wireless lans part 2 justin champion room c208 - tel: 3273

Wireless LANS Wireless LANS Part 2Part 2

Justin ChampionJustin ChampionRoom C208 - Tel: 3273Room C208 - Tel: 3273

www.staffs.ac.uk/personal/engineering_and_technology/jjc1www.staffs.ac.uk/personal/engineering_and_technology/jjc1

Wireless LANSWireless LANS

ContentsContents SpeedSpeed HIPERLANHIPERLAN Wi-FiWi-Fi Issues with radio communicationsIssues with radio communications


SpeedSpeed Measure in bits per second (bps)Measure in bits per second (bps) Kilo (Kbps)Kilo (Kbps)

1000 bits per second1000 bits per second MegaMega

1000 Kbps1000 Kbps Giga (Gbps)Giga (Gbps)

1000 Mbps1000 Mbps Terra (Tbps)Terra (Tbps)

1000 Gbps1000 Gbps Limited optical networks work at this speed and certainly Limited optical networks work at this speed and certainly

nothing which is wirelessnothing which is wireless Remember that in data transfer a Kilo = 1000 not the Remember that in data transfer a Kilo = 1000 not the

1024 used for data storage1024 used for data storage


HIPERLANHIPERLAN HIgh PERformance Local Area NetworkHIgh PERformance Local Area Network

HIPERLAN 1HIPERLAN 1 20 Mbps20 Mbps

HIPERLAN 2HIPERLAN 2 54 Mbps54 Mbps

Developed by ETSIDeveloped by ETSI European Telecommunication Standards InstituteEuropean Telecommunication Standards Institute

Wireless LANSWireless LANS Common termsCommon terms

ThroughputThroughput Is how much data is passing through a network in a Is how much data is passing through a network in a

given timegiven time

BandwidthBandwidth Is the amount of data that could be transferred in a Is the amount of data that could be transferred in a

given timegiven time

Wireless LANSWireless LANS HIPERLAN 2HIPERLAN 2

FeaturesFeatures QOSQOS Power Saving built into the technologyPower Saving built into the technology Operates in the 5 GHz rangeOperates in the 5 GHz range Strong Security using per session keys or long term key Strong Security using per session keys or long term key

usageusage DES or Triple-DES usedDES or Triple-DES used

Increased Throughput over other wireless technologiesIncreased Throughput over other wireless technologies Allows convergence with other backbone technologiesAllows convergence with other backbone technologies

ATM – This was originally the primary use of this technologyATM – This was originally the primary use of this technology EthernetEthernet 3G3G


Why is HIPERLAN 2 good?


Central ControlCentral Control This is referred to as the Access Point (AP)This is referred to as the Access Point (AP) Responsible forResponsible for

Allows packets to be sent from a backbone to the Allows packets to be sent from a backbone to the wireless devicewireless device

Informs devices which frequency to operate onInforms devices which frequency to operate on This allows for the optimum frequency to be selected, based This allows for the optimum frequency to be selected, based

on what else is happening with the interfaceon what else is happening with the interface

Each channel will be divided by 20 MHz giving 19 Each channel will be divided by 20 MHz giving 19 channelschannels

Each of the channels will be divided into 52 sub carriersEach of the channels will be divided into 52 sub carriers 48 of these are usable for data the other 4 are for 48 of these are usable for data the other 4 are for

synchronizationsynchronization


CommunicationsCommunications Multicast and Broadcast are supportedMulticast and Broadcast are supported Communications are connection orientatedCommunications are connection orientated

This gives a short setup time for communications to This gives a short setup time for communications to take placetake place

Movement within the network is allowedMovement within the network is allowed A device which recognises a stronger signal form A device which recognises a stronger signal form

another AP will connect to that APanother AP will connect to that AP All connections will be moved from the 1All connections will be moved from the 1stst AP to the AP to the

22ndnd.. During this process packets may be lost and the application During this process packets may be lost and the application

must request them again.must request them again.


