Available Tests
Modem operation can be placed in several loopback conditions. These
conditions are primarily for testing the digital and analog capabilities
of the modem by simulating the activities performed by these functions during
the communication process.
These loopback patterns perform diagnostics to help in determining whether
the source of a communication problem is a local modem, a remote modem,
or connections in between. Although these tests are oriented toward problems
in a new installation, they are also useful if a previously working modem
suddenly fails. Refer to the troubleshooting information provided in the
documentation accompanying the modem(s) for suggestions on remedying a communications
problem.
Failures in a point-to-point communication link, usually characterized by
unacceptably high error rates or total inability to communicate, may be
the fault of either the local or remote computer, the local or remote modem,
or the telephone company circuit. The modem diagnostic and test facilities
enable you to determine the source of the problem:
Local Analog Loopback: Tests the path that includes the local modem and
local computer
Local Analog Loopback with Self Test: Checks the operation of the local
modem with an internally generated test pattern
Remote Digital Loopback: Verifies the path that includes the local computer,
local modem, remote modem, and telephone circuit
Remote Digital Loopback with Self Test: Tests the path that includes the
local modem, remote modem, and telephone circuit with an internally generated
test pattern. This test requires a ITU-T compatible modem.
Local Digital Loopback: Tests the communication link, the local modem, and
the remote modem (permits a non ITU-T compatible, remote modem to engage
in a digital loopback test with the local modem).
All digital loopback tests must be performed while the modem is configured
for asynchronous operation. Before beginning, place the modem in the asynchronous
mode with the &Q0 command.
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