The ability of a web service to provide low-latency access to its contents is constrained by available network bandwidth. It is important for the service to manage available bandwidth wisely. While providing differentiated quality of service (QoS) is typically enforced through network mechanisms, in this paper we introduce a robust mechanism for managing network resources at the application level. We use transcoding to allow web servers to customize the size of objects constituting a web page, and hence the bandwidth consumed by that page, by dynamically varying the size of multimedia objects on a per-client basis. We leverage earlier work on characterizing quality versus size tradeoffs in transcoding JPEG images to dynamically determine the quality and size of the object to transmit. We evaluate the performance benefits of incorporating this information in a series of bandwidth management policies. We develop metrics to measure the performance of our system. We use realistic workloads...

Transcoding is becoming a preferred technique to tailor multimedia objects for delivery across variable network bandwidth and for storage and display on the destination device. This paper presents techniques to quantify the quality-versus-size tradeoff characteristics for transcoding JPEG images. We analyze the characteristics of images available in typical Web sites and explore how we can perform informed transcoding using the JPEG compression metric. We present the effects of this transcoding on the image storage size and image information quality. We also present ways of predicting the computational cost as well as potential space benefits achieved by the transcoding. These results are useful in any system that uses transcoding to reduce access latencies, increase effective storage space as well as reduce access costs.

Transcoding is a technique employed by network proxies to dynamically customize multimedia objects for prevailing network conditions and individual client characteristics. Transcoding can be performed along a number of different axes and the specific transcoding technique used depends on the type of multimedia object. Our goal in this paper is to understand the nature of typical Internet images and their transcoding characteristics. We focus our attention on transcodings intended to customize an image for file size savings. Our results allow the developers of a transcoding proxy server to choose the appropriate transcoding techniques for the important classes of Internet images. We analyze the characteristics of images available on the Web through a representative trace. We show that most GIF images accessed on the Internet are small

Mobile applications will increasingly depend upon multimedia information originating in the web and attempt to access this data over wireless networks that are more expensive and slower than typical wireline internet access from desktops. Transcoding is an important technique that can allow network proxy servers to offer differentiated service by customizing the delivered object size for the network bandwidth available on the "last hop" to the mobile client. We exploit technology that we had previously developed that characterized the quality versus size tradeoffs in transcoding JPEG images. This technology supplies more information for use in transcoding policy decision making. We evaluate the performance benefits of incrementally incorporating this information in a series of transcoding policies. The principal contribution of this work is the demonstration that it is possible to use informed transcoding techniques to balance the need for good quality of multimedia content while redu...

Advances in hardware imaging technology and user demand for convenient mobile electronic image capture are fueling the development of inexpensive image capture devices that can acquire images rivaling the image quality of photographic film. Improvements in the hardware imaging technology have to be matched with intelligent image storage mechanisms that are aware of local storage and battery constraints. In this paper, we explore using a dynamic, informed image transcoding technique to manage the consumed battery and storage resources in digital cameras. Such application aware technologies are fundamental for the mass consumer acceptance of these newer digital technologies. We show that this technique can allow the camera to store an order of magnitude more images. For a moderate number of images (e.g. 40), transcoding techniques can also maintain high quality images. The availability of fast wireless networks can allow the camera to capture 58 high quality images (51 uploaded) before ...

The ability of a web service to provide low-latency access to its content is constrained by available network bandwidth. While providing differentiated quality of service (QoS) is typically enforced through network mechanisms, in this paper we introduce a robust mechanism for managing network resources using application-specific characteristics of web services. We use transcoding to allow web servers to customize the size of objects constituting a web page, and hence the bandwidth consumed by that page, by dynamically varying the size of multimedia objects on a per-client basis. We leverage our earlier work on characterizing quality versus size tradeoffs in transcoding JPEG images to supply more information for determining the quality and size of the object to transmit. We evaluate the performance benefits of incorporating this information in a series of bandwidth management policies using realistic workloads and access scenarios to drive our system. The principal contribution of this...

New concepts such as the Application Level Framing (ALF) have been proposed to make network protocol implementations more efficient and to give the application programmer greater control over the data transmission. This paper describes early experiments with automated design and implementation of application-specific communication protocols based on the formal specification of the application using ESTEREL. A comparison is made between a hand coded JPEG player and its automated equivalent. The results show that the automated approach creates a better integrated implementation with the same level of performance. Keywords Efficient Communication Architectures, ALF, Integrated Implementation, Formal Specifications, User Level Protocols. 1.0 INTRODUCTION The rapid evolution of networking and the multiplication of new applications re-emphasizes the importance of the efficient (i.e. flexible and performant) communication supports. Implementations must be able to take maximal advantage of d...

In the emerging environment of massive image databases the display of a particular image at a workstation will be almost invariably preceded by its selection from a set of thumbnail images This paper explores the basics of image thumbnails, and the implications for efficient image storage. The advantages/disadvantages of alternate schemes for thumbnail generation are discussed., A measure of image compression is proposed to take into account the costs of multiple thumbs for each image accessed fully. Analysis suggests that to maximise the effective compression, requires the use of thumbs efficiently transferred that contain data required for whole image generation. To meet the needs of thumbnail-based retrieval, suggestions are made for the re-organisation of the code for block oriented image coding schemes leading to the specification and implementation of thumb-based vector quantization image coding, and a fast decoding thumb-fractal codec. A proposal for a thumb-oriented version of JPEG is outlined.

The lack of flexibility and efficiency of the traditional layered model has led researchers to consider new approaches when designing communication subsystems. In particular, one approach consists of implementing protocol subsystems tailored to application requirements. The Application Level Framing concept in which the communication subsystem is able to process data in chunks of application-specific size illustrates such adaptative and integrated approach. In this paper we discuss the impact of the ALF approach on both the design and the performance of the communication subsystems. Specifically, we examine the effects of ALF on the implementation of a server for digital images. We find that performance can be increased when using the ALF concept and that applications can benefit from the out-of-order processing. We multiply by two the throughput when applying ALF over Internet instead of TCP/IP. We show also that the choice of the Application Data Unit size is an important issue for perfor...

The pipeline is a simple and intuitive structure to speed up many problems. Novice parallel programmers are usually taught this structure early on. However, expert parallel programmers typically eschew using the pipeline in coarse–grained applications because it has three serious problems that make it difficult to implement efficiently. First, processors are idle when the pipeline is not full. Second, load balancing is crucial to obtaining good speedup. Third, it is difficult to incrementally incorporate more processors into an existing pipeline. Instead, experts recast the problem as a master/slave structure which does not suffer from these problems. This paper details a transformation that allows programs written in a pipeline style to execute using the master/slave structure. Parallel programmers can benefit from both the intuitive simplicity of the pipeline and the efficient execution of a master/slave structure. This is demonstrated by performance results from two applications. 1.