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ENUM Dip Indicator

Telephone Number Mapping (ENUM) transforms the telephone number into a universal identifier recognized across different devices and applications (voice, fax, mobile, e-mail, text messaging, location-based services and the Internet). ENUM can also be used to implement a variety of services like number portability, call forwarding etc. It uses a DNS NAPTR record to translate a telephone number into a Uniform Resource Identifier or IP address that can be used in Internet communications.

Since a call may span multiple network elements, to avoid redundant ENUM queries, the SBC supports (when configured) processing the enumdi parameter received on ingress INVITE. Similarly, if ERE/PSX performs an ENUM dip, the SBC sends this parameter in egress INVITE to the next network element identifying that an ENUM query has already been made for the 'TEL URI', thus preventing redundant queries further down the network.

The Feature Control Profile flag to enable processing of the enumdi parameter is "processEnumdi". For example,

% set profiles featureControlProfile <profile name> processEnumdi enable

If R-URI transparency flag (requestURI) is enabled, the SBC does not send enumdi indicator in egress signaling even if an ENUM dip is performed by ERE/PSX.

ENUM NAPTR Queries

The SBC performs ENUM queries to an external DNS to map E.164 telephone numbers to SIP trunk URIs, and then performs SIP routing based on the service URIs. ENUM translation requires an ENUM NAPTR (Naming Authority Pointer) query to resolve a telephone number to an FQDN, and then requires DNS queries to resolve the FQDN to an IP address and port number.

The result of a successful ENUM NAPTR query is a SIP URI telephone number received in the Request-URI resolved to a SIP URI. To perform an ENUM NAPTR query, the SBC reverses the order of the SIP URI telephone number digits, adds a dot in between each digit, adds the domain name, and finally performs the DNS NAPTR query.

By default, SBC sends ENUM NAPTR queries to the default public domain (.e164.arpa). If the ENUM database resides in a private domain, specify the private domain on the DNS-ENUM Service Definition screen.

For example, an ENUM query to an external DNS for the ENUM NAPTR record for the SIP URI sip:+1-212-555-5678@1.2.3.4 is sent using the format 8.7.6.5.5.5.5.2.1.2.1.e164.arpa. The SBC then uses the FQDN from the returned record to perform DNS queries which attempt to map the FQDN to an IP address and port number. The SBC returns the IP address and port number in a Request-URI in the policy response.

  • If the DNS cannot match a SIP URI telephone number with a SIP URI in the database, the DNS returns no record for that telephone number. The SBC then attempts to route the call through standard routing.
  • If the ENUM NAPTR query succeeds, but a trigger for performing a DNS query has not been provisioned on the SBC, the SBC uses the FQDN from the returned ENUM NAPTR record to attempt to perform Username routing.

When SBC queries an ENUM server and the NAPTR response contains two or more matches, the SBC orders the records in the response according to the “order” and “preference” fields. The SBC uses the first valid record which has the highest (numerically lowest) order and highest (numerically lowest) preference. The rest of the records are not used.

In a NAPTR response to ENUM query, any one of the following strings are recognized as indicating that a SIP address-of-record appears in the URI field:

  • E2U+sip
  • sip+E2U
  • E2U+SIP
  • SIP+E2U

In the following example, five records were received; the record with the rrk2 address is used because it has the highest order (100) and highest preference (10).

Provisioned records for (44) 1793601415:

5.1.4.1.0.6.3.9.7.1.4.4.e164.arpa. IN NAPTR 300 10 "u" "E2U+sip" "!^.*$!sip:rrk1@sonusnet.com!"

5.1.4.1.0.6.3.9.7.1.4.4.e164.arpa. IN NAPTR 100 10 "u" "E2U+sip" "!^.*$!sip:rrk2@sonusnet.com!"

5.1.4.1.0.6.3.9.7.1.4.4.e164.arpa. IN NAPTR 200 10 "u" "E2U+sip" "!^.*$!sip:rrk3@sonusnet.com!"

5.1.4.1.0.6.3.9.7.1.4.4.e164.arpa. IN NAPTR 100 20 "u" "E2U+sip" "!^.*$!sip:rrk4@sonusnet.com!"

5.1.4.1.0.6.3.9.7.1.4.4.e164.arpa. IN NAPTR 400 10 "u" "E2U+sip" "!^.*$!sip:rrk5@sonusnet.com!"

ENUM LNP

ENUM LNP enables number portability lookups in the IP network without the need to consult an external element in the SS7 network, thus simplifying call routing and networking operations.

The Routing Number must use one of the following formats:

  • Globalized number:  +1-555-614-8166 (specified in RFC4769)
  • National Number: 555-614-8166

To provision ENUM LNP, enter ported numbers into the SBC database via the NPA-NXX entity (or optionally Number Translation Criteria), and then provision the Enum Domain and Enum Service.

When a Routing Request triggers an ENUM LNP lookup, SBC uses the dialed number to form a domain name and puts it in an ENUM LNP query to the ENUM database. When the ENUM returns NAPTR resource records, the SBC selects the record with a particular service type, extracts the translated number and domain name from the NAPTR record, and uses them to perform routing. If the query returns no NAPTR record with a translated number, the SBC routes the call using the original dialed number.

ENUM CNAM

ENUM CNAM enables calling name lookups in the IP network without having to consult an external element in the SS7 network, thus simplifying call routing and network operations.

To provision ENUM CNAM, specify the trigger criteria in the Number Translation Criteria entity and specify ENUM CNAM as the lookup type. ENUM CNAM, provisioned through the DNS-ENUM Service Definition screen, uses the same triggering and escape criteria as SCP-based CNAM. When a Routing Request triggers an ENUM CNAM lookup, the SBC uses the calling number to form a domain name and puts it in an ENUM CNAM query to the ENUM database. When the ENUM returns NAPTR resource records, the SBC adds the caller name.

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