Subject: [Sipping] 3pcc, click-to-dial, ringing

From: Eric Cheung <[email-masked]>
Date: Mon, 28 Oct 2002 07:42:30 -0500

Hi Jonathan

Regarding the issue in 3pcc I-D call flows, where participant A does not
know when caller B is being alerted.  From your posting on May 16:

> Anyway, with that out of the way, of course an alerting tone can be
> provided to A. It is documented in Figure 7. If party B provides any
> kind of early media, whether its ringtone or announcements or whatever,
> they will be heard by A.
> 
> Now, the more complicated case is when B doesn't provide inband ringing.
> If, instead, it generates a 180 without SDP, or provides a other
> provisional response with an Alert-Info header. This is something that
> doesn't exist in circuit switched networks, and is unique to VoIP.
> Today, the best you can do is have the controller connect user A to a
> media server to play it an in-band ringing, which is far from desirable.
> We need some kind of standards-based way for the controller to tell one
> of the participants to generate some kind of media locally after it has
> answered the call. We have no standards for that today. One can always
> just invent some kind of header or something, but I think it is worth
> considering the problem more broadly. Sounds like a requirements
> document for enhanced 3pcc is in order...
> 

I wonder if you have had more thoughts on this?  I did not see anything
in the 3pcc-02 I-D that came out since.

IMHO, while the inband ringback tone provides some degree of backward
compatibility, it is not a good solution going forward.  For example,
what if a feature want to act on the condition equivalent to 180
RINGING.

Thanks
Eric
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