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Chapter 3 - AT Commands
3.10 Error Correction and Data Compression Commands
You can configure a modem to any of three different V.42 modes of operation (each mode can be with or
without compression). They are the non-error correction, autoreliable, and reliable modes. You can also turn
data compression on or off.
&En Error Correction Modes
n = 0, 1, or 2
Default: &E1
Select the modem’s error correction mode using the &E0, &E1, or &E2 command.
&E0 disables the modem’s V.42 error correction capabilities, and the modem functions as a
non-error correction modem.
&E1 enables autoreliable mode. During the handshaking procedures at the start of the
online connection, the modem queries whether the other modem is using V.42 error
correction. If the modem determines that the other modem is using V.42, it switches itself
into reliable (V.42) mode and enables error correction. If it determines that the other modem
is not using V.42, the modem remains in non-error correction mode.
&E2 enables reliable mode, in which the modem uses its V.42 error correction capabilities
for all transmissions. In reliable mode, the modem must be connected to a modem with a
V.42 protocol (MNP or LAP-M).
The V.42 standard includes MNP Class 3 and 4 and LAP-M error correction methods. The
V.42 mode select command (#L) selects which type of error correction the modem uses for
transmissions.
&En Data Compression
n = 14 or 15
Default: &E15
Data compression is normally enabled, providing &E1 (autoreliable mode) or &E2 (reliable
mode) has also been selected. However, you may wish to turn it off in certain
circumstances.
&E14 disables data compression.
&E15 enables data compression.
#Ln V.42 Error Correction Modes
n = 0–3
Default: #L0
The #L command selects the V.42 error correction method (MNP or LAP-M) the modem
uses when originating a call. In answer mode, the modem ignores the #L command and
accepts whichever V.42 mode, MNP or LAP-M, the originating modem offers.
#L0 causes the modem to negotiate the V.42 error correction method with the answering
modem, and to begin negotiation with LAP-M. 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 MNP.
#L1 enables MNP error correction and disables LAP-M.
#L2 enables LAP-M error correction and disables MNP.
#L3 enables LAP-M error correction and disables MNP, but skips the V.42 detection phase
used by the other commands. Both modems must be set with #L3.