关于无线局域网，下面叙述中正确的是()。
- A.802.11a和802.11b都可以在2.4GHz频段工作
- B.802.11b和802.11g都可以在2.4GHz频段工作
- C.802.11a和802.11b都可以在5GHz频段工作
- D.802.11b和802.11g都可以在5GHz频段工作
正确答案及解析
正确答案
解析
无线局域网标准的制定始于1987年，当初是在802．4L组作为令牌总线的一部分来研究的，其主要目的是用作工厂设备的通信和控制设施。1990年，IEEE 802．11小组正式独立出来，专门从事制定WLAN的物理层和MAC层标准。1997年颁布的IEEE 802．11标准运行在2．4GHz的ISM(Industrial Scientific and Medical)频段，采用扩频通信技术，支持1Mb／s和2Mb／s数据速率。随后又出现了两个新的标准，1998年推出的IEEE 802．11b标准也是运行在ISM频段，采用CCK(Complementary Code Keying)技术，支持11 Mb／s的数据速率。1999年推出的IEEE 802．11 a标准运行在U-NII (Unlicensed NationalInformation Infrastructure)频段，采用OFDM ( Orthogonal Frequency Division Multiplexing)调制技术，支持最高达54Mb／s的数据速率。目前的WLAN标准主要有4种，如表7-6所示。
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