ATM Rate Based Congestion Control and Routing with Cell LossPrevention/Bounds

ATM网络提供各种类型的服务，具有不同级别的QoS保证。两种越来越重要的服务是ABR（可用比特率）和UBR（未声明比特率）。ABR和UBR是比CBR（恒定比特率）和VBR（可变比特率）质量差的服务，因为它们只能使用剩余的干线带宽（由VBR和CBR留下的）。由于带宽不是预先预留的（除了可选的最小信元速率MCR），网络必须保护自己免受过多ABR和UBR输入业务引起的拥塞。在UBR中，多余的流量在过载的节点处被简单地丢弃。在ABR中，网络使用反馈控制机制来防止拥塞。本文主要研究反馈速率控制机制E-PRCA（EnhancedProportionalRateControlAlgorithm）的性能和应用，E-PRCA已经有了很多版本。大多数实现收敛到稳定状态，并在竞争的ABR连接之间提供公平的带宽共享。然而，很少有实现防止或至少限制信元丢失。通常，这个信元丢失问题被忽视，因为ABR是“尽力服务”，因此没有向客户承诺信元丢失保证。然而，更仔细的观察揭示了限制并且如果可能的话防止ABR信元丢失是有益的，因为：（a）诸如TCP的高层协议受到信元丢失的影响;（B）在多播连接中，在应用级的丢失恢复是昂贵的;以及（c）ABR正在成为容忍自适应速率调节的多媒体应用的（VBR的）有吸引力的替代方案。在本项目中，我们提出了四个任务：具有信元丢失预防/边界的ABR控制：起点将是SP-EPRCA方案，一种基于Smith预测器的速率控制方案，由本研究者及其合作者开发。已经为SP-EPRCA建立了细胞损失预防和界限的初步性质。我们计划在其他流行的ABR速率控制方案（例如，埃里卡）。我们将评估各种实现的性能（通过分析和模拟），得出关键参数（缓冲区分配，吞吐量，稳定性，公平性，响应能力等）之间的权衡，为各种网络和流量场景。ABR多播：我们计划将E-PRCA控制扩展到多播连接。同样，起点将是最近为SP-EPRCA提出的一项执行工作。主要的重点将是细胞丢失的预防，这是至关重要的，因为数据组播应用程序不受TCP错误和丢失recovery.ABR连接路由的保护：我们将攻击的问题，最佳路由ABR连接受到速率控制与细胞丢失的界限。信元丢失边界使得这个问题比仅仅找到具有期望的公平共享带宽的最短路径路由更复杂。我们将探讨单播和组播路由，后者依赖于有效的路由。应用：我们将评估ABR信元丢失预防和路由在包括TCP/IP支持在内的几个应用中的好处。我们还将比较ABR与UBR或VBR（视情况而定）的效率。

The ATM network offers various types of services, with different levels of QoS guarantees. Two services which are gaining increasing importance are ABR (Available Bit Rate) and UBR (Undeclared Bit Rate). ABR and UBR are services of lesser quality than CBR (Constant Bit Rate) and VBR (Variable Bit Rate) in that they can use only the residual trunk bandwidth (left over by VBR and CBR). Since bandwidth is not reserved in advance (except for an optional Min Cell Rate, MCR), the network must protect itself from congestion caused by excess ABR and UBR input traffic. In UBR, excess traffic is simply discarded at overloaded nodes. In ABR, the network prevents congestion using a feedback control mechanism. Namely, the input rate of each ABR source is regulated so as to match the available bandwidth on the path. The main focus of this research will be the feedback rate control mechanism, called E-PRCA (Enhanced Proportional Rate Control Algorithm) and its properties and applications.E-PRCA has been implemented in many versions. Most implementations converge to steady state and provide fair bandwidth sharing among competing ABR connections. However, few implementations prevent, or at least bound cell loss. Often, this cell loss problem is overlooked since ABR is "a best effort service" and thus the customer was not promised cell loss guarantees. However, a closer look reveals that it is beneficial to limit and if possible prevent ABR cell loss because: (a) Higher layer protocols, such as TCP, are impacted by cell loss; (b) In multicast connections, loss recovery at the application level is costly; and (c) ABR is becoming an attractive alternative (to VBR) for multimedia applications which tolerate adaptive rate regulation.In this project, we propose four tasks:ABR control with cell loss prevention/bounds: Starting point will be the SP-EPRCA scheme, a rate control scheme based on Smith Predictor and developed by this Investigator and his collaborator. Preliminary properties of cell loss prevention and bounds were already established for SP-EPRCA. We plan to explore the feasibility of cell loss bounds in other popular ABR rate control schemes (e.g., ERICA). We will evaluate the performance of various implementations (via analysis and simulations), deriving tradeoffs between key parameters (buffer allocation, throughput, stability, fairness, responsiveness, etc) for various network and traffic scenarios. Implementation complexity will also be evaluated.ABR multicast : We plan to extend the E-PRCA control to multicast connections. Again, starting point will be an implementation recently proposed for SP-EPRCA. The main focus will be cell loss prevention, which is critical here since data multicast applications are not protected by TCP error and loss recovery.ABR connection routing: We will attack the problem of optimally routing ABR connections subject to rate control with cell loss bound. Cell loss bounds make this problem more complex than merely finding the shortest path route with desired fair share bandwidth. We will explore both unicast and multicast routing, relying on efficient heuristics for the latter. Applications: We will evaluate the benefits of ABR cell loss prevention and routing in several applications including TCP/IP support. We will also compare the efficiency of ABR vs UBR or VBR as appropriate.