Subject: Re: [Ecrit] Issue 30: Summary

From: "Stark, Barbara" <[email-masked]>
Date: Tue, 31 Jan 2006 09:43:55 -0600

This seems generally reasonable to me, also.
However, there is an implicit expectation in the description below that I'm not quite comfortable with, in the "precedence" statement. That is, whether or not end of dialing string is automatically recognized for visited emergency numbers.
For devices that use a "Send" button, this isn't a problem. "Send" must always be pressed to indicate "end of dialing". For these, there would be no clash between a US "911" and UK "911xxx" dial string. If the user enters "911xxx" + "Send", then this must never be interpreted as "911". Similarly, "911" + "Send" is equally unambiguous (in this example).
SIP devices without a "Send" button generally employ a variety of mechanisms to recognize "end of dialing". 
 1. Some strings are automatically recognized; for example, when a user dials any "N11" string and has an ATA configured for US dialing plans, the ATA recognizes this string and automatically sends the SIP Invite without waiting any further.
 2. The user can usually press "#" to indicate end of dialing. Many users are unaware of this fact.
 3. If the user does not press another digit in 4 or 5 seconds (differs by device), this is interpreted as end of dialing, and the SIP Invite is sent.
What this means, is that, if a user enters a string that is not automatically recognized as being "complete", and the user doesn't press "#", there will be a 4 or 5 second delay between the time when the last digit is pressed and SIP signaling begins.
While I realize that this delay is generally undesirable, I would prefer that there be no requirement to automatically recognize "end of dialing" for visited emergency strings.
The flip side of this is that if the ATA's current dialing plan has an automatically escaped string that is shorter than the visited emergency number (e.g., an ATA might automatically recognize "00" as a complete string, and the visited emergency number is "000"), then the ATA logic needs to stop recognizing "00" as a complete string. I'm fine with this. The user can then dial "00" (+ timeout) or "00#", and also "000" (+ timeout) or "000#".
If done this way, the only clashes would be for exact matches.
Barbara
========================================
On Jan 28, 2006, at 12:25 PM, Stastny Richard wrote:
	1. By default, the device is set to use the home dialplan
	and home emergency numbers, either directly or via
	the home provider.
	2. If not at home, the device get its location and also
	the visited emergency numbers via some means
	3. The visited emergency numbers take precendence
	over the home dialling plan, if a clash occurs.
	(Note: your home provider may provide you with an
	escape code to override this, but then you definitely know
	what you are doing - e.g. to reach 911xxx local numbers in UK
	if you happen to be in the US.)
	Note: this may cause some emergency calls done wrong,
	but this is preferrable to missroute some real emergency calls

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From: "Brian Rosen" <[email-masked]>
Date: Tue, 31 Jan 2006 12:55:20 -0500

If you would like, I'll raise this with the PSAP and NENA folks.  I don't
think they will agree with you.

The visited emergency number has to work immediately, which means it has to
be recognized by a dial plan, and not depend on timeouts or # key presses.

I think they would say that the home emergency number could have the delay
or #.

You are proposing to change current behavior; as it stands now, if you bring
a phone into a country, it's the visited emergency number that works.  I do
understand that if you use an enterprise phone from a VPN or something
equivalent, everything breaks (you don't have the local emergency number,
you don't have correct location, and the call goes to the home psap).   I
think we really are better off with "both", even if that causes some kinds
of problems with home dial plans.  It's much easier to deal with Extension
999 doesn't work as a 3 digit number when I call from the UK as it does
"please remember to hit # or wait 4 seconds" to get help when you are in the
middle of London.

Brian

  _____  

From: [email-masked] [mailto:[email-masked]] On Behalf Of
Stark, Barbara
Sent: Tuesday, January 31, 2006 10:44 AM
To: [email-masked]
Subject: Re: [Ecrit] Issue 30: Summary

This seems generally reasonable to me, also. 
However, there is an implicit expectation in the description below that I'm
not quite comfortable with, in the "precedence" statement. That is, whether
or not end of dialing string is automatically recognized for visited
emergency numbers.

For devices that use a "Send" button, this isn't a problem. "Send" must
always be pressed to indicate "end of dialing". For these, there would be no
clash between a US "911" and UK "911xxx" dial string. If the user enters
"911xxx" + "Send", then this must never be interpreted as "911". Similarly,
"911" + "Send" is equally unambiguous (in this example).

SIP devices without a "Send" button generally employ a variety of mechanisms
to recognize "end of dialing". 
 1. Some strings are automatically recognized; for example, when a user
dials any "N11" string and has an ATA configured for US dialing plans, the
ATA recognizes this string and automatically sends the SIP Invite without
waiting any further.

