The transfer frame will be generated by the frame

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Unformatted text preview: Us) plus some parameters in the Transfer Frame Primary Header generated by COP-1. The Transfer Frame will be generated by the Frame Generation Procedure, as defined in reference [3]. The Frame Data Unit consists of the data to be inserted in the Transfer Frame Data Field. Within COP-1, control of sequentiality is maintained using the Frame Sequence Number, which must be present in each Type-A Transfer Frame. Type-A Transfer Frames are transmitted by the FOP-1 with their Frame Sequence Numbers arranged in strict up-counting order. The FARM-1 permits Type-A Transfer Frames to be accepted only if they are received bearing Frame Sequence Numbers in the proper up-counting sequential order. Upon detection of the first sequence error, the FARM-1 will reject all subsequent Type-A Transfer Frames on that Virtual Channel which do not contain the expected Frame Sequence Number. FOP-1 initiates retransmission either in response to a ‘Retransmit’ Flag in the CLCW or by detecting a timeout. FOP-1 performs retransmission by re-sending all unacknowledged Type-A Transfer Frames on that Virtual Channel. FOP-1 and FARM-1 also have a window mechanism to prevent a new Transfer Frame with the same Frame Sequence Number as that of a missing Transfer Frame from being transmitted or accepted. Valid Type-B Transfer Frames will always be accepted by FARM-1, and processed only to the extent of incrementing a counter for Type-B Transfer Frames in the CLCW. Type-B Transfer Frames are also used to send Control Commands from the FOP-1 to the FARM-1. Both Type-A and Type-B Transfer Frames are protected by the error correction/detection capability of the underlying Channel Coding Sublayer and also must pass the Frame Validation Check defined in reference [3]. Therefore, Type-B Transfer Frames accepted by CCSDS 232.1-B-2 Page 2-1 September 2010 RECOMMENDED STANDARD FOR COMMUNICATIONS OPERATION PROCEDURE-1 FARM-1 have a very high probability of being error-free. However, their sequentiality is not controlled by COP-1. 2.2 SERVICE TYPES NOTE – The TC Space Data Link Protocol provides two service types (SequenceControlled and Expedited) that determine how reliably s...
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This document was uploaded on 03/06/2014.

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