
3-8-95               Data transfer =S=P=E=E=D w/v42bis

     If you connect with v42bis and get transfers in the range shown below,
you  are doing fine, and probably transferring Compressed files  (Zip,  LZH
etc)  or Graphics (all of which v42bis cannot compress further). If you  do
well over the cps shown below then you are getting compression. The  amount
of  compression depends on the type of file. Some (spreadsheets,  database)
compress a lot, some very little (exe, com) and some in the middle  (text).
Modems  are  rated BPS (Bits Per Second) while most  software  reports  CPS
(Characters  Per Second). That's (roughly) 8 bits, plus start &  stop  bits
per  character and other 'overhead' during the transfer. (Zmodem or  Ymodem
1K) If your 14.4 RPI modem is not using RPI compatible software for 
V.42bis), speed will probably be a bit slower.

a 2400 w/v42bis is 290-320cps
a 9600 w/v42bis is 11-1200cps
a 14,400 w/v42bis is 15-1700cps
a 24K  w/v42bis is 26-2700cps
a 28K  w/v42bis is 3200cps +/-

     If the transfer seems slow, you can see your 'true' connect speed when
you  make  the  call by putting S95=1 in your init string.  Then  when  you
connect  it  will  give the carrier speed, instead  of  the  computer-modem
speed  in the CONNECT statement. (be sure Autobaud=OFF). The  higher  speed
modem  ca b se t fal bac t lowe connec  speed  i  th  lin qualit i poor.

     The  best transfer protocol is usually Zmodem. Then Ymodem  (sometimes
listed as Xmodem-1K) or Ymodem-Batch. Xmodem or Kermit can be VERY slow.  I
also  suggest  try using the 'next-higher' speed  modem-computer  than  the
modem-modem  supports.  IE:  14,400 to 19,200(or 38,400),  28K  to  38,400.
Setting  57,600 or higher sometimes actually be slower than setting 38,400 
or  19,200. Internal modems have 16550 UARTS, external modems rely on the 
computer Serial port UART. 8250/16450 is usually fast enough. 16550 is 
better though.

                                   Don Hinds - Zoom Tech
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