Re: [codec] #14: VAD and CNG?

[Brian Rosen <[e-mail]>]

Okay, you asked for it :)

In any country, the codes used in another country for emergency numbers are
used as service invocations for other services.  You have to know what
country you are in to know what emergency numbers are.  It is roughly
impossible (today) to know that with sufficient reliability.

You can place an emergency call to an e.164 in many countries.  This may
depend on which service.

The emergency call center (PSAP) can call you back.

A call placed to a call center can be transferred or upgraded to an
emergency call.  This happens with relay centers used by disabled
individuals.

In all of these circumstances, VAD must be disabled.  Emergency calling
systems are filled with a lot of complexity that handle seldom occurring
circumstances.  However, when it comes to saving lives, seldom occurring
circumstances are important.

Brian

ps - I have been working in this field for a number of years.  You can learn
a bit more about emergency calling from draft-ietf-ecrit-framework.  The
inability to turn off VAD in VoIP systems believed to have caused actual
harm according to some of my associates who work in PSAPs.




On 5/24/10 1:37 PM, "Christian Hoene" <[e-mail]> wrote:

> Hi Brian,
> 
>> I'll be happy to go into the details, but phones may not know they are in an
>> emergency call.  No phone knows this today.  There is some proposed
>> signaling that would tell them, IF the phone, and the service provider
>> implement it, but even then, there are circumstances where the phone won't
>> know.
> 
> If(called.number==112 || called.number==911 || called.number=XYZ)
> EmergencyCall();
> 
> See more at http://en.wikipedia.org/wiki/1-1-2
> It is so easy to know... I do not get your arguments.
> 
> With best regards,
> 
>  Christian 
> 
> 
>