Constraining queuing delay in WDM rings based on multi-token access protocol under asymmetrical traffic

WDM optical packet rings are a promising candidate for next generation metropolitan area networks (MAN), which are expected to support an increasing amount of traffic coming from a variety of applications and services (e.g., video on demand, video broadcasting, IP telephony). In this paper, we focus on multi-token WDM rings, where for each wavelength channel a special control packet, i.e., the token, rotates along the ring controlling the access to the medium. A parameter, called Target Token Interarrival Time (TTIT), is used to control the token holding time at each node. We show that multi-token WDM rings suffer from long queuing delays when loaded with highly asymmetrical traffic, typical e.g. of video applications. Two schemes are then proposed to constrain the queuing delay in multi-token WDM rings. Firstly, a queue management technique is adopted, where each queued packet is assigned to a token (i.e., to a wavelength channel) only at transmission time, beneficial when multiple tokens are simultaneously held at a node. Secondly, we propose to adapt TTIT to traffic characteristics, by setting specific values to each token in every node. By means of simulations on a 11-node 16-wavelength ring loaded with highly asymmetrical traffic, we show that a significant reduction in average and maximum queuing delay can be attained.