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Wireless LANs

Wireless LANs. 802.11. Presentation Material. Overview of 802.11 Overview Key amendments 802.11n PHY MAC Performance Important upcoming amendments 802.11p 802.11r 802.11s 802.11y. Overview of 802.11. 802.11 PHY Standards. http://grouper.ieee.org/groups/802/11/. External.

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Wireless LANs

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  1. Wireless LANs 802.11

  2. Presentation Material • Overview of 802.11 • Overview • Key amendments • 802.11n • PHY • MAC • Performance • Important upcoming amendments • 802.11p • 802.11r • 802.11s • 802.11y

  3. Overview of 802.11

  4. 802.11 PHY Standards http://grouper.ieee.org/groups/802/11/ External In progress Approved

  5. 802.11 MAC Standards http://grouper.ieee.org/groups/802/11/ External In progress Approved

  6. WiFi Alliance • Industrial consortium that promotes 802.11 • www.wi-fi.org • Certifies interoperability between vendors’ products • Certifies consistency with standards • Fills in the gap when 802.11 standards process is too slow (draft n) • WiFi success owes significant debt to WiFi Alliance • Line between 802.11 standards community and WiFi Alliance has gotten very blurry • Certifications • 802.11a/b/g/n WiFi • 802.11e Wireless Multimedia • Draft 2.0 n Millions of WiFi Chipset Shipped Wi-Fi Alliance, Introducing Wi-Fi Protected Setup™, January 3, 2007

  7. 802.11 Terminology • Basic Service Set (BSS): • A set of stations controlled by a single “Coordination Function” (=the logical function that determines when a station can transmit or receive) • Independent Basic Service Set (IBSS): • A Basic Service Set (BSS) which forms a self-contained network in which no access to a Distribution System is available • Extended Service Set (ESS): • A set of one or more Basic Service Sets interconnected by a Distribution System (DS) • Many different deployment scenarios, want common MAC http://wireless.ictp.trieste.it/school_2002/lectures/ermanno/802.11_Architecture.ppt

  8. Intended to combat “hidden nodes” in an uncoordinated network and generate fair access to channel Basic components: After waiting DIFS after last detected transmission, source sends Request to Send (RTS) Destination replies with Clear to Send (if OK) Data is then transferred and ACKed If an error occurs (e.g., collision), then station has to wait for DIFS + random backoff. Random backoff grows with # of collisions Network allocation vector Acts as virtual carrier sense Duration given in RTS/CTS fields DIFS = DCF Interframe Space SIFS = Short Interframe Space Distributed Coordination Function (DCF)

  9. Intended to provide service more appropriate for real-time applications Not widely utilized initially Basic steps Access node (AN) implementing PCF “wins” the channel by cheating (SIFS < PIFS < DIFS) AN announces contention free period in Beacon (realized in NAV) to lock out DCF Polls each client in its polling list Frames separated by PIFS If client fails to respond within PIFS, AN moves onto next At end of contention-free period a contention free message is sent ending the contention free period DCF holds until AN initiates another contention free period Various ratios permitted between contention based and contention free Point Coordination Function (PCF)

  10. 802.11 overhead • Significant overhead involved in 802.11 • RTS/CTS/ACK SIFS • TCP, IP, MAC framing • Real throughput is rarely come close to PHY raw rate http://www.cs.tut.fi/kurssit/TLT-6556/Slides/Lecture4.pdf wireless.ictp.trieste.it/school_2002/lectures/ermanno/System_Performance.ppt

  11. Past dates are standards approval dates. Future dates from 802.11 working group timelines Letters are working group (WG) designations. Letters assigned alphabetically as groups created. No WG/ WG document 802.11c MAC Bridging work incorporated into 802.1d 802.11l “typologically unsound” 802.11m doc maintenance 802.11o “typologically unsound” 802.11q too close to 802.1q 802.11x generic 802.11 standard 802.11t (test) will produce 802.11.2 802.11 Alphabet Soup Jun 1997 802.11 2 Mbps ISM Sep 1999 802.11a 54 Mbps UNII Sep 1999 802.11b 11 Mbps ISM Oct 2001 802.11d global roaming Jun 2003 802.11f interoperability Jun 2003 802.11g 54 Mbps ISM Oct 2003 802.11h spectrum management Jun 2004 802.11i security Oct 2004 802.11j Japanese spectrum Sep 2005 802.11e real time QoS Dec 2007 802.11k RRM measurements Mar 2008 802.11r fast roaming Mar 2008 802.11y US 3.65 GHz Sep 2008 802.11n 100 Mbps Jan 2009 802.11u external networks Feb 2009 802.11w packet security Mar 2009 802.11p vehicular (5.9) Aug 2009 802.11s mesh networks Aug 2009 802.11.2 test recommendations Sep 2009 802.11v network management http://grouper.ieee.org/groups/802/11/Reports/802.11_Timelines.htm

