Due to the characteristics of wireless channels, utility-based resource management in wireless networks requires a set of mechanisms that are different from those for wireline networks. This paper explores in detail why and how the requirements are different. In particular, we analyze the wireless network performance to find out the scheduling algorithm that maximizes total utility of the system. Unlike previous studies, this paper focuses on scenarios in which wireless networks are not fully loaded and all of the users are best-effort data users, i.e., there is no streaming user. Our first key conclusion is that Kleinrock's Conservation Law provides a valuable means to accurately capture the perceived rates of best-effort users in such systems. The queueing analysis further indicates that, within periods during which channel conditions are stable for each user, albeit differ from user to user, the max-utility scheduling algorithm can be derived using queueing theorem and can be readily implemented in actual systems for utility functions that are of exponential or log format. When further taking into account the time-variant nature of wireless channel conditions, our simulation results demonstrate that dynamic weighted fair queueing, with weights adjusted according to the channel conditions, can achieve highly desirable performance with great flexibility.

We propose a new mobile computing paradigm, in which an intelligent card (called an iCard) plugged into a mobile device serves as the centerpiece that provides enhanced networking and application capabilities to the mobile host. Placed between a mobile host and traditional network interfaces, iCard is device independent, easy to program, and offers enhanced security. This paper describes the overall concept of iCard, and the key elements in its hardware and software architecture. The hardware discussions focus on a particular design that we have put together for an actual prototype iCard. We share with readers the rationales behind various choices made in this design. On the software side, we have been developing application programs to be loaded onto the iCard using a StrongARM reference board. To demonstrate the strong potential of the new paradigm represented by iCard, we show how iCard is able to provide mobile IP functions without making any modifications to the host machines.

Wireless data networks will have a mix of user workloads since there will be a variety of wireless data terminal devices. Using computer simulation, we study the performance of an EDGE-based packet wireless network with various combinations of Web and dataphone users. We provide an understanding of the performance of a shared channel with mixed user workloads, and show that the number of users that can be supported can be determined using simple rules based on average traffic statistics.

In this paper, we analyze the performance of proxy functions for controlling the quality of service in wireless networks, where the proxy performs aggressive content reduction as a means to throttle traffic when the radio link is congested. The proxy may be located at different parts of the network, thus affecting the feedback delay from the base station to the proxy. A queueing model is constructed and solved to study the performance tradeoffs among system parameters and in particular, how the proxy performance is affected by the feedback control delay between base stations and the proxy. Using image compression as an example, we examine response time and fraction of compression as a function of the control delay. Our results reveal that the proxy function can effectively control response time in the case of link congestion, if the delay is reasonably small, e.g. when the proxy is located close to the radio link. We also find that to assess the effectiveness of the control mechanism, it is necessary to examine whether the proxy performs content reduction when and only when link congestion occurs. Towards this end, we study the system-state probabilities and the correlation between response time and compression.

We devise an integrated wireless network architecture using proxy servers to support mobility management. The technique takes advantage of the existing functionalities of proxy servers to provide mobility support for applications such as Web browsing and ftp, without modifying the IP protocol stack of the mobile host. The architecture uses proxy servers to force all packets originating from mobile hosts to a close-by mobility-aware router so that the latter can maintain active data connections during handoffs across different networks. By deploying multiple proxy and mobility-aware router pairs and by assigning mobile hosts to proxy servers dynamically, the proposed architecture provides efficient mobility management functionalities, and is inherently scalable.

Using analysis and simulation, we study the performance of Web-browsing and interactive data applications as perceived by the users of shared packet access networks. We use end-to-end page delays to characterise the user experience, and introduce a measure called equivalent circuit rate (ECR). The ECR for a user of a shared packet access network is the dedicated access circuit bit rate required to achieve the same user experience. Our analysis uses a simple closed queueing network model. The theoretical results agree well with simulations of TCP-based Web browsing workloads sharing an HFC cable data channel. We show that the mean page delay, ECR, and the number of users that can be supported are described using simple parameters that scale very well for different user and network rates. Our work also provides an effective comparison of shared and dedicated access at the application level.

