Computer Networks

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Data communication concepts
Data communication model :Modem:- It is the device which is change the analog signal to digital signal and digital signal to analog signal. PSTN :- Public Switching Telephone Networks. The fundamental purpose of a communication system is the exchange the data between two parts. The key element are:<i> <ii>

Source:-It is a device that generates data to be transmitted.

Transmitter:-It transforms and encodes the message or
information into electro magnetic , electric or optical signals that can be transmitted across a transmission system.

<iii>

Transmission system:-It is the device that accepts the signal
forms the transmission system and convert its into a form that can be handled by a destination devices.

<iv>

Receiver:-It is the device that accepts the signal from the transmission
System and convert its into a form that can be handled by a Destination devices.

<v>Destination:-The devices that accepts incoming data is called destination of the data. <vi>Protocol:- Protocol are the rules and regulation which guide and Controls entire data communication process.

Analog data

vs.

digital data
The data that can take some discrete values is called digital data.

The data that can be take any value in an interval is called analog data.

E.g.:- voice, video are continuously varying E.g.:-textual data. Patterns of intensity. temperature & Presser.

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Signals:- Signals are electric, electromagnetic or optical representation
of either analog or digital data.

Analog signal
Analog signal is a continuously varying electromagnetic that may over either wired or wireless media.

Digital signal
Digital data is a sequence of voltage pulses that may be transmitted over a wired medium.

Signaling:- Signaling is the physical propagation of the signal along a
suitable medium.

Analog data

Analog signal

Digital signal CODEC(coder decoder):- It converts analog data to digital signal and
vice versa.

Digital data

Analog signal

Digital data

Digital signal

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Transmission:-It is the communication of data by the propagation and
processing of signals. There are two types of data transmission based on the signal they transmit:<i> Analog transmission <ii> Digital transmission Analog transmission Digital transmission It is propagate through amplifiers. It assumes that analog signal repre(the signal may represent analog or -sent digital data. The signal is digital data) propagated through repeaters.

Not used.

The signals are propagated through repeaters.

Amplifiers:-It is the device used in analog transmission to boost the
energy of the signal so that the signal is represented over long distances. Repeaters:-Repeaters are the device which are used in digital transmission and it receives digital signal and regenerates the same digital signal for propagation. The transmission can also be categories based upon the number of signals they transmit as:(1) Serial transmission. (2) Parallel transmission.

(1)

Serial transmission:-

In this transmission scheme the signally element are sent down the line (medium, transmission system) one at a time. The signally elements can be one bit or more than one bits. 3

e.g.:-computers networks. USB->Universal Serial Bus

(2)

Parallel transmission:-

In this scheme the signaling elements or transmitted through parallel set of lines. e.g.:-I/O devices , Internal computer signal paths such as address bus , data bus , control bus. Synchronizing the transmitter and receiver is done by two transmission approaches:(i) Asynchronous (ii) Synchronous

(I) Asynchronous:- in this scheme the timing problem is avoided by not
Sending uninterrupted stream of bits. The data Transmitted one character at a time generally of 8-bits.The timing and synchronization maintain Within each character. The receiver resynchronize At the beginning of new character.

It is used to synchronize the receiver.

Parity bit:-It is set by the transmitter if the total number of one’s in the
character including the parity bit is even other wise it is reset in case of even parity.

(II) Synchronous:-In this, block of bits is transmitted in a steady
stream without start and stop codes. To prevent

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timing drift (shift ,move) between transmitter and receiver, there clocks must by synchronized. Two methods can be adopted for synchronizing the sender and receiver clocks:<I> Use of separate clock lines between sender and receiver.

<II>

Embedding the clocking information in the data signal.

It requires 20% less over hand as compared to asynchronous transmission.

Data transmission models

Simplex (Unidirectional)

Duplex (Bidirectional)

Half

Full 5

Duplex

Duplex

Multiplexing:-The two communicating station will not be able to utilized the full capacity of the medium. Therefore some mechanism is required to minimize the utilization of the medium. Multiplexing is a technique To combine multiple analog or digital signal into one signal. E.g.:-Telephone network. The reverse process of multiplexing is called demultiplexing. It is a technique to extract the original signal from the multiplexed signal at the receiving end.

Multiplexer is the device that accepts data from N input lines and combines them into one link to transmit over a medium is multiplexer. Demultiplexer is the device that accepts multiple data streams separated the data according to the channel and then delivers them to appropriate output lines is called demultiplexer. E.g.:-Radio. Channel:->It is the data communication path between sender and receiver. In generate, the channel are expressed as frequency bands.

