Subject: RE: [Sipping] Source Routing WAS How to Get Outbound Services fro m A Non-Local Proxy?

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 1 Aug 2001 02:33:19 -0400

> -----Original Message-----
> From: Gonzalo Camarillo [mailto:[email-masked]]
> Sent: Tuesday, July 31, 2001 10:44 AM
> To: Neil Deason; Jonathan Rosenberg; 'Dean Willis'; James Undery;
> Sudharsana krishnan P; Sipping (E-mail)
> Subject: Re: [Sipping] Source Routing WAS How to Get Outbound Services
> from A Non-Local Proxy?
> 
> 
> Hello,
> 
> I have changed the subject of this thread because this issue is not
> specific of 3GPP or of a UA that wants services from this home proxy.
> The source routing mechanism that we are looking for will be useful as
> well to generate replace URLs as defined in
> draft-rosenberg-sip-call-package-00.txt. These URLs have to 
> be globally
> routable. Let's assume that in order to make a SIP call to an Ericsson
> employee the INVITE has to traverse a proxy at ericsson.com (otherwise
> the firewall would not let it thru). If my UA wants to generate a
> replace URL to be sent in a NOTIFY it will look as follows:
> 
> sip:[email-masked];user=url

I had thought about using the user=url for this purpose as well, but its not
clear to me that this will always work. The ericsson.com proxy may not be
able to reach sip:[email-masked] directly; it may need to go through
the ericsson.se proxy first, and THEN to lmf.ericsson.se. I haven't really
come up with a way to generate a URL which I can be sure is globally
routable to a specific UA...

Gonzalo also writes:
> By the waym if we define user=url, we will have to add a parameter
> indicating which type of URL. It might be sip:tel:[email-masked], for
> instance...

No, you don't need another parameter. The user portion is a COMPLETE URL,
which would include the scheme. 

-Jonathan R.

---
Jonathan D. Rosenberg, Ph.D.                72 Eagle Rock Ave.
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---

From: Gonzalo Camarillo <[email-masked]>
Date: Thu, 02 Aug 2001 19:27:55 +0300

Hello Jonathan,

> routable to a specific UA...

In that example I was assuming that I knew that the only firewall
between me and the other party was at ericsson.com. But you are right,
because if I do not have this knowledge, I cannot use source routing.

For the general problem of a globaly routable URLs to be used as
"replace" URLs, I would suggest that we use the caller preferences
stuff.

That is, even if besides the firewall at ericsson.com, there were
another firewall at ericsson.se, I know that my public address is
[email-masked], and that INVITEs that are sent to that
address reach me in a number of devices. Now I am speaking on my SIP
phone at [email-masked]

In order to create a globaly routable URL I would provide my public URL
with an Accept-Contact header. Something like:

sip:[email-masked]?Accept-Contact:
<sip:[email-masked]>

The only thing I have to do is REGISTER [email-masked] in my usual
registrar.

However, since Accept-contact expresses only a preference, a proxy that
did not know about [email-masked] and did know about another way
to contact me might still route the INVITE there, making another device
ring (we do not want that!).

We could use Reject-contact to express that the only contact that we
would accept would be [email-masked]

However, in our scenario that would not work either, since the proxy at
ericsson.com has to route the INVITE to the proxy at ericsson.se and
this one will finally route the INVITE to lmf.ericsson.se. Therefore, if
we use Reject-Contact, the proxy at ericsson.com will not be able to
route the INVITE
, since [email-masked] is not directly routable from there.

What about defining new headers in the caller preferences draft called
Reject-contact-UA and accept-contact-UA? Proxies would ignore this
headers, but if a UA receives an INVITE and it contains a
reject-contact-UA with its URL, the UA will generate a response code to
be defined (something like "I am in the reject-contact-UA and thus I
will not alert the user") rather that alert the user.

Such headers would provide us with globaly routable URLs.

Opinions?

Regards,

Gonzalo

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