Re: [Sipping-emergency] Re: Emergency-req: 8-12

[Henning Schulzrinne <[e-mail]>]

> I'm getting lost in what is the context.  It looks to me like there are
> three cases.
> 
> a) someone uses IP-based phone or IM to call for help (sos/911) and this
> hits a gateway (either regular IP-PSTN gateway or IP to text messaging
> (e.g., SMS).  What is required in this case?

I was trying to avoid getting into the details of how the current system 
works and (more importantly) the properties it has, but maybe that's a 
bad idea.

The case you describe has two important sub-cases:

(1) The gateway is in the same town as the caller. (I'll say 'town' for 
simplicity; I mean 'same ECC serving area', but that's much longer...). 
In that case, the call reaches the right ECC. A problem arises if the 
phone has no E.164 phone number in the ECC calling area.

As an example, if I take my Vonage/Denwa phone from New York to 
Lexington, I might configure the right local Lexington, KY gateway, but 
the poor PSAP will see a 212 phone number and have no clue where I am or 
who I am.

(2) The gateway is in a different town. Since there are 5000 PSAPs in 
the US and it is unlikely that most service providers would use nearly 
that many gateways, this is a likely scenario. In addition to the 
problems in case (1), you are now connected to a gateway in the wrong 
city. Thus, if the Vonage gateway is in New York, my Lexington emergency 
call will reach the NYPD, which isn't going to be too helpful. I suspect 
that the New York 911 call taker things that I'm nuts if I tell them 
that the accident is a 1000 miles away.

This is described without example and more tersely in the section 
'Identifying the Appropriate Emergency Call Center'.

Would it be helpful to write it up at this level?


> b) someone uses IP-based phone or IM to call for help (sos/911) and this
> goes end-to-end IP.  (It appears to me that it might not be detectable to
> the caller whether a gateway will intervene so perhaps what is required
> should be the same as case a).)

This is indeed somewhat similar. The location problem is easier, since 
the caller could route the call to the right ECC.

> c) the receiving center is IP-based but calls come in from the PSTN.
> 
> Have I got this correct?
> 
> Now, if so, isn't this simple?  What is needed?  location information?
> time-stamps? some assuredness that the message is authentic?  ?

The primary problem, as alluded to in the beginning of the end-to-end 
section, is getting the call to the right PSAP/ECC. That's a fundamental 
requirement - you're not going to get useful emergency service 
otherwise. A secondary requirement is that the ECC gets location and 
other information (hazardous materials at your place, etc.). That's a 
longer-term issue, since *current* wireless systems don't deliver that, 
either. (They will, in the next few years.)

> 
> When I try to read the draft, I don't get it in clear language what is
> needed but my feelings are that it shouldn't be that complicated.  What am I
> missing?

In my view, this isn't complicated once you get down to the details.

Henning



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