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Chapter 5 - Error Correction, Data Compression, and Speed Conversion
5.5 V.42 Mode Select Command (
#L
)
The V.42 Mode Select command (
#L
) selects which type of error correction your MT2834MR6 will use for
transmissions. The V.42 standard implements both MNP Class 3 & 4 and LAP-M error correction protocols.
When you execute one of the
#L
commands, you instruct your MT2834MR6 how to operate with each
protocol. For example, the factory default setting (
#L0
) tells your MT2834MR6 to negotiate the protocol with
the remote modem.
The following sections detail the operation of the
#Ln
command.
5.5.1 #L0 Command
The #L0 command, which is the factory default, allows a pair of modems to negotiate which V.42 mode (MNP
or LAP-M) will be used.
5.5.1.1 Originate Mode
If both modems have LAP-M capability, the modems will use LAP-M mode. If one or both
modems do not have LAP-M capability and both have MNP, the modems will use the MNP.
5.5.1.2 Answer Mode
The answering modem will respond to either an MNP Link Request or a LAP-M ODP signal,
depending on which is issued by the originating modem.
5.5.2 #L1 Command
The #L1 command enables MNP error correction and disables LAP-M. This command is for originate mode
only. Answer mode still accepts MNP or LAP-M.
5.5.3 #L2 Command
The #L2 command enables LAP-M error correction and disables MNP. This command is for originate mode
only. Answer mode still accepts MNP or LAP-M.
5.5.4 #L3 Command
In the previous 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 “Protocol Establishment” to determine
parameters and 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, use the #L3 command to disable the Detection phase and go
directly to Protocol Establishment. Both modems must have #L3 in effect.