Susie Wee

On multiple description streaming with content delivery networks

We propose a system that improves the performance of streaming media CDN by exploiting the path diversity provided by existing CDN infrastructure. Path diversity is provided by the different network paths that exist between a client and its nearby edge servers; and multiple description (MD) coding is coupled with this path diversity to provide resilience to losses. In our system, MD coding is used to code a media stream into multiple complementary descriptions, which are distributed across the edge servers in the CDN. When a client requests a media stream, it is directed to multiple nearby servers which host complementary descriptions. These servers simultaneously stream these complementary descriptions to the client over different network paths. This paper provides distortion models for MDC video and conventional video. We use these models to select the optimal pair of servers with complementary descriptions for each client while accounting for path lengths and path jointness and disjointness. We also use these models to evaluate the performance of MD streaming over CDN in a number of real and generated network topologies. Our results show that distortion reduction by about 20 to 40% can be realized even when the underlying CDN is not designed with MDC streaming in mind. Also, for certain topologies, MDC requires about 50% fewer CDN servers than conventional streaming techniques to achieve the same distortion at the clients.

Adaptive and lazy segmentation based proxy caching for streaming media delivery

Streaming media objects are often cached in segments. Previous segment-based caching strategies cache segments with constant or exponentially increasing lengths and typically favor caching the beginning segments of media objects. However, these strategies typically do not consider the fact that most accesses are targeted toward a few popular objects. In this paper, we argue that neither the use of a predefined segment length nor the favorable caching of the beginning segments is the best caching strategy for reducing network traffic. We propose an adaptive and lazy segmentation based caching mechanism by delaying the segmentation as late as possible and determining the segment length based on the client access behaviors in real time. In addition, the admission and eviction of segments are carried out adaptively based on an accurate utility function. The proposed method is evaluated by simulations using traces including one from actual enterprise server logs. Simulation results indicate that our proposed method achieves a 30% reduction in network traffic. The utility functions of the replacement policy are also evaluated with different variations to show its accuracy.

Modeling path diversity for multiple description video communication

The use of multiple description (MD) video coding and path diversity has been proposed to provide improved performance over lossy packet networks [1]. The goal of this work was to develop models to accurately and quickly predict and compare the distortion of MD video coding and path diversity against conventional single description (SD) video delivered over a single path. In the process, we developed (1) a model for the loss process of a two-path path diversity system, and (2) a distortion model that maps the loss model to MD distortion values. Given these models we present a number of comparisons between MD video coding and path diversity and conventional SD video over a single path. The proposed model for path diversity may also be useful in other applications not related to MD coding. Furthermore, other forms of MD coding may be analyzed using similar models for MD distortion.

Segment-based proxy caching for Internet streaming media delivery

The proliferation of multimedia content on the Internet poses challenges to existing content delivery networks. While proxy caching can successfully deliver traditional text-based static objects, it faces difficulty delivering streaming media objects because of the objects sizes as well as clients rigorous continuous delivery demands. We present two techniques supporting segment based proxy caching of streaming media. We evaluated these techniques in simulations and real systems.

Mediascapes: Context-Aware Multimedia Experiences

Here we describe research addressing the next generation of mobility technology, which will deliver the right experience in the right moment. The maturing field of pervasive computing yields the technology and the challenges described here. We focus on rich interactive mobile experiences triggered by context information available from the users, their environment, and a wealth of context-enabled content. We call such applications mediascapes.

Segment-based streaming media proxy: modeling and optimization

Researchers often use segment-based proxy caching strategies to deliver streaming media by partially caching media objects. The existing strategies mainly consider increasing the byte hit ratio and/or reducing the client perceived startup latency (denoted by the metric delayed startup ratio). However, these efforts do not guarantee continuous media delivery because the to-be-viewed object segments may not be cached in the proxy when they are demanded. The potential consequence is playback jitter at the client side due to proxy delay in fetching the uncached segments, which we call proxy jitter. Thus, for the best interests of clients, a correct model for streaming proxy system design should aim to minimize proxy jitter subject to reducing the delayed startup ratio and increasing the byte hit ratio. However, we have observed two major pairs of conflicting interests inherent in this model: (1) one between improving the byte hit ratio and reducing proxy jitter, and (2) the other between improving the byte hit ratio and reducing the delayed startup ratio. In this study, we first propose and analyze prefetching methods for in-time prefetching of uncached segments, which provides insights into the first pair of conflicting interests. Second, to address the second pair of the conflicting interests, we build a general model to analyze the performance tradeoff between the second pair of conflicting performance objectives. Finally, considering our main objective of minimizing proxy jitter and optimizing the two tradeoffs, we propose a new streaming proxy system called Hyper Proxy. Synthetic and real workloads are used to evaluate our system. The performance results show that Hyper Proxy generates minimum proxy jitter with a low delayed startup ratio and a small decrease of byte hit ratio compared with existing schemes.

