Plus (+) Prefix and E.164 Support in Cisco Unified SRST
Cisco Unified SRST version 8.0 introduces support for DNs in E.164 format with a plus (+) prefix. SIP and SCCP IP phones can fallback to SRST and register with a DN in E.164 format with a + prefix. Assigning DNs in E.164 format ensures globally unique numbers; the + sign is prefixed in order to indicate that the number is in E.164 format.
Cisco Unified SRST and CUCM Express in SRST mode allow internal callers to use internal extensions for calling IP Phones that have numbers in E.164 format. A new dial plan pattern command has been introduced with Cisco Unified SRST v8.x to achieve the demotion of the E.164 number to the internally used shorter numbers. Although the standard dial plan pattern command expands to a longer PSTN format, for any DNs that are applied to phone lines, the new dial plan pattern command has the opposite function. In this case it allows internal callers to dial shorter, internally used extensions, which are expanded to the applied DNs in E.164 format. Outside callers dial the IP Phone directory numbers as configured—with a + prefix and the complete E.164 number. At the IP Phones, the calling-party number that is shown on the phone display can be transformed independently from the number that will be used for callback. This transformation is possible because of a newly introduced translation type in the voice translation profile, which is a translation rule of the callback number.