Randall, at 00:36 on Apr 27 1996, you wrote to Bill Grimsley...

RL> I want to set this Courier up to use MNP4. Russell said you use this in
RL> preference to v42. Know what settings to change??

MNP-4 can be forced by setting S27=32, or if you prefer, S27.5=1, which is
quite an elegant form of syntax, insofar as you can set or disable
individual bits with this method (i.e. S27.5=0 turns off that bit). 
Incidentally, some Rockwell clones can be a little troublesome with EC
negotiation (Zooms are particularly notorious for this), and S27=48 usually
allows the modems to connect with full error correction.

-------------------------------------------------------------------------
S27     0      Bit-mapped register.  To set the register, see the 
               instructions for S13.

               Bit     Value   Result
                0       1       Enable ITU-T V.21 modulation at 300 
                                bps for overseas calls.  In V.21 
                                mode, the modem answers both Bell 
                                103 and V.21 calls, but only 
                                originates V.21 calls.
                1       2       Enable unencoded (non-trellis-coded) 
                                modulation in V.32 mode; this option 
                                is part of the ITU-T V.32 
                                recommendation, but is rarely used.
                2       4       Disable V.32 modulation; used for 
                                testing HST modulation in Dual 
                                Standard modems.
                3       8       Disable 2100 Hz answer tone to allow 
                                two V.42 modems to connect more quickly.
                4       16      See below (*)
                5       32      See below (*)
                6       64      Reserved.
                7       128     Unusual software incompatibility.  
                                Some software may not accept 7200, 
                                12000, 14400, 16800, 19200 and 21600 
                                bps result codes.  This setting 
                                disables the codes and displays the 
                                9600 code instead.  The call's 
                                actual rate can be viewed on the 
                                ATI6 screen.

            (*) Error control handshaking options:  
                select the total values of bits 4 and 5.  

                Bit 4   Bit 5   Result
                0       0       Complete handshaking sequence:  V.42 
                                Detection, LAPM error control, MNP
                16      0       Disable MNP
                0       32      Disable V.42 Detection and LAPM
                16      32      Disable Detection phase, if you know 
                                that the remote modem does LAPM, but 
                                not the Detection phase.
------------------------------------------------------------------------

Russell is quite correct when he says that I used to force MNP-4, but now
that the USRs have 256-byte LAPM frames, as well as SREJ (Selective
REJect), I doubt that there's any real advantage in doing so any more.

In fact, the only additions I've made to my normal &F1 template init
string are &A3, for full connect info (i.e. CONNECT
33600/ARQ/V34/LAPM/V42BIS) and &K3, which permits BTLZ data compression
on LAPM connects, but disables MNP-5 data compression with MNP-4 connects.

Regards, Bill

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