Subject: [Sipping] Re: draft-schulzrinne-sipping-sos-04.txt

From: Paul Kyzivat <[email-masked]>
Date: Thu, 09 Jan 2003 09:53:25 -0500

I have a few comments about draft-schulzrinne-sipping-sos-04.txt.
(I haven't been following this work very closely, so perhaps some of 
these pertain to things that were in earlier drafts.)

I must say, these are really messy problems, so I am glad you are 
working on them.

Section 3.2 says:

    ... a UAC MAY use a "tel" URI [3,4] without phone-context, such as

    tel:911
    tel:112

The latest and greatest definition of the tel: uri that I can find is 
draft-antti-rfc2806bis-07.txt. According to that, the above tel: uris 
are syntactically incorrect. Either the number must be global or else it 
must contain a phone-context parameter.

Are there plans to change the definition of the tel uri, or is this 
language going to change?

In the case of a UAC that is using a local outbound proxy, is it 
required that the UAC specifically recognize these strings and deliver 
them to the proxy, or is it sufficient for it to deliver any and all 
dialed digit strings to the proxy as tel uris without attempting to 
recognize them itself? Is it sufficient to determine that the dialed 
number is complete by timeout on the input rather than by recognition?

Section 5 specifies that the UAC should insert location information into 
emergency calls. However, presumably location information should in 
general not be placed in non-emergency calls, so it is important that 
the UAC realize it is making an emergency call. In the case of dialed 
digit strings, it may only be the outbound proxy that can determine if 
the call is an emergency call. One way to handle this would be for the 
local outbound proxy to redirect requests to tel: emergency numbers to 
the corresponding sip:sos number. Then the UAC would be able to 
positively determine this is an emergency call and include the location 
information.

Section 9 says:

    We propose a new DHCP option that enumerates the valid local
    emergency identifiers, as a list of "tel", "sip" or "sips" URIs.

This doesn't seem sufficient. Most phone-like devices have provision for 
entering primarily sequences of digits, not tel: uris. It is up to the 
phone to translate a digit sequence into a valid uri. In general this 
requires some sort of dial plan. Without the dial plan, the phone may 
well not be able to generate anything that matches one of the specified 
tel uris.

	Paul

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