What is a PSAP?
A Public Safety Answering Point (PSAP) is a dispatch center staffed by emergency operators, which receives 911 calls and dispatches fire, police, or medical services, depending on the nature of the emergency. PSAPs are generally controlled at the city or county level.
What are ANI and ALI?
ANI (Automatic Number Identification) is the automatic display at the PSAP of the telephone number associated with the line which called 911. Each telephone number and the physical location to which it corresponds are stored in an ALI (Automatic Location Identification) database, managed by the local exchange carrier. In a 911 call, the PSAP uses the ANI to retrieve the caller’s physical address from the ALI database. Additionally, the ANI acts as a callback number should the PSAP lose its connection to the distressed caller. Both ANI and ALI are key capabilities of E911 service.
What is an ERL?
An Emergency Response Location (ERL) is a specific geographic location to which a 911 emergency response team may be dispatched. For increased accuracy, to reduce response times, or to meet state E911 legislation, the PBX administrator may break down an organization’s campus or buildings into several different ERLs. This allows the organization to provide the PSAP with a 911 caller’s precise location, rather than simply the organization’s main billing address.
For example, each building within a campus or floor/wing of a building may be considered its own ERL; within a given ERL there may be several phones or extensions. In some states, regulations require that organizations maintain ERLs of a specific size or identifiable area (e.g. one ERL per 1000 square feet or per floor).
What is an ELIN?
An Emergency Location Identification Number (ELIN) is a ten digit DID number purchased from the local exchange carrier (LEC), and is one way for organizations to provide specific location information to the PSAP for a 911 call. First, enterprise administrators assign an ELIN to each ERL; one ELIN can be used for many phones within an ERL, but each ERL requires at least one unique ELIN. This mapping of ELINs to ERLs must then be loaded into the regional ALI database.
During a 911 call, the ELIN takes the place of the caller’s telephone number as the ANI and is used to route the call to the appropriate PSAP. The PSAP uses the ELIN to query the ALI database and retrieve the caller’s location (i.e. ERL). Should the caller be disconnected, the PSAP can also use the ELIN to call back the extension directly (which requires a temporary mapping of the 911 caller’s number to the ELIN), bypassing the PBX attendant or auto-attendant.