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Modem 34336
To initiate the ALXST, use the Modem’s front-panel controls to go to the
LCD MAIN MENU. From page 2 of the LCD MAIN MENU, select TEST.
Go to the second page of the LOCAL TEST menu. Select ALXST.
The ANALOG ST (EXT) screen is displayed, with ON and OFF as the possible
selections. Select ON to activate the test.
The EIA status screen is displayed while the test is being conducted. If no
external loopback is present, the status screen displays an IDLE message.
If a loopback is present, handshake-sequence codes appear, followed by the
modem speed. If "ER" is present on the front panel, data errors occurred.
The ER indicator may flash on when the test is first turned on, but it should
quickly go out and remain off until the end of the test.
The information at the end of the previous section (for the ALBX test)
concerning signal loss, loss of carrier, and loss of RTS also applies to the
ALXST.
To end the test, press the ENT pushbutton to return to the ANALOG ST
(EXT) screen. Then select OFF.
7.7.6 D
IGITAL
L
OOPBACK
T
EST
(DLB)
Digital loopback testing determines the operational performance of the local
modem, the remote modem, and the telephone line as a composite system.
For the test, data must be sent and received at the remote modem. The test
regenerates the data and loops it back to the remote modem. As with the ALB
test, a comparison of the results of the DLB test indicates whether or not the
DTE is performing satisfactorily. A comparison of the results of the ALB and
DLB tests can help determine whether the modem or the telephone line is
defective.
In the DLB test, the data to be sent and received is originated and checked by
the DTE or external BERT. Figure 7-5 shows the data flow for this test.
In Hayes mode only, initiate the DLB test using the command &T3 (preceded
by AT). In any mode, initiate the DLB test using the modem’s front-panel
controls.
From page 2 of the LCD MAIN MENU, select TEST. Go to the second page of
the LOCAL TEST menu. Select DLB.