Subject: [Sipping] Call Forwarding Queries

From: "Gaurav Kheterpal" <[email-masked]>
Date: Thu, 1 Dec 2005 11:30:57 +0530

Hi,

I had some queries regarding the implementation of Call Forwarding in
SIP. I would like to implement the conventional CF modes - CFU (Always),
CFB (Busy), CFN (No Answer) and CFC (Calendar) on a SIP phone as on a
normal PSTN phone/ PBX.

1. For CFU: Is it better to use
a) The Forwarding URI as a CONTACT header in the REGISTER request
itself, so that no INVITES are received on the original URI. This would
make forwarding to be dependent on registration expiry so is it a good
idea?
b) OR respond to every INVITE request with a 302/ 301 (which one of
these) with the Forwarding URI as the CONTACT header? (And with reason
header as 'Forward Immediate')

2. For CFN:
a) In this case, should the callee ring for duration of timer B (default
= 64*500 ms = 32 sec) before we send out a response (typically a 302
again with reason as 'Forward no reply'). But in this case, most proxies
will themselves generate a 408 Request Timeout on expiration of timer B?
How to handle this?

3. For CF based on Calendar (particular date/ time settings), which
value of reason header should be used?

4. For DND (Do Not Disturb), some implementations return a 480 while
others return a 486 in response to an INVITE. Though I feel it's better
to use a 480 as compared to 486 for the same, I would like a second
opinion on this.

I'm referring to the draft-elwell-sipping-redirection-reason-01.txt
draft for REASON header.

Thanks for your guidance in advance.

Regards,
Gaurav

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From: [email-masked]
Date: Thu, 1 Dec 2005 11:44:27 +0530

Hi gauvav,

I think RFC 3880 ("Call Processing Language (CPL):A Language for User
Control of Internet Telephony Services") will be helpful for you.

Regards
Nagendra

             "Gaurav                                                       
             Kheterpal"                                                    
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                                       [Sip-implementors] Call Forwarding  
                                       Queries                             
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Hi,

2. For CFN:

Regards,
Gaurav

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From: Daniel-Constantin Mierla <[email-masked]>
Date: Thu, 01 Dec 2005 15:44:51 +0200

> make forwarding to be dependent on registration expiry so is it a good
Actual this is what a SIP proxy with registrar and user location does. 
Looks up the contact address of an user and sends the INVITE there. This 
is not permanent forward since the contact address may change with the 
new REGISTER.
> header as 'Forward Immediate')
With this implementation, you will get a redirect server.
> will themselves generate a 408 Request Timeout on expiration of timer B?
Depending on proxy implementation. There are some which allow you to 
handle such cases (get a 408) and try another destination if the first 
one times out (e.g., openser, ser ...) -- this is also known as serial 
forking.
> value of reason header should be used?
If the forwarding is decided based on time, then you have to check 
user's time, nothing related to headers or reasons.

To help better, do you want to implement this features in some self 
developed SIP server or you are looking for a solution that supports 
such features?

Daniel