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Computer Networks

Lecture 1 By, Ms.Syeda Asima Sarfraz

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Main Topics • Course Aims & Objective

• Study Material

• Introduction to data communications & networks – A communication Model

 – Data Communications – Data Representations

 – Data Flow

 – Computer Networks

 – Network Definition

 – Distributed Processing

 – Network Attributes• Connection Types

• Physical topology

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Course Aims & Objectives • Fundamental Concepts of data communication &

networks

• Understanding of layered architecture (OSI Model)

•

Transmission medias• Encoding & Modulation

• Error detection & flow & error control

• Network devices & LAN technologies

• Switched networks

• IP Addressing & sub netting concepts

• LAN implementation skills

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Study Material • Text Book/s

 – Data Communication & Networking

By Behrouz A.Forouzan

 – Data & Computer Communications

By William Stallings

• Internet

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Introduction to

Data Communication & Networks • Data

 – Refers to information presented in whatever form

is agreed upon by the parties creating and using

data

• Data Communication

 – Exchange of data between two devices via some

form of transmission medium such as wire/cable – Communication system is made up of hardware

and software

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Characteristics of 

Data Communication System • Effectiveness of data communication depends

upon three fundamental characteristics:

 – Delivery

• Must deliver to correct destination

 – Accuracy

• Must deliver data accurately

 – Timeliness• Must deliver data in timely manner

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Components of 

Data Communication System • Data Communication System has five

components – Message

• Data/information to be communicated

 – Sender• Device that sends data

 – Receiver• Device that receives message

 –Medium• Physical path by which message travels

 – Protocol• Set of rules that governs data communication 

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Data Representation • Data comes in different forms:

 – Text• Use Bit pattern

• No. of bits depends upon the no of symbols in language

• Bit pattern is called code• Process of representation is called coding

• ASCII, UNICODE etc.

 – Number• Use Bit pattern

• ASCII is not used for numbers

• Directly represented in binary pattern

• Its due to the simplification of mathematical operations

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Data Representation

 – Images• Use Bit pattern

• Image is divided into matrix of pixels

• Each pixel is assigned a bit pattern

•

For colored images pixel is decomposed into three primarycolors (RGB)

 – Audio• Its continuous not discrete

• Audio is converted into digital signal

 – Video• Its continuous

• Converted into digital 

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Data Flow • Simplex

 – Unidirectional

• Half Duplex

 – Each station can send and receive but not the

same time

• Full Duplex

 – Both stations can send and receive simultaneously

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Data Flow 

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Computer Networks  – Network is set of devices connected by

communication link

 – Devices are often referred to as Nodes

 – Node in a network can be computer, Printer or anyother device capable of sending and receiving

data

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Computer Network • A computer network, often simply referred to as

a network, is a collection of computers

• Devices interconnected by communicationschannels that facilitate communications amongusers

• Allows users to share resources

• Networks may be classified according to a widevariety of characteristics

• A computer network allows sharing of resourcesand information among interconnected devices.

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Distributed Processing • Most networks use distributed processing

• Task is divided among multiple computers

•

Instead of single large machine separatecomputers handle a subset of task

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Distributed Processing 

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Network Criteria • Performance

 – Can be measured in many ways

 – Transit time, response time

 – Depends upon number of factors• No of users

• Type of transmission medium

• Capabilities of connected hardware

• Efficiency of software

• Reliability – Measured by frequency of failure

 – Time taken to recover from failure

• Security – Protection from unauthorized access

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Computer Network Attributes • Physical structure of network can be seen

through,

 – Types of Connection

 – Physical Topology

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Type of Connection • There are two possible types of connections:

Point to Point:

• dedicated link between two devices

•

entire link capacity used by two devices

Multipoint

• Also called multi drop

• Connection is one in which more than two specificdevices share single link

• Channel capacity is shared(spatially or temporally)

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Thanks