ADTRAN DSU III TDM Manual page 34

Chapter 3. Operation
No wink from CO Switched 56 provider has encountered a service
Not Installed
OOS/OOF From
Net
Open Loop
DBU Line in RDL Remote end has initiated a test.
Test From Telco
DBU Test Pattern
Waiting for Call
3-4
problem (4-wire Switched 56).
No dial backup option is installed in the DSU III
TDM.
Out-of-service signal or out-of -frame condition
exists. The call cannot be completed because either
the called terminal or the called terminal's access
line is out-of-service or is faulty (2-wire and 4-wire
Switched 56).
The physical connection to the backup line has been
broken (2-wire and 4-wire Switched 56).
The network provider has activated the CSU
Loopback (2-wire and 4-wire Switched 56).
The DSU III TDM is currently performing a test with
a pattern.
The answering DSU III TDM is waiting on a call
from the remote end.
DSU III TDM User Manual 61200063L1-20