基于小尺寸缓存的提前预留机制是有效的竞争解决方案.为支持区分服务，本文研究了两优先级提前预留机制的阻塞模型，分析了变化缓存尺寸与载荷比率条件下光突发交换网络核心节点的阻塞性能.为降低两优先级提前预留机制的突发丢弃率，提出一种基于流量门限的提前预留机制.数值分析确定了合理的缓存尺寸与流量门限，实现了高、低优先级间的缓存使用平衡.仿真结果表明：与原有提前预留机制相比，基于流量门限的提前预留机制保持了全流量状态范围内的阻塞性能，并明显降低了中、低流量状态内的突发丢弃率.

Prereservation based small buffers is an efficient method for contention resolution in optical burst switching networks. In this paper, the blocking model of prereservation with twoclass state was studied in order to provide differentiated services, and a comprehensive analysis on the blocking performance was exhibited by varying buffer size and traffic ratio. In order to reduce the total loss probability of prereservation with twoclass state, a novel scheme named prereservation based trafficthreshold was proposed by constraining the buffered right of low priority within the specific traffic states. Additionally, through the detailed numercial analysis, the reasonable values of buffer size and trafficthreshold were gained, and the balance of buffer usage between high and low priority was achieved. The simulation results show that comaparing with the conventional prereservation schemes, prereservation based trafficthreshold maintains the total blocking performance in all traffic states and obtains a obvious reduction of burst loss probability in light and moderate traffic states.