Subject: [Sipping] RE: [Sip-implementors] Use of 181--Call is being forwarded

From: "Gaurav Kheterpal" <[email-masked]>
Date: Thu, 21 Dec 2006 13:25:57 +0530

I see what you mean. This was discussed quiet recently on the SIPPING Group.
Please refer to

http://www1.ietf.org/mail-archive/web/sipping/current/msg12363.html

http://www1.ietf.org/mail-archive/web/sipping/current/msg12359.html

I'm not sure whether a consensus was reached over it or not.

Regards,

Gaurav

  _____  

From: Ritesh Tiwari [mailto:[email-masked]] 
Sent: Thursday, December 21, 2006 1:04 PM
To: Gaurav Kheterpal
Cc: [email-masked]
Subject: Re: [Sip-implementors] Use of 181--Call is being forwarded

Hi Gaurav,

I dont understand why proxy will generate 181 response when this is an
end-to-end response? Then what and how proxy will fill as a To-Tag in 181?

thanks

Ritesh

 

On 12/21/06, Gaurav Kheterpal <[email-masked]> wrote: 

GK>> One of the uses of 181 is the scenario of 'Call Forwarding no No
Answer'.

The proxy sends back a 181 response to the caller to indicate that the 
original call is being forwarded to a new destination (URI) & subsequently
sends an INVITE to the new callee.

The difference between 181 and 3xx level forwarding is that 181 indicates
proxy level forwarding while 3xx response is mostly used in UA level 
forwarding.

Refer the call flow at http://www.tech-invite.com/Ti-sip-service-9.html.

And rfc 3261 also says all provisional
messages  except 100 trying must have "To" tag in the section 8.2.6.2.

GK>> The 'To' tag is of relevance in case of forking as there might be
multiple responses returned by UAS. The 'To' tag helps a UAC distinguish
between these final responses. 

I hope this helps.

Regards,
Gaurav

-----Original Message-----
From: [email-masked]
[mailto: <mailto:[email-masked]>
[email-masked]] On Behalf Of Ritesh Tiwari
Sent: Thursday, December 21, 2006 1:43 AM
To: [email-masked]
Subject: [Sip-implementors] Use of 181--Call is being forwarded 

Hi,

I don't understand the use of SIP response 181 "Call is being forwarded".
181 is a end-to-end response. And rfc 3261 also says all provisional
messages  except 100 trying must have "To" tag in the section 8.2.6.2.

thanks
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