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