Glossary of 911 Terms
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Emergency Notification Systems

emergency alert systems This section of our technical library presents articles written about Emergency Alert Systems and Disaster Recovery definitions, terms and related information.

The 911Broadcast emergency notification and alert service can deliver a large number of phone calls using a network of phone systems employing digital phone lines simultaneously. Should a disaster such as a snow storm, wild fire or flood hit your area, 911Broadcast systems can alert your community quickly providing specific instructions if an evacuation is required.

This service is available using our emergency broadcasting systems. If a dangerous chemical spill occurs in your community, you can target specific areas to call. If a severe snow storm hits your area, your community can be notified of school closings or event cancellations.

E911 Glossary

by Stephen J. Schmidt [and amended by DISPATCH Monthly Magazine]


Automatic Number Identification corresponds to the subscriber's seven digit telephone number. The ANI displays at the PSAP on the digital ANI display console.

ANI Failure

Failure of the end office to identify the call and provide the ANI (telephone number) to the tandem office; or, an ANI failure between the tandem office and the PSAP.


Automatic Location Identification provides for an address display of the subscriber calling 911. With ALI, the PSAP receives the ANI display and an ALI display on a screen. The ALI display includes the subscriber's address, community, state, type of service and if a business, the name of the business. The PSAP will also get a display of the associated ESN information (police, fire, rescue).

Alternate Routing

Alternate routing provides for a predetermined routing for 911 calls when the tandem office is unable to route the calls over the 911 trunks for a particular PSAP due to troubles or all trunks busy.

Anonymous Call

If a subscriber misdials and dials the seven digit number associated with the PSAP position, they will come in direct and ANI display as 911-0000 which will ALI as an anonymous call. The seven digit numbers associated with the PSAP positions are not published even to the PSAPs.

Call Detail Record

When the 911 call is terminated by the PSAP operator, the ANI will automatically print-out on the teletypewriter located at the PSAP. The printout will contain the time the call came into the PSAP, the time it was picked up by an operator, the operator number, the time the call was transferred, if applicable, the time the call was terminated and the trunk group number associated with the call. Printouts of the ALI display are now also available, if the PSAP has purchased the required equipment.

Default Routing

Provides for routing of 911 calls when there is an ANI failure. The call will be routed to the "default" ESN associated with the he NNX the caller is calling from. Default ESNs are preassigned in translations and are usually the predominant ESN for a given wire center.


Enhanced 911: Features available include selective routing, selective transfer, fixed transfer, alternate routing, default routing, Automatic Number Display, Automatic Location Identification, night service, default routing, call detail record.

End Office

Telephone central office which provides dial tone to the subscriber calling 911. The "end office" provides ANI (Automatic Number Identification) to the tandem office.


Emergency Service Number (XXX) that is assigned to the subscriber's telephone number in the tandem office translations The ESN represents a seven digit number by which the tandem office routes the call to the proper PSAP. PSAPs with ALI capabilities also receive a display of the ESN information which shows which police, fire and rescue agency serves the telephone number calling 911. An ESN is a unique combination of police, fire, and rescue service for purposes of routing the E911 call.

MSAG Master Street Address Guide

The MSAG ledgers are controlled by the municipality which has purchased the E911 ALI service, in that they assign which police, fire or rescue agency will serve a given street and number range. They do this by assigning an ESN to each street range, odd, even, community that is populated in the county or municipality served. These MSAGs are then used as a filter for service order activity into the E911 computer data base to assign ESNs to individual TN records. This insures that each customer will be routed to the correct agency for their particular address. In a non-ALI County, TAR codes are used by the Telephone company to assign ESNs to service conductivity and the County does not control the ESN assignment. TAR codes represent the taxing authority for the given subscriber which should correspond to their police, fire and rescue agencies. The MG method, of course, is more accurate because it is using the actual service address of the customer to route the call and provides the county with more flexibility in assigning fire and rescue district, etc. The Customer Services E911 Group maintains the E911 computer data base and interfaces with the County (customer) on all MSAG or data base activity.


