0049-2702-XXX Alliance Series Modems – USER MANUAL
08/05/2010
Rev. A
Page 148 of 197
The TIA/EIA status screen will be displayed while the test is being conducted. If no external
loopback is present, the status screen will display an “IDLE” message. If a loopback is present,
handshake sequence codes will appear (H-01, etc.), followed by the modem speed. Ensure that
test data is being generated. 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 – this is normal.
During the ALBX test, the modem will attempt to retrain upon loss of carrier. In switched
carrier mode, the modem will attempt to retrain upon loss of RTS.
To end the test, press the ENT pushbutton to return to the ANALOG LOOP (EXT) screen, and
then select OFF.
External Analog Loopback Self Test (ALXST)
The external analog loopback self test is available for
4-wire leased line mode only
.
The ALXST places the modem in analog loopback and causes data to be sent and received by an
internal 511-bit pattern generator and receiver; therefore, no DTE or external BERT is necessary.
As shown in Figure 6-4, the test circuit includes the leased lines (the external loopback).
IMPORTANT:
The ALXST may result in errors or may fail altogether even where conditions
are satisfactory for normal operation. This is because the test channel presented to the modem
during the ALXST includes all impairments of both the inbound and outbound channels
(amplitude distortion, delay distortion, noise, etc.). The main purpose of the ALXST is to verify
that the modem is connected to the leased line and that the leased line circuit is complete. The
test is not meant to assess the suitability of the leased line.
To run this test, follow these steps:
From screen 2 of the LCD MAIN MENU, select TEST. Go to screen 2 of the LOCAL TEST
menu and select ALXST.
The ANALOG ST (EXT) screen will be displayed, with ON and OFF as the possible selections.
Select ON to activate the test.
The TIA/EIA status screen will be displayed while the test is being conducted. If no external
loopback is present, the status screen will display an “IDLE” message. If a loopback is present,
handshake sequence codes will appear, followed by the modem speed. If “ER” is present on the
front panel, data errors have occurred.
