Also known as the directory number (DN). The logical address assigned to a subscriber, a telephone number comprises a series of digits conforming to a format defined by the ITU-T at the international level in E.164 and comprises a maximum of 15 digits, including a country code.Within that format, a national or regional authority sets the format for that domain.The North American Numbering Council (NANC) sets the format for the North American Numbering Plan (NANP), for example, including a country code, an area code, a central office prefix, and a line number. In the traditional landline context of the public switched telephone network (PSTN), each telephone number is assigned to a circuit. In cellular networks, each telephone number is assigned to a cellular telephone. See also E.164, ITU-T, NANC, and NANP.