HIPERLAN 2 LayersHIPERLAN 2 Layers

Physical

Data Link Control Layer

Convergence Layer

Higher OSI Layers

Wireless LANSWireless LANS PhysicalPhysical

Different encoding methods used for different ratesDifferent encoding methods used for different rates If the signal to noise ratio becomes higher a lower transmission If the signal to noise ratio becomes higher a lower transmission

speed will be selectedspeed will be selected

ModeMode ModulationModulation Code RateCode Rate Bit Rate MbpsBit Rate Mbps

11 BPSKBPSK ¾ ¾ 66

22 BPSKBPSK ¾ ¾ 99

33 QPSKQPSK ½ ½ 1212

44 QPSKQPSK ¾ ¾ 1818

55 16QAM16QAM 9/16 9/16 2727

66 16QAM16QAM ¾¾ 3636

77 64QAM64QAM ¾¾ 5454


Data transferred in several different sub carriersData transferred in several different sub carriers Referred to as Referred to as

Orthogonal Frequency Division Multiplex (OFDM)Orthogonal Frequency Division Multiplex (OFDM) The original bit pattern is re assembled at the destinationThe original bit pattern is re assembled at the destination

This technique allowsThis technique allows Better error handlingBetter error handling Reduction of multi-path propagationReduction of multi-path propagation

Multi-Path PropagationMulti-Path Propagation When a signal is sent it may bounce off several items before getting When a signal is sent it may bounce off several items before getting

to the receiverto the receiver Indicating that the same signal can be received more than once or at Indicating that the same signal can be received more than once or at

a time when it would cause a corruption of a packeta time when it would cause a corruption of a packet The further the distance travelled for the signal the higher the likely The further the distance travelled for the signal the higher the likely

hood of this happening.hood of this happening.


PhysicalPhysical Encoding the bits for transmissionEncoding the bits for transmission Binary Phase Shift Keying (BPSK)Binary Phase Shift Keying (BPSK)

Any change in the carrier wave indicates a 1 else 0Any change in the carrier wave indicates a 1 else 0

The less data encoded the less chance there is of The less data encoded the less chance there is of errorerror

Carrier

BPSK


QPSKQPSK Quadrature Phase Shirt KeyingQuadrature Phase Shirt Keying

Allows for streams of data to be encoded into the carrier waveAllows for streams of data to be encoded into the carrier wave Shifts the carrier by either 90 or 180 degreesShifts the carrier by either 90 or 180 degrees

16 QAM16 QAM Quadtrative Amplitude ModulationQuadtrative Amplitude Modulation By using Phase shifting and Amplitude changes encodes 4 bits at onceBy using Phase shifting and Amplitude changes encodes 4 bits at once

64 QAM64 QAM Same as 16 QAM but encoding 6 bitsSame as 16 QAM but encoding 6 bits

bb.watch.impress.co.jp/column/infra/2001/09/26/16qam.gif


Data Link Control LayerData Link Control Layer Responsible forResponsible for

MAC Access controlMAC Access control Responsible for the sharing of the radio linkResponsible for the sharing of the radio link Minimising the amount of time the link is requiredMinimising the amount of time the link is required Ultimately the responsibility of this is controlled by the access pointUltimately the responsibility of this is controlled by the access point

Logical Link ControllerLogical Link Controller Carried out error detectionCarried out error detection Retransmission of lost packetsRetransmission of lost packets Forward Error recovery FEC, with a number of redundant bits sent Forward Error recovery FEC, with a number of redundant bits sent

it is possible to recover small amounts of corrupted datait is possible to recover small amounts of corrupted data HIPERLAN uses Reed Solomon codes to carry this outHIPERLAN uses Reed Solomon codes to carry this out

Essential on a unreliable interface like radioEssential on a unreliable interface like radio


Convergence LayerConvergence Layer Adapts data sent from a lower/higher layer to Adapts data sent from a lower/higher layer to

the correct format.the correct format. This layer is the reason why HIPERLAN, is This layer is the reason why HIPERLAN, is

able to communicate with other technologiesable to communicate with other technologies As in transfer data fromAs in transfer data from

ATM – Cell based convergenceATM – Cell based convergence Ethernet – Packet based convergenceEthernet – Packet based convergence 3G - Packet based convergence3G - Packet based convergence


Transmission MediumTransmission Medium Uses Time Division duplexUses Time Division duplex

