A Probe-based Algorithm for QoS Speci cation and Adaptation

Multimedia services such as Video-On-Demand (VOD) will require a certain level of Quality of Services (QoS). However, the VOD service will be required to run on general purpose machines such as PCs or workstations and shared networks such as Ethernet and ATM (Asynchronous Transfer Mode) LANs due to the prohibitive cost of home networking. In this environment one problem is the speciication of application QoS 7] such as the video display frame rate prior to negotiation for QoS guarantees. This paper proposes an on-line probe-based algorithm to specify initial application QoS for continuous media and to determine the critical degradation point when performance degrades and adaptive mechanisms should be applied. This probe-based algorithm should be part of a negotiation phase. We will show the applicability of the probe-based algorithm on several VOD service experiments. The results show that it is worthwhile to perform probes in advance if the probe time is small with respect to the duration of the movie/video clip. The advantage of using on-line probes in QoS speciication is that the negotiated QoS value represents a realistic application QoS with respect to the current load of the VOD system.