A Parallel Packet Switch Achieving In-Order Cell Delivery with Combined-Input-and-Output Queuing Switches

Abstract

提出一种按序排队(in-order queuing,简称IOQ)PPS体系结构,通过在分流控制器引入固定尺寸的缓冲区,实现负载在每个交换平面的均匀分配;中间层组合输入输出排队(combined input-and-output queuing,简称CIOQ)交换平面受控于中央调度器,在每个时间槽(time slot),中央调度器将同一种匹配实施到每一个交换平面,称之为同步调度策略.可以证明,在该体系结构下,轮询(round robin)分派算法配合同步调度策略可以保证同一条流的信元按序从交换平面读出.进一步提出了严格最长队列优先同步调度算法,极大地减少了中央调度器需要维护的状态信息和信元重定序开销.与目前主流的PPS设计相比,IOQ PPS(in-order queuing parallel packet switch)实现机制简单,易于硬件实现.模拟结果表明,IOQ PPS具有最优的延迟性能.;An in-order queuing (IOQ) PPS architecture proposed in this paper uses a small fixed-size buffer in the demultiplexor to distribute traffic equally among switch planes, with central combined input-and-output queuing (CIOQ) switch planes under the control of a single scheduler that applies the same matching at each of the parallel switch planes during each cell slot. This operation is called synchronous scheduling. It is proved that the round robin demultiplexing algorithm along with synchronous scheduling guarantees cells of a flow can be read in order from the output queues of the switch planes. Furthermore, by using a synchronous scheduling called strict longest queue first (SLQF) algorithm this scheme reduces considerably not only the amount of state information required by the scheduler, but the communication overhead required to achieve cell reordering. Compared with existing PPS designs, IOQ PPS (in-order queuing parallel packet switch) is more practical to implement in hardware because of its simple implementation mechanisms, as the experimental results demonstrate, and it offers the best delay performance.