The Research Of Switch Fabric Based On Packet Order On The Output

Due to the rapid popularization of the Internet and the rapid development of various types of data services, the switching nodes in the core backbone network need to switch more and more traffic. Traditional single stage switching architecture, such as Crossbar structure and shared buffer structure, can not meet the requirements of large capacity switching as its poor scalability. In order to design scalable switching equipment with large capacity, the industry mainly uses multistage switch fabric. In the multistage switch fabric, the Clos structure with good expansibility is the preferred structure to construct the switch with high capacity and scalability.This thesis begins with a brief introduction to the various types of switch fabric, and then, according to the development requirements of the current switch system, this thesis proposes a switch fabric architecture base on packet order on the output. The architecture is based on the Memory-Memory-Memory Clos network switch fabric. In order to solve the problem of cell disorder caused by the middle stage buffer, this thesis adopts the method of controlling the degree of cell disorder and fulfilling the cell sorting and packet ordering in the output stage. There are two main ways to control the cell disorder: firstly, Credit scheduling is adopted to reduce the collision probability in the switch fabric caused by the different data flow with the same output port. Secondly, dynamic routing mechanism and link level load balancing mechanism are used to equallu deliver the flow to different modules to reduce the collision probability in the same switch element. The Method to accomplish packet order is maintain expected value for each data flow, and only the whole received packet whose packet id is the same with the expected value can execute the packet reorganization. If the waiting time exceeds a certain threshold, it is considered that the cell belong to the packet is lost, and the expected value is need to updata to reorganize the next packet.In order to ensure the system reliability and fault tolerance of the switching fabric, this thesis designed the flow control mechanism and the load balancing scheme based on the bundle connection under the link failure. The flow control mechanism can reduce the traffic flow when the network is congested. And the load balancing scheme based on the bundle connection under the link failure can dynamically adjust the input traffic according to the present link number.Finally, the simulation modeling of the switch fabric with packet order in the output is designed by using the OPNET simulation software. The simulation modeling verified many aspects of the switch system. Simulation results show that the switch fabric based on the packet order on the output has a better delay characteristic, and can work stably under the condition of the different traffic and different packet size. Although the loss of cell may bring certain influence to the switch performance, the switch fabric can use the flow control mechanisms to help the system recover to the normal state quickly. In addition, the load balancing scheme proposed in this thesis can effectively balance the link and the plane flow, so that the system can work more stably and effectively.