As more and more space missions look towards

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Unformatted text preview: s internationalization as the key to affordability, these standardized cross-support services will become increasingly important. Figure 2-1 illustrates the recommended CCSDS Telecommand System architecture in terms of a layered set of telecommand services: the operations within each layer are detailed in Issue 6 Page 2-1 January 1987 CCSDS REPORT CONCERNING TELECOMMAND: SUMMARY OF CONCEPT AND SERVICE APPLICATION PROCESS LAYER COMMAND DIRECTIVE TELECOMMAND, PART 3: DATA MANAGEMENT SERVICE SYSTEM MANAGEMENT LAYER TC APPLICATION DATA PACKETIZATION LAYER PACKET SEGMENTATION LAYER TELECOMMAND, PART 2: DATA ROUTING SERVICE SEGMENT TRANSFER LAYER TRANSFER FRAME CODING LAYER TELECOMMAND, PART 1: CHANNEL SERVICE CLTU PHYSICAL LAYER PHYSICAL WAVEFORM Figure 2-1: Issue 6 CCSDS Telecommand System Page 2-2 January 1987 CCSDS REPORT CONCERNING TELECOMMAND: SUMMARY OF CONCEPT AND SERVICE Figure2-2. The layers of TC service are functionally grouped into a "Data Management Service", a "Data Routing Service", and a "Channel Service". Each of these three major architectural components of service is separately specified in its own CCSDS technical Recommendation, i.e., References [2], [3], and [4]. The detailed retransmission protocols associated with the Data Routing Service are contained in Reference [5]. Taken as a whole, these four Recommendations (three architectural specifications and one detailed specification) form a system which provides the user with reliable and transparent delivery of telecommand information. The three main architectural components of service reflect increasing sophistication in terms of telecommand delivery. The Channel Service provides and controls a single reliable physical connection to the spacecraft. The Data Routing Service may be overlayed on the Channel Service to provide channel multiplexing capabilities, and to ensure the reliable delivery of buffers of telecommand data. The Data Management Service may be overlayed on the Data Routing Service to supply individually addressed end-to-end transportable command data units to each user, and to provide overall TC System coordination, integration, and management. Since each layer is independent of the layers above, individual missions may make their own decisions concerning how "high" in the layered hierarchy they wish to be compatible. 2 . 2 TELECOMMAND SERVICE CONCEPT The system design technique of layering is a key tool for transforming service concepts into sets of operational and data formatting procedures. Layering (the strategy of "dividing and conquering") allows a complex procedure such as spacecraft commanding to be decomposed into sets of relatively simple peer functions residing in common architectural strata. Within each layer, the functions exchange information using standard data formatting techniques and standard procedural rules or "protocols". Each layer of the TC System draws upon a well defined set of services provided by the layer below, and provides a similarly well defined set of services to the layer above. As lo...
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