802.11d

802.11d is supplementary to the media access control (MAC) layer in
802.11 to promote global use of 802.11 WLANs. Its basic premise is to provide
access points with the ability to communicate information on available
radio channels with sufficient user device power levels for maintaining
good signal quality while at the same time conserving energy.
The 802.11 standard cannot legally operate in some countries; therefore
the purpose of 802.11d is to add extra features and restrictions
that permit wireless networks to function within the rules of foreign
territories.

When dealing with countries whose physical layer radio requirements
are different from those of the United States, the 802.11 WLAN is inapplicable.
Due to these problems, equipment vendors do not wish to produce
equipment usable in foreign territories since there would be so
many different specifications it would be impossible to make a profit by
building custom country-specific products.

The most difficult problem is that users cannot roam around the
world and still expect their wireless NIC cards to function. The only
solution in such cases is to build a method to inexpensively flash to the
cards firmware that takes advantage of the unique requirements of the
country the hardware is shipped to.