1 overview neither the tm space data link protocol

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Unformatted text preview: = Single Bit Delay Figure 9-2: Pseudo-Randomizer Logic Diagram CCSDS 131.0-B-2 Page 9-3 August 2011 CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODING 10 TRANSFER FRAME LENGTHS 10.1 OVERVIEW Neither the TM Space Data Link Protocol (reference [1]) nor the AOS Space Data Link Protocol (reference [2]) specifies the length of Transfer Frames because there are constraints on the Transfer Frame length depending on the selected coding options. The constraints on Transfer Frame lengths specified in this section apply to both TM Transfer Frames and the AOS Transfer Frames. 10.2 GENERAL 10.2.1 Once selected, the Transfer Frame length shall be fixed for a Mission Phase on a particular Physical Channel. NOTE – The Transfer Frame lengths shown here do not include the length of the Attached Sync Marker (ASM) specified in section 8. 10.3 CASE 1: UNCODED The length of the Transfer Frames shall be any integer number of octets, as required by the using project, with a maximum of 2048 octets. 10.4 CASE 2: CONVOLUTIONAL ONLY The length of the Transfer Frames shall be any integer number of octets, as required by the using project, with a maximum of 2048 octets. 10.5 CASE 3: REED-SOLOMON ONLY NOTES 1 With the Reed-Solomon Codes specified in section 4, only certain specific lengths of Transfer Frames may be contained within the codeblock’s data space. In some cases these lengths can be shortened at a small sacrifice in coding gain. 2 Since these R-S codes have a symbol length of 8 bits, the length of the codeblock (in octets) is a multiple of the interleaving depth, which provides ‘octet compatibility’. 10.5.1 If necessary, Transfer Frame lengths shall be shortened in discrete steps by using virtual fill. CCSDS 131.0-B-2 Page 10-1 August 2011 CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODING 10.5.2 If high-speed efficiency is needed for ‘32-bit compatibility’ (with 32-bit processors, for example), then the length of the codeblock shall be a combined multiple of 4 and the interleaving depth. 10.5.3 When only octet compatibility is required, lengths for Transfer Frames (L in octets) shall be determined u...
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