Subject: [Sip] Thoughts on multiple registrations to an extension

From: Sidney San Martín <[email-masked]>
Date: Sun, 11 Oct 2009 18:33:39 -0400

Disclaimer: I'm not involved in the SIP community and not very  
familiar with its implementation or history.

Whenever I use an IP phone, I run into a nned to register the same  
extension on multiple devices, and I always get the recommendation to  
create more extensions and use hackery on the PBX to make 'em work  
like they're a single one. That's not good enough. The other protocols  
we use to communicate (XMPP, POP/IMAP/SMTP, even proprietary ones like  
AIM and old ones like POTS) are all friendly to multiple connections  
to the same account. Why's this functionality missing from SIP? There  
are only a few use cases, but they're huge ones:

- A user has a desk phone but also wants to take and place calls  
occasionally from a computer or mobile device over cellular data.  
Usually, the desk phone will be the only device registered.
- A user wants an extension represented in two or more geographically  
separate locations, say on a desk phone at home and a desk phone at work
- A house with extensions in several rooms. Right now, the "IP" part  
of IP telephony usually evaporates inside the home, where SIP gets  
bridged to POTS. That's great for retrofits, but as fewer people  
subscribe to landline service, there will come a time when new homes  
aren't wired for POTS. At the same time, many new homes ARE being  
wired with Ethernet.

What do you all think about this problem? (If it's already been  
discussed to death, feel free to lightly whack me over the head and  
point me to the right thread :).)

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From: "Dale Worley" <[email-masked]>
Date: Mon, 12 Oct 2009 10:09:32 -0400

> are only a few use cases, but they're huge ones:

Multiple registrations is a functionality that was built into SIP from
the beginning.  Many, many users of sipXecs have been using it for many
years and we have never seen a fundamental problem with it.  It is not
clear to me who would recommend to you that multiple registration does
not work in SIP.  Is it possible that you are confusing SIP with other
voice-over-IP protocols, some of which do not support multiple
registrations well?

If you have  tried to use multiple registrations and they have not
worked, please tell us about your experiences in detail.  I'm sure the
problem can be corrected.

Dale

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From: "Dale Worley" <[email-masked]>
Date: Mon, 12 Oct 2009 11:44:08 -0400

> voice-over-IP protocols, some of which do not support multiple

Sorry about that message, I mistook which mailing list I received it
via.  However, the above description is valid regarding SIP.

> problem can be corrected.

If you have trouble with the sipXecs system, please write to the
sipx-users mailing list (@list.sipfoundry.org).  If you have trouble
with other SIP systems, you can write to sip-implementors
(@lists.cs.columbia.edu).

Dale

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From: "Scott Lawrence" <[email-masked]>
Date: Mon, 12 Oct 2009 11:51:53 -0400

On Sun, 2009-10-11 at 18:33 -0400, Sidney San Martín wrote:
> like they're a single one. That's not good enough.

Then you should find other phones and/or other PBXs.  Multiple
registrations should just work with no hackery required.