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ISDN download performance and XP


Bluey Zee

Has anyone ever used an ISDN (64Kbps) connection successfully with Windows XP and if so, what did you have to do to get it running at full throttle?

I recently upgraded a machine from Windows 2000 to XP Professional and went from download speeds of 60-64Kbps to less than 30Kbps. Upload speed remains high at 64Kbps.

I measure these speeds by doing an FTP file transfer using a test site of the carrier (and ISP) and while it is not an absolute 100% accurate measure it does give a good comparison across machines.

The carrier does not (officially) support XP although they offer XP configuration documentation for the ISDN modem they supply and their helpdesk can offer no insights into what the problem might be frustrating both their techs and me alike real bad.

I have tried almost every bit of registry tweaking software I can lay my hands on taking care to backup and restore my registry every time I make a change but to no avail - that magical setting(s) continues to elude me.

I have a 2 channel connection and am able to do all the nice things like connecting at 128Kbps using both channels, dropping a channel when it is required for voice then grabbing it back again when available. All that bit works well except I can only get about half speed on download as mentioned.


el mafioso
hmm, have you checked the COM speed?
also try disabling/uninstalling every other protocol you don't need, maybe the famous QoS packet sheduler?

Bluey Zee

Thanks MeFo - COM speed is 115200 and all non-used protocols removed (including the infamous QoS).

Still having the problems but have somehow managed to get to 40Kbps (on occasion) :confused:



You should check with your ISP further. The lack of the official support of Windows XP could be the problem. While it shouldn't matter what OS you are running when you are trying to login to an ISP connection such as ISDN, there are known problems with this sort of issue.

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