Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-channel-sdpneg

Christian Groves <Christian.Groves@nteczone.com> Thu, 26 November 2015 22:56 UTC

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From: Christian Groves <Christian.Groves@nteczone.com>
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Subject: Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-channel-sdpneg
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Hello Juergen,

Thanks for the updates. Please see my responses below.

Regards, Christian

..snip..
>>
>> Sect.5.1.1 1st para last sentence: Reliability is now two parameters: 
>> max-retr & max-time
> [Juergen] Indeed, would propose to replace "reliability" with "maximal 
> number of retransmissions, maximal retransmission time, ...".
[CNG] OK
>>
>> Sect.5.1.1 1st para last sentence: Priority is not defined by the 
>> syntax however its part of DCEP. Do we need to add this?
> [Juergen] Indeed, that's missing. Would propose to extend the 
> 'dcmap-opt' ABNF rule correspondingly:
>     dcmap-opt       = ordering-opt / subprotocol-opt / label-opt
>                       / maxretr-opt / maxtime-opt / priority-opt
>                       ; Either only maxretr-opt or maxtime-opt
>                       ; is present.
> With 'priority-opt' being
>     priority-opt    = "priority=" priority-value
>     priority-value  = "0" / integer
>                       ; unsigned integer value indicating the priority of the data channel
>                       ; less than 2^16
>                       ; derived from 'Priority' of
>                       ; [I-D.ietf-rtcweb-data-protocol]
>
> And would further propose to add a new sub section after current 
> 5.1.1.8 (ordered Parameter) as follows:
>
> 5.1.1.8 priority Parameter
> The 'priority' parameter indicates the data channel's priority
> relative to the  priorities of other data channels, which may
> additionally exist over the same SCTP association.
> The 'priority' parameter maps to the 'Priority' parameter defined in
> [I-D.ietf-rtcweb-data-protocol]. The 'priority' parameter is optional.
> In the absence of this parameter "priority=256" is assumed.
>
[CNG] The proposal is OK for me. Perhaps it would be worth adding the 
priority parameter to one of the examples?

>>
>> Sect.5.1.1.1: "maxretr-value" should we actually add an ABNF value 
>> for this? The referred to draft doesn't have ABNF. Its a 2 byte integer
> [Juergen] Agree. How about:
>
>     maxretr-value   = "0" / integer
>                       ; number of retransmissions
>                       ; less than 2^32
>                       ; derived from 'Reliability Parameter' of
>                       ; [I-D.ietf-rtcweb-data-protocol]
[CNG] OK
>
>>
>> Sect.5.1.1.1: "maxtime-value" should we actually add an ABNF value 
>> for this? The referred to draft doesn't have ABNF. Its a 2 byte integer
> [Juergen] Agree. Similar as above, this could be
>     maxtime-value   = "0" / integer
>                       ; milliseconds
>                       ; less than 2^32
>                       ; derived from 'Reliability Parameter' of
>                       ; [I-D.ietf-rtcweb-data-protocol]
[CNG] OK
>
>>
>> Sect.5.1.1.1: The example for a=dcmap:4, wouldn't this be invalid as 
>> it contains both the max-time and max-retr parameters?
> [Juergen] Yes, indeed. One of both parameters needs to be removed. As 
> the preceding example for a=dcmap:3 contains the max-retr parameter 
> I'd propose to remove the max-retr parameter from the a=dcmap:4 line.
[CNG] OK
>>
>> Sect.5.2.3, pg.14, 7th bullet: "Closes any created data channels for 
>> which the expected "a=dcmap:" and "a=dcsa:" attributes  are not 
>> present in the SDP answer." Should this also refer to section 5.2.4 
>> on closure?
> [Juergen] Agree. Will add a reference to section 5.2.4.
[CNG] OK
>>
>> Sect.5.2.5: The miscellaneous section doesn't explicitly cover the 
>> case when a=dcmap is missing but a=dsca is included. I take it that 
>> its an error. Should we add this?
> [Juergen] Good point. I would also consider this as an error. Agree to 
> add related text, e.g.:
>
> SDP offer or answer has no "a=dcmap:" attributes but has "a=dcsa:" 
> attributes
> * This is considered an error case. In this case the receiver of such an
>   SDP offer or answer SHOULD ignore the "a=dcsa:" attributes and SHOULD
>   process the SDP offer or answer as per above case 'SDP offer has no
>   "a=dcmap:" attributes' or case 'SDP answer has no "a=dcmap:" 
> attributes'.
[CNG] OK
>
>>
>> Sect.6 1st para under fig.2: "So, the offerer should  close the ..." 
>> is this really a "MUST close"? There is text about reusing a data 
>> channel but does it apply in this case when no previous data channel 
>> has been extablished?
> [Juergen] Quite agree. As per the corresponding description in section 
> 5.2.3 ("The agent receiving such an SDP answer performs the 
> following:  o  Closes any created data channels for which the expected 
> "a=dcmap:" and "a=dcsa:" attributes are not present in the SDP 
> answer.") the SDP offerer in example 2 actually must close the data 
> channel with SCTP stream id 0.
> As the text in the paragraph after figure 2 is just focused on example 
> 2, should we actually say "...the offerer MUST close the data channel 
> for BFCP ...", or rather "... the offerer must close ..."?
[CNG] How about avoiding "must" or "should" by saying the " ... The 
offerer closes the data or BFCP ..."? That's descriptive of the example.

..snip..