No abstract
Abstract-In this note, we study several issues in the design of localized quality-of-service (QoS) routing schemes that make routing decisions based on locally collected QoS state information (i.e., there is no network-wide information exchange among routers). In particular, we investigate the granularity of local QoS state information and its impact on the design of localized QoS routing schemes from a theoretical perspective. We develop two theoretical models for studying localized proportional routing: one using the link-level information and the other using path-level information. We compare the performance of these localized proportional routing models with that of a global optimal proportional model that has knowledge of the global network QoS state. We demonstrate that using only coarser-grain path-level information it is possible to obtain near-optimal proportions. We then discuss the issues involved in implementation of localized proportional routing and present some practical schemes that are simple and easy to implement.Index Terms-Localized proportional routing, quality-of-service (QoS) routing.
With the growing popularity of the Internet, there is increasing interest in using it for audio and video transmission. Periodic network overloads, leading to bursty packet losses, have always been a key problem for network researchers. In a long-haul, heterogeneous network like the Internet, handling such an error becomes especially difficult. Perceptual studies of audio and video viewing have shown that bursty losses have the most annoying effect on people, and hence are critical issues to be addressed for applications such as Internet phone, video conferencing, distance learning, etc. Classical error handling techniques have focused on applications like FTP, and are geared towards ensuring that the transmission is correct, with no attention to timeliness. For isochronous traffic like audio and video, timeliness is a key criterion, and given the high degree of content redundancy, some loss of content is quite acceptable. In this paper we introduce the concept of error spreading, which is a transformation technique that takes the input sequence of packets (from an audio or video stream) and scrambles its packets before transmission. The packets are unscrambled at the receiving end. The transformation is designed to ensure that bursty losses in the transformed domain get spread all over the sequence in the original domain. Our error spreading idea deals with either cases where the stream has or does not have inter-frame dependencies. Perceptual studies have shown that users are much more tolerant to a uniformly distributed loss of low magnitude. We next describe a continuous media transmission protocol based on this idea. We also show that our protocol can be used complementary to other error handling protocols. Lastly, we validate its performance through a series of experiments and simulations.
This paper shows a methodology for user-driven, top down approach to research in quality of service issues in multimedia systems. As a case study, we show a development of metrics, validation by means of a user study, and a performance evaluation of a prototyping environments. What is used, the Berkeley Continuous Media Toolkit CMT is a popular environment that satis es this need. Form a human user's perspective, in order for multimedia demonstrations to be c omprehensible, the number of audio or video frames dropped and the timing delays in the ones that are displayed, need t o b e kept to a minimum. Therefore, it is important to know the frame dropping characteristics of CMT. In a series of experiments we monitored the variation of these parameters with respect processor and network loads. It was observed that loads a ect aggregate frame drops at lower rates and consecutive frame drops at higher rates. Because at a higher rates a large number of consecutive frames are dropped, the ones that are played appear in a more timely manner. As a solution to observed p r oblems, we present some QoS based approaches to control drop and delay parameters.
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