Subject: RE: [Sip] I-D ACTION:draft-ietf-sip-outbound-03.txt

From: "Christer Holmberg \(JO/LMF\)" <[email-masked]>
Date: Fri, 24 Mar 2006 10:49:45 +0100

Hi, 

>Assume that you use your SIP phone at home, which belongs to operator
A.
>Then you take your phone somewhere else, and connects it to a network  
>that belongs to operator B. In both cases the AoR of the registrar is  
>going to be the same, but you may have different outbound proxies.

>i may be old fashioned, but it used to be the case that if my pbone is
connected to internet via ISP A network and i move 
>it to ISP B network, i'm in both cases able to reach the internet
connected proxy (perhaps in ISP C network) of my own 
>domain. 

What if both ISP A and ISP B have an outbound proxy, and you do your DNS
lookup based on the AoR of the registrar in ISP C. Again, will you use
private ISP A DNS servers (or private ISP B DNS servers) in order to
find the appropirate outbound proxy?

Regards,

Christer

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From: Juha Heinanen <[email-masked]>
Date: Fri, 24 Mar 2006 13:32:12 +0200

> find the appropirate outbound proxy?

huh, i didn't know that ISP DNS servers are nowadays private.  my AoR is
sip:[email-masked].  are you saying that if i make a dsn query 

host -t SRV _sip._udp.tutpro.com
_sip._udp.tutpro.com SRV 0 0 5060 sip.tutpro.com.

in ISP A network, i may get some other result than the ne above?  if so,
there is nothing left of open internet.

-- juha

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From: Dean Willis <[email-masked]>
Date: Fri, 24 Mar 2006 09:33:52 -0600

> find the appropirate outbound proxy?

I think Juha's point may be that if ISP A and ISP B are really ISPs,  
as supposed to "IMS operators" or "VoISP operators that also provide  
an IP access network that really isn't the Internet", then nothing  
prevents him from talking directly to the service platform of C  
(which is in my terms a VoISP, not an ISP.

In the conventional ISP case (which is not the more complex "general"  
case we've been working on), this is the case.

Now, if one leaves the confines of a conventional ISP and roams onto  
a private network operated by an enterprise with a proxy-enabled  
firewall, the "talk directly to VoISP C" approach won't work.

This is actually pretty much consistent with the augmented 3261  
procedure:

1) If you have an outbound proxy configured, use that. Exit.
2) If your DHCP informs you of an outbound proxy, use that. Exit.
3) If there is a default proxy configured, use that. Exit.
4) Use the domain of your AOR to do a lookup ala 3263, and if that  
resolves, use it. Exit.
5) Fail.

I think what Juha is suggesting could perhaps be accommodated by a  
draft detailing the above common practice. This wouldn't be in-scope  
for SIP, but would be (I believe) for SIPPING.

--
Dean