Provides 8 ports for direct inward/outward dialing (DIOD) trunks
Each 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 the on Definity digital voice terminals (DCP and BRI) equipped with a 32 or 40 character alphnumeric display and with System 25/Merlin 7315H and 7317H terminals supported by Definity
