A simple priority scheme for local area networks and its analysis

A scheme which allows the existence of two priority classes on a channel, each using a standard carrier-sense multiple-access with collision detection (CSMA/CD) protocol, is introduced. The two priority classes considered are labeled the high-priority class (HP) and the low-priority class (LP) of users. The scheme is based upon the principle that the exclusive access right to the channel is given to the HP users after each successful transmission from all users on the channel. This is accomplished by reserving the channel for a time window during which only HP users can contend for accessing the channel using the CSMA/CD protocol. If the channel is not used during that window or if it is used by more than one HP user (which results in a collision), it is released once again for use by both types of users. The equilibrium throughput and delay equations for both types of users are derived. The effect of HP users´ percentage on the channel, the HP packet´s length, the width of the reservation window, and the channel traffic on the throughput and delay for both types of users is investigated. The priority scheme introduced lends itself well to the introduction of multiple classes of priority users on the same channel