Emergency Number Systems and Technology
Core concepts
Emergency number systems rest on the path from caller to answering point: originating network, selective router, PSAP CPE, and the call-handling equipment that delivers ANI (calling number) and ALI (location). Modern 9-1-1 separates the origination network from the location database; the caller's address is retrieved by querying ALI using the ANI as the key. Candidates must be fluent in the difference between wireline (static, address-based ALI) and wireless (Phase I cell/sector vs. Phase II x/y coordinates), and in NG9-1-1 concepts: ESInet, i3 architecture, LIS/LLo, LoST routing, and GIS-based dispatch boundaries replacing legacy selective-routing tables.
Technology vocabulary
Know ANI/ALI, selective transfer, ALI steering, default routing, trunking and CAMA, and call overflow/backup PSAP. For NG9-1-1, understand ESRP, LVF, EIDO, and EIDD as the functional elements of the i3 standard, and why location validation happens before a call is placed. Text-to-9-1-1, RTT, and MMS require an IP-capable origination path and a PSAP that can receive them - a common trap is assuming all 9-1-1 calls are location-accurate.
Traps
Questions often blend Phase I vs. Phase II accuracy, confuse ALI with GIS, or imply NG9-1-1 is fully deployed everywhere. Also watch for call-delivery vs. call-handling responsibility boundaries between the service provider and the PSAP.
Rule of thumb
Think of 9-1-1 as three layers: transport (how the call gets there), location (how we know where it is), and presentation (how the telecommunicator sees it). Most technology questions can be answered by asking which layer is being described.