[SR-Users] New SIP INVITE from UAS (new dialogue)

[Alex Balashov]

Hello Joao,

As a general rule, speaking broadly and methodologically, Kamailio - as 
a SIP proxy - is not a good vehicle for the initiation of calls, since 
it cannot, itself, be a party to a dialog. Synthesising an INVITE using 
uac_req_send() isn't going to work because there's no second party to 
the dialog. Where will the replies to the INVITE go? Kamailio itself 
cannot be a party.

There are, nevertheless, the ways to initiate a call from Kamailio using 
the 'dialog' module. The most straightforward is probably the 
'dlg_bridge' / 'dlg.bridge' (MI and RPC respectively) commands, which 
can be called externally to Kamailio,

http://kamailio.org/docs/modules/4.3.x/modules/dialog.html#idp3756384

or internally from route script, via the dlg_bridge() command:

http://kamailio.org/docs/modules/4.3.x/modules/dialog.html#idp3698368

The general idea here is that an INVITE is initiated to one party and 
then that party is REFER'd out to another party. REFER is a SIP method 
that is commonly used for unattended transfers and call forwarding. You 
can read more about it here:

https://www.ietf.org/rfc/rfc3515.txt

Of course, for it to work, party #1 has to support REFER.

-- Alex

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Alex Balashov | Principal | Evariste Systems LLC
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