Hi Brett,
Thank you for the reply,,
This sip proxy is statefull & maintains the sip session till the call is active.
Example:
Step-1: uac---->(invite)-----sip proxy----(invite)----uas
Step-2: uac<-----(200ok)-----sip proxy----(200ok)<----uas
Step-3: uac----->(refer)-----sip proxy-----------------uas
The sip proxy is light weight & have limited sip functionalities, this is the 
reason behind..

>> Yes; BYE with Also might still work with some older devices.  :)
>> https://tools.ietf.org/html/draft-ietf-mmusic-sip-cc-01
Will go through "draft-ietf-mmusic-sip-cc-01", 

>> The REFER is the SIP way to trigger a transfer.  Most of the other ways are 
>> proprietary, RFC 3725 type stuff, or things such as the transfer described 
>> within RFC 4730 section 3.4.
Will go through these links...

Regards
Mahu
-----Original Message-----
From: Brett Tate [mailto:br...@broadsoft.com] 
Sent: 30 October 2014 16:17
To: Mahudeswaran A; sip-implementors@lists.cs.columbia.edu
Subject: RE: [Sip-implementors] call transfer without using REFER

> Is it possible to transfer a call without using SIP REFER.
> Call path:
> [uac]-------[sip proxy]--------[uas]
> The SIP REFER is not supported in the above sip proxy.

As indicated by RFC 3261 section 16.3, the proxy does not need to support 
REFER.  It just needs to proxy the REFER.

" This protocol is designed to be extended.  Future extensions may  define new 
methods and header fields at any time.  An element MUST  NOT refuse to proxy a 
request because it contains a method or  header field it does not know about."

Thus if the proxy does not relay the REFER to the UAS, it is either 
non-compliant or providing a service (such as helping referred party avoid a 
potential unexpected billing situation).

> Is there a way to achieve call transfer without using sip refer...

Yes; BYE with Also might still work with some older devices.  :)

https://tools.ietf.org/html/draft-ietf-mmusic-sip-cc-01

The REFER is the SIP way to trigger a transfer.  Most of the other ways are 
proprietary, RFC 3725 type stuff, or things such as the transfer described 
within RFC 4730 section 3.4.
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