Re: [MMUSIC] DECISION: Default mechanism to map RTP data to m- line is based on PT?

On 6/26/13 7:37 AM, Harald Alvestrand wrote:
> I am on vacation now, so short answer:

You don't keep working while on vacation? :-)

> Apps that use m-lines for rtp session negotiation and not for stream
> control need no such association.
>
> If we mandate such association, we load those apps with extra luggage.

I still don't understand. If the m-lines are only used for session 
negotiation and not stream control then there is no need for multiple 
m-lines.

And note that what is being proposed is only that there be enough 
information available so that the association is *possible*. It isn't a 
requirement that the association actually be *done*. (But I don't see a 
case where it wouldn't be needed.)

Are you thinking of the case where there is just a bundle of one audio 
and one video m-line, because that is necessary in order to define the 
PTs for both audio and video? If so, then if the PTs are unique for the 
two m-lines, as they must be for it to work, then it is indeed possible 
to associate each packet with the proper m-line.

	Thanks,
	Paul

> Christer Holmberg <christer.holmberg@ericsson.com> wrote:
>
>     Hi Harald,
>
>     Just for my clarification: Assuming we are talking about
>     applications using RTP (instead of ANY BUNDLE application), is your
>     answer to Q3 still “no”?
>
>     In other words, do you think there might be RTP cases where it is
>     not needed to associate the RTP data with an m- line?
>
>     OR, do you think that BUNDLE simply shouldn’t say anything about how
>     to map RTP packets to m- lines?
>
>     Regards,
>
>     Christer
>
>     *From:*mmusic-bounces@ietf.org [mailto:mmusic-bounces@ietf.org] *On
>     Behalf Of *Harald Alvestrand
>     *Sent:* 26. kesäkuuta 2013 8:25
>     *To:* mmusic@ietf.org
>     *Subject:* Re: [MMUSIC] DECISION: Default mechanism to map RTP data
>     to m- line is based on PT?
>
>     On 06/25/2013 01:34 PM, Christer Holmberg wrote:
>
>         Hi,
>
>         Emil suggested that the default, “MTI”, mechanism for mapping
>         RTP data to m- lines should be based on PT. Applications are
>         allowed to use whatever other mechanisms, but usage of such
>         mechanisms must be negotiated (or, applications need to have
>         some other means knowing that the other endpoint support such
>         mechanisms).
>
>         *Q3*: Do we need to specify a default, MTI, mechanism for
>         mapping RTP data to m- lines?
>
>
>     No. This makes the assumption that all applications have the need to
>     map RTP data to m-lines; this assumption is not proven (and probably
>     cannot be - it's hard to prove a negative. It might be possible to
>     disprove it, though).
>
>
>     *Q4*: If Q3, do we mandate applications to support, and use (unless
>     applications are made aware of other mechanisms supported by all
>     endpoints) PT for mapping received RTP media?
>
>
>     If the WG disagrees with me on Q3, it might as well go down this
>     path. I have no strong opinion.
>
>
>     This means that, when mapping RTP to m- lines is required (whether
>     it is always mandated is discussed in another thread), within a
>     BUNDLE group each PT value must be unique to an individual m- line.
>
>     NOTE: If your answer to Q3 is “yes”, but your answer to Q4 is “no”,
>     please indicate which mechanism you prefer J
>
>     Regards,
>
>     Christer
>
>
>
>
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