© university of new hampshire interoperability laboratory wireless networking overview january 2006

© UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY

Wireless NetworkingWireless NetworkingOverviewOverview

January 2006

UNIVERSITY of NEW HAMPSHIRE

INTEROPERABILITY LABORATORY

Wireless Overview2

Presentation Goals:Presentation Goals:Presentation Goals:Presentation Goals:• What is 802.11 Wireless Networking • WLAN Past and Present

– 802.11b, 802.11a, 802.11g, WEP

• Future of WLAN– Enhanced Security (802.11i) – QoS (802.11e)– Mesh Networking (802.11s)– WAVE (802.11p)– High Speed (802.11n)

• Other types of wireless networking (WANs, MANs, PANs)

• What is 802.11 Wireless Networking • WLAN Past and Present

– 802.11b, 802.11a, 802.11g, WEP

• Future of WLAN– Enhanced Security (802.11i) – QoS (802.11e)– Mesh Networking (802.11s)– WAVE (802.11p)– High Speed (802.11n)

• Other types of wireless networking (WANs, MANs, PANs)



Wireless Overview3

The 802 Wireless SpaceThe 802 Wireless SpaceThe 802 Wireless SpaceThe 802 Wireless Space

Data Rate (Mbps)

Ran

ge

ZigBee802.15.4 802.15.3

802.15.3a802.15.3c

WPAN

WLAN

WMAN

WWAN

WiFi802.11

0.01 0.1 1 10 100 1000

Bluetooth802.15.1

IEEE 802.22

WiMaxIEEE 802.16

IEEE 802.20

Courtesy of Zigbee Alliance



Wireless Overview4

What is Wireless networking?What is Wireless networking?What is Wireless networking?What is Wireless networking?

• A Wireless Local Area Network (WLAN) is a type of local-area network that uses high-frequency radio waves rather than wires to communicate between nodes. WLAN is a flexible data communication system used as an alternative to, or an extension of a wired LAN.



Wireless Overview5

What are 802.11 WLANs?What are 802.11 WLANs?What are 802.11 WLANs?What are 802.11 WLANs?

• 802.11 is the part of the IEEE LMSC that defines wireless LAN networking

• First 802.11 wireless networks started showing up in the 90’s

• Designed to connect in different way depending on environment

– Stations can connect directly to one another (Ad-Hoc)

– Stations can connect to Access Points (APs) to gain access to other networks

• 802.11 is the part of the IEEE LMSC that defines wireless LAN networking

• First 802.11 wireless networks started showing up in the 90’s

• Designed to connect in different way depending on environment

– Stations can connect directly to one another (Ad-Hoc)

– Stations can connect to Access Points (APs) to gain access to other networks



Wireless Overview6

What is unique about wireless?What is unique about wireless?

• Difficult media– interference and noise– quality varies over

space and time– shared with “unwanted”

wireless devices– shared with non-802

devices (unlicensed spectrum, microwave ovens)

• Full connectivity cannot be assumed

– “hidden node” problem• Multiple international

regulatory requirements

• Category 5,6,7 cable– NEXT

– Medium characteristics are very stable

– Most links are switched point-to-point

• Network Capacity – Easier to run more cable

or fiber to expand capacity than to find unused spectrum.

• Category 5,6,7 cable– NEXT

– Medium characteristics are very stable

– Most links are switched point-to-point

• Network Capacity – Easier to run more cable

or fiber to expand capacity than to find unused spectrum.



Wireless Overview7

Regulatory BodiesRegulatory BodiesPolitical and Legal issuesPolitical and Legal issuesRegulatory BodiesRegulatory BodiesPolitical and Legal issuesPolitical and Legal issues• FCC Federal Communications Commission,

Part 15

• Industry Canada, GL36

• ETSI European Telecommunications Standard Institute, ETS300-328, 300-339

• MPHPT Ministry of Public Management, Home Affairs, Post and Telecommunications (Japan)

• FCC Federal Communications Commission, Part 15

• Industry Canada, GL36

• ETSI European Telecommunications Standard Institute, ETS300-328, 300-339

• MPHPT Ministry of Public Management, Home Affairs, Post and Telecommunications (Japan)



Wireless Overview8

Regulatory ApproachesRegulatory ApproachesRegulatory ApproachesRegulatory Approaches

• All unlicensed bands impose power limits

• ISM bands require spread spectrum depending on tx power, but is changing

• UPCS: Isochronous and asynchronous band, each with Spectrum Etiquette (rules regulating access and usage, e.g. Listen Before Talk (LBT))

• UNII bands & Mmwave bands: Minimal regulations e.g. power spectral density limits and emission limits

• All unlicensed bands impose power limits

• ISM bands require spread spectrum depending on tx power, but is changing

• UPCS: Isochronous and asynchronous band, each with Spectrum Etiquette (rules regulating access and usage, e.g. Listen Before Talk (LBT))

• UNII bands & Mmwave bands: Minimal regulations e.g. power spectral density limits and emission limits



Wireless Overview9

Licensed vs Unlicensed SpectrumLicensed vs Unlicensed SpectrumLicensed vs Unlicensed SpectrumLicensed vs Unlicensed Spectrum

•Licensed– Cell phones, police & fire radio, taxi dispatch, etc.

