Version 5.8 483 October 2009
SIP User's Manual 9. IP Telephony Capabilities
9.4 Emergency Phone Number Services
The device supports various emergency phone number services such as 911 (in North
America).
9.4.1 Enhanced 911 Support
The device supports the North American emergency telephone number system known as
Enhanced 911 (E911), according to the TR-TSY-000350 and Bellcore's GR-350-Jun2003
standards. The E911 emergency system automatically associates a physical address with
the calling party's telephone number, and routes the call to the most appropriate (closest)
Public Safety Answering Point (PSAP), allowing the PSAP to quickly dispatch emergency
response (e.g., police) to the caller's location.
Typically, the dialed emergency number is routed to the appropriate PSAP by the telephone
company's switch, known as a 911 Selective Router (or E911 tandem switch). If the PSAP
receives calls from the telephone company on old-style digital trunks, they are specially
formatted Multi-Frequency (MF) trunks that pass only the calling party's number (known as
Automatic Number Identification - ANI). Once the PSAP receives the call, it searches for the
physical address that is associated with the calling party's telephone number (in the
Automatic Location Identification database - ALI).
9.4.1.1 FXO Device Interworking SIP E911 Calls from Service Provider's IP
Network to PSAP DID Lines
The FXO device can interwork SIP emergency E911 calls from the Service Provider's IP
network to the analog PSAP DID lines. The standards that define this interface include TR-
TSY-000350 or Bellcore’s GR-350-Jun2003. This protocol defines signaling between the
E911 tandem switch (E911 Selective Router) and the PSAP, using analog loop-start lines.
The FXO device can be implemented instead of an E911 switch, by connecting directly to
the PSAP DID loop-start lines.
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