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9. COMPUTER NETWORKING

•A Network is a way of connecting different computers to allow data and message passing, and resource sharing.

•Early communication techniques included telegraphs (with morris code), telephones and teletypes.

•Advantages

-allows shared computers and peripherals

-provides communication and cooperation tools for people and computers

-increases reliability by having alternate computers available

-decreases isolation of many computers

•Applications,

-allows remote access to databases and libraries

-electronic mail

-distributed computational facilities

-remote control of applications

•The relationship between various network types is shown below

Example LAN Topologies

...

- Shared Media

- Distributed Control

- No media sharing

- Central Control

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•The Star Network topology uses many connections to a central server

-Central control

- Dedicated communication channels

- Single point of failure

- Often compatible with telephone wiring (voice/data integration)

-Typical minicomputer and mainframe environments

•When all computers are connected to the same network cable, there are a number of structures which may be used. The bus topology below is simpler, and the tree topology is more flexible

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and versatile. This approach uses a single cable which is easy to add to

...

Bus Topology

...

Tree Topology

R

R

R

R Repeater

• The ring topology below shows a closed loop of cable which can be simple to implement, but

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limited in capabilities

- Distributed control

-Entire communication capacity

capacity for any station

- Vulnerable to loss of shared communication facilities

-Primary vendors: IBM & Proteon

•An enhanced ring topology is pictured below

Characteristics

H O S T

N o . 3

- Control token passed from H O S T

N o . 2

node to node

- Only node with token can transmit

at a time

end of message

direction of message flow