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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 184.108.40.206 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 .
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’.
220.127.116.11 An abstract model of the Packet Processing Function is illustrated in figure 4-6.
User with PVN M Packet Service
User with PVN N Packets Packet
Channel Packets Idle Packet
Construction of Transfer Frame Data Field
and Generation of First Header Pointer
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.
18.104.22.168 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
b) generating the Transfer Frame Primary Header fields.
22.214.171.124 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.
- Spring '14