WiFi MAC Protocol

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WiFi MAC Protocol
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History

• WiFi is used to describe the underlying
  technology of wireless local area networks (WLAN)
  based on the IEEE 802.11 specifications
• WiFi developed by Kyle Brown
• IEEE 802.11 denotes a set of Wireless LAN/WLAN
  standards developed by working group 11 of the
  IEEE LAN/MAN Standards Committee (IEEE 802)

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First WiFi

• Intended for cashiers
• Called WaveLAN
• Vic Hayes
• Father of WiFi
• Helped design IEEE 802.11b, 802.11a and 802.11g

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MAC Protocol

• MAC stands for Medium Access Control
• Used to provide the data link layer of the
  Ethernet LAN system
• Job is to add a 14 byte header (Protocol Control
  Information (PCI)) before the data and append a
  4-byte Cyclic Redundancy Check (CRC) after the
  data

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Network-Level Architecture
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Network-Level Architecture Cont.
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IEEE 802.11 Standard

• PHY/MAC standard for wireless LANs
• First standardized in 1997
• Meet great success starting in 1999
• Several working groups
• IEEE 802.11a high speed extension to the 5GHz
  band
• 802.11b/g high speed extension to the 2.4GHz
  band
• 802.11e Quality of service (QoS) enhancement
  (still active)
• 802.11i Security enhancement
• 802.11s Mesh-networking support

Slide taken from http//www.cse.ucsc.edu/classes
/cmpe257/Spring05/lecture/lecture3.pdfsearch'802
.11e20MAC20protocol2C20powerpoint
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Protocols
Protocols Release Date Op. Frequency Date Rate (Typ) Date Rate (Max) Range (indoor)
Legacy 1997 2.4 2.5 GHz 1 Mbit/s 2 Mbit/s ?
802.11a 1999 5.15-5.35/5.47-5.725/5.725-5.875 GHz 25 Mbit/s 54 Mbit/s 30 meters (100 feet)
802.11b 1999 2.4 2.5 GHz 6.5 Mbit/s 11 Mbit/s 50 meters (150 feet)
802.11g 2003 2.4 2.5 GHz 11 Mbit/s 54 Mbit/s 30 meters (100 feet)
802.11n 2006 (draft) 2.4 GHz or 5GHz bands 200 Mbit/s 540 Mbit/s 50 meters (160 feet)
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Protocols
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IEEE 802.11 Group Standards
IEEE 802.11 The original 1 Mbit/s and 2 Mbit/s , 2.4 GHz RF and IR standard (1999)
IEEE 802.11a 54 Mbit/s, 5 GHz standard (1999, shipping products in 2001)
IEEE 802.11b Enhancements to 802.11 to support 5.5 and 11 Mbit/s (1999)
IEEE 802.11c Bridge operation procedures included in the IEEE 802.1D standard (2001)
IEEE 802.11d International (country-to-country) roaming extensions (2001)
IEEE 802.11e Enhancements QoS, including packet bursting (2005)
IEEE 802.11f Inter-Access Point Protocol (2003) Withdrawn February 2006
IEEE 802.11g 54 Mbit/s, 2.4 GHz standard (backwards compatible with b) (2003)
IEEE 802.11h Spectrum Managed 802.11a (5 GHz) for European compatibility (2004)
IEEE 802.11i Enhanced security (2004)
IEEE 802.11j Extensions for Japan (2004)
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IEEE 802.11 Group Standards Cont.
IEEE 802.11k Radio resource measurement enhancements
IEEE 802.11l (reserved and will not be used)
IEEE 802.11m Maintenance of the standard odds and ends.
IEEE 802.11n Higher throughput improvements using MIMO (multiple input, multiple output antennas)
IEEE 802.11o (reserved and will not be used)
IEEE 802.11p WAVE - Wireless Access for the Vehicular Environment (such as ambulances and passenger cars)
IEEE 802.11q (reserved and will not be used, can be confused with 802.1Q VLAN trunking)
IEEE 802.11r Fast roaming Working "Task Group r"
IEEE 802.11s ESS Mesh Networking
IEEE 802.11T Wireless Performance Prediction (WPP) - test methods and metrics Recommendation
IEEE 802.11u Interworking with non-802 networks (for example, cellular)
IEEE 802.11v Wireless network management
IEEE 802.11w Protected Management Frames
IEEE 802.11x (reserved and will not be used)
IEEE 802.11y 3650-3700 Operation in the U.S.
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802.11 Protocol Entities
Slide taken from http//www.cse.ucsc.edu/classes
/cmpe257/Spring05/lecture/lecture3.pdfsearch'802
.11e20MAC20protocol2C20powerpoint
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MAC in Detail

• Channel access mechanism
• Distributed Coordination Function (DCF)
• Carrier sense multiple access (CSMA) with
  immediate MAC-level ACK
• RTS/CTS(4-way handshaking) exchange (optional)
• RTS stands for Request-to-Send
• CTS stands for Clear-to-Send
• Point Coordination Function (PCF)
• Polled access through AP and distributed access
• Contention-free period (CFP) and contention
  period (CP)
• Seldom implemented in practice

Slide taken from http//www.cse.ucsc.edu/classes
/cmpe257/Spring05/lecture/lecture3.pdfsearch'802
.11e20MAC20protocol2C20powerpoint
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CSMA/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
• Efficient Backoff algorithm stable at high loads
• Exponential Backoff window increases for
  retransmissions
• Backoff timer elapses only when medium is idle
• Implement different fixed priority levels
• To allow immediate responses and PCF coexistence

