TYPES OF ENUM
Public User ENUM
With End User ENUM, the end user can provision his or her records in the ENUM registry in the public domain e164.arpa. (In other words, the end user is the registrant for the ENUM domain name within the domain e164.arpa.) End user ENUM implies that the end user has "opted in" to the ENUM service.
The DNS is publicly available to any Internet user. It uses a domain available on the public Internet, and various regulatory, industry and standards bodies moderate the domain's policies and practices. "End user opt in" is generally considered a good policy if end user data is publicly available on the Internet.
Private Infrastructure ENUM
Private ENUM uses the concepts of creating a domain name from a TN and resolving it to a URI. It does not, however, use the domain e164.arpa (or any other domain with regulatory oversight). Private ENUM is used when there is a closed user group that wants to use ENUM to exchange IP traffic.
An example of such a user group is a group of communications carriers that wants to exchange VoIP traffic. The user group that creates and uses the domain will also create the policies for the domain. There will be no regulatory oversight of this domain, because it is not intended for public use.
Public Infrastructure ENUM
National number administrators typically assign TNs to communications carriers, not to end users; the carrier then assigns the TN to the end user. Carriers have specific needs when it comes to provisioning routing information related to their customers' TNs. Carriers map TNs to internal network addresses to enable call routing and features; these addresses are not publicly available. The carrier's network and its associated addresses are highly secure, and access is strictly maintained and limited to other service providers. These characteristics have come to define the recent discussions of carrier ENUM.
