User's Manual

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

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.