There are five measure ways of multiplexing the signals:(I) FDM(Frequency Division Multiplexing) 6

(II) (III) (IV) (V)

TDM(Time Division Multiplexing) STDM(Statically Time Division Multiplexing) SDM(Space Division Multiplexing) WDM(wavelength Division Multiplexing)

Even parity 11100000 11000000 11000000

Correct data. Incorrect data. i.e. odd parity.

Parity bits detect or check the data. (Data is correct or incorrect)

(I)

FDM:-It is the multiplexing technique in which the total available frequency

bandwidth of the transmission medium is divided into different frequency channels. Each channel carry signals of a particular station. e.g.-Radio, Television.

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Bandwidth:-It is the difference between minimum frequency and maximum of the wires. To prevent interferences among signal the channels are separated by guard bands. The entire kind is available for station to transmit the signals into the respective allowed frequency bands.

Advantages of FDM:(i)Each station is allowed separated dedicated bandwidth. (ii)Single transmission is required for data transmission.

Disadvantages of FDM:(I)FDM may produce interference. (II)It is appropriate for analog signal and digital signal.

(II)WDM:-In this a number of source generated a ledger beam at different
wavelengths which are multiplexed and transmitted over single fiber optics cable. These multiplexed signal are then the demultiplexed at the receiving and send to receivers.

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(III)TDM:-It is used for digital signals. Here every station is allowed a fixed period of
time for data transmission. During this period the entire bandwidth of the medium is allowed to that station. E.g.:-Computer networks.

Advantages of TDM:(i)Single communication is required fro data transmission. (ii)TDM supports data comparison. Disadvantages of TDM:(i)TDM requires all the station to be synchronized. (ii)High burst speed of station is required.

(IV)STDM:-It avoids the program of different speeds of senders and receiver in
computer networks. Here the time slots are allocated dynamically on demand to the station for data transmission. The number of time slots are usually the number of input lines to the multiplexer. The multiplier scans the input buffers and then send the received signal to the transmission medium. At the receiving end the demultiplier receives signals and distribute to appropriate output buffers. *Here the multiplexer collects data from various stations and it sends the data only when its buffer is full, but incase of time division multiplexing the multiplexer sends the data even if the buffer is not full.

Overhead bits:-In STDM the data is transmitted with additional information known as header which are overhead bits. The header includes the following information:(A)Sender address. (B)Receiver address. (C)Control and multiplexing information.

Advantages of STDM:*It is most suitable for high traffic application. *It supports data comparison.

Disadvantages of STDM:*It is more costly and more difficult to implement as compare to other techniques. *It uses variable length bit representation of characters which requires complex methods for data encoding or decoding.

(v)SDM:-In this technology a communication channel is created by grouping
together a number of individual communication lines. Packaging of subscriber lines in a multi wire cable in public switching telephone networks.

Advantages of SDM:-

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*It provides a dedicated connection between sender and receiver. *It is a simple and easy to implement.

Disadvantage of SDM:*wastage of resources.

Computer network:-computers networks are connections of computers and
switching devices (Hubs, Switches, Routers etc) that are interconnected by some communication links (wires, cables, optical fibers, micro webs etc) for the purpose of exchanging of data and sharing various equipment.

Computer network

Need for the computer networks:(A)File sharing(Read, Write, Execute options) (B)Printer and other costly devices can be shared using computer network. (C) Application program sharing such as Ms word, Ms word etc. (D)System program sharing such as operating system. (E)communicational and collaboration among team members. (F)Inter networking.

Advantages of networking
(I) File services
*Sharing of server space. *Password protection. *Online file. *Sharing of both program and files. *File encryption.

(II) Print services
*Sharing cost of printers with network users. *Spooling of print jobs.

(III) Massage services

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*Chatting *E-mailing *Sending message to single or group of user.

(IV) Application services
*Sharing of applications *Sharing hardware resources. *Remote logging on any terminal in the networks. *Sharing of peripherals *Accessing databases. *Internet excess sharing.

PROBLEMBS OF NETWORKING
(A)In case of server cresses, network failures the entire process or operation will be disrupted. (B)Data security. (C)Data privacy.

SCOPE OF NETWORK APPLICATION
(I) Home application
*Shopping, Reservation. *Access to remote information using internet. *Interactive entertainment(Accessing TV, Video, Audio, Games etc).

