Data Communications

An Overview

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• This course intends to explain how data communications work

• It will give you the basis for understanding data communications in general

• And know how to connect PCs with other PCs

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What is Data Communication?• It is the process of communicating

information in binary form between two or more points.

• Sometimes called computer communication

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Brief History• A Scottish inventor proposed a simple

but profound system. The system uses 26 parallel wires (plus ground).

• 1833, Carl Friedrich Gauss used a code based on a 5X5 matrix

• 19th century, Samuel F.B. Morse invented the telegraph

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History… (2)• The telegraph replaced the Pony

Express• Morse’s invention merged the human

mind and equipment

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Data Communication Systems• Uses intelligent device to convert a

character or a symbol into coded form or vice versa.

• In Morse’s system the intelligent “devices” were the ___.

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Definitions• Codes – standard interpretations

between signalling elements and characters

• Characters – the letters, numbers, punctuation marks and other signs and symbols

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Definitions… (2)• Signalling elements – something that

is sent over a transmission channel and used to represent characters.

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Baudot Codes• Developed by Emile Baudot, a

French, in 1870’s• Each character has the same code

length (5 signalling elements)• Better suited for machines than

Morse’s codes• Not enough to include the digits

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EBCDIC• Stands for Extended Binary Coded

Decimal Interchange Code• Developed by IBM• It is an 8-bit code, enabling 256

characters to be represented• Used only in IBM mainframes

and other IBM-compatible systems

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ASCII• American Standard Code for

Information Interchange• Defined by American national

Standards Institute (ANSI) and by International Organization for Standardization or ISO

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ASCI… (2)• It is a 7-bit code, only 128 characters

can be represented• Formally known as ANSI standard

X3.4-1977

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Extended ASCII• Introduced by IBM in 1981• It is an 8-bit ASCII code• It supports the 7-bit ASCII standards

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Data Communication Systems• Any system or computers, computer

terminals or computer peripheral equipment used to transmit and/or receive information between 2 or more locations

• Network architectures outline the products and services for the individual components w/in data communications network to operate together

Simplified Communications Model - Diagram

Key Communications Tasks• Transmission System Utilization• Interfacing• Signal Generation• Synchronization• Exchange Management• Error detection and correction• Addressing and routing• Recovery• Message formatting• Security• Network Management

Simplified Data Communications Model

Networking• Point to point communication not

usually practical–Devices are too far apart–Large set of devices would need

impractical number of connections• Solution is a communications

network

Simplified Network Model

Wide Area Networks• Large geographical area• Crossing public rights of way• Rely in part on common carrier

circuits• Alternative technologies

– Circuit switching– Packet switching– Frame relay– Asynchronous Transfer Mode (ATM)