0 b 2 page 4 14 ccsds historical document november

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Unformatted text preview: ansferring data octets. Since the first octet transferred after Data Start goes TRUE corresponds to the first octet of the first TC Transfer Frame, the receiving end of the Transfer CCSDS 202.0-B-2 Page 4-14 CCSDS HISTORICAL DOCUMENT November 1992 CCSDS HISTORICAL DOCUMENT CCSDS RECOMMENDATION FOR TELECOMMAND: DATA ROUTING SERVICE layer may delimit this frame—and each of any successive TC Transfer Frames—by reading the FRAME LENGTH field in the first header, and then successively reading the FRAME LENGTH field in each subsequent header. The Data Start signal shall become FALSE (indicating “Data Stop”) when the Coding layer stops transferring octets because of a decoder failure or channel deactivation. Decoding failure may be caused by the normal end of the transmitted TC Frame(s), or by a genuine channel-induced error. If one or more valid FRAME LENGTH fields are detected by the receiving end of the Transfer layer and the number of octets received when the Data Stop condition occurs equals the number of octets specified by the FRAME LENGTH(s), then each Frame shall be passed on to the Frame Validation Check procedure (see 4.3.2) as it is delimited. If a valid FRAME LENGTH field is detected by the receiving end of the Transfer layer but the number of octets received when the Data Stop condition occurs is less than the number of octets specified by that FRAME LENGTH, this entire Frame shall be discarded since this indicates that a failure has occurred, possibly due to a channel error detected during reception of the data stream within the Channel Service layers below. If a valid FRAME LENGTH field is detected by the receiving end of the Transfer layer but the number of octets received when the Data Stop condition occurs is greater than the number of octets specified by that FRAME LENGTH, Fill Data was probably appended by the sending end Coding layer to complete the last TC Codeblock (Reference [4]). Because the receiving end Coding layer cannot distinguish between...
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This document was uploaded on 03/06/2014.

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