Integrating voice & data over a bus using ap-csma cd with various retransmission policies

Abstract EN

A variation on the carrier sense multiple access / collision detection (CSMA / CD) protocol for local area random access broadcast network is presented for supporting the facility of mixing both voice and data traffic over the bus LAN.

This protocol transmits into an idle channel with a dynamic probability P and back off with probability (1- P).

If P is too large, many collisions will occur in the channel.

On the other hand, a small P wills unnecessary reduces the number of packet transmissions.

An optimum value of P will reduce the number of collisions to a level at which throughput is maximized.

To handle the collision state, we examine various retransmission policies : The first one permits each packet being retransmitted randomly again and again until a fixed period of time.

The second policy is identical to the first except that the retransmission continues randomly until a fixed number of retransmissions are completed.

The third policy requires the retransmission to continue until certain number of retransmissions is completed or until certain period is elapsed which occur first.

Simulation results are presented to illustrate the effectiveness of the above approach in comparison with the traditional CSMA / CD that uses binary back off algorithm to handle the retransmitted packets in case of existing a collision on the channel.

It is shown that, by suitable choice of the control parameter and the appropriate retransmission policy, optimum throughput can be achieved and the voice packet loss due excessive delay may be kept below the threshold of 0.5 percent.