[Sls-slp] Your LFSR OID frame RIDs affecting USLP, TM, AOS SDLPs

Mon May 17 17:15:49 UTC 2021

Ken,
              Maximal pattern shift registers.  LFSR
              CCSDS is not supposed to make recommendations about implementation.  For implementing I understand that the Galois shift register is sometimes preferred over the Fibonacci form.  However, for understanding and for setting an initial seed, Fibonacci has tremendous advantage because WYSIWYG, if you remember that phrase from the early Apple computers, what you see is what you get.
              You might also remember that we had a recent go-around in the code and synch WG about how to show these shift registers and we (GSFC) were recommending Fibonacci with particular labeling of the cells so that the polynomial is directly related to the cells that are tapped.  Yes, I realize that this can also be done for the Galois form.  Another value of the Fibonacci with the particular cell numbering is that it is what MatLab uses.  So when people are doing simulations, no conversion is needed.
              As you might remember there is an ambiguity between the associated polynomial and the shift register labeling.  A particular pattern can be generated in one direction or the reverse.  We had a particular proposal and it turned out that MatLab used the same convention.     Our proposal was discarded since it would be too much editing to get all the books to follow the same convention, and maybe other reasons.
              But in any case, seems better from an understanding point of view to use Fibonacci.

Victor

From: Kazz, Greg J (US 312B) <greg.j.kazz at jpl.nasa.gov>
Sent: Monday, May 17, 2021 12:31 PM
To: Andrews, Kenneth S (JPL-332B)[JPL Employee] <kenneth.s.andrews at jpl.nasa.gov>
Cc: Sank, Victor J. (GSFC-567.0)[SCIENCE SYSTEMS AND APPLICATIONS INC] <victor.j.sank at nasa.gov>; Kazz, Greg J (US 312B) via SLS-SLP <sls-slp at mailman.ccsds.org>
Subject: Your LFSR OID frame RIDs affecting USLP, TM, AOS SDLPs

Hi Ken,

The SLP WG decided to put both of your diagrams into a new non-normative annex in USLP, TM, and AOS.
The text in the normative part of the link layer books will state:

The TFDZ of an OID Transfer Frame shall be generated by use of a 32-cell Linear Feedback Shift Register (LFSR) with polynomial 1 + D + D2 + D22 +D32, see Annex X.

Where Annex X is TBD and will be added by me to the document.

We have some questions and requests for you:

  1.  Why does the initialization data differ from one figure to the other one?
  2.  The ‘1’ in the figures are misleading to some WG members, please replace ‘1’ with D sub zero i.e., D0 in the figures.
  3.  Consensus of WG was to specify the initialization vector

Thanks!
Greg

Greg Kazz
Principal Engineer
Technical Group Supervisor,
PSSE/EEISE/PPSE (312B)
Jet Propulsion Laboratory
4800 Oak Grove Dr., M/S 301-490
Pasadena, CA 91109
1+(818)393 6529(voice)
1+(818)393 6871(fax)
email: greg.j.kazz at jpl.nasa.gov<mailto:greg.j.kazz at jpl.nasa.gov>

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