- t2e session la1er sol3es t2e pro9lem of dialo!ue discipline for application process-to-application process communication and pro3ide 3alue. T2e session ser3ice is pro3ided 91 t2e session protocol makin! use of t2e ser3ices a3aila9le from t2e transport la1er. T2e session ser3ice pro3ides t2e means for or!anised and s1nc2ronised e,c2an!e of data 9etween operatin! session ser3ices users. ' ' ' 1 Se+/.-es P+o/.0e0 to t)e P+esentat.on La?e+

Followin! are some of t2e ser3ices pro3ided 91 t2e ession la1erA ♦ ession connection esta9lis2mentA =na9les two presentation entities to esta9lis2 a session connection 9etween t2emsel3es. ♦ ession connection releaseA 0llows presentation entities to release a session connection in an ordinar1 wa1 wit2out loss of data. ♦ Normal data e,c2an!eA 0llows a sendin! presentation entit1 to transfer a session ser3ice data unit to a recei3in! presentation entit1. ♦ Interaction mana!ementA 0llows t2e presentation entities to control e,plicitl1 w2ose turn it is to e,ercise certain control functions. T2e followin! t1pes of interaction are definedA 6i7 two wa1 simultaneous- 6ii7 two wa1 alternati3e- 6iii7 one wa1. ♦ =,ception reportin!A "ermits t2e presentation entities to 9e notified of e,ceptional situations not co3ered 91 ot2er ser3ices. ' ' ' " F1n-t.ons Pe+fo+2e0 b? Sess.on La?e+

Most of t2e functions re8uired are implied 91 t2e ser3ices pro3ided. ♦ Mappin! of sessions connections to transport connectionA T2is is done on a one- to -one 9asis. ♦ ession connection flow controlA T2ere is no peer flow control in t2e ession ?a1er. To a3oid o3erload- t2e Transport la1er flow control is used. ♦ ession connection reco3er1A In t2e e3ent of a transport connection failure- t2e ession la1er ma1 contain t2e functions necessar1 to esta9lis2 a new transport connection in order to continue t2e session. ♦ ession connection releaseA =na9les t2e release of a session connection wit2out loss of data. ' ' 6 P+esentat.on La?e+ Computers ma1 use t2eir own wa1 of representin! data internall1. =,amples of differences includeA

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CHAPTER 5: OSI MODEL AND TCP/IP C2aracter setsA 0 CII 3s. =&C/IC Inte!ersA 9inar1 3s. &inar1 coded decimal oneCs complement 3s. TwoCs complement :ord siDeA 1% 9it 3s. 32 9it &it orderA left to ri!2t 3s. $i!2t to left &1te orderA left to ri!2t 3s. $i!2t to left

♦ ♦ ♦ ♦ ♦ ♦

T2e 8uestion is- La2ow can t2e information 9e transferred and still preser3e t2e meanin!KC 0!reements and con3ersions are needed to ensure t2at different computers can understand one anot2er. o t2e "resentation ?a1er will A ♦ =ncode structured data from t2e internal format used in t2e sendin! mac2ine to a suita9le pattern for transmission ♦ ♦ ♦ ♦ /ecode t2e data to t2e re8uired representation at t2e recei3in! mac2ine Two t2in!s are neededA 0 s1stem independent presentation of data- i.e.- a9stract s1nta, 0 common s1nta, 9etween t2e s1nta, for e,c2an!e- i.e.- transfer s1nta, P1+*ose of P+esentat.on La?e+

' ' 6 1

T2is la1er is responsi9le for ensurin! t2at information is presented to t2e e3entual user in a meanin!ful wa1. T2is la1er is concerned wit2 t2e wa1 t2e data is represented and t2e data structures emplo1ed in t2e representation. T2is la1er is concerned onl1 wit2 s1nta, and not wit2 semantics. <ne e,ample of "resentation ?a1er is I < ))22A Connection<riented "resentation er3ice /efinition. ' ' 9 A**l.-at.on La?e+ T2e purpose of t2e application la1er is to pro3ide a window for correspondent application processes to communicate 3ia an < I en3ironment. 0pplication processes e,c2an!e information 91 means of application entities- application protocols and presentation ser3ice ' ' 9 1 Se+/.-es P+o/.0e0 to A**l.-at.on P+o-ess

In addition to information transfer- t2ese ma1 includeA ♦ Identification of communication partners 91 name- address- and description. ♦ /etermination of t2e a3aila9ilit1 of t2e desired communication partners. ♦ ♦ =sta9lis2ment of t2e aut2orit1 to communicate. 0ut2entication of intended communication partners.

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CHAPTER 5: OSI MODEL AND TCP/IP /etermination of cost allocation met2odolo!1. /etermination of ade8uac1 of resources. /etermination of accepta9le 8ualit1 of ser3ice. 1nc2ronisation of applications. election of dialo!ue discipline. 0!reement on t2e responsi9ilit1 for error reco3er1. 0!reement on procedures for control of data inte!rit1. Identification of constraints on data s1nta,. ' ' 9 " F1n-t.ons Pe+fo+2e0 b? A**l.-at.on La?e+

♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦

♦ ♦

T2e application la1er contains all functions w2ic2 are re8uired for communication 9etween open s1stem not pro3ided 91 t2e lower la1ers. Communication 9etween application processes takes place 3ia application entities in t2e 0pplication la1er. T2ese entities are di3ided into user elements and application ser3ice elements. T2e latter are cate!orised asA Common 0pplication er3ice =lements 6C0 =7 pecific 0pplication er3ice =lements 6 0 =7 =,ample of 0 = is- File Transfer 0ccess and Mana!ement 6FT0M7.

' 6

Int+o01-t.on to TCP(IP Transmission control protocol>internet protocol 6TC">I"7 is 9est descri9ed as a suite of protocols t2at offers 2ost-2ost communication for users connected to di3erse networks. T2e networks could 9e "u9lic /ata Networks/epartment of /efence 6/o/7 0$"0N=T or 2i!2-speed local networks. /o/ uses t2e terminolo!1 HInternetH referrin! to t2eir collection of networks suc2 as ?0Ns- ?on! .aul and satellite nets. .owe3er- we will use t2e term in t2e less restricted sense as applied to an1 linked set of networks. In 1*%* t2e defence department 6/0$"0 or /efence 0d3anced $esearc2 "rojects 0!enc17 esta9lis2ed a four-node store-and-forward packet network. &1 1*(2 t2e network included researc2 and uni3ersit1 sites w2ose 2osts 2ad implemented se3eral protocols for end-end communication. T2e e3olution of t2e protocol proceeded and 91 1*)2 a suite of protocols 2ad 9een refined into w2at we call transmission control protocol 6TC"7 and t2e internet protocol 6I"7. ' 6 1 Inte+net3o+4.n5 an0 TCP(IP TC">I" is called a suite of protocols 9ecause it allows 2osts on different networks to communicate wit2 one anot2er. T2e term Internet is also used to descri9e an1 collection of linked networks. TC">I" can 9e 3iewed as t2e 9est current alternati3e to t2e I <

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CHAPTER 5: OSI MODEL AND TCP/IP stack for interopera9ilit1 9etween mac2ines. Most manufacturers 2a3e not implemented I < protocols 1et- 9ut 2a3e access to TC">I". T2ree major ad3anta!es of TC">I" areA ♦ Interopera9ilit1 9etween 2osts ♦ ♦ ♦ Internetworkin! capa9ilit1 implicit1 /ifferent networks are linked to!et2er 91 9rid!es and !atewa1s. &rid!es are two-la1er de3ices t2at interconnect local area networks t2at differ at t2e medium access control 6M0C7 la1er. ;atewa1s in t2e internet world are t2ree-la1er de3ices. More correctl1 t2e1 s2ould 9e called routers.

0s an e,ample- .ost F wants to use t2e ser3ices of .ost I. .ost F opens TC" connection t2rou!2 t2e internet to t2e 2ost. In addition.ost R needs a file stored on .ost F. 0not2er TC" connection is t2en esta9lis2ed to a file ser3er on F.

Figure -!
#.%.2 TC">I" 3s. I < Model 0lt2ou!2 de3eloped 9efore t2e definition of t2e I < model- TC">I" and its ser3ices fit closel1 into t2is arc2itecture. T2is model allows t2e communication software to 9e 9roken into modules as followsA ?a1er (A 0pplication ?a1er ?a1er %A ?a1er #A "resentation ?a1er ession ?a1er

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CHAPTER 5: OSI MODEL AND TCP/IP

?a1er 4A ?a1er 3A ?a1er 2A ?a1er 1A

Transport ?a1er Network ?a1er /ata ?ink ?a1er "21sical ?a1er

Figure -"
0ll la1ers are inte!rated to accomplis2 information transfer. In t2e same wa1- eac2 la1er of t2e TC">I" modelA ♦ &uilds or adds functionalit1 for its own use from t2e ser3ices of t2e lower la1ers ♦ ♦ ♦ "ro3ides a ser3ice to t2e o3erall network- w2ic2 allows standard interfaces and protocols to 9e placed into t2e appropriate la1ers Is independent and is defined 91 function Can 9e c2an!ed wit2out affectin! t2e ot2er la1ers

' 6 # F.le T+ansfe+ P+oto-ol an0 S.2*le Ma.l T+ansfe+ P+oto-ol T2e internet protocol suite 2as a file transfer protocol 6FT"7. FT" allows users to lo! onto a remote 2ost- list remote directories- and o9tain 2elp wit2 remote mac2ines file s1nta,. FT" also can con3ert 9etween file formats- e.!. =&C/IC to>from 0 CII. FT" allows a user to access multiple mac2ines in a sin!le session. It maintains separate

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CHAPTER 5: OSI MODEL AND TCP/IP TC" connections for control and data transfer. FT" is a sop2isticated protocol t2at does more t2an transfer files from one s1stem to anot2er 6from a ser3er to client7. It can for e,ample- 2andle t2ird part1 transfers. It s2ould also 9e mentioned t2at anot2er file transfer protocol e,ists t2at does not pro3ide all t2e e,pense and sop2istication of FT" called tri3ial file transfer protocol 6TFT"7. TFT" does not use a relia9le ser3ice like TC"B instead it uses anot2er unrelia9le packet deli3er1 s1stem. It is restricted to transferrin! small files. T2e simple mail transfer protocol 6 MT"7 is a standard for sendin! mail 9etween 2osts. T2e protocol does not specif1 2ow t2e mail s1stem accepts mail or 2ow t2e user interface presents t2e user wit2 incomin! mail- nor does it specif1 2ow mail is stored. <nce communication 2as 9een esta9lis2ed 9etween users- t2e sender can transmit one or more mail messa!es or e3en make a re8uest t2at t2e roles of sender and recei3er 9e re3ersed so messa!es can flow t2e ot2er wa1. MT" attempts relia9le operation 9ut does not !uarantee reco3er from 2osts t2at drop files. :2ile t2e main features are concerned wit2 messa!e transfer t2ere are some functions t2at deal wit2 destination 3erification and 2andlin!.

' 9

Re/.e3 $1est.ons 3#. H< I $eference model ena9les open s1stems to communicateH e,plain. 3%. /efine t2e terms la1er- interface- protocol- entit1 and primiti3es and !i3e e,amples of eac2. 3(. =,plain t2e difference in flow control performed at t2e data link la1er and flow control performed in t2e Network la1er. 3). :2at are t2e functions performed 91 t2e presentation la1erK 3*. :21 do we need a la1ered arc2itecture in a networkin! en3ironmentK 4+. $elia9ilit1 in data transmission is of prime importance. :2at are t2e la1ers t2at contri9ute to a relia9le data transferK 41. :2at is t2e commonalit1 9etween < I model and TC">I" protocol suiteK 42. /escri9e 2ow FT" makes use of TC">I".

