2 enabling tc user data units from different sources

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Unformatted text preview: ransfer Frame. (2) enabling TC User Data Units from different sources to be multiplexed together so that they may share one Virtual Channel. To accomplish service (1), the Segmentation layer breaks large TC User Data Units into smaller TC Segments or aggregates small TC Packets into a larger TC Segment or TC Frame Data Unit. To accomplish service (2), the Segmentation layer provides “Multiplexer Access Points” (MAPs). A TC User Data Unit arriving at the input to the Segmentation layer is allocated to a MAP at the sending end of the layer and is transferred to the corresponding MAP at the receiving end of the layer using the transfer service of the layers below. The layers below may provide one “real” physical channel, or may logically divide the real channel into multiple, named “Virtual Channels” (as defined in Section 4). Each of “m” (m = 1 to 64) Virtual Channels (VCs) may have “n” (n = 1 to 64) distinct MAPs associated with it. The orientation of the Segmentation layer is shown in Figure 3-1. Section 3.2 defines the format of the protocol data unit (the TC Segment), which is implemented within the Segmentation layer. Section 3.3 describes the procedures used within the Segmentation layer. It should be noted that the Segmentation layer does not include a telemetry reporting mechanism, since it relies on closed-loop procedures performed within the Transfer layer. CCSDS 202.0-B-2 Page 3-1 CCSDS HISTORICAL DOCUMENT November 1992 CCSDS HISTORICAL DOCUMENT CCSDS RECOMMENDATION FOR TELECOMMAND: DATA ROUTING SERVICE "MULTIPLEXER ACCESS POINTS" (MAPs) PROVIDED TO THE LAYER ABOVE S E G M E N T A T I O N 012 ••• 63 SEGMENTATION PROCESS-1 012 ••• 63 SEGMENTATION PROCESS-2 012 ••• 63 SEGMENTATION PROCESS-3 012 ••• 63 SEGMENTATION PROCESS-64 S E G M E N T A T I O N ••• VC-0 VC-1 VC-2 ••• VC-63 "VIRTUAL CHANNELS" PROVIDED BY THE LAYER BELOW Figure 3-1: Orientation of the Segmentation Layer 3.2 STANDARD DATA STRUCTURES WITHIN THE LAYER 3.2.1 TC FRAME DATA UNIT The TC Frame Data U...
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