Troubleshooting guide
Troubleshooting Guide
46
Unable to connect to NSU 
trunks
No fiber connection between the 
controller and NSU.
Fix the fiber connection, and ensure that 
the LEDs of both FIMs are solid green.
Universal NSU programming is 
not complete.
1. Ensure that the NSU is programmed as 
a Universal T1 or E1 (not T1 or CEPT).
2. Program the proper link descriptor with 
the proper integrated access, and 
assign to the corresponding NSU unit 
(for example: ISDN node for PRI 
protocol, T1D4 for T1D4, DPNSS for 
MSDN).
3. Program at least one trunk.
Layer 2 is down.  Layer 2 protocol mismatch. Check your IMAT database and verify with 
your Telco which protocol you should use.
IMAT fails to collect database 
files from the NSU.
When using IMAT to retrieve the 
database from the Universal NSU 
the database files do not appear 
to have been downloaded. The 
IMAT application simply does not 
provide information to identify 
success or failure to download the 
database. At the bottom left hand 
corner of the IMAT application, 
you will see “please select a menu 
option”. The maintenance logs 
can be downloaded, you will get 
the IMAT indication that the 
maintenance logs have been 
received.
Ensure that the NSU is actually running as 
ISDN node in the link descriptor under the 
integrated digital access field. If it is not, 
there are no DBA files, which represent the 
IMAT database. Maintenance logs are 
maintained on NSUs, which is why they 
can be downloaded.
Analog Service Unit
User can hear clicking sound 
while on a call on an external 
ASU ONS circuits.
Message Waiting voltage cycling. Refer to Mitel Knowledge Base article 
05-4409-00008.
Voice calls on ASU have an 
echo.
Faulty programming. Ensure that the ARS Call Progress Tone 
Detection form for the analogue trunks is 
programmed correctly and ensure that the 
Tone to Detect entry is left blank (i.e. no 
tone to detect). If the Tone To Detect entry 
is set to detect a tone, it may cause echo.
Table 11: Service Unit Troubleshooting
Symptom Probable Cause Corrective Action
Page 3 of 3










