Ericsson ZAT 19.2 Operation Manual page 270

allback/fallforward and automatic retrain -
In asynchronous mode the modem should be set-up to speed
conversion (+C1) and speed detection (+M2). Then DTE does
not need to adapt to the new speed.
When using fallback/forward or retrain together with a protocol
(V.42/MNP) there will be continuity in data during this transition.
No noise character will be introduced or any character lost. DTE
will only see a pause in data stream.
The fallback function is based on a comparison between the
quality of the received signal and a limit set by the user.
If the quality is below the specified limit during a time specified
by the user (See +S reg.43) the following tasks will be started
(depending on configuration):
13. 1.3 Auto retrain on, Fallback off:
Aulo retrain on
Fallback off
if line quality i is worse than set-up in +$14 and the line-speed is
2400, 4800, 7200, 9600, 12000 or 14400 an automatic retrain
will be initiated trying to improve theadaption to line. Automatic
retrain is not activated when using lower speed because these
standards will be selfsynchronising.
13.1.4 Fallback on:
CAS +&FB1 pt Fallback on
While the fallback function is enabled, no retrain will be initiated.
if the line quality is worse than set-up in register +S44, the
modem will start a fallback. Note that a fallback will not be
Started if the line speed is 1200bps or if the line speed is 4800
bps and the modem is not set-up with the command +&FV1.
13.1.5 Fallback on, Fallforward on:
AT+t&FB1 p= Fallback on
" | Fallforward on
Fallforward will only take place after a fallback, i.e. the modem
will not fallforward to a speed higher than after first handshake.
After a fallback the modem will compare the line quality with
both the fallback limit and the fallforward limit. When the line
quality become better than what Is set-up in register +S46 the
modem will calculate a time telling when to start a fallforward.
This time will be the value in register +s47 multiplied by the
number representing the line quality. Register +S47 is default
equal 1 min. If the line quality is equal to 5, the modem will wait
in 5 minutes before faliforward.
1 3-2 LZTR104006 R1.00
Zat 14.4/14.4-7 and 19.2/19.2-7