ports for direct inward/outward dialing (DIOD) trunks.
port provides a 2-wire interface to the central office (CO) public
exchange for incoming and outgoing calls.
CO provides caller names and numbers to the TN429D, which displays
them on DEFINITY digital voice terminals (DCP and BRI) equipped
with a 32- or 40-character alphanumeric display, and with System
25/MERLIN 7315H and 7317H terminals supported by DEFINITY.