Towards a Better-Than-Best-Effort Forwarding Service for Multimedia Flows

K. Jeffay
IEEE Multimedia
Volume 6, Number 4, October-December 1999
pages 84-88.

ABSTRACT: A salient requirement of interactive multimedia applications is that they transmit data continuously at uniform rates with minimum possible end-to-end delay. The majority of these applications do not require hard and fast guarantees of network performance, however, the current best-effort forwarding model of the Internet is frequently insufficient for realizing these requirements. Worse still, the requirement of uniform-rate transmission puts many multimedia applications at odds with current and proposed Internet network management practices which assume or require TCP-like reactions to packet loss. Multimedia flows present a potential threat to this regime given that their often high bandwidth requirements have the potential to starve TCP connections of bandwidth. Moreover, making these flows react to congestion in a TCP-like manner is not likely to work for all applications.

We are investigating a form of segregation between TCP and non-TCP continuous media flows based on active router-queue management. Our scheme, called class-based thresholds (CBT), uses queue occupancy thresholds to isolate TCP flows and to provide a better-than-best-effort forwarding service for flows in need of uniform-rate transmissions. CBT relies on a packet marking mechanism such as those proposed for realizing differentiated services on the Internet. When combined with existing active router queue management schemes such as RED, CBT provides performance for TCP that approximates that achievable under packet scheduling schemes, and acceptable performance for multimedia flows. CBT is a simple and efficient mechanism with implementation complexity and run-time overhead comparable to that of RED.

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