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Basics of Data Communication and Computer Networking

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BASICS OF DATA COMMUNICATION AND COMPUTER NETWORKING Basic Elements of a Communication S stem The following are the basic requirements for working of a communication system. !" T#e sen$e% &sou%ce' who creates the message to be transmitted (" A me$ium that carries the message )" T#e %ecei*e% &sin+' who receives the message In $ata communication fou% ,asic te%ms a%e f%e-uentl use$" T#e a%e. Data. A collection of facts in raw forms that become information after processing. Si/nals. Electric or electromagnetic encoding of data. Si/nalin/ . Propagation of signals across a communication medium. T%ansmission. Communication of data achieved by the processing of signals. Elect%onic communication. Telecommunication + data communications. Telecommunication. se of telephone! telegraph! and radio or television facility to transmit information! either directly or via computer. Data communication. Transfer of data or information between computers devices. COMMUNICATION T0PES  P1to1P Communication &Point to Point Communication' " o #one in networks where a single communication channel is not shared by all nodes. o $ut in this one! the communication channels are only shared between only two ad%oining nodes like in the case of ring topology. o To send the packet &data' between two nodes the packet is passed from the source node to its ad%oining node. pon receiving the packet the address part is checked and if the packet is not intended for that node then it is regenerated and passed to its ad%oining node according to the routing algorithms which play an important role in point to point communication. The packet is passed on like this till it reaches the destination. This type of transmission is done over the (ide Area )etwork &(A)' and *etropolitan Area )etwork &*A)'.  B%oa$castin/. o Type of transmission technology in which the transmission of data from one node to another node is made. o $roadcasting systems generally allow addressing a packet to all destinations by using a single code in the address fields. +t is done on the broadcast network. o A broadcast network have a single communication channel that is shared by all the other nodes! when the packet with this code is transmitted! it is received and processed by every machine on the network. An address field within the packet specifies for whom it is intended. A machine checks the address field if the packet is intended for itself otherwise the packet will be discarded. This mode of operation is called $roadcasting. This sort of transmission is generally done on ,ocal Area )etwork &,A)'. o -ome broadcast systems support transmission to a subset of the machine! which is known as multicasting when a packet is sent to a certain group. it is delivered to all machines subscribing to that group. Data Communication Data communication" Transmitting information from one location to other using wired and wireless networks &communication system'! over a communication channel! by means of electrical signals. Si/nals.  An //electric or electromagnetic encoding of data0 "  T 2es. !' Analo/ si/nals. The transmission pattern is in continuous wave form. +t varies over a continuous range with respect to sound! light and radio waves. +t is measured in 1olts and its frequency in 2ert3 &23'. Although these can be communicated via any media! these are more prone to data impairments such as noise and it is more difficult to separate such discrepancies from analog signals than from their digital counterparts (' Di/ital si/nals. +t may assume only discrete set of values within a given range.

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A digital signal is a sequence of voltage represented in binary form Mo$ulation. (hen digital data are to be sent over an analog form the digital signal must be converted to analog form. -o the technique by which a digital signal is converted to analog form is known as modulation. Demo$ulation" The reverse process! that is the conversion of analog signal to its digital form! is known as demodulation. Mo$em" The device! which converts digital signal into analog! and the reverse! is known as modem. Any form of signal may be transformed into the other form. 4or e5ample! a music file stored in computer &digital' transformed into audible music &analog'.

As nc#%onous an$ S nc#%onous T%ansmission   #ata transmission through a medium can be either asynchronous or synchronous. +n asynchronous transmission data is transmitted character by character as you go on typing on a keyboard. 2ence there are irregular gaps between characters. 2owever! it is cheaper to implement! as you do not have to save the data before sending. +n the synchronous mode! the saved data is transmitted block by block. Each block can contain many characters. -ynchronous transmission is well suited for remote communication between a computer and related devices like card reader and printers.

