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4 -
TESTING
The modem provides five testing features to identify fault location when transmission quality is not good:
local digital loopback, local analog loop back, local analog loopback with self-test, remote digital
loopback, and remote digital loopback with self-test. These tests are initiated with the &Tn command
described in Chapter 2.
4.1 Local Analog Loopback
The local analog loopback test checks the integrity of the local computer or terminal and the local modem.
During the test, the local modem internally loops data sent from the local computer or terminal back to
the same computer or terminal as shown in Figure 4-1. During the test, data is not transmitted to the
remote modem.
If characters are looped correctly during this test, both the modem and the local computer or terminal are
functioning correctly. If incorrect characters appear on the screen, either the local computer or terminal or
the local modem is in error.
To perform a local analog loopback, put the local modem in the command state. If it is on-line, issue the
escape command + + +, to return to the command state.
Example 1 - test timer disabled
Command:
Result:
Test message:
Escape:
Result code:
AT&Q0<CR>
ATS18=0&TI <CR>
CONNECT 56000
THE QUICK BROWN FOX JUMPS OVER THE
LAZY DOG 1234567890
+ + +
(return to the on-line command state)
OK
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