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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