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 eecient implementations of the tree-based algorithms are proposed. It is shown that the performance diierence between the studied algorithms is very small.