Fundamentals of Wireless Fundamentals of Wireless LANsLANs

Module 2Module 2

802.11 and Network Interface 802.11 and Network Interface CardsCards

ObjectivesObjectives

Identify the IEEE 802. standards.Identify the IEEE 802. standards. Identify the IEEE 802.11 standards.Identify the IEEE 802.11 standards.Understand the MAC and PHY layers of Understand the MAC and PHY layers of

802.11802.11Identify which client operating systems Identify which client operating systems

are supported.are supported.Determine the status of a client card by Determine the status of a client card by

observing the indicator lights.observing the indicator lights.Install and configure a Cisco Aironet PC Install and configure a Cisco Aironet PC

Card.Card.

802.11 Standards802.11 Standards 802.11a:802.11a: 5GHz, 54Mbps5GHz, 54Mbps 802.11b:802.11b: 2.4GHz, 11Mbps2.4GHz, 11Mbps 802.11d:802.11d: Multiple regulatory domains Multiple regulatory domains 802.11e:802.11e: Quality of Service (QoS)Quality of Service (QoS) 802.11f:802.11f: Inter-Access Point Protocol (IAPP)Inter-Access Point Protocol (IAPP) 802.11g:802.11g: 2.4GHz, 54Mbps2.4GHz, 54Mbps 802.11h:802.11h: Dynamic Frequency Selection (DFS) Dynamic Frequency Selection (DFS)

and and Transmit Power Control (TPC)Transmit Power Control (TPC) 802.11i:802.11i: SecuritySecurity 802.11j:802.11j: Japan 5GHz Channels (4.9-5.1 GHz)Japan 5GHz Channels (4.9-5.1 GHz) 802.11k:802.11k: MeasurementMeasurement 802.11m:802.11m: MaintenanceMaintenance 802.11n:802.11n: High-SpeedHigh-Speed

IEEE Standards for WLANsIEEE Standards for WLANs

802.11 standard is for WLANs and represent a family of 802.11 standard is for WLANs and represent a family of protocols that specify connectivity for fixed, portable, and protocols that specify connectivity for fixed, portable, and moving stations in a LANmoving stations in a LAN

802.11802.11 802.11b802.11b 802.11a802.11a 802.11g802.11g

802.15 provides the standards for Wireless Personal Area 802.15 provides the standards for Wireless Personal Area Network (WPAN)Network (WPAN)

802.16 provides the standards for Broadband Wireless 802.16 provides the standards for Broadband Wireless AccessAccess

802.11 and OSI Layers802.11 and OSI Layers

802.11 standards operate at the following layers 802.11 standards operate at the following layers of the OSI modelof the OSI model

Data link layer (Layer 2) Data link layer (Layer 2) Physical Layer (Layer 1)Physical Layer (Layer 1)

Purpose of the standards are to provide wireless Purpose of the standards are to provide wireless connectivity to automate rapid deployment ofconnectivity to automate rapid deployment of

Portable unitsPortable units Handheld unitsHandheld units Mounted units (on moving vehicles)Mounted units (on moving vehicles)

MAC ServicesMAC Services

802.11 standard focuses on the bottom two levels of the OSI model: PHY and Data link

IEEE 802.2 LLCIEEE 802.2 LLC

The Logical Link Control (LLC) is the The Logical Link Control (LLC) is the highest layer of the IEEE 802 reference highest layer of the IEEE 802 reference model model

LLC provides the following servicesLLC provides the following services

Unacknowledged connectionless servicesUnacknowledged connectionless services

Acknowledged connection-oriented servicesAcknowledged connection-oriented services

Acknowledged connectionless servicesAcknowledged connectionless services

IEEE 802.11 Logical IEEE 802.11 Logical ArchitectureArchitecture

IEEE 802.11 architecture consist of several IEEE 802.11 architecture consist of several componentscomponents

Basic Services Set (BSS)Basic Services Set (BSS)

Independent BSS (IBSS)Independent BSS (IBSS)

Distribution System (DS)Distribution System (DS)

Extended Services Set (ESS)Extended Services Set (ESS)

Basic Services Set (BSS)Basic Services Set (BSS)

Independent Basic Service Set Independent Basic Service Set (IBSS)(IBSS)

Extended Service Set (ESS) and Extended Service Set (ESS) and Distributed System (DS)Distributed System (DS)

Coverage may overlap to provide roaming capabilities

WLAN Security ServicesWLAN Security Services Security services in IEEE 802.11 are provided by the Security services in IEEE 802.11 are provided by the

