A frame may be any integral number of octets in

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Unformatted text preview: A frame may be any integral number of octets in length, from a minimum consisting of only a primary header (5 octets or 40 bits) to the maximum number of octets that can be counted by the "Frame Length" field in the header (256 octets or 2048 bits). The TC Frame is serially inserted into the "information" fields of as many Codeblocks as necessary. If the length of a frame is not exactly the same as the total data space of the Information fields in the required codeblocks, fill is added to the Information field of only the LAST codeblock. If more than one frame resides in a CLTU, frames are organized contiguously and any necessary fill is added only in the LAST codeblock of the CLTU. The necessary TC building blocks are the TC Frame, CLTU, and the codeblocks. These may be organized in several different ways depending on the performance required, operational convenience, accounting convenience, etc. Three organizations are described below: One frame per CLTU; multiple frames per CLTU; and multiple CLTUs. Frame performance may be assessed by considering the performance of a sequence of codeblocks and the effect of their organization into CLTUs. D-4.1 One Frame, One CLTU This section deals with the organization where each frame is contained in its own CLTU, as shown in Figure D-3. A codeblock rejection anywhere in the frame will cause rejection of that frame. CLTU ACQ TAIL START INFO P INFO P INFO P FRAME (CONTAINED IN INFO FIELDS) Figure D-3: Single Frame, Single CLTU Organization The probability of frame rejection is determined from a) the probability of missing a CLTU start, OR b) the probability of finding a CLTU start AND the probability of rejecting one or more codeblocks. Issue 6 Page D-12 January 1987 CCSDS REPORT CONCERNING TELECOMMAND: SUMMARY OF CONCEPT AND SERVICE For Strategy 1 (using TED mode, denoted by subscript A), <Prob. of frame rejection in a standalone CLTU, TED mode> = PFA = PSA + (1 - PSA) PCA [EQ. E] and for Strategy 2 (using SEC mode, denoted by subscript B), PFB = PSB + (1 - PSB) PCB [EQ. F] Examples. To illustrate the range of performance obtained with this organization (one frame per CLTU), let us consider the shortest and longest permitted frame lengths. The shortest frame permitted is just a header: 5 octets or 40 bits. This frame could be organized into a single 48-, 56- or 64-bit codeblock, or two 40-bit codeblocks. The probability of rejection for such a frame is shown in Table D-4. Table D-4: Probability of Rejection of a MINIMUM Length Frame as a Function of Codeblock Length Chosen __________________________________________________________________________ MINIMUM LENGTH FRAME CodeInforNo. of DeProbability of frame rejection block mation codecoding for channel BER of length, field, blocks mode 10-5 10-6 bits bits needed 10-4 ___________________________________________________________________________ 64 56 1 TED SEC 7.87x10-3 2.06x10-5 7.90x10-4 2.07x10-7 7.90x10-5 2.07x10-9 56 48 1 TED SEC 7.08x10-3...
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