TABLE OF CONTENTS As mentioned earlier, there are a variety of interconnection topologies used in local area networks. They are the global bus, the ring, and the star topologies.
A global bus is a single shared medium, which can only be used by one device at a time. The global bus is controlled by a variety of schemes. One of the simplest is the carrier sense multiple access scheme. This protocol works by using two principles: first, the delay taken to send a bit from one end of the bus to the other and, second, the ability to send and then listen to the medium. The protocol in its simplest form operates as follows:
Listen to the bus if busy, wait; if clear, send data.
Once data have been sent, continue to listen and compare what is heard against what was sent.
If what was sent matches what is heard for the entire end-to-end communications time, then I control the bus and can continue sending a message (the assumption here is that if I wait for an end-to-end transfer time, then all other nodes must have heard my message and will now delay if they wish to transmit).
When complete, go back into listen mode.
If I do not hear the same message that I sent, then a collision occurred on the bus. I immediately stop transmission and delay before trying to send again.
By using this simple protocol, devices on the network can send and receive...
