A Performance Study of a WTDMA Protocol with Trespassing for Optical LANs

Many medium access control protocols have been proposed for optical wavelength division multiplexing local area networks with a star topology. These protocols range from those based on the concept of fixed-assignment of communication subchannels, such as TDMA (Time Division Multiple Access); random-access to communication subchannels, such as DTWDMA (Dynamic Time-Wavelength Division Multiple Access); or hybrid protocols incorporating both fixed-assignment and reservation rules, such as HTDM (Hybrid TDM). This paper proposes and evaluates a novel hybrid protocol of fixed-assignment and randomaccess called “WTDMA with lightpath trespassing”. This protocol combines the most desirable aspects of fixed-assignment and randomaccess protocols, while limiting their drawbacks. The performance of the protocol is analysed by stochastic simulation. The obtained results show the addition of trespassing lowers the mean packet delay, and with collision avoidance, also increases throughput. These results justify the introduction of the WTDMA with trespassing protocol, and indicate the situations where its use is advantageous.