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C Loopback Tests
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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 moni-
tor. When the loop has been completed, the data on your PC’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 tele-
phone line, and the local modem are functioning properly.
Note: All loopback tests operate at all speeds except 300 bps.