Net3o%+s 6' 4ocal as in local a%ea net3o%+!  Cover a small area and have a finite! relatively small! number of users and (' Glo,al o% lon/1#aul  Cover long distance and have an unlimited number of users.  Telephone networks are long network. The effectiveness of a data communication system depends on three fundamental characteristics"  Deli*e% " The system must deliver data to the correct destination or only to the intended device or user.  Accu%ac " The system must deliver data accurately and unaltered.  Timeliness" The system must deliver data in a timely manner. +n the case of video! audio and voice data! timely delivery means delivering data as they are produced! in the same order that they are produced! and without significant delay. This kind of delivery is called %eal1time t%ansmission" Data Communication Com2onent 6. T%ansmitte%" -ends the message. E.g. a computer! workstation! telephone handset! video camera! and so on 7. Recei*e%. 8eceives the message. E.g. computer! workstation! telephone handset! television! and so on. 9. Me$ium. The channel: physical path over which the message is sent. +t can consist of twisted pair wire! coa5ial cable! fiber;optic cable! laser or radio waves &terrestrial or satellite microwave'. <. Messa/e" Central to all the components. +t=s the data that is being communicated. +t can consist of te5t! number! pictures! sound! or video or any combination of these. >. P%otocol" -et of rules that guide how the data is transmitted from encoding to decoding. +t represents an agreement between the communicating devices. (ithout a protocol! two devices may be connected but not communicating. Communication P%otocols5 Data communication soft3a%e Data communication soft3a%e.  Computers send and receive data across communication links through these.  Enables us to communicate with other systems.  +t instructs computer systems and devices as to how e5actly data is to be transferred from one place to another.

Perform the following functions for the efficient and error free transmission of data. !" Data se-uencin/" A long message to be transmitted is broken into smaller packets of fi5ed si3e for error free data transmission. (" Data Routin/" +t is the process of finding the most efficient route between source and destination before sending the data. )" Flo3 cont%ol" All machines are not equally efficient in terms of speed. 2ence the flow control regulates the process of sending data between fast sender and slow receiver. 6" E%%o% Cont%ol" Error detecting and recovering is the one of the main functions of communication software. +t ensures that data are transmitted without any error. P%otocol" The procedure of data transformation in the form of software.  Data T%ansmission Mo$es There are three ways for transmitting data from one point to another" !" Sim2le7 " a. Communication can take place in one direction. b. The receiver receives the signal from the transmitting device. c. +n this mode the flow of information is ni;directional. 2ence it is rarely used for data communication. (" 8alf1$u2le7" a. Communication channel is used in both directions! but only in one direction at a time. b. Thus a half;duple5 line can alternately send and receive data. )" Full1$u2le7. a. Communication channel is used in both directions at the same time. b. se of full;duple5 line improves the efficiency as the line turnaround time required in half;duple5 arrangement is eliminated. c. E5ample of this mode of transmission is the telephone line. Communication Me$ia. Wi%e$ an$ Wi%eless Wi%e$. !' Wi%e Pai%s" a. Commonly used in local telephone communication and for short distance digital data communication. sually made up of copper. b. Data t%ansmission s2ee$" [email protected] bits per second in a distance of 6AA meter. (' T3iste$ 2ai%" a. *ost widely used medium for telecommunication. Consist of copper wires! twisted into pairs. b. Brdinary telephone wires" two insulated copper wires twisted into pairs. c. Computer networking cabling" &wired Ethernet as defined by +EEE CA7.9' consists of < pairs of copper cabling that can be utili3ed for both voice and data transmission. d. 2elps to reduce crosstalk and electromagnetic induction. e. Data t%ansmission s2ee$" 7 million bits per seconds;6A billion bits per second. f. T3o fo%ms. Uns#iel$e$ T3iste$ Pai% &UTP' an$ S#iel$e$ t3iste$12ai% &STP '. )' Coa7ial ca,le" a. sed for cable television systems! office buildings! and other work;sites for local area networks. b. Consist of copper or aluminum wire wrapped with insulating layer typically of a fle5ible material with a high dielectric constant! all of which are surrounded by a conductive layer. c. The layers of insulation help minimi3e interference and distortion. d. Data t%ansmission s2ee$" 7AA million to more than >AA million bits per second. 6' O2tical fi,e%. a. Consists of one or more filaments of glass fiber wrapped in protective layers that carries data by means of pulses of light.

