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

[Christer Holmberg <[e-mail]>]

Hi Thomas,

I hope Paul can jump in on this one too, since it’s ABNF related :)

>> 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