 2. The user can usually press "#" to indicate end of dialing. Many users
are unaware of this fact. 
 3. If the user does not press another digit in 4 or 5 seconds (differs by
device), this is interpreted as end of dialing, and the SIP Invite is sent.

What this means, is that, if a user enters a string that is not
automatically recognized as being "complete", and the user doesn't press
"#", there will be a 4 or 5 second delay between the time when the last
digit is pressed and SIP signaling begins.

While I realize that this delay is generally undesirable, I would prefer
that there be no requirement to automatically recognize "end of dialing" for
visited emergency strings.

The flip side of this is that if the ATA's current dialing plan has an
automatically escaped string that is shorter than the visited emergency
number (e.g., an ATA might automatically recognize "00" as a complete
string, and the visited emergency number is "000"), then the ATA logic needs
to stop recognizing "00" as a complete string. I'm fine with this. The user
can then dial "00" (+ timeout) or "00#", and also "000" (+ timeout) or
"000#".

*****

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which it is addressed and may contain confidential, proprietary, and/or
privileged material. Any review, retransmission, dissemination or other use
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entities other than the intended recipient is prohibited. If you received
this in error, please contact the sender and delete the material from all
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---

From: Henning Schulzrinne <[email-masked]>
Date: Tue, 31 Jan 2006 20:58:47 -0500

While this is an interesting debate, I think we need to recognize that 
we're worrying about a very small fraction of users, with a likely 
decrease to zero over time, namely:

- overlap dialing (i.e., ATA-style devices rather than mobile)
- roaming or using a foreign VSP
- likely to be residential rather than office (PBX) use; I just don't 
see that many businesses deploying a PBX with a foreign VSP (and those 
businesses are likely to hand-tune their dial plan in any event)

I think the most common use of foreign dial plans will be *inbound* 
calls, e.g., from relatives and friends in the old home country.

Since this is indeed a rare case, we need to make sure it works 
correctly, precisely because visitors, babysitters and the like will 
have no clue, like Brian noted. However, it is probably less important 
that these rare emergency calls are delayed by a few seconds. The 
time-out delay noted seems well within the standard answer delay budget 
of most PSAPs.

On the other hand, given that the owner of the phone is likely to be 
aware of the special status of the foreign dial plan, I don't see much 
of a practical problem if he has to dial #9112345 for the rare cases of 
collision with a local number. Yes, there might be a mistake made and an 
accidental 911 call placed, but the number of such arrangements will be 
so small, that it is unlikely to matter.

Given that there is no perfect solution, I don't think we need to make a 
decision on this now; operational experience can dictate whether 911T 
(timeout) or 911. (immediate) is the right dial plan (or maybe even 
911C, where C stands for confirmation). We just need to design discovery 
protocols that allow for both options. By the time this stuff gets 
widely deployed, this may be about as relevant as rotary dials.

Stark, Barbara wrote:
> However, there is an implicit expectation in the description below that 
> I'm not quite comfortable with, in the "precedence" statement. That is, 
> whether or not end of dialing string is automatically recognized for 
> visited emergency numbers.
> 
> always be pressed to indicate "end of dialing". For these, there would 
> be no clash between a US "911" and UK "911xxx" dial string. If the user 
> enters "911xxx" + "Send", then this must never be interpreted as "911". 
> Similarly, "911" + "Send" is equally unambiguous (in this example).
> 
> SIP devices without a "Send" button generally employ a variety of 
> mechanisms to recognize "end of dialing".
> dials any "N11" string and has an ATA configured for US dialing plans, 
> the ATA recognizes this string and automatically sends the SIP Invite 
> without waiting any further.
> 
>  3. If the user does not press another digit in 4 or 5 seconds (differs 
> by device), this is interpreted as end of dialing, and the SIP Invite is 
> sent.
> 
> that there be no requirement to automatically recognize "end of dialing" 
> for visited emergency strings.
> 
> string, and the visited emergency number is "000"), then the ATA logic 
> needs to stop recognizing "00" as a complete string. I'm fine with this. 
> The user can then dial "00" (+ timeout) or "00#", and also "000" (+ 
> timeout) or "000#".
> 
> privileged material. Any review, retransmission, dissemination or other 
> use of, or taking of any action in reliance upon this information by 
> persons or entities other than the intended recipient is prohibited. If 
> you received this in error, please contact the sender and delete the 
> material from all computers. 117
> 
> 
> ------------------------------------------------------------------------
>