•Unlicensed– Industrial, Scientific, Medical (ISM) bands

• e.g. (900MHz, 2.4GHz, 5.8GHz)

– Unlicensed Personal Communication System•e.g. 1.910-1.920 GHz and 2.390-2.400 GHz

– Unlicensed National Information Infrastructure (UNII) bands•e.g. (5.2GHz)

•Licensed– Cell phones, police & fire radio, taxi dispatch, etc.

•Unlicensed– Industrial, Scientific, Medical (ISM) bands

• e.g. (900MHz, 2.4GHz, 5.8GHz)

– Unlicensed Personal Communication System•e.g. 1.910-1.920 GHz and 2.390-2.400 GHz

– Unlicensed National Information Infrastructure (UNII) bands•e.g. (5.2GHz)



Wireless Overview10

• band f (Hz) λ (m) T (K) comments

• ----- 10+00 10+08 10-11 1 Hz

• radio 10+01 10+07 10-10 AC power, submarine communication

• waves 10+03 10+05 10-08 1 kHz

• 10+05 10+03 10-06 LW radio, 1 km

• 10+06 10+02 10-05 AM radio, 1 MHz

• 10+07 10+01 10-04 SW radio

• 10+08 10+00 10-03 VHF TV & FM radio, UHF TV, 1 m

• 10+09 10-01 10-02 microwave ovens, 1 GHz, radar

• Micro- 10+10 10-02 10-01 radar, 1 cm

• waves 10+11 10-03 10+00 cosmic background, 1 mm

• 10+12 10-04 10+01 1 THz

• infrared 10+13 10-05 10+02 human bodies

• 10+14 10-06 10+03 1 µm, 1 eV

• 10+15 10-07 10+04 solar peak wavelength, 1 PHz

• visible 10+18 10-10 10+07 atomic diameter

• light

• band f (Hz) λ (m) T (K) comments

• ----- 10+00 10+08 10-11 1 Hz

• radio 10+01 10+07 10-10 AC power, submarine communication

• waves 10+03 10+05 10-08 1 kHz

• 10+05 10+03 10-06 LW radio, 1 km

• 10+06 10+02 10-05 AM radio, 1 MHz

• 10+07 10+01 10-04 SW radio

• 10+08 10+00 10-03 VHF TV & FM radio, UHF TV, 1 m

• 10+09 10-01 10-02 microwave ovens, 1 GHz, radar

• Micro- 10+10 10-02 10-01 radar, 1 cm

• waves 10+11 10-03 10+00 cosmic background, 1 mm

• 10+12 10-04 10+01 1 THz

• infrared 10+13 10-05 10+02 human bodies

• 10+14 10-06 10+03 1 µm, 1 eV

• 10+15 10-07 10+04 solar peak wavelength, 1 PHz

• visible 10+18 10-10 10+07 atomic diameter

• light



Wireless Overview11

Common ApplicationsCommon ApplicationsCommon ApplicationsCommon Applications

Technology Frequency FM radio 100 MHz Cordless phones 800 MHz, 2.4GHz, 5.8GHz 802.15.4 (Zigbee) 860 MHz, 915MHz, 2.4GHz Cellphones 900MHz, 1.8GHz, 1.9GHz Satellite radio (XM, Sirius) 2.3 GHz 802.11b/g (Wi-Fi) 2.4GHz 802.15.1 (Bluetooth) 2.4GHz 802.15.3 (WiMedia) 3-11GHz 802.11a (Wi-Fi) 5.1-5.3GHz, 5.8GHz 802.16 (WiMAX) 2-10, 11-66GHz



Wireless Overview12

2.4 GHz Interference2.4 GHz Interference2.4 GHz Interference2.4 GHz Interference

• Micro-wave oven • Bluetooth voice link

• Bluetooth PDA• 802.11b/g WLAN

• HomeRF PC• FHSS Cordless phone

• DSSS• Cordless phone

• Analog video link

• Micro-wave oven • Bluetooth voice link

• Bluetooth PDA• 802.11b/g WLAN

• HomeRF PC• FHSS Cordless phone

• DSSS• Cordless phone

• Analog video link



Wireless Overview13

Contrast to Wired LANsContrast to Wired LANsContrast to Wired LANsContrast to Wired LANs• Allowed packet error rates (PER)

– Ethernet BER = 10-9 (copper), 10-12 (fiber), – 802.11a FER 10% with 1000 byte Packets (equivalent

