High-Speed WLANs and WLAN Security

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High-Speed WLANs and WLAN Security Wireless CommunicationsHigh-Speed WLANs and WLAN Security2Objectives•Describe how IEEE 802.11a networks function and how they differ from 802.11 networks•Outline how 802.11g enhances 802.11b networks•Discuss new and future standards and how they improve 802.11 networks3IEEE 802.11a•802.11a standard maintains the same medium access control (MAC) layer functions as 802.11b WLANs–Differences are confined to the physical layer•802.11a achieves its increase in speed and flexibility over 802.11b through:–A higher frequency band–More transmission channels–Its multiplexing technique–A more efficient error-correction scheme4U-NII Frequency Band•IEEE 802.11a uses the Unlicensed National Information Infrastructure (U-NII) band–Intended for devices that provide short-range, high-speed wireless digital communications•U-NII spectrum is segmented into four bands–Each band has a maximum power limit•Outside the United States–5 GHz band is allocated to users and technologies other than WLANs5U-NII Frequency Band (continued)6U-NII Frequency Band (continued)7U-NII Frequency Band (continued)•Channel allocation–With 802.11b, the available frequency spectrum is divided into 11 channels in the United States•Only three non-overlapping channels are available for simultaneous operation–In 802.11a, eight frequency channels operate simultaneously•In the Low Band (5.15 to 5.25 GHz) and Middle Band (5.25 to 5.35 GHz)•Within each frequency channel there is a 20 MHz-wide channel that supports 52 carrier signals8U-NII Frequency Band (continued)9Orthogonal Frequency Division Multiplexing•Multipath distortion–Receiving device gets the signal from several different directions at different times•Must wait until all reflections are received•802.11a solves this problems using OFDM•Orthogonal Frequency Division Multiplexing (OFDM)–Splits a high-speed digital signal into several slower signals running in parallel–Sends the transmission in parallel across several lower-speed channels10Orthogonal Frequency Division Multiplexing (continued)•OFDM uses 48 of the 52 subchannels for data•Modulation techniques–At 6 Mbps, phase shift keying (PSK)–At 12 Mbps, quadrature phase shift keying (QPSK)–At 24 Mbps, 16-level quadrature amplitude modulation (16-QAM)–At 54 Mbps, 64-level quadrature amplitude modulation (64-QAM)•Turbo mode or 2X mode–Few vendors have implemented higher speeds[...]... networks function and how they differ from 802.11 networks•Outline how 802.11g enhances 802.11b networks•Discuss new and future standards and how they improve 802.11 networks 3IEEE 802.11a•802.11a standard maintains the same medium access control (MAC) layer functions as 802.11b WLANs –Differences are confined to the physical layer•802.11a achieves its increase in speed and flexibility... addition to security concerns regarding the handoff•802.11r is expected to enhance the convergence of wireless voice, data, and video 4U-NII Frequency Band•IEEE 802.11a uses the Unlicensed National Information Infrastructure (U-NII) band–Intended for devices that provide short-range, high-speed wireless digital communications•U-NII spectrum is segmented into four bands–Each band has a... 802.11b WLAN reception is slowed down by multipath distortion–802.11a solves this problem using OFDM 14IEEE 802.11g•Specifies that it operates in the same frequency band as 802.11b 15802.11g PHY Layer•Follows the same specifications for 802.11b•Standard outlines two mandatory transmission modes along with two optional modes•Mandatory transmission modes–Same mode used by 802.11b and must... United States–5 GHz band is allocated to users and technologies other than WLANs 12Orthogonal Frequency Division Multiplexing (continued) 22Summary•Operating in the 2.4 GHz ISM frequency range, 802.11b has a maximum data rate of 11 Mbps•The 802.11a has a maximum rated speed of 54 Mbps•IEEE 802.11a networks use the Unlicensed National Information Infrastructure (U-NII) band•In 802.11a,... reflected signals (multipath)•To extend the range of the WLAN •Interference with other WLANs can be a big problem 11Orthogonal Frequency Division Multiplexing (continued) 13Orthogonal Frequency Division Multiplexing (continued) 16802.11g PHY Layer (continued)•When both 802.11b and 802.11g devices share the same network–Standard defines how the frame header is transmitted at 1 or 2... expected to happen in 2008 20IEEE 802.11r•Amount of time required by 802.11 devices to associate and disassociate–It is in the order of hundreds of milliseconds•Support voice over wireless LAN (VoWLAN) in a business environment with multiple access points–802.11 standard needs a way to provide quicker handoffs•802.11 MAC protocol–Does not allow a device to find out if the necessary QoS resources... shift keying (BPSK) 7U-NII Frequency Band (continued)•Channel allocation–With 802.11b, the available frequency spectrum is divided into 11 channels in the United States•Only three non-overlapping channels are available for simultaneous operation–In 802.11a, eight frequency channels operate simultaneously•In the Low Band (5.15 to 5.25 GHz) and Middle Band (5.25 to 5.35 GHz)•Within each... frequency band–More transmission channels–Its multiplexing technique–A more efficient error-correction scheme 19IEEE 802.11n•Aimed at providing data rates higher than 100 Mbps using the 2.4 GHz ISM band•Bonds two 802.11 2.4 GHz ISM channels together –Uses OFDM to send two data streams at 54 Mbps•Implements multiple-in, multiple-out (MIMO) technology–Uses multiple antennas and also... two mandatory transmission modes along with two optional modes•Mandatory transmission modes–Same mode used by 802.11b and must support the rates of 1, 2, 5.5, and 11 Mbps–Same OFDM mode used by 802.11a but in the same frequency band used by 802.11b•Number of channels available with 802.11g is three–Compared with eight channels for 802.11a . Wireless CommunicationsHigh-Speed WLANs and WLAN Security 2Objectives•Describe how IEEE 802.11a networks function and how they differ from 802.11. into four bands–Each band has a maximum power limit•Outside the United States–5 GHz band is allocated to users and technologies other than WLANs 5U-NII
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