The Wi-Fi Alliance this week updated its list of certified wireless LAN products, announcing that more than 900 products from 116 companies have received certification.The group started testing products for interoperability in March 2000. It has four certifications, for IEEE 802.11a, 802.11b, 802.11g and the Wi-Fi Protected Access security protocol.Many products fail the certification tests on their first try, \u201cfor a number of reasons, including failed interoperability and performance,\u201d said Wi-Fi Alliance Managing Director Frank Hanzlik, in a statement. \u201cIf these products were not tested, technology consumers would experience these problems, resulting in product returns and additional customer support.\u201dProducts are tested at one of four independent labs, in Tokyo; San Jose; Winnersh, U.K.; or Taipei, Taiwan. Those that pass get to display the Wi-Fi Certified logo.Interoperability has been instrumental in the explosive growth of WLANs recently, as enterprise companies become more comfortable trusting a technology that is standardized.The Wi-Fi Alliance has been around since 1999, and it now has more than 200 members. In April of this year, it announced the first products certified for Wi-Fi Protected Access, and in July announced the first certifications for 802.11g.