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CHAPTER ! : INTRODUCTION TO LAN
C)a*te+ Ob,e-t./es @pon completion of t2is c2apter- 1ou will 9e a9le to A ⇒ learn t2e e3olution of ?0N and different components in3ol3ed in ?0NB ⇒ learn different ?0N topolo!ies and appl1 t2e concept in work placeB ⇒ learn a9out different c2annel allocation tec2ni8ues and appl1 t2e concept in workB ⇒ learn a9out t2e different medium access tec2ni8ues and appl1 t2e concepts. 6 1 LAN E/ol1t.on In t2e 1*%+s- computin! needs were 2andled 91 a central computer wit2 9atc2 processin! and time s2arin! capa9ilities. /um9 terminals were connected 3ia low-speed transmission facilities to a central computer. Time s2arin! pro3ided a dramatic impro3ement o3er t2e old 9atc2 s1stems- 9ut 2ad its own set of in2erent difficulties. Central processor s1stems 2ad to 2a3e t2e capa9ilit1 to perform lar!e- compute-9ound jo9s and 2ence were far from optimal for interacti3e tasks. &1 t2e 1*(+s- minicomputers were commonl1 used as a means of off-loadin! t2e central facilit1. uc2 mac2ines were !enerall1 located close to t2e user !roups utilisin! t2em. T2is allowed simpler- less costl1 connection met2ods. In addition- t2e mac2ines offered 9etter price>performance statistics for man1 t1pes of application. <f course- t2e multiple minicomputer approac2 to computin! is not wit2out its own set of pro9lems. ome jo9s re8uire more power t2an can 9e pro3ided on a sin!le mac2ine of t2is siDe. ?ocall1 !enerated data 9ases often contain information of 3alue to ot2er departments t2at ma1 use a different s1stem. T2us- t2e ne,t e3olutionar1 step in3ol3ed t2e interconnection of multiple minicomputers into a network. ;enerall1 speakin!- t2ese networks utilised t2e same p2ilosop21 as t2e lon! 2aul networks- despite t2e fact t2at t2e distances in3ol3ed were usuall1 relati3el1 small. T2e e,plosi3e !rowt2 of intelli!ent office e8uipment in t2e 1*)+s 6e.!. word processors- t1pesetters- and copiers7 coupled wit2 e3er increasin! num9er of intelli!ent terminals- 2as created a situation w2ere literall1 2undreds of computers can 9e found in man1 9usiness settin!s. T2is e8uipment !i3e local computin! control to t2e user 9ut does- 2owe3er- lack some of t2e facilities offered 91 a mainframe computer. Indeed- t2e re8uirement for intermac2ine communication is !reater t2an e3er 9efore. ince it is most cost effecti3e to store files and pro!rams on lar!e rotatin! disk dri3es- t2e personal computer terminal must 9e a9le to download needed information and>or pro!rams onto small flopp1 disk s1stems. :ord processors must 9e a9le to communicate directl1 wit2 t1pesettin! mac2ines for ma,imum efficienc1. ?ar!er line printers pro3ide 9etter price>performance ratio in outputtin! 3oluminous material t2an t2e dot matri, de3ices found on t2e t1pical personal computer terminal. =,tensi3e communication capa9ilit1 must 6 - 83

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CHAPTER 6 : INTRODUCTION TO LAN 9e pro3ided in order to make t2e most efficient use of t2e personal computer terminal. 0s we 2a3e o9ser3ed- wide are network 6:0N7 tec2nolo!1 was commonl1 used in t2e earl1 sta!es of local area networkin!. T2is was a conse8uence of t2e a3aila9ilit1 of t2e software and 2ardware products necessar1 to structure suc2 networks- rat2er t2an 9ecause suc2 a approac2 is optimal in t2e local en3ironment. .owe3er- t2e lon! 2aul approac2 is completel1 inappropriate- w2en 2undreds or e3en t2ousands of microprocessor-9ased s1stems re8uire communication ser3ices. 0 new communication s1stem was needed to deal wit2 t2e personal computer en3ironment and t2e ?0N e3ol3ed to satisf1 t2e need.

6 "

C)a+a-te+.st.-s of a LAN T2e Institute of =lectrical and =lectronics =n!ineerin! 6I===7 defines a ?0N as followsA H0 data communication s1stem allowin! a num9er of independent de3ices to communicate directl1 wit2 eac2 ot2er- wit2in a moderatel1 siDed !eo!rap2ic area o3er a p21sical communications c2annel of moderate data rates.H ♦ T2e followin! c2aracteristics can 9e seen in a t1pical ?0NA • ?imited !eo!rap2ical communication area In a ?0N- t2e communication takes place wit2in a moderatel1 siDed !eo!rap2ic area- 9etween +.# km to 1+ km in diameter. T2is is one of t2e t2in!s t2at distin!uis2 it from wide area networks 6:0Ns7. ?0Ns are t1picall1 confined to a sin!le 9uildin! or !roup of 9uildin! t2at are close to!et2er.

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CHAPTER 6 : INTRODUCTION TO LAN



T2e p21sical communication c2annel supports moderate data ratesran!in! from 1 to 1+ M9ps. T2ese rate are 9etween t2e 3er1 2i!2speed rates of links 9etween computers and perip2eral de3ices 6S 2+ M9ps7 and t2e rates supported 91 t2e wide area network 6*.% 59ps to 1.# M9ps7.



/edicated p21sical communication c2annel 0 ?0N communicates o3er a p21sical communications c2annel- suc2 as a dedicated ca9le or ot2er communications medium t2at is used to 2ook all t2e de3ices to!et2er. T2is p21sical c2annel can 9e 9ase9and transmission on a coa,ial ca9le- uns2ielded twisted pair- s2ielded twisted pair or optical fi9re- or 9road9and transmission on optical fi9re or coa,ial ca9le.



"eer-to-peer communication 0 ?0N allows a num9er of independent de3ices- suc2 as an1 com9ination of terminals- "Cs- workstations- printers- stora!e de3ices- and computers- to communicate directl1 wit2 eac2 ot2er. T2erefore in a ?0N- all communicatin! de3ices 2a3e t2e same status and communicate as peers. In ot2er words- no one de3ice controls t2e network. @sers select onl1 t2e data addressed to t2em o3er t2e network and eac2 user 2as e8ual opportunit1 to !ain access to t2e network.



?ow error rate T1picall1- t2e error rate is less t2an 1 9it error in 1+) 9its since t2e ?0N uses a common p21sical c2annel and si!nals are usuall1 in di!ital form.



?0N owners2ip ?0Ns are !enerall1 owned and operated 91 a sin!le entit1- i.e. t2e user or!anisation- indi3idual- or compan1. "u9lic telecommunication companies are not allowed.

6 #

Ma,o+ Ele2ents of a LANs ♦ T2e major elements of a ?0N areA • Ca9lin! 1stems

T2ere are t2ree major t1pes of ca9le used to connect "C stations in a ?0N en3ironmentB wire pair- coa,- and fi9re. :ire pair is t2e least e,pensi3e wit2 t2e lowest transmission speed capa9ilit1 and fi9re is t2e most e,pensi3e wit2 t2e 2i!2est potential transmission speed. Man1 ?0N networks will use more t2an one t1pe of ca9le in t2eir ca9lin! plan suc2 as fi9re for t2e ?0N 9ack9one and wirepair for connection to indi3idual stations. "rotocols "rotocols- are t2e rules w2ic2 !o3ern communication on networks. T2e t2ree most popular protocols used in t2e ?0Ns toda1 are

• -

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CHAPTER 6 : INTRODUCTION TO LAN C M0>C/- Token-$in!- and Token &us. C M0>C/ is t2e =t2ernet standard- Token-$in! is t2e I&M standard- and Token &us is t2e M0" standard used in t2e manufacturin! networks ori!inatin! wit2 ;eneral Motors. • Topolo!ies Topolo!ies descri9e t2e structure of ?0Ns. T2ere are p21sical topolo!ies w2ic2 deal wit2 t2e p21sical la1out and t2e lo!ical topolo!1 w2ic2 !o3erns t2e wa1 data is transmitted on t2e ?0N. T2e t2ree major topolo!ies include- 9usB rin!B and star. In some cases t2e p21sical and lo!ical topolo!ies on a particular ?0N differ. For e,ample- t2e Token-$in! operates lo!icall1 as a rin!9ut is p21sical laid out in a star structure.

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CHAPTER 6 : INTRODUCTION TO LAN

• -

;atewa1s connect ?0Ns to ot2er networks wit2 different protocols actin! as a form of protocol con3erter. T2is would include connections to :0Ns or ot2er ?0Ns. &rid!es are used to connect two or more ?0Ns wit2 common protocol.

"rotocols and topolo!1 will 9e co3ered in t2is c2apter. Ca9lin! 2as 9een co3ered in c2apter 3 and ;atewa1s and &rid!es 2a3e 9een co3ered in c2apter ). 6 % LAN To*olo5? ?0N topolo!1 represents t2e p21sical or lo!ical arran!ement of network stations in relation to eac2 ot2er. For e,ample- in t2e token 9us ?0N- t2e p21sical topolo!1 is a 9us 9ut it 9e2a3es lo!icall1 like a rin!. In close association wit2 t2e topolo!1 is t2e concept of transmission control for t2e interconnections of t2ese stations- primaril1 w2et2er it is distri9uted control or centralised control. T2ere are t2ree 9asic network topolo!iesA starB rin!B and 9us>tree. In implementation- t2e topolo!ies eac2 2a3e t2eir own ad3anta!es and disad3anta!es. ometimes a 219rid of t2ese topolo!ies ma1 9e used 6e.!.- rin!-star7. 6 % 1 R.n5 T2e rin! topolo!1 consists of a series of nodes connected 91 unidirectional transmission link to form a closed pat2. It can 9e 3iewed as a series of point-to-point links wit2 eac2 node as an acti3e tap listenin! for 9its transmitted to it from a precedin! node and re!eneratin! 6or repeatin!7 t2em 9it 91 9it to t2e ne,t node. It can onl1 do t2is in one direction on t2e rin! so t2at t2e nodes- or repeaters- 2a3e onl1 t2e simple task of se8uentiall1 rela1in! t2e information t2rou!2 t2e links. 0 node identifies a messa!e on t2e rin! as 9elon!in! to it 91 reco!nisin! its own identifier or address in t2e messa!e. @suall1 t2e source t2at sends t2e messa!e on t2e rin! will remo3e t2e repeated messa!e circulated 9ack to it from t2e precedin! section. .owe3ert2ere is t2e possi9ilit1 of unattended data or data fra!ments indefinitel1 circulatin! round t2e network due to t2e closed loop nature of t2e rin!. T2is can 9e controlled 91 t2e procedure in t2e access control mec2anism. T2e rin!s transmission control can 9e eit2er distri9uted or centralised. In t2e distri9utes control- t2e sendin! node can determine on its own w2en it ma1 9e!in transmittin! 9ased on t2e status of t2e rin! at t2at time. In t2is wa1- e3er1 node participates in t2e procedure to control access to t2e s2ared c2annel pro3ided 91 t2e rin! 6e.!. token access control sc2eme7. In t2e centralised control- one master station is responsi9le for initiatin! all data transfers 6e.!. I&M )1++ communication loop7. .ere- t2e master node polls t2e nodes around t2e loop- allowin! eac2 of t2em in turn to send

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CHAPTER 6 : INTRODUCTION TO LAN data if t2e1 2a3e 9een waitin! w2en t2e1 are polled. In t2is case t2e loop acts similar to a star in lo!ical operation. T2e ad3anta!es of rin! topolo!1 areA ♦ all wirin! is point-to-point. T2is permits mi,ed media t1pe of implementations- especiall1 optical fi9res connectionsB ♦ simplicit1 in its connecti3it1 and maintenanceB

♦ messa!es are re!enerated at eac2 node- !i3in! a lon!er distance of transmission as well as minimisin! transmission errors.

T2e disad3anta!es areA ♦ it is suscepti9le to man1 sin!le points of failure as an1 9reak in t2e rin! will 9rin! down t2e s1stemB ♦ more comple, access mec2anism is needed. T2e p21sical media used wit2 rin! topolo!1 are twisted pair and 9ase9and coa,ial ca9le. It is also well suited for optical fi9re implementation.

Active Taps

Figure !-1

6 % " Sta+ T2e star topolo!1 uses a central controller node as t2e 2u9 of t2e networkB all ot2er nodes are wired directl1 to t2e 2u9 in a radial or star-like manner. "oint-to-point communication sc2emes ena9lin! eac2 node to e,c2an!e data wit2 t2e 2u9 are used. 0ll communication 9etween t2e nodes passes t2rou!2 t2e 2u9. T2e star topolo!1 easil1 lends itself to centralised control of t2e communication w2ere91 t2e 2u9 will 9e responsi9le for mana!in! and controllin! all communication t2at e,ists 9etween all nodes. It can also 2a3e distri9uted control in t2e sense t2at end-stations can make a re8uest connection to t2e central 2u9 or anot2er station. In t2is case- t2e 2u9 9e2a3es like a switc2 pro3idin! t2e p21sical connections 9etween two stations upon re8uest from one of t2e stations 6e.!. "&F-?0Ns7.

