Proxies are emerging as an important way to reduce user-perceived latency and network resource requirements in the Internet. While relaying traffic between servers and clients, a proxy can cache resources in the hope of satisfying future client requests directly at the proxy. However, existing techniques for caching text and images are not appropriate for the rapidly growing number of continuous media streams. In addition, high latency and loss rates in the Internet make it difficult to stream audio and video without introducing a large playback delay. To address these problems, we propose that, instead of caching entire audio or video streams (which may be quite large), the proxy should store a prefix consisting of the initial frames of each clip. Upon receiving a request for the stream, the proxy immediately initiates transmission to the client, while simultaneously requesting the remaining frames from the server. In addition to hiding the latency between the server and the proxy, st...

Prefetching has been shown to be an effective technique for reducing user perceived latency in distributed systems. In this paper we show that even when prefetching adds no extra traffic to the network, it can have serious negative performance effects. Straightforward approaches to prefetching increase the burstiness of individual sources, leading to increased average queue sizes in network switches. However, we also show that applications can avoid the undesirable queueing e ects of prefetching. In fact, we show that applications employing prefetching can signi cantly improve network performance, to a level much better than that obtained without any prefetching at all. This is because prefetching offers increased opportunities for traffic shaping that are not available in the absence of prefetching. Using a simple transport rate control mechanism, a prefetching application can modify its behavior from a distinctly ON/OFF entity to one whose data transfer rate changes less abruptly, while still delivering all data in advance of the user's actual requests.

In this paper, we examine the transport and storage of video compressed with a variable bit rate (VBR). We focus primarily on networked video, although we also briefly consider other applications of VBR video, including satellite transmission (channel sharing), playback of stored video, and wireless transport. Packet video research requires careful integration between the network and the video systems; however, a major stumbling block has resulted because commonly used terms are often interpreted differently by the video and networking communities.

Real-time distribution of stored video over wide-area networks is a crucial component of many emerging distributed multimedia applications. The heterogeneity in the underlying network environments is an important factor that must be taken into consideration when designing an end-to-end video delivery system. In this paper, we present a novel approach to the problem of end-to-end video delivery over wide-area networks using proxy servers situated between local-area networks (LANs) and a backbone wide-area network (WAN). A major objective of our approach is to reduce the backbone WAN bandwidth requirement. Towards this end, we develop an effective video delivery technique called video staging via intelligent utilization of the disk bandwidth and storage space available at proxy servers. Using this video staging technique, only part of a video stream is retrieved directly from the central video server across the backbone WAN whereas the rest of the video stream is delivered to users loca...

VBR transmission of video over ATM networks has long been said to provide sub- stantial benefits, both in terms of network utilization and video quality, when compared with conventional CBR approaches. However, realistic VBR transmission environments will certainly impose constraints on the rate that each source can submit to the network.

The efficient distribution of stored information has become a major concern in the Internet which has increasingly become a vehicle for the transport of stored video. Because of the highly heterogeneous access to the Internet, researchers and engineers have argued for layered encoded video. In this paper, we investigate delivering layered encoded video using caches. Based on the stochastic knapsack theory, we develop a model for the layered video caching problem. We propose heuristics to determine which videos and which layers in the videos should be cached in order to maximize the revenue from the streaming service. We evaluate the performance of our heuristics through extensive numerical experiments. We find that, for typical scenarios, the revenue increases nearly logarithmically with the cache size and linearly with the link bandwidth that connects the cache to the origin servers. We also consider service models with request queuing and negotiations about the delivered stream quality and find that both extensions provide only small revenue increases.

The transfer of prerecorded, compressed video requires multimedia services to support large fluctuations in bandwidth requirements on multiple time scales. Bandwidth smoothing techniques can reduce the burstiness of a variable-bit-rate stream by prefetching data at a series of fixed rates, simplifying the allocation of resources in video servers and the communication network. Given a fixed client-side prefetch buffer, several bandwidth smoothing algorithms have been introduced that are provably optimal under certain constraints. This paper presents a comprehensive performance evaluation of bandwidth smoothing algorithms, based on a collection of metrics that relate directly to the server, network, and client resources necessary for the transmission, transport, and playback of prerecorded video. Due to the scarcity of available trace data, we have constructed a video capture testbed and generated a collection of twenty full-length, motion-JPEG encoded video clips. Using these ...

For distributed and network applications, efficient management of program state is critical to performance and functionality. To support domain- and application-specific optimization of data movement, we have developed the Internet Backplane Protocol (IBP) for controlling storage that is implemented as part the network fabric itself. IBP allows an application to control intermediate data staging operations explicitly as data is communicated between processes. As such, the application can exploit locality and manage scarce buffer resources effectively. In this paper, we discuss the development of IBP, the implementation of a prototype system for managing network storage, and a preliminary deployment as part of the Internet-2 Distributed Storage Initiative. 1

This paper presents a model and theory for streaming layered video. We model the bandwidth available to the streaming application as a stochastic process whose statistical characteristics are unknown a priori. The random bandwidth models short term variations due to congestion control (such as TCP-friendly conformance). We suppose that the video has been encoded into a base and an enhancement layer, and that to decode the enhancement layer the base layer has to be available to the client. We make the natural assumption that the client has abundant local storage and attempts to prefetch as much of the video as possible during playback. At any instant of time, starvation or partial starvation can occur at the client in either of the two layers. During periods of starvation, the client applies video error concealment to hide the loss. We study the dynamic allocation of the available bandwidth to the two layers in order to minimize the impact of client starvation. For the case of an infinitely-long video, we find that the optimal policy takes on a surprisingly simple and static form. For finite-length videos, the optimal policy is a simple static policy when the enhancement layer is deemed at least as important as the base layer. When the base layer is more important, we design a threshold policy heuristic which switches between two static policies. We provide numerical results that compare the performance of no-prefetching, static and threshold policies. I.

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