(II) Commerce
*E-commerce:-Using internet we can perform several commercial activities called E-commerce. The major forms of e-commerce are-….. (#) B2C(Business To Customer) E.g.-Website of companies, Online catalogs, Online purchases etc. (#) C2B(Customer To Business) E.g.-Customer complain, Customer order etc. (#) B2B(Business To Business) E.g.-Car manufacturing company placing order of tiers to tier company. (#) C2C(Customer To Customer) E.g.-Auction sites for sale and purchases goods

(III) Person to person communication 11

*Emailing *Chatting *Voice chat *Web cam

(IV) Mobile usage
*Connecting mobile devices such as laptop, mobiles, PDAs(personal Digital Application) using wireless technology such as Bluetooth, infrared or WAP(Wireless Application Protocol). *Wireless meter reading of electricity bills, water bills. *M-commerce(mobile-commerce)

(V) Resource sharing
*Both equipment and data can be shared.

SOCIAL ISSUES OF NETWORKING
(i) Privacy issues. Views posted on blocks, bulletin boards, chat rooms can be sensitive which may harm religious, cultural, social and political values. (iii) Hacking, credit cards founds, spam mail and other cyber crimes.

(ii)

Types of computer networks:(Based on architecture)

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SEVER BASED

PEER TO PEER

*In sever based networking one computer called server controllers data and resource that the other computers called clients on the network access. Sever is high performance and more powerful computer where as clients is low performance and less powerful computers. *The client machine request services from the server and the server caters to the request and provide desired services.

*In this computer networks there is no concept of server. A computer may act as server at one point of time and client at same other point of time. In this the data is distributed through out the network. *It is easy to built, small and inexpensive.

Example of the server based architecture:Example of the peer to peer based architecture:File server, Print server, Web server, Mail Small office LAN. server etc.

Types of computer networks
(Based on area coverage) (I)
(II) (III)

LAN(Local Area Network) MAN(Metropolitan Area Network) WAN(Wide Area Network)

(I) LAN:*It is privately owned. *It is smallest in size, covering small area such as building, campus etc. It covers a region within 10km range.

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*Data speed is about 10mbps to 1gbps. *LAN suffers from low error rates of about *The communication cost in negligible. *The communication media used twisted pair wire, co-axial cable, optical fiber in general. *Wireless LAN also be setup. to .

(II) MAN:*It may be privately owned or jointly owned. *It is larger than LAN but smaller than WAN. It covers an area up to 50km. *It provides high speed seamless interconnection within metropolitan area. *It provides very high speed data communication using fiber optics cables. *Wireless MAN can also be setup. *Error rate is higher than LAN but smaller than WAN( to ).

(III) WAN:*It is jointly owned by different organization and government. *It spans country wide or even world wise. *It commonly employees satellites, micro wed etc to communicate across different geographical area. *Data rate is about 1200mbps to 2mbps. *Error rate to .

*It involves high communication cost due to leased lines, satellites, telephone network etc.

Components of computer networks:(I) Server:-Server is a computer that contains different resources and data on the
network. e.g.:- File server, Web server, Mail server, Chat server

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(II) Work station/Client machine:-It is a computer used in engineering
application, software development and applications which require high graphics capability and computing power. It uses network resources provided by the server.

(III) Peripheral devices:-It are basically I/O devices.
e.g.:-CD-drive, DVD-drive, Keyboard, Mouse etc.

(IV) Transmission media:-It is a wired or wireless medium that helps transmit
data in network. e.g.:-Twisted pair wire, Co-axial cable, Fiber optical cable Bluetooth etc.

(V) NIC(Network Interface Card):-It is an expansion based that is placed
inside the computer to connect to the network. e.g.:-LAN card.

(VI) Network operating system:-It is a software that manages a network, data
transmitted and network traffic. e.g.:-Windows 2000 server, Windows XP server etc.

There are followings major functions:<A>Sharing of files and printers. <B>Administration of user account. <C>It allows network administrator to provides security to the users. <D>Monitoring network performance and ensuring that network is running
at optimal performance. e.g.:- Sun Solaris, Windows 2003 server, Novel Netware, Red Hat Linux.

(VII) Intermediary devices:-Intermediary devices such as hubs, switches,
routers, bridges, are used to connect server, clients, transmission media etc. It does the job of receiving the data from one device and forwarding to another device or intermediary device.

