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Modem 34336
Table 4-6. V.22 bis/V.22/V.21/V.23 FALLBACK.
MODE DESCRIPTION
V.22 bis 2400 bps asynchronous/ synchronous
V.22 1200 and 600 bps asynchronous/synchronous
V.21 300 bps asynchronous
V.23 1200/75 bps asynchronous
All modes are full duplex.
The operating mode is controlled through the SPEED LIMIT screens on the
LCD in all modes except Hayes mode. See Chapter 3 for details.
4.10.2 V.32 S
PEED
F
ALLBACK
This feature applies only to V.32 mode operation. It functions only if enabled
and the maximum speed is set (via the Speed Limit option) to the highest
available speed—9600 bps for the Modem, 14,400 bps for the Modem.
When V.32 Speed Fallback is enabled, the Modem automatically selects the
highest possible data rate, depending on the signal quality during handshake.
The Modem automatically selects either 9600 bps or the fallback rate of
4800 bps. The Modem selects either 14,400 bps or the fallback rate of
12,000 bps. If the error rate is one error in 1000 bits or lower, the Modem
connects at the highest available rate. If the error rate exceeds this threshold,
the Modem connects at the fallback rate. Fallback may also occur during
retrain sequences.
To configure the modem for automatic V.32 Speed Fallback, refer to
Appendix C. Follow the instructions to change the value identified in the
DATA PUMP OPTIONS diagram (Appendix C) as the V.32 Speed Fallback
parameter from 1 (default setting) to 0.
Rate Renegotiation Procedure (RRP)
Rate Renegotiation Procedure (RRP) is a third type of automatic fallback;
it can be controlled by the user.
Like V.32 Speed Fallback, RRP allows the Modem to automatically select the
highest possible data rate, depending on the signal quality. Unlike Speed
Fallback, RRP allows for data rate fallback or fallforward at any time during
data trans-mission. Retraining is not required. RRP may be used with either dial-
up lines or leased line operation.