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In t2e star topolo!1- t2e central 2u9 can 9e comple, and t2e endstations need onl1 possess simple communication re8uirements. It is well suited for communication s1stems wit2 terminal intensi3e re8uirements. T2e reliance on t2e central 2u9 91 t2e w2ole network ma1 pose t2e dan!er of sin!le point of failure. In addition- it ma1 9e costl1 to install due to t2e fact t2at man1 connections are needed from eac2 end-station. T2e p21sical medium used for t2e link is usuall1 s2ielded or uns2ielded twisted pair.

Figure !-2

6 % # 71s(T+ee T2e communication network in t2e 9us>tree topolo!1 is simpl1 t2e transmission media i.e.- no switc2es as in t2e star topolo!1 or repeaters as in t2e rin! topolo!1. 0ll stations are passi3el1 attac2ed t2rou!2 appropriate 2ardware interfacin!- directl1 to a linear transmission medium- or 9us- in a multipoint or 9roadcast manner. Information si!nals propa!ate awa1 from t2e transmittin! station in 9ot2 directions on t2e 9us to t2e terminated ends of t2e 9us. =ac2 node is tapped into t2e 9us and copies t2e messa!e as it passes t2at point in t2e transmission medium. T2e stations will identif1 t2e messa!es meant for t2em 91 reco!nisin! t2e addresses on eac2 messa!e. T2e 9us is a special case of t2e tree topolo!1 wit2 onl1 one trunk and no 9ranc2es. &us>tree !enerall1 uses distri9uted control e.!. 3ia a contention mec2anism suc2 as C M0>C/ or 91 token control sc2eme. Centralised control is also possi9le 91 2a3in! a pollin! mec2anism on a multidrop-9us confi!uration w2ere a master controller polls eac2 node to initiate data transfers. T2e &us>tree topolo!1 is well suited for 9road9and networkin! tec2ni8ues as well as t2ose of t2e 9ase9and tec2ni8ues. In t2is wa1 it allows ma,imum c2annel utilisation. It is 9ot2 simple and fle,i9le to insert or remo3e a station into or out of t2e network wit2out ser3ice

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CHAPTER 6 : INTRODUCTION TO LAN interruption as passi3e interfacin! components are used 9etween t2e stations and t2e 9us. .owe3er- t2e 9us>tree does face t2e followin! pro9lemsA ♦ it 2as a more difficult access control pro9lem 9ecause of t2e sin!le media used in a multi-access control pro9lemB ♦ 9alancin! electrical si!nals on t2e 9us as t2e 9us len!t2 3aries wit2 t2e addition or remo3al of nodes. T2e media used in 9ase9and 9us networks are s2ielded or uns2ielded twisted pair and 9ase9and coa,ial ca9le. For a 9road9and 9us>tree network- 9road9and coa,ial ca9le is used. $esearc2 is currentl1 in pro!ress to make t2e optical fi9re economicall1 feasi9le as t2e 9road9and medium for t2e 9us>tree network.

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CS260 &us

CHAPTER 6 : INTRODUCTION TO LAN





Tree

Figure !-3
6 ' C)annel Allo-at.on C2annel allocation is anot2er area of interest to ?0N . It is t2e procedure for di3idin! t2e communication resources- t2e c2annel capacit1- wit2 t2e ma,imum efficienc1. T2e c2annel refers to t2e p21sical medium used for transmission. T2e allocation procedure is independent of t2e access control mec2anism used for t2e c2annel. T2e access control mec2anism is t2e wa1 91 w2ic2 access to t2e c2annel created 91 t2e allocation procedure is controlled. For e,ample- we ma1 allocate a c2annel 91 di3idin! it into fre8uenc1 9ands- 9ut 2ow t2ese 9ands are used will 9e determined 91 t2e access control mec2anism. :e ma1 allow a master node to determine w2ic2 node pairs will own a !i3en 9and or- alternati3el1- we ma1 allow nodes to contend for a !i3en 9and. T2e concept of t2e access control mec2anism will 9e discussed later in t2is c2apter. ♦ :e 2a3e two wa1s of lookin! at c2annel allocationA • 91 t2e allocation tec2ni8ues used- i.e. space di3ision multiple, 6 /M7- time di3ision multiple, 6T/M7- fre8uenc1 di3ision multiple, 6F/M7- or a 219rid of t2eseB and • 91 si!nallin! met2ods for transmission used in t2e networkespeciall1 t2ose wit2 9us>tree topolo!1. T2e si!nallin! met2ods can 9e eit2er 9ase9and or 9road9and si!nallin!- w2ic2 !i3es rise to t2e names of networks suc2 as 9road9and and 9ase9and networks. In t2ese met2ods- t2e di!ital information to 9e transmitted o3er t2e

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CHAPTER 6 : INTRODUCTION TO LAN medium must first 9e encoded suc2 t2at t2e 9its are distin!uis2a9le at t2e recei3in! node6s7. T2e rate at w2ic2 t2e encoded 9it information is applied to t2e medium 91 a sendin! node is referred to as t2e transmission speed e,pressed in 9its per second. 6 ' 1 C)annel Allo-at.on Te-)n.B1es 6 ' 1 1 S*a-e D./.s.on M1lt.*le=.n5

T2is is merel1 a comple, wa1 of sa1in! t2at t2ere are multiple p21sical c2annels- w2ic2- w2en considered to!et2ermake up t2e ?0N communication facilit1. uc2 an allocation procedure- is of course- common in star topolo!ies. &ut is ne3er found in 9us or rin! networks. 6 ' 1 " F+eB1en-? D./.s.on M1lt.*le=.n5

T2is pro3ides an effecti3e wa1 of s2arin! a c2annel capacit1 amon! multiple users. F/M allocation procedures are principall1 found in 9us topolo!ies- alt2ou!2 t2e1 could 9e used eit2er in conjunction wit2 space di3ision multiple,in! or as a stand-alone 9asis to pro3ide circuits 9etween outl1in! nodes and t2e central node in a star network. F/M is impractical in t2e rin! networks 9ecause of t2e point-to-point connections of t2e c2annels. 6 ' 1 # T.2e D./.s.on M1lt.*le=.n5 @TDMA

T2is is t2e allocation mec2anism of c2oice in t2e rin! topolo!1- wit2 nodes 9ein! !ranted 691 t2e access control mec2anism7 e,clusi3e ri!2t to t2e c2annel for a time inter3al. Fi,ed T/M could also 9e used to pro3ide multiple independent c2annels for outl1in! nodes in a star topolo!1. T/M is an applica9le allocation procedure in a 9us network w2ere t2e access control mec2anism !rants e,clusi3e ri!2ts to t2e 9us to a sin!le node for a time inter3al lon! enou!2 to transmit its data packet. 6 ' 1 % Co2b.nat.on of FDM an0 TDM

0 network can use F/M to di3ide t2e c2annel 9andwidt2 and t2en use T/M to ena9le s2arin! of eac2 fre8uenc1 9and. T2is !i3es an e,tra milea!e on t2e usa!e of c2annel. <f courset2e cost and comple,it1 of suc2 s1stem would 9e more t2an t2at w2ic2 implements onl1 T/M or F/M. 6 ' 1 ' Co0e D./.s.on M1lt.*le=.n5 @CDMA ♦ C/M 2as onl1 a recent 2istor1 in t2e commercial usa!e of t2e tec2ni8ue. It is di!ital multiple,in! tec2ni8ue 9ased upon spreadspectrum t2eor1 of communication. It 2as two distinct cate!oriesA • direct-se8uence 6/ 7 spreadin!- 9ased on amplitude modulation

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CHAPTER 6 : INTRODUCTION TO LAN fre8uenc1 2oppin! 6F.7- 9ased on fre8uenc1 modulation



T2e si!nal meant for a !i3en user is assi!ned wit2 an identification code w2ic2 can 9e a distinct se8uence 6pattern7 of J1 or -1s for / modulation or a distinct se8uence or fre8uencies for F. modulation t2at onl1 userCs recei3er reco!nises. T2e recei3er knows in ad3ance 2ow t2e transmitter will spread t2e fre8uenc1 spectrum and ac8uires t2e si!nal and continues to track t2e transmitted pattern. For e,ample user1 !ets se8uence 1- user2 !ets se8uence 2and so fort2.

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CHAPTER 6 : INTRODUCTION TO LAN :2en a recei3er wants to listen to user 1- it follows 1 i.e.- it sees all user 1Cs ener!1 9ut onl1 a small fraction of t2e ot2ersC ener!1. C/M offers ad3anta!es in 9etter pri3ac1 in transmission- less fadin! pro9lems in 9uilt up areas- lesser 3ulnera9ilit1 to jammin! of t2e si!nal- fle,i9ilit1 in t2at it does not need precise time co-ordination 9etween transmitters as in t2e T/M- and potentiall1 it can 2andle 2i!2er capacit1 t2an F/M and T/M. It 2owe3er 2as increasin! error rates as t2e num9er of data users increases. <ne of t2e area in w2ic2 C/M is used in is t2e wireless ?0Ns implementations. 6 ' " 7aseban0 Net3o+4 T2e 9ase9and network uses 9asement si!nallin! tec2ni8ues for transmission- i.e.- transmittin! and recei3in! unmodulated si!nals. T2e encoded si!nal is directl1 applied to t2e medium eit2er as a continuos stream of 3olta!e transitions on a copper medium or as a stream of li!2t pulses on an optical fi9re medium. @nlike t2e si!nals in 9road9and network- 9ase9and si!nals tra3el in 9ot2 directions on t2e medium- impl1in! t2at onl1 a sin!le piece of t2e medium is needed . ince 9ase9and si!nals from eac2 station are usuall1 di!ital in natureit uses t2e entire p21sical c2annel 9andwidt2. T2is re8uires t2e network to use some form of T/M met2ods to allocate t2e resource amon! t2e stations. Time on t2e c2annel ma1 9e allocated 3ia one of se3eral procedures. /e3ices ma1 9e polled 91 some central Haut2orit1H or- alternati3el1ma1 own specific time slots. Iet anot2er interestin! alternati3e is 2a3in! de3ices contend for t2e use of t2e c2annel.

0n important 3aria9le to 9e considered w2en discussin! 9ase9and networks is t2e allocated time inter3al. Time inter3als can 9e of fi,ed len!t2- in w2ic2 case t2e amount of data w2ic2 a de3ice can transmit durin! its owners2ip of t2e c2annel is directl1 related to t2e speed of transmission. 0 second possi9ilit1 is to allow t2e de3ice to transmit a specified amount of data durin! its time slot. If t2e data unit is of fi,ed len!t2- t2ere is o93iousl1 no distinction 9etween t2is approac2 and t2e fi,ed-time met2od.

&ase9and data rates e,ceedin! 1++ M9ps are possi9le 6e.!. F//I networks7. .owe3er- practical limitations in some transmission media 6e.!. twisted pair7 result in t1pical 9ase9and network rates of up to 1% M9ps. &ase9and si!nals must 9e periodicall1 repeated o3er a lon! distance to a3oid data loss or interference due to si!nal de!radation.

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CS260 6 ' # 7+oa0ban0 Net3o+4s

CHAPTER 6 : INTRODUCTION TO LAN

Networks t2at transmit and recei3e modulated si!nals are known as 9road9and networks. T2e p21sical c2annel 9andwidt2 can 9e di3ided into fre8uenc1-9and c2annels. /ifferent de3ices can t2en emplo1 different carrier fre8uencies and multiple si!nals can simultaneousl1 reside on t2e transmission medium. <f course- t2e different fre8uenc1 c2annels can t2emsel3es 9e time di3ision multiple,ed- t2us pro3idin! an additional de!ree of s2arin!. ?0Ns usin! modulation and F/M are called 9road9and ?0Ns. T2ese are in3aria9l1 9us>tree topolo!1.

