MULTIRATE SCHEDULING OF VBR VIDEO TRAFFIC IN ATM NETWORKS

One of the major attractions of asynchronous transfer mode (ATM) netwo rks for transporting bursty video traffic is its ability to exploit th e multiplexing gains of packet switching while providing quality of se rvice guarantees. Unfortunately, most of the multiplexing mechanisms p roposed in the literature fail to exploit the multiplexing gains of AT M. In this paper, we propose a multirate service mechanism that allows a session to be served at different rates at different times. Applica tions generating bursty data, such as variable bit-rate (VBR) video, c an take advantage of multirate service by requesting a high rate of se rvice for brief periods of bursty arrivals and a much lower rate of se rvice for all other times. Consequently, the applications can improve their delay performance without reserving a high bandwidth for the ent ire duration of the sessions. Furthermore, the scheduler can multiplex the peaks and the lulls in service rates of different sessions and im prove the utilization of the system. Using MPEG video traces from a nu mber of applications, we show that multirate servers outperform single -rate PGPS (packet-by-packet generalized processor sharing) servers an d CBR (constant bit rate) servers in terms of number of connections ad mitted, while providing the same level of service guarantees. We also investigate the performance of multirate service when service quality need not be guaranteed. We refer to this as predictive service. We pro pose a measurement-based admission control procedure for predictive se rvice, and show that it helps increase the size of the admissible regi on even further.