This document introduces data communications and computer networks. It defines data communication as relaying binary messages between two points, and computer networks as interconnected autonomous computers. The goals of networks are resource sharing, high reliability through replication, cost savings, and powerful communication. Networks can enable access to remote information, email, banking, libraries, bulletin boards, and online shopping. Networks are classified by the distance between communicating processors, from circuit boards to planets. Connectivity alternatives include stand-alone computers, time-sharing, and local area networks that share resources and applications.

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 1

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 2

3. NETWORK CLASSIFICATION
F Networks are often classified by the distance of the
communicating processors from each other.
Interprocessor Processors located Example
Distance in the same
0.1 m Circuit Board Data Flow Machine
1m 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 3

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)
Applications
and
Data
Personal Computer
Introduction to Data Communications 4

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.
user enters commands here
applications execute here
Shared
Dumb Terminal Applications
Storage and
Shared Data
Host Computer
applications share
(shared processor)
data here
Dumb Terminal
Introduction to Data Communications 5

6. F Shared Resources
Multi-user sharing of devices and/or
peripherals
applications execute here
Shared
Personal Computer Local Area Applications
Network Storage and
Shared Data
Network
File Server
applications share
data here
Personal Computer
applications execute here
Issues:
1. Equitable sharing of devices
2. Integrity of data
Introduction to Data Communications 6

7. F Shared Logic and Resources
applications execute here user enters commands here
Personal Computer
Local Area
Network
Shared Shared
Applications Applications
Storage and Storage and
Shared Data Shared Data
Network
File Server Host Computer
(shared processor)
applications share applications share
data here data here
applications execute here
Introduction to Data Communications 7