Date   : Thu, 20 Dec 1984 06:52:00 MST (Thu)
From   : Keith Petersen <W8SDZ@SIMTEL20.ARPA>
Subject: 2400 baud modems

This is file 2400BAUD.TXT - relayed from the RCPM circuit:
--Keith

From:  Wayne Masters, Potpourri sysop
       (408) 378-7474 300/1200/2400 baud
       San Jose, Ca.

Subject: New 2400 baud modems         8/19/84

       Many of you have asked technical questions about the 2400 baud
modems now on the market (and more being introduced monthly).  As most
of you know by now Irv Hoff and I have been beta testing 2400 baud for
several months.  The test results are amazing to say the least.  Running
controlled tests on standard dial-up phone lines with random "noisy
connections", the number of "hits" on a given file transfer is less by
a factor of 10 using 2400 baud vs 1200 baud.  So it is concluded that
2400 baud technology is working and will soon be available on most
commercial and private dial-up systems.  Now, what is a "standard" 2400
baud modem?  

       You will no doubt see various technical descriptions of a given
2400 baud modem touting it's features.  Be sure the modem you choose has
this specification:

       CCITT recommendation for a V.22 bis modem communicating at 2400 bps.

       Further explanation of this CCITT standard:
Frequency- Bell 212A
Encoding modulation-  16 level psk  (quadrature AM or QAM)

       This sounds a lot like the Bell 212A standard for 1200 baud--and it
is.  The difference is in the encoding or modulation scheme.  Bell 212A 1200
baud uses 4 level psk and 2400 baud uses 16 level psk.  If you "listen" to
the 2400 baud carrier it will sound exactly like the familiar 1200/212A-
like "static" or a scratchy noise.

       Features to look for in your search for the "right" 2400 baud modem:

1.  Does it retain 300 baud bell 103 capability?  (most offer 1200 baud as
    a "fallback")
2.  Is it "smart"--a biggy if you intend to call other systems a lot.
3.  Does it offer autoanswer--a biggy if you run a remote system.
4.  Price--a real biggy

       So far, none of the modems on the market offer all these features
in a "standalone" modem.  That is one big reason why Irv Hoff and I have
been involved with Racal-Vadic--not only beta testing to prove 2400 baud
technology...but to get the features most users prefer designed into the
modem.  Others may follow some day but Racal Vadic will introduce their
"standalone" modem in time for Christmas 84 with the following features:

1.  Smart-autodialing.  It will recognize both the Hayes and Vadic commands.
2.  0-300 baud at both Bell 103 and Vadic protocols
3.  1200 baud at both Bell 212A and Vadic protocols
4.  2400 baud CCITT V.22 bis
5.  Price is expected to be $695.00 retail

      The first release will be an external RS-232 model.  Early 1985 will
see the single card slot version for IBM PC's and compatiables.

       In order for 2400 baud to be in "great demand" there must be systems
available for the users to access.  I am working with Racal-Vadic to 
identify RCP/M and RBBS systems where 2400 baud modems could be placed to
generate public interest in 2400 baud.  Sysop's should contact Potpourri
at 408-378-7474 if interested in participating.

       Now about software to support 2400 baud.

       Both MDM7 and MEX will support 2400 baud if the user modifies his
port overlay to setup his port for 2400 baud.

       For sysops who use BYE3, the problem is different.  Most 
implementations of BYE rely on the hardware's Data Available signal (DAV)
to trigger a check-for-carriage-return sequence at different baud rates.
If most hardware is like mine (Z80 SIO), if the hardware is set to look
at 300 baud and the modem answers at 2400 baud the DAV is never set and
you are in an endless loop.  Same thing happens if you set the hardware
to 2400 and the modem answers at 300.
       I modified BYE3 (version 26 and up) to handle TSTBAUD differently.
I chose to look at each baud rate in 2 second windows, 300 first, then
1200 and 2400, and loop thru this sequence until a C/R or L/F is detected.
The caller is never more than 4 seconds away from his calling speed but
must continue to issue c/r's until the familiar message "Nulls, if needed"
is displayed.  Sysop's who choose to use BYE3 need only add the "SET2400"
code into their port insert. 

       Well, enough for now.  Feel free to contact me if you are more
confused now than you were before reading this.

                     -wayne masters, Potpourri sysop-
                            408-378-7474