Wireless LANS Part 2 Justin Champion Room C208 - Tel: 3273 .
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Transcript of 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
Wireless LANSWireless LANS
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
Wireless LANSWireless LANS
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
Wireless LANSWireless LANS
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
Wireless LANSWireless LANS
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.
Wireless LANSWireless LANS
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
Wireless LANSWireless LANS PhysicalPhysical
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.
Wireless LANSWireless LANS
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
Wireless LANSWireless LANS PhysicalPhysical
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
Wireless LANSWireless LANS
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
Wireless LANSWireless LANS
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
Wireless LANSWireless LANS
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
Wireless LANSWireless LANS
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
Wireless LANSWireless LANS
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 LANSWireless LANS
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
Wireless LANSWireless LANS
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
Wireless LANSWireless LANS
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 LANSWireless LANS
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 LANSWireless LANS
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-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