Abstract: Multimedia services such as video-on-demand (VOD) will require certain level of quality of service (QoS). Yet, the VPD service will be required to run on general purpose machines such as PCs or workstations and shared networks such as Ethernet and LAN ATM because of cost requirements for home networking. In this environment, one of the problems will become the application QoS specification such as video display frame rate before any negotiation for QoS guarantee starts. This paper presents as on-line probe-based algorithm to specify initial QoS for continuous media and determine critical degradation point when performance degradation occurs and adaptive mechanisms should be applied. This probe-based algorithm should be a part of a negotiation phase to identify the actual application QoS and its degradation point.