1. Data Communications & Networking
Lecture-04
Course Instructor : Sehrish Rafiq
Department Of Computer Science
University Of Peshawar

2. Lecture overview
 Categories of Networks
 Internetworks
 An overview of the communication tasks
 Protocol Architecture
 Characteristics of a protocol

3. 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.

4. 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.

5. LAN(Local Area Network)

6. 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.

7. MAN(Metropolitan Area
Network)

8. 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.

9. WAN(Wide Area Network)

10. Internetworks
 When 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.

11. 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

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

13. Transmission System utilization
 Transmission 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.

14. 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.

15. 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.

16. Exchange Management
 If 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.

17. Error Detection and Correction
 Error 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.

18. Flow Control
 Flow Control is required to assure that the source does not
overwhelm the destination by sending data faster than they can be
processed and absorbed.

19. Addressing and routing
 When 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.

20. Recovery
 Recovery 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.

21. Message formatting
Message 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.

22. Security
 The 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.

23. Network Management
Finally, 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.

24. Protocol Architecture
Instead 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.

25. A Simplified Architecture for File
Transfer
Computer Y Computer Z
Files and File Transfer Commands
File Transfer File Transfer
Application Application
Communication Communications-related data units Communication
service module service module
Network access Network access
module Communic
Communic module
ations
ations
Network
Network
Network Interface Network Interface
Logic Logic

26. Characteristics of a Protocol
Direct/Indirect
Monolithic/Structured
Symmetric / Asymmetric
Standard / Non Standard

27. Suggested Readings
Section 1.1,Section 1.4, Section 2.1 of Data and computer
communications sixth edition by william stallings
Section 2.4 Categories of networks Data communications
and networking 2nd edition by Behrouz A foruzan

28. Thanks!!!