Virtual queueing techniques for ABR service: improving ABR/VBR interaction

Several algorithms have been proposed for the switch behavior for congestion control of available bit rate (ABR) services. Schemes such as the enhanced proportional rate control algorithm (EPRCA) and the dynamic max rate control algorithm (DMRCA), which use the queue length as the congestion indicator to make a simple approximation of the fair share converge to the actual fair share, have become popular, because they offer a good performance and are simple to implement. In particular, with no VBR traffic in the network, DMRCA has been shown to achieve fairness in all situations, good buffer control, and robust performance. First we show that the performance of these schemes may degrade when ABR traffic interacts with highly-bursty VBR traffic. If VBR traffic induces congestion in the network, the length of the ABR queue cannot serve as a reliable indicator of congestion caused by ABR traffic, and the schemes perform poorly, introducing considerable unfairness. Then, we propose a simple technique to solve these problems. The switch constructs the length of a virtual queue which is not affected by the instantaneous behavior of VBR traffic, and does not depend on how the two types of traffic are served in order to share the common link capacity; thus, it can serve as a reliable indicator of congestion. We use this technique in DMRCA with virtual queueing (DMRCA-VQ), and show that the new scheme achieves fair rate allocation to the ABR connections also in the presence of highly-bursty VBR traffic. The DMRCA-VQ maintains the low hardware complexity of DMRCA. The virtual queueing technique is a solution for the more general problem of separating rate allocation based on the queue length from scheduling of multiple queues for sharing a common resource