[CESG] Why renaming GSCID inf revised CCSDS SCID Code Assignment Control Procedures?

Shames, Peter M (312B) peter.m.shames at jpl.nasa.gov
Tue Jul 12 16:58:44 UTC 2016

Dear Gippo,

I appreciate your attention to detail and looking at this early on, but I have to differ re some conclusions.   I note the following:

-          The term GSCID was defined as “GSCID = VN . SCID” where the “.” means concatenation.

-          The terms SCID and GSCID are used more or less interchangeably in the CCSDS 320x0b document, but they mean different things.  This is a flaw in the current document that I have tried to remedy.

-          The term SCID is defined specifically in the various protocol documents, 320x0 just references it.

-          The term GSCID does not appear in any of our protocol documents, TC, TM, or AOS.  They tend to call the combination of the VN (actually the TFVN) and the SCID an MCID, not a GSCID.

-          If you search the CCSDS files you will find that the only reference to GSCID is in this 320x0 document, and not in any others.
All of that said, I think that there is really no impediment in the way of extending the definition of GSCID to include the frequency band, because globally, in fact, the frequency band has from the beginning been a part of the actual physical and logical link layer signal.  We just did not acknowledge this until now.
But if you are worried about some confusion for others we could introduce a new term for the FB . VN . SCID combination.  I’m reluctant to call it a “Super” SCID, that sounds like a kid’s toy.   ;-}  And in truth, I think that this is more of a Global SCID than the current definition, and which the protocol docs call an MCID.  In effect we have given the same thing two different names, surely that is not a good approach?  Maybe we should align this book with all of the existing protocol docs and call the VN . SCID combo an MCID and the FB . VN . SCID combo the GSCID?
I am open to other suggestions.
Regards, Peter

From: CESG <cesg-bounces at mailman.ccsds.org> on behalf of Gian Paolo Calzolari <Gian.Paolo.Calzolari at esa.int>
Date: Tuesday, July 12, 2016 at 6:18 AM
To: CCSDS Engineering Steering Group - CESG Exec <cesg at mailman.ccsds.org>
Cc: Tom Gannett <thomas.gannett at tgannett.net>
Subject: [CESG] Why renaming GSCID inf revised CCSDS SCID Code Assignment Control Procedures?

Dear CESGers,
        in order to gain time and not to delay eventual Poll and start of Agency Review, I would like to anticipate that as SLS AD I wonder about the need of renaming GSCID in revised CCSDS SCID Code Assignment Control Procedures.

In fact the revised book includes a new definition of GSCID (see snapshot) that is conflicting with the definition in the Blue Book in force (see second snapshot) as the new one also refers to Frequency Band.

First of all I think that it is not appropriate modifying a term used for so many years (and for sure spread in "billions" of documents from many agencies) also considering that the the prefix "Global" is widely used for e.g. the Global VCID and Global MAP ID (for sure in SLE and SLS books) without considering the Frequency Band.
Therefore there would be a discrepancy of meaning about the term Global between the GSCID and the GVCID

Last, but not list the book title "CCSDS Global Spacecraft Identification Field" points to a field i.e. a portion of data that is normally contained in transfer frames. In other words while the actual GSCID matches completely the contents of some bits of a Frame Header, the proposed future GSCID will not.

As a conclusion I would retain the current definition of  GSCID while adding a new definition for the  concatenation of the frequency band (FB), 2-bit Version Number (VN) and the SCID.
This could be called Universal SCID, Super SCID, Supreme SCID, Frequenced SCID or whatever you prefer.    [Please consider some humour in some proposed definitions.]


Gian Paolo

PS Of course I did not perform a complete review of the document.......

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