网络恢复机制可用性的定义及其应用

对于用户和业务提供者，网络生存性变得越来越重要。生存性是设计和规划新的电信网（如ＳＤＨ网和ＡＴＭ网）面临的一个根本的、亟待解决的问题。在过去的几年中，已提出几种应用于ＳＤＨ和ＡＴＭ网络中的不同的恢复机制。但在比较和评价恢复机制的性能时，以往只采用一种简单的方法。为克服该方法的缺陷，本文提出了面向用户和面向网络工程师的恢复机制可用性的定义。在后者的可用性分析中，考虑网络生存性对空闲容量的要求。由于一个网络的状态空间很大，进行可用性精确分析是不可行的，本文建议采用ＯＲＤＥＲ算法来近似测量可用性。同时还给出了恢复机制可用性定义的应用。一个应用是：网络工程师利用可用性定义，设计一个具有成本有效性的生存网络。另一个应用是：在ＡＴＭ生存网络的ＣＡＣ协商参数中，增加了一组新的参数—生存性性能参数。最后在计算机模拟中验证了：在评价恢复机制性能时，两个可用性的定义比传统方法更有效和更有意义

Definitions of Restoration Mechanism Availability and Their Applications

Network/service survivability is increasingly becoming important to customers, as well as telecommunication service providers and network operators. So survivability is an important problem demanding prompt solution in design and planning of new telecommunications networks (e.g., SDH networks and ATM networks). In the past a few years, different restoration mechanisms for SDH and ATM networks have been developed . The previous literature comparing and evaluating the restoration mechanisms only uses a simple method. In order to overcome the shortcomings in the traditional method, this paper proposed the customer oriented and network engineer oriented definitions of restoration mechanism availability. In the second definition, the extra spare capacity requirement in the network is taken into account in the availability analysis. Because an exact measurement of the availability is infeasible due to the large number of failure states in the network. An ORDER algorithm to get a reasonable subset to approximately measuse the availability is recommended. Then, applications of the definitions are given. One application is how this definition is used by network planner/engineer to construct a cost effective survival network. Another application is that a new group of parameters - survivability quality of service (SQoS) is defined and added to CAC (Connection Admission Control) of ATM survivable network. Finally, the simulation using two definitions has done, the simulation results prove that two definitions of availability can evaluate restoration mechanisms more sufficient and more meaningful.