Subject: [SIP] Forcing call setup through home proxy (solution?)

From: Jörgen Björkner <[email-masked]>
Date: Fri, 19 May 2000 09:46:17 +0200

As I said before, some services to set up a call might depend on information
that only is available in the callers home network, and for security or
policy reasons might be impossible to access from other networks. In this
case MUST the call setup signaling go through the home network.

I belive that this could be solved by adding a route header field containing
the address of the home server in the Invite message. If you follow the spec
must the first proxy in the visited network route the Invite to the home
proxy. This method allows for optimizing call setup when there is no service
that requires routing through the home network, and a method to indicate
when so should be the case.

/Jörgen

>*	When the caller is roaming, under certain circumstances (related
>to the type of value added services required & the set of services
>supported by the visited network &  the possibility to transfer a user
>profile--see my previous messages) it is possible to avoid sending
>signalling back to the caller home domain. This applies to calls towards
>the fixed network (which may be routed by TRIP) and for calls to local
>mobiles. For roaming mobiles you fall back to the prvious case: still
>you don' t need to send signalling to the caller home domain, but you
>have a RTT to the callee home domain.

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From: "Adam B. Roach" <[email-masked]>
Date: Fri, 19 May 2000 05:49:02 -0500 (CDT)

>As I said before, some services to set up a call might depend on =
>information
>policy reasons might be impossible to access from other networks. In =
>this
>I belive that this could be solved by adding a route header field =
>containing
>the address of the home server in the Invite message. If you follow the =
>spec
>must the first proxy in the visited network route the Invite to the =
>home
>proxy. This method allows for optimizing call setup when there is no =
>service
>that requires routing through the home network, and a method to =
>indicate

At the third bakeoff, I went around to a number of people and
asked how their proxies would behave if my client did this sort of
thing. I got a variety of mixed answers, none of which were
very encouraging. Some people wouldn't process it, for example,
unless it had a To: tag (since routes can't appear on leg
setup messages, or so goes the thinking). Most would completely
forgo their internal logic and blindly forward the message
(thus making their purpose only to add to the number of hops
in the call signalling route).

I've been mulling this problem since. I don't think there's
really a good solution; however, I want to run something by
the group.

Back in the day, you could manually route e-mail messages through
a variety of servers by specifying an email address of the format
[email-masked]. Upon receiving this,
ericsson.com would turn the last % into an @ and continue
routing the message. This could be indefinitely chained
to produce something like [email-masked]
which would route the message through ericsson.com, then host1,
then host2, and finally deliver it to host3.

So, what if we specified a fairly simple username convention
stating that proxies MAY do something similar; for example,
you could send something like:

INVITE sip:[email-masked] SIP/2.0

...to the machine "localservices.mycompany.com". When the
machine "firewall.mycompany.com" received the message, based on
the presence of an escaped @ sign in the user field, he would
strip the machine name in the request URI, expand the rightmost
escaped @, and use that for his new request URI:

INVITE sip:[email-masked] SIP/2.0

Questions? Comments? Is there enough interest in this to
warrant putting together a formal document?

-- 
Adam Roach, Ericsson Inc. |  Ph: +1 972 583 7594 | 1010 E. Arapaho, MS L-04
[email-masked]   | Fax: +1 972 669 0154 | Richardson, TX 75081 USA

---

From: Michael Thomas <[email-masked]>
Date: Sat, 20 May 2000 10:58:48 -0700 (PDT)

> then host2, and finally deliver it to host3.

   Would this not lead to the need for a SIP
   version of ORBS?

	      Mike, half serious