Designs of high quality streaming proxy systems

Researchers often use segment-based proxy caching strategies to deliver streaming media by partially caching media objects. The existing strategies mainly consider increasing the byte hit ratio and/or reducing the client perceived startup latency (denoted by the metric delayed startup ratio). However, these efforts do not guarantee continuous media delivery because the to-be-viewed object segments may not be cached in the proxy when they are demanded. The potential consequence is playback jitter at the client side due to proxy delay in fetching the uncached segments, which we call proxy jitter. Thus, for the best interests of clients, a correct model for streaming proxy system design should aim to minimize proxy jitter subject to reducing the delayed startup ratio and increasing the byte hit ratio. However, we have observed two major pairs of conflicting interests inherent in this model: (1) one between improving the byte hit ratio and reducing proxy jitter, and (2) the other between improving the byte hit ratio and reducing the delayed startup ratio. In this study, we first propose an active prefetching method for in-time prefetching of uncached segments, which provides insights into the first pair of conflicting interests. Second, we further improve our lazy-segmentation scheme which effectively addresses the second pair of the conflicting interests. Finally, considering our main objective of minimizing proxy jitter and optimizing the two trade-offs, we propose a new streaming proxy system called Hyper Proxy by effectively coordinating both prefetching and segmentation techniques. Synthetic and real workloads are used to systematically evaluate our system. The performance results show that the hyper proxy system generates minimum proxy jitter with a low delayed startup ratio and a small decrease of byte hit ratio compared with existing schemes

Comparing application- and physical-layer approaches to diversity on wireless channels

Diversity techniques often arise as appealing means for improving the performance of multimedia communication over certain types of channels with independent parallel components (e.g., multiple antennas, frequency bands or time slots). Diversity can be obtained by channel coding across parallel components at the physical layer. Alternatively, the physical layer ca present an interface to the parallel components as separate, independent links thus allowing the application layer to implement diversity in the form of multiple description source coding. We compare these two approaches in terms of average end-to-end distortion as a function of channel signal-to-noise ratio (SNR). When specialized to the case of an independent, identically distributed Gaussian source over Rayleigh fading channels, our results suggest that parallel channel coding at the physical layer is more efficient than independent channel coding combined with multiple description source coding. More generally, we provide intuitive guidelines for allowing system designers to identify which types of systems are preferable under different scenarios of practical interest.

Research and design of a mobile streaming media content delivery network

Delivering media to large numbers of mobile users presents challenges due to the stringent requirements of streaming media, mobility, wireless, and scaling to support large numbers of users. This paper presents a mobile streaming media content delivery network (MSM-CDN) designed to overcome these challenges. The MSM-CDN is a network overlay consisting of overlay servers on top of the existing network; these overlay servers are control points that facilitate end-to-end media delivery and mid-network media services. This paper presents an overview of the MSM-CDN system architecture, and describes the testbed prototype that we built based on these architectural principles. The MSM-CDN provides a new platform for media delivery, and we describe a number of research directions related to the MSM-CDN.

A system architecture for managing mobile streaming media services

A mobile streaming media content delivery network (MSM-CDN) overlay system provides a scalable method for delivering media streams to a large number of clients. With the availability of such a streaming infrastructure, it becomes possible to implement enhanced media services. For example, the wide range and variability of network conditions, as well as processing and display capabilities of these devices will effectively require media streams to be adapted in the network. Each streaming session needs to be tailored to these changing environments in a practical and scalable manner. Media transcoding services can be performed by the servers of the MSM-CDN overlay, providing this flexibility. Due to the computational and bandwidth requirements of real-time video transcoding, these services require management of the placement of these tasks on the most appropriate servers, to make best use of the distributed resources available within the network. In this paper we address the media service assignment problem using the notion of service-location management (SLM). An effective load balancing system requires appropriate resource monitoring. We propose alternate SLM resource monitoring schemes. Using media transcoding as a representative service, we compare the performance of these schemes on an MSM-CDN testbed. We present our conclusions on which of these alternate implementations is both most reliable and most extensible to serve a large numbers of mobile client requests.