Acacia's licensing efforts are based on five patents, all of which cover basically the same thing: patents #5,253,275, #5,550,863 and #6,002,720 are "open continuations" of patent #5,132,992, an "Audio and Video Receiving and Transmission System," which was issued in July 1992. The fifth patent, #6,144, 702, is described as a "division" of the '992 patent and was approved in November of 2000.
http://www.extremetech.com/print_art...a=34898,00.asp