Course Instructor : Sehrish Rafiq

Department Of Computer Science

University Of Peshawar

Data Communications & NetworkingLecture-04

Lecture overviewCategories of NetworksInternetworksAn overview of the communication tasksProtocol ArchitectureCharacteristics of a protocol

Categories of Networks

In to which category a network falls is determined by its size, its ownership, the distance it covers and its physical architecture.

LAN(Local Area Network)A local Area network is usually privately owned and links the

devices in a single office, building or campus.LAN size is limited to a few kilometers.LAN’s are designed to allow resources to be shared between

personal computers or work stations. In addition to size LAN are distinguished from other types of

networks by their transmission media and topology.Most common topologies:Bus,Ring & Star.

LAN(Local Area Network)

MAN(Metropolitan Area Network) A MAN is designed to extend over an entire city.

It may be a single network such as cable television network or it may be a means of connecting a number of connecting a number of LANs in to a larger network so that resources may be shared LAN-to-LAN.

A MAN may be wholly owned and operated by a private company such as local telephone company.

MAN(Metropolitan Area Network)

WAN(Wide Area Network)A WAN provides long distance transmission of voice, data, image

and video information over large geographic areas that may comprise a country, a continent or even the whole world.

WANs may utilize public, leased or private communication devices usually in communications and can therefore span an unlimited number of miles.

A WAN that is wholly owned and used by a single company is often referred to as enterprise network.

WAN(Wide Area Network)

InternetworksWhen two or more networks are connected, they became an

internetwork or internet.

The Internet from “I” is a Wide area network while the internet from “i” refers to the interconnection of networks.

Internet can be thought as internet but the reverse is not necessarily true.

History of Internet 1960,A project of ARPA of US department of

Defense Stanford Research Institute University of California at Los Angeles University of California at Santa Barbara University of Utah Features Redundant lines Decentralized Computing 1980, NSF and other Government agencies 1991,Commercial traffic April 1995,US government action 2000,30 million users on 10 million

computers,240000 networks, 100 countries Monthly growth

Communication Tasks Transmission System utilization Interfacing Signal generation Synchronization Exchange Management Error Detection & Correction Flow Control Addressing Routing Recovery Message formatting Security Network Management

Transmission System uti l izationTransmission System utilization refers to the need to make

efficient use of transmission facilities that are typically shared among a number of communicating devices.

Various techniques (referred to as multiplexing) are used to allocate the total capacity of a transmission medium among a number of users.

Congestion Control techniques may be required to assure that the system is not overwhelmed by excessive demand for transmission services.

Interfacing & Signal generation

To communicate a device must interface with the transmission system.

Once an interface is established, signal generation is required for communication.

The properties of the signal such as form and intensity must be such that they are:

capable of being propagated through the transmission system Interpretable as data at the receiver.

Synchronization

Not only must the signals be generated to confirm to the requirements of the transmission system and receiver, but there must be some form of synchronization between transmitter and receiver.

Exchange ManagementIf data are to be exchanged in both directions over a period of

time, the two parties must cooperate. e.g. Telephone.

For data processing devices more will be done than simply establishing a connection, certain conventions must be decided upon.

These conventions may include whether both devices may transmit simultaneously or must take turns, the amount of data to be sent at one time, the format of the data and what to do if certain contingencies such as an error arise.

Error Detection and CorrectionError detection and correction are required in circumstances

where errors cannot be tolerated.

This is usually the case with data processing systems.

For example in transferring a file from one computer to another it is simply not acceptable for the contents of the file to be accidentally altered.

Flow ControlFlow Control is required to assure that the source does not

overwhelm the destination by sending data faster than they can be processed and absorbed.

Addressing and routingWhen a transmission facility is shared by more than two devices,

the source system must indicate the identity of the intended destination.

The transmission system must assure that the destination system and only that system receives the data.

Further the transmission system may itself be a network through which various paths may be taken.

A specific route through this network must be chosen.

RecoveryRecovery techniques are needed in situations in which an

information exchange ,such as a database transaction or file transfer, is interrupted due to a fault somewhere in the system.

The objective is either to be able to resume activity at the point of interruption or atleast to restore the state of systems involved to the condition prior to the beginning of exchange.

Message formattingMessage formatting has to do with an agreement between

two parties as to the form and format of the data to be exchanged or transmitted, such as the binary code for characters.

SecurityThe sender of data may wish to be assured that only the intended

receiver actually receives the data.

And the receiver of the data may wish to be assured that the received data have not been altered in transit and the data actually come from the purported sender.

Network ManagementFinally, a data communication facility is a complex system

that cannot create or run itself.

Network Management capabilities are needed to configure the system, monitor its status, react to failures and overloads and plan intelligently for future growth.

Protocol ArchitectureInstead of implementing the logic for communication

between two computers as a single module, the task is broken up in to subtasks, each of which is implemented separately as a structured set of modules.

That structure is referred to as a protocol architecture.

A Simplif ied Architecture for Fi le Transfer

File Transfer Application

Communication service module

Network access module

File Transfer Application

Communication service module

Network access module

Files and File Transfer Commands

Communications-related data units

Network Interface Logic

Communications

Network

Communications

Network

Network Interface Logic

Computer Y Computer Z

Characteristics of a ProtocolDirect/IndirectMonolithic/StructuredSymmetric / AsymmetricStandard / Non Standard

Suggested ReadingsSection 1.1,Section 1.4, Section 2.1 of Data and computer

communications sixth edition by william stallingsSection 2.4 Categories of networks Data communications

and networking 2nd edition by Behrouz A foruzan

Thanks!!!