E.163 was an ITU-T standard for describing telephone numbers for the public voice network (PSTN). In the United states this was formerly refered to as a 'Directory number'. This standard has been superseded by E.164 in 1997. The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU). ... This article needs to be cleaned up to conform to a higher standard of quality. ... The public switched telephone network (PSTN) is the concatenation of the worlds public circuit-switched telephone networks, in much the same way that the Internet is the concatenation of the worlds public IP-based packet-switched networks. ... E.164 is an ITU-T recommendation which defines the international public telecommunication numbering plan used in the PSTN and some other data networks. ...