Modem Configuration - Maximum Speed

[Tom]

I have an external ISDN modem (can't get DSL where I
live). To get optimum throughput from it, I would like to
use the serial port at 230400 baud. I have a high speed
serial port capable of 230K, and that capability is
recognized in the serial port properties in Win2K Device
Manager. The modem is configured with a top speed of
230K. But when I try to create a dial-up connection using
that combination, the Modem Configuration dialog box for
the Dial-up Connection only allows a maximum speed of
115200. Unfortunately, that speed is used when the
connection is made, overriding the serial port and modem
defaults, and placing the speed limit well below the
hardware's capability.

What gives? Is DUN that dumb? I installed SP3, and the
symptom persists. Then I tried SP4. It expands the top
Dial-up connection speed above 230400. But no joy. Some
script somewhere is still resetting the baud rate to
115Kbaud before sending the dial-up modem command, even
though all visible settings now say use 230400.

Does anyone know of a fix for this?

What is really frustrating is that communicating at 230400
was no problem in Windows 98. I may be forced to
downgrade my OS to get my full Internet connection speed
back.

Tom

 

[William]

Is it a quad channel (a ISDN modem that can handle 2 BRI cards)? ISDN is 64K
per channel. I have always noticed that win 9x lies about the real speed
with certain modems. I had a hays Accura 14.4 or it might have been a US
robotics that I set the port to 115200. Sure is enough it said 115200 when
connected but in reality is was only 14400 or just little less. NT is a
little more accurate in that department.

Unless this is some special ISDN that I have never heard of before.

If it is a quad then you may need an updated driver from the modem
manufacturer or ISDN provider.

 

[Guest]

Yes, this ISDN modem has 2 B channels for a total
throughput of 128K baud.

Your modem connect speed isn't lying. Modems have two
connect speeds, one for the phone line side (which in this
case is 128K), and one for the serial port. You always
want the serial speed to be at least twice the speed of
the phone connection so you can take advantage of modem
data compression. With most serial port hardware, the
maximum baud rate is 115200. With a 115K serial port
speed, I'm not even reaching the uncompressed capability
of the modem. At 230K baud, I can take advantage of both
full speed and data compression.

The problem appears to be in Windows Dial-up Networking.
The hardware drivers for the serial port and the modem
recognize the high speed capabilities of the hardware.
Something in DUN is limiting the speed to what it thinks
should be a top speed of 115200.

Tom