0049-2702-XXX Alliance Series Modems – USER MANUAL
08/05/2010
Rev. A
Page 75 of 197
model in Chapter 2) and are also limited by the Speed Limit option minimum and maximum data
rate and symbol rate settings. If satisfactory performance cannot be attained at any of the
available data rates, the ALX will initiate a GSTN cleardown (line disconnect). If the originate
modem attempts to negotiate a rate that is lower than the minimum rate setting of the answer
modem, the answer modem will initiate a GSTN cleardown.
The default setting for RRP is enabled. To change the RRP option, refer to Appendix C and the
DATA PUMP OPTIONS diagram. Change the Rate Renegotiation Procedure (RRP) setting
shown in the diagram to 0 (disable) or 1 (enable). (This is the only way the RRP option can be
changed.)
When RRP is disabled, Speed Limit Fallback will function as described below (only during
handshaking or retraining).
Speed Fallback
This section applies only to Hayes, V.25bis, dumb and leased line modes (except V.29).
Speed Fallback applies only to V.34/V.32/V.32bis/V.32terbo and 19.2 Kbps proprietary
operation. When Speed Fallback is enabled (the default setting), the ALX modem will
automatically select the highest possible connect rate (data rate), depending on the signal quality
during handshaking, as explained below:
For these models… …the modem will
automatically select:
…or will fall back to:
ALX V.34,
ALX V.34M
28.8 Kbps
26.4, 24.0, 21.6, 19.2, 16.8, 14.4, or 12.0 Kbps
or 9600, 7200, 4800 or 2400 bps
ALX V.32/19.2,
ALX V.32/19.2M
19.2 Kbps
16.8, 14.4 or 12.0 Kbps
or 9600, 7200 or 4800 bps
ALX V.32/14.4,
ALX V.32/14.4M
14.4 Kbps
12.0 Kbps
or 9600, 7200 or 4800 bps
ALX V.32,
ALX V.32M
9600 bps
7200 or 4800 bps
The error rate threshold is one error in 10,000 bits. If the error rate exceeds this threshold, the
ALX will fall back to a lower connect rate.
Fallback may also occur during retrain sequences.
Speed fallback functions when the modem is in manual or automatic originate mode or manual
or automatic answer mode.
To disable or enable automatic Speed Fallback, refer to Appendix C and the DATA PUMP
OPTIONS diagram. (This is the only way the Speed Fallback setting can be changed.)
Note:
All models can fall back to speeds lower than those listed in the above table. See
previous
Operating Mode Fallback
section. The criterion for speed fallback is signal quality,