ATM Networks: Bandwidth Allocation and Congestion Control

ATM provides a very high speed network infrastructure suitable for local, campus and wide area networks, capable of supporting a broad range of applications. There are still several areas of ATM which require further work. One such area is bandwidth allocation. In essence, bandwidth allocation is required in order to guarantee performance for real time traffic connections (e.g. voice and video). On the one hand, peak bandwidth allocation is inefficient. On the other, "statistical" bandwidth allocation is very difficult, especially in a heterogeneous traffic environment. In this paper, we introduce a bandwidth allocation technique based on virtual private networks, which can overcome some of these problems. Another critical area in ATM is congestion control of "best effort" traffic, i.e. traffic which is not allocated any bandwidth, rather, it "fills in" the bandwidth left over by the guaranteed traffic. Hence the name of ABR (available bit rate) traffic. ABR traffic must be flow controlled at the source, to avoid congestion in the ATM network. In this paper, we present a feedback control algorithm for ABR traffic in which source rates are adjusted according to virtual circuit queue levels at intermediate nodes along the path. We propose a simple and classical proportional controller, plus a Smith predictor to overcome instabilities due to large propagation delays. This scheme outperforms the proportional rate control algorithm.