Design of a fair bandwidth allocation policy for VBR traffic in ATM networks

Since variable bit rate (VBR) traffic is inherently bursty, dynamic bandwidth allocation is appropriate for ATM streams carrying VBR traffic. In order to provide QoS guarantees and the reduce the computational complexity, a mixture of guaranteed bandwidth with dynamic adaptive allocation should be implemented. Typical dynamic allocations to competing streams are done in the form of linear proportion to the bandwidth requirements. We show that during temporary link congestion such proportional arrangements can give rise to unequal queue growth and degraded QoS, even for streams with identical long term traffic characteristics and QoS requirements. In this paper, four allocation algorithms are presented and analyzed in terms of their fairness and QoS potential for VBR traffic. We propose and show that a novel allocation strategy, termed as minmax, solves the mentioned problem of unfairness. By maintaining a fair distribution of buffer contents across the streams, minmax policy can achieve better and fairer QoS performance compared to the traditional methods. Four allocation policies for handling MPEG VBR video streams are simulated in the context of a wireless ATM medium access control. The results show that the minmax strategy can reduce losses by an order of magnitude, while decreasing delays substantially.