Data Com

Computer communication & networking

Dharmendra Arora

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Computer/Data Communication • Transfer of data or information between computer devices • Eg. ATM, Railways/Airlines Reservations etc.

Dharmendra Arora

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Facilitating data communication • • •

Network & communication systems are designed to convey information from origin to destination. Network: LAN-covers small/finite area, small number of users; WAN/Globalcovers great distance, unlimited users 2 principles of communication system 1. All the elements of communication system are designed to facilitate the exchange of information. 2. Receiver must understand the message. Dharmendra Arora

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Data communication system Sender

Encoder Switching Device COMMUNICATION CHANNEL

Decoder

RECEIVER Dharmendra Arora

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Elements of data communication system 1. 2. 3. 4. 5. 6.

Sender: originating computer that transmits the data (file/keyboard input). Data communication device at sender: converts the data into a form that can be transmitted eg. Modem. Communication channel: carries the data from place to place eg. Phone line. Switching Device: decides the path of transmitted data eg, switch, routers etc. Data communication device at receiver: converts the data into a form that the receiver computer can understand. Receiver: receiving computer that receives the data (can display, print, or store) Dharmendra Arora

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Hardware and software used • Data communication is accomplished by set of hardware and software – H/W: terminals, routers, hub, switch, cables, storage devices etc. – s/w: dialers, network monitoring programs etc.

Dharmendra Arora

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Some concepts-ASCII • ASCII Standards (American Standard of Code for Information Interchange)-creates a common ground for communication by defining standard code to represent 128 characters. It uses seven bits to define each character, by assigning a decimal value to each character. Eg. A=>65=>01000001; a=>97=>01100001

Dharmendra Arora

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Some Concepts-Bandwidth • Hertz- unit of measuring bandwidth, one cycle/sec=one hertz • Bandwidth-no. of cycles that can be sent through a transmission channel in one second • Communication Rate-speed at which data travel over a communication channel; measured in bits per second or baud Dharmendra Arora

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Some Concepts- Digital / Analog Communication • Continuous but variable electrical waves. Can travel through general channels like telephone lines. • Discreet electronic units transmitted in extremely rapid succession. Uses special equipment as channel which is expensive.

Dharmendra Arora

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Some Concepts- Synchronous and Asynchronous Communication • Basically it’s the way in which coded characters are assembled for transmission and reception. • In Sync. Transmission characters are transmitted as groups, preceded and followed by control characters. Data byte are sent at regular intervals. And the reception takes place in precisely same frequency. • Speedy transmission but inaccurate (because of lesser control characters)

Dharmendra Arora

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Some Concepts- Synchronous and Asynchronous Communication • In Async. Transmission each character is transmitted separately, preceded by start bit and followed by stop bit. Data bits are sent at irregular intervals. • Slower but accurate. • Doesn’t require complex and costly hardware. Dharmendra Arora

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Some Concepts- protocols • Protocols are technical guidelines that govern the exchange of signal transmission and reception between equipments. • Only devices using same protocol can communicate directly with each other; both h/w and s/w are designed to handle specific protocols. Eg. TCP/IP for internet. Dharmendra Arora

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Some concepts-Simplex • Simplex mode-communication channel used in one direction only; rarely used • Half-duplex mode-commun. Channel used in both directions, but only in one direction at a time eg. wireless. • Full duplex mode-commun. Channel used in both the directions at once eg. telephone.

Dharmendra Arora

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Some Concepts-Multiplexing • It is a form of data transmission in which one communication channel carries several transmissions at same time.

Dharmendra Arora

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Channels • Twisted pair • Co-axial • Optical fiber • Microwave • Infrared • Satelite etc. Dharmendra Arora

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Connecting The Elements

NETWORKING

Dharmendra Arora

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Network • Two or more computers/points/nodes connected together by communication paths. • Primarily can be categorised as LAN & WAN

Dharmendra Arora

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Network Topologies • Topology-is the layout of the connections formed between the computers. • Main Topologies – Bus – Star – Ring Dharmendra Arora

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Bus Topology Broadcast Bus

• If one computer transmits all others can listen simultaneously • failure of single computer does not affect rest • Computers can easily be added/removed in network Dharmendra Arora • Failure of bus causes failure of entire network

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Star • When the data must go through a central point • Center computer is a server • Every message is first sent to server which then retransmits to destination • If server goes down, network goes down Dharmendra Arora

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Ring • Computers are connected in a ring/loop manner • Each computer can talk to any other in the ring by sending signal • If any of the computer fails network fails • Difficult to add/remove computer Dharmendra Arora

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Components • Terminal / Workstation • NIC/NIU • Gateway • Hub • Cable • Network Operating System Dharmendra Arora

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WAN • VPN • Public • Packet switching/Circuit Switching

Dharmendra Arora

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Thanks Dharmendra Arora [email protected] m Dharmendra Arora

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