Transmission on t2e medium is onl1 in one direction. 0n1 9road9and s1stem re8uires two c2annels on w2ic2 data must mo3e. 0n out9ound c2annel is used for traffic lea3in! t2e 2eadend. T2e s1stemCs 2eadend is simpl1 a si!nal processor t2at takes an in-9ound si!nal and upcon3erts it to an out9ound

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CHAPTER 6 : INTRODUCTION TO LAN c2annel. :2en a de3ice transmits- it alwa1s does so on t2e in-9ound c2annel and listens and recei3es on t2e out9ound c2annel. &ot2 c2annels can reside on a si!nal ca9le or can- as wit2 :an!Cs 9road9and s1stem- use two ca9les - one for in9ound traffic and- t2e ot2er for out9ound traffic. Now t2e full ran!e of fre8uencies offered 91 t2e medium is a3aila9le- 9ut t2e cost of t2e s1stem is increased 91 t2e two-ca9le re8uirement and t2e necessit1 of 2a3in! two taps at e3er1 node. T2e transmission medium is t1picall1 ca9le tele3ision 6C0T'7 coa,ial ca9le. ♦ :it2 t2e a3aila9ilit1 of multiple su9-c2annels in a 9roadcast networkdifferent c2annels can 9e used to satisf1 different re8uirements. T2ere are t2ree kinds of su9-c2annel allocations for t2ese re8uirements A • • /edicated ser3ice t1pe - a portion of ca9le 9andwidt2 is reser3ed for e,clusi3e use 91 two de3ices. witc2ed ser3ice t1pe - t2is re8uires t2e use of a num9er of fre8uenc1 9ands. /e3ices are attac2ed to a Hfre8uenc1 a!ileH modems w2ic2 can 9e accessed in a wa1 similar to a dial-up line. Multi-access ser3ice t1pe - t2is is t2e most common and allows a num9er of attac2ed de3ices to 9e supported at t2e same fre8uenc1. 0s wit2 9ase9and- it needs some form of access control mec2anism to ena9le distri9uted- peer communications amon! t2e de3ices.



6 ' % 7aseban0 /s 7+oa0ban0 T2e ad3anta!e of a 9road9and network is t2at it can carr1 analo! as well as di!ital information 6e.!.- full 9and-widt2 3ideo can 9e distri9uted alon! wit2 data7. 0not2er ad3anta!e of t2e 9road9and network is its a9ilit1 to accommodate multiple- special-purpose applications on a non-interferin! 9asis- e3en to t2e e,tent of containin! su9networks operatin! on T/M principles. &road9and networks also pro3ide lon!er distance of transmission and potentiall1 more 9andwidt2 t2an t2e 9ase9and networks 0 disad3anta!e is t2e need for radio-fre8uenc1 6$F7 modems w2ic2 are often more e,pensi3e t2an t2e relati3el1 simple transcei3ers used in 9ase9and sc2emes. 0not2er disad3anta!e is t2at t2e propa!ation dela1 t2rou!2 a 9road9and network is likel1 to 9e muc2 !reater t2an t2at in a 9ase9and network. It is also more e,pensi3e t2an t2e 9ase9and network.

It s2ould 9e noted t2at t2e term H9road9andH was co-opted into t2e local network 3oca9ular1 from t2e telecommunications world- 9ut wit2 a c2an!e in meanin!. In t2e local network conte,t- t2e term refers to t2e transmission tec2ni8ues usin! analo! si!nallin! 6suc2 as F/M- F/M>T/M7 on coa,ial ca9le. &road9and- as in &I /N- 2olds a 3er1 different meanin! in t2at it 2as not2in! to do wit2 transmission

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CHAPTER 6 : INTRODUCTION TO LAN tec2ni8ues. In &I /N it means t2at t2e si!nals occupies a 3er1 lar!e fre8uenc1 9and spectrum t2at can 9e 3aried on a demand 9asis.

6 6

A--ess Cont+ol ♦ 0ccess control deals wit2 2ow to re!ulate t2e use of a s2ared medium and is a ke1 tec2nical issue for ?0N. 0ccess control is e,ercised at two main areasA • Centralised Control - w2ere91 a desi!nated controller 2as t2e aut2orit1 to !rant access to t2e network. 0 station wis2in! to transmit must wait until it recei3es permission from t2e controller.

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CHAPTER 6 : INTRODUCTION TO LAN • /istri9ute control - w2ere91 t2e stations collecti3el1 perform a medium access control function to d1namicall1 determine t2e order in w2ic2 stations transmit. ♦ 0d3anta!es of centralised control areA • fewer pro9lems in co-ordinatin! t2e acti3ities of multiple de3icesB • !reater access control in terms of priorities- o3errides- and !uaranteed 9andwidt2 to eac2 stationB and • less intelli!ence in indi3idual de3ices- t2us simplif1in! t2eir network interfaces. ♦ /isad3anta!es of centralised control areA • 2i!2er risk of sin!le point of failure affectin! t2e entire networkB • and • reduced efficienc1 if t2e control point 9ecomes a 9ottleneckB o3er2ead ma1 9e unaccepta9le if propa!ation dela1 is 2i!2.

♦ T2e pros and cons for distri9uted control are mirror ima!es of t2e pre3iousl1 discussed points. T2e access control can 9e e,ercised 91 t2e followin! access control tec2ni8uesA • 1nc2ronous tec2ni8ues - a specific capacit1 is dedicated to a connection 6e.!. in di!ital "&F7. uc2 tec2ni8ues are not optimal in a 9roadcast network 9ecause t2e needs of t2e stations are !enerall1 unpredicta9le. • 0s1nc2ronous tec2ni8ues - w2ere t2e capacit1 of t2e c2annel is allocated more or less in response to immediate needs. T2is is t2e more preferred tec2ni8ue. Contention and round ro9in sc2emes fall under t2is cate!or1.

6 6 1 Ro1n0 Rob.n ♦ Token-passin! $in!

0 small frame or free token is circulated round t2e rin! w2en all stations are idle. 0 station wis2in! to transmit must wait until it detects a passin!

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CHAPTER 6 : INTRODUCTION TO LAN token. :2en a station recei3es a token- it seiDes it 91 c2an!in! one 9it in t2e token- and transformin! it into a 9us1 token- w2ic2 is actuall1 a start-of-frame se8uence for a frame. T2e station t2en appends and transmits t2e remainder of t2e fields needed to construct a frame. T2e transmittin! station inserts a new token on t2e rin! w2en 9ot2 of t2e followin! conditions are metA

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CHAPTER 6 : INTRODUCTION TO LAN

• •

t2e station 2as completed transmission of its frameB and t2e leadin! ed!e of its transmitted frame 2as returned 6after makin! a complete circle of t2e rin!7 to t2e station.



:2en t2e transmittin! station releases a new free token- t2e ne,t downstream station wit2 data to send will 9e a9le to seiDe t2e token and transmit. T2e use of t2e token !uarantees t2at onl1 one station at a time ma1 transmit. T2e token passin! rin! sc2eme ma1 also 9e used in 9uses wit2 orderin! of nodes. Collision a3oidance T2e collision a3oidance sc2eme uses t2e distri9uted round ro9in tec2ni8ue. 0 specific collision a3oidance sc2eme is t2e carrier sense multiple access wit2 collision a3oidance 6C M0>C07 met2od. =ac2 station listens to t2e carrier w2ile a transmission is in pro!ress. 0fter t2e transmission ends- eac2 station waits for a specific period of time- 9ased on its position in a lo!ical list of stations. If no ot2er station 2as started transmittin! 91 t2e time a particular stationCs time 2as elapsed- it ma1 9e!in transmission.0n e,ample of t2e collision a3oidance sc2eme is t2e I /NCs &asic $ate Interface 6&$I7- w2ere91 a passi3e 9us is used for connectin! multiple I /N terminals to t2e Network Termination 6NT7 de3ice.

6 6 " Content.on In t2is sc2eme- no control is e,ercised to determine w2ose turn it is. T2e applied traffic is non-deterministic and man1 stations ma1 simultaneousl1 seek to access t2e medium. 0ll stations randoml1 contend for time on t2e medium- transmittin! w2ene3er t2e transmission medium is a3aila9le. T2eir principal ad3anta!e is t2at t2e1 are simple to implement and efficient- under li!2t to moderate load. Contention tec2ni8ues are usuall1 appropriate for 9urst1 traffic. C M0>C/ is one e,ample of contention tec2ni8ue. Ca++.e+ sense 21lt.*le a--ess 3.t) -oll.s.on 0ete-t.on @CSMA(CDA C M0>C/ wit2 Collision /etection 6C M0>C/7 is t2e most commonl1 used contention sc2eme. C M0>C/ consists of two partsA t2e carrier sense multiple access part in w2ic2 t2e station uses t2e listen9efore-talk sc2emeB and t2e collision detect 6C/7 part w2ic2 uses t2e listen-w2ile-talkin! sc2eme. In t2is sc2eme- a station wis2in! to transmit listens to t2e medium to determine w2et2er anot2er transmission is in pro!ress. If t2e medium is idle- t2e station ma1 transmit. <t2erwise- t2e stations 9ack off for some period of time and tr1 a!ain. 0 station continues to listen to t2e medium w2ile it is transmittin!. If a collision is detected durin! transmission- t2e station immediatel1 ceases transmittin! t2e messa!e and transmits a 9rief jammin! si!nal to ensure all stations know t2at t2ere 2as 9een a collision. 0fter transmittin! t2e si!nal- t2e station waits for a random amount of time and t2en attempts to transmit a!ain.

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CS260 6 9 Re/.e3 $1est.ons

CHAPTER 6 : INTRODUCTION TO LAN

43. :2at are t2e t1pical c2aracteristics of a ?0NK 44. :2at are t2e t1pical components of ?0NK 4#. :2at are t2e ad3anta!es of t2e rin! topolo!1 compared to t2e star topolo!1K 4%. /escri9e different c2annel allocation tec2ni8ues. 4(. :2at is t2e difference 9etween c2annel allocation and access controlK 4). :21 do we need a access control mec2anism in ?0NK /escri9e t2e access control mec2anism in token rin! network. 4*. :2at is t2e difference 9etween C M0>C0 and C M0>C/K #+.

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CHAPTER "
C)a*te+ Ob,e-t./es 0fter completin! t2is c2apter- 1ou will 9e a9le to A ⇒ plan for a ?ocal 0rea Network implementationB ⇒ make t2e ri!2t decisions a9out 2ardware and softwareB ⇒ learn t2e installation and confi!uration of network software and 2ardware componentsB ⇒ administer a ?ocal 0rea Network. 9 1 Plann.n5 fo+ a LAN I2*le2entat.on :2en 1ou plan for t2e implementation of a ?ocal 0rea Network 6?0N7- t2e t2ree factorsA people- process and or!anisations 9ecome more clearl1 defined wit2 addition of detailed re8uirements for t2e user- t2e jo9- and t2e work!roup. Iour 2ardware and software c2oices must 9e considered in li!2t of user re8uirements- t2e need of t2e jo9- and t2e siDe of t2e or!anisational 9ud!et. T2e 9est solutions will meet t2e need for adapta9ilit1- and scala9ilit1 and will pro3ide work!roups wit2 a platform for completin! tasks wit2out placin! unrealistic 9urdens on t2e or!anisation. In t2e plannin! process- 1ou s2ould consider se3eral t2in!sA ♦ T2e first consideration is makin! up a user !roup. ♦ ♦ ♦ ♦ ♦ electin! workstation 2ardware electin! a network 2ardware platform electin! a network topolo!1 /esi!nin! t2e p21sical location of t2e e8uipment electin! t2e Network <peratin! 1stem 6N< 7

9 1 1 Ma4.n5 U* Use+ G+o1*s T2e initial consideration for makin! up a user !roup is to determine w2at t2e makeup of t2e work!roup will 9e. :2o will 9e workin! to!et2erK Iou need to know t2is to determine w2o will need remote access- or per2aps an independent ser3er. T2e workflow amon! users will determine 2ow 1ou set up work!roups and assi!n work!roup mana!ers. T2e work!roup re8uirements will determine w2at kind of application software or Network <peratin! 1stem 1ou need- and also !i3es 1ou preliminar1 idea of printer set-up- menu desi!n- and user communication. T2e num9er of users w2o will 2a3e access to t2e network and 2ow t2e1 will use it will 9e a determinin! factor in 1our decision a9out w2ic2 network software and 2ardware to purc2ase. T2is information

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CS260

CHAPTER is essential to a3oid 2a3in! to immediatel1 up!rade t2e network or justif1 2a3in! 1++ or #+ e,tra user licenses t2at !o unused. 9 1 " Sele-t.n5 Wo+4stat.on Ha+03a+e Iou s2ould select 2ardware for t2e network 9ased on t2e needs of t2e application and t2e scenario for !rowt2 of t2e or!anisation. T2e older and less powerful workstations can 9e connected wit2 a network to allow s2arin! of file and application. :it2 t2e a9ilities pro3ided 91 t2e network operatin! s1stem- t2eir work life can 9e e,tended. ♦ In t2e selection process for network components- 1ou must answer man1 8uestions concernin! 2ow will 3arious mac2ine- applications meet t2e needs of t2e network. <ften t2e 9est start is 9e!innin! wit2 t2e most 9asic considerations- suc2 as A • • :2at are t2e !oals for t2e or!anisation t2at t2e network installation is supposed to supportK .ow man1 people will need network access toda1B 2ow man1 ne,t 1earB 2ow man1 in t2e ne,t fi3e 1earsK :2at are 1our !oals in e,pandin! 1our 9usiness and 1our emplo1ee 9aseK :ill users need remote accessK .ow important is securit1 to 1our or!anisationK :2o needs access to critical information and w2o does notK .ow man1 of t2e e,istin! computer 2ardware can 9e incorporated into t2e new s1stem.

