Absrrucr-The congestion control mechanisms used in TCP have been the focus of numerous studies and have undergone a number of enhancements. However, even with these enhancements, TCP connections still experience alarmingly high loss rates, especially during times of congestion. To alleviate this problem, the IETF is considering active queue management mechanisms, such as RED, for deployment in the network. In this paper, we first show that the effectiveness of RED depends, to a large extent, on the appropriate parameterization of the RED queue. We then show that there is no single set of RED parameters that work well under different congestion scenarios. In light of this observation, we propose and experiment with more a d a p tive RED gateways which self-parameterize themselves based on the traffic mix. Our results show that traffic cognizant parameterization of RED gateways can effectively reduce packet loss while maintaining high link utilizations under a range of network loads.KqwordsCongestion control, Internet, TCP, RED, queue management.

The Internet today provides no support for privacy or authentication of multicast packet. However, an increasing number of applications will require secure multicast senices in order to restrict group membership and enforce accountability of group members. A major problem associated with the deployment of secure multicast delivery services is the scalability of the key distribution protocoL This is particularly true with regard to the handling of group membership changes, such as member departures and/or expulsions, which necessitate the distribution of a new session key to all the remaining group members.As the frequency of group membership changes increases, it becomes necessary to reduce the cost of key distribution operations. This paper explores the use of batching of group membership changes to reduce the frequency, and hence the cost, of key redistribution operations. It focuses explicitly on the problem of cumulnrive member removal and present an algorithm that minimizes the number of messages required to distribute new keys to the remaining group members. The algorithmis used in conjunction with a new multicast key management scheme which uses a set of auxiliary keys in order to improve scalability. In contrast to previous schemes which generate a fixed hierarchy of keys, the proposed scheme dynamically generates the most suitable key hierarchy by composing different keys. Our cumulative member removal algorithm uses Boolean function minimization techniques, and outperforms all other schemes known to us in terms of message complexity.

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In a video-on~rnand (VOD) system, it is desirable to provide the user with interactive browsing firnctions such as "fast forward" and "fast backward." However, these functions usualty require a significant amount of additional resources ti'om the VOD system in terms of storage space, retrieval throughput, network bandwidth, etc. Moreover, prevalent video compression techniques such as MPEG impose additional constraints on the process since they introduce inter-frame dependencies. In this paper, wc devise metlmds to support variable rate browsing for MPEG-like video stmarns and minimize the additional resources required. Specifically, we consider retrieval for a disk-array-based video server and address the problem of distributing the retrieval requests across the disks.Our overall approach for interactive browsing comprises (1) a storage method, (2) placement and sampling methods, and (3) a playout method, where the placement and sampling methods are two alternatives for video segment selcdon. 'llte segment sampling scheme supporta browsing at any desired speed, while minimizing the variation on the number of video segments skipped between samplings.On the other hand, the segment placement scheme supports completely uniform segment sampling across the disk array for some specific speedup rates. Experiments for the visual effect of the proposed segment skipping approach have been conducted on MPEG data. It is shown that the proposed method is a viable approach to video browsing.

Multimedia storage servers provide access to multimedia objects including text, images, audio, and video. The design of such servers fundamentally di ers from conventional servers due to: 1 the real-time storage and retrieval requirements, as well as 2 the large storage space and data transfer rate requirements of digital multimedia. In this paper, we present an overview of the architectures and algorithms required for designing digital multimedia storage servers.