This test will request the remote modem to do a digital loopback. During testing, the local
modem will send a remote digital loopback request to the remote modem according to V.54. If
the remote modem supports V.54 and is programmed to grant this kind of request, it will resend
all received data back, and the local terminal or computer will receive all data it sends out. This
test is applicable when the remote modem and local modem both provide V.54 Remote Digital
Loopback capability. The Control Level field of the LCD screen for the initiating modem will be
indicated as 'RLB', and for accepting modem will be indicated as 'LDL'. The U-1496E will have
the TST LED indicator ON during the test.
This test can be initiated by either the remote or local modem when modems are on-line.
((MODE-26))
REMOTE DIGITAL LOOPBACK WITH SELF-TEST (AT&T7)
This test generates data from the modem itself instead of input data from the RS-232 cable. The
data will go through the same path as the Remote Digital 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 of the initiated
modem will change to a Bit Error Rate Meter. The left reader displays accumulated bit errors and
the right reader displays accumulated bits sent. On U-1496E, the TST LED flashes for any bit
error. This test is applicable when the remote modem and local modem both provide V.54
Remote Digital Loopback capability. The Control Level field of the LCD screen for initiated
modem will be indicated as 'RLBST', and for accepted modem will be indicated as 'LDL'.
This test can be initiated by either the remote or local modem when modems are on-line.
((MODE-27))
LINE CONDITION STATUS DISPLAY
The LCD screen display of this section only applies to the U-1496 and U-1496R models.
Regarding data being transmitted on telephone line circuits, there are a lot of factors that can
affect the data in transit. The U-1496 can measure four major line impairments. From the
impairment readings, you can understand the current line condition. The U-1496 also logs line
events over a long period so you know what the line condition has been. We will describe these
readings and logs as follows:
Note: The readings displayed are just for reference and not to be taken for measurements.
((MODE-28))
Signal to Noise Ratio (S/N)
This reading is expressed in 0.1 dB resolution. The higher the speed, the higher the S/N ratio
required. The modem measures the S/N ratio by measuring the distance between the
demodulated signal point and the ideal signal point. The modem measured S/N ratio is generally
about 2 dB higher than what is actually on the line because the modem rejects some of the out
of band noise. For V.22/22bis, the difference can be as high as 8 dB because modems only use
part of the 3KHz bandwidth and rejects more than half of the voice band noise.
Receiving Power Level (RX)
