Paul, at 22:19 on Jan 30 1996, you wrote to David Drummond...

PE> 1. After receiving an "AT" command at a particular baud 
PE> rate, the modem does not adjust to that baud rate, and 
PE> instead stays at the rate at the time of last "AT&W".

DD> As it is supposed to do (according to the docs).

PE> If the docs say that, then the modem is fucked by design.
PE> If the docs don't say that, then the modem has a bug in it.

PE> I suspect the latter.  However, you'll have to tell me which
PE> bit of the docs you are referring to, because I can't find
PE> hide nor hair of that nomatter where I look.

A few relevant extracts from the Courier on-line manual...

==========================================================================
Data Rates

The modem can be set to a fixed or variable serial port rate.  A fixed rate 
sets the modem for the highest possible throughput and provides the best 
performance.  A variable rate allows the modem to switch to match the more 
limited rate on the phone connection.

Your software must support fixed or variable serial port rates, and must be 
set to either of the two settings.  NOTE:  Your software may refer to these 
options with terms like locked serial port (fixed rate) or autobaud (variable 
rate).

&Bn     Serial port rate variable or fixed.

        &B0     Variable rates.  When the modem switches its connection rate 
                to connect with a modem operating at a different rate, it 
                also switches its serial port rate.  The software or 
                terminal also switches serial port rates to match the 
                connection rate.  

        &B1     Fixed rate.  Default.  The modem always communicates with 
                the terminal or computer at the rate at which you have set 
                the terminal or software, regardless of the connection rate.  
                For the greatest throughput, set the serial port to 115.2K, 
                57.6K, 38.4K bps for high speed calls and to at least 9600 
                bps for 2400-bps calls.

                This setting is not affected by the &N setting.  However, 
                the serial port rate must be equal to or higher than the &Nn 
                rate.

        &B2     Fixed for ARQ calls/Variable for non-ARQ calls.  Answer mode 
                only.  When the modem goes off hook and connects in ARQ 
                mode, it shifts its serial port rate up to a user-specified 
                rate, for example, 38.4K bps.  If the connection is not 
                under error control, the modem behaves as if it were set 
                to &B0 and switches its serial port rate to match the 
                connection rate of each call.

                To implement this feature, first set your software to the 
                desired rate.  Then send the modem the AT &B2 [other 
                settings] &W command.  

                The modem stores the rate of the command in NVRAM along 
                with the settings.  Each time it makes an ARQ connection, 
                the modem checks NVRAM for the specified serial port rate. 

                When sending subsequent configurations to NVRAM, be sure 
                your software is set to your selected serial port rate, 
                so that the correct rate is maintained.

=========================================================================
Throughput Guidelines 

The following guidelines should help to make the most of the modem's 
advanced performance features.  In many instances, experimentation 
and experience will indicate what works best for your applications.

1. Optimal throughput is attained under the following conditions:
   
   *  The communications software allows fixing the serial port rate 
      higher than the connection rate, by setting the software to 
      115.2K, 57.6K, or 38.4K bps and setting the modem to &B1.

      If the software automatically switches serial port rates to follow 
      the connection rate, the modem's serial port rate must be also set 
      to follow the connection rate for each call, &B0, and throughput 
      will be limited. 

      Installations with specialized software may want to enable a fixed 
      serial port rate for ARQ calls and a variable serial port rate for 
      non-ARQ calls.  See the &B2 command in Chapter 4.

========================================================================
Typical Throughput

The maximum connection rate between two V.34 modems is 28.8K bps.  
Ocassionally, connections occur at 26.4K, 24K, and 21.6K bps because 
line quality differs from location to location  Line conditions and 
data rate affect throughput.  Also remember, your serial port rate 
must match or exceed your connection rate.  If you set your serial port 
rate at 19.2K bps, the V.34 modem will only connect at or below 19.2K bps.

=========================================================================
FRONT PANEL INDICATORS

         Symbol  Meaning            Status

         HS      High Speed         All calls above 2400 bps:  ON during call 
                                    progress, after completion of dialing; OFF 
                                    during HST-mode link negotiations at 2400 
                                    bps, then ON during connection.  Remains 
                                    ON after disconnect until next call is 
                                    originated or answered, or the modem 
                                    is reset. 

         AA      Auto Answer/       Answer mode only:  ON when your modem is 
                  Answer            in Auto Answer mode, and when answering a 
                                    call; in HST-mode, goes OFF if the channel 
                                    is reversed and your answering modem 
                                    transmits at 450 or 300 bps.  Also goes 
                                    OFF when the modem originates a call.  
                                    Flashes ON for incoming ring detect.

