[Sls-sea-dls] SDLS EP GVCID Issues

[Gian.Paolo.Calzolari at esa.int]

OK, David. 
On the other hand it is not the task of SDLS to explain something defined in other standard. 
Still a NOTE with a warning can help. 

Regards

Gian Paolo

Sent from my iPhone

> On 15. Jul 2019, at 15:26, David Koisser <David.Koisser at esa.int> wrote:
> 
> Hi Gian Paolo,
> 
> As you said, it needs to be implemented "with some caution". However, I think standards should either avoid pitfalls like this entirely (if possible) or hint at them *very* clearly. It should be crystal clear how to process frames. This is especially true for a security standard. 
> 
> I don't think the current version does enough to hint at the inherent ambiguity of the GVCID, which took me quite a while to actually notice.
> 
> Cheers,
> David
> Gian Paolo Calzolari---15/07/2019 11:04:56---David, I am mot sure I fully capture your issue/doubts.
> 
> 
> From:	Gian Paolo Calzolari/esoc/ESA
> To:	"David Koisser (external)" <David.Koisser at esa.int>
> Cc:	"Lucas, John P.\(GSFC-5960\)" <john.p.lucas at nasa.gov>, "SLS-SEA-DLS" <sls-sea-dls-bounces at mailman.ccsds.org>, "sls-sea-dls at mailman.ccsds.org", "Kazz, Greg J (313B)" <greg.j.kazz at jpl.nasa.gov>, "Matt Cosby" <matt.cosby at goonhilly.org>
> Date:	15/07/2019 11:04
> Subject:	Re: [Sls-sea-dls] SDLS EP GVCID Issues
> 
> 
> David,
> I am mot sure I fully capture your issue/doubts.
> There are indeed different definitions sometimes coming ether from real difference (TM and AOS do not have MAPs) or from some different terminology for historical reasons.
> 
> The general definition is indeed GVCID = TFVN + SCID + VCID & GMAPID = TFVN + SCID + VCID + MAPID with the caveat that the MAP Identifies may not exist and that the total length depends on the applied standard.
> Implementers need to implement it with some caution.
> 
> The mapping between USLP and Proximity is due - as far as I remember - that Proximity-1 never really defined a GVCID.
> 
> Greg & Matt, copied here, may add more comments.
> 
> Note also tat there a pending corrigendum (not yet on web but approved) for CCSDS 320.0-M-7 CCSDS Spacecraft Identification Field Code Assignment Control Procedures. Magenta Book. Issue 7. November 2017.
> 
> Regards
> 
> Gian Paolo
> 
> "David Koisser (external)" ---15-07-2019 10:21:41---Hello everyone, We noticed some more issues regarding the GVCID / MAPID. After checking,
> 
> 
> From:	"David Koisser (external)" <David.Koisser at esa.int>
> To:	"sls-sea-dls at mailman.ccsds.org"@esa.int
> Cc:	"Lucas, John P.\(GSFC-5960\)" <john.p.lucas at nasa.gov>
> Date:	15-07-19 10:21
> Subject:	[Sls-sea-dls] SDLS EP GVCID Issues
> Sent by:	"SLS-SEA-DLS" <sls-sea-dls-bounces at mailman.ccsds.org>
> 
> 
> 
> Hello everyone, 
> 
> We noticed some more issues regarding the GVCID / MAPID. After checking, it turns out different standards have very different interpretations. I attached screenshots of the regarding sections of the blue books for your convenience. 
> 
> The SDLS EP GVCID seems to be an aggregate of the longest defined versions of the respective fields. To my knowledge SDLS EP seems to be the only and first document, which specifically defines a (merged) GVCID. All other standards only define them as GVCID = TFVN + SCID + VCID & GMAPID = TFVN + SCID + VCID + MAPID (without sizes). In USLP the relation between old and new frames is defined, but only for Proximity-1 (see C1.1). I am not sure if this is more clearly explained somewhere else. 
> 
> In SDLS EP I see two problems. First, there is no explanation or justification for the lengths. Second, this may possibly lead to severe bugs, e.g. overflowing a TM VCID bigger than what fits in the defined 3 bits, like 16 bits in USLP or worse, 6 bits in TC (with identical TFVN as TM). Improper sanity checks here may even lead to security critical bugs. 
> 
> Cheers, 
> David 
> 
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