ENUM — DNS Telephone Number Mapping
ENUM is how SIP networks look up where to route a call to a phone number. Essential for VoIP providers, number portability implementations, and understanding how PSTN-to-SIP calls are routed.
What It Defines
ENUM maps E.164 telephone numbers to Internet resources using DNS NAPTR records. A number like +12025551234 becomes 4.3.2.1.5.5.5.5.2.0.2.1.e164.arpa in DNS, resolving to SIP URIs, email addresses, or web URIs. Enables VoIP number lookup and number portability signaling.
Canonical (Normative)
Related References
The canonical publication point for finalized RFCs. If a protocol is standardized as an RFC, the RFC Editor text is the normative final reference. Published by the IETF, IRTF, IAB, and independent stream.
Related Specs
Every phone number your app touches — Twilio, AWS SNS, WhatsApp, SIP — uses E.164. Getting number formatting and parsing right (libphonenumber patterns) requires understanding CC/NDC/SN structure.
SIP is the PSTN of the internet. Every VoIP platform (Twilio, Vonage, AWS Chime, Asterisk, FreeSWITCH) speaks SIP. Building any communications product requires understanding INVITE flows, registration, and codec negotiation via SDP.
DNS is the phone book of the internet. Every domain, email MX record, SPF/DKIM TXT record, and service discovery entry depends on it.