Authentication servicesAuthentication services Wireless Equivalent Privacy (WEP) mechanismWireless Equivalent Privacy (WEP) mechanism

Scope of WEB security services provided is limited to Scope of WEB security services provided is limited to station-station data exchangestation-station data exchange

WEP implementations encrypt the MAC service data units WEP implementations encrypt the MAC service data units (MSDU)(MSDU)

WEP is viewed as a logical layer service located within the WEP is viewed as a logical layer service located within the MAC sublayer and designed to meet the following security MAC sublayer and designed to meet the following security goalsgoals

ConfidentialityConfidentiality Data integrityData integrity Access controlAccess control

MAC Access MethodsMAC Access Methods

Before gaining access to the medium, a station (STA) can Before gaining access to the medium, a station (STA) can use one of two methodsuse one of two methods

The fundamental access method of the IEEE 802.11 is carrier The fundamental access method of the IEEE 802.11 is carrier sense multiple access with collision avoidance (CSMA/CA)sense multiple access with collision avoidance (CSMA/CA)

For WLANs this is known as the Distributed Coordination Function For WLANs this is known as the Distributed Coordination Function (DFC)(DFC)

Used within both ad hoc and infrastructure network configurationsUsed within both ad hoc and infrastructure network configurations

An optional access method IEEE corporate is the Point An optional access method IEEE corporate is the Point Coordination Function (PCF)Coordination Function (PCF)

Creates contention free (CF) accessCreates contention free (CF) access Used only within infrastructure configurationsUsed only within infrastructure configurations

Coexistence of DCF and Coexistence of DCF and PCFPCF

DCF and PCF can both operate concurrently in the DCF and PCF can both operate concurrently in the same BSS with the two access methods same BSS with the two access methods alternatingalternating

First the CD period First the CD period Followed by a contention periodFollowed by a contention period

All frame transmissions under the PCF use an All frame transmissions under the PCF use an interframe space (IFS) smaller than that of a DCFinterframe space (IFS) smaller than that of a DCF

The use of smaller IFS for PCF implies a priority The use of smaller IFS for PCF implies a priority for point-coordination traffic over stations for point-coordination traffic over stations operating in DCF modeoperating in DCF mode

802.11 PHY Functional 802.11 PHY Functional EntitiesEntities

High Rate PHY Modulation High Rate PHY Modulation Formats and Data RatesFormats and Data Rates

Four modulation formats and data rates specified for Four modulation formats and data rates specified for the High Rate PHYthe High Rate PHY

Differential binary phase shift keying (DBPSK) modulation for 1 Differential binary phase shift keying (DBPSK) modulation for 1 MbpsMbps

Packet binary convolutional coding (PBCC) mode for enhanced Packet binary convolutional coding (PBCC) mode for enhanced performanceperformance

Differential quadrature phase shift keying (DQPSK) modulation Differential quadrature phase shift keying (DQPSK) modulation for 2 Mbpsfor 2 Mbps

Complementary code keying (CCK) modulation scheme for 5.5 Complementary code keying (CCK) modulation scheme for 5.5 Mbps and 11 MbpsMbps and 11 Mbps

CCK BenefitsCCK Benefits

One benefit of the CCK modulation method is that it One benefit of the CCK modulation method is that it

Is capable of increasing the 802.11b standard’s data rate from Is capable of increasing the 802.11b standard’s data rate from 2 Mbps to 11 Mbps2 Mbps to 11 Mbps

This is accomplished while continuing to use DQPSK by:This is accomplished while continuing to use DQPSK by:

Increasing the data rate from 1 Mbps to 1.375 MbpsIncreasing the data rate from 1 Mbps to 1.375 Mbps

Taking data in 8-bit blocks (8*1.375=11)Taking data in 8-bit blocks (8*1.375=11)

Six of the 8-bits are eight chips long and clocked at 11 Mbps Six of the 8-bits are eight chips long and clocked at 11 Mbps and used to choose 1 to 64 complimentary codesand used to choose 1 to 64 complimentary codes

The other 2 bits are combined with the code in the DQPSKThe other 2 bits are combined with the code in the DQPSK

Orthogonal Frequency Orthogonal Frequency Division Multiplexing (OFDM)Division Multiplexing (OFDM) OFDM is a method used in the 802.11a standardOFDM is a method used in the 802.11a standard

A technique that divides a communication channel into a number of A technique that divides a communication channel into a number of equally-spaced frequency bands and reduces multipath interferenceequally-spaced frequency bands and reduces multipath interference

