| With the increasing demand for communication technology,ground communication limited by terrain and landform cannot meet the requirements of communication globalization,while satellite communication has been widely applied in many fields of various countries by virtue of its advantages of large coverage and free from adverse environment constraints.At the same time,the on-board switch,as the payload of the satellite communication system,can realize the efficient forwarding of each end user’s information in the satellite communication system.Due to the particularity of spaceborne switching,such as the particularity of switching interface,transmission frame format and protocol processing,the common switching chip cannot meet the technical requirements.Therefore,a customized implementation scheme of one requirement and one scheme can only be adopted according to the actual special requirements.According to the project "Design and Implementation of Space Special Packet Switching" undertaken by the laboratory,this paper focuses on the design and implementation of special packet switching unit based on standard Ethernet frame.Firstly,this paper introduces the research background and main techniques of on-board exchange.Secondly,by analyzing the project requirements,a switching unit implementation scheme is proposed to separate the data channel and control channel in the switching unit.The functions of the data channel and control channel are divided respectively,and the functions of each module involved in each channel are briefly described.Thirdly,the SRIO interface used by the control channel is designed,and then the core modules of the internal data channel are designed in detail.The data processing module,entry management module,queue selection and control module and transmission management module are described in turn.Next,the core modules of the switch internal control channel are designed in detail,and the control frame receiving control module,unicast processing module,register processing module,MAC query processing module and sending control module are described in turn.Fourthly,a software simulation environment is built to test the basic functions of the switching unit.Fifthly,the board level debugging environment is built to verify the performance of the switching unit.The final test results show that the design scheme is correct and reasonable,the work is stable,and it can meet the needs of the project,to achieve the expected design objectives.The innovation of this paper lies in: firstly,the design and implementation of the hierarchical search for destination MAC address strategy for three layer unicast frames.For the data frame whose destination IP address can be completely equal to the IP address of a unicast entry,the fast search based on array is carried out to improve the search speed.Otherwise,the range matching search based on dichotomy is adopted.Secondly,a virtual port is designed and introduced as the destination port for the internal processing of broadcast data frames,and a queue selection and control module is set separately for this virtual port to ensure the priority of broadcast frames forwarding.Thirdly,a dedicated control channel supporting self-defined control frames based on SRIO interface is designed and implemented,which is independent from the data channel to reduce the impact on real-time forwarding of data frames. |
