The way our SIP net works is that phone B sends out a
BYE with an ALSO header in it.  The ALSO header will
have the SIP address of phone C.  

B --------------> Proxy
   BYE with ALSO

Proxy ---------------> C
         INVITE, from A

A is on hold

C ----------------> Proxy
       180


Proxy ------------->  A
          180

A ----------------> Proxy
         200

Proxy ---------------> C
           200

A <====================> C


For more info check out:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121newft/121t/121t3/dtsipgv2.htm#xtocid1219618


--- Hrishikesh Saria <[EMAIL PROTECTED]>
wrote:
> 
> 
> How do I support call transfer when a session has
> already been started.
> 
> The scenario is like this
> 
> A         ---------------->         B
>                invite
> 
> A         <---------------            B
>               180  
> 
> A         <---------------            B
>               200 
> 
> _________________________
> 
>     Media has started
> 
> Now B has to  to transfer the call to C so that the
> media between A and B is terminated and the media is
> started between A and C.
> The point is B has to make the transfer.
> 
> How is this possible using the SIP protocol.
> 
> 
> 


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