ENUM dialing allows an endpoint to be contacted by a caller
dialing an E.164 number - a telephone number - even if that
endpoint has registered using a different format of alias.
Using ENUM dialing, when an E.164 number is dialed it is
converted into a URI using information stored in DNS. The VCS
then attempts to find the endpoint based on the URI that has
been returned.
The ENUM dialing facility allows you to retain the flexibility of
URI dialing whilst having the simplicity of being called using
just a number - particularly important if any of your callers are
restricted to dialing via a numeric keypad.

ENUM dialing is enabled separately for incoming and outgoing
calls.

Outgoing Calls

To allow locally registered endpoints to dial out to other
endpoints using ENUM, you must

configure at least one ENUM zone, and

•

configure at least one DNS Server.

•

This is described in the section

Configuring ENUM Dialing for

outgoing calls

Incoming Calls

To enable endpoints in your enterprise to receive incoming calls
from other endpoints via ENUM dialing, you must configure a
DNS NAPTR record mapping your endpoints’ E.164 numbers to
their SIP/H.323 URIs. See the section

Configuring ENUM dialing

for incoming calls

for instructions on how to do this.

Overview

The VCS supports outward ENUM dialing by allowing you
to configure ENUM zones on the VCS. When an ENUM
zone is queried, this triggers the VCS to transform the

E.164 number that was dialed into an ENUM domain which is
then queried via DNS.
Note however that ENUM dialing relies on the presence of
relevant DNS NAPTR records for the ENUM domain being
queried. These are the responsibility of the administrator of that
domain.

When a VCS is attempting to dial a destination endpoint using
ENUM, the general process is as follows:

The user dials the E.164 number from their endpoint.

The VCS converts the E.164 number into an ENUM domain as

follows:

the digits are reversed and separated by a dot

the name of the domain that is hosting the NAPTR records

for that E.164 number is added as a suffix.

DNS is then queried for the resulting ENUM domain.

If a NAPTR record exists for that ENUM domain, this will

advise how the number should be converted into one (or
possibly more) H.323/SIP URIs.
The VCS begins the search again, this time for the converted

URI as per the

URI dialing process

. Note that this is

considered to be a completely new search, and so local
transforms and administrator policy will therefore apply.

If an ENUM zone and/or a DNS server have not been
configured on the local VCS, calls made using ENUM
dialing could still be placed if the local VCS is neighbored

with another VCS that has been appropriately configured for
ENUM dialing. Any ENUM dialed calls will go via the neighbor.
This configuration is useful if you want all ENUM dialing from
your enterprise to be configured on one particular system.

Process

Enabling ENUM Dialing