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Appendix B - Technical Specifications
Appendix C: Loopback Tests
Introduction
Each time you turn on your modem, it performs an automatic self-test to ensure proper
operation. Your modem also has three diagnostic tests: local analog loopback, remote
digital loopback, and local digital loopback. These ITU-T V.54 loopback tests isolate
telephone circuit and transmission problems.
In a loopback test, data from your computer loops through the circuits of your modem
and/or a remote modem before it appears on your monitor. When the loop has been
completed, the data on your computer’s monitor should match the original data.
The local analog loopback test allows you to verify that the modem’s transmitter and
receiver circuits are functioning properly.
The local digital loopback allows you to verify that the local computer or terminal, the two
modems, and the transmission line between them are functioning properly.
The remote digital loopback test allows you to verify that the remote computer or
terminal, the remote modem, the serial ports, the telephone line, and the local modem
are functioning properly.
Note: All loopback tests operate at all speeds except 300 bps.