# Distinctive Ringing (TI/D4)

Distinctive ringing allows station users to distinguish between an internal and an external call by identifying the associated ringing pattern. Similarly, calls carried across T1 or CEPT (T1/D4 is only T1) channels can be identified as being from an external trunk via a T1 or CEPT channel. A "Calling Line Category" indication is included in the messaging to allow the system to determine the audible ringing type to be given. One of these types of ringing pattern is given:

- Internal, for incoming on-net calls (industry standard or multiline sets, or dedicated analog or digital trunks).

- External, for off-net calls (CO trunk, DID trunk) and calls from the attendant.

- Programmable internal or external, for incoming calls from analog tie trunks (MSDN/DPNSS only). See System Options form for programming instructions.