In message <20010126163313.C6452@ls.berkeley.edu>, Tom Holub writes:
> This is true, as far as it goes. The problem is not only in the
> modem; to get speeds above 33.6K, you'll need to connect it to a
> digital phone line (ISDN or T1 PRI). When I found that out I
> basically gave up, but if I recall I found the modems at
> datacommwarehouse.com.
A couple of notes to expand on what Tom said:
- The reason the client modems only transmit at a lower speed is noise
introduced by digital-analog conversions. The modem takes your
digital signal, converts it to analog (audio) for transmission to the
telephone company central office. But the CO converts it to a
(different) digital format caled "PCM" (I think; "pulse code
modulation" or something) for the telephone network.
Because the server modems have a digital line, they just compute the
PCM directly from your digital signal. Fewer conversions means lower
noise, so higher speeds are possible.
- If you buy a 56K server modem you'll find that it comes with caveats
saying that it won't actually transmit at 56Kbps. The fastest speed
allowed by the FCC (due to signal strength limits) is 53Kbps. Actual
speed depends on the client's phone line conditions. The bulk of the
connections to our modems are in the low to mid 40's, although a very
small number of calls do actually connect at 53Kbps.
-- George C. Kaplan gckaplan@ack.berkeley.edu Communication & Network Services 510-643-0496 University of California at Berkeley------------------------------------------------------------------------ The following was automatically added to this message by the list server:
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