At 10:24 PM 11/22/2002 +0700, Dr. Jeffrey Race wrote:
On Thu, 21 Nov 2002 12:22:27 EST, [email protected] wrote:
>1) The maximum possible modem-to-modem connect speed through the PSTN is
V.34
>33,600 bps. To get V.90 speeds you must have a V.90 modem connected to a
>"digital modem" at the central office. In other words, there is only one
>analog hop in a V.90 connection. V.90 works fine for internet access, but
>V.90 is not possible for two analog modems connected through the PSTN.
>
>3) The maximum 33,600 bps rate for a V.34 modem requires an extremely clean
>channel. For example, this rate can only be achieved on about 5% of the
>connections through the North American PSTN. On the other hand, a good
V.34
>modem will achieve rates of at least 26 K on over 90% of the connections
>through the PSTN.
Comment please:
I have two USR 5560 PC Card modems hooked up back to back over a very
clean circuit (basically just two battery-feed circuits connected by
two 1 uF capacitors). My terminal program always reports connection
at 31200 V42bis whether I enable or disable compression. Why might I not
get 33600? Could it be something about the modems?
Near-end echo is an issue for V.34 modems, and it sounds like you've got
the modems connected across a nearly "0 ohm" loop, which means there's no
circuit loss between the two modems to attenuate echo. If you have some
artificial line (or real telephone-type twisted pair wire), try putting the
equivalent of 3kft to 6kft of line between the modems -- that should
improve your connect speed.
When I used to use a V.34 modem at my desk at my old employer, I didn't get
very good connect speeds through the PBX, but I was only 100 ft. from the
PBX itself. I put 3kft of artificial line modules in-line with my desk
analog line, and my connect speeds perked right up. <g>
Thanks to all of you who offered comments on this.
Jeffrey Race
- John
