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13.1
Fallback
The modem
fallback from:
19200 to 16800
16800 to 14400
14400 to 12000
12000 to 9600
9600 to 7200
7200 to 4800
If the +&FVO command is enabled the fallback may only take place
inside the current modem standard, i.e. only from 14400 to 7200 in
V.32 bis, from 9600 to 4800 bps in V.32 and from 2400 to 1200bps in
V.22 bis. This kind of fallback has been standardised, and may be
used with other modem types using the same standards. Fallback
from 4800 to 1200 bps. (+&FV1) will only work when using modem of
the same type.
13.1.1 Fallback during handshake (+&FH1):
This kind of fallback is only possible in V.32 and V.32bis.
If +&FH1 is enabled, the modem will during handshake decide if
the line quality is good enough for 14400, 12000, 9600 or 7200
bps. This handshake is compatible with other types of V.32 and
V.32bis modems.
13.1.2
Automatic retrain(+&FR1):
Automatic retrain applies to the speeds 14400, 12000, 9600,
7200, 4800 and 2400 bps only. If the modem receiver is out of
synchronisation a retrain may help. A retrain implies no changes
in speed.
The fallback function will operate in all operating modes
(Asynchronous with or without protocol, and synchronous) on
switched lines. This function will not be active on leased lines.
To be able to continue the communication after a fallback or
fallforward, both the modem and DTE (terminal or host
computer) should be capable of the new speed.
For a synchronous connection this means that 114 transmit
clock should be used. The modem will then indicate the speed
for both the transmitter and receiver.
LZTR104006 R1.00
1 3-1
Zat 14.4/14.4-7 and 19.2/19.2-7
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