2-23-95                   V.34  Modems


     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.34 from Rockwell also supports FVast. 

%E2 is default so your V.34 modem will fall back/forward if the line 
conditions  warrant. Rarely will you ever see fall forward. 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 V.34 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 V.34 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
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