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Appendix B – Modem Commands
Data Modem - Connection Rate and Error Correction.
The MA30120 modem by default will auto negotiate the "carrier speed" (modulation protocol) and "type" (error
control protocol) with the remote modem. The auto negotiation process starts at V92 speeds and works it way
down to 300bps. The connection type refers to 1 of 2 basic methods of handling user data, with error correction
or without it. A carrier without error correction is referred to as a "Normal" mode connection.
Applications that desire high speed modem connections (V.92, V90, V.34bis) and pass significant amounts of
data (dial up Internet access) work best when the modems connect with error correction (V.44 or V.42). V.42
incorporates two methods of error correction (LAPM and MNP).
It may be benefical to use the Modulation Strap index to preset the speed at which the carrier negotiations start
at.
Other applications may desire modem connections without error correction (normal mode connections). These
types of application usually pass smaller amounts of data at slow rates (Point of Sale, ATM, proprietary data,
etc, at 1200 or 2400 bps for example). Applications that desire normal mode connections may react differently
to error control protocol negotiations and/or the time it takes to determine error correction will not be used. In
certain situations it may be desirable to control or disable error control protocol negotiations (V.42).
Error correction commands mostly apply in both answer & originate modes, however some apply only in one
mode.
In Answer mode, if the intention is to allow only V.42 type connections (LAPM or MNP), set S36 to a value of 4.
In Answer mode, if the intention is to allow only LAPM connection (disallow MNP or normal mode connections)
set S36=0.
In Answer mode, if the intention is to force a normal mode connection with a remote modem that dials in with
Auto Reliable mode enabled, set S50 to a value between 1 & 9 (depending on client modem variables). If the
remote modem originates with error correction off, S50 controls how long the MultiAccess modem will wait
before indicating connect. The minimum value for S50 is 1 (100 milliseconds).
In Originate mode, if the intention is to connect only with V.42 Error Correction (either via LAPM or MNP) set
S36=4.
In Originate mode, if the intention is to connect only in Reliable MNP mode, disable LAPM with S23 = 0 and set
S36=4.
In Originate mode, if the intention is to connect only in Normal mode (No Error Correction) regardless of client
modem, set S23=0, S17=0, and S36=1.
MultiAccess Communications Server MA30120 User Guide
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