综合业务网中IEEE802.4优先级控制准公平性探讨

令牌总线介质访问协议提供了选择优先级的机制,优先级机制的功能是把网络信道首先分配给优先级较高的信息帧,而当高优先级帧足够发送时,才发送优先级较低的帧。通常信息帧优先级分为4个级别。考虑到综合业务高负载的特点,需要对IEEE802.4优先级协议进行改进。其出发点是既要尽可能保证高优先级信息的发送,又防止出现低优先级信息(特别是优先级最低信息)长时间得不到发送的局面。该文提出的策略,比较合理地解决了这一问题。其实质是在合理范围内牺牲高优先级业务的服务质量,适当换来部分提高低优先级业务的服务质量。模拟实验验证,该文改进的IEEE802.4协议是适合于综合业务数字网优先级控制的。

The Discussion on Quasi-fairness of Priority Control in IEEE802.4 of Integrated Service Networks

The Token-Bus Media Access Protocol provides mechanism of selecting priority,which ensures that the VC can be allocated to the frame with higher priority firstly.Only when the number of higher priority frame reaches some extent ,the frame with lower priority can be sent.Usually,four types of priority are considered.Allow ing for the heavy load of integrated service,we need to better the priority protocol of IEEE802.4.With the purpose to prevent lower priority information frame (especially the lowest rank information)from waiting for such a long time ,the improved strategy is presented.The motif is properly enhancing QoS(Quality of Service)for the low rank information at the cost of the decrease of QoS for the high one.Simulation results show that the improved IEEE802.4protocol is adapt ed to priority control of integrated service digital networks(ISDN).