Avaya Definity TN2198 ISDN-BRI 2 Wire U Interface (Refurbished)Key Features: The TN2198 allows connection to the ANSI standard 2 wire U interface 2 wire interface from the TN2198 connects to an NT1 network interface 4 wire interface on other side of the NT1 may connect to 1 or 2 telephones 12 ports interface at the ISDN U reference point Requires packet control circuit pack (TN778) on R6si and packet bus equipped on R6vs