Faster processors are quickly enabling a new class of computationally intensive applications that actively transform information flows. Performing such computation at the terminal end is contrary to current trends toward low-power terminal devices. Moreover, scalability and efficiency concerns are also encouraging service providers to outsource computation when operating under loaded conditions. To address the problem of deploying such applications, we introduce the JOURNEY network model, which provides computation as an integrated network service. Contrary to other distributed computing models, JOURNEY does not attempt to guarantee that a given computational job will indeed be completed. Instead, the JOURNEY model trades off such hard guarantees in favor of architectural simplicity, and hence scalability. In order for the JOURNEY model to be applicable to real-time multimedia flows, we introduce the notion of soft quality-of-service (QoS) that provides a probabilistic bound on the unprocessed packet rate (UPR). Based on this notion, we describe a packet-processing admission control algorithm that additionally takes into consideration a flow's real-time constraints. We also propose a computing router architecture that is based on cluster technology. This architecture can track technology advances in both routing and computing independently. We further present a motivating multimedia application that employs a semantically driven video transcoding service within the JOURNEY framework we implemented, and describe our experience along with performance measurements.

A dynamic framework for quality-of-service (QoS) control of video in distributed multimedia applications is presented The framework allows flexible and efficient video delivery with application-level QoS support. Key components of the framework are: client QoS renegotiation, server source rate control and dynamic bandwidth allocation. The soft-QoS requirements of the application are communicated among the framework components using distributed software objects, called service contracts. A proof-of-concept prototype of a video browser with user-level control of soft-QoS is implemented within the proposed framework. Experiences with the prototype and its performance are discussed. Results suggest that the framework is particularly suitable for the mobile multimedia scenario allowing mobile applications to maintain soft-QoS while roaming without compromising network utilization.

We describe a mobile call admission control algorithm (M-CAC) for mobile multimedia terminals roaming within coverage areas consisting of multiple microcells. The method targets consistent soft-QoS for admitted connections with high utilization of radio resources, exploiting both temporal and spatial statistical multiplexing. We compare the performance of M-CAC to the performance of the default algorithm (all calls are accepted, provided there is enough bandwidth in the originating microcell). Results of our simulations demonstrate that a reasonably good connection-level soft-QoS can be achieved with moderate increase of cost of connections (determined by efficiency of bandwidth utilization).

A new service class, called VBR/sup +/ has been proposed for multimedia applications on ATM networks. VBR/sup +/ extends the functionality of the traditional VBR service with the added capability of dynamic resource renegotiation. It makes the specification and modification of the usage parameter controls flexible, and potentially can increase the network resource utilization through statistical multiplexing. These advantages come at the expense of a more complex connection admission controller which should be designed to handle bandwidth renegotiation efficiently. A connection admission controller for the VBR/sup +/ service class is proposed. We identify the desirable features of a VBR/sup +/ connection admission controller, and present a novel one that can achieve them through (1) dynamic resource partitioning, and (2) dynamic resource redistribution among active connections. Simulation results showing the performance of the controller using a number of actual video traces are presented. The results show that the controller is robust in admitting a variety of video sources with widely different traffic burstiness. By partitioning the resource pool dynamically, and distributing resources among contending connections fairly, it can maintain very good quality, and can achieve high utilization. Comparison with the traditional VBR service reveals that the CAC is able to provide comparable quality with higher network utilization.

This paper presents a medium access level VBR bandwidth allocation scheme for wireless ATM (WATM) networks. After introducing a wireless ATM system model and the associated dynamic TDMA/TDD medium access control (MAC) scheme, an algorithm for VBR slot allocation is proposed. The algorithm combines information from user parameter control (UPC) at the call admission control (CAC) level with rapid MAC level estimates of the requirements for each VBR virtual circuit (VC). The method described is applicable to both conventional VBR and VBR+ in which UPC parameters are dynamically renegotiated as source bit rate requirements vary. Simulation experiments using statistically multiplexed MPEG-1 video are carried out for a typical 25 Mbps dynamic TDMA/TDD wireless ATM access link scenario. Experimental results show that, for the VBR video under consideration, the proposed scheme can achieve throughputs in the range of 60-70% while maintaining reasonable QoS.

This paper accompanies a demonstration of a variable bit-rate (VBR) video server with scalable quality-of-service (QoS) control. Multimedia applications dynamically demand different QoS grades from servers and networks during a session. Since video is a critical component of distributed multimedia applications, video servers have to be responsive to the applications' requirements and to the availability of resources on heterogeneous terminals and networks. For this purpose a video server has to dynamically scale the source's quality in the control space formed by frame resolution, quantization and display rate. Experiences with a proof-of-concept implementation of a server with scalable QoS control show that it is able to jointly match the target quality of applications, the processing limitations of terminals and the capacity limitations of networks.

A scheme for delivery or variable bit-rate (VBR) video over asynchronous transfer mode (ATM) networks where bandwidth can be renegotiated during the duration of a call between the video source and the network is considered. Renegotiation can be initiated by either the video source or the network. The video bandwidth requirement is characterized by a usage parameter control (UPC) consisting, in general, of peak rate, burst length, and sustained rate. A baseline design is outlined where rate-control adjusts the source's rate while a new UPC is requested from the network. When granted, the new UPC allows the source to maintain its target quantization and delay requirements. Rate control epochs may be extended when the network blocks UPC requests or sets a lower UPC value to temporally deal with congestion. Simulation results are presented for VBR MPEG video. The results show that with a moderate renegotiation rate the scheme tracks the bandwidth requirements of the source. As a result, the video quality and bandwidth efficiency can be maintained.

A variable-bit-rate (VBR) MPEG video compression encoder is introduced, and the performance of a statistically multiplexed asynchronous transfer mode (ATM) network supporting a number of such VBR video sources is evaluated. Bit-rate characteristics obtained from a detailed simulation are provided for a VBR MPEG encoder for CCIR601 video (operating in the 5-10 Mb/s regime) appropriate for medium-quality multimedia or broadcasting applications. The results presented include bit-rate traces and signal-to-noise-ratio data for typical test sequences, along with summary statistics such as the marginal distribution of frame rate. Data from a study of statistical multiplexing on an ATM network are also given. Simulation results for an ATM statistical multiplexer with N>>1 VBR MPEG sources are presented in terms of key performance measures such as cell loss rate and delay versus throughput. The results confirm that ATM channel efficiencies of approximately 80-90% can be obtained at reasonable cell loss rate and delay levels.>