Abstract Performance enhancing proxies have drawn considerable interests from the network community as an effective approach to improve user experience in cellular networks. Previous research on this subject has been focusing on the design of proxy servers as well as the functions that these servers provide. In this paper, we study the placement of proxy servers, especially the approach of incorporating proxies into cellular networks, which allows better, faster, and more secure proxy services. We discuss various factors that must be considered when placing proxies inside cellular networks, including the information requirements of the proxies, the network requirements for supporting the proxy functions, and mobility management. Using GPRS as an example, we lay out a procedure for adding proxies into data transmission paths in cellular networks. Copyright © 2001 John Wiley & Sons, Ltd.

We investigate the ability of multiple descriptions (MD) and layered coding to improve the quality of video transmitted over EGPRS networks. One-layer video sent over a single channel on such a network has a fairly sharp quality transition, depending on a user's location. Either the video can be transmitted reliably (if the video rate is less than or equal to what the channel can sustain), or it is subjected to many lost packets. In this system, MD and layered video may offer two ways to improve the video quality beyond that of the one-layer video. First, each sub-stream can be sent on a separate channel, essentially doubling the assigned bandwidth and increasing the video quality. Second, MD and layered video are more error resilient than one-layer video, potentially improving the video quality seen by users in poor locations. We find that for the system scenarios considered, one and two-layer coding outperform MD coding, depending upon the number of wireless channels used for the video transport.

This paper evaluates the use of packet scheduling to provide multiple service classes for bursty data traffic. In particular, we study the performance of the weighted fair queueing algorithm by simulating various scenarios in a packet cellular wireless network similar to an EDGE (Enhanced data rate for GSM evolution) system. The results show that, due to the burstiness of data traffic, traditional work-conserving packet scheduling algorithms such as weighted fair queueing cannot achieve the desired performance unless the system is heavily loaded. Similar results hold even when using priority queueing, which is an extreme form of weighted fair queueing. We also find that best effort traffic should be managed carefully to avoid inefficient usage of the network, especially in a low capacity cellular environment.

Performance enhancing proxies have drawn considerable interests from the network community as an effective approach to improve user experience in cellular networks. Previous research on this subject has been focusing on the design of proxy servers as well as the functions that these servers provide. We study the placement of proxy servers, especially the approach of incorporating proxies into cellular networks, which allows better, faster, and more secure proxy services. We discuss various factors that must be considered when placing proxies inside cellular networks, including the information requirements of the proxies, the network requirements for supporting the proxy functions, and mobility management. Using GPRS as an example, we lay out a procedure for adding proxies into data transmission path in cellular networks.

Video smoothing is a promising technique for reducing the bandwidth variability of video in order to improve network efficiency. This paper presents a general optimal video smoothing algorithm based on the concept of dynamic programming. The algorithm generates the optimum transmission schedule for different requirements by setting the constraints and the cost function accordingly. It can be used to study the smoothing of both stored video and real time video. In particular, for stored video, we show how the number of rate changes in the smoothed video is affected by the renegotiation cost and buffer size, assuming that the transmission rate is allowed to be lower than the reserved rate. For the real time system, we study the impact of various system parameters, including playout delay, client buffer site, and server buffer size, on the performance of video smoothing.

In this paper, we present an adaptive prefetch scheme for network use, in which we download files that will very likely be requested in the near future, based on the user access history and the network conditions. Our prefetch scheme consists of two parts: a prediction module and a threshold module. In the prediction module, we estimate the probability with which each file will be requested in the near future. In the threshold module, we compute the prefetch threshold for each related server, the idea being that the access probability is compared to the prefetch threshold. An important contribution of this paper is that we derive a formula for the prefetch threshold to determine its value dynamically based on system load, capacity, and the cost of time and system resources to the user. We also show that by prefetching those files whose access probability is greater than or equal to its server's prefetch threshold, a lower average cost can always be achieved. As an example, we present a prediction algorithm for web browsing. Simulations of this prediction algorithm show that, by using access information from the client, we can achieve high successful prediction rates, while using that from the server generally results in more hits.

In this paper, we study prefetch techniques in the WWW, in which we predict which files will be needed in the near future and download some of them before they are requested by the user. Our prefetch scheme includes two algorithms: the prediction algorithm and the threshold algorithm. The prediction algorithm estimates the probability with which each file will be requested in the near future. The threshold algorithm computes the prefetch threshold for each server. An important contribution of this paper is a formula we derived to determine the prefetch threshold dynamically based on the system load capacity and the cost of time and system resources to the user. Simulations driven by trace files show that using access information from the client can achieve high successful prediction rates, while using that from the server can result in more hits in general. We have also developed a prefetch program at the client site which assists users in browsing faster and more efficiently.