Dial-Up Networking Automatic Redial May Stop After 15 Attempts (258838)

The information in this article applies to:

Microsoft Windows NT Server 4.0
Microsoft Windows NT Workstation 4.0
Microsoft Windows 95
Microsoft Windows 98

This article was previously published under Q258838

SYMPTOMS

If you have a dial-up connection configured to automatically redial your Internet service provider (ISP), you may receive the following error message after the fifteenth automatic redial attempt:

Could not detect modem. It may be in use, turned off, or not installed properly

CAUSE

Newer modems that are based on the Rockwell chip set, and U.S. Robotics/3Com modems may have "blacklisting" enabled (this may be country-specific, depending on the manufacturer of the modem). After 15 attempts the modem, in accordance with ITU standards, "blacklists" the phone number. When this occurs, you cannot redial the number until an internal modem time-out has expired or you reboot the computer.

RESOLUTION

Modify the modem initialization string to include one of the following commands. Please refer to the documentation for your modem for details.

Command	Modem type
%TCB	Rockwell based
S40=2	U.S. Robotics/3Com
S40=7	U.S. Robotics/3Com

This command prevents the modem from "blacklisting" a number and allow repeated redials up to 99 times.

STATUS

This behavior is a limitation of the modem configuration files supplied with your modem. Contact your modem manufacturer for updated files. To support delayed and "blacklisted" responses, the modem's unique ID .inf file should contain the necessary registry keys.

MORE INFORMATION

Most modern modems keep a table of the most recently dialed numbers in memory with a count against each number dialed. Commonly, after a number has been dialed 15 times, the modem refuses to dial the number again until a certain time period has elapsed, thus "blacklisting" or delaying the number.

Modification Type:	Minor	Last Reviewed:	12/21/2004
Keywords:	kb3rdparty kbDialUp kbHardware kbprb KB258838