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 metro Wavelength Division Multiplexing (WDM) ring networks with a fixed receiver and a tunable transmitter at access nodes [1], [2]. In this paper, we focus on the unslotted version of the optical CSMA/CA MAC which is a fullydistributed 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 Gbps line rate, we demonstrate a combination of the LQF scheduling and the PRR with a retransmission counter provides good fairness (fairness index [3] of 0.9995) with high bandwidth efficiency and small delay spread, under highly unbalanced traffic conditions.