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By Computer will not Dial a particular phone number
Andrew P Edit MessageUploaded - 17 Nov 2001 02:43

Following on after a working connection to the Internet, my new computer suddenly just started doing a single click instead of dialling the Internet.

Further testing showed that the only difference between a situation which dialled and a situation which didn't dial was the phone number in the Dial-Up-Networking (DUN) entry.

The system is Win2000 pro, the modem is shown in the diagnostics a a Conexant HCF-PCI Modem.


Bill Williams

Edit MessageUploaded - 17 Nov 2001 02:54

In the old days, BT (or was it the Post Office that long ago) insisted on regulations in modems such that if they dialled a number too often and didn't get through, then that number was placed on a blacklist within the modem. The blacklist prevents the modem from dialling that particular number and the whole regulation is intended to prevent nuisance calls by equipment that has gone wonky.

I had thought that this regulation had been quietly dropped years ago, but it seems that it is still relevant and modems for use in the UK are obliged to include it.

As we found on detailed investigation, the default state of dialup on Win2000 is to retry dialling every 5 seconds. This will almost invariably trigger the blacklist even if the ISP phone line is busy for just a short period. So this retry interval must be increased significantly. I need to find a copy of the blacklist regulation to find the most suitable interval; try 61 seconds for the time being.

I will try to find a long term solution, meanwhile a work around is to add extra redundant digits to the end of the phone number of the ISP. These extra digits are ignored by the ISP but are enough to fool the modem into thinking that this number is not on its blacklist.


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