Subhabrata Sen

Optimal proxy cache allocation for efficient streaming media distribution

We address the problem of efficiently streaming a set of heterogeneous videos from a remote server through a proxy to multiple asynchronous clients so that they can experience playback with low startup delays. We determine the optimal proxy prefix cache allocation to the videos that minimizes the aggregate network bandwidth cost. We integrate proxy caching with traditional server-based reactive transmission schemes such as hatching, patching and stream merging to develop a set of proxy-assisted delivery schemes. We quantitatively explore the impact of the choice of transmission scheme, cache allocation policy, proxy cache size, and availability of unicast versus multicast capability, on the resulting transmission cost. Our evaluations show that even a relatively small prefix cache (10%-20% of the video repository) is sufficient to realize substantial savings in transmission cost. We find that carefully designed proxy-assisted reactive transmission schemes can produce significant cost savings even in a predominantly unicast environment such as the Internet.

Integrated scheduling of multimedia and hard real-time tasks

An integrated platform which is capable of meeting the requirements of both traditional real-time control processing and multimedia processing has enormous potential for accommodating various kinds of new applications. However, except for the simplest of situations, few, if any, research or commercial systems successfully provide architectural and OS mechanisms which can efficiently support both hard real-time computation and multimedia soft real-time computation. The authors propose a multimedia server execution on multiprocessor real-time operating systems to provide different classes of guarantee to support both types of processing. The multimedia server supports multiple periodic multimedia streams with a capability for graceful QoS degradation during system overload. They (i) develop several multimedia server scheduling algorithms, (ii) evaluate the performance of these algorithms, and (iii) discuss realistic system implementation issues on the SGI IRIX/REACT/PRO operating system.

Using Windows NT for real-time applications: experimental observations and recommendations

Windows NT was not designed as a real time operating system, but market forces and the acceptance of NT in industrial applications have generated a need for achieving real time functionality with NT. As its use for real time applications proliferates, based on an experimental evaluation of NT, we quantitatively characterize the obstacles placed by NT. As a result of these observations, we provide a set of recommendations for users to consider while building real time applications on NT. These are validated by the use of NT for a prototype application involving real time control that includes multimedia information processing. The results of the above study should provide system designers with guidelines, as well as insight, into the design of an architecture based on NT for supporting applications with components having real time constraints.

A smoothing proxy service for variable-bit-rate streaming video

Provisioning network resources for multimedia streaming is complicated by the bursty, high-bandwidth traffic introduced by compressed video, as well as the variability of the throughput, delay, and loss properties of the Internet, and the lack of end-to-end control by any one service provider. To address these problems, we propose that proxies should perform online smoothing by transmitting frames into the client playback buffer in advance of each burst, to reduce network resource requirements without degradation in video quality. This paper describes the practical systems issues we have encountered in building a smoothing proxy service using off-the-shelf components, in the context of an MPEG-2/RTP streaming testbed.

Playback restart in interactive streaming video applications

Low latency is crucial in networked multimedia applications such as on-demand streaming audio and video. In this paper we consider the problem of restarting or resuming playback following an interactive operation such as fast forward, rewind, or indexed jump in stored on-demand video. We present two approaches to restart playback after an interactive operation, and develop algorithms to compute the latencies incurred in restarting playback. Using long MPEG-1 traces, with an optimal smoothing technique to transmit data for regular playback, we demonstrate that the latencies incurred under our approaches are very small. We next examine the latencies incurred when restarting playback in a video server under two policies for sharing its bandwidth: (a) one in which only regular playback bandwidth is available to restart playback and (b) one in which additional free server bandwidth (if any) is accessible. We find playback restart latencies to be similarly low under both policies, suggesting that the simpler approach (a) is sufficient.

