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PN 88300150
5.5
V.42 Mode Select Command (#L)
The V.42 Mode Select command (#L) selects which type of error correction your MT2834MR will use for
transmissions. The V.42 standard implements both MNP Class 3 & 4 and LAP-M error correction
protocols, and by executing one of the #L commands you are instructing your MT2834MR how to operate
with each protocol. For example, the factory default setting (#L0) tells your MT2834MR to negotiate the
protocol with the remote modem, and to prefer MNP 3 & 4.
The following details the operation of the #Ln command:
1. #L0 Command (factory default setting)
The #L0 Command allows a pair of modems to negotiate which V.42 mode (MNP or LAP-M) will be
used.
Originate Mode
a.
If both modems have LAP-M capability, the modems will use LAP-M mode.
b.
If one or both modems do not have LAP-M capability and both have MNP, the modems will use
the MNP.
Answer Mode
a.
The answering modem will respond to either an MNP Link Request or LAP-M ODP signal,
depending on which is issued by the originating Modem.
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.
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.
4. #L3 Command
In the above 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, the
#L3 command to disable the Detection phase and go directly to Protocol Establishment. Both
modems must have #L3 in effect.
5.6
Modes of Operation
You can configure your MT2834MR in one of three different V.42 modes of operation (each mode can be
with or without compression). These are the Normal, Reliable and Auto-Reliable modes. The modes and
data compression features are selected with commands covered in Section 5.13.
Normal Mode (&E0)
In the Normal mode of operation, the MT2834MR's error correction capabilities are disabled, and the
modem functions as a normal (non-error-correcting) modem.
Reliable Mode (&E2)
In Reliable mode, the MT2834MR uses its V.42 error correction capabilities during all transmissions.
When in Reliable mode, the MT2834MR must be connected to another modem with a similar V.42
protocol activated (MNP or LAPM). If the modems cannot establish a V.42 error correction connection,
the modem will time out and hang up.
4/3/01
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