Comparison of contention resolution algorithms for a cable modem MAC protocol

A reservation-based MAC protocol has been adopted by standards bodies as the basic protocol for data communication within the upstream channel of a cable plant. The available capacity is divided in two separate channels. One is a random access channel, or contention channel, used to send requests to the head-end, with the possibility of collisions occurring therein. When collisions happen, they are resolved by using a contention resolution algorithm (CRA). The second channel is a data channel to send user information in a collision-free manner. Adaptive algorithms are used to divide the system capacity dynamically, between the data and contention channels depending on the system requirements. In this paper the performance and implementation issues of p-persistence and tree-based CRAs under this adaptive environment are compared. While the complexity of the p-persistent algorithm remains as simple as in a traditional Aloha channel, traditional implementations of the tree-based algorithms becomes more complex. Simple and efficient implementations of the tree-based algorithms are proposed. It is shown that the performance difference between the studied algorithms is very small.