Multi-Tech Systems MT4X56USB - Manual (Page 62)

MultiModemUSB User Guide
MT4X56USB 62
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.
Digital Analog Analog Digital
Computer or Terminal Local MultiModemUSB Remote MultiModemUSB Computer or Terminal
AT&T6
OK
AT&T6
OK
UUUUUUUUU
UUUUU
Figure 6-2. 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.