Subject: [SIP] Call Transfer Using REFER Method.

From: Sekhar Banerjee <[email-masked]>
Date: Mon, 26 Feb 2001 13:49:17 -0800

> Hi All,
> 
> 	We are having a hard time trying to figure out how to make the
> Transferee send the Invite to the Transfer Target through the proxy when
> REFER is used to transfer the call. Could you shed some light on how this 
> can be achieved.
> 
> Transferee	    Transferor       Proxy		Transfer Target
> 
> Invite|--------------------------->
>       |<----------------------- 100 Trying
>       |             <---------- Invite
>       |         200 -------------->
>       |<----------------------- 200
> Ack   |--------------------------->
>       |             <---------- Ack
>       |        Invite(c=0)-------->
>       |<----------------------- Invite(c=0)
> 200 Ok|--------------------------->
>       |             <---------- 200 Ok
>       |         Ack -------------->
>       |<----------------------- Ack
>       |            Invite(TT)----->
>       |                         Invite ------------->
>       |                           <--------------- 200
>       |                 <-------- 200
>       |        Ack	-------------->
>       |                           Ack -------------->
>       |        Bye	 -------------> 
>       |                           Bye -------------->
>       |                           <--------------- 200
>       |                 <-------- 200
>       |        Refer  ------------>
>       |<------------------------- Refer
> 200 Ok|--------------------------->
>       |            <------------- 200 OK
> Invite|--------------------------------------------->
>       |<------------------------------------------- 200 Ok
> Ack   |--------------------------------------------->
> Bye   |--------------------------------------------->
>       |<------------------------------------------- 200 Ok
> 
> 	We would like to see the last Invite and Bye go through the proxy
> too
> so that the proxy can control that call. Would a Record-Route in the Refer
> help me achieve this goal ? Or a route header embedded in the referred-to 
> header ? Is the transferor mandated to use the route header thus provided?
> 
>     Is there anybody out there that has implemented supervised call
> transfer
> using the Refer method so that the proxy is involved in the messaging for
> all
> the three calls? If so, we would appreciate to find out how you
> accomplished
> this (in a billable manner).
> 
> TIA,
> Ragunath/Shriram.
> 

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