Avaya SBC supports the E.164 Number Mapping (ENUM) protocol. Telephone numbers in the PSTN are organized by using the format specified in the E.164 standard. Conversely, the Internet uses the Domain Name System (DNS) to link domain names to IP addresses. ENUM defines a method to convert a telephone number into a format that can be used with the DNS to look up addressing information such as Uniform Resource Identifiers (URIs). Numbers that conform to the numbering plan defined in E.164 are:

• Limited to 15 digits.

• Prefixed with a plus sign (+) to indicate that the number includes an international country calling code.

ENUM translates E.164 numbers to URIs by using Naming Authority Pointer (NAPTR) records stored in DNS. With ENUM, calls can be completed over the Internet instead of transferring the call to PSTN. Therefore, ENUM provides cost savings for businesses that communicate with other enterprises by using SIP. If the number is unavailable in the ENUM database, Avaya SBC routes the call to the service provider to send the call to the PSTN.