Definity TN767E DSI / ISD PRI Interface Circuit Pack (TN767E) - TN767 B/C/D supports DS1 Digital Connectivity. Supports CO, TIE, DID, and Off-Premises Stations (OPS) port types using robbed bit signaling protocol Supports ISDN-PRI in Release 6 and higher. TN 767E is required to communicate with conversant and for enhanced maintenance capabilities of the 120A CSU.