Self-Stabilizing Group Communication for Mobile Environments

组通信服务是动态分布式系统中应用的重要组成部分，在动态分布式系统中，处理器和通信链路可以重复地发生故障和恢复，这种动态行为特别适用于移动的环境，在这种环境中，处理器可以不断地改变它们的物理位置。群通信设施的主要特点是：（1）向每个处理机指出它当前可以与哪些其它处理机通信;（2）使群内的处理机以有序和可靠的方式相互通信。开发容错软件的一种典型方法是对故障部件的行为进行一定的限制。然而，在现实中，有一个非零的概率，任何这样的假设将暂时违反;事实上，这种概率随着时间的推移而增长。特别地，移动的通信网络暴露于其水平难以提前预测的环境噪声。因此，通过假设系统最初是一致的并且每个后续步骤都保持一致性来接近正确性可能过于乐观。自稳定算法示波器，以优雅的方式处理临时故障。自稳定算法可以在任何全局状态下启动，由于故障的任意组合可以达到该全局状态，并且总是确保实现算法的任务，假设设计师的假设保持足够长的时间间隔。这项研究的目标是设计自我-稳定组通信业务，并将这些业务应用到移动的网络中。组服务，在这种服务中，新组的建立确保了与以前的化身有关的消息被丢弃。各种同步假设将被考虑，以确定必要和充分条件，指定的初始化组服务。一种方法是使用瞬态故障检测器，当检测到不一致时，该检测器将触发建立一个新组。不可能的结果将被开发，以表明哪些系统配置是必要的，下界的结果将被证明揭示的程度上的最优的解决方案获得。研究的第二部分将研究不同的移动的应用程序如何利用开发的自稳定组通信服务。第三部分的研究将探讨组通信服务之间的相互作用和其他，较低的水平，移动的services.Group通信服务已被纳入几个现有的学术和工业trialdistributed系统。然而，它们中没有一个是自稳定的，也没有一个是专门为移动的环境定制的。自稳定和群组通信是动态通信网络特别是无线网络设计的重要范例，本项目所提出的新方法无疑将有助于未来实现鲁棒的群组通信系统。

Group communication services form important building blocks for applications in dynamicdistributed systems, where processors and communication links can repeatedly fail and recover.Such dynamic behavior is especially descriptive of mobile environments, in which processors canchange their physical location continually. The key features of a group communication facility are(1) indicating to each processor with which other processors it can currently communicate, and (2)letting processors within a group communicate with each other in an ordered and reliable manner.A typical approach to developing fault-tolerant software is to assume certain limitations on thebehavior of faulty components. However, in reality there is a non-zero probability that any suchassumptions will be temporarily violated; in fact, this probability grows with time. In particular,mobile communication networks are exposed to environmental noise whose level is hard to predictin advance. Thus, it may be too optimistic to approach correctness by assuming that the systemis consistent initially and each subsequent step maintains consistency. Self-stabilizing algorithmscope with temporary faults in an elegant way. A self-stabilizing algorithm can be started in anyglobal state, which could be reached due to an arbitrary combination of failures, and always en-suresthat the task of the algorithm is achieved, assuming that the designer's assumptions hold forsufficiently long intervals.The goal of this research is to design self-stabilizing group communication services and applythese services to mobile networks.One part of the research will focus on the specification and design of initialized group services,in which the establishment of a new group ensures that messages related to previous incarnationsare discarded. Various synchrony assumptions will be considered in order to identify the necessaryand sufficient conditions for the specified initialized group services. One approach to be investi-gatedis using transient fault detectors that will trigger the establishment of a new group wheneverinconsistency is detected. Impossibility results will be developed to indicate which system assump-tionsare necessary; lower bound results will be proved to shed light on the degree of optimality ofthe solutions obtained. A second part of the research will study how different mobile applicationscan take advantage of the self-stabilizing group communication services developed. A third partof the research will explore the interactions between the group communication services and other,lower level, mobile services.Group communication services have been incorporated in several existing academic and indus-trialdistributed systems. However, none of them is self-stabilizing and none of them is specifi-callytailored for mobile environments. Self-stabilization and group communication are importantparadigms for the design of dynamic communication networks, and in particular wireless net-works.There is no doubt that the new methods developed in this project will contribute to futureimplementations of robust group communication systems.