High-Speed WLANs and WLAN Security

High-Speed WLANs and WLAN Security

Wireless Communications

High-Speed WLANs and WLAN

Security

Objectives

• 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 networks

IEEE 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 scheme

U-NII Frequency Band

• IEEE 802.11a uses the Unlicensed National

Information Infrastructure (U-NII) band

– Intended for devices that provide short-range, speed wireless digital communications

high-• 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 WLANs

U-NII Frequency Band (continued)

U-NII Frequency Band (continued)

U-NII Frequency Band (continued)

U-NII Frequency Band (continued)

Orthogonal 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 channels

– 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

Orthogonal Frequency Division

Multiplexing (continued)

Orthogonal Frequency Division

Multiplexing (continued)

Orthogonal Frequency Division

Multiplexing (continued)

IEEE 802.11g

• Specifies that it operates in the same frequency

band as 802.11b

802.11g 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 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

802.11g PHY Layer (continued)

• When both 802.11b and 802.11g devices share the same network

– Standard defines how the frame header is transmitted

Other WLAN Standards

• Future of WLANs will include:

– Additional standards that are currently under

development by the IEEE

– New standards that are just beginning to appear in new equipment

IEEE 802.11e

• Approved for publication in November 2005

• Defines enhancements to the MAC layer of 802.11

– To expand support for LAN applications that require Quality of Service (QoS)

• 802.11e allows the receiving device to acknowledge after receiving a burst of frames

• Enables prioritization of frames in distributed

coordinated function (DCF) mode

IEEE 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 uses the reflected signals (multipath)

• To extend the range of the WLAN

• Interference with other WLANs can be a big problem

IEEE 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 are available at a new AP

• 802.11r is designed to resolve these issues

– In addition to security concerns regarding the handoff

• 802.11r is expected to enhance the convergence of wireless voice, data, and video

– Connect the wireless APs to each other over the

wireless communications channels

• 802.11s will provide the solution when it is ratified by the IEEE

– Which is expected to happen in 2008

Summary

• 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, eight frequency channels can operate

• The 802.11a standard made changes only to the

physical layer (PHY layer)

– Of the original 802.11 and 802.11b standard

• 802.11g preserves the features of 802.11b but

increases the data transfer rates to those of 802.11a

• 802.11e standard adds QoS to 802.11 standards

Summary (continued)

• 802.11n is a proposed standard that will increase the speed of WLANs to 108 Mbps

• 802.11r is a proposed standard for fast roaming

• HiperLAN/2 is a high-speed WLAN specification

that is similar to the IEEE 802.11a