Most mobile computers today are equipped with wireless infrared ports based on the Infrared Data Association (IrDA) standard. The IrDA specifications undergo several restrictions: the communication is aimed, short-range and point-to-point; the speeds range from 2.4 kbps to 4 Mbps. The recent advances in the speed and in the extension of range and angle of infrared communications, together with the requirement of more sophisticated mobile networking capabilities, have emphasized the need to overcome the IrDA restrictions enhancing the capabilities of the existing standard. This need gave birth to Advanced Infrared (AIr), an IBM project that seeks to define the next generation infrared data communications system. The IrDA community is currently in the process of adopting the proposed AIr communication system as a new standard.
The AIr medium access control (AIr MAC) protocol coordinates the access to the infrared medium between various AIr devices. Its main features are a connectionless data transfer mechanism, a Request-To-Send/Clear-To-Send (RTS/CTS) collision avoidance protocol for multipoint-to-multipoint connectivity and the dynamic data transfer rates.
This report proposes an experimental study of the AIr MAC protocol performance. Four prototyped AIr stations have been operated in different scenarios to investigate how some protocol options (reservation termination, data frames acknowledgement, backoff algorithm and slot synchronization mechanism, RTS body format) have an effect on some selected performance evaluation parameters (throughput, data frame loss/drop and packet success rate, channel access delay), particularly under critical coverage conditions and imperfect transceiver parity. It turns out that channel reciprocity (transceiver parity), backoff window adjustment policy and RTS body rate are key factors for the protocol performance.
By: D. Bernasconi
Published in: RZ3094 in 1998
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