NPD (Numbering Plan Digit)

NPD (Numbering Plan Digit) is a component of the traditional 8-digit 9‑1‑1 signaling protocol between the Enhanced 9‑1‑1 Control Office and the PSAP CPE. Identifies 1 of 4 possible area codes.

NENA-STA-010, NENA i3 Standard for Next Generation 9-1-1