Opnet Simulation For Virtual Channel Multiplexing Based On CCSDS AOS Protocol

With the rapid development of space science, the spatial datagenerated by space missions have multiple types and the transmissionrates range from a few bps to several Gbps. in order to meet those newrequirements, CCSDS (the consultative committee for space datasystem) have proposed a new data link layer protocol–advanceorbiting system (AOS) based on traditional remote control andtelemetry protocol. AOS transfers the length-variable user datapackets into fixed format–Transfer Frame (TF) which is suitable fortransmit on physical channel. An important concept–virtual channelis introduced for the multiple-user share the same physical channel bythe method of time division.Multiplexing method will greatly affect the efficiency of the AOSimplement, but the protocol itself does not make any provision forchannel multiplexing option. Users need to select the appropriatescheduling algorithm based on actual demand. In protocol,multiplexing of channels include two levels: packet channelmultiplexing and virtual channel multiplexing. The former level refersto encapsulate different type user data packets into fixed-lengthmultiplex protocol data unit (MPDU), the later level indicatesmultiplex TFs in multiple VCs into one physical channel.In this paper, we proposed a new schedule algorithm–adaptivedynamic channel multiplexing based on analysis the requirement ofdifferent spatial data. In the phase of packet channel multiplexing,using adaptive frame generation for the user packet that transmissionrate is low and high efficiency frame generation for high transmissionrate. The wait time for adaptive frame generation is based on thethroughput of corresponding VC. On the stage of virtual multiplexing,we first divided the VCs into synchronization VCs and asynchronousVCs. The time slice proportion between syn and asyn VC is based on the average injection rate from users, but reserve the minimum limitfor asyn VC avoid the circumstance of―starvation‖. Then for syn VCswe use weighted-polling scheduling and for asyn VCs we use dynamicpriority method.On OPNET network simulation platform, we implement theproposed algorithm, select the channel throughput, latency, bufferusing depth as parameters, compare this method with fixed priority,time slice weighted polling scheduling algorithm. The results showthat the adaptive dynamic scheduling algorithm can automaticallyadjust generation wait time based on output bandwidth to achieve agood balance between delay and MPDU multiplexing efficiency.Dynamic priority scheduling algorithm consider both the urgency,priority, and queue length of TF that can guarantee the real-time of theplatform data and maximized the throughput of payload data.Compared with fixed priority and time slice weighted-pollingalgorithm, it plays a good role in a balanced the requirements ofdifferent types transmission data.