94
MINI-MODEM V.92
A.3 Local Digital Loopback Test (V.54 Loop 2)
The local digital loopback test is identical to the remote digital loopback test with
one exception. Instead of using your modem to signal a remote modem to place
itself in digital loopback mode, your modem is placed in digital loopback mode
while the remote modem is not. Data is entered and transmitted from the remote
modem, sent across the phone line to your modem, and looped back to the
remote modem.
Figure A-3. Local digital loopback test.
T
EST PROCEDURE
1. Using your communication program, set the baud rate to 9600 and go into
terminal mode. Type AT and press ENTER; you should get an OK message.
2. Dial the remote modem and establish your on-line connection.
3. Type the escape sequence +++AT and press ENTER to bring your modem
into on-line 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.
Computer or Terminal
Computer or Terminal
Local Mini-
Modem V.92
Digital
Digital
Analog
Analog
Remote Mini-
Modem V.92
