CICQ交换机中一类服务可保障的调度策略研究

A New Service Guaranteed Scheduling Policy for Buffered Crossbar Switches

具备QoS保障能力的快速调度算法是高速交换机的首选.基于EPFTS(Ethernet-oriented physical frame timeslot switching)和CICQ(combined input-crosspoint-queued)交换技术的特点,提出了一类新的调度策略———TRWFS(ti meslot reservation weighted fair scheduling).为确保各端口对上保障业务的预留带宽,TRWFS以各端口对上保障业务预留时槽数为调度权重,以优先调度保障业务和平衡各保障业务的盈余时槽(surplus timeslot,定义为现实系统和理想系统之间的服务差额)为业务调度准则.基于该调度策略进一步提出了两种实现算法———TRWFS-I和TRWFS-II,总体上使实现TRWFS的时间复杂度降至O(1).性能分析和仿真实验结果均表明两种调度算法都达到了服务保障的设计目标,仿真实验结果还表明CICQ排队方式下与其他调度算法相比,TRWFS和轮询调度综合的调度机制具有交叉缓存容量要求更低的优点.

Fast scheduler with service guarantee performance is preferred in high speed switching networks. Based on the features of EPFTS （Ethernet-oriented physical frame timeslot switching） and CICQ （combined input-crosspoint-queued）, a new scheduling policy called timeslot reservation weighted fair scheduling （TRWFS） is introduced. In order to provide bandwidth guarantee service to guarantee- required （GR） traffic, TRWFS takes the total reserved timeslots of aggregated GR traffic on each I/O port pair as the basic scheduling weight and forwards traffic according to the following principles： 1） Giving dispatching priority to GR traffic and 2） Trying to balance the surplus timeslots （defined as service discrepancy between the actual packetized system and the idealized fluid system） for GR-traffic on each I/O port pair. In order to apply TRWFS and decrease the implementation complexity of TRWFS to constant time complexity O （1）, two scheduling algorithms-TRWFS_ Ⅰ and TRWFS_Ⅱ are further presented. Analysis and simulation results demonstrate that the two TRWFS algorithms both reach the design objective. Moreover, simulation results show that TRWFS/round-robin combined scheduling scheme in CICQ switches require fewer crosspoint buffer compared with other schemes.