Re: [core] Comments on draft-ietf-core-yang-cbor-06
Robert Wilton <rwilton@cisco.com> Mon, 09 July 2018 15:37 UTC
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To: Carsten Bormann <cabo@tzi.org>, Michel Veillette <Michel.Veillette@trilliant.com>
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From: Robert Wilton <rwilton@cisco.com>
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Date: Mon, 09 Jul 2018 16:37:09 +0100
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Subject: Re: [core] Comments on draft-ietf-core-yang-cbor-06
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On 09/07/2018 16:23, Carsten Bormann wrote: > 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. Yes, I completely agree. I'm not convinced that it is worth optimizing for the case where the protocol knows the SID of the parent node, and hence deltas can be used for the top node. Always using 0 as the parent of the root node just seems to facilitate simpler interop. However, it is worth adding a caveat to my statement that I'm reviewing the encoding more from a RESTCONF protocol perspective rather than constrained devices so simplicity is more important me to saving a small number of bytes. If saving those few extra bytes for delta SIDs over absolute SIDs for the top level SIDs is critical then I think that another solution would be to put an extra non-presence container in the data model. Hence the NP-container uses a absolute SID and all children use deltas again. Of course, this depends on the data model being written in CBOR+SID friendly way. Thanks, Rob > > 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 >> >> >> >> >> _______________________________________________ >> core mailing list >> core@ietf.org >> https://www.ietf.org/mailman/listinfo/core > . >
- [core] Comments on draft-ietf-core-yang-cbor-06 Robert Wilton
- Re: [core] Comments on draft-ietf-core-yang-cbor-… Andy Bierman
- Re: [core] Comments on draft-ietf-core-yang-cbor-… Robert Wilton
- Re: [core] Comments on draft-ietf-core-yang-cbor-… Carsten Bormann
- Re: [core] Comments on draft-ietf-core-yang-cbor-… Carsten Bormann
- Re: [core] Comments on draft-ietf-core-yang-cbor-… Robert Wilton
- Re: [core] Comments on draft-ietf-core-yang-cbor-… Michel Veillette
- Re: [core] Comments on draft-ietf-core-yang-cbor-… Andy Bierman
- Re: [core] Comments on draft-ietf-core-yang-cbor-… Robert Wilton
- Re: [core] Comments on draft-ietf-core-yang-cbor-… Carsten Bormann
- Re: [core] Comments on draft-ietf-core-yang-cbor-… Michel Veillette