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APPENDIX B: Loopback Tests
6. Your modem passes this test if the data received on your monitor are the same
as the data entered from your keyboard. If different data appear on your
monitor, your modem is probably causing the problem, though it could also
be your computer. If your modem passes this test, but you are receiving errors
while on line, the remote modem or the phone line could be at fault.
B.3 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.
Figure B-2. Remote digital loopback test.
T
EST
P
ROCEDURE
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.
AT&T6
OK
Computer or Terminal Local MultiModem Remote MultiModem Computer or Terminal
Digital Analog DigitalAnalog
AT&T6
OK
UUUUUUUUU
UUUUU
Local Portable
USB Modem
Remote Portable
USB Modem