[Spce-user] Using REFER method for transfer

[Jon Bonilla (Manwe)]

El Wed, 19 Sep 2012 17:47:35 +0200
Imanol Pardavila <imanol.pardavila at ibercom.com> escribió:

> Hi,
> I've just started testing sip:provider CE, and I have my first question. 
> When I try making a transfer for my endpoint, I get a Forbidden message. 
> As I can see in the pcap file, it seems that sip:provider CE doesn't 
> allow REFER method. Can it be enabled on any config file?
> Thanks
> Imanol


You can enable it if you want. It's disabled by default to avoid fraud as if
the refer is forwarded to your pstn gws and they accept that method, customers
can receive a local call, be transferred to an international destination and
the peer gw owner pays the bill. Be careful with enabling REFER method!

What can you do to enable it:

- First, you'll need to enable the method itself in the proxy configuration
  using a customtt template. In kamailio.cfg file add it to the list of allowed
  methods:

-if(is_method("INVITE|ACK|CANCEL|BYE|OPTIONS|PRACK|UPDATE"))
+if(is_method("INVITE|ACK|CANCEL|BYE|OPTIONS|PRACK|UPDATE|REFER"))

That would be enough for the proxy as REFER is only sent in-dialog and no
further confguration would be needed.

- The second part is that you need to whitelist some headers in sems sbc in
  order REFER to work. Sems has a list of allowed headers and removes the rest.
  In ngcp.sbcprofile.conf you could disable header filtering or add the needed
  headers to the whitelist:

-header_list=P-D-Uri,P-Preferred-Identity,P-Asserted-Identity,Privacy,Allow,Supported,P-Out-Socket[%
IF kamailio.proxy.presence.enable == "yes"
%],Event,Expires,Subscription-State,Accept[% END %]

+header_list=P-D-Uri,P-Preferred-Identity,P-Asserted-Identity,Privacy,Allow,Supported,P-Out-Socket[%
IF kamailio.proxy.presence.enable == "yes"
%]Expires,Accept[% END %], Refer-To, Subscription-State, Event

That should be enough. This has be written without checking so I don't warranty
the result. Maybe I forgot some headers but a ngrep capture could help you
dealing with that.

I also don't know the result or impact of the billing process when a call is
ended due a REFER. 

And please, take in consideration the security risks before enabling this
method. Make sure your gws don't allow REFER.



cheers,

Jon

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