Re: [MMUSIC] Changes for draft-ietf-mmusic-trickle-ice-sip-14 - ABNF

[Christer Holmberg <[e-mail]>]

Hi,

>>I hope Paul can jump in on this one too, since it’s ABNF related :)
>
>I've been doing my best to ignore these drafts. :-)
>
>I'll have to do some reading for context. Just looking at this thread in
>isolation my first thought is that this seems to be defining a new
>attribute with the definition including the "a=" which we are really
>trying to avoid.

It is not defining a new attribute per se, but it is defining the usage of
the attribute within the ‘application/trickle-sdp-sdpfrag’ message body.

Regards,

Christer






>>>> However, I think there are some issue with the ABNF (not related to
>>>>Adam¹s
>>>> issue).
>>>>
>>>> For example, the syntax says:
>>>>
>>>>    ice-pwd-attribute      = %s"a" "=" ice-pwd-att
>>>>
>>>> Then the draft says:
>>>>
>>>>    with ice-pwd-attribute from [I-D.ietf-mmusic-ice-sip-sdp],
>>>
>>> which says
>>>
>>> ice-pwd-att           = "ice-pwd:" password
>>> i.e. doesn't introduce a second a=
>> 
>> First, I think the structure in draft-ice-sip-sdp is wrong. It shall be
>>something like:
>> 
>>        Attribute Name: ice-pwd
>> 
>>        Attribute Value: ice-pwd-att
>> 
>>        Usage Level: media
>> 
>>        Charset Dependent: No
>> 
>>        Mux Category: TBD
>> 
>>      The Augmented BNF syntax [RFC5234] for the attribute is:
>> 
>>        ice-pwd-att = password
>>        password = blah blah...
>> 
>> Now, whether we should use that syntax also in trickle-ice I don't
>>know. I would like to hear Paul's opinion.
>> 
>>>> In my reading, this would result in:
>>>>
>>>>    a=a=ice-pwd:asd88fgpdd777uzjYhagZg
>>>>
>>>> Is this what you want?
>>>
>>> No, and with the above syntax we do not get the a=a=
>>>
>>>> If you want to use the syntax of draft-ietf-mmusic-ice-sip-sdp, why
>>>>not do
>>>> it directly? Something like:
>>>>
>>>> session-level-field = ice-pwd-att /
>>>>                        Š
>>>>                        Š
>>>>
>>>> ;ice-pwd-att as defined in [I-D.ietf-mmusic-ice-sip-sdp]
>>>>
>>>> Or, have I missed something?
>>>
>>> The trickle-ice-sdpfrag syntax uses just a subset of SDP attributes
>>>and isn't  build as open as  the SDP syntax , the above doesn't work.
>> 
>> I am not suggesting an open SDP syntax - I am suggesting the reference
>>the specific syntax for the ice-pwd attribute.
>> 
>> Regards,
>> 
>> Christer
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> On 06/05/18 21:31, "Thomas Stach" <[e-mail]> wrote:
>> 
>> All,
>> 
>> during IESG review we got the below proposal by Adam for changing the
>> ABNF to allow for more encoding flexibility.
>> 
>> Unless somebody objects, I'd provide the proposed change by end of the
>> week.
>> 
>> It would affect the "session-level-fields" as proposed below and in a
>> similar way the  "pseudo-media-descriptions" and
>> "trickle-ice-attribute-fields"
>> 
>> Excerpt from Adam'S IESG review:
>> 
>> §9.2:
>> 
>> The syntax for "session-level-fields", "pseudo-media-descriptions", and
>> "trickle-ice-attribute-fields" include extremely strict rules around
>> ordering of
>> fields (e.g., including ice-ufrag before ice-pwd would be syntactically
>> invalid). That level of strictness seems unlikely to lead to
>>interoperable
>> implementations.
>> 
>> If the intention is to be rigid in this fashion, please add prominent
>> prose
>> that warns implementors that fields MUST appear in the order specified,
>> and
>> that all other orders are invalid and MUST be rejected.
>> 
>> If that's *not* your intention (and I suspect it isn't), then please fix
>> the
>> syntax definition to allow for arbitrary ordering of attributes in the
>> same way
>> as SDP does. For example:
>> 
>>       session-level-fields = *(session-level-field CRLF)
>> 
>>       session-level-field = bundle-group-attribute /
>>                             ice-lite-attribute /
>>                             ice-pwd-attribute /
>>                             ice-ufrag-attribute /
>>                             ice-options-attribute /
>>                             ice-pacing-attribute /
>>                             end-of-candidates-attribute /
>>                             extension-attribute-fields
>>                                    ; for future extensions
>> 
>> 
>> Regards
>> 
>> Thomas
>> 
>> 
>> 
>> 
>