Subject: RE: [Sipping] SIP URL's with telephony numbers

From: "Michael O'Doherty" <[email-masked]>
Date: Wed, 28 Nov 2001 15:57:08 -0000

Ben,

Comments below:

>> I think in practice there will likely be scenarios where it is done 
>> whether we like it or not - for example an outbound proxy that wants to 
>> bar all calls to a particular username at a particular domain or a proxy 
>> which is doing some sort of legal intercept and which wants to catch all 
>> calls going to a particular username at a particular domain. Or to take 
>> a telephone number example, an outbound proxy which wants to allow 
>> normal telephone numbers but bar premium telephone numbers.
>> 

>Your first two examples just requires a URL match, not an 
>interpretation. The last one can only really be done at the destination 
>domain (e.g. the domain of the gateway) or with tel urls.

Well, I think it actually requires URL equivalence depending on the
interpretation scheme the host domain uses (i.e. not just matching strings
for instance - we may want it to match/not match depending on whether a
password or even some variable part of the username is present) but it is a
small point and I fully agree that this is messy and needs knowledge of the
host domains interpretation scheme.

>And as people design each of those scenarios, they should use care not 
>to attempt to interpret URLs that don't belong to their domain. You 
>simply _cannot_ depend on a URL pointing to a domain that you do not 
>control to mean what you think it means. (Unless you have some sort of 
>agreement with that domain that includes URL interpretation.)

The last point is indeed the key and I think it is not unreasonable to
expect that such inter domain agreements will develop for some services
which involve billing (such as calls out to the PSTN ...).

Note that I don't think that any of this implies a need for change in the
spec - systems can choose whether or not to do this type of thing depending
on their needs.

---

From: "Conroy, Lawrence (SMTP)" <[email-masked]>
Date: Wed, 28 Nov 2001 17:57:16 +0000

>Ben,
<snip>
>interpretation scheme the host domain uses (i.e. not just matching 
>strings for instance - we may want it to match/not match depending 
>on whether a password or even some variable part of the username is 
>present) but it is a small point and I fully agree that this is 
>messy and needs knowledge of the host domains interpretation scheme.

To which I reply,

 From a historical perspective, I seem to remember (pre tel: url, pre 
DCS time) thinking
that user=phone and user=ip were very useful due to compuswerve 
having user-ids that
looked like french phone numbers but weren't.

As was pointed out to me at the time (by Jonathon), these are only 
HINTS and are not really
needed, as it's the destination domain that interprets the user-part. 
This has not changed
at all since then (which I seem to remember was in 1998). Thus if a 
mid path proxy wants to
do something nefarious, it can, but the draft/RFC does not go out of 
its way either to help
or hinder. Any hacks based on interpretation are just that; hacks. 
(Maybe useful hacks, but...)

My vote's to leave it as is.
BR,
   Lawrence
-- 
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