Abstract: The network availability differs in the Quality of Service (QoS) of different network services and constrains each other with performance expense. In order to solve the problems, Markov chain theory was introduced, a new Markov Chain and QoS based Network Availability (MCQNA) evaluation model was constructed on the basis of defining the matching degree of service capability based on the minimum service expense. Firstly, starting from the QoS indicator that could best reflect the characteristics of network availability and considering the performance overhead, the cost function was defined and the state transition matrix was given. Then, through the analysis of relationship between stationary state and network availability, the stationary distribution was solved and used as the dynamic weight of operation cost of QoS. The network availability evaluation characterized by the minimum operation cost of service was realized. The simulation results show that, the ergodic transition matrix constructed by the proposed model has the stationary distribution, and it is feasible to evaluate the network availability. According to the QoS standards of different services, the proposed model can be used to measure the network availability effectively for specific services.

Key words: Quality of Service (QoS), network availability, Markov chain, performance expense, stationary distribution

摘要： 针对网络可用性在不同网络业务中的服务质量（QoS）存在差异，且与性能花费相互制约的问题，引入了马尔可夫链理论，在定义了基于业务开销最小的服务能力匹配度的基础上构建了基于马尔可夫链和QoS指标的网络可用性（MCQNA）评价模型。首先，从最能反映网络可用特征的QoS指标出发，兼顾性能开销，同时定义了代价函数，并且给出了状态转移矩阵；然后，通过平稳状态与网络可用性关系的分析，求解出平稳分布并作为QoS运行开销的动态权重，实现了以业务运行代价最小为特点的网络可用性评判。仿真结果表明，所提模型构建的遍历性转移矩阵存在平稳分布，对网络可用性评判是可行的。该模型能针对不同业务的QoS标准，且有效针对具体业务衡量网络的可用性。

关键词: 服务质量, 网络可用性, 马尔可夫链, 性能开销, 平稳分布