ITR: Active Queue Management for Scalable Network Services: Theory and Internet Practice

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Two of the largest issues facing the Internet today are the problems of (1) providing quality-of-service to applications that require some form of "guarantee" of bandwidth availability and/or end-to-end delay, and (2) the problem of avoiding congestion between traditional best-effort flows. Packet scheduling has been the mechanism traditionally used for quality-of-service guarantees while end-system adaptations in the transport layer have been the dominant form of congestion control. Typically, the problems of congestion control and quality-of-service have been addressed as largely independent concerns and separate mechanisms have been developed for each . The essence of this project is to study the interplay between congestion control and quality-of-service and the mechanisms that have been employed for realizing each. The starting point is an investigation of using active queue management(AQM) techniques in network routers to provide both congestion control and quality-of-service for IP flows. Active queue management refers to the practice of manipulating the queue of packets at an outbound network interface on a router to bias the performance of network flows. For example, discarding packets from the queue is an active queue management mechanism that is used in the RED (random early detection) congestion avoidance mechanism. There does not yet exist any fundamental theoretical understanding of how individual AQM mechanisms effect the performance of network flows. From the perspective of Internet service providers this problem is compounded by the fact that there is little, if any, understanding of how AQM mechanisms can be tuned to realize specific performance goals. The impact of AQM mechanisms on broader measures of network performance is unknown because a framework for analyzing AQM performance does not yet exist. This is in contrast to other approaches for quality-of-service such as packet scheduling. Packet schedulers have been carefully analyzed and frameworks exist for computing bounds on performance metrics such as delay, delay-jitter, packet loss, etc. The main goal of this project is to develop the theoretical underpinnings and engineering principles to guide the construction and deployment of AQM for the Internet. This requires an analytic and empirical study of AQM mechanisms for the purpose of understanding the costs, benefits, and scalability limitations of using AQM for congestion control and quality-of-service. The project also contributes to the overall understanding of principles of resource management in routers. In addition, novel AQM schemes that provide new, scalable solutions for quality of service and congestion control are developed.Specific objectives include the following: 1. Develop an analysis framework for understanding the performance of AQM mechanisms. A novel aspect is consideration of both network-centric performance metrics such as link utilization, and end-systemor user-centric measures such as response time. 2. Develop and analyze novel AQM and hybrid AQM-packet scheduling schemes that realize a spectrum of quality-of-service and congestion control services. A key contribution here is a demonstration of the costsand benefits of using packet scheduling v. AQM for scalable implementations of services. 3. Demonstrate the effectiveness of the AQM schemes through a case study in managing a research network and supporting an advanced, real-time, distributed-virtual-environment application. The results of this project can have a significant impact on the evolution of the Internet to support new levels of service quality and control congestion while ensuring scalability for very large numbers of users and devices.