RDNIS is Redirected Dialed Number Information Service. RDNIS contains Type of Number (TON), Presentation, and Redirecting Number (RGN), and Reason (busy, no answer, etc.). When redirecting calls, the Originally Called Number (OCN) contains, as its name suggests, the number that was originally called.
The RGN identifies the telephone number redirecting a call. For example, if one forwards a call on busy from home to another number, RGN contains the home number. This is useful if, for example, one is running a voice mail system and wants one incoming number to which everyone can forward calls. The RGN can then be used to determine the appropriate mailbox. This usually only works on a PRI.
Q.931 supports RDNIS Type of Number (TON), Presentation, and Redirecting Number (RGN). It is (IE) 115 on a DMS-100 switch, IE 116 on National-ISDN-2.
A note about wireless phones: the ‘forward all calls’ feature does not necessarily send RDNIS, but ‘forward when busy’, ‘forward when unavailable’, and ‘forward when unreachable’ are supposed to send RDNIS. Functionality may depend on wireless provider more than PRI provider.
Groupe Telecom and Bell Canada both support this on their PRIs.