Version 1.0, August 31, 2001, Copyright, Hugh Jack 1993-2001

31.6.1 Introduction

 

· The relationship between various network types is shown below

 

· The Star Network topology uses many connections to a central server

 

· When all computers are connected to the same network cable, there are a number of structures which may be used. The bus topology below is simpler, and the tree topology is more flexible and versatile. This approach uses a single cable which is easy to add to

 

· The ring topology below shows a closed loop of cable which can be simple to implement, but limited in capabilities

 

· An enhanced ring topology is pictured below

 

· Significant issues in networks are,

  1. Network power - does the network distribute power, or does each station need to be separately powered.
  2. Network tees - to tap into the network cable simple connections can be used, or the connection can have circuitry.
  3. Transmission type - switched voltage levels (baseband), single band FSK (carrierband), multiple frequency FSK (broadband). The FSK methods allow much higher network speeds.
  4. Bus access - When network nodes share the same wire they may try to talk at the same time (this is called a network collision). Different schemes for dealing with collisions include,
    1. CSMA/CD (Collision Sense Multiple Access/Collision Detection) - if two nodes start talking and detect a collision then they will stop, wait a random time, and then start again.
    2. CSMA/BA (Collision Sense Multiple Access/Bitwise Arbitration) - if two nodes start talking at the same time the will stop and use their node addresses to determine which one goes first.
    3. Master-Slave - one device one the network is the master and is the only one that may start communication. slave devices will only respond to requests from the master.
    4. Token Passing - A token, or permission to talk, is passed sequentially around a network so that only one station may talk at a time.