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Data flow from the top to the bottom of the figure

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Unformatted text preview: is figure is not intended to imply any hardware or software configuration in a real system. Depending on the services actually used for a real system, not all of the functions may be present in the protocol entity. The procedures described in this subsection are defined in an abstract sense and are not intended to imply any particular implementation approach of a protocol entity. CCSDS 132.0-B-1 Page 4-14 September 2003 CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL Packet Serv ice VC Acces s Serv ice VC _FS H Serv ice VC _O C F Serv ice VC Frame Serv ice Packet MC _FS H Proces s ing Serv ice MC _O C F Virtual C hannel G eneration Serv ice MC Frame Virtual C hannel Multip lex ing Serv ice Mas ter C hannel G eneration Mas ter C hannel Multip lex ing All Frames G eneration Figure 4-5: Internal Organization of Protocol Entity (Sending End) 4.2.2 PACKET PROCESSING FUNCTION The Packet Processing Function shall be used to transfer variable-length Packets in the fixed-length Data Field of Transfer Frames. NOTE – There is an instance of the Packet Processing Function for each Virtual Channel that carries Packets. The Data Field of Transfer Frames shall be constructed by concatenating Packets together until the maximum Data Field length is exceeded. Any Packet that exceeds the maximum Data Field length shall be split, filling the Data Field completely, and starting a new Data Field on the same Virtual Channel with the remainder. Construction of the next Frame Data Field shall continue with the concatenation of Packets until it overflows. If Packets of multiple versions are to be transferred on a Virtual Channel, Packets of these versions shall be multiplexed into a contiguous string of Packets before constructing Data Fields. The First Header Pointer field shall be set to indicate the location of the first octet of the first Packet that starts within the Data Field of the Transfer Frame. If no Packet starts within the Data Field, the F...
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