## 2 Efficient Network AOS Comprehensive Multiplexing Model  
Spacecraft network traffic can be categorized into three types based on its different characteristics, as follows: synchronous traffic, asynchronous real-time traffic, and asynchronous non-real-time traffic. Synchronous traffic data refers to data that are essential for maintaining the basic operation of the spacecraft and determine the success or failure of the mission. This includes data such as remote control, telemetry, mission management, and astronaut health monitoring data. These data typically have low transmission rates and exhibit periodic synchronization characteristics. They have strict requirements for data transmission reliability and arrival latency. Asynchronous real-time service data consist of real-time platform and payload data generated during spacecraft operations, including voice, image, crew, and payload data. These data streams often exhibit significant randomness and have higher demands for transmission reliability and low latency. Asynchronous non-real-time service data pertain to non-real-time data generated by spacecraft operations, such as space experiment data, delayed payload data, and delayed telemetry data. These data typically have higher transmission rates and more relaxed latency requirements but have stricter demands for transmission efficiency and low packet loss rates. To enhance the flexibility and scalability of the multiplexing model, hierarchical architecture is employed for the model design. Additionally, a decision layer is introduced based on the traditional multiplexing architecture, as shown in Figure 1.  
Figure 1: AOS comprehensive multiplexing model. The model is divided into the following three layers: the packet multiplexing layer, the virtual channel multiplexing layer, and the decision layer. The packet multiplexing layer connects and segment data packets sent by different users, which have different formats but the same service requirements, into fixed-length protocol data transmission frames. These frames are then transmitted over the same virtual channel. The virtual channel multiplexing layer schedules the input transmission frames with different service requirements according to a specific algorithm, enabling data from different virtual channels to be transmitted over the same physical channel. The decision layer allocates virtual channel scheduling slots for different service types, making comprehensive scheduling decisions for different types of virtual channels to achieve optimal multiplexing performance. In this model, one buffer is allocated for each virtual channel at the packet multiplexing layer and the virtual channel multiplexing layer. The packet multiplexing layer buffer is used for temporary storage of data before frame generation. For synchronous services, the buffer capacity is determined by the maximum amount of data arriving in the virtual channel within two framing intervals. For asynchronous services, the buffer capacity is determined by the maximum amount of framed data in the framing algorithm. The virtual channel multiplexing layer buffer is used for temporary storage of data before virtual channel scheduling. For synchronous services, since there is no burst, the rate is low and the scheduling priority is the highest, the buffer capacity requirement is low, and usually the buffer capacity within ten frames is sufficient. For asynchronous real-time services, the burst data volume of different virtual channels is mainly considered, and the selection of buffer capacity needs to ensure that the burst data volume can be cached once, and a certain amount of buffer space margin is added on this basis. For asynchronous non-real-time services, since their overall priority is the lowest and the data volume is large, the buffer capacity needs to ensure the burst data volume once, and, at the same time, the data volume during the waiting time for other virtual channels must be considered, so a larger buffer capacity is usually required.