Thursday, July 07, 2005

FAQs: Definition of User and Carrier (infrastructure) ENUM 

Currently the issues User ENUM, Carrier (or Infrastructure) ENUM and VoIP peering are discussed in various bodies.

I will try to give defintions (from my point of view) of User and Carrier ENUM. The definitions are also related to the discussions on VoIP peering (Interconnect) via the public Internet.


User ENUM in allows end-users to link either existing E.164 phone numbers or phone numbers assigned specificly for this purpose to applications reachable via URIs on the Internet. The decision to request the domain associated to the E.164 number (opt-in) and to fill the domain with ressource records of choice is with the end-user. If an existing E.164 number is used, the end-user must prove the right to use this number with the request of the associated domain.

Carrier ENUM

Carriers use E.164 numbers currently as their main naming and routing vehicle. Carrier ENUM in or another public available tree allows Carriers to link Internet based resources such as URIs to E.164 numbers (Note: this is the other way round then User ENUM). This allows Carrier in addition to the interconnect via the PSTN (or exclusively) to peer via IP-based protocols. Carriers may announce all E.164numbers or number ranges they host, regardless if the final end-user device is on the Internet, on IP-based closed NGNs or on the PSTN, provided an access (e.g. SBC or gateway) to the destination carriers network is available on the Internet.There is also no guarantie for the originating carrier querying Carrier ENUM that he is able to access the ingress network element of the destination carriers network. Additional peering and accounting agreements requiring authentication may be necessary. The access provided may also be to a shared network of a group of carriers, resolving the final destination network within the shared network.

The usage of ENUM within a carriers network or within shared networks in private ENUM trees is out of scope.

A virtual VoIP provider on the Internet may provide his end-users access to User ENUM and at the same time also may access Carrier ENUM, provided he has peering agreements with other Carriers. He may also populate Carrier ENUM with the numbers he is hosting. It is at his discretion if he provides other Carriers access to the users holding this numbers with or without special peering agreements.

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