Subject: [Sipping] SOS: emergency numbers

From: Henning Schulzrinne <[email-masked]>
Date: Thu, 12 Feb 2004 09:07:34 -0500

[Let me try to tease out separate issues in the discussion and see if we 
can make progress that way. In some cases, we're revisiting old ground, 
so the proponents of the 'old' solution will have to chime in.]

One of the core problems, spanning the architecture and sos drafts, is 
the question: what is an emergency number, how do systems find out and 
who needs to know?

The current proposal is a bit of hybrid, in that there are pre-defined 
numbers (112, 911, 000, etc.) and acquired numbers. Numbers are acquired 
using three different mechanisms: XCAP to the home domain, XCAP to the 
visited domain (following the configuration draft methodology) and DNS 
based on knowledge of the current country code. None of these mechanisms 
existed in the first iterations of the -sos- draft, so it may be 
appropriate to revisit the issue.

Thus, a streamlined proposal would be:

(1) No protocol pre-defined numeric identifiers, not even 112 and 911. 
(Devices with personalization devices, such as SIM cards, may pre-load a 
dialplan, see (3).)

(2) Any digit string NNN (not just emergency numbers) dialed and 
unrecognized gets translated into sip:NNN@aord;user=dialstring (as 
discussed at the last IETF meeting). AORD is then responsible for 
recognizing this as an emergency number, based on the current and 
possibly home country of the caller.

An alternative is to translate these dialstrings into 
sip:NNN@outbound-proxy;user=dialstring, e.g., using the DHCP-provided 
outbound proxy address. I think this might be better, but that's a more 
general discussion.

(2a) In general, digit strings that match a dialplan MAY become tel 
URIs, after they have been suitably normalized by the dialplan 
transformation rules. This does not apply to emergency numbers, where 
(3) applies.

(3) Any digit dial string recognized as an emergency number gets 
translated into sos*@AORD.

AORD = address of record domain, i.e., the domain part of my address of 
record.

The device owner decides whether to acquire only the geographically 
local dialplan (MUST) or also his 'home' dialplan (MAY).

Is this acceptable?

Henning

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