BER = 1.25x10-5 )

• Data rates– Ethernet 10, 100, 1000, 10000 Mbits/sec– 802.111-54 Mbits/sec– Auto-negotiation vs. Basic & Extended rate sets

• Point-to-point vs. Broadcast medium• CSMA/CD vs CSMA/CA• Security issues • Power drain

• Allowed packet error rates (PER)– Ethernet BER = 10-9 (copper), 10-12 (fiber), – 802.11a FER 10% with 1000 byte Packets (equivalent

BER = 1.25x10-5 )

• Data rates– Ethernet 10, 100, 1000, 10000 Mbits/sec– 802.111-54 Mbits/sec– Auto-negotiation vs. Basic & Extended rate sets

• Point-to-point vs. Broadcast medium• CSMA/CD vs CSMA/CA• Security issues • Power drain



Wireless Overview14

Wired vs. Wireless Data RatesWired vs. Wireless Data RatesWired vs. Wireless Data RatesWired vs. Wireless Data Rates

• Ethernet has auto-negotiation– Link setup as 10, 100, 1000, or 10,000 Mb &

half or full duplex

• 802.11 has basic and extended rate sets– Beacons contain rate sets for basic & extended– 11g may transmit at any of 12 defined rates– 11b (HRDS) uses extended 11& 5.5 Mb rates,

but also uses 1&2 Mb base rates to communicate with legacy devices

• Ethernet has auto-negotiation– Link setup as 10, 100, 1000, or 10,000 Mb &

half or full duplex

• 802.11 has basic and extended rate sets– Beacons contain rate sets for basic & extended– 11g may transmit at any of 12 defined rates– 11b (HRDS) uses extended 11& 5.5 Mb rates,

but also uses 1&2 Mb base rates to communicate with legacy devices



Wireless Overview15

WWANs, WMANs, WLANs, WPANSWWANs, WMANs, WLANs, WPANSWWANs, WMANs, WLANs, WPANSWWANs, WMANs, WLANs, WPANS

• Wide Area Network & Cellular– Ardis, CDPD, 3G,

• Metropolitan Area Network– 802.16, 802.11?

• Local Area Network– 802.11, Hiperlan2, HomeRF, RangeLAN2

• Personal Area Network– 802.15.1 ~ Bluetooth, – 802.15.3 ~ WiMedia , W-USB– 802.15.4 ~ Zigbee– RFID

• Wide Area Network & Cellular– Ardis, CDPD, 3G,

• Metropolitan Area Network– 802.16, 802.11?

• Local Area Network– 802.11, Hiperlan2, HomeRF, RangeLAN2

• Personal Area Network– 802.15.1 ~ Bluetooth, – 802.15.3 ~ WiMedia , W-USB– 802.15.4 ~ Zigbee– RFID



Wireless Overview16

0

10

20

30

40

50

60

70

80

90

100

1 10 100 1000

Range (meters)

Da

ta R

ate

(M

bp

s)

Approximate Data Rate vs. Approximate Data Rate vs. Range for existing devicesRange for existing devicesApproximate Data Rate vs. Approximate Data Rate vs. Range for existing devicesRange for existing devices

WPANs

WLANs

WMANs

WWANs



Wireless Overview17

IEEE 802.11 (WLANs) IEEE 802.11 (WLANs) IEEE 802.11 (WLANs) IEEE 802.11 (WLANs)

• Modulation: BPSK, QPSK, 16QAM, 64QAM– Direct Sequence Spread Spectrum (DSSS)

– Frequency Hopping Spread Spectrum (FHSS)

– Orthogonal Frequency Division Multiplexing (OFDM)

– Multi-Input, Multi-Output (MIMO) systems being discussed in 802.11 Task Group N.

• Data rates up to 56 Mbps, proprietary speeds of 108 Mbps

• Range up to 300 meters

• 2.4 GHz & 5 GHz operating bands

• Marketing group: Wi-Fi Alliance http://www.wi-fi.org

• Modulation: BPSK, QPSK, 16QAM, 64QAM– Direct Sequence Spread Spectrum (DSSS)

– Frequency Hopping Spread Spectrum (FHSS)

– Orthogonal Frequency Division Multiplexing (OFDM)

– Multi-Input, Multi-Output (MIMO) systems being discussed in 802.11 Task Group N.

