[Kamailio-Users] Transfer/Refer of calls

[Klaus Darilion]

Geir O. Jensen schrieb:
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> Hi, just noticed that we can't transfer calls...
> 
> We use SNOM UA's for our enduser and run Kamailio 1.4 as our SIP router.
> Kamailio routes all external calls to a remote SIP gateway (telco).
> Which is the same gateway that accepts calls from the PSTN and relays it
> via SIP to us.
> 
> Now, the issue seems to be that when we do an attended call transfer the
> UA sends a refer message to the GW... which the GW doesn't support!
> 
> Is there any other way of doing transfers/refer with Kamailio (or does
> anyone know a workaround for the SNOM UA's?)

No. Call transfer uses REFER requests and REFER is end2end. So, if one 
of the parties is the GW up your PSTN provider, then the GW needs to 
support REFER. Ask your provider for REFER support.

Another workaround woulb be to have a B2BUA in your network.

E.g instead of

client ---- proxy -------------------------------gateway of provider

use


client ---- proxy ---- virtual-GW ---------------gateway of provider


The B2BUA can be seen as a virtual-GW (border element, SBC, call it 
whatever you like). This is a setup I usually use: my proxy uses a 
"virtual gateway" which is completely under my control. This virtual GW 
writes CDRs, and handles multiple PSTN providers (also useful as for 
example you can change PSTN providers without changing the Kamailio 
configuration). Furthermore, such a "GW" is under your control and you 
can configure it to allow REFER.

For the B2BUA you can user ASterisk, Freeswitch, ......

regards
klaus


> 
> Thanks for any insight, this is about to become a showstopper for our
> telephone service :(
> 
> - - Geir
> 
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