The VoIP Peering Puzzle: ENUM Standards and Operation
In a recent tutorial, VoIP Planet took a high-level view of one of the key technical issues — address translation — that must be resolved in order for end-to-end VoIP services to become widespread and readily available. That translation is required because telephone numbers adhere to one addressing standard, known as E.164, (the International Public Telecommunication Numbering Plan, developed by the ITU-T — see www.itu.int); and Internet-connected workstations use Internet Protocol addresses, developed by the Internet Engineering Task Force (IETF) as part of their protocol specifications for IP version 4 (IPv4) and IP version 6 (IPv6).
http://www.voipplanet.com/backgrounders/article.php/3648066