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Chapter 11. Troubleshooting
78 ISU 128 User Manual 61202.029L2-1
2. Disconnect the ISU 128 from the ISDN line. From a functioning voice
phone, call the local directory number(s) provided with your line. Calling
a good ISDN line with nothing connected usually results in a ring or fast
busy tone. If someone answers or a not-in-service intercept is received,
there is probably something wrong with the translation of the ISDN line.
The phone service provider should be able to help.
3. If the ISU 128 continues to read Link Down, there is a physical problem
with the ISDN phone line (more than likely, a problem with the Layer 1
setup). The problem may be one or more of the following:
• The ISU 128 software setup
• The ISU 128 hardware
• The wiring on your premises
• The telephone service provider's wiring
• The telephone service provider's hardware
• The telephone service provider's software setup
To isolate the problem, perform the following procedure:
A. Make sure the ISU 128 is configured for dial line service. Check that
CONFIG, Netw. options, Dial Line, is selected on the menu.
B. Try another piece of functioning ISDN equipment with a U-interface
on the ISDN line.
C. Talk to your service provider and ensure you have an ISDN Basic
Rate U-Interface with 2B1Q line coding (wrong options are an S or T
interface or AMI line coding).
D. Ensure that your ISDN phone line is connected to the actual telephone
line (U-interface) provided by your telephone company. Make sure your
ISDN line is not connected though another piece of equipment such as
an NT1 in a wiring closet somewhere.
E. Make sure nothing else is bridged across the ISDN line pair.
F. With a minimum of extra wiring, try connecting to the ISDN line pair
at the point where service provider's wiring ends.