Because Internet access rates are highly heterogeneous, many video content providers today make available different versions of the videos, with each version encoded at a different rate. Multiple video versions, however, require more server storage and may also dramatically impact cache performance in a traditional cache or in a CDN server. An alternative to versions is layered encoding, which can also provide multiple quality levels. Layered encoding requires less server storage capacity and may be more suitable for caching; but it typically increases transmission bandwidth due to encoding overhead. In this paper we compare video streaming of multiple versions with that of multiple layers in a caching environment. We examine caching and distribution strategies that use both versions and layers. Our analytical results indicate that mixed distribution/caching strategies provide the best overall performance.

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. 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.

This paper proposes the concept of cumulative inter-ADU (application data unit) jitter for use in studying the performance of a multimedia system. The concept models the ADU arrivals from a network by keeping the running total of the differences between inter-ADU spacings at the arrival instants and the generation instants. For a given playback delay, the concept can be used to estimate the number of late ADUs. This estimation is done at the entry to the playback buffer rather than at the exit as with existing media synchronization. Extensive simulation results have shown that the ADUs indicated as late by the cumulative inter-ADU jitter are indeed discarded by the playback algorithm. We illustrate its applications by examples. In particular, we highlight the significance of the concept in improving media synchronization algorithms and network-level controls from an application-level perspective.

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. We investigate delivering layered encoded video using caches. Based on a stochastic knapsack model 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. We evaluate the performance of our heuristics through extensive numerical experiments. We also consider two intuitive extensions to the initial problem.

We study the interaction between error control and media synchronization. We approach the problem by considering a virtual application data unit (ADU) network with error control within the network boundary and media synchronization outside the network boundary. We introduce the concept of cumulative inter-ADU jitter, which is the running total of the differences between inter-ADU spacings at the receiver and at the sender, to model the ADU departure process from the network observed at the entry of the playback buffer. We investigate how different error control schemes, network and source characteristics influence the process on one hand and how the process affects the choice of playback delay in order to minimize ADU losses on the other hand. Our numerical results, obtained through simulation, verify the analysis and reveals that jitter control within the network is not as important as controlling the bandwidth and the delay, especially in the presence of error control and variable bit rate source.

Considering the limited bandwidth of the wireless link, it is important that the error control mechanism in wireless networks be spectrally efficient. Towards this end, we develop a hybrid error control architecture which takes into account the use of hierarchical video coding. Additionally, the architecture also includes a module which estimates the packet error rate and round trip time observed by the receiver and adjusts the level of redundancy used based on the estimate. By choosing different options in the architecture, we get different error control schemes. In this paper, we investigate the performance of five different error control schemes, namely ARQ, pure FEC, hybrid FEC/ARQ, hybrid FEC/ARQ with priority-dependent redundancy, and adaptive hybrid FEC/ARQ with priority-dependent redundancy. We evaluate the performance of these schemes using MPEG-2 video traces. The results show that pure FEC offers the worst overall performance. The ARQ scheme offers the best performance under low bit error rate and short round trip time, while the priority-aware hybrid FEC/ARQ with or without FEC adaptation offers the best performance under other conditions.