Unslotted optical CSMA/CA MAC protocol with fairness control in metro WDM ring networks

Optical carrier sense multiple access with collision avoidance (CSMA/CA) is a media access control (MAC) protocol proposed for future metropolitan area wavelength division multiplexing (WDM) ring networks with a fixed receiver and a tunable transmitter at access nodes. In this paper, we focus on the unslotted version of the optical CSMA/CA MAC which is a fully-distributed and asynchronous protocol. We present the results of design and performance evaluation of fairness control schemes based on longest queue first (LQF) scheduling and two random routing algorithms - full random routing (FRR) and partial random routing (PRR). Through extensive network-level simulation of a WDM ring network with 10 nodes and 10 wavelengths on a 100 km ring at 10 Gbit/s line rate, we demonstrate a combination of the LQF scheduling and the PRR with a retransmission counter provides good fairness (fairness index of 0.9995) with high bandwidth efficiency and small delay spread, under highly unbalanced traffic conditions.