Any condition that results in the 911 call going to the wrong PSAP. A call can be misrouted if the ESN and associated routing information are incorrect in the E911 data base and/or tandem data base. A call can also be misrouted if the call is an ANI failure, which automatically default routes.

N11 Assignments

The FCC has assigned several three-digit numbers for emergency and non-emergency access, and has posted a complete explanation on their Web site.

Night Service

Night service works the same as alternate routing in that the calls coming into a given PSAP will automatically be routed to another preset PSAP when all trunks are made busy due to the PSAP closing down for the night.


This condition means the PSAP received a call, but no telephone number displayed on the ANI console. The PSAP should report this condition immediately to the SSC/MAC.

No Displays

A condition where the PSAP ALI display screen is blank. This type of trouble should be reported immediately to the SSC/MAC. If all screens at the PSAP are blank, it is an indication that the problem is in the circuits from the PSAP to the E911 computer. If more than one PSAP is experiencing no display, it may be a problem with the Node computer or the E911 computer. The SSC/MAC should contact the MMOC to determine the health of the HOST computer.


Public Safety Answering Point, usually the police, fire and/or rescue groups as determined by the local municipalities. A "ringin" will not have ANI or ALI capabilities, but just receives calls or transferred calls from another PSAP.

PSAP Not Receiving Calls

If a PSAP cannot receive calls or request retrievals from the E911 host computer, i.e., cable cut, the calls into that PSAP must be rerouted to another PSAP. The Switching Control Center must be notified to reroute the calls in the tandem office E911 translations.

Tandem Office

Telephone central office which serves as a tandem (or hub) for all 911 calls. Must be a 1AESS type of central office. The tandem office translations contain the TN/ESN relationships which route the 911 call to the proper SAP. The tandem office looks up the ANI (TN) that it receives from the end office and finds the ESN (routing information) which corresponds to a seven digit number ringing in at a PSAP.

Record Not Found

If the host computer is unable to do a look up on a given ANI request from the PSAP, it will forward a Record Not Found message to the PSA ALI screen. This is caused by service order activity for a given subscriber not being processed into the E911 data base, or HOST computer system problems whereby the record cannot be accessed at that point in time

Selective Routing

The capability to route a call to the particular PSAP serving the address associated with the TN making the 911 call. Selective routing is achieved by building TN/ESN translations in the tandem central office. These translations are driven by the E911 data base which assigns the ESN to each telephone number based on the customer's address. Service order activity keeps the E911 data base updated. The E911 data base, in turn, generates recent change to the tandem office (through the SCC or RCMAC) to update the TN/ESN translations in the tandem data base.

Selective Transfer

Provides the PSAP with the ability to transfer the incoming 911 call to a fire or rescue service for the particular number calling 911 by pushing one button for fire or rescue. For example, if an incoming 911 call was reporting a fire, the PSAP operator would push the fire button on the ANI console; the call would go back to the tandem office, do a lookup for the seven digit number associated with fire department, for the ESN assigned to the calling TN, and automatically route the call to that fire department. This differs from "fixed" transfer which routes every call to the same fire or rescue number whenever the fire or rescue button is pushed. The PSAP equipment is optioned to provide either fixed or selective transfer capabilities.

Spurious 911 Call

Occasionally, the PSAP will get a call that is not associated with a subscriber dialing 911 for an emergency. It could be a subscriber who has not dialed 911, but is dialing another number, or has just picked up their phone and was connected with the PSAP. These problems are equipment related, particularly when the calls originate from electromechanical or step by step offices, and are reported by the E911 Center to Network Operations upon receipt of the PSAP inquiry reporting the trouble. The PSAP may get a call and no one is there; if they call the number back, the number may be disconnected or no one home. Again these are network troubles and must be investigated. Cordless telephones can also generate "spurious" calls in to the PSAPs. Generally, the PSAP will hear conversation on the line, but the subscribers are not calling 911. The PSAP may report spurious calls to to repair if they become bothersome, for example, the same number ringing in continually.