Subject: [Sip] Sending an announcement!!

From: Kolinowitz Bernd <[email-masked]>
Date: Tue, 2 Sep 2003 15:49:46 +0200

Hi!

We want to implement a typical PSTN feature in our SIP proxy. If caller A sends an INVITE (including audio in the sdp) to the sip-proxy, the proxy should send an announcement (like a jingle) to caller A while it is trying to reach the callee.

We are now searching for a way to implement the feature concerning RFC 3264 (offer/answer model of SDP). First we thought to answer with early media, that means to send a 183 response including the SDP for the announcement and demanding a PRACK request.
Next we have thought to forward the 200 response from the callee to the caller. 
Now there is our problem: What should the caller do with the SDP?

The good version: He accept the SDP from the callee as an answer of his SDP offer in the first INVITE-request and sends an empty ACK.
The bad version: The SDP in the 200 response will be treated as a new offer and he sends an SDP answer in the ACK request.

How will the client react? Is there another way to realize this feature?

Thanks in advance
Bernd

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---

From: "Christian Stredicke" <[email-masked]>
Date: Tue, 2 Sep 2003 19:44:32 +0200

Hi Bernd, 

just include the announcement UA in the forking. If then someone else
picks up (what a surprise) the phone has to deal with it. It will then
receive another SDP answer.

Please also take a look at Alert-Info.

CS

> -----Ursprüngliche Nachricht-----
> Von: [email-masked] [mailto:[email-masked]] Im Auftrag von
> Kolinowitz Bernd
> Gesendet: Dienstag, 2. September 2003 15:50
> An: 'SIP list'
> Betreff: [Sip] Sending an announcement!!
> 
> 
> Hi!
> 
> We want to implement a typical PSTN feature in our SIP proxy. If
caller A
> sends an INVITE (including audio in the sdp) to the sip-proxy, the
proxy
> should send an announcement (like a jingle) to caller A while it is
trying
> to reach the callee.
> 
> We are now searching for a way to implement the feature concerning RFC
> 3264 (offer/answer model of SDP). First we thought to answer with
early
> media, that means to send a 183 response including the SDP for the
> announcement and demanding a PRACK request.
> Next we have thought to forward the 200 response from the callee to
the
> caller.
> The good version: He accept the SDP from the callee as an answer of
his
> SDP offer in the first INVITE-request and sends an empty ACK.
> The bad version: The SDP in the 200 response will be treated as a new
> offer and he sends an SDP answer in the ACK request.
>

---

From: Rohan Mahy <[email-masked]>
Date: Tue, 2 Sep 2003 12:04:49 -0700

Hi,

Depending on how you implement this feature you may no longer be just a 
proxy.  I can think of three ways to accomplish this behavior.

1) the proxy inserts an Alert-Info header in the 180 responses returned 
by the callee.  This header contains a URL which points to the jingle.  
This puts a very small amount of work on the UAC, and requires almost 
no work on the proxy (best of both worlds)

2) a user agent which is co-located with the your proxy sends an INVITE 
with Join request to the UAC (this session has its own separate SDP).  
This puts all the hard work on the UAC, and is more desirable if you 
want to be involved for an extended period of time.

3) your device becomes a B2BUA, and uses 3pcc to INVITE an announcement 
service to play the jingle, then uses lots of reINVITEs, UPDATEs, 
PRACKs, and reliable provisionals to manipulate the session with the 
UAC.  this is the most complicated for you, but still requires PRACK 
and UPDATE to be supported (all 6 possible combinations of 
offer/answer) to be implemented on the UAC.

Hope this helps.

Note: in future you should send these types of questions to 
[email-masked] instead.

thanks,
-rohan

On Tuesday, September 2, 2003, at 06:49 AM, Kolinowitz Bernd wrote:

> caller A sends an INVITE (including audio in the sdp) to the 
> sip-proxy, the proxy should send an announcement (like a jingle) to 
> caller A while it is trying to reach the callee.
>
> early media, that means to send a 183 response including the SDP for 
> the announcement and demanding a PRACK request.
> the caller.
> his SDP offer in the first INVITE-request and sends an empty ACK.