Black Box 32144, Руководство пользователя

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79
CHAPTER 4: General Operation and Special Features
Table 4-3. 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 minimum and maximum rate
settings of the Speed Limit option.
If satisfactory performance cannot
be attained at any of the available
data rates, the modem 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.
RRP will function only if Speed
Fallback is enabled (factory
default) and if the V.32 Mode
option is set to V.32 bis (factory
default). (Both are Summary Setup
options.)
The factory default setting for
RRP is enabled. To change the RRP
option, refer to
Appendix B
,
Fig. B-
7 . Change the Rate Regeneration
Procedure (RRP) parameter shown
in the diagram to 0 (disable) or 1
(enable). (This is the only way the
RRP option can be changed.)
The operating mode can be
controlled by the user through the
SPEED LIMIT screens on the LCD
in all modes except Hayes mode.
See
Chapter 3
for details.
NOTE
If you want to select 1200/75
bps for both the maximum
and minimum rate, V.22
bis/V.22/V.21/V.23 fallback
must also be selected.
4.3.2 A
UTOMATIC
R
ATE
A
DJUSTMENT
Both sections below apply to both
dial line and leased line operation.
Rate Renegotiation Procedure (RRP)
If Rate Renegotiation Procedure
(RRP) is enabled, the modem will
automatically fall back or fall
forward to a lower or higher data
rate at any time during data
transmission (without retraining)
in response to changes in signal
quality. Data rate adjustments are
limited to the range of 4800 to
14,400 bps and are also limited by