40_3 - A Composable Service Model With Loss and a...

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Unformatted text preview: A Composable Service Model With Loss and a Scheduling Algorithm Sami Ayyorgun Research & Development in Advanced Network Technology Los Alamos National Laboratory P.O. Box 1663, M.S. D451 Los Alamos, New Mexico 87545 sami@lanl.gov Rene L. Cruz Dept. of Electrical & Computer Engineering University of California, San Diego 9500 Gilman Drive La Jolla, CA 92093-0407 cruz@ece.ucsd.edu Abstract We show the composability of a new service model that we propose, which incorporates packet loss. The new model is based on guaranteeing at least a cer- tain fraction of the all packets of a flow, which is to be served through a network element, to meet their dead- lines assigned via a service curve. We also propose a scheduling algorithm to deliver the services as specified by the new service model at a multiplexer. The correct- ness of the proposed algorithm is also shown. 1 Introduction Most real-time multimedia applications such as Internet phone and video conferencing are very sensitive to packet delay, jitter, and loss. The performance of protocols for these applications, such as RTP, are also affected by the severity of these undesired phenomenons. A few service and trac models focusing on the delay and/or jitter as- pect of multimedia applications have been previously pro- posed in the literature, e.g., [1, 2, 3, 4, 5, 6, 7]. For the most part, these models do not allow for packet loss. On the other hand, advantages could be taken from the toler- ance of these applications to loss up to a certain degree; specifically, for better link utilization. For example, for In- ternet phone, it has been reported that packet loss up to 20 percent could be tolerated, depending on how the voice is encoded and transmitted [8]. Thus, a service model which incorporates loss facilitates a utilization of these advan- tages. This provides the first motivation for this study. Another motivation is provided by some new transmis- sion and coding schemes which have been proposed in re- cent years for the distribution of information over lossy packet-based networks [9, 10]. These schemes often re- quire at least a certain fraction of all the packets in a com- munication session to be successfully received/decoded for reliable communication. Thus, these new schemes also call for a service model which incorporates packet loss. One of the service models that we have mentioned in the first paragraph is called the service-curve model which is introduced in [3, 6]. Adopting a discrete-time formulation, a network element is said to deliver a service curve S to an input ow R if the corresponding output ow G satisfies the following condition G ( n ) > min k 6 n { R ( k ) + S ( n k ) } for all n , where S is an unbounded, non-decreasing function defined from the integers to the non-negative integers, that S ( n ) = 0 for all n 6 0....
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40_3 - A Composable Service Model With Loss and a...

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