In recent years, technological advances and bandwidth availability have brought about a web of new multimedia and real-time applications, such as internet telephony, interactive TV, video-on-demand, and videoconferencing. These applications have important uses in a wide range of activities from education and health care to entertainment. Their full deployment will clearly have a huge impact on the quality of our lives and the society as a whole. Such applications, however, are very bandwidth demanding, very sensitive to congestion, and require real-time and reliable communication. Although appropriate protocols, such as the Asynchronous Transfer Mode (ATM) protocol and an enhanced version of Internet's TCP/IP protocol (with RSVP), already exist, Quality of Service (QoS) provisioning remains one of the fundamental open problems that need to be addressed before real-time applications can be reliably supported. If congestion is not an option, restricting the number of users that are allowed in the network becomes an extremely useful tool in guaranteeing QoS. The central goal of this research is to devise such an admission control procedure and test its performance in practice. To provide QoS guarantees the network should prevent congestion which causes packet losses due to buffer overflows and excessive delays. A worst case based admission control algorithm (which allocates to calls bandwidth equal to their peak rate) leads to significant underutilization of the network resources, since traffic is typically bursty, i.e., the peak rate is not sustained for long. To achieve more efficient use of the resources the proposed approach will permit some congestion phenomena which will be occurring infrequently enough to allow for the provision of statistical QoS guarantees. More specifically, it is desired to operate the network in a regime where loss probabilities and probabilities of excessive delays are particularly small (e.g., on the order of 10^{-6}). Real-time app lications can tolerate such small frequencies of congestion phenomena. This research will draw upon methods developed in applied probability, optimization, and optimal control theory, and will use, extending whenever necessary, many of the ideas developed recently by the PI. Calculating congestion probabilities for non-trivial traffic models is particularly hard. The proposed work will therefore resort to asymptotic results using large deviations theory (a subfield of applied probability) as the main analytical tool. Issues that are considered as prerequisites for successful admission control will be first resolved. Among them the proposed research will address: -Traffic Modeling. The aim is to propose models that capture the statistical properties of the traffic which are relevant to admission control. -Performance analysis. The goal is to asymptotically estimate congestion probabilities in a multiclass and multihop network environment. The final product of the proposed work will be an admission control algorithm that provides statistical QoS guarantees to admitted calls and possesses the following characteristics: -Support for multiple service classes. Applications will be bundled in service classes based on the statistical character of the traffic they generate and on their QoS requirements. -Full utilization of available bandwidth. The controller will be flexible enough to investigate different bandwidth allocation strategies among service classes and deny admission only when there is no feasible allocation that guarantees QoS to all connected calls. -End-to-End QoS guarantees. Real-time implementation. More information about this project can be obtained from the Web at http://ionia.bu.edu/
