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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/ In progress Approved External 802.11 MAC Standards http://grouper.ieee.org/groups/802/11/ In progress Approved External WiFi Alliance • Industrial consortium that promotes 802.11 Millions of WiFi Chipset Shipped – 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 Wi-Fi Alliance, Introducing Wi-Fi Protected Setup™, January 3, 2007 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): BSS http://wireless.ictp.trieste.it/school_2002/lectures/ermanno/802.11_ Architecture.ppt – A Basic Service Set (BSS) which forms a self-contained network in which no access to a Distribution System is available IBSS • 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 BSS Di st Sy ribu st tio em n BSS Distributed Coordination Function (DCF) • 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 Point Coordination Function (PCF) • 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 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 802.11 Alphabet Soup Jun 1997 Sep 1999 Sep 1999 Oct 2001 Jun 2003 Jun 2003 Oct 2003 Jun 2004 Oct 2004 Sep 2005 Dec 2007 Mar 2008 Mar 2008 Sep 2008 Jan 2009 Feb 2009 Mar 2009 Aug 2009 Aug 2009 Sep 2009 802.11 802.11a 802.11b 802.11d 802.11f 802.11g 802.11h 802.11i 802.11j 802.11e 802.11k 802.11r 802.11y 802.11n 802.11u 802.11w 802.11p 802.11s 802.11.2 802.11v 2 Mbps ISM 54 Mbps UNII 11 Mbps ISM global roaming interoperability 54 Mbps ISM spectrum management security Japanese spectrum real time QoS RRM measurements fast roaming US 3.65 GHz 100 Mbps external networks packet security vehicular (5.9) mesh networks test recommendations network management 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 http://grouper.ieee.org/groups/802/11/Reports/802.11_Timelines.htm 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 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) • – Hybrid Coordination Function • • • • • Shorter random backoffs for higher priority traffic 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 802.11j and spectrum (Oct 2004) • 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 2.4 GHz Lower Upper U.S. 2.402 2.48 Europe 2.402 2.48 Japan 2.473 2.495 Spain 2.447 2.473 France 2.448 2.482 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 802.11h (Oct 2003) • Make 802.11h act like Hiperlan2 – • Avoid radars in 5 GHz band • Avoid radars • – – • Listens and discontinues use of a channel if a radar is present – Interference reduction Range control Power consumption Savings Bounded by local regulatory conditions • http://cisco.com/en/US/netsol/ ns340/ns394/ns348/netqa090 0aecd802570a1.html New Logic (IP company) has chips Uniform channel utilization Transmit Power Control (TPC) – – – Mandated in Europe beginning 2005 Cisco support in 1Q 05 (claimed March 05) – Dynamic Frequency Selection (DFS) – • • http://www.newlogic.com/pres s_room/press_releases/20050 120083419.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/ne ws/st/showArticle.jhtml?article ID=16503607 Security • 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) 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)