Dilip D. Kandlur

A self-configuring RED gateway

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 random early detection (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 adaptive RED gateways which self-parameterize themselves based on the traffic mix. The 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.

The BLUE active queue management algorithms

In order to stem the increasing packet loss rates caused by an exponential increase in network traffic, the ietf has been considering the deployment of active queue management techniques such as Red [14]. While active queue management can potentially reduce packet loss rates in the Internet, we show that current techniques are ineffective in preventing high loss rates. The inherent problem with these queue management algorithms is that they use queue lengths as the indicator of the severity of congestion. In light of this observation, a fundamentally different active queue management algorithm, called Blue, is proposed, implemented, and evaluated. Blue uses packet loss and link idle events to manage congestion. Using both simulation and controlled experiments, Blue is shown to perform significantly better than Red, both in terms of packet loss rates and buffer size requirements in the network. As an extension to Blue, a novel technique based on Bloom filters [2] is described for enforcing fairness among a large number of flows. In particular, we propose and evaluate Stochastic Fair Blue (SFB), a queue management algorithm which can identify and rate-limit nonresponsive flows using a very small amount of state information.

Stochastic fair blue: a queue management algorithm for enforcing fairness

This paper describes and evaluates stochastic fair blue (SFB), a novel technique for enforcing fairness among a large number of rows. SFB scalably detects and rate-limits non-responsive flows through the use of a marking probability derived from the blue queue management algorithm and a Bloom (1970) filter. Using analysis and simulation, SFB is shown to effectively handle non-responsive flows using an extremely small amount of state information.

Key management for secure lnternet multicast using Boolean function minimization techniques

The Internet provides no support for privacy or authentication of multicast packets. However, an increasing number of applications require secure multicast services 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 re-distribution operations. It focuses explicitly on the problem of cumulative member removal and presents an algorithm that minimizes the number of messages required to distribute new keys to the remaining group members. The algorithm is 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.

Optimization of the grouped sweeping scheduling (GSS) with heterogeneous multimedia streams

Grouped Sweeping Scheduling was proposed in [1] as a general formulation of a class of disk arm scheduling schemes. This class includes, for example, the fixed-order and SCAN scheduling schemes. An optimum design was presented for the homogeneous case, i.e., when all multimedia streams have the same characteristics. In this paper we examine the more general situation in which a mixture of different format multimedia streams, with different characteristics, coexist on the disk. The emphasis is to present and prove a simple procedure for optimizing GSS in this heterogeneous situation. Finally, we discuss how GSS can be used in dynamic settings to support heterogeneous request streams.

Grouped sweeping scheduling for DASD-based multimedia storage management

This paper presents a new formulation of DASD (direct access storage device) disk arm scheduling schemes for multimedia storage management. The formulation, referred to as grouped sweeping scheduling (GSS), provides a framework for minimizing the buffer space required in the retrieval of multimedia streams. In GSS, the set ofn media streams that are to be served concurrently is divided intog groups. Groups are served in fixed order and streams within each group are served in an elevator-like SCAN scheme. Hence, the fixed order (FIFO) and SCAN schemes are special cases of GSS wheng=n andg=1, respectively. In this paper an optimization problem is formulated in which the buffer requirement is minimized with respect to the two design parameters:g and the size of the service unit, i.e. the number of blocks accessed in each service cycle. This formulation initially assumes that all media streams have the same playout requirements. A procedure of complexityO(1) is developed in computing the optimum solution to this problem. The proof of optimality and comparisons between the optimized GSS scheme and FIFO and SCAN are also presented. The paper also discusses the effect of disk arrays in the GSS formulation and issues related to operating GSS in a dynamic setting where streams arrive and depart in random order. Finally, the GSS scheme is extended to support heterogeneous media streams where each stream may have its own playout requirement.

Design and analysis of a grouped sweeping scheme for multimedia storage management

This paper presents an efficient grouped sweeping scheme (GSS) for disk scheduling to support multimedia applications. The GSS scheme provides a formulation for balancing the two conflicting requirements: on the one hand we want to reduce the amount of seek delay, while on the other hand the worst case bound on the time between two consecutive services to the same request stream needs to be minimized. The GSS approach leads to a general formulation covering a family of disk scheduling schemes. Two previously proposed approaches, a fixed order round-robin scheme and a more sophisticated elevator type scheme, are special cases of the GSS formulation. Our analysis shows that by properly setting the grouping factor the optimized GSS scheme can lead to substantially lower buffer requirement, particularly when compared with that of the round-robin scheme. We develop an efficient procedure to determine the optimum value of the grouping factor. We also incorporate the effect of disk arrays in the GSS formulation and discuss how GSS can be used in dynamic settings such as to provide interactive service in an integrated media environment.

Support for fully interactive playout in disk-array-based video server

In a video-on-demand (VOD) system, it is desirable to provide the user with interactive browsing functions such as “fast forward” and “fast backward.” However, these functions usually require a significant amount of additional resources from 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, we devise methods to support variable rate browsing for MPEG-like video steams 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 selection. The segment sampling scheme supports 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.

Understanding and improving TCP performance over networks with minimum rate guarantees

A large number of Internet applications are sensitive to overload conditions in the network. While these applications have been designed to adapt somewhat to the varying conditions in the Internet, they can benefit greatly from an increased level of predictability in network services. We propose minor extensions to the packet queueing and discard mechanisms used in routers, coupled with simple control mechanisms at the source that enable the network to guarantee minimal levels of throughput to different sessions while sharing the residual network capacity in a cooperative manner. The service realized by the proposed mechanisms is an interpretation of the controlled-load service being standardized by the Internet Engineering Task Force. Although controlled-load service can be used in conjunction with any transport protocol, our focus in this paper is on understanding its interaction with Transmission Control Protocol (TCP). Specifically, we study the dynamics of TCP traffic in an integrated services network that simultaneously supports both best-effort and controlled-load sessions. In light of this study, we propose and experiment with modifications to TCPs congestion control mechanisms in order to improve its performance in networks where a minimum transmission rate is guaranteed. We then investigate the effect of network transients, such as changes in traffic load and in service levels, on the performance of controlled-load as well as best-effort connections. To capture the evolution of integrated services in the Internet, we also consider situations where only a selective set of routers are capable of providing service differentiation between best-effort and controlled-load traffic. Finally, we show how the service mechanisms proposed here can be embedded within other packet and link scheduling frameworks in a fully evolved integrated services Internet.

A multimedia desktop collaboration system

Desktop multimedia conferencing, which can enhance the quality of collaboration between remote participants, is considered. The architectural and implementation issues involved in the design of such an application are discussed. A prototype desktop conferencing system is presented. It provides a multiparty collaborative environment which integrates high-quality video and audio with a shared workspace manager. Some of the distinguishing features of this system are the flexibility to support various types of collaboration, full-motion (30-frames/s) video, support for multiple video windows, and unconstrained audio. The shared workspace manager allows existing X-windows applications to be used concurrently by the participants in the conference.<<ETX>>