[CESG] Late input from SEA on the CESG-P-2020-02-006 CSTS FF poll

Sat Jan 16 00:48:42 UTC 2021

Dear Erik, Holger, Tom, et al,

Please accept this late input from SEA on this poll.  I took the time to actually review the spec in some detail and it took rather longer than  I expected.  I was hoping that this FF-CSTS spec would meet all of the planned requirements for this forward frame service.  Unless I somehow overlooked some important features that are documented deep in the bowels of this 218 page specification I am afraid that I have to conclude that it has missed the mark.

The “mark” in my understanding, is that this spec was supposed to define the list of features that follows below.  These are drawn from the original SISG Space Internetworking Strategy report that first defined the features of this forward frame service intended to accommodate DTN (and IP) traffic, from the SCCS-ARD/ADD where these features were documented in the context of the rest of the CCSDS protocol stacks and Earth Space Link Terminal (ESLT, otherwise known as a ground station plus its associated control center elements), and the features that already existed in the EF-CLTU Orange Book that was created because there was no other documented service for handling the synchronous AOS frame protocol for forward links.

  1.  Ability to provide an “SLE-like” forward link service for synchronous link protocols, initially AOS, but now to include USLP
  2.  Provide encoding in the ESLT for this forward link frame stream
  3.  Ability to accept input frame streams from more than one user source
  4.  Ability to multiplex frame streams from all of the input sources, including some that are not directly from FF-CSTS itself
  5.  Ability to keep a synchronous forward link filled, if necessary by inserting fill frames in the ESLT
  6.  Ability to integrate the protocol PDUs from DTN, IP, CFDP, or other data sources, from “agents” instantiated in the ESLT, to create frames that encapsulate these PDUs, and to integrate these in the multiplexed frame stream (see items 3 & 4)

As best I can tell this spec fails to accomplish items 5 and 6 at all, and it appears to give only passing acknowledgement to items 2 or 4.  These are mentioned as being features that are needed somewhere in the ESLT, but there is not a section of the document, nor even an informative annex, let alone a normative one, that would suggest what was really intended nor how to accomplish it.  In my judgement this is a significant oversight and renders this document inadequate to the task at hand which was to document how these services were to be provisioned and integrated.

Unfortunately, from my point of view, instead of addressing these absolutely required services the document as presented spends a lot of “real estate” documenting how this new service can be made to handle TC forward asynchronous frames.  Since there is already a perfectly serviceable SLE F-CLTU that provides this service this seems like an unnecessary effort.  The only conceivable rationale that occurs to me is that this TC forward service is very much like that needed for USLP variable length frame forward service.  That said, I really have to question whether it would have been better to just modify SLE F-CLTU to accommodate USLP variable length frames instead of weighing this document down with this added baggage.

It appears that in this document we got far fewer of the essential features than were required and, at the same time, more features than were really useful.

While I recognize that a large amount of work has been expended to get this document to this point, in my estimation it falls far short of what is really required.  It does not provide all of the features called for in the IOAG SISG, nor that were documented in the SCCS-ARD Magenta Book, nor does it appear to provide all of the features in the F-CLTU Orange Book which has for years been supporting major operational missions.  It was intended to provide services that could meet all of these requirements, and it seems to have failed to do so.

Accordingly, I cannot support publishing this document in its current form.

With respect, Peter Shames

________________________________________________________

Peter Shames
CCSDS Systems Engineering Area Director

Jet Propulsion Laboratory, MS 301-490
California Institute of Technology
Pasadena, CA 91109 USA

Telephone: +1 818 354-5740,  Fax: +1 818 393-6871

Internet:  Peter.M.Shames at jpl.nasa.gov
________________________________________________________

We must recognize the strong and undeniable influence that our language exerts on our ways of thinking and, in fact, delimits the abstract space in which we can formulate - give form to - our thoughts.

Niklaus Wirth

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