Fairness in DQDB revisited: A new solution

The DQDB (Distributed Queue Dual Bus) system consists of a linear arrangement of nodes that communicate with each other using two contra-flowing buses; the nodes use an extremely simple protocol to send messages on these buses. This simple and elegant protocol has been found to be very challenging to analyse. It has been long recognized that DQDB suffers from inherent access unfairness problems and several solutions to this problem have been proposed in the literature. Unfortunately, none of these solutions is completely satisfactory. The main contribution of this work is to propose a new way of looking at fairness in a DQDB system. Our scheme is very simple and efficient to implement and compares favorably with the leading rate-controlled schemes proposed in the literature. In addition, simulation results show that in the presence of non-uniform loads, such as a file server being brought up, our scheme converges rapidly to a fair steady state.