Computer Network Course

Lecture 1

Introduction

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Computer Network

Why network

Communications Model

Network types

Network Software

Layering

Protocol

Stack models

A network is a set of devices (often referred to as nodes) connected

by communication links. A node can be a computer, printer, or any

other device capable of sending and/or receiving data generated by

other nodes on the network. A link can be a cable, air, optical fiber,

or any medium which can transport a signal carrying information.

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Why Network

Resource Sharing

Reliability and Availability

Communication Medium

Access Information

E- Commerce

Person to Person Communication

Others

Some of Network applications

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A Communications Model

Source

generates data to be transmitted

Transmitter

Converts data into transmittable signals

Transmission System

Carries data

Receiver

Converts received signal into data

Destination

Takes incoming data

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Simplified Communications Model - Diagram

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Simplified Data Communications Model

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Types of Networks

Classification according to the covered distance

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Type of Networks

Classification according to the access techniques

Point to Point (Switched) Network

• Circuit switched networks

• Packet switched networks

Broadcast Network

• Local Area Networks

• Wireless LAN

• Satellite networks

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Type of Networks:

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Broadcast Networks

Network Software

Protocol Hierarchies

Design Issues for the Layers

Connection-Oriented and Connectionless Services

Service Primitives

The Relationship of Services to Protocols

Protocol

Key Features of a Protocol

Syntax

• Concerns the format of the data blocks

• Indicates how to read the bits - field delineation

Semantics

• Includes control information for coordination and error handling

Timing

• Includes speed matching and sequencing

Protocol Hierarchies

Layers, protocols, and interfaces.

The job of sending

message from source to

destination would be

complex without divided

the job into tasks, using

the concept of Layers

Protocol Hierarchies

Example: information flow

Design Issues for the Layers

Addressing

Error Control

Flow Control

Multiplexing

Routing

Connection-Oriented and Connectionless Services

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Unacknowledged connectionless service.

Acknowledged connectionless service.

Acknowledged connection-oriented service.

Connection-Less

Connection

Oriented

AcknowledgedUN-Acknowledged

“Best Effort” Better Quality

Reliable Delivery

Service Primitives

Five service primitives for implementing a simple

connection-oriented service.

Service Primitives

Packets sent in a simple client-server interaction

on a connection-oriented network.

Relationship of Services to Protocols

Reference Models

The OSI Reference Model

The TCP/IP Reference Model

A Comparison of OSI and TCP/IP

The OSI reference model.

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OSI Application Layer

Provides access to the OSI environment for users

Provides distributed information services

OSI Presentation Layer

Provides independence to the application processes from

differences in data representation (syntax)

OSI Session Layer

Provides the control structure for communication between

applications

Establishes, manages, and terminates connections (sessions)

between cooperating applications

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OSI Transport Layer

Provides reliable, transparent transfer of data between end points

Provides end-to-end error recovery and flow control

OSI Network Layer

Provides upper layers with independence from the data

transmission and switching technologies used to connect systems

Responsible for establishing, maintaining, and terminating

connections

OSI Data link Layer

Provides for the reliable transfer of information across the

physical link

Sends blocks (frames) with the necessary synchronization, error

control, and flow control

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OSI Physical Layer

Concerned with transmission of unstructured bit stream over

physical medium

Deals with accessing the physical medium

Mechanical characteristics

Electrical characteristics

Functional characteristics

Procedural characteristics

The TCP/IP reference model.

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Protocols and networks in the TCP/IP model

initially.

The reference model to be used in this course.

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