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Modem 34336
NOTE
The ALBX test may result in errors or may fail altogether even where
conditions are satisfactory for normal operation. The test channel
presented to the modem during the ALBX test includes all impairments
of both the inbound and outbound channels (ampli-tude distortion, delay
distor-tion, noise, etc.). The main purpose of the ALBX test is to verify
that the Modem is connected to the leased line and the leased-line circuit
is complete. The test is not meant to assess the suitability of the leased
line.
Initiate the ALBX test using the Modem’s front-panel controls, as explained
in the following paragraphs.
Make sure the local modem is not in communication with the remote
modem, the data rate is the same as the DTE’s data rate, and the DTR circuit
is on. (If TR is present on the EIA status screen, the DTR circuit is on.)
From the second page of the LCD MAIN MENU, select TEST. Go to the
second page of the LOCAL TEST menu. Select ALBX.
The ANALOG LOOP(EXT) screen is displayed, with ON and OFF as the
possible selections.
Select ON to activate the test. In general, the "DSR during ALB test" option
discussed in Chapter 2 should be left ON (default selection) to avoid
disrupting the DTE and DTE software operations.
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 (H-01, etc.), followed
by the modem speed. Ensure that test data is being generated and watch for
data errors. By transmitting test data and comparing it with the received
copy, the DTE and modem are checked for proper operation. During the
ALBX test, RD (receive data) may appear on the status screen even though no
data is being received.
On a flat line, the Modem in ALBX test mode trains and remains running
across the following range of signal loss: in V.32 mode, 0-51 dBm (0-52 dBm
at 12,000 bps); for V.33 operation, 0-47 dBm; and for Bell 208A/B operation,
0-37 dBm. If signal loss exceeds the limits, the test may not start or may be
halted.
During the ALBX test, the modem attempts to retrain upon loss of carrier.
In switched carrier mode, the modem attempts to retrain upon loss of RTS.
To end the test, press the ENT pushbutton to return to the ANALOG
LOOP(EXT) screen. Then select OFF.