Black Box 32144 Manual page 56

MODEM 32144
LINE LEVELS SCREEN. This
screen shows the preset level of the
transmit signal (TX) and the
measured level of the receive
signal (RX).
The RX value is the approximate
local receive level of the incoming
signal. The range of measurement
for RX is from 0 to –43 dBm in 1.5-
dBm increments. If the signal level
is less than the carrier detect
threshold, <CD will be displayed.
ECHO CHARACTERISTICS
SCREEN. This screen displays the
characteristics of the echo portion
of the receive signal. Specifically, it
shows milliseconds of delay and the
offset frequency in Hertz.
CHANNEL FREQUENCY
OFFSET. This screen displays the
frequency offset of the receive
signal in Hertz.
THROUGHPUT SCREEN. This
screen functions only if error
correction has been enabled. It
shows the rate (in bits per second)
at which characters are being
accepted by the modem from the
DTE.
PACKET SCREEN. The packet
screen functions only when error
correction is enabled. It has three
components, as explained next.
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• SIZE. Shows size of data packets
(MNP) or blocks (V.42/V.42
bis) currently being
transmitted. MNP uses
"shorter" packets to transmit
through noisy lines and
"longer" packets (which allow
greater throughput) when line
conditions are good. The
maximum MNP packet size is
256 characters (MNP classes 4
and 5) or 64 (MNP classes 1-3).
The block size for V.42/V.42 bis
is fixed at 128 characters.
• TRANSMITTED (TX). Number
of packets or blocks transmitted
since the connection was
established (or since counter
reset).
• ERRORS (ER). Number of
retransmissions (due to data
errors) since the connection
was established (or since the
counter was reset).
To reset the TX and ER counters,
press pushbutton 2 while the
packet screen is displayed.
MODE AND RATE SCREEN.
This screen shows the following
data:
• MODE. Below MODE, this
screen indicates the error-
correction status:
- NORMAL, Error correction and
buffer mode are both inactive.