Description
This item is from the PC Hardware
FAQ, by Willie Lim and Ralph Valentino with numerous
contributions by others. (v1.25).
3.22 Why does my fast modem connect at a lower speed?
For 28.8 modems that connect at lower speeds such as 22, 24 or 26.4,
this is perfectly normal. The usable channel capacity of the
telephone system with a ideal connection is just over 28.8k. In
reality, you'll very rarely see a 28.8k connection so don't expect
it. When the two modems connect, they will evaluate the connection
quality and pick a corresponding speed. If you have your modem set up
correctly, it will retrain every once in a while and increase or
decrease your connection speed based on the current line quality.
For modems that connect at considerably lower than expected speeds
(such as 2400 for a 9600+ modem), there are two possibilities. The
first possibility is that the remote modem can't handle the higher
speed. There is nothing you can do about this except call a faster
modem. The other possibility is that you have your serial port / comm
software set up incorrectly.
When you connect your PC to another machine through modems, there are
actually three connections being made: PC1 to modem1, modem1 to modem2
and modem2 to PC2. The speed of the modem (2400,9600,14.4,28.8) is
the rate (more or less) at which the modem1 will speak to modem2. The
PC to modem connections are based on the speed your COM port is set
to. If you set the COM port speed to 2400, the modem to modem speed
will drop accordingly. For this reason, you want to set the COM port
speed at least as high as the modem to modem speed. In actuality, the
modem to modem protocol may support compression and achieve data
transfers faster than the connection speed so you want to set your COM
port higher than your modem to modem connection. For a 28.8 modem,
set the COM port to 38.4k, 57.6k, or 115k. While higher is always
(potentially) better, some software/operating systems have trouble
with very high COM port speeds, so start with 38.4k and see how it
goes.
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pc, hardware, faq, frequently asked questions, repair, computer
