Introduction to Data Communications 1

INTRODUCTION TO DATA COMMUNICATIONS

DEFINITION OF TERMS F Data Communication is the act of relaying a message

or information in binary form between two points (the transmitter and the receiver).

F Computer Network is an interconnected collection of

autonomous computers. Autonomous means that there should no clear

master/slave relationship between the computers.

NETWORK GOALS F Resource Sharing. One goal of establishing computer

networks is to facilitate sharing of programs, equipment, and data without any regard to the physical location of resource and the user.

F High Reliability. Computer networks provide high

reliability by having alternative sources of supply. For example, all files could be replicated on two or three machines, so if one of them is unavailable (due to hardware failure), the other copies could be used.

Introduction to Data Communications 2

F Cost Savings. Small personal computers connected in

a network have a much better price/performance ratio than large ones such as mainframes.

F Communication Medium. A computer network can

provide a powerful communication medium among widely separated employees. Networks can enhance human-to-human communication.

USES OF DATA COMMUNICATION AND NETWORKS F Access to Remote Information F Electronic Mail

F Electronic Banking F Electronic Newspaper and Libraries F Electronic Bulletin Boards F Value-Added Services F On-line Department Stores/Groceries F Interactive Entertainment

Introduction to Data Communications 3

NETWORK CLASSIFICATION F Networks are often classified by the distance of the

communicating processors from each other.

Interprocessor Distance

Processors located in the same

Example

0.1 m Circuit Board Data Flow Machine 1 m System Multicomputer

10 m Room Local Area Network 100 m Building Local Area Network

1 km Campus Local Area Network 10 km City Metropolitan Area

Network 100 km Country Wide Area Network

1,000 km Continent Wide Area Network 10,000 km Planet The Internet

Data flow machines are highly parallel computers with

many functional units all working on the same program.

Multicomputers are systems that communicate by

sending messages over very short, very fast buses. A Metropolitan Area Network (MAN) is basically a

bigger version of a LAN and normally uses similar technology.

Introduction to Data Communications 4

CONNECTIVITY ALTERNATIVES F Stand Alone Sharing of diskettes Modem and the public telephone

system

Temporary physical connection

Local area network (but the network

software is enabled only when needed)

Personal Computer

ApplicationsandData

Introduction to Data Communications 5

F Shared Logic Sharing the capability of a single

processor with more than one user time sharing In multiprocessor systems, shared logic

means sharing the main processors or support processors with more than one user.

Host Computer(shared processor)

SharedApplicationsStorage andShared Data

Dumb Terminal

Dumb Terminal

user enters commands here

applications execute here

applications sharedata here

Introduction to Data Communications 6

F Shared Resources Multi-user sharing of devices and/or

peripherals

Issues: 1. Equitable sharing of devices 2. Integrity of data

SharedApplicationsStorage andShared Data

applications execute here

applications sharedata here

Personal Computer

Personal Computer

applications execute here

Local AreaNetwork

NetworkFile Server

Introduction to Data Communications 7

F Shared Logic and Resources

SharedApplicationsStorage andShared Data

user enters commands here

applications sharedata here

Personal Computer

Local AreaNetwork

Host Computer(shared processor)

SharedApplicationsStorage andShared Data

applications sharedata here

applications execute here

applications execute here

NetworkFile Server