• Data rates up to 56 Mbps, proprietary speeds of 108 Mbps

• Range up to 300 meters

• 2.4 GHz & 5 GHz operating bands

• Marketing group: Wi-Fi Alliance http://www.wi-fi.org



Wireless Overview18

Medium VariationsMedium Variations

Copyright 1996 IEEECopyright 1996 IEEE

Desk

Doorway



Wireless Overview19

Open System Interconnect (Open System Interconnect (OSIOSI) Model) ModelOpen System Interconnect (Open System Interconnect (OSIOSI) Model) Model

• A framework for Networking• A framework for Networking

Physical

Data Link

Network (TCP/IP)

MAC

Upper Layers (4-7)

End User 1

Physical

Data Link

Network (TCP/IP)

MAC

Upper Layers



Wireless Overview20

Encapsulation of LayersEncapsulation of LayersEncapsulation of LayersEncapsulation of Layers

Data

Physical

Data Link

Network (TCP/IP)

MAC

Upper Layers

FH DS OFDM

Payload IP Hdr

MAC Hdr CRC32 P a y l o a d

PLCP HDR P a y l o a d



Wireless Overview21

802.11 Wireless LAN PHY802.11 Wireless LAN PHY802.11 Wireless LAN PHY802.11 Wireless LAN PHY

• 802.11 – 2.4GHz, 1-2Mbps, DSSS/FHSS/IR

• 802.11a – 5GHz, 6-54Mbps, OFDM

• 802.11b – 2.4GHz, 1-11Mbps, CCK (extension of DSSS) or PBCC (optional)

• 802.11g – 2.4GHz, 1-54Mbps, OFDM or PBCC (optional)

• 802.11n – task group looking at MIMO systems

• 802.11 – 2.4GHz, 1-2Mbps, DSSS/FHSS/IR

• 802.11a – 5GHz, 6-54Mbps, OFDM

• 802.11b – 2.4GHz, 1-11Mbps, CCK (extension of DSSS) or PBCC (optional)

• 802.11g – 2.4GHz, 1-54Mbps, OFDM or PBCC (optional)

• 802.11n – task group looking at MIMO systems



Wireless Overview22

1990 1997 1999 2003 2004 2005 2007 2008

802.

11 b

egun

802.

11 b

ase

stan

dard

2.4G

Hz

2mbi

t FH

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stan

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2.4G

Hz

11M

b H

RD

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802.

11a

stan

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5GH

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OF

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OF

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TG

i (se

curi

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TGn (MIMO)

TG

e (Q

oS)

TGs (Mesh)

802.11 at a Glance802.11 at a Glance802.11 at a Glance802.11 at a Glance



Wireless Overview23

802.11 at 2.4GHz802.11 at 2.4GHz802.11 at 2.4GHz802.11 at 2.4GHz

• Why still an interest in the 2.4GHz band?– Available spectrum worldwide

• Why still an interest in the 2.4GHz band?– Available spectrum worldwide



Wireless Overview24

802.11 at 5.8GHz vs. 2.4GHz802.11 at 5.8GHz vs. 2.4GHz802.11 at 5.8GHz vs. 2.4GHz802.11 at 5.8GHz vs. 2.4GHz

• Currently 12 non-overlapping channels• Fewer non-802.11 interferers• Shorter distances

– less interference with co-located networks– More APs required for same coverage area

• Higher frequency means higher power consumption

• OFDM phy layer nearly identical to Hiperlan2 phy

• Currently 12 non-overlapping channels• Fewer non-802.11 interferers• Shorter distances

– less interference with co-located networks– More APs required for same coverage area

• Higher frequency means higher power consumption

• OFDM phy layer nearly identical to Hiperlan2 phy



Wireless Overview25

2.4 GHz Channel Allocation2.4 GHz Channel Allocation2.4 GHz Channel Allocation2.4 GHz Channel AllocationRegulatory Domains

CHNL_ID Frequency(MHz)

X’10’FCC

X’20’IC

X’30’ETSI

X’31’Spain

X’32France

X’40’Japan

X’41’Japan

1 2412 X X X - - - X

2 2417 X X X - - - X

3 2422 X X X - - - X

4 2427 X X X - - - X

5 2432 X X X - - - X

6 2437 X X X - - - X

7 2442 X X X - - - X

8 2447 X X X - - - X

9 2452 X X X - - - X

10 2457 X X X X X - X

11 2462 X X X X X - X

12 2467 - - X - X - X

13 2472 - - X - X - X

14 2484 - - - - X -



Wireless Overview26

5 GHz Channel Allocation (USA)5 GHz Channel Allocation (USA)5 GHz Channel Allocation (USA)5 GHz Channel Allocation (USA)



Wireless Overview27

802.11a802.11a• 5-GHz band• Uses orthogonal frequency division multiplexing (OFDM)

– Not spread spectrum• Multiple carrier signals at different frequencies• Some bits on each subcarrier

– Similar to FDM but all subcarriers dedicated to single source• Data rates 6, 9, 12, 18, 24, 36, 48, and 54 Mbps• 52 subcarriers modulated using BPSK, QPSK, 16-QAM, or

