Ovidiu Sas wrote:

Basic 911 Service require:

Does not apply to E911 services!

> 
> Called Party Hold
> =================
> Enables the PSAP attendant to retain control of the call connection
> and to hold the line up for manual tracing even if the calling party
> goes on-hook. This is a useful feature to locate people who did not
> communicate all of the data needed for response by the PSAP and to
> trace nuisance calls. Called party hold can only be provided with
> direct dedicated trunk facilities.

As the Internet is packet-switched there is no line to hold.
Your PSAP end-device may remember SIP and IP addresses of callers.


> Forced Disconnect
> =================
> Allows the PSAP attendant to disconnect any call on a 9-1-1
> trunk. This feature prevents intentional jamming of the PSAP lines by
> persons dialing all of the 9-1-1 trunks and refusing to hang up. This
> feature is useful during situations where the system is inundated with
> calls about a single emergency. The PSAP operator can quickly
> ascertain if this is a new emergency, if not, quickly state that
> emergency services are responding and clear the line with the forced
> disconnect feature.

Disconnecting SIP emergency calls is as easy as disconnecting any
other calls -- you just send a BYE. Then, co-operating end-devices 
will stop sending packets. No lines, no need to disconnect them.

You may have non-cooperating devices which continue sending packet 
or even send unsolicited packets. However this is a broader denial 
of service issue which is not necessarily specific to 911.


> Idle Circuit Tone Application
> =============================
> Provides a means of determining upon answering a call whether the
> calling party has already disconnected the call or is still on the
> line, but unable to speak. If the caller abandoned the line just
> before the PSAP attendant answered, a distinct tone is heard by the
> PSAP. If the caller is unable to verbally respond but is still on the
> line, no tone will be heard.

Finding out of a call was terminated is easy and can be implemented
in various ways as product UI feature. PSAP attendent's phone may flash
red if a phone is active and flesh green otherwise.

I'm not really sure there is reliable way of finding out a caller
is unable to speak, left phone without haning up, etc.


> Ringback
> ========
This feature is used in conjunction with called party hold to reach a
caller who has hung-up before the PSAP has obtained all of the
necessary emergency data. Single party service and direct dedicated
trunks are required.

Ringback is easy. The PSAP attendant or better his device just needs
to remember from where it was called. Absolutely no change to SIP
required.