• • •

4uestion suc2 as t2ese will lead to more specific ones concernin! t2e actual use of t2e indi3idual workstations in t2e network. 9 1 # Sele-t.n5 Net3o+4 Ha+03a+e ?ocal 0rea Networks run on a s1stem of ca9les- 2u9s- routersser3ers and ot2er perip2erals. /ifferent topolo!ies and different met2odolo!ies ma1 re8uire different network 2ardware and ca9lin!. ♦ ?ocal 0rea Networks normall1 are connected 91 one of t2e four t1pes of ca9le A • Coa,ial Ca9le It is relati3el1 immune to noise 6=lectroma!netic Interface7 and is common c2oice in areas w2ere t2e en3ironment is nois1. It is most often used in =t2ernet and 0$Cnet topolo!ies.



@ns2ielded Twisted-"air 6@T"7 It can 9e used in nearl1 e3er1 situation- e,cept t2ose re8uirin! fi9re-optic ca9le installation. @T" comes in se3eral !rades and dependin! on t2e t1pe of networksome attention must 9e paid to !rade.



2ielded Twisted-"air 6 T"7

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CHAPTER It is noise resistant and capa9le of carr1in! si!nals o3er a lon!er distance t2an @T".



<ptical Fi9re <ptical fi9re is t2e most efficient option and t2e most e,pensi3e. If 1ou need 3er1 2i!2-speed transmissionpractical immunit1 to electroma!netic interference and en3ironmental 2aDards- and send si!nals o3er lon! distance 61++ 5M7- t2en t2is is t2e 9est c2oice. &ecause of its lar!e 9ase of installed fi9re- t2e telep2one compan1 mi!2t 9e t2e 9est c2oice for information and possi9le installation. Iour selection of a network topolo!1 will 9e a !uidin! factor in c2oosin! w2ic2 media will 9est suit t2e needs of t2e network. T2e c2oice ma1 also 9e influenced 91 w2at t1pe of ca9lin! is alread1 installed. Network desi!n can 9e an important factor in eliminatin! t2e need for 2u9s and concentrators- w2ic2 can 9e a real sa3in! in effort and mone1.

-

9 1 % Sele-t.on of Net3o+4 To*olo5? T2e topolo!1 1ou select for t2e network will 2a3e an impact on 2ow t2e workstations- ser3ers- and ot2er network components are arra1ed. Iou s2ould consider t2e distance limitations for routin! different t1pe of media. T2ere will 9e a increased costs for t2e addition of concentrators and 2u9s and additional si!nal-mana!ement e8uipment to ser3e workstations o3er lon!er distances. T2e concept of t2e ri!2t tool for t2e ri!2t jo9 is important to consider. ♦ T2e selection of network topolo!1 also depends on t2e same t2ree factors A people- process and or!anisation. &elow are t2e some factors to consider in definin! network topolo!1 selection A • • • • • • "21sical location of t2e user T1pe and amount of network usa!e "resentl1 a3aila9le facilities to t2e or!anisation ?e3el of relia9ilit1 re8uired for network operation pecial re8uirement suc2 as lar!e data stora!e capacit1securit1 and need for remote access- or inter networkin! Future re8uirements suc2 as to adopt t2e network to faster 9ack9one networks wit2 fi9re optics or ot2er 2i!2 9andwidt2 transmission media Maintenance support re8uired to ensure t2at t2e network is mana!ed and maintained



9 1 ' P)?s.-al Lo-at.on of Net3o+4 "lannin! t2e p21sical location of workstations- ser3ers- and t2e perip2erals is an important part of t2e desi!n of t2e network. T2e

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CHAPTER p21sical location of components must allow for maintenance- securit1and access and also pro3ide a location wit2 ade8uate 3entilation to keep t2e mac2ines from o3er2eatin!. Wo+4stat.ons T2e p21sical location and confi!uration of t2e workstation and its attac2ed componentsB t2e monitor- ke19oard- mouse- di!itiser and so on - are determined 91 considerations of user needs- comfort and a3aila9le workplace. T2e decisions 1ou make a9out ca9lin! determine t2e distance t2e workstationB ma1 9e from ser3er or 2u9 and w2at options are a3aila9le for routin! t2e ca9le. T2e selection of a workspace for t2e user will 9e more of a factor t2en t2e len!t2 of t2e ca9le attac2in! t2e workstation to t2e network. T2e workstation s2ould 9e er!onomicall1 situated to facilitate a !ood p21sical workin! en3ironment for t2e user and to support work!roup lo!istics. Se+/e+ T2e ser3er is t2e 2eart of a ?ocal 0rea Network. T2e Network <peratin! 1stem 6N< 7 and network application pro!rams reside in it. If t2e ser3er is down- t2e network is down. er3er performance will 9e 9etter and it will 2a3e a lon!er life if 1ou take care in plannin! its location. Iou must pro3ide a clean en3ironment free of dust wit2 !ood 3entilation for coolin!. Iou also need enou!2 space for maintenance to 9e performed easil1- a clean sta9le power suppl1- and a locka9le door to protect t2e ser3er from an1 tamperin!. 0 major consideration for t2e location of t2e ser3er is securit1. In practice- t2e ser3er operation is so mission critical to or!anisations it s2ould 9e kept in a Hrestricted roomH. T2is stops unaut2orised personnel from turnin! it off or tamperin! wit2 it in ot2er wa1scostin! t2e or!anisation time and mone1. Net3o+4 P+.nte+s an0 Ot)e+ Pe+.*)e+als Network printer and ot2er perip2erals suc2 as plotters- s2ould 9e located in area accessi9le to users. If t2e1 are attac2ed to t2e ser3er- t2e1 s2ould 9e closed to it. "arallel ca9lin! s2ould not e,ceed 2# feet. If t2e1 cannot 9e located t2at close to t2e ser3er- t2en ot2er met2od of attac2ment will 9e necessar1 suc2 as connectin! directl1 to t2e ?0N or to a dedicated workstation and let t2e workstation ser3e as print ser3er. T2e c2aracteristics of t2e printer selected- t2e t1pe and siDe of t2e network- t2e capa9ilities of t2e ser3er- t2e needs of users- t2e jo9 to 9e done- and t2e 9ud!et constraints of t2e or!anisation s2ould all 9e considered. 9 1 6 Sele-t.n5 Net3o+4 O*e+at.n5 S?ste2 T2e Network <peratin! 1stem 6N< 7 resides in t2e ser3er and pro3ides t2e connecti3it1 t2at completes t2e networkin! s1stem and creates t2e en3ironment in w2ic2 t2e network operates.

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CHAPTER

T2e selection of Network <peratin! 1stem does depend on man1 factors. ome of t2e important factors and !uidelines are A Platfo+2 S1**o+t an0 7+oa0 F1n-t.onal.t? 0 facilit1 for t2e implementation of tec2nolo!ies across multi3endor computin! platform is one of t2e important ad3anta!es of ?ocal 0rea Networkin!. T2e Network <peratin! 1stem must support a wide 3ariet1 of 2ardware and software to effecti3el1 pro3ide a seamless connection- one t2at makes t2e user interface consistent across multi3endor 2ardware- di3erse <peratin! 1stems- and e3en different networks. T2e Network <peratin! 1stem must 9e a9le to e,ploit t2e e,istin! 2ardware and software to pro3ide needed capacit1 and functionalit1 for a distri9uted processin! en3ironment. A Cons.stent an0 Int1.t./e Use+ Inte+fa-e 0n interface t2at looks t2e same across t2e network will 2elp keep user producti3e and reduce confusion. T2ere are some instances w2ere a mi!ration to ?ocal 0rea Networkin! is prompted mainl1 91 a desire for a more intuiti3e- user-friendl1 interface. Ease of Installat.on an0 Conf.51+at.on Most 9usiness cannot afford to disrupt operations for 3er1 lon!. T2e easier t2e software is to install- confi!ure- and learn to use t2e less time 1our operation will lose. Co2*et.t./e an0 Fle=.ble P+.-.n5 T2ere are simple- ine,pensi3e implementations of Network <peratin! 1stem and t2ere are also comple,- e,pensi3e ones. T2e solution for 1our needs will 2a3e to 9e somet2in! t2at fits wit2in 1our 9ud!et constraints. &e prepared to ne!otiate for price 3ersus performance. A**l.-at.on S-alab.l.t? It is t2e ke1 to keepin! 1our network at itCs 2i!2est le3el of performance. T2e application t2at 1ou c2oose needs to 9e adapta9le to future needs. T2e1 need to 9e porta9le to different operatin! s1stems and platforms. Iou must 9e a9le to e,pand t2em and pro3ide for addin! of more users- dealin! wit2 c2an!es in a3aila9le computin! platforms and up!radin! network components for increased performance. Mo01la+ Co2*onent O*t.ons T2e N< s2ould 9e a9le to pro3ide a scalea9le solution for networks. If 1ou can 9u1 w2at 1ou need for now and still plu! in w2at 1ou 9u1 later to do more of t2e jo9- t2en 1ou will 9e a9le to pick and c2oose just t2ose functions t2at 1ou need for 1our situation.

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CS260 S.n5le!*o.nt Mon.to+.n5

CHAPTER

0 in!le-point monitorin! makes it possi9le for w2ole network to 9e watc2ed for pro9lems from one console. It facilitates securit1 and it also pro3ides data to 9e anal1sed 91 a protocol anal1ser or network monitor. Confl.-t!f+ee S?ste2s Coe=.sten-e Conflict-free s1stems coe,istence for t2e s1stem alread1 installed and operatin! on 1our network is important. &ackward compati9ilit1 is anot2er aspect of network t2at 1ou can e,ploit to en2ance t2e usa!e and lifetime of components. Se-1+.t? Mana5e2ent 0 sin!le interface securit1 mana!ement s2ould 9e defined- auditedand maintained so t2at complete control of securit1 can 9e mana!ed 91 polic1 administration. E/ent Mana5e2ent ♦ =3ent mana!ement is a facilit1 t2at responds to s1stem e3ents on a network and is administered from a sin!le point. /ependin! on a predefined e3ent polic1- t2e =3ent Mana!er can take a num9er of actionsA • • • • • • $espond to messa!es uppress messa!es ?aunc2 pro!rams or scripts Forward messa!es to ot2er platform Initiate e,ecution of ot2er platforms =sta9lis2 data9ase alertin!

P+oble2 Mana5e2ent T2is facilit1 allow 1ou to maintain asset information- suc2 as warrant1 information- maintenance details concernin! 2ardware and software- and a lo! of trou9le tickets t2at can 9e used to monitor fault patterns. Sto+a5e Mana5e2ent Mainframe standard stora!e mana!ement s2ould 9e maintained across t2e network. Iou s2ould 2a3e automated arc2i3e facilit1 t2at can define retention policies and monitor t2e media and t2e statistics on tapes and dri3e errors. Reso1+-e A--o1nt.n5 =na9les 1ou to monitor resource usa!e on t2e network for 9ud!etin! and c2ar!e 9ack. T2e C"@ usa!e can 9e monitored alon! wit2 disk spaces and processes.

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CS260 Pe+fo+2an-e Mon.to+.n5

CHAPTER

Monitorin! C"@ usa!e and I>< rates will pro3ide 1ou wit2 3alua9le information on s1stem performance.

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CS260 Stan0a+0

CHAPTER

♦ tandard must 9e a part of t2e desi!n to allow operation in di3erse en3ironments on different computin! platforms. Iou will need to consider implementin! t2e followin! standards in 1our network A • • • • • NM" 6 imple Network Mana!ement "rotocol7 for network interopera9ilit1 4? 6 tandard 4uer1 ?an!ua!e7 for data9ase access <?= 6<9ject ?inkin! and =m9eddin!7- an $"C for application interopera9ilit1 C<$&0 6Common <9ject $e8uest &roken 0rc2itecture7- an $"C locator for application interopera9ilit1 TC">I"- I"F> "F 6Transmission Control "rotocol > Internet "rotocol7- 6Internet "acket =,c2an!e > e8uenced "acked =,c2an!e7 for 2etero!eneous communications.