64-QAM– Depending on rate – Subcarrier frequency spacing 0.3125 MHz– Convolutional code at rate of 1/2, 2/3, or 3/4 provides forward

error correction



Wireless Overview28

1 Mbps & 2 Mbps 802.111 Mbps & 2 Mbps 802.111 Mbps & 2 Mbps 802.111 Mbps & 2 Mbps 802.11

• Barker sequence – 11 chips in length – 1 Mbit = 1 bit sent as

Barker sequence

– 2 Mbit = 2 bits sent using Barker sequence

• Barker sequence – 11 chips in length – 1 Mbit = 1 bit sent as

Barker sequence

– 2 Mbit = 2 bits sent using Barker sequence

+1-1

+1-1 -1 -1 -1 -1+1+1 +1+1+1

Power

Frequency

Power

Frequency

• Signal symbol is spread with a sequence

• Wider Bandwidth

• Less Power DensityBinary AdderModulator(DBPSK orDQPSK)

PPDU

PN CodeCarrier

TransmittedSignal

(+1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1)

(Analog)(Digital)

DSSS Transmitter



Wireless Overview29

802.11b802.11b• Extension of 802.11 DSSS scheme• 5.5 and 11 Mbps• Chipping rate 11 MHz

– Same as original DS-SS scheme– Same occupied bandwidth– Complementary code keying (CCK) modulation to

achieve higher data rate in same bandwidth at same chipping rate

– CCK modulation complex• Overview on next slide

– Input data treated in blocks of 8 bits at 1.375 MHz• 8 bits/symbol 1.375 MHz = 11 Mbps• Six of these bits mapped into one of 64 code sequences• Output of mapping, plus two additional bits, forms input to

QPSK modulator



Wireless Overview30

802.11 FH802.11 FH802.11 FH802.11 FH

• Slow hopper – hop lasts up to 0.4 seconds per channel

• 1 & 2 Mbps data rates

• 79 channels, 1 MHz spacing

• Not much current interest

• Slow hopper – hop lasts up to 0.4 seconds per channel

• 1 & 2 Mbps data rates

• 79 channels, 1 MHz spacing

• Not much current interest



Wireless Overview31

Frequency

Tim

e



Wireless Overview32

ComponentsComponentsComponentsComponents

• BSS - Basic Service Set (Infrastructure)

• IBSS - Independent BSS (Ad-hoc or peer-to-peer)

• ESS - Extended Service Set

• STA – Station – e.g. Client card

• AP – Access Point

• DS – Distribution System

• BSS - Basic Service Set (Infrastructure)

• IBSS - Independent BSS (Ad-hoc or peer-to-peer)

• ESS - Extended Service Set

• STA – Station – e.g. Client card

• AP – Access Point

• DS – Distribution System



Wireless Overview33

802.11 Architecture802.11 Architecture802.11 Architecture802.11 Architecture

BSS

BSS 2

STA 1

STA 2

STA 3

STA 4

AP

AP

DS

ESS802.11 Components



Wireless Overview34

What’s In A Wireless MAC?What’s In A Wireless MAC?What’s In A Wireless MAC?What’s In A Wireless MAC?• CSMA/CA Carrier Sense Multiple Access /

Collision Avoidance• Virtual carrier sense – the NAV• RTS/CTS – hidden node problem• Access by Interframe spacing• Fragmentation• Retries• Powersave state• Synchronization• Privacy – WEP (wired equivalent privacy)• Multiple data rates

• CSMA/CA Carrier Sense Multiple Access / Collision Avoidance

• Virtual carrier sense – the NAV• RTS/CTS – hidden node problem• Access by Interframe spacing• Fragmentation• Retries• Powersave state• Synchronization• Privacy – WEP (wired equivalent privacy)• Multiple data rates



Wireless Overview35

IEEE 802.11 MAC Frame IEEE 802.11 MAC Frame FormatFormat

Stallings Chapter 17 Wireless LANs



Wireless Overview36

MAC Frame Fields MAC Frame Fields (1)(1)

• Frame Control:– Type of frame– Control, management, or data– Provides control information

• Includes whether frame is to or from DS, fragmentation information, and privacy information

• Duration/Connection ID:– If used as duration field, indicates time (in s) channel will be

allocated for successful transmission of MAC frame– In some control frames, contains association or connection

identifier• Addresses:

– Number and meaning of address fields depend on context– Types include source, destination, transmitting station, and

receiving station



Wireless Overview37

MAC Frame Fields MAC Frame Fields (2)(2)

• Sequence Control:– 4-bit fragment number subfield

• For fragmentation and reassembly

– 12-bit sequence number – Number frames between given transmitter and

receiver

• Frame Body:– MSDU (or a fragment of)

• LLC PDU or MAC control information

• Frame Check Sequence:– 32-bit cyclic redundancy check

Stallings Chapter 17 Wireless LANs



Wireless Overview38

MAC FramesMAC FramesMAC FramesMAC Frames

• Management– Beacon & Probe Response– Authentication, Deauthentication– Association, Re-association, Disassociation– Action frames

• Control– ACK, RTS, CTS, PS-POLL

• Data– Data, Null-Data, QoS

• Management– Beacon & Probe Response– Authentication, Deauthentication– Association, Re-association, Disassociation– Action frames

• Control– ACK, RTS, CTS, PS-POLL

• Data– Data, Null-Data, QoS



Wireless Overview39

CSMA-CA ExplainedCSMA-CA ExplainedCSMA-CA ExplainedCSMA-CA Explained

• Reduce collision probability where mostly needed.