Transmission Packet FormatTransmission Packet Format Each packet which is transferred is a defined Each packet which is transferred is a defined

size of 2 ms in lengthsize of 2 ms in length


Transmission Packet FormatTransmission Packet Format

Mac Frame Mac Frame Mac Frame Mac Frame

BCH FCH ACH DL Phase UL Phase RCH’s

2 ms

Wireless LANSWireless LANS Transmission Packet FormatTransmission Packet Format

Broadcast Channel (BCH)Broadcast Channel (BCH) Transmission PowerTransmission Power Starting point of the FCH and lengthStarting point of the FCH and length Starting point and Length RCHStarting point and Length RCH Identifier for the AP and networkIdentifier for the AP and network

Frame Control Channel (FCH)Frame Control Channel (FCH) Description of how transmit and receive resources are allocated in this Description of how transmit and receive resources are allocated in this

frameframe Access Feedback Channel (ACH)Access Feedback Channel (ACH)

Give information on previous attempts at accessing the RCHGive information on previous attempts at accessing the RCH Downlink (DL) Phase & Uplink (UL) PhaseDownlink (DL) Phase & Uplink (UL) Phase

Allows the transmission/receipt of packets of 54 bytes in sizeAllows the transmission/receipt of packets of 54 bytes in size Random Access Channel (RCH)Random Access Channel (RCH)

Used to request transmission resources – uplink and downlinkUsed to request transmission resources – uplink and downlink Transmission at this time takes place based on the fact that nothing Transmission at this time takes place based on the fact that nothing

else is transmittingelse is transmitting


Summary of HIPERLANSummary of HIPERLAN Quality of service is given by controlling the amount of Quality of service is given by controlling the amount of

transmissionstransmissions Each device must request permission to transmit or receiveEach device must request permission to transmit or receive

This is given on the basis of the quality of service requiredThis is given on the basis of the quality of service required

IssuesIssues Expensive at the moment due to the radio technologyExpensive at the moment due to the radio technology Not widely availableNot widely available

FutureFuture HiperManHiperMan

High speed access on a metropolitan wide basisHigh speed access on a metropolitan wide basis HiperPanHiperPan

High speed access on a personal basisHigh speed access on a personal basis


Wireless Fidelity (Wi-Fi)Wireless Fidelity (Wi-Fi) Is a generic name for a set of IEEE standards namelyIs a generic name for a set of IEEE standards namely

IEEE 802.11IEEE 802.11 IEEE 802.11AIEEE 802.11A IEEE 802.11BIEEE 802.11B IEEE 802.11GIEEE 802.11G

Any product with this logo is able to interoperate with Any product with this logo is able to interoperate with each othereach other

The products are certified by the Wi-Fi AllianceThe products are certified by the Wi-Fi Alliance


StandardsStandards IEEE 802.11AIEEE 802.11A

54 Mbps54 Mbps 5 GHz range5 GHz range Modulation OFDMModulation OFDM

IEEE 802.11BIEEE 802.11B 11 Mbps11 Mbps 2.4 GHz Range2.4 GHz Range Modulation of DSSSModulation of DSSS

IEEE 802.11GIEEE 802.11G 20 Mbps20 Mbps 2.4 GHz Range2.4 GHz Range Modulation of OFDMModulation of OFDM


Frequency 2.4 GHzFrequency 2.4 GHz More commonly known as the ISM bandMore commonly known as the ISM band

Industrial Scientific Medical (ISM)Industrial Scientific Medical (ISM) Intended as worldwide free usage radio bandIntended as worldwide free usage radio band

No license requiredNo license required

Widely used forWidely used for Wireless LAN technologyWireless LAN technology

Actual usage will differ between countriesActual usage will differ between countries Usage must be none commercialUsage must be none commercial Same frequency asSame frequency as

Microwave OvensMicrowave Ovens Cordless PhonesCordless Phones Other wireless DevicesOther wireless Devices


Wireless Fidelity (Wi-Fi)Wireless Fidelity (Wi-Fi) OperatesOperates

In the same manner as the Ethernet networksIn the same manner as the Ethernet networks A device waits for silence on the radio frequencyA device waits for silence on the radio frequency

Carrier Sense Multiple Access (CSMA)Carrier Sense Multiple Access (CSMA)

