Subject: [SIP] Registrar providing location services

From: "Eber Mello" <[email-masked]>
Date: Thu, 4 May 2000 16:49:12 -0700

Hi,

Please, I have a few questions regarding the behavior of a SIP
registrar providing location services vis-a-vis the
action (proxy or redirect) present on the REGISTER message.

1) Should a proxy- *and* redirect capable SIP server chooses
either to proxy or redirect a request based on the policy of the
user addressed on the request, expressed by the user's REGISTER
message? In other words, the location services provided by the
registrar would return how - proxy or redirect, the user wants
to be reached as well as a contact list?

2) Can a user register contacts that are actually
well known SIP URLs of other users, as below?

userA@domainX registers with action=PROXY, contact1=userB@domainY
and contact2 = userC@domainZ.

3) Consider that userB and userC are also registered with the same
registrar,
as follows:

userB@domainY registers with action=REDIRECT, contact=addressK@domainM
and userC@domainZ registers with action=PROXY, contact=addressL@domainN

=> lets suppose that addressK@domainM and addressL@domainN are not
locally registered

When queried about the location of 'userA', should the location server
recurse on the contacts of userA whenever it sees a SIP URL of a user
also registered locally to it?

4) If the answer to the previous questions are YES, than the location server
would return REDIRECT to addressK@domainM and PROXY to addressL@domainN -
what is
a scenario that the spec explicitly tries to avoid by enforcing that
all contacts on a REGISTER must have the same 'action'.

Thanks,

Eber Mello
SS8 Networks Canada.
www.ss8networks.com
phone: 613-5921418

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From: Igor Slepchin <[email-masked]>
Date: Thu, 04 May 2000 17:58:33 -0400

Eber Mello wrote:
> message? 

That's up to you. You can either honor user preferences or overwrite
them.
 
> well known SIP URLs of other users, as below?

Sure.
 
> also registered locally to it?

If domainM and domainN are served by the same proxy, it's a nice idea to
do the recursive lookup. Nothing catastrophic happens if you don't - the
proxy will just have to do the same lookup when it gets the request it
just proxied to itself.
 
> all contacts on a REGISTER must have the same 'action'.

I guess the question is about what to do when the recursed Contact has
the action different from that in the first Contact. Well, that's up to
the proxy: it can overwrite that action or, if this turns out to be the
last Contact to try, it can overwrite the action from the first Contact.

---
Igor Slepchin

---

From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 04 May 2000 23:05:32 -0400

Some additional comments:

> last Contact to try, it can overwrite the action from the first Contact.

It should generally do whatever would happen if the domains were all

> and userC@domainZ registers with action=PROXY, contact=addressL@domainN

 the following would happen:

1. an INVITE arrives at proxy1 for userA@domainX. Based on its
registrations, it proxies this to userB@domainY and userC@domainZ

2. one invite goes to domainY and one to domainZ. domainY looks up
userB, and sends a 300 redirect with Contact addressk@domainM. domainZ
looks up userC, and proxies to addressL@domainN.

3. the 300 redirect arrives at the first proxy, which proxies to
addressk@domainM. The proxy for domainN receives the INVITE for
addressL@domainN, and does whatever its configured to do.

Now, should any of these domains be served by the same proxy, the
behavior should be exactly the same as if they were not served by the
same proxy. So, if domainX, domainY, domainZ are all served by one
proxy, that proxy would have ended up proxying the received request to
addressk@domainM and addressL@domainN.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (732) 741-4778
http://www.cs.columbia.edu/~jdrosen         PHONE: (732) 741-7244
http://www.dynamicsoft.com

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From: "Eber Mello" <[email-masked]>
Date: Fri, 5 May 2000 10:02:16 -0700

Please, see my question/comment bellow.

> addressL@domainN, and does whatever its configured to do.

I guess it is also accepted for a Proxy Server to return that 300 redirect
back to the UAC - if that is the best response received among all, instead
of recursing on it. Better still is if the proxy server can have some
internal
criteria to decide whether to recurse on the returned address or not, say,
if
the address is not a SIP URL but rather a generic URI than the server
returns
the response to the UAC, otherwise it sends an Invitation to that address.
Does that make sense?

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From: Jonathan Rosenberg <[email-masked]>
Date: Mon, 08 May 2000 01:27:13 -0400

Eber Mello wrote:
> of recursing on it.

Sure.

> Better still is if the proxy server can have some
> internal

Yup. Proxying to http URLs is not that useful. 

-Jonathan R.