– Stations are waiting for medium to become free.

– Select Random Backoff after a Defer, resolving contention to avoid collisions.

• Reduce collision probability where mostly needed.

– Stations are waiting for medium to become free.

– Select Random Backoff after a Defer, resolving contention to avoid collisions.

Copyright 1996 IEEE, doc Copyright 1996 IEEE, doc

• Efficient Backoff algorithm stable at high loads.

− Exponential Backoff window increases for retransmissions.− Backoff timer elapses only when medium is idle.



Wireless Overview40

No Yes No Yes Yes No

NAV=0?

Start

Sense Medium (PCA)

Medium Idle?

Random Back-off

Time

Transmit Frame

Collision?

Frame Transmission

Complete

This flowchart illustrates the operation of the CSMA/CA contention-based 802.11 DCF medium access protocol.



Wireless Overview41

Hidden Node ProblemHidden Node ProblemHidden Node ProblemHidden Node Problem



Wireless Overview42

RTS & FRAG exampleRTS & FRAG exampleRTS & FRAG exampleRTS & FRAG example



Wireless Overview43

NAV ExampleNAV ExampleNAV ExampleNAV Example

CTSRTS

Frag 1ACK

Frag 2ACK

Station 3

Station 4



Wireless Overview44

MAC OverheadMAC OverheadMAC OverheadMAC Overhead

• Fragmentation and RTS settings in MAC

• Legacy equipment

• Hidden nodes

• Retries

• DCF back-off algorithm

• Fragmentation and RTS settings in MAC

• Legacy equipment

• Hidden nodes

• Retries

• DCF back-off algorithm



Wireless Overview45

MAC Layer OverheadMAC Layer OverheadMAC Layer OverheadMAC Layer Overhead

22 11 2 11

1



Wireless Overview46

Locating a NetworkLocating a NetworkLocating a NetworkLocating a Network

•Passive Scanning– Stations listen for a beacon frame

– Based on the information contained, station may or may not attempt association

•Active Scanning– Station sends a probe request / listens for

response

– Attempt to associate based on information in response

•Passive Scanning– Stations listen for a beacon frame

– Based on the information contained, station may or may not attempt association

•Active Scanning– Station sends a probe request / listens for

response

– Attempt to associate based on information in response



Wireless Overview47

Starting an Infrastructure NetworkStarting an Infrastructure NetworkStarting an Infrastructure NetworkStarting an Infrastructure Network

• Station Probes for APs with desired SSID– (Service Set Identifier)

• Authentication• Association• Data transfer• Deauthentication and/ or Dissassociation

• Station Probes for APs with desired SSID– (Service Set Identifier)

• Authentication• Association• Data transfer• Deauthentication and/ or Dissassociation

sta APbc Probe Req

Probe RespAck

Auth req

Ack

Ack

Auth resp

Assoc. req



Wireless Overview48

Infrastructure vs. Ad HocInfrastructure vs. Ad HocInfrastructure vs. Ad HocInfrastructure vs. Ad Hoc

Infrastructure• All traffic goes through

AP• Possible use of a Point

Coordinator for polled access

• Requires Association• Usually connects to a

separate wired network

Infrastructure• All traffic goes through

AP• Possible use of a Point

Coordinator for polled access

• Requires Association• Usually connects to a

separate wired network

Ad Hoc• All communication is

direct• Distributed nature of

BSS functions• No association• Typically no network

services found on a wired network available (DHCP, domain servers, etc.)

Ad Hoc• All communication is

direct• Distributed nature of

BSS functions• No association• Typically no network

services found on a wired network available (DHCP, domain servers, etc.)



