Carrier ENUM is a global Telephone Number DNS system advocated by the GSMA for resolving NGN routing address.
The single root architecture provides a hierarchical structure of ENUM registries linked by a series of registry delegations. The single root architecture enables automated discovery of ENUM data in different registries around the world.
In this model, the registries are logically organised into “Tiers”. Delegations between Tiers are based on the country code and network code elements of the E.164 number plan.
Tier 0 contains delegations per country code to national Tier 1 registries. GSMA is administering a Tier 0 in PathFinder.
Tier 1 registries contain delegations per network code to Tier 2 service provider registries in non-number portability countries. In number portability countries, Tier 1 registries contain delegations per network code and subscriber identity combination to Tier 2 service provider registries.
In this model, there is only one source of data for any given MSISDN, ie. the data is authoritative.
The querying party queries the Tier 0, Tier 1 and Tier 2 registries in turn to acquire the end point information which is stored in the Tier 2. The Tier 0 and Tier 1 queries enable the querying party to find the correct Tier 2 automatically, see use cases.
A service provider populates information against a number which it wishes to be discovered. This information is typically a list of gateways into its network for services associated with a number. There can be multiple services per number as well as multiple gateways per service with preferences attached. Taking the example of a subscriber using a SIP based voice service, the SP would populate a point of interconnect where the SIP/IP based voice traffic can be processed. In this way, the SP directs traffic to appropriate points of interconnect where firewalls and accounting systems are established. Using this approach, a variety of interconnect strategies may be implemented by service providers and their agents.
PathFinder acquires number portability data from authoritative sources around the world and uploads them into its central registry. Where uploading is not possible, the external sources are referenced on a per number basis.
Users can query a legacy number in PathFinder and receive either the E212 MCC, MNC or a GSPID identifying the destination operator. In some countries, information may also be available in the form of an alternate GSPID for virtual operators such as MVNOs and “white label” voice services. The MCC MNC codes are uniquely allocated to each mobile operator by the ITU and therefore accurately signal the destination network. The GSPID and AltGSPID are five digit numbers allocated to networks which do not have a MCC MNC code. This allows PathFinder to signal fixed operator destinations with equal accuracy.
