Subject: RE: [SIP] Registrar cancelation of registers

From: Baniel Uri-CUB001 <[email-masked]>
Date: Mon, 11 Jun 2001 19:26:57 -0500

David
 
We have discussed the issue back a few months ago. One of the recommendations was to use the 'subscribe and notify' mechanism, when registration may serve as an implicit subscription to being notified for de-registration event. You may also want to take a look at the R5 3GPP relevant spec (23.228)
 
Uri

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-----Original Message-----
From: David Simons [mailto:[email-masked]]
Sent: Monday, June 11, 2001 7:20 PM
To: [email-masked]
Cc: David Simons; Robert Brown
Subject: [SIP] Registrar cancelation of registers

One of the limitation I see in SIP is that a registrar has no way of indicating to a UAC that it's registration is no longer valid.  There doesn't seem to be a mechanism to cancel registrations.  I can think of two scenarios were this could be very useful.  First, a registrar needs to shutdown but it has recently accepted one hour registrations.  It would be nice if the registrar could indicate to the UAC that its registration is no longer valid and should re-register after a while.  In the second scenario a service wants to minimize the amount of resources that a users consumes on the Registrar.  This could be done by deigning new registration but the new registrations are the ones most likely to be called successfully.  Or you could say you want to remove registration for the lowest q-values.  I'd be interesting in the thoughts of others on this group.

One solution I've considered is to send a CANCEL with the same FROM, TO, and Call-ID as the REGISTER to the UAC, In effect canceling the registration.  This doesn't seem to conform to RFC2543bis03.  This solution would be canceling a request that had a final reply.   Also the CANCEL wouldn't be sent by the requester.  Then there is the use of BYE that could be an option but BYE only seems to address INVITE.

Comments?

Regards, 

David J. Simons

Development Lead

Microsoft Windows RTC

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---

From: "Sriram Parameswar" <[email-masked]>
Date: Tue, 12 Jun 2001 08:58:35 -0500

David,
 
There was a long discussion thread on this very topic - when 3GPP introduced
it. In short - the 3GPP approach is to 'NOTIFY' the subscriber when there
has been a network initiated de-registration. 
 
Regards,

Sriram

__________________________________________ 
Sriram Parameswar              Phone: 972-685-8540 
Wireless IP MultiMedia (WIPMM)   Fax: 972-685-3563 
Nortel Networks, Richardson USA  Email: [email-masked] 

-----Original Message-----
From: David Simons [mailto:[email-masked]]
Sent: Monday, June 11, 2001 7:20 PM
To: [email-masked]
Cc: David Simons; Robert Brown
Subject: [SIP] Registrar cancelation of registers

One of the limitation I see in SIP is that a registrar has no way of
indicating to a UAC that it's registration is no longer valid.  There
doesn't seem to be a mechanism to cancel registrations.  I can think of two
scenarios were this could be very useful.  First, a registrar needs to
shutdown but it has recently accepted one hour registrations.  It would be
nice if the registrar could indicate to the UAC that its registration is no
longer valid and should re-register after a while.  In the second scenario a
service wants to minimize the amount of resources that a users consumes on
the Registrar.  This could be done by deigning new registration but the new
registrations are the ones most likely to be called successfully.  Or you
could say you want to remove registration for the lowest q-values.  I'd be
interesting in the thoughts of others on this group.

One solution I've considered is to send a CANCEL with the same FROM, TO, and
Call-ID as the REGISTER to the UAC, In effect canceling the registration.
This doesn't seem to conform to RFC2543bis03.  This solution would be
canceling a request that had a final reply.   Also the CANCEL wouldn't be
sent by the requester.  Then there is the use of BYE that could be an option
but BYE only seems to address INVITE.

Comments?

Regards, 

David J. Simons

Development Lead

Microsoft Windows RTC

---

From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 12 Jun 2001 16:33:10 -0400

> From: [email-masked] [mailto:[email-masked]]
> Sent: Tuesday, June 12, 2001 10:24 AM
> To: 'David Simons'; [email-masked]
> Cc: Robert Brown
> Subject: RE: [SIP] Registrar cancelation of registers
> 
> 
> 
> If the clients don't care, this is correct -- there is no way for
> registrars to indicate this information. This issue has been raised
> uncountable times over the past couple of years on the list; the
> group consensus is that we will not add a mandatory mechanism for
> this sort of thing.
> 
> On the other hand, the presence work going on in the SIMPLE working
> group *does* provide an interesting mechanism to provide the same
> functionality -- assuming, that is, that the client cares.
> 
> If a client *wants* to be notified when his registration is no longer
> valid, he may send a SUBSCRIBE message for his own presence to his
> registrar. In this way, just like anyone else subscribed to his
> presence, he will receive a NOTIFY message when his registration
> disappears.

To add to that, there are two uses for the network deregistration. One is to
simply notify clients as an FYI, and another is to cause them to re-register
at another server in order to replicate registration state at the backup
server. The former is covered by presence, as has been noted. The latter is
best served, as Mike Thomas pointed out, by having a back end data
replication. In fact, asking clients to re-register to reconstruct state at
another server has a whole bunch of problems, all of which were discussed
previously on the list. They include:

1. it results in a flood of registrations, which can cause packet loss and
processing overloads. 

2. it won't work for clients that are users of the system, but haven't yet
registered (they won't know about the change to another registrar)

3. It results in a trasitory period where the contact list in the new server
is not up to date; that can result in failed calls during the transition.

So, the proposed approach is that the registrar is accessed via DNS SRV, and
when one fails or is shut down, clients gradually re-register with a backup.
The data is transferred to the backup using some implementation specific
means. 

SIP does allow for existing registrations to be removed by clients, by the
way. A re-REGISTER is sent, with an expires=0 for the contact that is to be
removed.

-Jonathan R.

-----Original Message-----
From: David Simons [mailto:[email-masked]]
Sent: Monday, June 11, 2001 7:20 PM
To: [email-masked]
Cc: David Simons; Robert Brown
Subject: [SIP] Registrar cancelation of registers

One of the limitation I see in SIP is that a registrar has no way of
indicating
to a UAC that it's registration is no longer valid.  There doesn't seem to
be a
mechanism to cancel registrations.  I can think of two scenarios were this
could be very useful.  First, a registrar needs to shutdown but it has
recently
accepted one hour registrations.  It would be nice if the registrar could
indicate to the UAC that its registration is no longer valid and should
re-register after a while.  In the second scenario a service wants to
minimize
the amount of resources that a users consumes on the Registrar.  This could
be
done by deigning new registration but the new registrations are the ones
most
likely to be called successfully.  Or you could say you want to remove
registration for the lowest q-values.  I'd be interesting in the thoughts of
others on this group.
One solution I've considered is to send a CANCEL with the same FROM, TO, and
Call-ID as the REGISTER to the UAC, In effect canceling the registration.
This
doesn't seem to conform to RFC2543bis03.  This solution would be canceling a
request that had a final reply.   Also the CANCEL wouldn't be sent by the
requester.  Then there is the use of BYE that could be an option but BYE
only
seems to address INVITE.
Comments?
Regards,
David J. Simons
Development Lead
Microsoft Windows RTC

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