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WiFi MAC Protocol. 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

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history
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)”
first wifi
First WiFi
  • Intended for cashiers
  • Called WaveLAN
  • Vic Hayes
    • “Father of WiFi”
    • Helped design IEEE 802.11b, 802.11a and 802.11g
mac protocol
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
ieee 802 11 standard
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.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint

802 11 protocol entities
802.11 Protocol Entities

Slide taken from: http://www.cse.ucsc.edu/classes/cmpe257/Spring05/lecture/lecture3.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint

mac in detail
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.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint

csma ca explained
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.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint

csma ca ack protocol
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.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint

csma cd
CSMA/CD
  • CSMA stands for Carrier Sense Multiple Access
  • CD stands for Collision Detection
  • Allows for Retransmission Back-Off
rts cts based access
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.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint

frame formats
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.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint

address field description
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.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint

applications
Applications
  • Wireless Access Point (WAP)
  • Wireless Routers
  • Wireless Ethernet Bridge
  • Range Extender
gaming applications
Gaming Applications
  • Nintendo DS
  • Sony PSP
  • Xbox 360
  • Playstation 3
  • Nintendo Wii
problems performance issues
Problems / Performance Issues
  • Interruption by other devices
  • High power consumption
  • When setup the network defaults to open mode
  • Large area coverage
security issues
Security Issues
  • WEP encryption is breakable
  • Spoofing authorized MAC addresses
  • Wardriving and Warchalking
question summary conclusion
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.
references
References
  • http://en.wikipedia.org/wiki/Image:Wi-Fi_logo.png
  • http://en.wikipedia.org/wiki/Wi-Fi
  • http://www.tate.org.uk/liverpool/ima/rm5/images/cashier_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/images/wireless2bad.png
  • http://www.circuitcity.com/IMAGE/product/detail/dlk/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/bd/Blue_infrared_light.jpg/300px-Blue_infrared_light.jpg
  • https://weather.unisys.com/satellite/images/sat_ir_us.gif
  • http://en.wikipedia.org/wiki/IEEE_802.11#802.11_legacy
  • http://microwave.gotovim.ru/pics/microvawe.jpg
  • http://reviews.cnet.com/i/qg/tvpc/power_tv.jpg
  • http://acni.dnsalias.net/sites/batist/Picture%20Library/1/Open-door.jpg
  • http://www.cse.ucsc.edu/classes/cmpe257/Spring05/lecture/lecture3.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint
  • http://www.ece.cmu.edu/~cpyue/PatrickWebFiles/AR5110.jpg
  • http://www.personaltelco.net/albums/album26/DSC00152.jpg
  • http://www.blurtek.com/uploaded_images/belkin-n-726511.jpg
  • http://www.erg.abdn.ac.uk/users/gorry/eg3561/dl-pages/crc.html
  • http://www.erg.abdn.ac.uk/users/gorry/eg3561/lan-pages/csma-cd.html
  • http://www.erg.abdn.ac.uk/users/gorry/eg3561/lan-pages/mac.html
  • http://ieeexplore.ieee.org/iel5/9858/31043/01443506.pdf