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VFAST
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1994-05-12
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4-9-94 V-Fast Modems
There is no set standard for V-Fast modems and won't be until spring
sometime. Meanwhile 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. 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 inrease 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). There will be some (yet
unknown) charge to upgrade to the ITU v.34 standard.
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.
Don Hinds - Zoom Tech
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