Research On An Efficient Self-routed Switching Scheme Used In Three-stage Clos Network

With the high-speed development of network and the explosion of communicationtraffic, the bandwidth requirement of network is increasing greatly. As the service nodesof network, switching equipments such as switches and routers have gradually become abottleneck restricting the network performance.In recent years, the research on switching network equipments mainly focuses ontwo points: one is about the architecture of switching fabric, and the other is about thescheduling algorithms of switching network. The single-stage switching fabric cannotbe applied to switching systems with large-scale expansion due to the complexityrestrictions. Therefore, the multi-stage structure constituted by a plurality of switchingelements, such as three-stage Clos structure, becomes a common solution in buildinglarge switching network.Many scheduling algorithms for three-stage Clos network have been proposed,including the random dispatching (RD) scheme, the concurrent round-robin dispatching(CRRD) scheme and so on, however, these algorithms still have some disadvantagesespecially when used under high-speed and high-load conditions. For example, some ofthe schemes such as the CRRD, need to take certain arbitration strategies and twomatching steps, which not only leads to a high computational complexity, but alsoinevitably causes a large amount of control information transferring between the stages,thus greatly affects the overall switching performance.Using self-routed technology without complex arbitration mechanism or multiplematching steps will make the switching process easier to handle. However, thistechnique is easy to cause internal network blocking because of the port conflict, andthe internal blocking probability will increase when the network load becomes higher orthe burst traffic increases, thus resulting in the increase of end-to-end delay and thedecrease of network performance. Therefore, the key point of self-routed switchingscheme design is to reduce the continuous conflict or long-term blocking in theswitching fabric, thereby reducing end-to-end delay of cells.To solve the problems above, we proposed an efficient self-routed scheme called BA-CIS (Bandwidth Arbitration and Cell Interleaving Scheme) based on three-stageClos network. Firstly, it is a cell-based and self-routed scheme without complexmatching process in many traditional switch scheduling algorithms such as the CRRD.Secondly, the scheme takes the “bandwidth reservation and allocation” strategy in orderto prevent traffic blocking in the output port at the output stage. Thirdly, this schemecan distribute the continuous cells of the packet discretely by the way of “cellinterleaving”, ensuring that cells belonging to a given stream are transmitted into thefabric at well-spaced intervals of time, thus greatly reducing the continuous obstructionwithin the switching fabric.Finally, we simulated and built a three-stage Clos switching network modelsupporting the BA-CIS scheme using the C++language in the Windows environment,realized the algorithm and examined the performance of BA-CIS in a variety ofscenarios. Simulation shows that the “cell interleaving” strategy, as the core of BA-CISscheme, contributes a lot to enhance the network performance. When the average lengthof packets or the size of switch windows becomes, the scheme can still perform well.Besides, this scheme can well support hot business environment or mixed businessenvironment. In addition, the scheme performs a good stability when the network scaleexpands. The average network delay in BA-CIS is significantly decreased whencompared with some other traditional switching methods such as the CRRD.