- Performs maintenance functions for Definity
- Functions include Packet Bus reconfiguration that allows diagnosis and correction of recoverable Packet Bus failures before Link Access Procedure on the D-Channel (LAPD) links fail
- ISDN - PRI testing that originates and terminates loopback tests on ISDN facilities
- TN 771D is required in all standard reliability Primary Port Networks (PPNs) and critical reliability Expansion Port Networks (EPNs).
All standard reliability PPNs when packet endpoints (BRI and/or ASAI) are supported