An enhanced admission control scheme for deterministic and predictive services

Abstract

Providing guaranteed Quality of Service in a packet switched network is still a research issue. In particular, real-time video and audio applications require deterministic end-to-end delay bounds and a limitation of the delay jitter. The scheduling disciplines used within the network nodes must be able to provide local delay bounds. Admission control algorithms verify whether the scheduler can accept an additional channel without violation of guarantees made for channels already established.

Within this paper we concentrate on admission control algorithms. First we introduce and compare two promising existing approaches: The Tenet scheme, introduced by the Tenet Group at the University of California in Berkeley, and the CSZ scheme that is a possible scheme for the use within the Internet. Our comparison shows that both approaches have disadvantages that we want to overcome with our own admission control algorithm.

We provide a deterministic service class, that allows data transmissions without packet losses and delay bound violations. This class is well suited for applications that know their traffic characterisation in advance. A second class are predictive services that just requires a rough peak rate allocation. The traffic behaviour is measured, so that for new admission requests not the peak load but the measured usage is used. We combine the deterministic service of the Tenet approach and the predictive service of the CSZ scheme. The admission control for the predictive service is extended to work together with a Rate Controlled Static Priority scheduler. Furthermore, we have improved the measurement scheme by using PI regulators which provide a better estimation of the current load behaviour than the mechanism of the CSZ scheme.