Until recently, however, wireless LANs were too slow for most enterprise applications.based on the IEEE 802.11 standdrd, they ran at 1M to 2M bit/sec.
Now a new high-rate extension to the standard, 802.11b, lets wireless networks support data rates to 11M bit/sec.
Ratified in 1997, the original 802.11 standardunited the wireless industury by defining a low-level protocol architecture that worked with conventional upper-layer enterprise protocol stacks. Also, 802.11 maintained compatibility with the three most popular radio transmission types: direct sequence spread spectrum, frequency-hopping spread spectrum, and infrared.
Essentially, this new architecture added intelligence at the medium access control（MAC）layer 2 and at the physical（PHY）layer 1, fosteing cooperation between the two layers in performing the critical tasks involved with initiating and maintaining wireless communi-cations.
For instance, to ensure reliability of the wireless link, MAC and PHY work together to determine if a clear path exists before they start a transmission.
During transmission, they employ special collision-avoidance and arrival-acknowledgment techniques that are not required in wired ethernet LANs.（To be continued）
有了便携式和无线局域网，用户在离开其办公桌的时候，不管是在会议室、公共区域还是在远处办公室，都能享有更高的生产效率。
然而，时至今日，无线局域网对多数企业应用来说还是太慢。依据IEEE802.11标准，他们运行速度为1兆至2兆位/秒。
现在对此标准的一个新的更高速扩展，能让无线网支持高达11兆位/秒的数据速率。
最初的802.11标准是在1997年提出的，通过定义能与常规的上层企业协议组一起工作的低级协议体系结构，把无线行业团结起来了。802.11也保持了与三种最流行的无线电传输方式（直接顺序扩频、跳频扩频和红外线）的兼容性。
本质上，这种新的体系结构在介质接入控制（MAC）层（第二层）和物理层（第一层）增加了智能，建立这两层之间在执行及开始和保持无线通讯的关键任务时的协作关系。
例如：为确保无线连接的可靠性，MAC层和物理层一起工作，以确定在他们开始传输之前是否有一条清晰的路径。
在传输过程中，他们采用有线以太网不需要的、特殊的避免碰撞和到达应答技术。(末完待续)
文章来源于领测软件测试网 https://www.ltesting.net/
