Computer communication

1. Computer communication Networks

2. Terminator Terminator ‘Workstation’ ‘Client’‘Terminal’ ‘Node’ Computer Backbone Server (optional) Topologies Bus Network

3. Terminator Terminator ‘Workstation’ ‘Client’‘Terminal’ ‘Node’ Computer Backbone Server (optional) Topologies Network interface card (NIC) Bus Network T connector – plugs into NIC

4. 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.

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 • Bus topologies were popular in the early 1990’s. Today, better technologies (switched Ethernet) have superseded simple bus topologies.

6. 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.

7. Topologies Bus Network • Collisions on a Bus network

8. 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

9. Topologies Star Network • Common network • Connected by switches and hubs. • Better performance than bus networks

10. Topologies Classifications of Networks • Can you come up with definitions of the following • LAN • WAN • MAN • PAN • VPN

11. 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.

12. Topologies Task Answer questions on page 129.