Black Box Modem MD1640A Manual De Usuario

codings except under an unusual line condition called impulse noise.

turns Trellis coding off and

turns Trellis coding on

(factory default).

If line conditions deteriorate, the Series II Modem automatically drops
its transmission speed (“fallback”). The 

command controls the

different ways the Modem falls back. During operation, if the error rate
becomes too great, the modem performs a retrain. If after the retrain,
the error rate is still too high for 33600 bps operation, the modem
initiates a retrain at 4800 bps. If after the first retrain the modem
returns on line at 33600 bps, the modem then starts a counter and a
timer. If three retrains occur within a two minute period, the modem
falls back to 4800 bps.

Entering 

(or 

) allows no fallback when on-line. 

allows the Modem to fallback (based on the error rate or if three
retrains have occurred within a two minute period) from 33.6K to 31.2K
to 28.8K to 26.4K to 24K to 21.6K to 19.2K to 16.8K to 14.4K to 12K to
9.6K to 4.8K bps.  The

command enables incremental fall back

from 33.6K to 4.8K, but also enables incremental fall forward (from
4.8K to 33.6K) if the phone line improves. 

is the factory default

setting.

With the Series II Modem 336+ (MD1640A), entering

sets up the data pump so that it will not transmit a 5

second 2100 Hz signal. Entering 

allows the modem

to transmit a 5 second 2100 Hz signal and is the factory default.

The 

command is used for control of cleardown at disconnect in

V.32, V.32bis, V.34 and V.34 enhanced modes.

A cleardown usually adds 1-2 seconds to the time it takes for the modem
to go on-hook after a disconnect. A cleardown makes a disconnect by
the remote modem easier to detect and a subsequent re-connection
more likely. Enter 

to execute a cleardown at

disconnect (default); and enter 

to disable the

cleardown function.