Operates in Operates in AD-Hoc mode orAD-Hoc mode or Uses a Access point (AP) to allow connection to wired Uses a Access point (AP) to allow connection to wired

infrastructureinfrastructure


Wireless Fidelity (Wi-Fi)Wireless Fidelity (Wi-Fi)

CSMA RTS

CTS

Data

ACK

Access Point

RTS = Request to Send

CTS = Clear to Send

Data =

ACK = Acknowledgment

Wireless LANSWireless LANS Wi-Fi 802.11b transmissionsWi-Fi 802.11b transmissions

Carried out using Direct Sequence Spread Spectrum Carried out using Direct Sequence Spread Spectrum (DSSS)(DSSS) The original signal is combined with a Pseudo random Number The original signal is combined with a Pseudo random Number

(Code Word)(Code Word) The code word is referred to as the Baker CodeThe code word is referred to as the Baker Code This allows improved reliability in data transmission rather than just This allows improved reliability in data transmission rather than just

sending data.sending data. A wider bandwidth is required for the transmissionA wider bandwidth is required for the transmission

Each part of the packet is then sent on a different frequencyEach part of the packet is then sent on a different frequency Total required bandwidth is 22 MHzTotal required bandwidth is 22 MHz

The receiver puts this information back together againThe receiver puts this information back together again This method is used due to the ability to send large amounts of This method is used due to the ability to send large amounts of

data at oncedata at once

Wireless LANSWireless LANS Wi-FI Data PacketWi-FI Data Packet

Only the Data part is sent at full speedOnly the Data part is sent at full speed The rest is sent at 1 MbpsThe rest is sent at 1 Mbps

Wireless LANSWireless LANS Wi-FiWi-Fi

Wired Equivalent Privacy (WEP)Wired Equivalent Privacy (WEP) Uses either 40 or 128 bit RS4 symmetric encryptionUses either 40 or 128 bit RS4 symmetric encryption

The standard does not define how to distribute the keys!The standard does not define how to distribute the keys! Discussion of cracking the encryption algorithm real-time!Discussion of cracking the encryption algorithm real-time!

http://www.isaac.cs.berkeley.edu/isaac/wep-faq.htmlhttp://www.isaac.cs.berkeley.edu/isaac/wep-faq.html, 2003), 2003) When used 40 Bit encryption reduces throughput by 20%When used 40 Bit encryption reduces throughput by 20%

Trying to avoid the Pringle situation, which was embarrassing for the Trying to avoid the Pringle situation, which was embarrassing for the technology and users of ittechnology and users of it

news.bbc.co.uk/1/hi/sci/tech/1860241.stmnews.bbc.co.uk/1/hi/sci/tech/1860241.stm, 2002), 2002) War Driving, users accessing wireless networks without permissionWar Driving, users accessing wireless networks without permission Wi-Fi is targeted with wall chalking indicating locations to connectWi-Fi is targeted with wall chalking indicating locations to connect

The technology is targeted as it is widely used and availableThe technology is targeted as it is widely used and available Radio Signal PropagationRadio Signal Propagation

Radio signals can not be restricted to a geographic area without Radio signals can not be restricted to a geographic area without expensive specially built buildingsexpensive specially built buildings

Wireless LANSWireless LANS Wi-FiWi-Fi

Wireless LANSWireless LANS Wi-Fi - FutureWi-Fi - Future

IEEE 802.16 (WiMax) IEEE 802.16 (WiMax) 802.16a is intended as a wireless metropolitan technology802.16a is intended as a wireless metropolitan technology First devices should be appearing in Late 2004First devices should be appearing in Late 2004 Allows 120 MbpsAllows 120 Mbps Uses the 10 to 66 GHz frequencyUses the 10 to 66 GHz frequency

This will require no interference, so transmitters and receivers will This will require no interference, so transmitters and receivers will need to be placed on the roofneed to be placed on the roof

Transmission up to 30 MilesTransmission up to 30 Miles Currently a limit on receivers which is the hundredsCurrently a limit on receivers which is the hundreds

Standards GroupStandards Group grouper.ieee.org/groups/802/16/index.htmlgrouper.ieee.org/groups/802/16/index.html


SummarySummary HiperLan2HiperLan2 ISMISM Wi-fiWi-fi

wireless lans part 2 justin champion room c208 - tel: 3273

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