         CD      Carrier Detect     ON if DIP switch 6 is OFF (factory 
                                    setting) and the Courier receives a valid 
                                    data signal (carrier) from a remote modem, 
                                    indicating that data transmission is 
                                    possible.  Also ON when the CD override 
                                    is on, DIP switch 6 ON.  

         OH      Off Hook           ON when the Courier takes control of the 
                                    phone line to establish a data link.

         RD      Received Data      Flashes when the modem sends result codes 
                                    or passes received data bits to the 
                                    computer or terminal.  

         SD      Send Data          Flashes when the computer or terminal 
                                    sends a data bit to the Courier.

         TR      Data Terminal      ON if DIP switch 1 is OFF (factory 
                   Ready            (setting) and the modem receives a DTR 
                                    signal from the computer or terminal.  
                                    Also ON when the DTR override is on, DIP 
                                    switch 1 ON.

         MR      Modem Ready/       ON when the Courier is powered on. 
                 Test Mode          Flashes when the modems retrain, including 
                                    online fallback, or while the modem is in 
                                    Test mode.

         RS      Request to        ON if your terminal or software supports 
                   Send            RTS and sends the RTS signal.  OFF if the 
                                    Courier is set to &R2 (Received Data 
                                    hardware flow control) and the computer or 
                                    terminal lowers RTS.

         CS      Clear to Send      ON until the modem lowers CTS when 
                                    Transmit Data hardware flow control is 
                                    enabled (&H1, &H3).  Always ON during 
                                    synchronous connections. 

         SYN     Synchronous        ON when the modem is set to &M1, &M6,
                    Mode            &M7 and enters synchronous mode.  Flashes 
                                    when Dial Security is in operation.

         ARQ/    Error Control/     Data Mode:  Automatic Repeat Request.  ON 
         FAX                        Fax Operations  when the Courier is set to 
                                    &M4 or &M5 and successfully
connects with 
                                    another modem under error control.  
                                    Flashes randomly when the Courier 
                                    retransmits data to the remote modem.
                                    Fax Mode:  Flashes steadily to indicate 
                                    fax mode.
============================================================================
Table B.3--&F1 Hardware Flow Control Default Template

NVRAM Options                    Setting   Description
Handshake option                   B0      ITU-T answer sequence
Error control/sync                 &M4     Normal/error control
Data compression                   &K1     Enabled
Transmit data hardware             &H1     Hardware flow control

Rec'd data hardware flow control   &R2     Enabled
Rec'd data software flow control   &I0     Disabled
Serial port rate select            &B1     Serial port rate fixed higher 
                                           than connect rate
Link rate select                   &N0     Variable 

Result code subset                 X7      Extended.  Includes all codes        
                   
                                           except VOICE
Protocol response codes            &A3     Full protocol codes
Tone/Pulse dialing                 P       Pulse dial
Online local echo                  F1      Disabled
Speaker control                    M1      ON during dial through connect

Remote Digital Loopback (RDL)      &T5     Deny RDL
Normal/Leased/Cellular line        &L0     Normal phone line
Data Set Ready operations          &S0     Override enabled
Break handling                     &Y1     Clear buffer, send immediately

Stored telephone number           &Z0-9=0  Blank
Pulse dial make/break ratio       &P0      U.S./Canada
Guard tone                        &G0      U.S./Canada

Word length*               8
Parity* 0                  None
DTE rate* (Kbps)           19.2    _

*  Detected by the modem from the AT prefix of the &W command that 
   writes your defaults to NVRAM.  Set your software to the desired word 
   length, parity, and serial port rate defaults before sending the modem 
   the AT . . . &W string.

===========================================================================
&Bn     Serial port rate variable or fixed.
        &B0 Variable rates.
        &B1 Fixed rate.  Default.  The modem always communicates with the 
            computer at the rate at which you have set the terminal or 
            software, regardless of the connection rate.  
    
            This setting is not affected by the &N setting.  However, the 
            serial port rate must be equal to or higher than the &Nn rate.

&B2 Fixed for ARQ calls/Variable for non-ARQ calls.  Answer mode 
            only.  When the modem goes off hook and connects in ARQ mode, 
            it shifts its serial port rate up to a user-specified rate, 
            for example, 38.4K bps.  If the connection is not under error 
            control, the modem behaves as if it were set to &B0 and 
            switches its serial port rate to match the connection rate of 
            each call.

==========================================================================
%Bn     Remotely configure the Courier's serial port rate.  See Appendix D.
        %B0  110 bps            %B6   9600 bps
        %B1  300 bps            %B7   19,200 bps
        %B2  600 bps            %B8   38,400 bps
        %B3  1200 bps           %B9   57,600 bps
        %B4  2400 bps           %B10  115,200 bps
        %B5  4800 bps

==========================================================================
Regards, Bill

--- Msgedsq/2 3.20