ENUM(Telephone Number Mapping)

ENUM(Telephone Number Mapping),this abbreviation of hidden behind a great originality: namely through the best and most cheap routing ways, can be in the world any place to use the same phone number. You can like registered domains as registered ENUM number. At present a lot of registration institution and VOIP service providers offer free this kind of service. For example, if the call fong is fax machine, you can set the rules to a different routing ways. ENUM don't need to call fong must use telephones.

introduction

ENUM is IETF Telephone Number Mapping working group (Telephone by business group, called fang ENUM) definition of an agreement, the RFC2916 - RFC2916 titled "e. 164 Number and domain name system (e. 164 by and DNS)". It defines will e. 164 number into domain forms on DNS server database and the method of each by e. 164 number of domain name can be transformed into corresponding series of Uniform Resource Identifier (Uniform Resource Identifier), thus make international unification of e. 164 phone number becomes can in the Internet use the network address of the resources. ENUM can use telephone Numbers for Registrant (Registrant) E-mail, IP telephone number, unified news, IP fax or personal web pages and so on many kinds of information. E. 164 number is traditional telecom network use vital resources, DNS system is the important foundation, Internet ENUM will combine traditional telecom service, beneficial to based on IP packet switching the direction of development, to promote ENUM is two nets eventually fusion is of important significance of technology.

ENUM is a new standard, has not yet widely, but it will bring telecom and personal mobility industry a new revolution.

Working process

ENUM defines as follows process, will phone number mapping for DNS system of records:

A e. 164 number by the following several parts, between different parts can be used "-" and ". "or Spaces such as connection: ENUM + country code (1 ~ 3 digits) - area code (n digits) - telephone number (15 - n digits).

For example: Beijing of a telephone number just written standard of e. 164 format should be: + 86-10-6 2618501

The first step, will be a telephone number processing becomes a standard of e. 164 number format, such as: + 86-10-6 2618501

The second step, remove all but the most left the "+" from all connection identifier, becomes: + 861062618501

Third step, remove "+" sign, and will 105816260168 flip: number

Fourth step, in each number between with domain name separator ". ": 1.0.5.8.1.6.2.6.0.1.6.8

Fifth step, in the above numeric string end with the ". 1.0.5.8.1.6.2.6.0.1.6.8 e164. TLD ": j j e164 TLD

So, a telephone number becomes a DNS domain of form. Each e. 164 number formation of domain name can be corresponding multiple network resource records, called uniform resource identifier (URI), it is to use another IETF Suggestions 2915 defines the format RFC, called "the name Authority Pointer Naming Authority" (Pointer, abbreviation NAPTR).

RFC2915 definition of written format:

Domain TTL scale-up Type Preference Flags Service Regexp made Replacement

For example, the following is ENUM DNS server writing format:

J j ORIGIN 1.0.5.8.1.6.2.6.0.1.6.8 $e164 cn

IN NAPTR 10 10 "u" "mailto + E2U" "^. * $!!!" lee@cnnic.net.cn mailto:

IN NAPTR 10 10 "u" "HTTP + E2U" "^. * $!!!!!! http://likecloud.cnnic.net.cn!" .

IN NAPTR 10 10 "u" "sip + E2U" "! ^. * $! Sip: / / likecloud. Cnnic.net. Cn!" .

IN NAPTR 10 20 "u" "sip + E2U" "^. * $!!!" fengw@cnnic.net.cn sip: .

The typical application of ENUM

To illustrate the ENUM purposes, we can see the following this using ENUM established by PSTN user launched based on IP network terminal calls, the typical process as shown in figure 1 shows:

Step 1: originating user dial the e. 164 number, dial-up way by national regulation, such as long-distance call dial "0", international prefix prefix call dial "0 figure 1

0."

Step 2: PSTN business provider according to call the position of the factors will launch call transferred to the corresponding gateway,

Step 3: the gateway must contain ENUM function, it can be dialed users of digital according to stipulated rule convert ENUM domain forms. If the user dial number isn't whole number, the gateway should be able to will be lost data supplement qi, so that it can form a complete valid domain name. For example: the user dial the number for:

32341234, complete number should be: + 8610323412343. Then gateway in ENUM DNS server search in this domain,

Step 4: return and the domain DNS records related all business,

Step 5: gateway in DNS lookup provisions of host address record.

Step 6: DNS server hosting SIP returns provisions IP address;

Step 7: through based on IP network will continue the call to designated IP address,

Step 8: SIP server will call succeeded to provisions of users user agent client. When the objective square response, must the response surveillance back to the originating local switches.

In the above example is used in SIP clients, in actual applications can also use other client agreement (if h.323).

Based on ENUM from one IP phone call to the process of an outgoing call PSTN (see figure 2.

If the example in step 3 ENUM resource records return the fixed-line number is processed, then call will be transfer to a PSTN the phone. This example shows the actual ENUM with traditional telecommunication network "call forwarding" functionality.

ENUM registration service is itself a can develop business, current telephone number, management organization and telecom service providers can carry on the business. ENUM registration service in addition to the above phone number registration processes outside, still should include telephone number after ENUM domain name registration for owners of alteration, MLL services, changing the record, cancellation, billing, owe etc process.

Service system structure

The DNS ENUM services is a global three-layer service system structure, the top Tier 0) is to maintain (e. 164 distribution among country code (including geographical country code, network code, global service code and group country code) to form the domain names mapped to the corresponding national ENUM top domain name server address records in intermediate Tier 1) (for each country internal ENUM top DNS server, responsible for the management of telephone number domain mapped to the corresponding analytical resource records server, bottom Tier 2) (DNS server will be responsible for real number analytical to the corresponding service record. Such a system structure of the main aim is to ensure global ENUM DNS services of unity and interoperability, and make ENUM become a global access network addressing resources. Tier 0 ENUM of registration institution (enabled) is the only global; Generally, each country Tier 1 registration institution is the only, use Integrated coding scheme areas (Numbering Plan done Area, such as the national code 1) need to pass the relevant national special discussion agreed Plan; Tier 2 registration institution can have multiple.