The current model for multicast transmission of video over the Internet assumes that a fixed average bandwidth is uniformly present throughout the network. Consequently, sources limit their transmission rates to accommodate the lowest bandwidth links, even though high-bandwidth connectivity might be available to many of the participants. We propose an architecture where a video transmission can be decomposed into multiple sessions with different bandwidth requirements using an application-level gateway. Our video gateway transparently connects pairs of sessions into a single logical conference by manipulating the data and control information of the video streams. In particular, the gateway performs bandwidth adaptation through transcoding and rate-control. We describe an efficient algorithm for transcoding Motion-JPEG to H.261 that runs in real-time on standard workstations. By making the Real-time Transport Protocol (RTP) an integral component of our architecture, the video gateway in...

Limiting the energy consumption of computers, especially portables, is becoming increasingly important. Thus, new energy-saving computer components and architectures have been and continue to be developed. Many architectural features have both high-performance and low-power modes, with the mode selection under software control. The problem is to minimize energy consumption while not significantly impacting the effective performance. We group the software control issues as follows: transition, load-change, and adaptation. The transition problem is deciding when to switch to low-power, reduced-functionality modes. The load-change problem is determining how to modify the load on a component so that it can make further use of its low-power modes. The adaptation problem is determining how to create software that allows components to be used in novel, power-saving ways. We survey implemented and proposed solutions to software energy management issues created by existing and suggested hardware innovations.

The emergence of powerful portable computers, along with advances in wireless communication technologies, has made mobile computing a reality. Among the applications that are finding their way to the market of mobile computingthose that involve data managementhold a prominent position. In the past few years, there has been a tremendous surge of research in the area of data management in mobile computing. This research has produced interesting results in areas such as data dissemination over limited bandwith channels, location-dependent querying of data, and advanced interfaces for mobile computers. This paper is an effort to survey these techniques and to classify this research in a few broad areas. Index Terms---Mobile computing, databases, data dissemination, bandwith, location-dependent queries, interfaces, transaction management. ------------------------------ ###p### ------------------------------ 1INTRODUCTION OBILE computing has become a reality thanks to the convergen...

By integrating wireless, video, speech and real-time data access technologies, a unique shopping assistant service can be created that personalizes the attention provided to a customer based on individual needs, without limiting his movement, or causing distractions for others in the shopping center. We have developed this idea into a service based on two products: a very high volume hand-held wireless communications device, the PSA (Personal Shopping Assistant), that the customer owns (or may be provided to a customer by the retailer), and a centralized server located in the shopping center to which the customer communicates using the PSA. The centralized server maintains the customer database, the store database and provides audio/visual responses to inquiries from tens to hundreds of customers in real-time over a small area wireless network. 1.

To meet the service demands created by the Internet's exponential growth, operators are scrambling to deploy application-level services, including Web caches, commerce servers, and intelligent transformation proxies for mobile "thin clients." On the one hand, the Internet's growth rate places unprecedented scalability and robustness demands on these services; on the other hand, that same growth rate demands that new services be developed, deployed, and evolved at a pace that is precipitous even by the standards of today's desktop software development cycles. We demonstrate that for a certain class of applications, these apparently conflicting goals can be reconciled by completely separating the application logic from the runtime support for scalability and high ...

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* An increasing number of applications execute over a set of computing and communication resources and have end-to-end quality of service (QoS) requirements. Given a system and an application with specific flow structure and QoS requirements, this paper describes an integrated QoS-based allocation and routing algorithm that determines which computing and communication resources to utilize for this application. More specifically, the algorithm finds the best flow path for an application, subject to application flow and QoS constraints, so as to optimize system objectives (e.g., minimize total system utilization or balance the load). The paper also introduces a-optimal algorithm that, relative to the optimal algorithm, significantly reduces the run-time of the algorithm with a minor degradation in the optimality of the solution. The-optimal algorithm is guaranteed to produce a result that is at most-units sub-optimal. The paper also analyzes the optimality and run time of the solution a...

Distributed multimedia systems require a resource management scheme that can support a large number of diverse applications and still provide timing guarantees to each application. An important component of the resource management scheme is an allocation and routing algorithm that determines which system resources to reserve for each application based on these two objectives. Unfortunately, most work on allocation and routing has ignored application timing requirements. Not only is there a need for an algorithm that addresses both objectives, but current trends towards network computer-based distributed intranets composed of high-powered computing, storage and communication resources require an integrated allocation and routing strategy to avoid local minimas [CS96a]. This paper describes an integrated allocation and routing algorithm that determines an optimal flow path (if any) that minimizes resource load (indirectly increases the number of applications the system can support) and m...

The rapid deployment of wireless access technology, along with the emergence of high speed integrated service networks, promises to provide users with ubiquitous access to multimedia information in the near future. We are building an experimental testbed system, SWAN (Seamless Wireless ATM Network), to mimic this emerging networking environment. Our wireless access network is organized according to a nanocellular design with base stations serving as a gateway for communication between the wired network and the mobile hosts in a cell. Normally, a mobile host sends and receives traffic through the base station in its current cell. But SWAN also supports direct ephemeral networking between a limited number of cooperating mobile hosts within a small domain. The heart of the testbed is a networking subsystem, FAWN (Flexible Adapter for Wireless Networking) that interfaces the standard PCMCIA bus to an RF modem. The FAWN interface is used with a PC or workstation connected to a wired backbone network or a portable device such as a laptop or palmtop computer. In addition, a user interface consisting of an LCD display, audio I/O, and a bar code reader has been built. When interfaced with FAWN this results in a portable wireless multimedia terminal. 1.

The architecture of a device that is optimized for wireless information access and display of multimedia data is substantially different than configurations designed for portable stand-alone operation. The requirements to reduce the weight and energy consumption are the same, but the availability of the wireless link, which is needed for the information access, allows utilization of remote resources. A limiting case is when the only computation that is provided in the portable terminal supports the wireless links or the I/O interfaces, and it is this extreme position that is explored in the InfoPad terminal design. The architecture of the InfoPad terminal, therefore, can be viewed as essentially a switch which connects multimedia data sources in the supporting wired network to appropriate InfoPad output devices (e.g., video display), and connects InfoPad input devices to remote processing (e.g., speech recognizer server) in the backbone network.