9 "

Installat.on an0 Conf.51+at.on of a LAN T2is section descri9es t2e installation and confi!uration of a ?ocal 0rea Network 6?0N7. T2e !oal of a network is to connect computers and de3ices suc2 as printers- scanners- communication de3ices- stora!e de3ices- and ot2er perip2eral components in suc2 a wa1 as to ma,imise t2e utilit1 and a3aila9ilit1 of resources to t2e user. 0 network can ran!e from small work!roups consistin! of few personal computers 6"Cs7 attac2ed to a sin!le file ser3er to lar!e enterprise-wide networks encompassin! 2undreds or e3en t2ousands of "Cs s2arin! information wit2 3arious file ser3ers- as well as mini and mainframe computers. uc2 lar!e networks can link s1stems in different cities or e3en different continents. "C users toda1 can c2oose from se3eral widel1 supported operatin! s1stem. T2e most popular of t2ese H/esktop =n3ironmentsH include Microsoft /< M :indows- 0pple Macintos2- @NIF and < >2. 0 !ood Network < s2ould support all of t2ese operatin! s1stems. T2is means t2at t2e network can allow users of dissimilar applications- computers and operatin! s1stems to work to!et2er. :2ile t2is section focuses mainl1 on t2e /< en3ironment- it can 9e 9eneficial to all network users. T2ere are numerous 2ardware options for use wit2 network. ?iterall1 2undreds of makes and models of "Cs can 9e used as network workstations and man1 of t2em are suita9le as file ser3ers. T2ere are a 3ariet1 of popular met2ods for interconnectin! t2ese computers and num9er of manufacturers of products t2at support eac2 met2od. 9 " 1 Ha+03a+e Installat.on ♦ Installin! t2e ?0N 2ardware is one of t2e most difficult tasks of installin! a ?0N en3ironment. It often in3ol3es 2irin! outside contractors for ca9le installation and re8uires some knowled!e a9out 2ow t2e "C works internall1. T2e t1pes of tasks in3ol3ed are A

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CS260

CHAPTER Confi!urin! and installin! ?0N adapter cards for eac2 "C and ser3er t2at will 9e part of t2e ?0N. Installin! ca9lin! 9etween "Cs- ser3ers- and ot2er 2ardware suc2 as 2u9s and adapters. Installin! one or more ser3ers wit2 2ard disks and attac2ed s2ared printers. Installin! proper power suppl1 and power conditions.

• • • •

processor

Ha+03a+e ReB1.+e2ents fo+ F.le Se+/e+ C"@ 0 "C 6or "C compati9le7 "entium runnin! more t2an 1%% M.D. er3ers are alwa1s 2un!r1 for T2e more 1ou 2a3e- t2e and 9etter t2e

$0M memor1. faster t2e operation performance of t2e network. $ecommendation is 12) M& of $0M. .0$/ /I 5 -

for 1our

0 2ard disk wit2 sufficient stora!e network. <ne Network Interface Card. Network ca9lin! 6=t2ernet- 0$CnetT- Token $in! etc.7 Install a Modem to allow ser3er software wit2 remote pa!in! pro9lem arises.

NIC C0&?IN; 1+ &ase M</=M

-

mana!ement to pa!e 1ou if a

-

C/-$<M - 0 C/-$<M dri3e will pro3ide facilit1 installin! software and if re8uired to access -$<M stored data. &0C5@" @NIT Install a &ackup @nit to safe!uard a!ainst data dama!e.

Conf.51+at.on an0 Installat.on of a Net3o+4 Inte+fa-e Ca+0 @NICA $ead carefull1 t2e installation instructions for t2e NICs 9efore attemptin! to install t2em. tick to t2e e,act ca9le specified 91 t2e manufacturer of t2e NICs. @sin! t2e wron! ca9le can pre3ent t2e network from operatin! at all or- cause intermittent pro9lems t2at ma1 9e 3er1 difficult to trace 9ack to t2e ca9le. &efore 1ou can 9e!in t2e installation process- 1ou will 2a3e to take off t2e co3ers of all 1our mac2ines. Iou will 2a3e to find out w2at kind of adapter cards are alread1 installed and if t2ese cards use I$4s or /M0. T2en 1ou 2a3e to confi!ure eac2 ?0N adapter cards for t2e mac2ine it will !o into. Iou s2ould record t2is information on a works2eet. 0lt2ou!2 NICs are preconfi!ured at t2e factor1- in

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CHAPTER man1 cases 1ou cannot use t2e defaults settin!s. First 1ou 2a3e to c2an!e t2e /I" switc2es 91 mo3in! s2ortin! 9locks around different sets of pins on t2e ?0N adapter 9oards. T2en 1ou 2a3e to c2an!e t2e followin! settin!s if necessar1. Interrupt $e8uest i!nal 6I$47 line /irect Memor1 0ccess 6/M07 c2annel &ase I>< 0ddress Connector > Ca9le t1pe $emote $eset tation Num9er or Node 0ddress &ase Memor1 0ddress Ca9le Mediums and Ca9le Topolo!1 T2ree t1pes of ca9le are used in ?0Ns toda1A Twisted-"air- Coa,ial Ca9le and Fi9re <ptics. T2e ca9le used is determined 91 t2e manufacturer of t2e ?0N adapter card 2ardware. In most ?0Nst2ese mediums are not interc2an!ea9le. =ac2 t1pe of ca9le 2as a different cost and different transmission c2aracteristics t2at affect ?0N performance and t2e siDe of t2e ?0N. Topolo!1 is t2e sc2eme used to interconnect t2e "Cs on t2e ?0N. T2e topolo!1 used is determined 91 t2e ?0N adapter manufacturer. T2e major topolo!ies are 9us- star- rin! and tree. T2e topolo!1 can influence t2e ease of installation of t2e ?0N. In !eneral- 9us and tree topolo!1 are t2e simplest in 9ot2 casesB and star and rin! are t2e more difficult. /ifficulties in installation and e,pansion are also affected 91 t2e siDe of t2e p21sical facilities in w2ic2 t2e ?0N is 9ein! installed. Ha+0 D.s4 T2e file ser3er must contain at least one 2ard disk dri3e. T2is contains t2e Network <peratin! 1stemCs files and utilities as well as t2e application software and data. T2e 2ard disk is prepared wit2 Network < own format routine as part of t2e installation. To protect data from t2e 2ard disk controller failure if 1ou want to duplicate data o3er one or more 2ard disk- 1ou need an e,tra 2ard disk. Ens1+e P+o*e+ Po3e+ S1**l? an0 Po3e+ Con0.t.ons 1. C2eck t2e operatin! en3ironment and power re8uirement for network e8uipment in t2e followin! areasA • • • Temperature > .umidit1 "ower Consumption "ower Fre8uenc1

♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦

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CS260 .eat /issipation Ma,imum 0ltitude "ower ource "ower $e8uirements

CHAPTER

• • • •

2. @se dedicated power lines and !rounded outlets to connect network components onl1. 3. @se power-conditionin! e8uipmentA ♦ @se @ninterrupta9le "ower uppl1 6@" 7 to protect ser3er 2ardware from power fluctuations wit2 a re!ulatin! @" . In addition to protectin! ser3er 2ardware from dama!e caused 91 power sur!es and 3olta!e spikes a @" protects data 2eld in $0M durin! a power failure. ♦ If usin! a @" is not feasi9le- tr1 to e8uip network 2ardware wit2 power conditionin! de3ices suc2 as ?ine-sur!e suppressers or Ferro-resonant isolation transformers. Connect network 2ardware t2rou!2 at least one of t2ese de3ices to protect t2em from minor power sur!e. "rotect network e8uipment from static electricit1 91 takin! followin! protecti3e measures A • • • • Treat carpets wit2 anti-static c2emicals. @se protecti3e co3ers for carpets suc2 as anti-static t1pe. ;round e8uipment t2rou!2 a one me!. <2m resister to 9leed off t2e static slowl1. Make sure t2at t2e personnel workin! on open e8uipment c2assis take precautionar1 measures suc2 as wearin! !rounded wrist straps.



Do-12entat.on ♦ 0fter installation and confi!uration of 2ardware- record t2e followin! 2ardware information for future reference A • • • • • • • File ser3er A name- make and model $0M A Memor1 siDe Non-network 9oards A t1pe and settin! Network 9oards A associated ?0N dri3ers- network num9erI>< address- memor1 address- interrupt- and station address. Flopp1 disk dri3es A diskette siDe and stora!e siDe Internal disks A make- model and stora!e siDe /isk coprocessor 9oards A /C& dri3ers and I>< address

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CHAPTER /isk su9s1stems A num9er of dri3es- dri3e t1pe- stora!e siDenum9er of 2eads and c1linders Mirrored disks

• •

9 " " Loa0.n5 an0 Conf.51+at.on of Net3o+4 O*e+at.n5 S?ste2 T2e network operatin! s1stem pro3ides a platform for network ser3ices t2at com9ines network access wit2 operatin! s1stem software. T2is is usuall1 not application software 9ut rat2er an inte!rated operatin! s1stem. T2e Network <peratin! 1stem 6N< 7 runs in t2e file ser3er and controls s1stem resources and information processin! for t2e network. T2e most popular Network <peratin! 1stem is No3ellCs Net:are 6more t2an (+ percent7 9ut t2ere are ot2er manufacturers of N< s. T2e major N< are A No3ellCs Net:are &an1an 'IN= I&M ?0N er3er Microsoft :indows NT 0d3anced er3er

♦ ♦ ♦ ♦

♦ T2e followin! is t2e procedure for Installin! of Network <peratin! 1stem 6N< 7 for No3ellCs Net:are w2ic2 is most popular. • • • • • • • • • • • • • • • • Fulfil t2e 2ardware re8uirement =nsure proper power suppl1 and power condition et up 2ardware Make workin! copies if N< comes in diskettes /ecide file ser3er 9ootin! met2od $un installation pro!ram for N< Create and format /< partition Name t2e file ser3er 0ssi!n an I"F internal network num9er ?oad appropriate disk dri3er Create network disk partition ta9le Mirror or duple, t2e disk 6optional7 Create and mount 3olumes Cop1 I T=M and "@&?IC files to t2e 2ard disk ?oad ?0N dri3er wit2 appropriate frame t1pe Create file ser3er 9oot files

9 " # Installat.on an0 Conf.51+at.on of Wo+4stat.ons ♦ "repare :orkstation .ardware A

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CHAPTER 0 I&M "C or compati9le 6FT- 0T- )+))- 2)%- 3)%- 4)% or "entium etc.7 =nsure t2e workstation 2as 1.2 M& of free disk space Install t2e network 9oard and keep record of t2e followin! informationA • • • • • &ase I>< address Interrupt 6I$47 Frame T1pe Node 0ddress

• • •

Install workstation client software ?oad appropriate ?0N dri3er Install necessar1 files needed to connect to t2e network Customise network connection 91 editin! confi!uration files ?o!in to t2e network

9 #

Net3o+4 A02.n.st+at.on T2e jo9 of network administration - maintainin! and operatin! t2e networkfalls to t2e Network 0dministrator. T2is is t2e person tasked wit2 o3erseein! t2e present needs of t2e or!anisation- predictin! t2e futureen2ancin! t2e network and administerin! da1-to-da1 network operations. T2e network administratorCs jo9 9e!ins wit2 t2e initial set-up of t2e network and confi!uration of t2e 2ardware and software components to operate as a network. T2e confi!uration of t2e network operatin! s1stem 6N< 7 is one of t2e first important steps in creatin! user en3ironment. 9 # 1 C+eat.n5 D.+e-to+? St+1-t1+e T2e network administrator s2ould esta9lis2 and maintain a worka9le director1 structure. 0 ser3erCs disk is di3ided into 2ierarc21 of directories and files. T2e director1 2as a s1stem of access and function to promote t2e 9est utiliDation of t2e resources 91 t2e users on t2e network. T2is or!anisation of t2e director1 s1stem is important. It needs to not onl1 to 9e lo!ical for t2e user 9ut it must facilitate 9est use of t2e 2ardware and data resources as well.

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CHAPTER

/urin! t2e installation process- N< creates four s1stem directories A ?<;IN- I T=M- "@&?IC and M0I?. 9 # " Sett.n5 U* Use+ A--o1nts Its a !ood idea to set up accounts wit2 correspondin! access ri!2ts. T2e s1stem default- created in t2e initial p2ase of settin! up of t2e network- t2at will appl1 to t2e majorit1 of users on t2e network. /efault settin! will appl1 to new users added to t2e network later and facilitate t2e !rantin! of ri!2ts and access to directories and application and data files. Iou must also confi!ure for access to network perip2erals. 9 # # Sett.n5 U* F.le Mana5e2ent P+o-e01+es ♦ Network administrator of t2e network 2a3e access and ri!2ts t2at none of t2e users ma1 2a3e. T2ese ri!2ts are re8uired to perform t2e followin! file mana!ement tasks A 0ddin!- deletin! or makin! ot2er c2an!es to t2e director1 Creatin! su9-directories /efinin! director1 and file owners2ip Namin! trustee Modif1in! files

9 # % Allo-at.n5 Net3o+4 Reso1+-es ♦ Iou also need to allocate disk space for applications and users. .ere are some su!!estion to consider A • • ;roup 1our network application to!et2er. ;roup 1our utilit1 pro!ram to!et2er.

