Guaranteeing Hard Real-Time Deadlines in FDDI Networks

成功使用分布式系统的关键是 硬实时应用程序是及时执行 计算任务通常驻留在不同的节点上， 为了实现共同的目标而互相沟通。 如果没有一个完整的解决方案， 支持及时交付的通信网络 任务间消息。研究的主要重点是解决 与保证同步消息期限有关的问题， 也就是说，无论发生什么情况（网络故障除外）， 信息将在截止日期之前发送。 我们有 选择FDDI（光纤分布式数据接口）网络， 这项研究，因为他们非常适合硬实时 通信，不仅由于其高带宽，而且由于 他们的属性有界令牌旋转时间。 但 有界令牌旋转时间本身不足以保证 实时截止日期。同步容量分配是 在实现这一业绩目标方面同样至关重要。 在 在这个项目中，我们专注于设计和分析 同步容量分配以保证消息的截止期限。 该项目包括四个相关的任务：我们首先解决 最优性的问题。一个最优方案达到最高 最坏情况下的利用率，因此提供了最佳机会， 保证一组同步消息。然后，我们研究 局部分配方案使用局部信息， 为节点分配同步容量。 他们有优势 能够调整一个节点上的参数， 干扰他人的业务。 接下来，我们将扩展我们的 考虑实际需要的变化的基本模型。 为 例如，某些应用程序不需要绝对的截止日期 保证，即，偶尔错过最后期限是可以接受的。 我们在设计和分析中将这些想法形式化， 分配方案，以提高其适用性。 TTRT（目标令牌循环时间）的选择也会影响 保证最后期限的机会;这是作为解决 项目的最后一项任务。

The key to the success in using a distributed system for hard real-time applications is the timely execution of computation tasks which usually reside on different nodes and communicate with one another to accomplish a common goal. End-to-end deadline guarantees are not possible without a communication network which supports the timely delivery of intertask messages. The main focus of the research is to address issues related to guaranteeing synchronous message deadlines, i.e., no matter what happens (except a network failure), the messages will be transmitted before their deadlines. We have selected FDDI (Fiber Distributed Data Interface) networks for this study because they are well suited for hard real-time communications, due not only to their high bandwidth, but also to their property of bounded token rotation time. However, a bounded token rotation time alone is not sufficient to guarantee hard real-time deadlines. Synchronous capacity allocation is equally critical in achieving this performance objective. In this project, we concentrate on design and analysis of synchronous capacity allocation to guarantee message deadlines. The project consists of four related tasks: We first address the issue of optimality. An optimal scheme achieves the highest worst case utilization and hence offers the best chance to guarantee a set of synchronous messages. Then, we study localized allocation schemes which use local information to allocate synchronous capacity to a node. They have the advantage of being able to adjust the parameters on one node without disturbing the operations of others. Next, we will extend our basic model to consider variations needed in practice. For example, some applications do not require an absolute deadline guarantee, i.e., occasionally missing a deadline is acceptable. We formalize these ideas in the design and analysis of allocations schemes in order to improve their applicability. Selection of TTRT (Target Token Rotation Time) also affects the chance of guaranteeing deadlines; this is addressed as the last task in the project.