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

Andy Bierman <andy@yumaworks.com> Mon, 09 July 2018 17:04 UTC

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From: Andy Bierman <andy@yumaworks.com>
Date: Mon, 09 Jul 2018 10:04:01 -0700
Message-ID: <CABCOCHQm7j+pUWHfLGAEic1CM2O-H-4hHP96vvuTHSgTigvVpw@mail.gmail.com>
To: Robert Wilton <rwilton=40cisco.com@dmarc.ietf.org>
Cc: Carsten Bormann <cabo@tzi.org>, "draft-ietf-core-yang-cbor@ietf.org" <draft-ietf-core-yang-cbor@ietf.org>, "core@ietf.org" <core@ietf.org>
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Subject: Re: [core] Comments on draft-ietf-core-yang-cbor-06
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On Mon, Jul 9, 2018 at 9:39 AM, Robert Wilton <
rwilton=40cisco.com@dmarc.ietf.org> wrote:

>
>
> On 09/07/2018 17:20, Carsten Bormann wrote:
>
>> On Jul 9, 2018, at 18:09, Robert Wilton <rwilton@cisco.com> wrote:
>>
>>> ambiguity as to whether the top level nodes are using absolute or delta
>>> sids
>>>
>> We don’t need to be able to include “absolute SIDs”(1) into the delta
>> positions in the encoding.
>> The deltas are always deltas.  They just happen to be relative to a
>> context SID at the top of the tree; mostly, that is 0 (but that’s what we
>> are also discussing here).
>>
> Apologies if my terminology was confusing.
>
> I agree, that we are discussing whether the parent of the top level nodes
> should always have a SID of 0, or otherwise if it should be explicitly
> specified.
>
> For me, one of the big advantages of CBOR over schema based encodings like
> protobuf, is that the structure of the encoded data is self describing.  I
> think that it is worth spending a few extra bytes in the encoding to get
> this property.  So, if I get a bad CBOR message that I can't interpret then
> I can easily convert it into a human readable structure to debug the
> problem (or know the CBOR itself is invalid/corrupt).  I see that requiring
> external knowledge for the parent SID of the top level nodes seems to take
> a step away from that.
>
>
I was thinking the same thing.
Do you really want to deploy a protocol that is near impossible to debug
with wireshark?



> E.g. if the device accidentally gives a response for the wrong node in the
> tree, and if the response relies on the SID in the request to be fully
> decodeable then the response will somewhat look like garbage and it will be
> harder to debug.  Is this worth saving a couple of bytes for?
>
>
Decoding SIDs incorrectly can crash the device or set the wrong object so I
would
say that correctness in NM is important no matter how many bytes it takes.



> Thanks,
> Rob
>

Andy


>
>
>
>> Grüße, Carsten
>>
>> (1) there is no need for this term; SIDs are SIDs and SID deltas are SID
>> deltas.  The map key positions in YANG-CBOR are always SID deltas.
>>
>>
>> .
>>
>>
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