Subject: RE: [Sipping] How to Get Outbound Services from A Non-Local Proxy ?

From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 3 Aug 2001 14:31:38 -0400

> -----Original Message-----
> From: Juha Heinanen [mailto:[email-masked]]
> Sent: Friday, August 03, 2001 2:25 AM
> To: Neil Deason
> Cc: Gonzalo Camarillo; Cullen Jennings; James Undery;
> [email-masked]; Sipping (E-mail)
> Subject: RE: [Sipping] How to Get Outbound Services from A Non-Local
> Proxy?
> 
> 
> Neil Deason writes:
> 
>  > DNS incapable clients ignore record route to send to a
>  > local out bound proxy. I think there are going to be times
>  > when a proxy may want to have this flexibility over
>  > routing too, allowing outbound proxies for proxies.
>  > (This just came up on the SIP list under 'RE: [Sip]
>  > proxy routing of a request' for those trying to keep up
>  > with mult lists).
> 
> i too think that it is a good idea to always consider the route header
> as specifying a loose source route.  if a ua or another proxy has been
> configured with an outbound proxy, it simply forwards the message to
> that and leaves the route header as is.  so this is purely a
> configuration issue in the ua or proxy and has nothing to do with dns
> capabilities as the current text incorrectly says.

Well, the text is based on the strict routing interpretation of the route
headers. 

The idea of making the meaning of the Route headers more loose is
interesting, but I wonder how it would work. How would a UA or proxy know
that it should obey the top route as opposed to send it elsewhere? In the
case of an outbound proxy, for example, how does a UA know that the top
route isn't already its outbound proxy (a very likely case)? This is not a
problem in IP loose source routing, where the scenarios for popping the top
entry are well defined.

-Jonathan R.

(PS, this is one of the items I will be discussing during the bis open
issues agenda item in London)
---
Jonathan D. Rosenberg, Ph.D.                72 Eagle Rock Ave.
Chief Scientist                             First Floor
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[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com 

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---

From: Juha Heinanen <[email-masked]>
Date: Fri, 3 Aug 2001 22:52:48 +0300 (EEST)

> problem in IP loose source routing, where the scenarios for popping the top

if a ua has been configured to use an outbound proxy, it must always do
so no matter what the contents of route set is.  if it doesn't always
use the outbound proxy, then it is very highly likely that a firewall
will prevent the message going anywhere and the ua can't talk to anyone.

now the question remains, what should the ua place in the request-uri
and in the route header.  if the topmost entry in the route set is the
same as the outbound proxy, then the ua can safely use that in the
request-uri and pop it out from the route header.

if it is not the same or if the ua doen't know if it is the same (due to
dns incapabilities, for example), then the ua would send the message
using request uri

sip:user@outbound-proxy

and use the route set as the route header.

none of this is currently clearly specified in bis-04 and i have today
in my hands shiping products from several vendors that don't
interoperate due to the vendors not knowing what to do about these
things.  so i would like to place a very high priority in fixing these
fundamantal problems in the current spec before going any further with
any sip extensions, since those doen't do us any good when not even the
basic calls don't go through.

also, as i have told earlier, i vote for interpering the route in the
route header and in the request uri loose.

-- juha

---

From: "Dean Willis" <[email-masked]>
Date: Sat, 4 Aug 2001 17:33:18 -0500

> problem in IP loose source routing, where the scenarios for popping the
top

Perhaps the concept of a "preferred route" header might be appropriate.

Logic of message receiver in the presence of "preferred route" (PR).

Does this node correspond to the target of the top PR?
If yes, pop the top PR and iterate the route handling.
If not, route the message toward the target of the top PR, using whatever
routing techniques that node would use for a SIP message with a request-URI
having a domain part equal to the PR. This could include default routes,
static routes, TRIP routes, DNS, ENUM, etc.

With this approach, a stupid UA wanting outbound services from an arbitrary
remote proxy could simply add a PR header for that remote proxy, then send
the message to the default proxy. Eventually, the message would be delivered
to the remote proxy, which would pop the PR and then apply any needed
service logic.

How that UA gets knowledge of which arbitrary remote proxy to target with a
PR is an entirely seperate problem.

Questions: Should the PR be a header, or a request-URI parameter?

--
Dean

---

From: Juha Heinanen <[email-masked]>
Date: Sun, 5 Aug 2001 08:55:18 +0300 (EEST)

dean,

i don't see how your "preferred route" differ from loose source route.
sip already has enough headers and parameters.  makinmg it clear that
the route header specifies a loose source route should be enough.

besides, "preferred" is a bad name if the ua really wants the message to
go to the entity/entities listed in the pr header, since prefered to me
means like a wish that someone may not need to fulfill.

-- juha

---

From: Gonzalo Camarillo <[email-masked]>
Date: Mon, 06 Aug 2001 19:25:29 +0300

Hello,

We should have in mind that the Record-Route in the 200 OK will be valid
thru the session. Subsequent requests have Record-Route just for
consistency (this is needed to be RFC2543 compliant). Therefore, we
should look at how pre-loaded Route headers interact with Record-Route
in the 200 OK.

As Jonathan suggested, let's discuss this in the bis-related-issues
presentation.

Regards,

Gonzalo

-- 
Gonzalo Camarillo                    Phone :   +1 212 939 71 71
Columbia University                  Mobile:  +358 40 702 35 35
472 Computer Science Building        Fax   :  +358  9 299 30 52
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New York, NY 10027                   
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---

From: "Neil Deason" <[email-masked]>
Date: Mon, 6 Aug 2001 17:40:56 +0100

> From: Gonzalo Camarillo [mailto:[email-masked]]
> Sent: 06 August 2001 17:25
> To: Juha Heinanen
> Cc: Dean Willis; Jonathan Rosenberg; Neil Deason; Cullen
> Jennings; James
> Undery; [email-masked]; Sipping (E-mail)
> Subject: Re: [Sipping] How to Get Outbound Services from A Non-Local
> Proxy?
>
>
> Hello,
>

Pre-loaded Route headers can take an initial request to a proxy
server. That server then makes a decision about Record-Routing
to stay on the signalling path for the remainder of the call
leg. So what possible interation between a pre-loaded route
and the Record-Route set in a 200 OK can there be?

> As Jonathan suggested, let's discuss this in the bis-related-issues

Sounds good.

Cheers,
Neil
--
Ubiquity Software Corporation, UK        http://www.ubiquity.net