Computer communication

Networks

Topologies

Bus Network

Terminator ‘Workstation’‘Client’

‘Terminal’‘Node’

Computer

TerminatorBackbone

Server(optional)

Topologies

Bus Network

Terminator ‘Workstation’‘Client’

‘Terminal’‘Node’

Computer

TerminatorBackbone

Server(optional)

Network interface card (NIC)T connector – plugs into NIC

Topologies

Bus Network• All components are connected via a backbone.

• At each end of the backbone is a terminator which stops signals ‘bouncing back’ down the network.

• Each network interface card is passive: they all listen to the backbone for signals addressed for them.

• Signals are sent in both directions of the backbone at the same time.

• Only one computer can transmit successfully at any one time, however this is not regulated so collisions and data corruption do occur.

• A protocol called CSMA-CD (carrier sense multiple access collision detection) is used to handle this problem.

Topologies

Bus Network• Bus networks work well under small loads: small

number of computers, small demand for resources. Under heavy loads it can be very slow or completely grind to a halt.

• If a machine goes down it doesn’t affect the network.

• A break in the backbone will result in the whole network going down.

• Bus topologies were popular in the early 1990’s. Today, better technologies (switched Ethernet) have superseded simple bus topologies.

Topologies

Bus Network• Collisions on a Bus network

– Problems arises when two computers transmit onto the bus a the same time. The voltage pulses form each computer will eventually collide, resulting in higher voltage swings. A protocol is used to decrease the chance of this. This is CSMA/CD – Carrier Sense Multiple Access with Collision Detection.

Topologies

Bus Network• Collisions on a Bus network

Topologies

Ring Network

• Each computer is responsible for passing the message on.

• Can use token passing • Special packet is passed

around altered by a computer if it needs to send data

Topologies

Star Network

• Common network• Connected by switches and

hubs.• Better performance than

bus networks

Topologies

Classifications of Networks• Can you come up with definitions of the

following– LAN– WAN– MAN– PAN– VPN

Topologies

Classifications of Networks• Can you come up with definitions of the

following– LAN – Local Area Network– WAN – Wide Area Network– MAN – Metropolitan Area Network– PAN – Personal Area Network.– VPN – Virtual Private Network.

Topologies

Task

Answer questions on page 129.