ZyXEL Communications U-336E, User Manual

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Diagnostics & Troubleshooting 111
Dialing Indicator
The V34 LED will flash on and off for 1/2 second each to indicate
that the modem is dialing. This flash will continue after dialing until
a carrier is detected. Therefore, the V34 LED will also flash in
leased-line modem connections when one modem is trying to
handshake but the other modem is not turned on.
Handshaking And Retrain Indicator
The V34 LED will flash on and off in 1/2 second intervals to
indicate that the modem is handshaking or retraining.
Line Condition Status Display
Regarding data being transmitted over telephone line circuits, there
are many kinds of line impairments that can affect the data being
received by the remote modem.
Your modem can measure four major line impairments. From the
impairment readings, you can understand the current line condition.
Your modem 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:
O O
N
OTE
: T
HE READINGS DISPLAYED ARE NOT MEASUREMENTS AND SHOULD ONLY BE
USED AS A REFERENCE
.
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. For V.32/V.32bis, 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 the modem only uses part of the 3 KHz bandwidth
and rejects more than half of the voice band noise.