Transmits light which can travel over e5tended distances and not affected by electromagnetic radiation. c. Data t%ansmission s2ee$" may reach trillions of bits per second. i. 2undreds of times faster than for coa5ial cables and ii. Thousands of times faster than a twisted;pair wire. iii. This capacity may be further increased by the use of colored light! i.e.! light of multiple wavelengths. d' +nstead of carrying one message in a stream of monochromatic light impulses! this technology can carry multiple signals in a single fiber. Wi%eless tec#nolo/ies 6' Te%%est%ial mic%o3a*e" a. se Earth based transmitter and receiver. b. The equipment looks similar to satellite dishes! are usually placed on top of buildings! towers! hills! and mountain peaks c. se low;gigahert3 range! which limits all communications to line;of;sight. d. Path between relay stations spaced appro5! <C km &9A mi' apart. 7' Communications satellites" a. ses microwave radio signals as their telecommunications medium which are not deflected by the Earth=s atmosphere. b. The satellites are stationed in space! typically 9>!<AA km &77!AAA mi' &for geosynchronous satellites' above the equator. c. Capable of receiving and relaying voice! data! and T1 signals. Ban$3i$t# Term for data;handling capacity of a communication service. +t is the range of frequencies that is available for the transmission of data. )arrow the range of frequencies in a communication system is! more restricted is the flow of information in such a system. Bau$" nit to measure the communication data transfer rate. +dentical to bits per second.9AA baud is 9AA bits per second. Communication companies such as American Telephone and Telegraph &ATDT' and (estern nion are called common carriers. They provide three general classes of service for both voice and data communication" 6' Na%%o3,an$. 2andles low data volumes. DTR. <> to 9AA baud. The low;speed devices might use narrow band communications. 7' 9oice,an$" 2andles moderate data volumes. DTR. 9AA and [email protected] baud. Applications" Bperating a C8T to running a line printer. *a%orly for telephone voice communication hence! the term voiceband. 9' B%oa$,an$. 2andles very large volumes of data. DTR. 6 million baud or more. E.g. 2igh; speed data analysis and satellite communications


MODEM &mo$ulato%1$emo$ulato%' A device that     *odulates an analog carrier signal to encode digital information for easy transmission and #emodulates such a carrier signal to decode the transmitted information to reproduce the original digital data. Can be used over any means of transmitting analog signals! from light emitting diodes to radio. +t modulates outgoing digital signals from a computer or other digital device to analog signals for a conventional copper twisted pair telephone line and demodulates the incoming analog signal and converts it to a digital signal for the digital device. 4rom early 6??C! most new personal computers came with >@ Ebps modems.

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$y comparison! using digital +ntegrated -ervices Di/ital Net3o%+ a$a2te% instead of a conventional modem! the same telephone wire can now carry up to 67C Ebps. (ith #igital -ubscriber ,ine &#-,' systems! now being deployed in a number of communities! bandwidth on twisted;pair can be in the megabit range.

T 2es of Mo$ems 4an$line Mo$ems Wi%eless Mo$ems 4AN Mo$ems  4an$line Mo$ems. o Connect to the public switched telephone network &P-T)' through a %ack&8F;66'! or regular phone %ack. o A telephone cable with a 8F;66 plug connects the modem to the nearest phone %ack! which also conforms to the 82;66standard. o 4an$line mo$ems t 2es.  Inte%nal mo$ems. • A circuit board that plugs into one of the e5pansion slots of the computer. • Cheaper than e5ternal modems! but when problems occur! fi5ing and troubleshooting the modem can sometimes prove to be quite difficult. • The telephone line plugs into the modem port in the back of the computer. • *ost internal modems come installed in the computer you buy. • +nternal modems are more directly integrated into the computer system and! therefore! do not need any special attention. • +nternal modems are activated when you run a communications program and are turned off when you e5it the program. • This convenience is especially useful for novice users. • Disa$*anta/e" Their location" inside the computer. (hen you want to replace an internal modem you have to go inside the computer case to make the switch.  E7te%nal mo$ems. • Attached to the back of the computer by way of a cable that plugs into the modem port. • +t is usually less e5pensive and very portable. +t can be used with other computers very easily by unplugging it and plugging it into another computer. • This is the simplest type of modem to install because you don=t have to open the computer. • 2ave their own power supply &does not drain any power from the computer' and connect with a cable to a computer=s serial port. • The telephone line plugs into a socket on the rear panel of the modem. • Gou also can monitor your modem=s connection activity by watching the status lights.  9oice5$ata5fa7 mo$ems. • Can be hooked up to your telephone and used to send information to your computer. • Gour computer can also send information to a fa5 machine. • *ost computer modems are modems with fa5ing capabilities.  PC Ca%$ mo$em. • #esigned for portable computers! is the si3e of a credit card and fit into the PC Card slot on notebook and handheld computers and can be removed when not needed. • E5cept for their si3e! PC Card modems are like a combination of e5ternal and internal modems. • Plugged directly into an e5ternal slot in the portable computer! so no cable is required other than the telephone line connection.

