3-9-95                      V-Fast Modems

      VFAST modems come with a 14.4 Owners Manual and insert for VFC 
commands.

     V.34 has been approved for 28K modems. We have no price for updates 
yet (should be soon). There will be  some  (yet  unknown) charge to upgrade 
to the ITU  v.34  standard.  You should  still  be  able  to connect with  
new  v.34 if they are Rockwell v34.  Rockwell v34 is  keeping compatible  
with  Vfast code too. Other v34 modems you can connect at 14.4 or less only. 

     The early Vfast from Rockwell and others each have come out with their
own  'standard' for V-Fast. Rockwell based modems should connect  at  Vfast
speeds  to each other, and the V.24 from Rockwell will also support  FVast.
They connect at V-fast speed on normal voice phonelines. In fact V-fast  is
supposed to be better than v32(bis).

Use %E1 so your V-fast modem will fall back if the line conditions  warrant
when  negotiating the connection. Even between like modems (two Zooms)  you
may  not  see 28K connections. Using a slower speed may  actually  increase
throughput  on  'poor' lines. Forcing a higher connect speed  often  causes
throughput  to be substantially less than that of the slower connect  speed
because  of errors and repeated blocks. Between unlike modems  the  highest
connect may be as low as 14,400 (which is the V32bis ITU standard).


     Set  the VFast modem to 38,400 bps, in theory up to 115,000  bps  with
compression. Some computers will handle this OK, though a compression  that
high is VERY rare. I recommend 38,400 bps for 99% of normal use to get  the
fastest  throughput,  sometimes you may have to fall back  to  19,200.  Use
RTS/CTS Flow, AT&F&C1&D2 init. We haven't tested the Vfast with any 
bidirectional protocols.

                              Line Quality

     To test the quality of your lines on v32bis modems, Type +++ and  wait
until you get OK. (do NOT press [Enter]).   This puts you in command  mode.
Then you can enter AT%L?%Q?  and it will give you numbers for signal  level
&  line quality.   You should get 15-30 for %L? preferably 18-25,  and  for
%Q?  lower  is  better.  11 or below is what you should get.  You  can  try
forcing  higher  speeds  using the Fx commands (see  Appendix)  to  see  if
quality   drops  at  the higher speed. To go back  online  enter  ATO.  Try
including %E3 in the init string, for retraining.  AT&F&C1&D2%E3    should
work just fine.

NOTE:  Make sure your computer is Grounded (really grounded) and the  modem
(or  cable) is screwed down (in). That seems to cure a lot of  problems.  A
SysOp in Holland discovered this.

                                        Don Hinds - Zoom Tech
##include=c:\text\signa.tif



