The NANP divides the territories of its members into numbering plan areas (NPAs) which are encoded numerically with a three-digit telephone number prefix, commonly called the area code. Each telephone is assigned a seven-digit telephone number unique only within its respective plan area. The telephone number consists of a three-digit central office code and a four-digit station number. The combination of an area code and the telephone number serves as a destination routing address in the public switched telephone network (PSTN). For international call routing, the NANP has been assigned the international calling code 1 by the International Telecommunications Union (ITU). The North American Numbering Plan conforms with ITU Recommendation E.164, which establishes an international numbering framework.