Slide taken from http//www.cse.ucsc.edu/classes
/cmpe257/Spring05/lecture/lecture3.pdfsearch'802
.11e20MAC20protocol2C20powerpoint
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CSMA/CA ACK Protocol

• Defer access based on Carrier Sense
• Clear Channel Assessment (CCA) from PHY and
  Virtual Carrier Sense state
• Direct access when medium is sensed free longer
  then DIFS, otherwise defer and backoff
• Reciever of directed frames to return an ACK
  immediately when CRC correct
• When no ACK received then retransmit frame after
  a random backoff (up to maximum limit)

Slide taken from http//www.cse.ucsc.edu/classes
/cmpe257/Spring05/lecture/lecture3.pdfsearch'802
.11e20MAC20protocol2C20powerpoint
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CSMA/CD

• CSMA stands for Carrier Sense Multiple Access
• CD stands for Collision Detection
• Allows for Retransmission Back-Off

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RTS/CTS Based Access

• Duration field in RTS and CTS frames distribute
  Medium Reservation information which is stored in
  a Net Allocation Vector (NAV)
• Defer on either NAV or CCA indicating Medium
  Busy
• Use RTS/CTS is optional but must be implemented
• Use is controlled by a RTS_Threshold parameter
  per station
• To limit overhead for short frames

Slide taken from http//www.cse.ucsc.edu/classes
/cmpe257/Spring05/lecture/lecture3.pdfsearch'802
.11e20MAC20protocol2C20powerpoint
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Frame Formats

• MAC Header format differs per Type
• Control Frames (several fields are omitted)
• Management Frames
• Data Frames
• Includes Sequence Control Field for filtering of
  duplicates caused by ACK mechanism

Slide taken from http//www.cse.ucsc.edu/classes
/cmpe257/Spring05/lecture/lecture3.pdfsearch'802
.11e20MAC20protocol2C20powerpoint
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Address Field Description

• Addr 1 All stations filter on this address.
• Addr 2 Transmitter Address (TA)
• Identifies transmitter to address the ACK frame
  to
• Addr 3 Dependent on To and From DS bits
• Addr 4 Only needed to identify the original
  source of WDS (Wireless Distribution System)
  frames

Slide taken from http//www.cse.ucsc.edu/classes
/cmpe257/Spring05/lecture/lecture3.pdfsearch'802
.11e20MAC20protocol2C20powerpoint
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Applications

• Wireless Access Point (WAP)
• Wireless Routers
• Wireless Ethernet Bridge
• Range Extender

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Gaming Applications

• Nintendo DS
• Sony PSP
• Xbox 360
• Playstation 3
• Nintendo Wii

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Problems / Performance Issues

• Interruption by other devices
• High power consumption
• When setup the network defaults to open mode
• Large area coverage

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Security Issues

• WEP encryption is breakable
• Spoofing authorized MAC addresses
• Wardriving and Warchalking

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Question Summary / Conclusion

• What is WiFi MAC Protocol?
• It is the underlying technology of wireless local
  area networks (WLAN) based on the IEEE 802.11
  specifications that provides the data link layer
  of the Ethernet LAN system.
• Who came up with WiFi MAC Protocol?
• The IEEE Task Groups and created the IEEE 802.11
  or IEEE 802.11x Committee, however IEEE only sets
  specifications. WiFi Alliance runs the
  certification program.
• What is the difference between DCF and PCF?
• DCF uses carrier sense multiple access with
  immediate MAC-level ACK and contains RTS/CTS
  optional exchange. PCF uses polled access
  through AP and distributed access cotains a
  contention-free period and a contention period
  and is seldom implemented in practice.

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References

• http//en.wikipedia.org/wiki/ImageWi-Fi_logo.png
• http//en.wikipedia.org/wiki/Wi-Fi
• http//www.tate.org.uk/liverpool/ima/rm5/images/ca
  shier_lg.jpg
• http//www.art-events.de/systeme/images/wlan3.jpeg
  
• http//www.aria.co.uk/mainimages/wpn802a.jpg
• http//media.pugetsoundsoftware.com/ask-leo.com/im
  ages/wireless2bad.png
• http//www.circuitcity.com/IMAGE/product/detail/dl
  k/EC.DLK.DWLG710.JPG
• http//www.wsdmag.com/Files/32/8624/Figure_01.gif
• http//www.os2warp.be/wireless/wireless_comparison
  .jpg
• http//ei.cs.vt.edu/history/50th/IEEE.logo.GIF
• http//tab.computer.org/tcca/images/ieee.jpg
• http//upload.wikimedia.org/wikipedia/en/thumb/b/b
  d/Blue_infrared_light.jpg/300px-Blue_infrared_ligh
  t.jpg
• https//weather.unisys.com/satellite/images/sat_ir
  _us.gif
• http//en.wikipedia.org/wiki/IEEE_802.11802.11_le
  gacy
• http//microwave.gotovim.ru/pics/microvawe.jpg
• http//reviews.cnet.com/i/qg/tvpc/power_tv.jpg
• http//acni.dnsalias.net/sites/batist/Picture20Li
  brary/1/Open-door.jpg
• http//www.cse.ucsc.edu/classes/cmpe257/Spring05/l
  ecture/lecture3.pdfsearch'802.11e20MAC20protoc
  ol2C20powerpoint
• http//www.ece.cmu.edu/cpyue/PatrickWebFiles/AR51
  10.jpg