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Introduction

Chapter 1

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Computer network

computer network, often simply referred to as a

network, is a collection of hardware components

and computers interconnected by

communication channels that allow sharing of

resources and information.Where at least one

process in one device is able to send/receive

data to/from at least one process residing in aremote device.

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Uses of Computer Networks

Business Applications

Home Applications

Mobile Users Social Issues

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Business Applications of Networks

A network with two clients and one server.

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Business Applications of Networks (2)

The client-server model involves requests and replies.

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Home Network Applications

Access to remote information

Person-to-person communication

Interactive entertainment Electronic commerce

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Home Network Applications (2)

In peer-to-peer system there are no fixed clients and servers.

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Home Network Applications (3)

Some forms of e-commerce.

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Mobile Network Users

Combinations of wireless networks and mobile computing.

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Network Hardware

Local Area Networks

Metropolitan Area Networks

Wide Area Networks Wireless Networks

Home Networks

Internetworks

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Broadcast Networks

Types of transmission technology

Broadcast links Point-to-point links

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Broadcast Networks (2)

Classification of interconnected processors by scale.

V i l i ibl f

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Various topologies are possible for

broadcast LANs.

Bus

Ring

Star

Mesh

Tree Hybrid

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Bus Topology

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Ring Topology

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Star Topology

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Tree topology

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Mesh Topology

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Hybrid Topology

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Metropolitan Area Networks

A metropolitan area network based on cable TV.

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Wide Area Networks

Relation between hosts on LANs and the subnet.

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Wide Area Networks (2)

A stream of packets from sender to receiver.

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Wireless Networks

Categories of wireless networks:

System interconnection

Wireless LANs

Wireless WANs

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Wireless Networks (2)

(a) Bluetooth configuration

(b) Wireless LAN

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Wireless Networks (3)

(a) Individual mobile computers

(b) A flying LAN

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Home Network Categories

Computers (desktop PC, PDA, shared peripherals

Entertainment (TV, DVD, VCR, camera, stereo, MP3)

Telecomm (telephone, cell phone, intercom, fax)

Appliances (microwave, fridge, clock, furnace, airco) Telemetry (utility meter, burglar alarm, babycam).

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Internetworks

A collection of interconnected networksis called an internetwork and internet.

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Network Software

Protocol Hierarchies

Design Issues for the Layers

Connection-Oriented and Connectionless Services

Service Primitives The Relationship of Services to Protocols

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Protocol Hierarchies

Most networks are designed as a stack of layers

to reduce the design complexity.

The purpose of each layer is to offer certain

services to the higher layers, shielding those

layers from the details of how the offeredservices are actually implemented.

The fundamental idea is that a particular piece of

software provides a service to its users but keepsthe details of its internal state and algorithms

hidden.

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Layer n on one machine carries on a

conversation with layer n on another machine.

The rules and conventions used in thisconversation are collectively known as the layer

n protocol.

Basically a protocol is an agreement betweenthe communicating parties on how

communications is to proceed.

N t k S ft

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Network SoftwareProtocol Hierarchies

Layers, protocols, and interfaces.

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In reality, no data is directly transferred from layer n on

one machine to layer n on another machine.

Instead each layer passes data and control informationto the layer immediately below it, until the lowest layer

is reached.

Below layer 1 is the physical medium through which

actual transmission occurs.

The Interfaces defines which primitive operations and

services the lower layer makes available to the upper

one.

Each layer must perform a specific collection of well-

understood functions.

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Defining a clear cut interface makes it easy to

replace an old implementation by a new one

provided that it gives the same services as theolder one.

A set of layers and protocols is called a network

architecture. Niether the details of the implementation nor the

specification of the interfaces is a part of the

architecture because they are kept hidden. A protocol stack is a list of protocols used my a

system.

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Example information flow supporting virtual communication in layer 5.

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Design Issues for the Layers

Addressing: A means is required for a process on onemachine to specify with whom it wants to talk because

of multiple destinations.

Data Transfer: It needs to be specified that how many

logical connections can a system provide. For. Eg:some systems provide 2 logical connections: one for

normal data and one for urgent data.

Error Control: Errors are bound to occur because the

physical communication circuits are not perfect. Both

the communicating parties need to decide on which

error control technique needs to be used.

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Flow Control: When the speed differs on the senders

side and the receivers side, a mechanism is needed to

assure the sending party that all the packets are being

received. This can involve some kind of feedback from

the receiver. Or they can decide the transmission speed

before hand.

Message size: If the process insists on breaking anarbitrarily long message into very small packets which

will be very inefficient to send individually, then a

number of small packets that belong to different

messages can be assembled that are going in the samedirection/ destination, and furthur can be diassembled

at the destination.

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Multiplexing: When it is very expensive to set

up a separate connection for different or

unrelated conversations, then the sameconnection can be used

Routing: Choosing the best path when a number

of paths are available.

