However these same layers are implicit in the

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Unformatted text preview: r, these same layers are implicit in the telemetry documentation, and hence Figure 2-3 synthesizes the equivalent TLM System layers for the purpose of illustration. As shown in Figure 2-3, there are two possible protocol mechanisms inherent to the TC System for reporting command transfer status and verification information to the sending end via the TLM System. The primary mechanism is the Command Link Control Word (CLCW), which contains key information concerning the status of receipt of TC Transfer Frames by the receiving end of the TC Transfer layer. The CLCW is periodically sampled by the TLM System, and is returned to the sending end of the TC Transfer layer via the CLCW word in the trailer of the standard CCSDS TLM Transfer Frame. The information conveyed in the CLCW is used by the sending end of the TC Transfer layer to continue, retransmit or otherwise modify the transmission of the stream of TC Transfer Frames. Reliable, mission-independent operations within the TC Transfer layer form the cornerstone of the CCSDS telecommanding concept. The closed-loop retransmission protocols between the sending and receiving ends of the TC Transfer layer (using the CLCW reporting services of the TLM Transfer layer) are specified in Reference [5]. A second reporting loop conceptually exists within the higher Packetization layer, where TLM Packets may be prepared by the receiving end of the layer to acknowledge receipt or indicate problems with the TC Packets it received from the TC Segmentation layer. These reporting TLM Packets may then be sent back to the sending end of the TC Packetization layer via the TLM System. However, at present the CCSDS has made no attempt to standardize any reporting procedures within the Packetization layer, since these are likely to involve missionunique processes. The TC Packetization layer therefore relies fully on the standardized, guaranteed service provided by the Transfer layer. Issue 6 Page 2-7 January 1987 CCSDS REPORT CONCERNING TELECOMMAND: SUMMARY OF CONCEPT AND SERVICE EVENT SENDING TC APPLICATION PROCESS LAYER SENDING TC SYSTEM MGMT LAYER PKT SENDING TC PACKETIZATION LAYER SENDING TC SEGMENTATION LAYER CLCW SENDING TC TRANSFER LAYER SENDING TC CODING LAYER SENDING TC PHYSICAL LAYER RECEIVING TLM APPLICATION PROCESS LAYER RECEIVING TLM SYSTEM MGMT LAYER * CMD RECEIVING TC APPLICATION PROCESS LAYER * RECEIVING TC SYSTEM MGMT LAYER RECEIVING TLM PACKETIZATION LAYER RECEIVING TC PACKETIZATION LAYER RECEIVING TLM SEGMENTATION LAYER RECEIVING TC SEGMENTATION LAYER RECEIVING TLM TRANSFER LAYER CLCW RECEIVING TC TRANSFER LAYER RECEIVING TLM CODING LAYER RECEIVING TC CODING LAYER RECEIVING TLM PHYSICAL LAYER RECEIVING TC PHYSICAL LAYER SENDING TLM APPLICATION PROCESS LAYER SENDING TLM SYSTEM MGMT LAYER SENDING TLM PACKETIZATION LAYER SENDING TLM SEGMENTATION LAYER SENDING TLM TRANSFER LAYER SENDING TLM CODING LAYER SENDING TLM PHYSICAL LAYER * THESE LAYERS DO NOT EXIST IN REFERENCE [5]. Figure 2-3: Issue 6 Telecommand/Teleme...
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