ESN
1. Emergency Service Number A three-digit number that is assigned to the caller's telephone number in the tandem office translations. The emergency...
Definition:
Emergency Service Central Office Number. The information delivered to the PSAP when there is an ANI failure between
the end office and the 9‐1‐1 Control Office. When ANI is not available, the 9‐1‐1 call is default routed and the ANI display
at the PSAP will be "911‐0TTT" (or 911‐TTTT) with TTT identifying the incoming trunk group. When an ANI is not
available and a 9‐1‐1 call is default routed, the ANI display at the PSAP will be “911‐0123,” with the last three digits (123)
being the central office number.