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

ATM网络提供各种类型的业务，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（未申报比特率）。ABR和UBR是一种质量不如CBR （Constant Bit Rate）和VBR （Variable Bit Rate）的业务，因为它们只能使用VBR和CBR留下的中继剩余带宽。由于带宽没有预先预留（除了可选的最小单元速率MCR），因此网络必须保护自己免受过量ABR和UBR输入流量引起的拥塞。在UBR中，多余的流量在过载的节点上被丢弃。在ABR中，网络使用反馈控制机制来防止拥塞。即调节每个ABR源的输入速率，使其与路径上的可用带宽相匹配。本研究的重点将是反馈速率控制机制，称为E-PRCA（增强型比例速率控制算法）及其特性和应用。E-PRCA已在许多版本中实现。大多数实现都收敛到稳定状态，并在竞争的ABR连接之间提供公平的带宽共享。然而，很少有实现可以防止或至少防止绑定单元丢失。由于ABR是“尽力而为的服务”，因此没有向客户承诺蜂窝丢失保证，因此通常忽略了这个蜂窝丢失问题。然而，仔细观察就会发现，限制并尽可能防止ABR细胞损失是有益的，因为：(a)更高层的协议，如TCP，会受到细胞损失的影响；(b)在多播连接中，应用级的损失恢复代价高昂；以及(c) ABR正成为多媒体应用的一个有吸引力的选择（以取代VBR），这些应用可容忍自适应的速率调节。在这个项目中，我们提出了四个任务：ABR控制与细胞损失预防/边界：起点将是SP-EPRCA方案，这是一个基于Smith预测器的速率控制方案，由本研究者和他的合作者开发。SP-EPRCA预防细胞损失的初步性质和界已经建立。我们计划在其他流行的ABR速率控制方案（如ERICA）中探索cell loss bounds的可行性。我们将评估各种实现的性能（通过分析和模拟），得出针对各种网络和流量场景的关键参数（缓冲区分配、吞吐量、稳定性、公平性、响应性等）之间的权衡。实现的复杂性也将被评估。ABR组播：我们计划将E-PRCA控制扩展到组播连接。同样，起点将是最近为SP-EPRCA提出的实施方案。主要的焦点将是防止单元丢失，这在这里是至关重要的，因为数据多播应用程序不受TCP错误和丢失恢复的保护。ABR连接路由：我们将研究ABR连接的最优路由问题，该问题受限于具有小区损失边界的速率控制。小区损失边界使得这个问题比仅仅寻找具有期望的公平共享带宽的最短路径路由更复杂。我们将探索单播和组播路由，依赖于后者的有效启发式。应用：我们将在包括TCP/IP支持在内的几个应用中评估ABR单元丢失预防和路由的好处。我们还将酌情比较ABR与UBR或VBR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.