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WiFi MAC Protocol PowerPoint Presentation

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On : Nov 13, 2014

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  • Slide 1 - 1 WiFi MAC Protocol
  • Slide 2 - 2 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)”
  • Slide 3 - 3 First WiFi Intended for cashiers Called WaveLAN Vic Hayes “Father of WiFi” Helped design IEEE 802.11b, 802.11a and 802.11g
  • Slide 4 - 4 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
  • Slide 5 - 5 Network-Level Architecture
  • Slide 6 - 6 Network-Level Architecture Cont.
  • Slide 7 - 7 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
  • Slide 8 - 8 Protocols
  • Slide 9 - 9 Protocols
  • Slide 10 - 10 IEEE 802.11 Group Standards
  • Slide 11 - 11 IEEE 802.11 Group Standards Cont.
  • Slide 12 - 12 802.11 Protocol Entities Slide taken from: http://www.cse.ucsc.edu/classes/cmpe257/Spring05/lecture/lecture3.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint
  • Slide 13 - 13 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
  • Slide 14 - 14 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
  • Slide 15 - 15 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
  • Slide 16 - 16 CSMA/CD CSMA stands for Carrier Sense Multiple Access CD stands for Collision Detection Allows for Retransmission Back-Off
  • Slide 17 - 17 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
  • Slide 18 - 18 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
  • Slide 19 - 19 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
  • Slide 20 - 20 Applications Wireless Access Point (WAP) Wireless Routers Wireless Ethernet Bridge Range Extender
  • Slide 21 - 21 Gaming Applications Nintendo DS Sony PSP Xbox 360 Playstation 3 Nintendo Wii
  • Slide 22 - 22 Problems / Performance Issues Interruption by other devices High power consumption When setup the network defaults to open mode Large area coverage
  • Slide 23 - 23 Security Issues WEP encryption is breakable Spoofing authorized MAC addresses Wardriving and Warchalking
  • Slide 24 - 24 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.
  • Slide 25 - 25 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
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Description : WiFi MAC Protocol * * * 802.11 legacy The original version of the standard IEEE 802.11 released in 1997 specifies two raw data rates of 1 and 2 megabits per second ...

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