Subject: RE: [Sipping] sip-911, Preventing dialog termination

From: "Kozdon, Peter" <[email-masked]>
Date: Fri, 1 Mar 2002 10:26:18 -0800

In the early days there was 911 - this service simply delivered a call to a
PSAP - with NO location information, etc.. Even this basic service is not
ubiquitous in the US today with a few areas still having to dial a local
number to reach emergency services.  In those cases it is highly beneficial
to keep the call up so that the PSAP can find out from the caller where
he/she is located, etc.. This basic 911 service is typically associated with
a single CO switch, where in the worst case they could do a wire trace to
find out where the call was originated (I suspect that this is why there is
a need to keep the connection up - in many of these CO's - if either of the
2 parties in call does not "hang up" - then the connection would is kept up
- no disconnect supervision from the PSAP.

Today, many areas in the US have E-911 service - this provides information
related to the location of the caller, enables the use of tandem CO
switches, etc.. I would be very surprised if a connection could be reliably
kept up in all cases after a disconnect at the callers device, however, as
the PSAP has location information (via ANI (automatic number identification)
and ALI (automatic location information)) this should be much less of a
concern. 

In the UK the 999 service  has had location identification for over 20
years, in some countries a common number for emergency services is only just
being introduced and in many others it is way off.

We must enable a reliable delivery service to what ever emergency number is
required depending on deployment, IMHO this may require additional localized
intelligence in the GSTN gateway through which the call is delivered. I
support the concept of the "sos.*@local-domain" alias proposed, this would
enable the "local proxy" and/or "local gateway" to be customized to support
local variations. The problem will, however, be to determine the
"local-domain" associated with the "local gateway" -- this will not always
be the same as the domain where the user is register.

Peter Kozdon  

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] 
Sent: Friday, March 01, 2002 5:04 AM
To: Henning Schulzrinne
Cc: Farahmand, Fardad; 'Dean Willis'; [email-masked]
Subject: Re: [Sipping] sip-911, Preventing dialog termination

From:  Tom Gray@MITEL on 03/01/2002 08:04 AM

911 and like calls cannot be placed on hold. This includes both hard hold
which is the customary type of hold and soft hold which is used as part of a
transfer service. This effectively bars the custom services mentioned below.
I would be very surpised in DMS did not obey this standard since it is a
common example used int eh feautre interaction literature and Nortel is an
active participant in this community.

It can cause problems as when someone goes into 3 way call mode to make an
emergency 911 call for someone he is conversing with. After calling 911 he
cannot swap back to his distressed correspondent or conference him into the
911 call since this would place the 911 service on hold. However I suppose
the general benefit of this service outweighs these handicaps.

Tehre are other serivices whcih also require that there be callee control of
disconnect. This includes calls to operator services. Call trap services to
foil abusive callers  and more that I don't recall off hand.

SIP if it is to be a practical way of creating public services must be able
to handle 911  and other services requiring callee control of disconnect
properly.

Henning Schulzrinne <[email-masked]> on 02/28/2002 07:30:31 PM

To:   "Farahmand, Fardad" <[email-masked]>
cc:   "'Dean Willis'" <[email-masked]>, [email-masked] (bcc:
Tom
      Gray/Kan/Mitel)

Subject:  Re: [Sipping] sip-911, Preventing dialog termination

I should point out that I had a discussion on this topic with some folks in
the (U.S.) 911 community. Opinions diverged - some claimed that switches
restricted services, while other disagreed, saying (e.g.,) that this might
have been done in the past, but was no longer feasible with modern switches.
It appears that this may well be dependent on the LEC and maybe the
particulars of the local CO. Apparently, you get some really strange results
when three-way calling gets involved, with two 911 operators on the line.

As long as the PSAP has a reliable call-back address, even midcall
disconnects are not that big a deal. As Dean hints at, that's about the best
you can do for mobiles in any event. Here are some quotes:

"I can't speak for Call Transfer however Call Waiting and Three Way Calling
are still available to the 9-1-1 caller.  At least it is here in a DMS
environment."

"From my experience, most switches (5ESS, DMX-100, and GTD5EAX) disable
custom calling features for the entire call when calling to N11 services in
a manner similar to when they are establishing a call to another number.  In
other words, the switch deals with the 911 call like when you are listening
to a ringing signal (i.e.  no call waiting, no call transfer, no 3-way
calling, etc.).

ANSI T1S1 is the standards group that is responsible for the PSTN signaling
standards for the US and Canada. T1S1.7 is specifcally tasked with the
architecture, services and signaling. ANSI T1.628-2000 and ANSI T1.628a-2001
seem to be the governing ANSI documents relating to ECS (Emergency Calling
Services). You might look there."

I don't have access to the documents.

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_______________________________________________
Sipping mailing list  https://www1.ietf.org/mailman/listinfo/sipping
This list is for NEW development of the application of SIP
Use [email-masked] for questions on current sip Use
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_______________________________________________
Sipping mailing list  https://www1.ietf.org/mailman/listinfo/sipping
This list is for NEW development of the application of SIP
Use [email-masked] for questions on current sip
Use [email-masked] for new developments of core SIP

---

From: Henning Schulzrinne <[email-masked]>
Date: Fri, 01 Mar 2002 18:44:42 -0500

> being introduced and in many others it is way off.

Do you have a reference or listing of where these types of location
identification services are available?

> be the same as the domain where the user is register.

The idea was that the first proxy is more likely, statistically
speaking, to be closer to the caller and thus more likely to reach the
right PSAP, particularly in cases of international roaming. Clearly,
this isn't always the case, with VPNs and such, but it seems like the
best heuristic under the circumstances.