0049-2702-XXX Alliance Series Modems – USER MANUAL
08/05/2010
Rev. A
Page 73 of 197
Operating Mode Fallback
This section applies to Hayes, V.25bis and dumb mode only.
When the ALX modem originates or answers a call, it determines from the “handshake” routine
with the other modem the most efficient operating mode supported by the other modem and
automatically enters that mode (subject to maximum and minimum speed limits you can select
via the Speed Limit option).
The Alliance Series modems will attempt to use V.34/V.32terbo/V.32bis/V.32 modulation (in
that order of preference) to connect at the highest possible rate, depending on the modulations
supported by the ALX and the modem at the other end of the communication link. (Fallback
operation may also be affected by the selected communication standard. For further information,
see the Communication Standard option in Chapter 2.)
For situations where the other modem does not support V.34, V.32terbo, V.32bis or V.32
modulation, the ALX modem supports two fallback alternatives: V.22bis/Bell 212A/Bell 103
fallback operation (the default setting) and V.22bis/V.22/V.21/V.23 fallback operation.
For
communication within the United States, use the default setting for Operating Mode
Fallback – V.22bis/Bell 212A/Bell 103.
Operating mode fallback functions when the modem is in either manual or automatic originate
mode or manual or automatic answer mode.
Default Fallback Operation
The preferred operating mode is V.34 (28.8 Kbps – 2400 bps) for the ALX V.34 and V.34M, and
V.32terbo/V.32bis/V.32 (19.2 Kbps – 4800 bps) for the ALX V.32/19.2 and V.32/19.2M. For
all other ALX models, the preferred mode is V.32/V.32bis. However, if the other modem does
not support any of these modes, the ALX will fall back to one of the modes listed below. The
fallback modes are listed in the order in which they are attempted by the ALX in normal
operation:
V.22bis/Bell 212A/Bell 103 Fallback (Default):
MODE DESCRIPTION
V.22bis
2400 bps asynchronous/synchronous
Bell 212A
1200 bps asynchronous/synchronous
Bell 103
0-300 bps asynchronous
All modes are full duplex.