Subject: Re: Gateways and registration

From: Sean Olson <[email-masked]>
Date: Thu, 6 Jan 2000 17:43:34 -0600 (CST)

> 
> The SIP specification does not require that gateways register with a SIP
> server.  Thus, the server is never notified if the gateway goes offline.  By
> contrast, protocols such as H.323 have a different concept for Registration
> and a server can detect when a gateway goes down or offline if registration
> expires.
> 
> Is there some way to provide equivalent functionality in SIP?  If not, is
> the concept of gateway registration under consideration for a future draft
> of the spec?
> 

Although not required by the SIP standard, there is absolutely nothing to 
keep you from doing this other than the fact that there are better 
mechanisms. TRIP might be one avenue to consider. 

> Thanks.
> Linden deCarmo
> Netspeak Corporation
> 902 Clint Moore Road
> Suite 104
> Boca Raton, FL 33487

-----------------------------------------------------------------
Sean Olson            mailto:[email-masked]
Ericsson Inc.         tel:(972)583-5472 
                      fax:(972)669-0154

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From: Henning Schulzrinne <[email-masked]>
Date: Fri, 07 Jan 2000 09:31:33 -0500

> mechanisms. TRIP might be one avenue to consider.

The slight difficulty is that SIP registers users, so a gateway
"representing" phone numbers would have to register a lot of individual
users. This is another reason TRIP is preferable, since it has
mechanisms to aggregate reachability information. It is not clear to me
that creating a wildcard user, with all the possible permutations, would
be wise. Obviously, if you know your proxy server, nothing prevents you
from registering

415*@gateway

or whatevever format you choose.

Henning

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From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 07 Jan 2000 09:55:55 -0500

The additional difficult with SIP REGISTER isn't just the wildcarding
problem, but that the semantics are wrong. If multiple gateways register
a single number (aka, multiple Contacts with the same To field), the
result is that the proxy will *fork* a call to these, in all likelihood,
which is not at all what you want. Choosing of a gateway for terminating
calls depends a lot on policy information, and requires additional
information also not provided in a REGISTER message. TRIP does all this
for you, and also works for getting routing information from other
domains (thats its main job, in fact). A TRIP implementation on a
gateway is actually very simple, since you don't need any of the policy,
import, aggregation processing from TRIP, just the exporting operation.
In fact, I would argue that a gateway implementation of TRIP is simpler
than implementing some kind of REGISTER extension.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       200 Executive Drive
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