Real-time scheduling for multimedia services using network delay estimation
Gibbon, John F.
MetadataShow full item record
A multimedia system combines audio, video, graphics, and text into one presentation. Each of these multimedia data types has distinct temporal characteristics. For example video has a specific number of frames that must be displayed per second. There are also temporal relationships that exist between the media. In a movie application, the audio and video streams must be synchronized to achieve a lip syncing effect. In our system, we manage these temporal requirements through the scheduling of the communication channel; multimedia data is retrieved across the network at the appropriate time so that temporal presentation requirements are met. This real-time scheduling forms a basis for the limited a priori (LAP) scheduler. The scheduler assumes that it knows enough about the system a priori to schedule the next period or limited portion of the presentation. By considering only one period at a time, the scheduler can adapt to dynamic user input or changing communication channel characteristics. A network delay model and retrieval delay estimation are used by the LAP scheduler when scheduling objects so that they arrive before their playout deadlines. This modeling and estimation also allow the LAP scheduler to decide when there are changes in the communication channel performance that require adjustments to the retrieval schedule. Furthermore, they enable the LAP scheduler to lower the resource requirements of a multimedia presentation when there is less than sufficient network bandwidth or buffer space for normal playout. The characteristics of the LAP scheduler are first described by analyzing the delay estimation techniques. Properties of the LAP scheduler are further investigated by using performance results from an FDDI network simulation and from an implementation of the LAP scheduler between two Unix workstations interconnected by an Ethernet network. The LAP scheduler wss found to satisfy the proposed objectives for multimedia data retrieval. However, its performance is hindered by the difficulty in predicting network traffic patterns, the normal approximations in the estimation process, and the lack of scheduling for resources other than the communication channel.
Thesis (Ph.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at email@example.com. Thank you.