Shape of a Network

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

Four types Bus Network Star Network Ring Network Mesh

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

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

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

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

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

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

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

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

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

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

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

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