Subject: [SIP] URL Generalization for Portability (was TRIP)

From: S_S_Dinesh/India/[email-masked]
Date: Mon, 8 May 2000 14:10:12 +0530

Jonathan Rosenburg wrote:
> I wonder if we can't think about this problem in more general terms.

yes, please!

> In the SIP model, each proxy owns some piece of the namespace
> (engineering.dynamicsoft.com, for example), and is therefore responsible
> for the definition of the user space (jdrosen@) within that domain.
> Thats why each proxy can, an usually will, perform some kind of URI
> translation independent from other proxies. Our underlying assumption
> was that usernames only have meaning within their domain. For example,
> with sip:[email-masked], only a dynamicsoft.com proxy knows how
> to handle jdrosen. There might be jdrosen's in other domains that aren't
> me. However, in the case of telephone numbers, the proxy that owns the
> domain does not necessarily own the user space. sip:[email-masked],
> for example, uses a user name that is not "owned" by gateway.com, in the
> sense that this name has valid semantics outside of gateway.com. Other
> domains, like wcom.com, would know how to handle this number as well.
> Its possible that we might even see things besides phone numbers as user
> names that are valid across multiple domains. An example is (heaven
> forbid), social security numbers (in the US, at least):

The underlying problem here is differentiating between a phone-number and a
service-name-which-looks-like-a-number. Yes, the user=phone gives a hint on
nature od address, the "+" encodding gives a hint on the scope of address,
but it is still muddy.

There was some discussion of this problem wrt DCS during the November
interim meeting. It was suggested that a cross-domain destination which is
a
phone number could be better represented by a tel: URL than by confusing
the
scope of the user part of a sip: URL. This simplilifies life greatly.

Something like

     INVITE [email-masked]
     To: tel:5551212;trans=lnp?gdbs

could be used to indicate to gateway.carrier.com that premium gateway
service is requested towards the PSTN location identified by telephone
number 5551212, that LNP and GDBS translation have been applied, and that
the phone number is of local scope for the gateway. Incidentally, I think I
just noticed a minor anomaly in the tel-url grammar -- don't see how to
encode more than one future-extension field . . .

--
Dean

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