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CS260 &e stin!1 wit2 allocatin! user access and ri!2ts.

CHAPTER

• •

Create pu9lic directories for network data files. T2en restrict access to t2ose files so t2at onl1 t2ose users w2o 2a3e access to t2e application files can use t2ose data files. Make a place in t2e structure for user to keep pri3ate files. 0llocate disk space to users to promote 9etter stora!e 2ousekeepin!.

• •

9 # ' Ma4.n5 7a-41*s Makin! 9ackups is t2e process of creatin! duplicate copies of data to protect a!ainst data loss. 0 network contains man1 s1stem and data files t2at need to 9e 9acked up. 0s a network administrator- 1ou are responsi9le for de3elopin! a 9ackup strate!1 t2at is appropriate for 1our particular situation. 9 # 6 Establ.s) Ro1t.nes ♦ 0s t2e network administrator- 1ou must esta9lis2 dail1 and weekl1 maintenance routines. Tasks t2at s2ould 9e done A • • • • • • • • • 0ddin! new users Cleanin! up 2ard dri3es Installin! up!rades /oin! 9ackup and arc2i3in! $estorin! dama!ed or lost files and data Monitorin! t2e networkCs traffic flow Trou9les2ootin! Collectin! data for accountin! and optimisation ;eneratin! reports for mana!ement

9 # 9 Ma.nta.n.n5 t)e Net3o+4 ♦ 0 9i! part of administrator jo9 is to maintain t2e network- t2ese includes A • • • • • =sta9lis2in! network documentation "ro3idin! support for t2e network user /e3elopin! trainin! Mana!in! t2e confi!uration of t2e network =,perimentin! wit2 new tec2nolo!ies

9 # : Establ.s).n5 Se-1+.t? P+o-e01+e ♦ "asswords and file>director1 ri!2ts and access controls will pro3ide a le3el of protection from intruders into t2e network- 9ut attention must 9e !i3en to p21sical securit1 of t2e network components as well. T2e

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CHAPTER network file ser3er and ot2er network components suc2 as 9rid!esrouters- terminal connectors and @" s1stem s2ould 9e locked in a room and access !i3en onl1 to t2e network administrator and maintenance personnel. T2e 9est wa1 to ensure ser3er securit1 is to practice !ood confi!uration mana!ement 91 o9ser3in! t2e followin! A • • • • • • ?oad t2e file ser3er onl1 from aut2orised distri9uted software Make onl1 aut2orised c2an!es to confi!uration Maintain a cop1 of t2e current ?0N confi!uration works2eet "eriodicall1 re3iew de3ice confi!urations Maintain a 9ackup of t2e ser3er software Test software 9efore introducin! it into network

9 # ; Plann.n5 fo+ t)e F1t1+e ♦ In addition to t2e precedin! jo9s- t2e person w2o is responsi9le for t2e mana!ement of t2e ?0N must keep a9reast of new tec2nolo!1 and 9e a9le to respond to an e3er-increasin! user demand for t2e network. .is attention must 9e focused towardA • • • • 9 % Increasin! network performance 0ssessin! new 2ardware and software products =,pandin! network ser3ices Connectin! wit2 ot2er networks

Re/.e3 $1est.ons #1. :21 is plannin! important for t2e implementation of a ?ocal 0rea NetworkK /escri9e t2e steps in t2e plannin! process for t2e implementation of a ?0N. #2. :2at is t2e selection criteria for a network operatin! s1stemK #3. :2en 1ou desi!n t2e p21sical la1out of a ?0N- w2at are t2e factors t2at 1ou must considerK #4. /escri9e t2e detailed procedures for t2e installation and confi!uration of a ?0N. ##. /escri9e t2e role of a network administrator durin! t2e installation and confi!uration of a ?0N. #%. /escri9e t2e responsi9ilities of a network administrator in t2e postimplementation of a ?0N. #(. Is network topolo!1 important in t2e implementation planK If 1est2en e,plain t2e reasons. #). .ow do 1ou safe!uard 1our network e8uipment a!ainst dama!es from power distur9ances or from intrudersK

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CHAPTER #*. :2at are t2e securit1 measures 1ou s2ould appl1 in a ?0N en3ironmentK %+. /escri9e t2e 2ardware and software re8uirement for t2e file ser3er and workstation.

-

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C)a*te+ Ob,e-t./es @pon completion of t2is c2apter- 1ou will 9e a9le toA ⇒ learn a9out different t1pes of Telecommunication networksB ⇒ learn t2e t1pical telecommunication ser3ices pro3ided 91 a telecommunication ser3ice pro3ider and appl1 t2e concepts in real lifeB ⇒ learn and appl1 t2e concepts of t2e $outer- &rid!e and ;atewa1B ⇒ learn and appl1 t2e concepts of tar?0N 1+ and I&M Token $in! network. : 1 T?*es of Tele-o221n.-at.on Net3o+4s T2ere are man1 different wa1s to define 3arious t1pes of telecommunication networks. T2is matri, ma1 9e used for a simple classification. In one dimension- we ma1 define t2e networks 91 application suc2 as 3oice or data ser3ices. T2e ot2er dimension defines t2e domain 91 identif1in! w2et2er t2e network is pu9lic or pri3ate. T2e pu9lic switc2ed telep2one network 6" TN7 is t2e most familiar one. It pro3ides t2e 3oice ser3ices as well as 3oice !rade data ser3ices. /ata ser3ices in t2e pu9lic domain include t2e circuit-switc2ed pu9lic data network 6C "/N7 and t2e packet-switc2ed pu9lic data network 6" "/N7. In t2e pri3ate domain- t2e pri3ate line networks 6"?N7 ma1 pro3ide eit2er 3oice or data ser3ices. T2e1 are !enerall1 used 91 9i! corporations. T2ese networks ma1 9e confi!ured eit2er as switc2ed ser3ices or nonswitc2ed ser3ices. Non-switc2ed ser3ices are also referred to as dedicated ser3ices- nailed-up ser3icesc2annelised ser3ices- or simpl1 special ser3ices. ?ocal area networks 6?0N7 e3ol3ed from computer networkin!. T2e1 are !enerall1 limited in a small !eo!rap2ical area and transmit 2i!2-speed data. T2ere are special considerations wit2 respect to t2e topolo!1- access mec2anism and protocol. 0t t2e centre of t2e dia!ram is t2e Inte!rated er3ices /i!ital

Figure #-1
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CHAPTER ! : TELECOMMUNICATION SER"ICES AND NETWORK PRODUCTS Network 6I /N7- w2ere 3oice and data ser3ice 6eit2er pri3ate or pu9lic7 ma1 9e inte!rated 91 means of standardiDed interfaces.

: "

Se+/.-es P+o/.0e0 b? Tele-o221n.-at.on Se+/.-e

P+o/.0e+s

T1picall1 telecommunication ser3ice pro3iders offer a wide ran!e of ser3ices w2ic2 include telep2one as well as data communication related ser3ices. ome of t2e t1pical ser3ices pro3ided are discussed 9elowA ♦ /omestic and International Telep2one er3ices T2e user can use a modem for data communication usin! t2is ser3ice. ♦ /i!ital ?eased ?ine er3ice T2is di!ital leased line ser3ice is speciall1 en!ineered for pri3ate data communication networks. Its applications are wide ran!in!- 3oice cum data communication- disaster reco3er1 networks- 2i!2-speed remote printin! and di!ital "&F network. /i!ital leased line can support different speed for t2e users w2ic2 can ran!e from 2-4++ 9ps to 14+ M9ps or more. :2en t2e su9scri9er su9scri9es to t2is ser3ice- 2e 2as to install a di!ital interface unit w2ic2 is t2e interface 9etween t2e su9scri9ers computer and t2e di!ital leased line. <nce a su9scri9er su9scri9es to t2is ser3ice- t2e line 9ecomes a dedicated link and no modem is re8uired for data communication. T1picall1 t2ese line will 9e su9scri9ed 91 companies w2o want to 2a3e t2eir own network of computers. For t2is t1pe of ser3ice- ser3ice pro3iders c2ar!e t2e followin!A • • • ♦ Installation c2ar!e of di!ital interface unitB Mont2l1 rentalB Mont2l1 access c2ar!e.

0nalo! ?eased ?ine er3ices

0nalo! leased line ser3ices are similar to di!ital leased line ser3ices. T2e onl1 difference is t2at t2e su9scri9er needs to use modem for data communication. u9scri9ers will 9e c2ar!ed 9ased on mont2l1 rental and mont2l1 access. T1picall1 t2ese sorts of ser3ices will 9e used 91 companies w2ere transmission speed re8uired is minimal. ♦ "acket witc2 er3ice T1picall1 t2e ser3ice pro3ider will 2a3e a packet switc2ed network. 0ccess to t2is packet switc2ed network is 3ia leased circuit 6up to %4 59ps7 or dial-up62.4 59ps7. 0 su9scri9er to t2is t1pe of packet switc2ed network can 2a3e t2e followin! t1pes of connectionA • "u9lic /ial-up 0ccessA

T2e su9scri9er is connected to t2e packet switc2ed network e,c2an!e 3ia t2e pu9lic switc2ed telep2one network 6" TN7. For connection- t2e su9scri9er needs to simpl1 dial t2e pu9lic port num9er of t2e packet switc2ed network. =ac2 su9scri9er is !i3en a confidential user name known as Network @ser Identit1. It ser3es as a password for access. • "ri3ate /ial-up 0ccessA

imilar to t2e pu9lic dial-up access e,cept t2at t2e su9scri9ers are !i3en a dedicated port num9er to dial in. T2e num9er is e,clusi3e for t2eir use. • /edicated 0ccessA

T2e su9scri9er is connected to t2e packet switc2ed network e,c2an!e 91 a leased line. T2e su9scri9er occupies a dedicated port of t2e packet switc2 network w2ic2 is known as Network @ser 0ddress. T2is is to facilitate recei3in! calls from ot2ers. • Tele, 0ccessA

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CHAPTER ! : TELECOMMUNICATION SER"ICES AND NETWORK PRODUCTS T2e su9scri9er esta9lis2es a connection to t2e packet switc2ed network 91 callin! t2e tele, access port usin! a tele, mac2ine. imilar to t2e pu9lic dial-up access- t2e su9scri9er re8uires a Network @ser Identit1. T2e su9scri9er to t2e packet switc2ed network t1picall1 needs to pa1 for t2e followin!A • • • Mont2l1 su9scription c2ar!e 6depends on t2e t1pe of connection7 @sa!e c2ar!e 6includes 3olume and duration7 ?ine rental c2ar!e 6includes line installation and mont2l1 rental7



