Subject: [Sip] Inform a SIP Location Server about temporary moved users

From: Werner Rades <[email-masked]>
Date: Tue, 23 Jan 2007 14:53:40 +0100

Hi all,

I want to start a discussion on a - in my opinion - existing problem
with "roaming" SIP users. Let's describe the problem:
Guess we have two locations at our company. Each location has it's own
SIP proxy (siteA.mydomain.tld and siteB.mydomain.tld) and users homed at
one of theses two proxys. Thus users can register at their home
registration server (their home proxy). So each user can be reached via
sip:<user>@<proxy-at-site>. If the user is at this desk there is no
problem. In case of an arriving call the UA at the registered IP of the
user is invited via SIP. So the call get's established.

Let's guess userA from siteA (sip:[email-masked]) is out for 
hollidays and he want to redirect all his calls to this voicemail box. 
Then he has a few possibilitys:
(a) set a call redirection at his phone (so the phone sends a
"temporarily moved" message to the proxy, the proxy can redirect the
invite to his new location e.g. [email-masked])
(b) ask his administrator for setting a static redirect at the location
server (proxy) at siteA so that it redirects the invite to his new
location e.g. [email-masked]
(c) use a protocol like DUNDI to find the user in the list of peered
location server (proxys) to redirect the call to these address. (TRIP
also can't solve the problem)
(d) use ENUM and alter the NAPTR record to e.g. 
[email-masked] (would only work if a call arrives at his 
e.164 number, not for "direct" calls to [email-masked])

In my opinion all these posibilities are less satisfactory. The most
interesting thing is a "static" redirect from the proxy server of the
users home location (proxy siteA.mydomain.tld), but the users
administrator would beat us to death.
If we use the redirect from the phone (384 moved temporary) the phone
needs to stay connected to the network (if we use a softphone or want to
use the hardphone for other purposes then the invite could not be
handled by the phone and the proxy doesn't get informed about the moved
user).
DUNDI would not make it possible to support a user moving out of the
dundi administrative domain (e.g the user went out to work at home and
has his sip client at home registerd with a sip provider, e.g.
[email-masked]) and ENUM would not cover directed calls to
[email-masked].

I think it would be great if we would have a sip command that the
authenticated user could send to his home registration server (proxy or
location server at siteA) and tell this server where the user has
temporary moved to.
This is more efficient than setting this at the phone (if it should 
persist for more than a short), because of the phone can be turned of or 
temporary used by another user from siteA.

The same procedure is well known from conventional PBX distributors.
They store the redirect information provided from the user to the phone
in the PBX. So if you disconnect the phone the call redirection is still
active.

I have searched the web for a similar possibility in the SIP RFCs, but
found no coresponding function.

Is this still covered by any RFC and I was not able to found it?
How do you think about this idea for a SIP command that can provide this
functionality?

Thanks for your comments and thoughts on this topic...

Best regards,
Werner

Mit freundlichen Grüßen

Werner Rades
--------------------------
BCA-Services Ltd.
IT-Department
Dachauer Str. 20

D-80335 München / Munich

eMail [email-masked]
Web:  http://www.bca-itservices.com

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---

From: Diego B <[email-masked]>
Date: Tue, 23 Jan 2007 16:09:55 +0200

Hi;
CPL can do this.
If userA sends to the Proxy a CPL file with his new Forward preferences,
the proxy will know where to find him ( or where to redirect calls to him )
by applying the rules in the CPL script.

Now the question is if your proxy supports CPL :)
or any other way to configure Forward rules for users
like Forward Unconditional to voice mail.

Regards
Diego B

Werner Rades wrote:
> persist for more than a short), because of the phone can be turned of 
> or temporary used by another user from siteA.
>

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From: Paul Kyzivat <[email-masked]>
Date: Tue, 23 Jan 2007 09:38:46 -0500

Werner,

What you are asking for is essentially a standardized implementation of 
a particular service. (Call forward unconditional.) There is a new BOF 
(BLISS) starting up to look at this. That would be a place to go to 
pursue this further.

	Paul

---

From: [email-masked]
Date: Tue, 30 Jan 2007 12:47:45 -0500

From: Werner Rades <[email-masked]>

I don't see what the difficulty is.  Of necessity, any calls to
userA's AOR will be routed through a proxy.  The proxy's first
preference will be to send the call to userA's phone, the second
preference will be to send it to the voicemail system.  So there are
three straightforward ways to handle this situation:

- The user directs the proxy to temporarily remove the phone from the
  list of contacts for the AOR.  (There should be a user interface on
  the proxy for this.)

- There can be a setting on the phone so that it immediately gives a
  4xx response to all incoming calls.  This will cause the proxy to
  immediately send the call to voicemail.

- The user can unplug the phone!  This causes its registration to
  expire, so the proxy will send all calls to voicemail.

The essential philosophical points are:

- The phone is not responsible for routing calls, only for deciding
  whether to accept a call that is routed to it.

- Voicemail is implemented as a second-choice contact point for the
  AOR.

Dale