Information for IETF relevant to E.164-DNS Interworking March 15 1. Operational information on E.164 1.1 E.164 number formats Recommendation E.164 (revised in 1997) specifies three different structures for the international public telecommunication number (E.164 number). -International public telecommunication number for geographic areas. -International public telecommunication number for global services. -International public telecommunication number for Networks. Number structure for geographic areas: +--------------+ +---------------------------+ +-------------------+ | Country Code | | National Destination Code | | Subscriber Number | +--------------+ +---------------------------+ +-------------------+ <-1 to 3 digits-><----------- National Significant Number----------> <---------------------------Max 15 digits------------------------- > Number structure for global services: +--------------+ +------------------------------------------+ | Country Code | | Global Subscriber Number | +----------- --+ +------------------------------------------+ <--- 3 digits--> <------------------------Max 15 digits--------------------- > Number structure for Networks: +--------------+ +---------------------+ +------------------------+ | Country Code | | Identification Code | | Subscriber Number | +--------------+ +---------------------+ +------------------------+ <-- 3 digits---> <--- 1 to 4 digits ---> <---------------------------Max 15 digits------------------------ > 1.2 Characteristic and usage E.164 Country Code (CC) for geographic areas are allocated to a specific country, countries in an integrated numbering plan, e.g. North America, or a specific geographic area. The format of the National Significant Number (NSN) is a national matter and the use of National Destination Codes (NDCs) is also a national matter. Country codes assigned or reserved for global services are: 800 Universal International Freephone Number (UIFN); 808 Universal International Shared Cost Number (UISCN); 878 Universal Personal Telecommunication (UPT) 979 Universal International Premium Rate Number (UIPRN). For Network country codes, currently 2 digit Identification Codes (IC) have been allocated for international Networks which meet criteria specified in Recommendation E.164.1. Also, 1 digit ICs have been allocated for Global Mobile Satellite Systems (GMSSs). 1.3 E.164 numbering resource administration E.164 numbering resources are administered by entities to which the CC or CC+IC is assigned by the ITU. More specifically, planning and utilization of numbering resources following a specific CC for a geographic area are under the responsibility of that area (a specific country, countries in an integrated numbering plan, e.g. North America, or a specific geographic area). The administration of Global Subscriber Numbers for UIFNs is the ITU-TSB's (Telecommunication Standardization Bureau) responsibility, as well as the mapping data between a GSN and a service provider is maintained by the TSB. The administration of the numbering resources following an IC are the responsibility of the Network, the assignee of the IC. Information about "who is responsible for which CC or CC+IC" is administered and maintained by ITU-TSB. The ITU-TSB maintains a list of E.164 CCs (and ICs), and it periodically publishes an Operational Bulletin that includes changes to the list. 1.4 Dialling plans E.164 numbers, short codes, service codes and prefixes are categorized in dialling plans. A prefix is an indicator consisting of one or more digits that allows the selection of different types of number formats, networks and/or services. Prefixes are not part of the number and are part of a dialling plan. The uses and the formats of prefixes are a national matter. In accordance with Recommendation E.123, the symbol "+" is recommended as a notation to indicate that an international prefix is required. Short codes, e.g. emergency, or service codes may be used based on the national numbering plan. Those codes are not universal and typically valid only within a numbering domain identified with the same CC or CC+IC. 1.5 Impact of numbering plan changes A numbering plan under a CC or CC+IC is determined by the administrator of that numbering plan and can change according to its decision at any time. Although administrators are encouraged to inform subscribers and other resource administrators of significant national numbering plan changes well in advance of their implementation, changes to a numbering plan can impact subscribers and network operators in other areas. The country code of an area may also change due to political reasons, e.g. unification of countries. Difficulties experienced in opening new numbering resource and changing existing schemes have recently resulted in ITU-T Study Group 2 putting forward a proposal to TSAG (Telecommunication Standardization Advisory Group) to undertake a study that outlines the difficulties and identifies options that could assist in resolving them. Provision of international telephone calls often requires the translation of not only the E.164 CC but also significant digits of the national number for routing at the systems in the originating country. Thus, data for E.164 number translation is not centralized but distributed among systems in multiple countries. When a major numbering plan change is made, some countries might adopt parallel running operation to allow both old and new codes in order to facilitate the transitions, while other countries might not. These requirements in consequence bring the need for quasi-real-time synchronized updates of number translation tables in switching systems when national numbering plan changes, (e.g. an area code change), are made. Close operational coordination has been required between the administrator of a national numbering resource and the relevant network providers. If a conflict of data exists in systems in different networks, a significant amount of calls will be lost or mis-routed. The announcements of numbering plan changes reported to the ITU-TSB during 1999 amount to 145 times in total. This figure does not include changes to be made without report to ITU. Major changes have affected tens of million of subscribers. Examples of previous, current and future major changes include France (1996), Japan (1999), the UK (2000) and United Republic of Tanzania (2000 /2001). All of them have made or will make changes to their national numbering plans. 1.6 Associated information to E.164 numbers on call setup It is a national matter to decide whether prefixes should be signalled between domestic networks. At the Network Node Interface (NNI), types of number formats are identified by signalling information, i.e. Nature of Address indicator, in typical implementation, i.e. signalling system No.7 ISUP. 2.Potential requirements on E.164-DNS 2.1 Number data administration Data about the top level administrators of national E.164 numbering resources identified by an E.164 CC or CC+IC is maintained by ITU. In general, national E.164 numbering resources are allocated to subscribers through network operators or service providers by the administrator, according to national regulation. It has not been clarified how E.164 in DNS will be utilized for telecommunication services, and how significantly it will impact existing subscribers. However, taking account of operational requirements including numbering plan changes, the administration of DNS data relevant to national E.164 numbering resource should also be carefully organized to maintain on-time updates in synchronization with PSTN. This is viewed as a major requirement. Note that mobility matters, and possible DNS suitability, continue to be discussed. 2.2 Information besides E.164 number When a DNS query is utilized to provide any PSTN service, it should be taken into account that the query may need additional information besides the E.164 number, such as signalling information, prefixes, carrier selection information, etc., to conform with national assignments. 2.3 Propagation When a numbering plan change is made in a country or network, the update of relevant E.164 number data in DNS needs to be coordinated with the change. This is not an insignificant task but is an essential element of any successful change. If multiple copies of the data are distributed in different areas, their update should be incorporated almost simultaneously depending on the application of DNS to services. --------------------------------------------------------------------