Multitech MULTIMODEM MT5634ZBA-USB User Manual page 55

Remote Digital Loopback Test (V.54 Loop 2)
The remote digital loopback test tests the phone lines and the circuits of both your
modem and a remote modem. In this test, your modem must be on line with another
modem that is set up to respond to a request for remote digital loopback. (Note that
some modems might not support remote digital loopback or might have it disabled.) Data
from your computer or terminal is transmitted through your modem and over the phone
line to the remote modem, where it is then looped back to your modem.
AT&T6
OK
UUUUUUUUU
UUUUU
Computer or Terminal
Figure C-2. Remote digital loopback test.
Test Procedure
1. Arrange to have &T6 set on the remote test modem.
2. 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.
3. Dial the remote modem and establish your online connection.
4. Type the escape sequence +++AT and press ENTER to bring your modem into
online command mode.
5. Type AT&T6 and press ENTER. The local modem responds to this command by
transmitting an unscrambled marking signal, which causes the remote modem to
place itself in digital loopback mode. Then the local modem exits online command
mode and enters data mode.
6. Enter data from your keyboard. For this test, typing multiple uppercase U characters
is a good way to send an alternating test pattern of binary ones and zeroes. Data
received by the remote modem enters its analog receiver, is converted to digital data,
is reconverted into analog, and then is transmitted back to your modem. Your modem
passes this test if the data received on your monitor is the same as the data entered
from your keyboard.
7. 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.
Digital Analog Analog Digital
Local MultiModem Remote MultiModem Computer or Terminal
Appendix C - Loopback Tests
AT&T6
OK
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