Study On Multi - Level Multi - Plane Switching Fabric Switching Mechanism

Along with the rapid development of Internet and its data services, there are more and more demand of Internet switching and routing systems. Switching fabric as the core of switching and routing systems, not only to be able to competent high-speed and reliable switching tasks, but also to be able to adapt to and cope with large-scale switch capacity. Single-stage switching fabric such as crossbar and even simple multi-stage switching fabric such as benes,clos structure has been unable to meet the demand of large capacity switching. So a larger multi-stage multi-plane switching structure has more applications. Multi-stage multi-plane switching systems integrate multiple input and output line cards, then format large information processing capacity to meet the demand of Tbps level switching.This paper studies the switching mechanism of multi-stage multi-plane switching structure. Switching mechanism refers to the basic data unit format used in the packet forwarding of switching network.In packet switching network there are two types of switching mechanism, fixed length cell based mechanism and variable length packet based mechanism. And variable length packet mechanism has two method, logical cutting packet switching and direct packet switching.Different switching mechanism calls for different scheduling algorithm.At first, we summarize various algorithm of different switching mechanism in single-stage switching fabric, and make improvements and selection, then use them in the multi-stage multi-plane switching fabric.Matching algorithm PB-iSLIP used in logical cutting packet switching has been changed to CPB-iSLIP to meet the demand of centralized scheduling in crossbar structure.Round-Robin algorithm used in direct packet switching has been improved to PRR to avoid the unfairness when RR service the VOQ queues.RR and PRR has been compared by simulation, and prove that PRR algorithm has better delay characteristics.SAND chip of DUNE company has been used as the reference model, build a multi-stage multi-plane switching fabric simulation platform of PPS structure, every fabric plane is a three-stage clos switching fabric.In this model, according to the distributed scheduling method,we apply different algorithms in different stage to achieve three switching mechanism.Including the flow control algorithm in input and output stage,the load balance algorithm in input stage,the route matching algorithm in middle stage,and also the packet cutting and reassembling algorithm.Besides,when achieve the direct packet switching,also need to change the middle stage hardware model,using the CICQ crossbar with VOQ structure.By analyze the simulation result, we conclude that the logical cutting packet switching mechanism has better performance,because it avoid the disadvantage of cell disorder when use fixed length cell switching mechanism,and use less complex hardware and algorithm when compare with the direct packet switching mechanism.