Now a new high-rate extension to the standard，802．11b，lets(1)networks support data rates to 1 1 M bit／see．Ratified in 1997，the-original 802．11 standard united the wireless industry by defining a(2)protocol architecture that worked with conventional upper—layer (3)．Also，802．11 maintained compatibility with the three most popular radio transmission types： (4)spread spectrum，~equency-hopping spread spectrum，and infrared(5) ，this new architecture added (6)alt the medium access control(MAC)layer 2 and at the physical(PHY)(7) ，forcing(8)between the two layers in performing the critical tasks involved with initiating and maintaining wireless communications．For instance，to ensure(9)of the wireless link，MAC and PHY work together to determine if a，(10)path exists before they start a transmission．