Multirate Scheduling of VBR Video Traffic in ATM Networks

One of the major attractions of Asynchronous Transfer Mode (ATM) networks for transporting bursty video traac is its ability to exploit the multiplexing gains of packet switching while providing quality of service guarantees. Unfortunately, most of the multiplexing mechanisms proposed in the literature fail to exploit the multiplexing gains of ATM. In this paper we propose a multirate service mechanism that allows a session to be served at diierent rates at diierent of times. Applications generating bursty data, such as VBR video, can take advantage of multirate service by requesting for a high rate of service for brief periods of bursty arrivals and a much lower rate of service for all other times. Consequently, the applications can improve their delay performance without reserving a high bandwidth for the entire duration of the sessions. Furthermore, the scheduler can multiplex the peaks and the lulls in service rates of diierent sessions and improve the utilization of the system. Using MPEG video traces from a number of applications, we show that multirate servers outperform single rate PGPS (Packet-by-packet Generalized Processor Sharing) servers and CBR (Constant Bit Rate) servers, in terms of number of connections admitted, 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 propose a measurement based admission control procedure for predictive service and show that it helps increase the size of the admissible region even further.