Tc packets with different destinations as denoted by

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Unformatted text preview: -defined data units, but not both. TC Packets with different destinations, as denoted by the Application Process Identifier in the TC Packet Header, may be carried on a single MAP or Virtual Channel and may be aggregated within a single TC Frame Data Unit. Figure 3-3 shows how TC Packets assigned to one MAP are aggregated or segmented to form TC Segments/Frame Data Units. CCSDS 202.0-B-2 Page 3-5 CCSDS HISTORICAL DOCUMENT November 1992 CCSDS HISTORICAL DOCUMENT CCSDS RECOMMENDATION FOR TELECOMMAND: DATA ROUTING SERVICE TC PACKET HDR CMD DATA TC PACKET HDR CMD DATA TC PACKET HDR Aggregation SEG HDR SEGMENT DATA FIELD FRAME DATA UNIT CMD DATA Segmentation SEG HDR SEGMENT DATA FIELD FRAME DATA UNIT SEG HDR SEGMENT DATA FIELD FRAME DATA UNIT Figure 3-3: Example of the Segmentation Procedure 3.3.2 RECEIVING END SEGMENTATION PROCEDURES The receiving end of the TC Segmentation layer performs the following processing steps: (1) Accepts a stream of multiplexed TC Segments/Frame Data Units on one Virtual Channel from the Transfer layer. (2) Sorts these Segments according to the MAP IDs which appear in their Segment Headers. (3) a. For TC Frame Data Units containing a segment of a TC User Data Unit: reassembles the Segments (less headers) for each MAP, using the Sequence Flags, in order to recreate the original TC User Data Unit. b. For all other TC Frame Data Units: extracts the TC Packets or TC User Data Unit, using the Frame and Packet Length fields. (4) Passes the resulting TC User Data Unit(s) to the layer above. CCSDS 202.0-B-2 Page 3-6 CCSDS HISTORICAL DOCUMENT November 1992 CCSDS HISTORICAL DOCUMENT CCSDS RECOMMENDATION FOR TELECOMMAND: DATA ROUTING SERVICE 4 TRANSFER LAYER: STANDARD DATA STRUCTURES AND PROCEDURES 4.1 OVERVIEW OF THE LAYER The TC Transfer layer is the “heart” of the standard conventional TC System. It is this layer which takes care of most of the operations required to move sets of user TC data reliably from the sending end of the system to the receiving end in space. S...
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This document was uploaded on 03/06/2014.

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