ENUM (E.164 Number Mapping) functionality

What is ENUM 

E.164 Number Mapping (ENUM) is a standard that uses DNS to map telephone numbers to web addresses or URLs. ENUM provides a single number to replace the multiple numbers and addresses for user's home phone, business phone, fax, cell phone and email. A server with ENUM support lookups a dialled telephone number in the ENUM database of the DNS to see if there is a way to set up the call instead of just calling out on the PSTN telephone line. You can dial a telephone number and reach a SIP, H.323 or any other Internet telephony user. 

How it works

ENUM works by translating standard telephone numbers into internet addresses (URL or IP address). Servers that support ENUM search any dialed phone number in the ENUM tree of the DNS to locate substitute ways to setup a call outside of the standard PSTN telephone line.

ENUM lookup is executed in the following way:

• Take the number you want to call and normalize it into E.164 format - in other words, by removing any leading zero and punctuation and adding the country code. For example, for an Italian number "0461 1715111", the country code is +39 and so the normalized number is +39 0461 1715111
• Choose the ENUM suffix. The official ENUM tree defined by the IETF uses the e164.arpa ENUM suffix. There are several third-party suffixes as well, such as e164.org and for the sip5060.net service, use the suffix e164-addr.sip5060.net
• Perform a DNS lookup, typically looking for NAPTR records

Registration of ENUM number

An ENUM number is registered much like how you would register a domain. Many VoIP providers are providing this as a free service. Registration needs to be done through a registration service such as Ripe with the standardized ENUM request form. This is then registered with the International Telecommunication Union, Telecommunication Standardization Sector, Telecommunication Standardization Bureau (ITU-T TSB). After this the number is registered and ready for international use.

Configuration

To be able to execute the lookup in ENUM database, you need to proceed with the following configuration:

Step 1. Enable external connection to LDAP Server

• Go to WMS -> Settings -> System -> LDAP/ Radius server
• Check off Enable external connections to LDAP
  
  

Step 2. Configure routing of calls via ISDN line

To perform ENUM lookup, you need to configure ISDN trunk group. Before configuring, make sure that BRI/PRI media gateway are provisioned to your PBX. Trunk groups are added in WMS -> Trunks -> Trunk Group.

Step 3. Add Dialplan applications

Add the following Dialplan applications:

• Authenticate user 
• Set -> Caller number
• Custom application -> Set(DESTINAZIONE=${ENUMLOOKUP(+39${EXTEN},sip,c,1,1,enum.rtrt.it))}
  where
  <ENUMLOOKUP> - the function that executes the lookup in enum.rtrt.it branch
  <+39> - the country code
• Custom application -> GotoIf($["${DESTINAZIONE}" != "1"]?chiamateNoRTRT,${EXTEN},1)
  It is executed in case a phone number is not present in ENUM database
• Custom application -> Dial(SIP/03247517/+39${EXTEN} 
  where
  <03247517> - a number that is dialed in case ENUMLOOKUP function is not executed because a lookup number is not present in ENUM database
• Trunk group -> route calls through the specified trunk group