This document specifies guidelines for the assignment of Numbering Plan Area (NPA) codes. NPA codes are the first three digits of the 10-digit North American Numbering Plan (NANP) format (the format is made up of 10 digits in the form of NXX-NXX-XXXX). NPA codes have traditionally been used to identify distinct exclusive geographic areas, commonly referred to as area codes.
CODE FOR INFORMATION INTERCHANGE (WITH ANSI X3.4-1977) (SUPERSEDING FIPS-PUB-1-1, FIPS-PUB-1-7, FIPS-PUB-1-15, FIPS-PUB-1-35, AND FIPS-PUB-1-36) (NO S/S DOCUMENT) (WITHDARWN 7/29/97)
INTERFACE BETWEEN DATA TERMINAL EQUIPMENT (DTE) AND DATA CIRCUIT-TERMINATING EQUIPMENT (DCE) FOR OPERATION WITH PACKET-SWITCHED DATA NETWORKS (PSDN), OR BETWEEN TWO DTES, BY DEDICATED CIRCUIT (ANSI X3.100)(NO S/S DOCUMENT)