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The cards are powered by the computer! which is fine unless the computer is battery;operated. 8unning a PC Card modem while the portable computer is operating on battery power drastically decreases the life of your batteries.

Wi%eless Mo$ems. o They are radio transmitters:receivers installed into mobile computing devices. o sing these! one can connect to a network while being mobile. o nlike landline modems! wireless modems do not plug into an 8F;66 %ack. 4AN Mo$ems. o Allow shared remote access to ,A) &,ocal Area )etwork' resources. o Comes fully preconfigured for single particular network architecture such as Ethernet or Token 8ing and:or particular network software such as +PH! )et$+B-! and )et$E + etc.

Wo%+in/ of Mo$em  *odems convert analog data transmitted over phone lines into digital data so that computers can read.  They also convert digital data into analog data so it can be transmitted. This process involves modulating and demodulating the computer=s digital signals into analog signals that travel over the telephone lines.  +n other words! the modem translates computer data into the language used by telephones and then reverses the process to translate the responding data back into computer language.

COMPUTER NETWORK  An interconnection of various computer systems located at different places! linked together with a medium and data communication devices for the purpose of communicating data and sharing resources. -erver" The computer that provides resources to other computers on a network. )odes" +n the network the individual computers! which access shared network resource.

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C#a%acte%istics of a Com2ute% Net3o%+  The primary purpose of a computer network is to share resources" o Gou can play a C# music from one computer while sitting on another computer o Gou may have a computer that doesn=t have a #1# or $lu8ay &$#' player. +n this case! you can place a movie disc &#1# or $#' on the computer that has the player! and then view the movie on a computer that lacks the player. o Gou may have a computer with a C#:#1#:$# writer or a backup system but the other computer doesn=t have it. +n this case! you can burn discs or make backups on a computer that has one of these but using data from a computer that doesn=t have a disc writer or a backup system. o Gou can connect a printer &or a scanner! or a fa5 machine' to one computer and let other computers of the network print &or scan! or fa5' to that printer &or scanner! or fa5 machine' o Gou can place a disc with pictures on one computer and let other computers access those pictures. o Gou can create files and store them in one computer! then access those files from the other computer&s' connected to it. Conce2t of Net3o%+in/.  A computer network! often simply referred to as a network! is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information.

)etworks may be classified according to a wide variety of characteristics such as the medium used to transport the data! communications protocol used! scale! topology! and organi3ational scope. The rules and data formats for e5changing information in a computer network are defined by communications protocols.

P%o2e%ties of Net3o%+  4acilitate communications" sing a network! people can communicate efficiently and easily via email! instant messaging! chat rooms! telephone! video telephone calls! and video conferencing.  Permit sharing of files! data! and other types of information. +n a network environment! authori3ed users may access data and information stored on other computers on the network. The capability of providing access to data and information on shared storage devices is an important feature of many networks.  -hare network and computing resources" +n a networked environment! each computer on a network may access and use resources provided by devices on the network! such as printing a document on a shared network printer.  #istributed computing uses computing resources across a network to accomplish tasks. BENEFITS OF NETWORK  File s#a%in/" )etwork file sharing between computers gives you more fle5ibility than using floppy drives or Iip drives. )ot only can you share photos! music files! and documents! you can also use a home network to save copies of all of your important data on a different computer. $ackups are one of the most critical yet overlooked tasks in home networking.  P%inte% 5 2e%i2#e%al s#a%in/" Bnce a home network is in place! it=s then easy to set up all of the computers to share a single printer. )o longer will you need to bounce from one system or another %ust to print out an email message. Bther computer peripherals can be shared similarly such as network scanners! (eb cams! and C# burners.  +nternet connection sharing" sing a home network! multiple family members can access the +nternet simultaneously without having to pay an +-P for multiple accounts. Gou will notice the +nternet connection slows down when several people share it! but broadband +nternet can handle the e5tra load with little trouble.  *ulti;player games" *any popular home computer games support ,A) mode where friends and family can play together! if they have their computers networked.  +nternet telephone service" 1oice over +P &1o+P' services allows you to make and receive phone calls through your home network across the +nternet.  2ome entertainment" )ewer home entertainment products such as digital video recorders &#18s' and video game consoles now support either wired or wireless home networking. 2aving these products integrated into your network enables online +nternet gaming! video sharing and other advanced features. T0PES OF NETWORK Base$ on c#a%acte%istics 3e cate/o%i:e $iffe%ent t 2es of net3o%+s"  F%om an en$ use%;s 2oint of *ie3 t#e%e a%e three basic types"  ,ocal Area )etwork  (ide Area )etwork  *etropolitan Area )etwork  Base$ on To2olo/ &Geomet%ic A%%an/ements of a Com2ute% S stem'"  -tar )etwork  8ing )etwork  $us )etwork  Base$ on P%otocol  The protocol defines a common set of rules and signals that computers on the network use to communicate.  Bne of the most popular protocols for ,A)s is called Ethernet.  Another popular ,A) protocol for PCs is the +$* token;ring network.  Base$ on A%c#itectu%e.  Peer to Peer

