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MultiModemBA User Guide
V.42 Mode Select #L
The V.42 standard implements both MNP Class 3 & 4 and LAP-M error correction methods. The V.42
Mode Select command (#L) selects which type of error correction (MNP or LAP-M) your modem
uses for transmissions.
The various #L command options are as follows.
#L0 Command The #L0 Command allows a pair of modems to negotiate which V.42
mode (MNP or LAP-M) will be used in their transmissions.
Originate Mode
a. If both modems have LAP-M capability, the modems use LAP-M
mode.
b. If one or both modems do not have LAP-M capability and both
have MNP, the modems use the MNP mode.
Answer Mode
a. The answering modem responds to either an MNP Link Request
or LAP-M Originator Detection Pattern (ODP) signal depending on
which the originating modem issues.
#L1 Command The #L1 Command sets your modem to MNP error correction and
disables LAP-M. This command is for Originate mode only. In
Answer mode, the modem still accepts MNP or LAP-M.
#L2 Command The #L2 Command sets your modem to LAP-M error correction, and
disables MNP. This command is for Originate mode only. Answer
mode still accepts MNP or LAP-M.
#L3 Command In the prior commands, the modems use a two phase process to
establish a V.42 connection (detection to establish whether the
remote modem is also error correcting, and then protocol
establishment to determine parameters and to establish the error
correction connection). If you know that the other modem is a V.42
error correcting modem, and you wish to use LAP-M, the #L3
command disables the detection phase and goes directly to protocol
establishment. Both modems must have #L3 in effect.
Auto-Reliable Buffering $A
In Auto-Reliable mode, the modem is given four seconds to establish a Reliable connection. After this
four-second period, the modem drops to Normal mode. Any data which is received during this period
is typically discarded. The $A command can be used to cause the modem to buffer (save) data that
is received during this Auto-Reliable time-out period. This data will then be output by the modem after
the CONNECT message.
AT$A0 = Discard data received during auto-reliable time period.
AT$A1 = Buffer data received during auto-reliable time period.
The factory default is $A0.