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Blacklisting  (Updated 14-Mar-03)

Blacklisting - when a modem won't dial particular number(s).

Blacklisting is country specific: telecommunications regulations vary from country to country across the world, and a number of countries have regulations limiting the number of times you can legally call the same busy number in a specific period of time.

When blacklisting becomes active, attempts to dial out will fail - various modems may respond differently. Some may respond with a blacklisted or delayed message. After the country-defined time has elapsed, dialing will again work.

There are several methods that can be used to work around blacklisting:

Select a country for modem installation/dialing that does not require blacklisting (U.S. is one); however, depending upon your country's telephony standards, the modem may not properly dial, recognize dial-tone, ring and/or busy, although it may be possible to dial blind - (add x1 to extra settings).

Change the date/time in Windows to a later date/time. (Double-click the time in Windows' System Tray to change the time.)

Some ISPs may have more than one phone number that can be used to reach the same modem bank - change the last digit of the phone number and check to see if your ISP answers with a modem.

Use a modem-specific command that disables or modifies blacklisting:

Rockwell/Conexant modems - you may be able to disable blacklisting with the command: (AT) %TCB 
AT*D - displays delayed numbers;  AT*B - displays blacklisted numbers.
  If %TCB works, it may be added to the modem initialization string.

Lucent/Agere modems - AT%T21,1d,0 disables blacklisting - see Blacklisting section of this page.

TOPIC chipset - AT %D0 - disables blacklisting

Another trick that may work: if you use a different number as the number to dial, the modem may treat it as a different number for blacklisting, even though the call is routed to the same number. For example, if the ISP phone number is 555-5555, and your phone company allows codes like *## to enable or disable calling features, you could use:

555-5555  until blacklisted, then use *70555-5555, etc.

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