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Overview

DNS ENUM (Electronic Numbering, E.164 Number Mapping) is a critical protocol in modern telecommunications, particularly in Voice over LTE (VoLTE) and Voice over New Radio (VoNR) networks. It provides a standardized method for mapping telephone numbers to various communication services and endpoints using the Domain Name System (DNS) infrastructure.

DNS ENUM is a protocol that translates telephone numbers into Internet-based Uniform Resource Identifiers (URIs) using the Domain Name System (DNS). It adheres to the standards specified in RFC 6116.

ENUM Query Structure

DNS ENUM queries utilize a hierarchical domain name structure. ENUM uses NAPTR (Naming Authority Pointer) DNS records for service resolution. Each NAPTR record contains:

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Code Block
IN NAPTR 100 10 "u" "E2U+sip" "!^.*$!sip:18005551234@domain.com!" .

Service Parameters

Supported services in VoLTE and VoNR ENUM include:

  • E2U+sip: SIP-based communication

  • E2U+mailto: Email contact

  • E2U+h323: H.323 communication

  • E2U+voice:tel: Traditional telephony

  • E2U+im: Instant messaging

Role of DNS ENUM in VoLTE and VoNR

In VoLTE, ENUM enables number resolution for voice calls by bridging the gap between traditional telephone numbers and IP-based addressing. Here's a breakdown of its function and the network elements involved:  

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  1. Originating UE (User Equipment): A user on a VoLTE phone dials a number. The phone sends a SIP INVITE message to the network.

  2. ENUM Query: The P/I/S-CSCF initiates an ENUM query to find the destination's SIP URI. This query involves:

    • Reversing the dialed number (e.g., +1-555-123-4567 becomes 7.6.5.4.3.2.1.5.5.5.1).

    • Appending ".e164.arpa" to create a domain name (e.g., 7.6.5.4.3.2.1.5.5.5.1.e164.arpa).  

    • Querying DNS servers for NAPTR records associated with this domain.  

  3. DNS Resolution: The DNS system resolves the ENUM query, potentially traversing through root servers, country code top-level domains (ccTLDs), and authoritative name servers.

  4. NAPTR Records: The DNS servers return NAPTR (Naming Authority Pointer) records. These records contain information about available services and how to access them, including the all-important SIP URI.  

  5. SIP Routing: The P/I/S-CSCF uses the SIP URI from the NAPTR record to route the call towards the destination network.


Error Codes ;

'0' : 'No error',
'1' : 'Format error',
'2' : 'Server failure',
'3' : 'No such name',
'4' : 'Not implemented',
'5' : 'Refused',
'6' : 'Name exists',
'7' : 'RRset exists',
'8' : 'RRset does not exist',
'9' : 'Not authoritative',
'10': 'Name out of zone',

Troubleshooting in AGILITY

DNS ENUM sessions can be found under drop down menu :

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