摘要： 从周期性系统能力规划思想出发，提出基于“服务时间”尺度的接纳控制机制LBAC (延迟限定的接纳控制)，与已有的度量方法相比较，服务时间这一尺度能够更准确地表达系统负载。文章给出了LBAC 的形式化表示及其调度算法。通过在一个Web 集群服务器的应用级Web 交换机中实现表明，LBAC 机制通过自动保持所接纳的请求量与系统服务能力之间的匹配，既能够满足系统吞吐量和限定的延迟时间要求，同时有效地防止了系统超载。

关键词: 接纳控制；负载平衡；服务时间；服务质量

Abstract: Based on the idea of system capacity planning periodically, LBAC(latency-bounded admission control) mechanism which employs service time as its basic system load metric is put forward. Compared to other current metrics, service time can relatively indicate the system load more accurately. The formal representation and scheduling algorithm of LBAC are illustrated. The experimental result of the implementation of LBAC in Web switch of cluster-based Web server is presented as well. The result shows that through dynamically maintaining the match between the amount of requests admitted and the processing ability of the system, LBAC mechanism can adaptively meet the needs of system throughput and bounded delay time and prevent the system from overload effectively

Key words: Admission control; Load balance; Service time; Quality of services (QoS）