Shape of a Network

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
• 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 cant 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