Re: [MMUSIC] Review of 4566bis

Christer Holmberg <christer.holmberg@ericsson.com> Tue, 02 June 2015 15:24 UTC

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From: Christer Holmberg <christer.holmberg@ericsson.com>
To: Paul Kyzivat <pkyzivat@alum.mit.edu>, Roni Even <ron.even.tlv@gmail.com>, "mmusic@ietf.org" <mmusic@ietf.org>
Thread-Topic: [MMUSIC] Review of 4566bis
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Date: Tue, 2 Jun 2015 15:24:30 +0000
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Subject: Re: [MMUSIC] Review of 4566bis
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Hi,

>>> I do not think that general media level overrides session level value 
>>> works for the b= attribute Roni
>>
>> b= is not an attribute :)
>>
>> Anyway, my suggestion would be that the DEFAULT RULE for all SDP elements that can occur both on 
>> session and media level should be that the media level overrides the session level. Then, in cases where 
>> it does not apply, it should be explicitly stated.
>
> I do think this *would have been* the right thing to do from the beginning. But I am uncertain 
> if it is the right thing to do *now*, for backward compatibility reasons.
>
> Before doing so we will need to do an exhaustive study of all current attribute definitions that are registered 
> in IANA as valid at both session and media level - to ensure that their meaning won't be changed by this.

I agree.

And, I am not saying we shall apply the media-overrides-session rule to all attributes - I am saying that it needs to be clear to which attributes the rule applies, and to which it doesn't.

Leaving it unspecified will not bring compatibility, and the whole purpose of a bis is to correct bugs and clarify things which are unclear :)

I would assume that, in most cases, the media-overrides-session rule DOES apply.

And, we must make sure that, when new attributes are defined, it is indicated whether the rule applies or not.

Regards,

Christer


>> -----Original Message-----
>> From: mmusic [mailto:mmusic-bounces@ietf.org] On Behalf Of Paul 
>> Kyzivat
>> Sent: 31 May, 2015 8:43 PM
>> To: mmusic@ietf.org
>> Subject: Re: [MMUSIC] Review of 4566bis
>>
>> On 5/31/15 9:38 AM, Christer Holmberg wrote:
>>
>> Good list Christer!
>>
>> I have comments on a few of your issues:
>>
>>> Q6_2:
>>>
>>> In some of the sub-sections, it is indicated that a media-level 
>>> attribute value overrides a session-level attribute value. As far as 
>>> I know, that applies to all attributes (that can be present both on 
>>> the session-level and media-level), so there should be a generic 
>>> statement about that.
>>>
>>> This is similar to the comment on the c= line.
>>
>> I used to think this, but I think there are some exceptions. (But I 
>> don't
> offhand
>> remember what they are.)
>>
>>> Section 6.7:
>>>
>>> ---------------
>>>
>>> Q6-7_1:
>>>
>>> The text says:
>>>
>>>      "If any one of these appears in a media section then it applies 
>>> for
>>>
>>>      that media section.  If none appear in a media section then the 
>>> one
>>>
>>>      from session level, if any, applies to that media section."
>>>
>>> There should be a general statement in the draft about session level 
>>> information applying to the media level.
>>
>> I wish there could be a general statement, but it is hard, given
> exceptions.
>> Perhaps there could be a general statement with note that it can be
> overridden
>> in particular cases.
>>
>> But in any case, *this* is different, because it says that the 
>> presence of
> any
>> *one* of four different attributes at media level overrides the 
>> presence
> of any
>> one of those four at session level.
>>
>>> Section 6.11:
>>>
>>> -----------------
>>>
>>> The text says that the attribute "specifies the language" of the 
>>> session description.
>>>
>>> There has been some confusion about what that really means, so I 
>>> think it would be good to clarify that it applies to any textual 
>>> information that may be provided within the description.
>>>
>>> It would also be good to explicitly indicate that the attribute is 
>>> not related to languages used in the actual media streams.
>>
>> +1
>>
>> 	Thanks,
>> 	Paul
>>
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