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

[Paul Kyzivat <[e-mail]>]

On 5/7/18 3:41 PM, Christer Holmberg wrote:
> Hi Thomas,
> 
> I hope Paul can jump in on this one too, since it’s ABNF related :)

OK. I have taken a brief look at the full syntax in the draft.

It is a challenge to find a way to reference the definitions you need 
without duplication!

If this is truly to define a fragment, so that any valid SDP, after 
stripping out the stuff you don't want to include, is a valie fragment, 
then you must allow any ordering of the relevant attribute fields. At 
the moment you mandate a particular ordering.

Also at the moment you indicate some attributes as required and some 
optional. I see no practical way to (in ABNF) distinguish between 
optional and required while allowing arbitrary ordering.

There is also a question about how to handle extension attributes. You 
currently handle this by referencing the generic syntax of an attribute 
from rfc4566. But of course this doesn't have a way to restrict to 
ice-relevant attributes.

This can all be addressed by making the syntax "looser" and then 
restricting it further via normative text.

But this all needs more discussion. So lets discuss this more before 
deciding.

	Thanks,
	Paul