Wireless Overview49

802.11e (TGe) - QoS 802.11e (TGe) - QoS 802.11e (TGe) - QoS 802.11e (TGe) - QoS

• 4 Queues for different priorities– Higher priority traffic gets sent first (i.e. VoIP, Video,…)

• Direct communication between wireless stations in an infrastructure network– Reduces medium utilization– Normally stations must go through the AP

• Block Acknowledgements– Reduce number of management frames

• EDCA & HCCA modes– More efficient methods for coordinating who, what, and

when stations get access to medium

• 4 Queues for different priorities– Higher priority traffic gets sent first (i.e. VoIP, Video,…)

• Direct communication between wireless stations in an infrastructure network– Reduces medium utilization– Normally stations must go through the AP

• Block Acknowledgements– Reduce number of management frames

• EDCA & HCCA modes– More efficient methods for coordinating who, what, and

when stations get access to medium



Wireless Overview50

802.11h – TPC & DFS802.11h – TPC & DFS802.11h – TPC & DFS802.11h – TPC & DFS

• Transmitter Power Control– Needed for use of U-NII bands in EU

• Dynamic Frequency Selection

• Transmitter Power Control– Needed for use of U-NII bands in EU

• Dynamic Frequency Selection



Wireless Overview51

802.11i (TGi) - security802.11i (TGi) - security802.11i (TGi) - security802.11i (TGi) - security• WEP – Wired EQUIVALENT Privacy

– Only covers data payload and is point to point• Management(beacons) and MAC data header sent in the clear

– Many papers published on WEP’s weaknesses

• WPA – WiFi Protected Access Mode– TKIP protocol uses RC4 engine from WEP– Includes a 4-way handshake

• Other security features in TGi– Port based authentication: 802.1x, RADIUS– Stronger cryptography: AES – Advanced Encryption Standard

• End to End Solutions can always be used– SSH – secure shell, Stunnel – secure tunnel, VPN – virtual

private network

• WEP – Wired EQUIVALENT Privacy– Only covers data payload and is point to point

• Management(beacons) and MAC data header sent in the clear– Many papers published on WEP’s weaknesses

• WPA – WiFi Protected Access Mode– TKIP protocol uses RC4 engine from WEP– Includes a 4-way handshake

• Other security features in TGi– Port based authentication: 802.1x, RADIUS– Stronger cryptography: AES – Advanced Encryption Standard

• End to End Solutions can always be used– SSH – secure shell, Stunnel – secure tunnel, VPN – virtual

private network



Wireless Overview52

802.11n – High speed802.11n – High speed802.11n – High speed802.11n – High speed• High Throughput Group

– Looking to achieve speeds of >100Mbs

• Improve MAC efficiency– Using lots of the improvements for QoS, this would reduce the

management overhead needed

• Higher data rates– Using MIMO and OFDM to get more data though– Use higher constellation sizes (256 QAM)– Higher bandwidth channels

• 40MHz instead of 20MHz

– Takes advantage of multipath

• There are still multiple proposals about how to actually do this

• High Throughput Group– Looking to achieve speeds of >100Mbs

• Improve MAC efficiency– Using lots of the improvements for QoS, this would reduce the

management overhead needed

• Higher data rates– Using MIMO and OFDM to get more data though– Use higher constellation sizes (256 QAM)– Higher bandwidth channels

• 40MHz instead of 20MHz

– Takes advantage of multipath

• There are still multiple proposals about how to actually do this



Wireless Overview53

802.11p – Vehicular Wireless802.11p – Vehicular Wireless802.11p – Vehicular Wireless802.11p – Vehicular Wireless• Enable Wireless connections in vehicle-to-vehicle as

well as vehicle-to-roadside locations– Would enable download of information about what is around

you and what is going on– Could allow for more advanced services for cars

• EZPass type applications• Accident prevention/preparation could occur • Traffic and road condition report downloads • More intelligent car navigation services

• Hard to do because vehicles are moving fairly quickly– Various nodes move in and out of range within seconds

• Range of ~1000 ft.• 6Mbs in the 5.9GHz band

• Enable Wireless connections in vehicle-to-vehicle as well as vehicle-to-roadside locations– Would enable download of information about what is around

you and what is going on– Could allow for more advanced services for cars

• EZPass type applications• Accident prevention/preparation could occur • Traffic and road condition report downloads • More intelligent car navigation services

• Hard to do because vehicles are moving fairly quickly– Various nodes move in and out of range within seconds

• Range of ~1000 ft.• 6Mbs in the 5.9GHz band



Wireless Overview54

802.11s – Mesh Networking802.11s – Mesh Networking802.11s – Mesh Networking802.11s – Mesh Networking

• Mesh Networks are getting more and more popular– Many large cities are deploying large metropolitan mesh networks

• Philadelphia is one of the most notable

– Allows for large networks to be built without the need for lots of cabled

infrastructure.

• Takes a lot from Internet Protocol (IP) routing systems to allow for hopping through a network– “routing” needs to occur at the MAC layer and at the IP layer in order

to deliver traffic to the clients or APs which are located across the network

• Many proprietary methods already exist– Tropos

– Strix

• Mesh Networks are getting more and more popular– Many large cities are deploying large metropolitan mesh networks

• Philadelphia is one of the most notable

– Allows for large networks to be built without the need for lots of cabled

infrastructure.

