IP Telephony: What is Enum?

Every computer connected to the Internet has what is known as an IP address. These are of the form 127.0.0.1 – that is, there are four segments with values from 0 to 255. Some IP addresses are reserved for internal network use and thus will never be seen on the public network. Enum is an IP telephony protocol that is used in “VoIP peering”. it is used to uniquely tie an international phone number to a domain name so that the number can be associated with DNS (Domain Name System) services.

What happens is that any international phone number (including the country code) is reversed and turned into part of the “e164.arpa” web domain. Example: +1 555 987 6543 is converted to the domain name 3.4.5.6.7.8.9.5.5.5.1.e164.arpa (or e164.org). There are other variations that use a company’s domain name as well. Enum can be used in SIP-based VoIP systems such as Asterisk. I’ve only just summarized a more complex topic, with the intent of expanding in the future.