ZyXEL Communications U-1496 series User Manual page 100

The U-1496E has only LED indicators. The TST LED will be ON during power-on self-test, and
OFF after the test if the test is OK. The SQ LED will flash if the test fails. The number of flashes
indicates the error number corresponding to the above error message.
Analog Loopback Test, Local Digital Loopback Test, Remote Digital Loopback Test, Analog
Loopback Test with Self-Test, and Remote Digital Loopback Test with Self-Test can all be
selected from the terminal or LCD front panel under the `DIAGNOSTIC' menu. Use the front
panel or AT&T0 command to terminate the test.
ANALOG LOOPBACK TEST (AT&T1)
This test can check almost every part of the modem and RS-232 cable except the telephone line
outgoing interface. During Analog Loopback testing, data from the terminal or computer is sent
through an RS-232 cable into the modem's transmitter and is modulated to an analog signal then
loopbacked to the receiver, demodulated to digital form and sent through the RS-232 cable back
to the terminal or computer's screen. You can tell if anything is wrong by looking at the screen.
The screen should show whatever data you have sent to the modem. Also, the Control Level
field of the LCD screen will be indicated as `ALB'. The U-1496E will have the TST LED ON
during the test. This test can only be initiated when the modem is off-line.
((MODE-23))
ANALOG LOOPBACK WITH SELF-TEST (AT&T8)
This test generates data from the modem itself instead of input data from an RS-232 cable. The
data will go through the same path as the Analog Loopback Test does. In asynchronous mode,
the pattern is printable ASCII characters. You can see the result on the screen. In synchronous
mode, the pattern is scrambled binary 1 and the Throughput Meter will change to a Bit Error Rate
Meter. The left reader displays accumulated bit errors while the right reader displays
accumulated bits sent. The U-1496E TST LED flashes for any bit error. The Control Level field of
the U-1496 LCD screen will be indicated as 'ALBST', which stands for ALB with self-test.
This test can only be initiated when modem is Off-line. The following Bit Error Rate Meter
example shows 11120 Kbits sent, 22 bits in error. When the number exceeds 99999 Kbits, it will
reset itself back to zero.
((MODE-24))
LOCAL DIGITAL LOOPBACK TEST (AT&T3)
This test will loopback the digital form data demodulated from the receiver to the input of the
transmitter. During testing, all data received from the remote modem will be returned to the
remote modem. This test is applicable when the remote modem does not provide V.54 Remote
Digital Loopback capability. Also, the Control Level field of the LCD screen will be indicated as
'LDL'. The U-1496E TST LED indicator will be ON.
This test can be initiated by the local modem when the modems are on-line.
((MODE-25))
REMOTE DIGITAL LOOPBACK TEST (AT&T6)