1. Shape of a Network

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
Signal bounce – caused by signal 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
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
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
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