Client -erver Architecture

4ocal A%ea Net3o%+ &4AN'.  -upplies networking capability to a group of computers in close pro5imity to each other such as in an office building! a school! or a home.  seful for sharing resources like files! printers! games or other applications. A ,A) in turn often connects to other ,A)s! and to the +nternet or other (A).  *ost local area networks are built with relatively ine5pensive hardware such as Ethernet cables! network adapters! and hubs.  (ireless ,A) and other more advanced ,A) hardware options also e5ist.  Bne ,A) can be connected to other ,A)s over any distance via telephone lines and radio waves.  *ost ,A)s connect workstations and personal computers. Each node &individual computer' in a ,A) has its own CP with which it e5ecutes programs! but it is also able to access data and devices anywhere on the ,A). This means that many users can share e5pensive devices! such as laser printers! as well as data. sers can also use the ,A) to communicate with each other! by sending e;mail or engaging in chat sessions.  There are many different types of ,A)s; Token!ring networks! Ethernets! and A8Cnets being the most common for PCs. Wi$e A%ea Net3o%+s &WANs'  sually refers to a network which covers a large geographical area! and use communications circuits to connect the intermediate nodes.  A ma%or factor impacting (A) design and performance is a requirement that they lease communications circuits from telephone companies or other communications carriers.  Transmission rates are typically 7 *bps! 9< *bps! <> *bps! 6>> *bps! @7> *bps &or sometimes considerably more'. Met%o2olitan A%ea Net3o%+ &MAN'  +t is one of a number of types of networks &see also ,A) and (A)'. A *A) is a relatively new class of network! it serves a role similar to an +-P! but for corporate users with large ,A)s. NETWORK TOPO4OG0   Topology refers to the way the computers or workstations in the network are linked together. According to the physical arrangement of workstations and nature of work! there are four ma%or types of network topology. These are" o Sta% Net3o%+  sed to connect one or more small computers or peripheral devices to a large host computer or CP .  *any organi3ations use the star network or a variation of it in a time;sharing system! in which several users are able to share a central processor. +n a time; sharing setup! each terminal receives a fi5ed amount of the CP Js time! called a time slice. +f you are sitting at a terminal and cannot complete your task during the time slice! the computer will come back to you to allow you to do so. Actually! because the CP operates so much faster than terminals! you will probably not even notice that the CP is away.  $y establishing time;sharing! many people in a large organi3ation can use a centrali3ed computing facility. Time;sharing can also be purchased from an outside service! which is an economical way to operate for a small company that cannot afford its own large computer.  4requently used in a ,A) to connect several microcomputers to a central unit that works as a communications controller. +f the user of one microcomputer wants to send a document or message to a user at another computer! the message is routed through the central communications controller.

