Re: [core] Comments on draft-ietf-core-yang-cbor-06

Carsten Bormann <cabo@tzi.org> Mon, 09 July 2018 15:23 UTC

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From: Carsten Bormann <cabo@tzi.org>
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Date: Mon, 09 Jul 2018 17:23:06 +0200
Cc: Robert Wilton <rwilton@cisco.com>, "draft-ietf-core-yang-cbor@ietf.org" <draft-ietf-core-yang-cbor@ietf.org>, "core@ietf.org" <core@ietf.org>
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To: Michel Veillette <Michel.Veillette@trilliant.com>
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Subject: Re: [core] Comments on draft-ietf-core-yang-cbor-06
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It is much less confusing to always talk of deltas in the structure.

Just say that the context SID value (the one that the delta is computed from) is 0 at the root of a tree.

Grüße, Carsten


> On Jul 9, 2018, at 17:18, Michel Veillette <Michel.Veillette@trilliant.com> wrote:
> 
> Hi Robert
>  
> Andy also asked for a clarification about the encoding of the root data node identifier (absolute vs. delta).
> Section 4.4.1. have a sentence addressing this topic.
>    It is important to note that the protocol or method
>    using this mapping may carry a parent SID or may have the knowledge
>    of this parent SID based on its context.  In these cases, delta
>    encoding can be performed based on this parent SID which minimizes
>    the size of the encoded data.
>  
> A similar sentence need to be added to section 4.2.1.
> We also need to clarify that the protocol or method using this encoding must mandate which approach is implemented, the data serialized don’t carry this information.
>  
> Regards,
> Michel
>  
> From: Robert Wilton [mailto:rwilton@cisco.com] 
> Sent: Monday, July 9, 2018 11:00 AM
> To: draft-ietf-core-yang-cbor@ietf.org; core@ietf.org
> Subject: Comments on draft-ietf-core-yang-cbor-06
>  
> Hi,
> 
> I've read this draft, and think that it is well written.
> 
> There is one area of the draft that is somewhat unclear to me when using SID encodings:  Is the root node(s) of a request or a response always an absolute SID value, or could it still be a delta?
> 
> In particular:
> 
> Sec 2.1 indicates that the translation to/from SID deltas is stateless, which implies to me that the root node(s) of a request/response would always be an absolute SID value.
> 
> Sec 4.2.1 gives an example using a absolute SID for the top node.  It then has this text: "
> 
>    On the other hand, if the serializer is aware of the parent SID, 1716
>    in the case 'system-state' container, root data nodes are encoded
>    using deltas.
> "
> I think that it is quite plausible that the serializer may know the SIDs for all nodes in the data tree, which the text implies it could then use a relative SID for the top node.  Particularly, if the top level node was explicit from the request.
> 
> Hence, I think that this draft could probably benefit in being more explicit on exactly when a top level node uses an absolute SID, and in what scenarios it may end up using a a relative SID.  If this distinction is down to the protocol being used, then perhaps that could be stated?
> 
> One other nit:
> 
> Section 4.4.1 says "delta encoding can be performed", but I think that this should probably be "delta encoding MUST be performed".
> 
> Thanks,
> Rob
>  
> 
>  
> 
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