4 the first header pointer field shall be set to

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Unformatted text preview: irst Header Pointer shall be set to ‘11111111111’. CCSDS 132.0-B-1 Page 4-15 September 2003 CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL The Packet Processing Function may generate ‘idle’ data in the absence of sufficient Packets supplied from the users at release time. The mechanism for generating idle data shall be to create an Idle Packet of appropriate length defined by reference [6]. NOTE – The shortest Idle Packet is seven octets in length (i.e., a six-octet header plus one octet of idle data). If the area to be filled in a Data Field is less than seven octets, then the Idle Packet will spill over into the beginning of the next Frame Data Field. If it is necessary, the Packet Processing Function may generate an ‘idle’ Data Field by setting the First Header Pointer to ‘11111111110’. An abstract model of the Packet Processing Function is illustrated in figure 4-6. Packet Service User with PVN M Packet Service User with PVN N Packets Packet Processing Function for a Virtual Channel Packets Idle Packet Construction of Transfer Frame Data Field and Generation of First Header Pointer Transfer Frame Data Fields Virtual Channel Generation Function Figure 4-6: Abstract Model of Packet Processing Function 4.2.3 VIRTUAL CHANNEL GENERATION FUNCTION NOTE – The Virtual Channel Generation Function is used to build the basic structure of Transfer Frames. It is also used to build the structure and the Primary Header of the Transfer Frames for transmission on each Virtual Channel. There is an instance of the Virtual Channel Generation Function for each Virtual Channel. Transfer Frames shall be assembled by: a) placing a Transfer Frame Data Field (received from the Packet Processing Function) or a VCA_SDU (received from the VCA Service user) into the Transfer Frame Data Field; and b) generating the Transfer Frame Primary Header fields. A Virtual Channel Frame Count shall be generated independently for each Virtual Channel and placed into the Primary Header. CCSDS 132.0-B-1 Page 4-16 September 2003 CCSDS RECOMMENDATION FOR...
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This document was uploaded on 03/06/2014.

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