asterisk users - Feb 2012 - Reffered By header is missing from SIP INVITE in call transfer scenarios

Hi,
    We are facing an issue with asterisk in the case of call-Transfer scenarios.
Our requirement is to identify whether an incoming call is a fresh incoming call
or a Transferred call from some other clients.

We have a setup, where in the asterisk1.6 (as SIP server) is running in Linux
machine, and three SIP clients(say A,B,C) registered to asterisk server are
running in three different windows machines.

With the above said setup, there is a call made from SIP client-A to SIP
client-B through asterisk. The incoming call got answered in SIP client-B and
transferred the call to SIP client-C via asterisk.
Here the SIP client-B sends a REFER SIP message to Asterisk and a new INVITE
(corresponds to the REFER SIP) is sent to SIP client-C. But there is no REFFERED
BY Header added in the INVITE SIP message which is sent to SIP client-C.
Due to this we are not able to identify the incoming call as Transferred call.

So, we have two questions:
1)       Are there any configuration changes in Asterisk to solve this (so that
the asterisk handles the transfer in SIP signaling)?
2)       Is there any other way in which we can identify a call as forwarded
call?


Best regards,
Rajib
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