Shape of a Network

1. Shape of a Network 10/10/07

2. Topology • The way the computers are cabled together • Four different layouts • Logical topology describes the way data travels across the network

3. Four types • Bus Network • Star Network • Ring Network • Mesh

4. Bus Network • Simplest/easiest • Linear • Single cable – trunk • Computers are passive participants • Any computer (node) can pass a message • Transmissions are limited to one computer at a time – one computer is the master • Other computers must wait until the line is free

5. Collision • Data runs into each other • CSMA/CD – carrier sense multiple accesses with collision detection • Both nodes must back off and wait for line to be free • Single bounce – caused by single that continues uninterrupted to the end of the bus and then keeps bouncing back and forth along the cable, keeping other nodes from using the line • Terminator – absorbs signals and keeps them from bouncing back along the trunk

6. Disrupting Communication • Break in the cable • Physically separated • One end is disconnected • All activity stops • Computers can still function as stand-alone • Just can’t communicate or share resources

7. Network Expansion • Cable in a bus network can be expanded in one of two ways: • Barrel connector – connects two pieces of cable to make longer • Connectors weaken signal • Continuous cable is preferable • Repeater – used to connect two cables • Boosts signal before it sends it on its way • Better than connector because allows signal to travel further and still be correctly received

8. Advantage/Disadvantage • Advantages • Easy to implement • Require less cable • Nodes relatively easy to add and remove • Disadvantages • Problems more difficult to pinpoint • Breaks mean a breakdown in entire network • Too many nodes slow network

9. Star Network • Like arms of octopus • Stretches out in different directions • Hub – device in the middle • Hub – connects nodes in the arms • Hub participates actively in the network boosting signals as they pass • It can be a passive wiring panel that simply relays transmission through the network

10. Advantages/Disadvantages • Advantages • Centralized resources and management • Expandable • Nodes added easily • Problems are easier to find • Break in cable brings down only the node directly affected • Disadvantages • Requires great deal of cable • If central point fails, everything shuts down

11. Ring Network • Nodes form a circle • Data travels from node to node • Each node communicates with only two others: • The one that transmits to it • The one to which it transmits • The failure of one node can bring down the whole system

12. Token Passing • A way to avoid collisions and help data run smoothly • Computers pass a small collection of bits – tokens • A node has to wait until it has a token to transmit data • Computer then modifies token to let other nodes know that a token is in use • Token travels at speed of light – 186,000 miles per second

13. Advantages/Disadvantages • Advantages • Each node has equal opportunity to transmit • Do not require a lot of cable or fancy equipment • Disadvantages • Problems are difficult to find • Break in cabling brings down network

14. Mesh Network • Computer is connected to every other computer by separate cable

15. Advantages/Disadvantages • Advantages • Provides redundant or backup paths • If one cable is broken, another takes over the traffic • Easy to find problems • Disadvantages • Expensive to install because of all the cabling