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Connection-oriented services It is like a telephone system where to talk to someone,

you have to pick up a phone, dial the number, talk andthen hang up.

Similarly a user who wishes to communicate has to first

set up a connection, use it and then terminate it.

Acts like a tube where the data is inserted at one end by

the sender and extracted at the other end by the

receiver.

In some cases after the connection is setup, both theparties can decide on the parameters like message size,

quality of srevice etc.

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Connectionless service

It is like a postal system where a post card

contains the address of the receiver and is sent.

Each message is sent through the system

independent of all the others.

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Each service is characterized by quality of service

Could be reliable/Non reliable.

For a reliable service, acknowledgements can beused which introduces overhead and delays which

are often worth it but sometimes undesirable,

A reliable connection-oriented service isappropriate in a file transfer situation.

Reliable connection oriented service has two

variations- Message sequences and byte streams.

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Where as the delays introduced by

acknowledgements are not acceptable is case of

digitized voice traffic. Not all applications require setting up

connections. For. Eg: e-mail.

Various other services are:

Datagram service: e.g. telegram service

Acknowledged datagram service.: sending aregistered letter

Request-reply.: query to the local library

C i O i d d C i l

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Connection-Oriented and Connectionless

Services

Six different types of service.

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Service Primitives

Five service primitives for implementing a simple connection-

oriented service.

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Service Primitives (2)

Packets sent in a simple client-server interaction on a

connection-oriented network.

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Services to Protocols Relationship

The relationship between a service and a protocol.

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Reference Models

The OSI Reference Model

The TCP/IP Reference Model

A Comparison of OSI and TCP/IP A Critique of the OSI Model and Protocols

A Critique of the TCP/IP Reference Model

f d l

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Reference Models

The OSI

referencemodel.

f d l (2)

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Reference Models (2)

The TCP/IP reference model.

R f M d l (3)

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Reference Models (3)

Protocols and networks in the TCP/IP model initially.

C i OSI d TCP/IP M d l

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Comparing OSI and TCP/IP Models

Concepts central to the OSI model

Services

Interfaces

Protocols

A C i i f h OSI M d l d P l

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A Critique of the OSI Model and Protocols

Why OSI did not take over the world

Bad timing

Bad technology Bad implementations

Bad politics

B d Ti i

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Bad Timing

The apocalypse of the two elephants.

A C i i f h TCP/IP R f M d l

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A Critique of the TCP/IP Reference Model

Problems: Service, interface, and protocol not distinguished

Not a general model

Host-to-network layer not really a layer No mention of physical and data link layers

Minor protocols deeply entrenched, hard to replace

H b id M d l

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Hybrid Model

The hybrid reference model to be used in this book.

E l N t k

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Example Networks

The Internet

Connection-Oriented Networks:

X.25, Frame Relay, and ATM

Ethernet

Wireless LANs: 802:11

Th ARPANET

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The ARPANET

(a) Structure of the telephone system.

(b)Barans proposed distributed switching system.

Th ARPANET (2)

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The ARPANET (2)

The original ARPANET design.

Th ARPANET (3)

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The ARPANET (3)

Growth of the ARPANET (a) December 1969. (b) July 1970.

(c) March 1971. (d) April 1972. (e) September 1972.

NSFNET

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NSFNET

The NSFNET backbone in 1988.

I t t U

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Internet Usage

Traditional applications (19701990)

E-mail

News Remote login

File transfer

A hit t f th I t t

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Architecture of the Internet

Overview of the Internet.

ATM Virt al Circ its

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ATM Virtual Circuits

A virtual circuit.

ATM Virtual Circuits (2)

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ATM Virtual Circuits (2)

An ATM cell.

The ATM Reference Model

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The ATM Reference Model

The ATM reference model.

The ATM Reference Model (2)

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The ATM Reference Model (2)

The ATM layers and sublayers and their functions.

Ethernet

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Ethernet

Architecture of the original Ethernet.

Wireless LANs

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Wireless LANs

(a) Wireless networking with a base station.

(b) Ad hoc networking.

Wireless LANs (2)

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Wireless LANs (2)

The range of a single radio may not cover the entire system.

Wireless LANs (3)

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Wireless LANs (3)

A multicell 802.11 network.

Network Standardization

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Network Standardization

Whos Who in the Telecommunications World

Whos Who in the International Standards World

Whos Who in the Internet Standards World

ITU

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ITU

Main sectors Radiocommunications

Telecommunications Standardization

Development

Classes of Members

National governments

Sector members

Associate members

Regulatory agencies

IEEE 802 Standards

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The 802 working groups. The important ones are

marked with *. The ones marked with are

hibernating. The one marked with gave up.

Metric Units

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Metric Units

The principal metric prefixes.