Re: [MMUSIC] draft-ejzak-mmusic-data-channel-sdpneg and draft-ejzak-mmusic-msrp-usage-data-channel

[Paul Kyzivat <[e-mail]>]

On 11/12/14 9:09 AM, Juergen Stoetzer-Bradler wrote:

> On 12.11.2014 04:17, Christian Groves wrote:
>> Hello
>>
>> I had a chance to look over the latest draft in more details. Some
>> comments/questions:
>>
>> 5.1.1.1: To enforce the text about dcmap-opt the ABNF could be updated:
>>    dcmap-opt       = ordering-opt / subprotocol-opt / label-opt
>>                      / ( maxretr-opt / maxtime-opt )
>
> [Juergen] Actually, I am not sure if this would formally prevent
> maxretr-opt and maxtime-opt  from both being present simultaneously, as
> we would still have
>      dcmap-value = dcmap-stream-id [ SP dcmap-opt *(";" dcmap-opt) ]
> (allowing an arbitrary number of "dcmap-opt").
> My understanding of RFC 5234's definition of "alternation" has so far
> been that
>       dcmap-opt = ordering-opt / subprotocol-opt / label-opt /
> maxretr-opt / maxtime-opt
> and
>      dcmap-opt = ordering-opt / subprotocol-opt / label-opt / (
> maxretr-opt / maxtime-opt )
> are actually equivalent.
> Right now don't see a "compact" way of strengthening the actual ABNF
> rules without having to list all possible parameter combinations and
> permutations.

Yes. I agree. There is no good way to do this in ABNF. One could get 
"closer", with something like:

    dcmap-value     = dcmap-stream-id
                      *(";" dcmap-non-max-opt)
                      [dcmap-max-opt]
                      *(";" dcmap-non-max-opt)
    dcmap-non-max-opt = ordering-opt / subprotocol-opt / label-opt
    dcmap-max-opt     = maxretr-opt / maxtime-opt

Note that this separates the stream-id from the opts with ";" rather 
than " ". (It would be much harder while preserving the space.)

But this still syntactically allows multiple use of the non-max-opts 
(e.g. multiple occurrences of ordering-opt.) So there is still a need 
for normative text to forbid that. IMO it is more straightforward to do 
all of these constraints in text.

	Thanks,
	Paul