Abstract
Recent advances in computer communications, especially highly interactivedistributed applications and those relying on the transfer of multimedia information and in particular, continuous media flows. It is essential that QoS is guaranteed in a system, considering distributed system area, the transport protocol and themultiservice network. Quality of Service (QoS) in distributed multimedia systems provides a unifying theme on which the functions and facilities of the new integrated standards can be constructed. The objective of thispaper is tofocusonseveral QoS parametersat different levelsand Enhanced Adaptive Mechanismis proposed in order to improve the performance in distributed multimediaapplications.
Highlights
Nowadays most networks, operating systems, and databases, many resources are shared, the activities of other users can lead to large and sudden variations in resource accessibility
The following sections givean overview of the notion of Quality of Service (QoS) on several levels and how they are related to each other.After that, the main aspect of resource management is discussed. Implementation mechanisms such as admission testing, resource reservation, scheduling, policing, are debatedandthen Enhanced Adaptive Mechanism have been proposed in order to improve the performance in multimediaapplications
If adaptation is too fast, thesystem is susceptible to measuring errors and may overreact or oscillate.Many multimedia applications use some kind of feedback
Summary
Nowadays most networks, operating systems, and databases, many resources are shared, the activities of other users can lead to large and sudden variations in resource accessibility. In simple best-effort approaches every stage of a video pipeline, for instance drops data when there are insufficient resources to process it (not enough network bandwidth, buffer overflow, CPU too busy, and so on). The qualityof component streams can differ considerably, when some data is retrieved from a localserver and some over a congested network transmitting continuous media data in real-time over the Internet does not allowthe use of a reliable protocol such as TCP. Is late data itself useless, but with a reliable protocol italso delays the delivery of subsequent data, potentially stalling the entire pipeline Because of these problems, an unreliable UDP is preferred, and the application must deal with packet loss and out-of-order delivery. Evenassessing quality based on a QoS specification is a non-trivial problem, which can be addressed using a formal error model
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