Admission Control in High Speed Multimedia Networks

近年来，技术进步和带宽可用性带来了新的多媒体和实时应用的网络，如互联网电话、交互式电视、视频点播和视频会议。这些应用在从教育和医疗保健到娱乐的广泛活动中具有重要用途。 他们的全面部署显然将对我们的生活质量和整个社会产生巨大影响。 然而，这样的应用对带宽要求很高，对拥塞非常敏感，并且需要实时和可靠的通信。 虽然适当的协议，如异步传输模式（ATM）协议和互联网的TCP/IP协议的增强版本（与RSVP），已经存在，服务质量（QoS）供应仍然是一个基本的开放的问题，需要解决之前，实时应用程序可以可靠地支持。 如果拥塞不是一个选项，限制网络中允许的用户数量就成为保证QoS的一个非常有用的工具。本研究的中心目标是设计这样的准入控制程序，并在实践中测试其性能。 为了提供QoS保证，网络应该防止拥塞，这会导致由于缓冲区溢出和过度延迟而导致的分组丢失。 基于最坏情况的接纳控制算法（其向呼叫分配等于其峰值速率的带宽）导致网络资源的显著未充分利用，因为业务通常是突发的，即，峰值速率不会持续很长时间。为了实现更有效地利用资源，所提出的方法将允许一些拥塞现象，这将不经常发生，足以允许提供统计QoS保证。更具体地，期望在丢失概率和过度延迟的概率特别小的情况下操作网络（例如，约10^{-6}）。实时应用可以容忍这种小频率的拥塞现象。 这项研究将借鉴应用概率，优化和最优控制理论中开发的方法，并将使用，必要时扩展，PI最近开发的许多想法。计算非平凡交通模型的拥塞概率是特别困难的。 因此，拟议的工作将诉诸渐近结果使用大偏差理论（应用概率的一个子领域）作为主要的分析工具。 被认为是成功准入控制的先决条件的问题将首先得到解决。其中，拟议的研究将涉及： - 交通建模。 我们的目的是提出模型，捕捉相关的准入控制的流量的统计特性。 - 业绩分析。 目标是渐近估计拥塞概率在一个 多类和多跳网络环境。 所提出的工作的最终产品将是一个准入控制算法，提供统计QoS保证承认的呼叫，并具有以下特点：-支持多种服务类别。 应用程序将根据统计数据捆绑在服务类中， 它们生成的流量的特性以及它们的QoS要求。 - 充分利用可用带宽。 控制器将足够灵活，以调查不同的带宽 服务类之间的分配策略，并且仅当 不存在保证所有连接呼叫的QoS的可行分配。 - 端到端QoS保证。 实时执行。 有关此项目的更多信息，请访问 http://ionia.bu.edu/

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/