Switching to VoIP

This is the Title of the Book, eMatter Edition

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Emergency Dispatch/911

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349

You’ll won’t hear any DTMF tones in the recording as long as you use

a phone with out-of-band signaling, such as SIP Info.

Emergency Dispatch/911

E911, or Enhanced 911, is the common American PSTN’s public safety protocol for

emergency situations. PSTN subscribers dial 911 and are connected to the fire

department or police dispatcher at the closest PSAP (public safety answer point).

Between the subscriber’s CO and the PSAP are dedicated trunks that carry ALI

(automatic location identification) signals from the phone company to the PSAP, so

that emergency personnel can know the geographic location of the emergency taking

place. This is particularly useful for fires and emergency medical responses.

E911 on the PSTN

The federal government mandates that all ILECs are required to provide 911 signal-

ing service by way of dedicated trunks. In turn, the local public safety authorities col-

lect a tax, usually through phone bills, to fund operation of the system. Public

Utilities Commissions enforce the compliance of 911 operations, and the FCC

approves standards that are used in the system.

Competitive LECs that don’t have switching facilities can use those of the ILECs in

order to route 911 calls.

E911 on wireless providers’ networks

In addition to LECs, wireless voice ...