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APPENDIX B: Loopback Tests
T
EST
P
ROCEDURE
1. Open your communications software and go into terminal mode. Type AT
and press ENTER; you should get an OK message. Type AT\N and press
ENTER to disable error correction.
2. Dial the remote modem and establish your online connection.
3. Type the escape sequence +++AT and press ENTER to bring your modem
into online command mode.
4. Type AT&T3 and press ENTER. Once you receive an OK message from your
modem (if responses are enabled), your modem is placed in digital loopback
mode.
5. Have someone enter data from the remote keyboard. For this test, typing
multiple uppercase U characters is a good way to send an alternating test
pattern of binary ones and zeros. The data received by your modem enters its
analog receiver, is converted to digital data, is reconverted into analog, and
then is transmitted back to the remote modem. Your modem passes this test if
the data received on the remote monitor is the same as the data entered from
the remote keyboard.
6. To exit the test, type the escape sequence +++AT and press ENTER. This puts
the modem in online command mode. The modem should respond with an
OK message. If you wish to stay on line with the remote modem for normal
data transmission, type AT&T and press ENTER to exit the test, then type
ATO and press ENTER to return on line. If you wish to terminate the call,
type ATH and press ENTER to hang up.