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A tc segment is the specific form of the tc frame

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Unformatted text preview: ggregating very small user messages into larger pieces and multiplexing these pieces to provide responsive virtual access to the channel for all users. A “TC Segment” is the specific form of the “TC Frame Data Unit” containing a Segment Header. B-2 TC SEGMENTATION LAYER SERVICE SPECIFICATION The services provided by the Telecommand Segmentation layer are as follows: (1) The layer breaks long user data structures from the layer above (i.e., TC Packets, or other user data structures which have been generated by a non-standard higher layer) into pieces (“TC Frame Data Units”) which will fit the data field of TC Transfer Frames, and reassembles them after passage through the Transfer layer. (2) The layer optionally aggregates multiple TC Packets into a single TC Frame Data Unit, which fits into the data field of a TC Transfer Frame and separates them after passage through the Transfer layer. (3) The layer provides a mechanism for multiplexing different TC Frame Data Units together onto a single Virtual Channel, for the purpose of flow control. The Segmentation service described in this Recommendation is designed to support the standard CCSDS telecommand Packetization layer (Reference [3]). It can also provide CCSDS 202.0-B-2 Page B-2 CCSDS HISTORICAL DOCUMENT November 1992 CCSDS HISTORICAL DOCUMENT CCSDS RECOMMENDATION FOR TELECOMMAND: DATA ROUTING SERVICE services to other non-standard higher-layer TC processes as long as the interface requirements of the Segmentation layer are satisfied. SENDING END RECEIVING END TELECOMMAND DATA SOURCES TELECOMMAND DATA SINKS USER DATA UNITS DATA ROUTING SERVICE BOUNDARY p 0 1 ••• n ••• MULTIPLEXER ACCESS POINTS (UP TO 64 PER VIRTUAL CHANNEL) n 1 0 ••• 1 SEGMENTATION LAYER SENDING ENTITY p 1 0 ••• 0 SEGMENTATION LAYER RECEIVING ENTITY TC FRAME DATA UNIT ••• 0 1 2 3 4 TRANSFER LAYER SENDING ENTITY m ••• VIRTUAL CHANNELS (UP TO 64) m TC TRANSFER FRAME FOP FARM CLCW IN TELEMETRY 4 3 2 1 0 TRANSFER LAYER RECEIVING ENTITY COP Figure B-1: TC Data Routing Service Ele...
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