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TANDBERG Gatekeeper User Guide
Page 44 of 105
10. ENUM Dialing
10.1. About ENUM Dialing
ENUM provides another DNS-based dialing scheme. Users dial an E.164 number - a telephone number -
which is converted in to an H.323 URI by the DNS system. The rules for URI dialing are then followed to
place the call. This allows you to retain the flexibility of URI dialing whilst having the simplicity of calling
using just a number.
Before the DNS lookup can be performed, the E.164 number must be transformed into a host name. To
do this, the digits are reversed and separated by a dot -- similar to the way DNS PTR records are formed.
The DNS zone is then appended.
For example, if an ENUM root of e164.example.com is being used, and the dialed number is +47 67
125 125, then the transformed host name is 5.2.1.5.2.1.7.6.7.4.e164.example.com
RFC 3761 [8], which defines the ENUM standard, specifies that the DNS zone for ENUM is e164.arpa.
Use of this DNS zone requires that your E.164 numbers are assigned by an appropriate national
regulatory body. Not all countries are yet participating in ENUM, so it may be useful to use an alternative
DNS zone for ENUM. This could either be within your corporate DNS zone or could use a public ENUM
database such as http://www.e164.org
The DNS zone used for ENUM contains NAPTR records as defined by RFC 2915 [7]. These provide the
mapping between E.164 numbers and H.323 URIs.
The Gatekeeper may be configured with up to 5 DNS zones to search for a NAPTR record. It will iterate
through them in order, stopping when the first record is found.
10.2. Configuring ENUM
10.2.1. Enabling ENUM support
ENUM support is disabled by default.
To enable ENUM support on your Gatekeeper, either:
enter the command:
xConfiguration Gatekeeper ENUM Mode: On
or navigate to Gatekeeper Configuration > Gatekeeper and in the ENUM section, tick the Allow ENUM
resolution box.
10.2.2. Managing ENUM DNS zones
You are provided by default with the global ENUM DNS zone: e164.arpa. To change this or add other
DNS zones, either:
enter the command:
xConfiguration Gatekeeper ENUM DNSSuffix [1..5 ]: <zone_name>
or navigate to Gatekeeper Configuration >Gatekeeper and in the ENUM section, enter details in the DNS
Suffix... fields (see Figure 19).
Note: If you have a number of Gatekeepers and Border Controllers neighbored together, it is
recommended that ENUM support is enabled on only one of them. If ENUM is enabled on more
than one system, call set up could become unpredictable.