• Takes a lot from Internet Protocol (IP) routing systems to allow for hopping through a network– “routing” needs to occur at the MAC layer and at the IP layer in order

to deliver traffic to the clients or APs which are located across the network

• Many proprietary methods already exist– Tropos

– Strix



Wireless Overview55

IEEE 802.15 (WPANs)IEEE 802.15 (WPANs)IEEE 802.15 (WPANs)IEEE 802.15 (WPANs)

• 802.15.1 adoption of Bluetooth 1.0/1.1 standard into IEEE

• 802.15.2 coexistence of WPANs and WLANs in the 2.4GHz band

• 802.15.3 high rate WPAN – 802.15.3a UWB PHY task group

• 802.15.4 low rate WPAN– Zigbee

• 802.15.1 adoption of Bluetooth 1.0/1.1 standard into IEEE

• 802.15.2 coexistence of WPANs and WLANs in the 2.4GHz band

• 802.15.3 high rate WPAN – 802.15.3a UWB PHY task group

• 802.15.4 low rate WPAN– Zigbee



Wireless Overview56

Bluetooth & 802.15Bluetooth & 802.15Bluetooth & 802.15Bluetooth & 802.15

• Frequency band: 2.4 GHz

• Range: 10 meters

• Power: 0 or 10 dBm (1mW or 10 mW)

• Data rate: 3 Mbps signaling rate

• “replace the wire”

• FH physical layer - 1600 hops/sec

• Frequency band: 2.4 GHz

• Range: 10 meters

• Power: 0 or 10 dBm (1mW or 10 mW)

• Data rate: 3 Mbps signaling rate

• “replace the wire”

• FH physical layer - 1600 hops/sec



Wireless Overview57

802.15.3 Standard802.15.3 Standard802.15.3 Standard802.15.3 Standard

• Frequency Range 2.4-2.4835 GHz

• Symbol rate 11 Msymbols/s (22-66Mbps)

• Base Modulation OQPSK – Optional 16,32, & 64QAM up to 66Mbps

• RF Bandwidth < 22 MHz

• Number of channels at least 4

• Transmit power 0 to 8 dBm

• Range 10 m

• Frequency Range 2.4-2.4835 GHz

• Symbol rate 11 Msymbols/s (22-66Mbps)

• Base Modulation OQPSK – Optional 16,32, & 64QAM up to 66Mbps

• RF Bandwidth < 22 MHz

• Number of channels at least 4

• Transmit power 0 to 8 dBm

• Range 10 m



Wireless Overview58

IEEE 802.16 (WiMAX)IEEE 802.16 (WiMAX)IEEE 802.16 (WiMAX)IEEE 802.16 (WiMAX)

• Developed from DOCSIS 1.1 (Data Over Cable Service Interface Specification)

• Developed from DOCSIS 1.1 (Data Over Cable Service Interface Specification)



Wireless Overview59

Additional ResourcesAdditional ResourcesAdditional ResourcesAdditional Resources

• Higher layer Protocols– http://www.ietf.org/html.charters/manet-charter.html– http://www.ietf.org/html.charters/mip4-charter.html– http://www.ietf.org/hmtl.charter/mip6-charter.html

• Service Discovery– http://www.upnp.org/– http://www.artima.com/jini/index.html

• Geier, Jim. Wireless LANs. Pearson Education, 2001.• Security

– Schneier, Bruce. Applied Cryptography, Second Edition. John Wiley & Sons, Inc. 1996. (http://www.counterpane.com/applied.html)

• Standards Committees– http://grouper.ieee.org/groups/802/dots.html

• Higher layer Protocols– http://www.ietf.org/html.charters/manet-charter.html– http://www.ietf.org/html.charters/mip4-charter.html– http://www.ietf.org/hmtl.charter/mip6-charter.html

• Service Discovery– http://www.upnp.org/– http://www.artima.com/jini/index.html

• Geier, Jim. Wireless LANs. Pearson Education, 2001.• Security

– Schneier, Bruce. Applied Cryptography, Second Edition. John Wiley & Sons, Inc. 1996. (http://www.counterpane.com/applied.html)

• Standards Committees– http://grouper.ieee.org/groups/802/dots.html



Wireless Overview60

Additional Resources Additional Resources (2)(2)Additional Resources Additional Resources (2)(2)

• Zigbee Alliance

– http://www.zigbee.org

• WiMAX Forum

– http://www.wimaxforum.org

• Bluetooth

– http://www.bluetooth.com

• Wireless News– http://www.wi-fiplanet.com

– http://www.unstrung.com

• UWB Forum– http://www.uwbforum.org



Wireless Overview61

ReferencesReferencesReferencesReferences

• http://hypertextbook.com/physics/electricity/em-spectrum/

• Stallings, William. Data and Computer Communications. Prentice Hall: New Jersey, 2000.

© university of new hampshire interoperability laboratory wireless networking overview january 2006

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