Subject: RE: [Sipping] Early media; a summary after the IETF

From: "Mark Watson" <[email-masked]>
Date: Thu, 3 Apr 2003 14:30:12 +0100

Christer,

I meant the part that allows you to ask the termination to 'play a tone
until you get incoming media, then play that' - or perhaps I've missed
something and that is already possible too ?

It is the use of RTP packets themselves as an implicit indication that there
is early inband media, compared to defining an explicit signalling
indication that I think is a bad design. If you only have the former,
implicit, indication available, then I see nothing wrong with your proposal
wrt H.248.

...Mark

> -----Original Message-----
> From: Christer Holmberg [mailto:[email-masked]]
> Sent: 03 April 2003 13:50
> To: Watson, Mark [MOP:EP10:EXCH]
> Cc: 'Gonzalo Camarillo'; Taylor, Tom-PT [CAR:5N00:EXCH];
> [email-masked]; Jon Peterson
> Subject: Re: [Sipping] Early media; a summary after the IETF
> 
> 
> 
> Hi Mark,
> 
> Just a short question: what do you mean "is not completely 
> supported in
> H.248 yet"? It's a package, which has been standardized, so from that
> point of view I think it as "supported" as anything else...
> 
> Or, did I missunderstand you?
> 
> I would also like to hear your arguments why/what you don't think is
> good design? The fact that in H.248 an event can stop a 
> signal, or what?
> 
> I do agree, which I also mentioned in the mail, that there may be some
> issues. Those, however, are more related to the Context model.
> 
> Regards,
> 
> Christer Holmberg
> Ericsson Finland
> 
> 
>

---

From: Christer Holmberg <[email-masked]>
Date: Fri, 04 Apr 2003 09:59:10 +0300

Hi,

> >I meant the part that allows you to ask the termination to 'play a
> tone until you get incoming media, then play that' - or perhaps I've
> missed something and that is already possible too >?

My understanding of H.248 is that it is possible to do so, as long as it
happens on the same termination.

> >It is the use of RTP packets themselves as an implicit indication
> that there is early inband media, compared to defining an explicit
> signalling indication that I think is a bad design. If >you only have
> the former, implicit, indication available, then I see nothing wrong
> with your proposal wrt H.248.

I think it is important to notice that the "H.248 solution" above may
not work very well in networks where we have early media. The reasons is
that the MG really doesn't know if the media is early or not (if the
"final" media reaches the MG before the 200 OK). So, in a forking
scenario it would have to accept and forward all media, which again may
lead to media mixing. So, one would have to assume that there is NO
early media, and that the RTP packet detected actually comes from the
node which has answered the call and sent 200 OK.

IF we have early media, and we don't want media mixing, I guess we still
have to wait for 200 OK before we forward media. But, then we again have
the risk of media clipping, since we may have forwarded media from
another early leg (to avoid clipping), or we haven't forwarded any media
at all...

Regards,

Christer Holmberg
Ericsson Finland

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