Another common use of the star network is the feasibility of connecting several microcomputers to a mainframe computer that allows access to an organi3ationJs database.  Access and control of star network typically is maintained by a 2ollin/ s stem" Polling means that the central computer or communications controller KpollsK or asks each device in the network if it has a message to send and then allows each in turn to transmit data. o Bus to2olo/ .  Connects networking components along a single cable or uses a series of cable segments that are connected linearly.  A network that uses a bus topology is referred to as a Lbus network.0  Cheapest way of connecting computers to form a workgroup or departmental ,A)! but it has the disadvantage that a single loose connection or cable break can bring down the entire ,A).  $us topology is used for" • -mall workgroup ,ocal Area )etworks &,A)s' whose computers are connected using a thin;net cable. • Trunk cables connecting hubs or switches of departmental ,A)s to form a larger ,A). • $ack;boning! by %oining switches and routers to form campus;wide networks. o Rin/ to2olo/ .  )etwork stations are connected along a single path whose ends are %oined to form a circle. The circle might be logical only. The physical arrangements of the cabling might be star like! with a hub or concentrator at the center.  A ring network is based on a ring topology.  The ring topology is commonly used in the following kinds of networks" • Token ring networks" The ring of a token ring network is concentrated inside a device called a *ultistation Access nit &*A '. • 4iber #istributed #ata +nterface &4##+' networks" The ring in this case is both a physical and logical ring and usually runs around a campus or collection of buildings to Net3o%+ A%c#itectu%e  Pee%1to12ee% A%c#itectu%e o +n this each workstation has equivalent capabilities and responsibilities. o Peer;to;peer networks are generally simpler and less e5pensive! but they usually do not offer the same performance under heavy loads.  Client5Se%*e% A%c#itectu%e o +n this each computer or process on the network is either a client or a server. o -ervers are powerful computers or processors dedicated to managing disk drives &file servers'! printers &print servers'! or network traffic &network servers'. o Clients are less powerful PCs workstations on which users run applications. Clients rely on servers for resources! such as files! devices! and even processing power. IMPORTANT TERMS USED IN NETWORKING  !' 9oice Messa/in/ a. -imilar to electronic mail e5cept that it is audio message rather than te5t messages that are processed. i. A sender speaks into a telephone rather than typing! giving the name of the recipient and the message. ii. That sender=s voice signal is then digiti3ed and stored. iii. The system can then either deliver the message at a specified time in future or it can be retrieved from a database by the recipient. iv. The message is reconverted back into its analog format when it is delivered or retrieved so that the recipient hears it as the original sender=s voice on a telephone. b. 1oice messaging requires a computer with an ability to store the audio messages in digital form and then convert them back in an audio form upon verification.

c. d. (' 8u, a. b. c.

Each user has a voice mailbo5 in secondary storage and special equipment converts the audio message to and from the digital form. The main advantage of voice mail over electronic mail is that the sender does not have to type. 1oice mail also makes it easy to include people in the firm=s environment in a communication network. +ts %ob" anything that comes in one port is sent out to the others. Every computer connected to the hub Lsees0 everything that every other computer on the hub sees. The hub itself is blissfully ignorant of the data being transmitted. 4or years! simple hubs have been quick and easy ways to connect computers in small networks.

)' S3itc# a. A switch does essentially what a hub does but more efficiently. $y paying attention to the traffic that comes across it! it can Llearn0 where particular addresses are. b. 4or e5ample! if it sees traffic from machine A coming in on port 7! it now knows that machine A is connected to that port and that traffic to machine A needs to only be sent to that port and not any of the others. c. The net result of using a switch over a hub is that most of the network traffic only goes where it needs to rather than to every port. Bn busy networks this can make the network significantly faster. 6' Route% a. 8outers come in all shapes and si3es from the small four;port broadband routers that are very popular right now to the large industrial strength devices that drive the internet itself. b. A simple way to think of a router is as a computer that can be programmed to understand! possibly manipulate! and route the data its being asked to handle. c. 4or e5ample! broadband routers include the ability to Lhide0 computers behind a type of firewall which involves slightly modifying the packets of network traffic as they traverse the device. d. All routers include some kind of user interface for configuring how the router will treat traffic. The really large routers include the equivalent of a full;blown programming language to describe how they should operate as well as the ability to communicate with other routers to describe or determine the best way to get network traffic from point A to point $. <' Net3o%+ Re2eate% a. A repeater connects two segments of your network cable. +t retimes and regenerates the signals to proper amplitudes and sends them to the other segments. b. (hen talking about! ethernet topology! you are probably talking about using a hub as a repeater. 8epeaters require a small amount of time to regenerate the signal. c. This can cause a propagation delay which can affect network communication when there are several repeaters in a row. d. *any network architectures limit the number of repeaters that can be used in a row. 8epeaters work only at the physical layer of the B-+ network model. =' B%i$/e a. A bridge reads the outermost section of data on the data packet! to tell where the message is going. +t reduces the traffic on other network segments! since it does not send all packets. b. $ridges can be programmed to re%ect packets from particular networks. $ridging occurs at the data link layer of the B-+ model! which means the bridge cannot read +P addresses! but only the outermost hardware address of the packet. c. +n our case the bridge can read the ethernet data which gives the hardware address of the destination address! not the +P address. d. $ridges forward all broadcast messages. e. Bnly a special bridge called a translation bridge will allow two networks of different architectures to be connected. $ridges do not normally allow connection of networks with different architectures.


