´Tiered contention multiple access´ (TCMA), a QoS-based distributed MAC protocol

Distributed multiple access techniques provide quality of service through prioritization of access. Tiered contention multiple access (TCMA) is a CSMA/CA protocol that differentiates between traffic priority classes with respect to the following: arbitration time; persistence factor; the MAC layer dwell-time limit. The arbitration time is the idle time required before transmission may be attempted. The persistence factor is the coefficient multiplying the contention window size in successive retransmission attempts following a collision. The MAC layer dwell-time limit restricts the time a packet spends in the MAC layer. Several variations of TCMA are possible. Features of TCMA have been adopted as the EDCF MAC protocol presently under review for adoption into the IEEE 802.11 standard. Simulation results are presented comparing the performance of TCMA to the legacy 802.11 MAC protocol.