Prefix caching assisted periodic broadcast for streaming popular videos

The bandwidth-intensive and long-lived nature of high quality digital video makes it a challenging problem to transmit such video over the Internet. In this paper, we propose a scalable and flexible framework integrating proxy-based prefix caching with periodic broadcast of the suffix of a video from the server, for efficiently streaming a set of popular videos to a large number of asynchronous clients. We develop a methodology for (i) determining appropriate prefix and suffix transmission schemes based on a principle of decoupling the two transmissions from each other, and (ii) optimally allocating the proxy buffer space among the set of videos. A buffer allocation algorithm is presented that minimizes the aggregate bandwidth usage on the server-proxy path. Our studies show that our approach yields a buffer allocation close to the optimal solution minimizing both server-proxy and proxy-client path bandwidth usage for practical settings where the proxy-client path bandwidth is much cheaper than the long-haul server-proxy path bandwidth. When the proxy buffer is allocated to a set of videos using our scheme, a total buffer space of just 5-20% of the video repository is adequate to realize substantial reductions in the aggregate bandwidth usage on the server-proxy path.

Streaming CBR transmission of VBR stored video

Data transmission across a network using constant-bit-rate (CBR) service simplifies admission control and resource management techniques. We consider lossless, starvation- free, streaming CBR transmission of compressed digital video, which is known to exhibit significant, multi-time- scale rate variability. This transmission uses work-ahead transfer into available client buffers to send data at a rate significantly below the peak rate of the original video. The goal of any video transmission scheme is to minimize resources requirements such as client buffer, transmission rate, channel holding time and playback startup latency. We identify, for CBR video transmissions, formal structural properties of the tradeoffs among these resources. Specifically, we show that, (i) the minimum feasible client buffer requirement as a function of playback startup latency is unimodal with one minimal value, (ii) the minimum feasible CBR rate is a convex decreasing function of the startup latency, and (iii) the corresponding channel holding time is piecewise linear concave increasing function of the startup latency. Using these structural properties, we then develop an O(N log N) algorithm that computes the minimum client buffer size and the associated CBR rate and playback startup latency required to transmit a VBR video. This is a significant improvement over an existing O(N2 log N) algorithm to solve the same problem. We next quantitatively examine the resource tradeoffs using MPEG-1 traces, and find that both the CBR transmission rate and minimum client buffering requirement can be substantially reduced by requiring only very small playback startup latencies.

Incorporation of multimedia capabilities in distributed real-time applications

In this paper, we consider the problems and benefits of developing an integrated platform that handles the timing requirements of a real-time industrial control application and the processing of multimedia streams. In particular, this paper explores various application scenarios which can benefit from an integrated real-time control system. We propose an architecture based on open systems and identify key research issues at different levels of the control hierarchy that need to be overcome in order to incorporate multimedia capabilities into a distributed industrial control application. A real-time Multimedia database is a key component in this platform and it can aid in the decision making processat the managementlevel, potentially resulting in reduced costs and improved operation of an industrial plant.

GRE Encapsulated Multicast Probing: A Scalable Technique for Measuring One-Way Loss

Internet service providers increasingly wish to monitor the performance of customer traffic within their networks. This paper addresses the problem of scalably performing one-way loss measurements across specific network paths. Our solution addresses the issue of scale by exploiting measurement features of the deployed network infrastructure to a large degree. There are three components. Firstly, GRE tunneling is used to control the path followed by measurement traffic in the network. Secondly, innovative probing methods, coupled with standard measurement capabilities, such as NetFlow, are used to isolate the performance of groups of measurement packets. Thirdly, we exploit and extend tomographic inference methods in order to extract the performance of probe traffic on customer paths within the network. This combination yields a powerful yet lightweight method to determine customer performance within the network.

Using multicast for streaming videos across wide area networks

In this paper, we study streaming multiple videos from a remote server to asynchronous clients through a group of proxies, using multicast on both the wide area server-proxy paths and the local area proxy-client paths. In this setting, we present an algorithm to determine the optimal cache allocation among videos at each proxy and develop an efficient streaming video distribution scheme. Our evaluations show the benefits of even a small proxy cache and quantify the gains from using multicast on the server-proxy paths.