On adaptive bandwidth sharing with rate guarantees

The objective of research in fair queueing schemes has been to efficiently emulate a fluid-flow generalized (weighted) processor sharing (GPS) system as closely as possible. A primary motivation for the use of fair queueing has been its use as a means of providing bandwidth guarantees and as a consequence end-to-end delay bounds for traffic with bounded burstiness. The rate guarantees translate to scheduling weights which are set when admission control is done. A consequence of fair queueing systems closely emulating GPS is that when one or more connections are not back-logged, any "excess" bandwidth is distributed to back-logged connections in proportion to their weights. However weights are set based on the long-term requirements of traffic flows and not in any state-dependent manner that reflects instantaneous needs. We question the notion that the queueing system should closely emulate a GPS system. Instead of emulating GPS, we propose three modified scheduling schemes which preserve the rate guarantees of fair queueing (and hence preserve deterministic delay bounds) but adaptively redistribute the excess bandwidth such that either losses are reduced or delays equalized. We compare the performance of the proposed schemes to that of fair queueing using different traffic sources such as voice and video, as well as sources which have aggregate long-range dependent behavior. We find that the proposed schemes, in comparison to packet GPS (PGPS), reduce packet losses and curtail the tails of delay distributions for real-time traffic and hence permit the use of significantly smaller playout buffers for the same network load.