The hardware address is also called the *AC &media access control' address. To determine the network segment a *AC address belongs to! bridges use one of the following" i. Transparent $ridging" They build a table of addresses &bridging table' as they receive packets. +f the address is not in the bridging table! the packet is forwarded to allsegments other than the one it came from. This type of bridge is used on ethernet networks. ii. -ource route bridging" The source computer provides path information inside the packet. This is used on Token 8ing networks

>' Route% a. There is a device called a router which will function similar to a bridge for network transport protocols that are not routable! and will function as a router for routable protocols. b. +t functions at the network and data link layers of the B-+ network model. ?' Gate3a a. A gateway can translate information between different network data formats or network architectures. b. +t can translate TCP:+P to AppleTalk so computers supporting TCP:+P can communicate with Apple brand computers. c. *ost gateways operate at the application layer! but can operate at the network or session layer of the B-+ model. d. Mateways will start at the lower level and strip information until it gets to the required level and repackage the information and work its way back toward the hardware layer of the B-+ model. TE4ECONFERENCING  8efers to electronic meetings that involve people who are at physically different sites.  Telecommunication technology system allows meeting participants to interact with one another without travelling to the same location.  Three different types of teleconferencing e5ist" audio teleconferencing! video teleconferencing and computer conferencing. o Au$io Confe%encin/  se of voice communication equipments to establish an audio link between geographically dispersed persons! one that allows them to conduct a conference.  The conference call was the first form of audit conferencing and is still in use. -ome firms install more elaborate systems consisting of private! high;quality audio communications circuits that can be activated with the flip of a switch.  #oes not require a computer. +t only requires a two;way audio communications facility.  $est suited for firms that are spread over a wide area. 2owever! since it is a form of synchronous communication that requires all participants to be present at the same time! it is difficult to schedule conferences when time 3ones are far apart. o 9i$eo Confe%encin/.  se of television equipment to link geographically dispersed conference participants.  The equipment provides both sound and picture. ,ike audio conferencing! video conferencing also does not necessarily require a computer.  (ith video conferencing! participants can see and hear each other. Menerally! participants gather in relatively e5pensive! specially equipped rooms that can handle the comple5ities of simultaneous video and audio transmission.  There are three possible video conferencing configurations. • One1Wa 9i$eo an$ Au$io. 1ideo and audio signals are sent from a single transmitting site to one or more receiving sites. This is a good way for a pro%ect leader to disseminate information to team members at remote locations.

• •

One1Wa 9i$eo an$ T3o1Wa Au$io" People at the receiving sites can talk to people at the transmitting site! while everyone views the same video images. T3o1Wa 9i$eo an$ Au$io" The video and audio communications between all sites are two;way. Although this is the most effective of the electronically aided conferencing approaches!it can be the most e5pensive as well.


Com2ute% Confe%encin/.  There is a fine line between this system and Email. $oth use the same software and hardware.  Two factors determine this application! who uses the system! and the sub%ect matter.  E;mail is available to anyone who has access to the network and that includes practically everyone in the office. Also! the E;mail system can be used for any purpose.  Computer conferencing! on the other hand! is the use of a networked computer that allows particular task.  Computer conferencing is more disciplined form of E;mail.  nlike an audio conference! a! computer conference group can consist of large number of participants. Bne of the largest computer conferences was formed within +$* to include anyone who had an interest in the +$* PC.  +ts members e5ceeded <A!AAA! and there were over <!AAA separate topic areas.  Computer conferencing differs from audio and video conferencing because it can be used within a single geographic site.  A person can use computer conferencing to communicate with someone in the office ne5t door.

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