Uses multiple subcarriers of which there are 52, spaced 312.5 KHz apartUses multiple subcarriers of which there are 52, spaced 312.5 KHz apart

Data is sent on 48 carriers simultaneously, Data is sent on 48 carriers simultaneously,

Each carrier carries a portion of the user dataEach carrier carries a portion of the user data

Four subcarriers used as pilots where each subcarrier is orthogonal Four subcarriers used as pilots where each subcarrier is orthogonal (independent) of each other(independent) of each other

The time to transmit each bit increases in proportion to the number of The time to transmit each bit increases in proportion to the number of carrierscarriers

North American 802.11bNorth American 802.11b

There are three non-overlapping IEEE 802.11b There are three non-overlapping IEEE 802.11b High Rate operating channel used in North High Rate operating channel used in North American and operating between 2400 MHz and American and operating between 2400 MHz and 2483 MHz frequency range2483 MHz frequency range

Channel 1 at 2412 MHzChannel 1 at 2412 MHz

Channel 6 at 2437 MHzChannel 6 at 2437 MHz

Channel 11 at 2452 MHzChannel 11 at 2452 MHz

Frequency Range of Frequency Range of OperationOperation

Products conforming to the 802.11a standard have a Products conforming to the 802.11a standard have a

Data Rate of 54 MbpsData Rate of 54 Mbps

Operate in a frequency range of 5 GHzOperate in a frequency range of 5 GHz

Benefits of using 5 GHz spectrum is offset by its lack of Benefits of using 5 GHz spectrum is offset by its lack of backwards compatibility with 802.11b (2.4 GHz)backwards compatibility with 802.11b (2.4 GHz)

Due to the mismatched frequencies of 802.11a and 802.11b Due to the mismatched frequencies of 802.11a and 802.11b frequenciesfrequencies

Vendors are producing products that contain two radios, for Vendors are producing products that contain two radios, for both the 2.4 and 5 GHz rangeboth the 2.4 and 5 GHz range

802.11g Standard for 802.11g Standard for WLANsWLANs

Major advantages of 802.11g Major advantages of 802.11g

Achieves a data rates up to 54 Mbps in Achieves a data rates up to 54 Mbps in the 2.4 frequency rangethe 2.4 frequency range

Provides interoperability among and Provides interoperability among and between all WLAN seeds working at the between all WLAN seeds working at the 2.4 GHz2.4 GHz

Eliminates the need for a complete Eliminates the need for a complete equipment upgradeequipment upgrade

Infrared PHYInfrared PHY

IR PHY operate in indoor environments onlyIR PHY operate in indoor environments only

Uses near-visible light in the 850-nm to 950-nm Uses near-visible light in the 850-nm to 950-nm signaling rangesignaling range

Does not require a clear line of sight between the Does not require a clear line of sight between the receiver and transmitterreceiver and transmitter

IR PHY does not pass through walls therefore the IR PHY does not pass through walls therefore the signal is attenuated passing through most interior signal is attenuated passing through most interior windowswindows

Cisco Aironet Wireless Cisco Aironet Wireless AdaptersAdapters

Also known as client adapters and are Also known as client adapters and are radio modules that provide wireless data radio modules that provide wireless data communication betweencommunication between

Fixed portable or mobile devicesFixed portable or mobile devices

Other wireless devices Other wireless devices

Transfer of data packets through the wireless Transfer of data packets through the wireless infrastructureinfrastructure

Installing Client AdaptersInstalling Client Adapters After physically installing a Cisco Aironet adapter the correct After physically installing a Cisco Aironet adapter the correct

driver is required for functionality of the carddriver is required for functionality of the card

The Operating System that can support the Aironet drivers must The Operating System that can support the Aironet drivers must be consideredbe considered

Drivers are provided with the client adapter for Windows 95, 98, ME, Drivers are provided with the client adapter for Windows 95, 98, ME, NT, 2000, XP, Windows CE 2.x, 3.x, and 4.xNT, 2000, XP, Windows CE 2.x, 3.x, and 4.x

Drivers for ME, 2000, and XP are also included on the Windows install Drivers for ME, 2000, and XP are also included on the Windows install CDCD

Cisco Aironet offers support for Linux and Macintosh as wellCisco Aironet offers support for Linux and Macintosh as well

The best way to obtain specific software drivers is to download them The best way to obtain specific software drivers is to download them from the CCO sitefrom the CCO site