: #

De/.-es fo+ LAN Inte+-onne-t.on :2en two s1stems are not directl1 connected to eac2 ot2er and connecti3it1 is t2rou!2 an intermediar1- t2e intermediar1 is called a rela1 in t2e I < terminolo!1. T2ere can 9e man1 rela1s on t2e pat2 9etween two s1stems. < I reference model uses a se3en-la1er protocol suite for t2e network arc2itecture. If a rela1 s2ares a common la1er k protocol wit2 ot2er s1stems- 9ut does not participate in a la1er kJ1 protocol in t2e process of rela1in! information- t2e rela1 is known as la1er k rela1. <ne of t2e most 9asic interconnection de3ices is a repeater. T2is is la1er one rela1 de3ice i.e. it operates at t2e p21sical la1er. It can not control or route information. 0 9rid!e operates at t2e data link la1er. T1picall1it looks at t2e packet address to see if it is destined for anot2er su9net. 0 router on t2e ot2er 2and operates at t2e network la1er- 2as more intelli!ence capa9ilities 9ecause it can 2andle se3eral le3els of addressin!. 0 !atewa1 operates at t2e top four la1ers of t2e < I reference model. It can interconnect networks or media wit2 different arc2itectures and protocols. :e will discuss eac2 of t2ese 9asic t1pes in t2e ne,t few pa!es. Not all 3endor products fit neatl1 into t2ese 9asic cate!ories. Man1 3endors 2a3e de3eloped 219rid products t2at perform functions traditionall1 associated wit2 two or more of t2ese cate!ories. For instance- a router performs t2e functions of a 9rid!e and also 2as some router capa9ilities. To add to t2e confusion- t2e word !atewa1s- 9rid!es- and routers are often used in !eneric sense. :2at No3ellCs Netware refers to as a 9rid!e is a router in < I terminolo!1. 0 !atewa1 in TC">I" terminolo!1 is a router in < I terminolo!1. T2us one 2as to 9e careful in readin! trade ma!aDines and 3endor information. : # 1 7+.05es 0 9rid!e is a de3ice t2at operates at t2e data link la1er and rela1s frames 6packets7 9etween ?0Ns. 0 9rid!e 2as a num9er of p21sical ports and- at most- one su9 network of an internet is connected to eac2 suc2 port of t2e 9rid!e. 0lt2ou!2 man1 9rid!es operate on networks of similar arc2itecturesuc2 as =t2ernet to =t2ernet- or token rin! to token rin!- 9rid!es can also 9e 9etween ?0Ns wit2 dissimilar M0C su9 la1er protocols as lon! as t2e1 follow same ??C protocol. For instance- a 9rid!e can connect an =t2ernet ?0N wit2 a Token $in! ?0N since t2e1 s2are a common )+2.2 ??C format. .owe3er- suc2 interconnection 9etween dissimilar networks often re8uire a 2i!2er le3el protocol con3ersion t2an pro3ided 91 9rid!es. T2erefore- 9rid!es connectin! dissimilar ?0Ns could present relia9ilit1 pro9lems. 0 9rid!e does not pro3ide flow control and t2ere can 9e con!estion wit2in a 9rid!e. To deal wit2 con!estion- 9rid!e must 2a3e t2e a9ilit1 to temporaril1 9uffer frames. "rotocols at t2e 2i!2er la1ers must t2en deal wit2 t2e issue of reco3erin! frames t2at are eit2er lost or discarded 91 a 9rid!e w2en its 9uffer !ets full.

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Figure #-2
♦ &rid!es are commonl1 used to interconnect ?0Ns of same t1pe 6e.!. all coa, =t2ernets7 or to 9reak up a lar!e sin!le ?0N into a num9er of smaller interconnected ?0Ns t2at are all of t2e same t1pe. T2e 9reak up of a sin!le ?0N into interconnected ?0Ns is often desira9le for t2e followin! reasonsA • T2e performance of a sin!le ?0N deteriorates rapidl1 w2en t2e total network traffic increases 9e1ond a certain le3el. &1 9reakin! up t2e ?0N into smaller ?0Ns in w2ic2 t2e major traffic is wit2in eac2 smaller ?0N wit2 some traffic 9etween ?0Ns- as a result dela1 and t2rou!2put of eac2 indi3idual ?0N and t2e performance of t2e network for t2e user can 9e si!nificantl1 impro3ed. &rid!es are t2e main 3e2icles used for interconnectin! t2e indi3idual smaller ?0Ns 6all of t2e same t1pe7 in suc2 cases. • 0 !roup of interconnected smaller ?0Ns is less 3ulnera9le to failures t2an a sin!le ?0N. If a component ?0N fails- t2e rest of t2e internet can continue to function- per2aps at a decreased le3el of effecti3eness w2ereas a failure in t2e case of a sin!le lar!er ?0N spannin! t2e w2ole or!anisation can 9rin! t2e operation of t2e w2ole or!anisation to a 2alt. • Man1 or!anisations are war1 of sensiti3e information suc2 as personnel or financial information- 9ein! placed on t2e ?0N. Isolatin! suc2 information on smaller ?0Ns and pro3idin! interconnection to ot2er ?0Ns t2rou!2 9rid!es makes t2e securit1 issue more mana!ea9le. T2e 9rid!es can ensure t2at onl1 aut2orised users 2a3e access to sensiti3e information on t2e ?0Ns to w2ic2 t2e1 are connected.

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Figure #-3
Consider a 9rid!e connectin! ?0N F and ?0N I. :2en t2e 9rid!e recei3es a frame from ?0N F- it eit2er forwards t2e frame to ?0N I 6i.e. allows to pass t2rou!27 or filters it 6i.e. does not allow it to pass t2rou!27. 0 9rid!e must t2erefore make a decision on w2et2er to forward>filter a frame. :2en a 9rid!e is connected to more t2an two ?0Ns- it must also decide to w2ic2 ?0N or ?0Ns t2e frame will 9e forwarded if t2e frame is not filtered. ♦ T2ere are two met2ods commonl1 used for makin! suc2 decisions. T2ese areA • Transparent 9rid!in! met2od

In t2is approac2 t2e 9rid!es of t2e internet carr1 t2e re8uired Hintelli!enceH to make t2e decision a9out forwardin! a frame. T2e forwardin! mec2anism is t2us transparent to t2e communicatin! stations. T2e 9rid!e 2as a !reater processin! responsi9ilit1 in t2is met2od and t2e stations 2a3e an easier task since t2e1 need not concern t2emsel3es wit2 t2e 9rid!esC decisions. • ource routin! met2od

In t2is approac2 t2e source station makes t2e decision as on 2ow to route t2e frames t2rou!2 t2e 9rid!es. T2e 9rid!es merel1 carr1 out t2e routin! determined 91 t2e source. T2us in t2is met2od t2e processin! responsi9ilit1 on t2e source station is increased w2ile t2e task of t2e 9rid!es is simpler. : # " ROUTERS In man1 cases- an or!aniDation ma1 need to access de3ices on 3arious networks. For instance- ?0Ns ma1 2a3e a 2ierarc2ical arc2itecture. T2ere ma1 also 9e a need to access de3ices on a :0N o3er a pu9lic or pri3ate switc2ed network- for e,ample- to access pu9lic data9ases. For suc2 purposes- a suita9le internet workin! de3ice is a router.

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S!stem ;

Router

S!stem 2

Figure #-4
♦ 0 router is a de3ice operatin! at t2e < I network la1er 6i.e. la1er t2ree7 and can 9e used to pro3ide internetworkin! amon! dissimilar networks. T2e routers can accommodate se3eral differences amon! t2e networks t2at t2e1 can interconnect. ome of t2ose are listed 9elowA • /ifferent addressin! sc2emesA ince 9rid!es !enerall1 use a flat addressin! sc2eme- t2e1 need a !lo9al addressin! sc2eme for t2e entire internet. In contrast- t1picall1 routers use a 2ierarc2ical addressin! sc2eme. In t2e simplest sc2eme- t2e address of a station of t2e internet wit2 routers is a pair of t2e form 6su9network- address wit2in su9network7. T2us t2e su9networks can use different addressin! sc2emes as lon! as t2ere is a !lo9al wa1 of identif1in! t2e su9networks. • /ifferent ma,imum packet siDesA /ifferent su9networks 2a3e different restrictions on t2e ma,imum packet siDes t2e1 can 2andle. T2us- t2e router must 9reak up packets from one su9network into smaller packets for anot2er su9network. T2is process is referred to as se!mentation. 0t t2e destination- packets t2at 2a3e 9een se!mented will 2a3e to 9e reassem9led 91 t2e network la1er 9efore it can 9e passed to t2e 2i!2er la1er. 0 router must s2are a common network protocol wit2 t2e stations and routers t2at are directl1 attac2ed to it. In addition- for successful communication 9etween end stations- t2e stations must s2are t2e same protocols a9o3e t2e network la1er. : # # Gate3a?s ;atewa1s are de3ices t2at ma1 operate at all se3en la1ers of < I. T2e1 ma1 9e responsi9le for connectin! incompati9le proprietar1 networks- electronic mail s1stems- con3ertin! and transferrin! files from one s1stem to anot2er- or ena9lin! interopera9ilit1 9etween dissimilar operatin! s1stems or data9ase mana!ement s1stems. ome sample !atewa1 products areA • ;atewa1s 9etween networks suc2 as N0 and /=Cnet- or 9etween N0 and TC">I"B and



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CS260

CHAPTER ! : TELECOMMUNICATION SER"ICES AND NETWORK PRODUCTS • ?0Ns in different or!anisation or e3en wit2in t2e same or!anisation ma1 9e usin! different email s1stems suc2 as ccAMail- uucp and =as1?ink. T2ese s1stems 2a3e differences in t2e formatsaddressin! sc2emes- routin!- etc. In order to pro3ide transparent connecti3it1 9etween suc2 dissimilar e-mail s1stems- e-mail !atewa1 products suc2 as oft witc2 Central 2a3e 9een de3eloped. "rotocol standards suc2 as F.4++ 2elp in t2e con3ersion process.

Figure #: % LAN P+o01-ts ♦ Sta+LAN

1+ tar?0N 1+ is a local area network wit2 a star wirin! topolo!1 in w2ic2 eac2 computer is connected to a central 2u9. T2e ad3anta!e of t2is topolo!1 is t2at it is simple to install. 0lso- if one network de3ice failst2e rest of t2e network is unaffected. T2e network 2ardware is supported wit2 software. T2us meetin! t2e re8uirements for 8uick and eas1 access to s2ared information and resource. T2e platform is 9uilt on standard t2at com9ine t2e stren!t2s of @NIF and M -/< to support inte!rated- porta9le applications on an open multi3endor arc2itecture. 0TTT offers two 3ersions of tar?0N Network 2ardwareA a 1M9ps 3ersion for smaller confi!uration and a 1+M9ps 3ersion for lar!er networks and 2i!2er traffic 3olume. T2e 1+M9ps 3ersion also operates o3er optical fi9re and is compati9le wit2 =t2ernet s1stems. T2e discussion will 9e 9ased on tar?0N 1+. ♦ Feat1+es an0 A**l.-at.on T2e tar?0N network offers a complete solution wit2 t2e 2ardware- networkin!- and application software. T2e tar?0N 1+ network can connect up to 12 de3ices. Fi9re optics is used for distant connections and to address securit1 concerns. Network users ma1 access resources suc2 as applications software and files up to 1#.* ;91tes t2rou!2 @NIF operatin! s1stem ser3ices. 0s1nc2ronous communication facilities and terminal emulation software allow users to access 9ot2 on-net and off-net 2osts. tar?0N 1+ network !i3es a wide ran!e of connecti3it1 options for implementin! networkin! strate!ies. @sers ma1 access t2e network from a remote "C. Networks ma1 9e 9rid!ed to one anot2erlinked to computer networks- or a9le to access remote networks 3ia F.2# facilities. T2e networks are

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CS260

CHAPTER ! : TELECOMMUNICATION SER"ICES AND NETWORK PRODUCTS compati9le wit2 =t2ernet. 0pplications and Communication software and Network Mana!ement packa!e are ot2er features offered wit2 t2e tar?0N 1+ network. • I7M To4en!R.n5 Net3o+4 I&M Token-$in! network is I&MCs major entr1 into t2e ?0N market and a critical element in t2eir o3erall data communications strate!1. It will ser3e as one of t2e major 9uildin! 9locks of I&M Networks in t2e ne,t couple of decades. • • • T2e token-$in! is a star-wired rin! topolo!1. T2e protocol it uses is t2e token passin! protocol of t2e I=== )+2.# standard. It utilises s2ielded or uns2ielded twisted pair- or optical fi9re.

• It uses 9ase9and si!nallin! and can operate at eit2er 4M& or 1% M& dependin! on t2e t1pe of adapter card used. • ?0N. It will support (2 stations on uns2ielded wire pair or 2%+ stations on s2ielded pair on a sin!le

• "C ?0N pro!ram in t2e /< en3ironment and t2e < >2 er3er>$e8uester software on < >2 stations are t2e main software packa!es used wit2 t2e Token-$in! to 2andle t2e client>ser3er functions. • T2e ?0N Mana!er pro!ram is used for t2e network mana!ement functions.

• 0 network station can ser3e as a 9rid!e to anot2er token rin! usin! I&M Token-$in! network 9rid!e pro!ram. e3eral ?0Ns can 9e joined wit2 a 9ack9one ?0N usin! 9rid!es. : ' Re/.e3 $1est.ons %1. /escri9e t2e different t1pes of telecommunication networks. %2. :2at are t2e t1pical ser3ices pro3ided 91 telecommunication ser3ice pro3idersK %3. :21 is a 9rid!e used in a networkK %4. :2at is t2e difference 9etween transparent 9rid!in! and source routin! met2odK %#. :2at are t2e functions of a routerK %%. :2at is t2e difference 9etween a 9rid!e and a routerK %(. :21 do we need a ;atewa1K %). :rite down some of t2e features of t2e I&M Token $in! network. %*. :2at are some of t2e considerations for c2oosin! a particular ?0NK

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