Subject: [SIP] Call Transfer Using REFER Method.

From: Ragunath Devarasu <[email-masked]>
Date: Mon, 26 Feb 2001 14:58:24 -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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