Subject: Re: [SIP] Informing UA after network initated deregistration?

From: William Marshall <[email-masked]>
Date: Thu, 8 Mar 2001 19:55:50 -0500 (EST)

In addition to the "panic - I'm about to crash/power down" case,
there are also various administrative reasons to remove a registration.
Like, for instance, you've been cut off for not paying your bill.
Or your prepaid account has gone empty.  If the UA is giving the
user some indication that a registration is active, and it is enabled
to receive incoming calls, that is now bogus information.  We'd like
the information displayed to the user to be accurate, at least.

Bill Marshall
[email-masked]

-----original message-----
From: "Henning G. Schulzrinne" <[email-masked]>
Subject: Re: [SIP] Informing UA after network initated deregistration?
Date: Thu, 08 Mar 2001 19:24:03 -0500

Michael Thomas wrote:
> 
> Er, how can the registrar NOTIFY something if it
> forgot?
> 

I guess this is the "panic - I'm about to crash/power down" message. One
semi-reasonable case that was brought up last time was taking down the
registrar for maintenance. The solution, I believe, was to remove the
registrar from the SRV list and somehow bulk-copy the registrations to
the buddies.

> Another means of doing this is to posit a
> registrar that explicitly doesn't do what you are
> positing by whatever replication mechanism
> necessary. I've been under the impression that SIP
> expects high availability of registrars. Saying
> that registrars (unlike proxies) can roll over and
> die with all of its registration state is taboo as
> far as I've ever heard.

I think that's about the only realistic option and not that hard
(indeed, you can do this with almost-regular SIP registrars if each
registrar also proxies each new registration to its buddies). In the
"controlled crash" scenarios, it is unlikely that you will have the time
to notify 100,000 registrands. In any event, you cannot guarantee that
you reach all of them. Even if you do somehow, you now have 100,000
registrands pounding the poor substitute registrar with requests in very
short order.

I suspect that most industrial-strength registrars will use a reliable
backend database that handles replication and load sharing. There are
plenty of brand name companies, using either in-memory or classical disk
technology, that deal with this problem as a matter of course. (To name
a non-commercial alternative, even mysql has a primitive version of this
functionality.)

<snip>

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---

From: Michael Thomas <[email-masked]>
Date: Thu, 8 Mar 2001 17:13:04 -0800 (PST)

> the information displayed to the user to be accurate, at least.

   I don't see why this needs to be dealt with by the
   registrar. This could easily be done by the proxies.
   Registration just tracks your reachability. Whether
   that entitles you to service is completely
   orthogonal. It would be a lot simpler to just
   let the registration evaporate normally and
   take care of this elsewhere.

	     Mike

---

From: "Bob Penfield" <[email-masked]>
Date: Fri, 9 Mar 2001 08:13:04 -0500

If the registration expiration is on the order of hours, requiring the UA to
re-register, it will find out fairly soon. You would still need to reject
any outgoing or incoming calls for from/to that UA.

---

From: "Henning G. Schulzrinne" <[email-masked]>
Date: Fri, 09 Mar 2001 09:39:53 -0500

I'm not sure how premature timeout for REGISTER is useful for prepaid
accounts. From what I understand about pre-paid cellular, while the
outbound and inbound minutes are limited, the validity of the account is
based on longer time periods, such as three months which is well known
ahead of time. Thus, these accounts don't just randomly expire, but in
most such cases, expire predictably. Also, there is no major harm if a
registration lingers for at most an hour and the prepaid account balance
is zero. Incoming calls will simply fail with an appropriate error code
("402 Your callee is broke and hasn't paid his bill. Please contact
repo-man.com if you also got stiffed.").

For non-payment of regular accounts, again, this is not something which
is done at hourly intervals.

If fraud is involved and thus the provider wants to cut off service
immediately, notifying the "customer" may not rank that high on the
priority list.

In any event, billing-related expirations probably require more
higher-level intervention, so that notifications or email ("Your account
balance is zero, please go to paynow.com to refill your account.") are
more likely to work, rather than (say) a way to tell an end system to
register elsewhere at the SIP level.
-- 
Henning Schulzrinne   http://www.cs.columbia.edu/~hgs