Communication channels & wired Transmission
Communication Medium Terminologies:15

transfer data from source to destination over a network is called transmission medium. (II) Communication Channel:-It is a path way in a transmission medium over which signals are transferred between remote devices. (III) Channel capacity:-The maximum rate at which data can be transmitted over a given communication path under a given condition is referred to as the channel capacity. E.g:-19.2kbps (IV) Data rate:-The data rate of a channel is defined as the amount of data that can be transmitted over the media in a specific time. It is usually less than or equal to the channel capacity because some additional overhead bits(address of source, address of destination flow, flow control information, error control information etc.) are also transmitted along with the data.

(I)

Transmission medium:-The wired or wireless mediums used to

(IV)

Bandwidth:-The difference between upper limiting frequency and lower limiting frequency that can be transmitted over a transmission medium is called bandwidth of the medium. The data rate is directly prepositional to the bandwidth of the medium. Error rate:-The rate at which error occurs in the signal is called error
rate of the medium. E.g.:to .

(V)

Transmission impairments:-With any communication system the signal
that is received may differ from the signal that is transmitted due to various transmission impairments. It degrades the quality of signals or introduce bit errors. The most significant transmission impairments are:@ Attenuation:-The strength of a signal falls of with distance over any transmission medium this phenomena is called attenuation. The amplifiers are used as remedy for this problem. @ Delay distortion:-It occurs because the velocity of propagation of signal through a wired medium varies with frequency. The velocity tends to be height near the control frequency of the bandwidth. The various frequency component of a signal will arrive at the receiver at different times which causes signals to be impaired. @ Noise:-They are unwanted signals that are inserted into the main signals. There are four categories of noise:*Thermal noise:-It occurs due to thermal a agitation of electrons. It is present in all the system and can’t be eliminate. *Enter modulation noise:-The some or multiple of frequencies that share the medium is called enter modulation noise. *Cross talk:-It is unwanted coupling between the signal paths. E.g.:-Cross talk, Entwisted pair wire. *Impulse noise:-It is wire non-continuous external signal consisting of irregular pulses of short duration or pulses of relatively high amplitude. E.g.:-lighting.

Types of communication medium:-

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1.Wired Medium(Guided Medium) 2.Wireless Medium(Unguided Medium) 1.Wired Medium:-It is the Cheapest and most commonly used medium. It uses
physical medium such as wires for data transmission. The three most popular wired medium:(A) Twisted pair cable:-It consists of two insulated copper wires twisted together in helical form. The wires are twisted to reduce interference between the two signals. It is most popularly used in telephones and computer networks.

cable are:-

The sub categories of twisted pair

@ Shielded twisted pair cable:-In this there is a shied over each pair of wires. The shield provides reliable data communication by protecting the signals from external interference.

@ Unshielded twisted pair cable:-In this there is no shied over pair of wires and therefore signals may be affected by external disturbances.

Features of twisted pair cable:# # # # Low cost. Suitable for both analog and digital communication. It is flexible and convenient to install. Low data rate.

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# Short range. # Limited bandwidth about 100MHz. # Problem of attenuation. (B)Coaxial cable:-It consists of inner copper wire insulated from outer conductor(Braid),Copper mesh. The entire arrangement is further surrounded by protective jacket such as protected plastic wires.

Features of coaxial cable:# Low cost but higher as compare twisted pair cable. # More bandwidth. # Problem of attenuation. # High installation cost. # Limited data rate. Types of coaxial cable:• Based band co-axial cable • Broad band co-axial cable *Based band co-axial cable:-In this base band transmission method is used. In this method audio or video signals are transmitted at their original frequency without modulation of the signals. It is suitable for short distance communication. Base band co-axial cable is basically 50Ω cable.

Features:*No modulation. *Low error rate. *Easy to install and maintain. *Less expenses as compare to broad band cable. *Reasonable bandwidth. *Provide better shielding than twisted pair cable.

*Broad band coaxial cable:-In this the signals are multiplexed into one cable and they are transmitted at a frequency which may be different from there original frequency. It is used for transmitting data, audio signals and video signals for high speed communication. The channel is allocated to the signal using frequency division multiplexing technique. It is used for transmission of signals for distances up to 100 Km.

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Features of the Broad band coaxial cable:• • • •



It covers longer distances. It is suitable for transmission of data, voice & video signals. It provides grater bandwidth. It maintenance cost and installation cost is higher than base band coaxial cables. Its design is very complex.

(C) fiber optic cables:The fiber optic cable consists of :@ Inner core:-

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