  12. 802.11 a/b/g • Common MAC • RTS/CTS scheme to handle hidden nodes • Random backoffs to handle collisions 802.11b PHY 2.4 GHz (ISM) 14 overlapping channels 802.11g PHY 2.4 GHz (ISM) 14 overlapping channels 802.11a 5 GHz (UNII) 23 orthogonal channels

  13. 802.11e (Sept 2005) • Enhances QoS for Voice over Wireless IP (aka Voice over WiFi ) and streaming multimedia • Changes changes • Enhanced Distributed Coordination Function (EDCF) • Shorter random backoffs for higher priority traffic • Hybrid Coordination Function • Defines traffic classes • In contention free periods, access point controls medium access • Stations report to access info on queue size. • Schedules as it sees fit • WMM (WiFi MultiMedia) • WiFi Alliance profile of 802.11e • Available Sept 2004 (Cisco, IBM, Netgear, Atheros) • Handoff problems (to be addressed by 802.11r?) • Spectralink moving away from proprietary voice over WiFi implementation

  14. Opens up Japanese spectrum for 5 GHz operation New Logic Support Jan 05 US 5.47 – 5.725 GHz released in Nov 2003 Alternate bandwidths 802.11j and spectrum (Oct 2004) 2.4 GHz 5 GHz • US • UNII Low 5.15 – 5.25 (4) 50 mW • UNII Middle 5.25 – 5.35 (4) 250 mW • UNII Upper 5.725-5.825 (4) 1 W • 5.47 – 5.725 GHz released in Nov 2003 • Europe • 5.15-5.35 200 mW • 5.47-5.725 1 W • Japan • 4.9-5.091 • 5.15-5.25 (10 mW/MHz) unlicensed

  15. Make 802.11h act like Hiperlan2 Avoid radars in 5 GHz band Dynamic Frequency Selection (DFS) Avoid radars Listens and discontinues use of a channel if a radar is present Uniform channel utilization Transmit Power Control (TPC) Interference reduction Range control Power consumption Savings Bounded by local regulatory conditions Mandated in Europe beginning 2005 Cisco support in 1Q 05 (claimed March 05) http://cisco.com/en/US/netsol/ns340/ns394/ns348/netqa0900aecd802570a1.html New Logic (IP company) has chips http://www.newlogic.com/press_room/press_releases/20050120083419.shtml Probably killed off HiperLAN/2 PHY similar to 802.11a MAC like ATM Phillips decided to not make any HiperLAN/2 chips http://www.eetuk.com/bus/news/st/showArticle.jhtml?articleID=16503607 802.11h (Oct 2003)

  16. Original WEP security was flawed Fixed by 802.11i which Defined secure (but slow) handoff procedures Added AES for encryption CCMP WPA - WiFi Protected Access WiFi Alliance “brand” (http://www.wi-fi.org) TKIP 802.1x Products began Spring 2003 WPA-2 WiFi Alliance “brand” Implements 802.11i Products beginning Sept 2004 WiFi Certified EAPs (for WPA, WPA2) EAP-TLS (previously tested) EAP-TTLS/MSCHAPv2 PEAPv0/EAP-MSCHAPv2 PEAPv1/EAP-GTC EAP-SIM All non-proprietary EAPs (e.g., no LEAP -Cisco) Security

  17. WLAN Summary • Wildly successful because of ease of deployment, price • Moving to OFDM/MIMO (802.11n) • Moving into additional bands (802.11y, 802.11j) • New applications (802.11e) • Extending capabilities with numerous PHY and MAC amendments • Building interoperability with other standards (802.11u, 802.21)

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