Multiplex frames by virtual channel monitor frame

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Unformatted text preview: TRANSMISSION AS REQ'D. OUTPUT: BUFFER OF TC DATA BITS (REPRESENTING, E.G., TRANSFER FRAMES). RELIABLY SERVICE DELIVER TRANSFER FRAMES TRANSFER FRAMES FUNCTION: RECONSTITUTE ORDERED SET OF TRANSFER FRAMES. PERFORM FRAME ACCEPTANCE AND VALIDATION CHECKS. REPORT STATUS OF SAME VIA CONSTRUCTED CLCWs. EXTRACT SEGMENTS. COMMAND LINK CONTROL WORD (CLCW) INPUT: "CLEAN" TC DATA PLUS FILL BITS. DATA START/STOP INDICATORS. STATUS CODING LAYER Figure 3-5: TC Transfer Layer Reporting Mechanism" (FARM) at the receiving end of the layer in order to set up the receiving parameters. The sending end of the layer passes the assembled TC Frames to a "Frame Operation Procedure" (FOP), which provides the control of their transmission to the spacecraft. The FOP batches the TC Frames and delivers them to the layer below (the Coding layer) as buffers of serial information bits (corresponding to one or more back-to-back frames) for encoding and transmission to the spacecraft. At the receiving end of the TC Transfer layer, the inputs from the layer below are "clean" decoded information bits and data stop/start indicators which mark the gross boundaries of the buffers of bits that were given to the Coding layer at the sending end: however, trailing fill bits Issue 6 Page 3-9 January 1987 CCSDS REPORT CONCERNING TELECOMMAND: SUMMARY OF CONCEPT AND SERVICE may have been inserted by the encoding process. The Transfer layer therefore uses the length information in each TC Frame to delimit each frame in the buffer, and to discard any trailing fill. The reconstructed, delimited frames are input to the receiving-end FARM, which performs validation and acceptance checks based on sequence information and other criteria that are fully specified in Reference [3]. The status of frame acceptance by the FARM is telemetered back to the FOP at the sending end via the Command Link Control Word (CLCW) in the trailers of standard Telemetry Transfer Frames. The pair of peer-layer procedures executed by the FOP and FARM are together known as a "Command Operation Procedure" (COP). Based on CLCW reports from the FARM, the FOP makes appropriate retransmission decisions for frames which were rejected or otherwise missed by the FARM, according to the rules of the governing COP. Under closed-loop retransmission control of the selected COP, and utilizing the errorprotection services of lower layers, the TC Frames are assembled at the receiving end of the layer so that they are error-free, in sequence and with no omission or duplication. Once this service is guaranteed, their data contents are then stripped and passed to higher layers. Three COPs, which are recursively related to each other, are presently defined. In order of increasing complexity they are: (1) COP-0 COP-0 operates on the principle of sequential frame acceptance and retransmission, without frame sequence numbering. The FOP initiates the transmission of TC Frames whose sequence numbers are not used. The FARM only accepts frames if they are received withou...
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