Multiple Service Classes for Rate Adaptive Streams

Abstract

Our previous work [19–21] investigated optimal support of rate adaptive multimedia streams. In particular, we identified the optimal distribution of network bandwidth among competing streams, i.e., the optimal adaptation policy, which maximized our Quality of Service (QoS) metric, defined as the client average normalized time-average subscription level. The optimal adaptation policy (for a single link) was identified as granting the maximum subscription level to as many small volume streams as possible and granting the minimum subscription level to the remaining large volume streams, where stream volume is the product of the stream duration and the maximum subscription level, i.e., the number of bits associated with the stream at its finest resolution encoding. This type of volume discrimination may prove unsatisfactory to clients of large volume streams with heterogeneous QoS requirements.

In this work we introduce a link architecture supporting multiple service classes, where each service class is characterized by a distinct QoS guarantee. Intuitively, large volume streams, which would suffer under the volume discriminatory nature of the optimal adaptation policy for a single service class, might be willing to pay a price to obtain a higher degree of QoS protection offered by a “premium” service class. We introduce a capacity scaling appropriate for studying large numbers of clients sharing large capacity links. We identify the optimal adaptation policy for a link supporting multiple service classes, and obtain closed form expressions for the asymptotic QoS within each class under the optimal adaptation policy. We demonstrate that the same asymptotic QoS can be obtained under an appropriately designed admission control policy which eliminates the need for dynamic adaptation. Finally, we compare the benefits of offering multiple service classes over a single service class architecture in a case study which investigates how to multiplex small volume audio streams and large volume video streams on a congested link.