Re: [Sipping-emergency] Emergency Scenarios Document

[Henning Schulzrinne <[e-mail]>]

>       centresin the PSTN, the scenarios involving stationary or nomadic SIP 

spelling

>       phones are described and then alternative strategies for supporting 
>       the information flows for the scenarios needed to meet these 
>       requirements are examined.  The analysis presented here is a 
>       necessary step in defining the SIP specific requirements for invoking 
>       emergency assistance and understanding the level of functionality 
>       that can be provided by existing SIP devices and network elements and 
>       that which requires further development. 

>       in the European Market in general, or 000 in Australia.  (Globally 

I thought it was European Community?

>       there are about 60 different emergency services numbers in use [4].)  

>       This document uses the term SIP phone to denote a device which plugs 
>       into a wired network.  This can be a either a physical phone device 
>       or a PC running a software based SIP client (often referred to as a 
>       SIP softphone).  These devices can be stationary or nomadic. 

Why a wired network? I think the issues for a PDA or laptop or even a 
phone (via an Ethernet-to-802.11 bridge) that connects via an 802.11 
hotspot are fairly similar.

> 
>       Scenarios involving cellular phones using SIP signalling are not 
>       necessarily considered, because the current expectation is that they 
>       use the emergency service solutions devised for cellular phones in 
>       general. However, it is anticipated that many aspects of a general 
>       SIP signaling solution could apply to those scenarios.  The 
>       requirements for Wi-Fi enabled devices (e.g. a SIP softphone with Wi-
>       Fi access, a Wi-Fi phone etc.) using SIP signalling are considered 
>       from the perspective that these devices can be represented as nomadic 
>       SIP users and thus addressed by several of the scenarios described in 
>       this document. 

I would not make the distinction up front.

>       "legacy" is used to refer to "Enhanced 911" functionality.) 

You mean 'basic 911'?

>       the difference in medium and the fact that a different number may be 
>       dialed to initiate the call.  

I think all single-number systems support TDD on the same number; that's 
at least true for 911, as far as I know.

>       (1) The caller requires an easily-remembered, location-independent 
>           means of identifying an emergency call.  Moreover, it must be 
>           possible to indicate whether this is a voice call or one to be 
>           directed to a text ECC. 

I don't think so. I think the 911 destination listens for the TDD modem 
tone and then switches to a TDD. This is not by number.

> 
>       (5) The ECC operator can stay in touch with the caller, even though 
>           the telephone set goes on hook for an intervening period.  An 
>           example of when this is useful is if the caller, feeling unwell, 
>           accidentally drops the telephone back onto its cradle, but then 
>           is able to retrieve it. 

As discussed previously, this is not a universal feature. This is more 
of an urban legend at this point :-)

> 
>       (6) Emergency calls are given priority handling in call processing 
>           and high quality media connections.  (The quality of media 
>           connections is outside the scope of this document.) 

Again, I don't think this is generally true, at least in the US.


> 
>       (7) The caller can be held accountable for the call, to dissuade 
>           callers from misuse of the system. 

If you ignore pay phones :-)

> 
>    3.3   Legacy System Operation 
> 
>       In the legacy network, the public telephone system operator is 
>       responsible for maintaining the mapping database.   

This is imprecise - at least in the US, there is no 'the' telephone 
system operator. It is generally the ILEC, but I think it would be 
unhelpful to imply that we live in pre-1984/pre-1996 land.

>       the location.  Alternatively, various locations can be identified 
>       within the business and assigned a pseudo directory number (DN), 

Even for phones with DID, extensions are usually not visible to the 
outside. (I've tried it - all of our extensions show up as 7000. We have 
DID in 7000 to 7199.)

>       A special arrangement at the switch serving the ECC allows the 
>       emergency operator to hold open the voice path back to the caller as 
>       long as necessary, even if the caller goes on-hook.  It should be 
>       noted that this functionality is not supported for ISDN. Thus, the 
>       operator can also ring the caller's line in this situation or others 
>       where it might be necessary.  

I would qualify this as "In analog switches, ....". Most switches today 
are effectively ISDN (or equivalent), so this feature is likely only 
available to a tiny fraction of end systems.

>    4.1   A General Look At The Problem 

at the

>       signalling passes through other intelligent elements -- SIP proxies 
>       and a gateway -- before reaching the telephone network.  The SIP 

A SIP proxy isn't mandatory.

[More in next message.]



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