Wireless Local Area Networks WLANs Raj Jain Professor of CSE Washington University in Saint Louis Saint Louis MO 63130 Jain cse wustl edu These slides are available on line at http www cse wustl edu jain cse574 06 Washington University in St Louis CSE574s 5 1 2006 Raj Jain Overview IEEE 802 11 1 Features 2 MAC 3 Physical Layers 4 Current Activities 5 Next Generation 802 11n 6 Enhanced Quality of Service 802 11e Washington University in St Louis CSE574s 5 2 2006 Raj Jain WiFi Almost all wireless LANs now are IEEE 802 11 based Competing technologies e g HiperLAN can t compete on volume and cost 802 11 is also known as WiFi Wireless Fidelity Fidelity Compatibility between wireless equipment from different manufacturers WiFi Alliance is a non profit organization that does the compatibility testing WiFi org Washington University in St Louis CSE574s 5 3 2006 Raj Jain IEEE 802 11 Features Original 802 11 at 1 and 2 Mbps Supports both Ad hoc and base stations Spread Spectrum No licensing required Three Phys Direct Sequence Frequency Hopping 915 MHz 2 4 GHz Worldwide ISM 5 2 GHz and Diffused Infrared 850 900 nm bands Supports multiple priorities Supports time critical and data traffic Power management allows a node to doze off Washington University in St Louis CSE574s 5 4 2006 Raj Jain Hidden Node Problem A B C C cannot hear A It may start transmitting while A is also transmitting A and C can t detect collision Only the receiver can help avoid collisions Washington University in St Louis CSE574s 5 5 2006 Raj Jain 4 Way Handshake Access Access Point Point Ready to send Mobile Mobile Node Node Clear to send Data Ack Washington University in St Louis CSE574s 5 6 2006 Raj Jain IEEE 802 11 MAC Carrier Sense Multiple Access with Collision Avoidance CSMA CA Listen before you talk If the medium is busy the transmitter backs off for a random period Avoids collision by sending a short message Ready to send RTS RTS contains dest address and duration of message Tells everyone to backoff for the duration Destination sends Clear to send CTS Other stations set their network allocation vector NAV and do not transmit for that duration Can not detect collision Each packet is acked MAC level retransmission if not acked Washington University in St Louis CSE574s 5 7 2006 Raj Jain IEEE 802 11 Architecture Server Server Distribution System IBSS Access Access Point Point Station Station Station Station Basic Service Set Washington University in St Louis Access Access Point Point Station Station 2nd BSS CSE574s 5 8 Ad hoc Ad hoc Station Station Station Station Ad hoc Ad hoc Station Station Ad hoc network 2006 Raj Jain IEEE 802 11 Architecture Cont Basic Service Area BSA Cell Each BSA may have several wireless LANs Distribution System DS wired backbone Extended Service Area ESA Multiple BSAs interconnected via Access Points AP Basic Service Set BSS Set of stations associated with an AP Extended Service Set ESS Set of stations in an ESA Independent Basic Service Set IBSS Set of computers in adhoc mode May not be connected to wired backbone Ad hoc networks coexist and interoperate with infrastructurebased networks Washington University in St Louis CSE574s 5 9 2006 Raj Jain IEEE 802 11 Priorities DIFS PIFS Busy SIFS Contention Window Random Backoff Frame Time Carrier Sensed Initial interframe space IFS Highest priority frames e g Acks use short IFS SIFS Medium priority time critical frames use Point Coordination Function IFS PIFS Asynchronous data frames use Distributed coordination function IFS DIFS Washington University in St Louis CSE574s 5 10 2006 Raj Jain Time Critical Services Super Frame Contention Free Contention Period Period PCF Access DCF Access Time Beacon Timer critical services use Point Coordination Function The point coordinator allows only one station to access Coordinator sends a beacon frame to all stations Then uses a polling frame to allow a particular station to have contention free access Contention Free Period CFP varies with the load Washington University in St Louis CSE574s 5 11 2006 Raj Jain North American Channels 2 4 GHz Band Only 3 non overlapping channels Channel 9 Channel 5 Channel 7 Channel 3 2400 Channel 1 2402 2412 Channel 6 2422 2432 2483 5 Channel 11 2442 2452 2462 2472 2482 60 64 5 GHz Band 12 non overlapping channels 5150 36 40 44 5180 5200 5220 5240 5260 5280 149 153 157 161 5745 5765 5785 5805 5725 Washington University in St Louis 48 52 CSE574s 5 12 56 5300 5825 5320 5350 2006 Raj Jain IEEE 802 11 Physical Layers Issued in four stages First part in 1997 IEEE 802 11 Includes MAC layer and three physical layer specifications Two in 2 4 GHz band and one infrared All operating at 1 and 2 Mbps Two additional parts in 1999 IEEE 802 11a 1999 5 GHz band 54 Mbps 20 MHz OFDM IEEE 802 11b 1999 2 4 GHz band 11 Mbps 20 MHz Fourth part IEEE 802 11g 2003 2 4 GHz band 54 Mbps 20 MHz OFDM Washington University in St Louis CSE574s 5 13 2006 Raj Jain IEEE 802 11 Activities 802 11c Bridge Operation Completed Added to IEEE 802 1D 802 11d Global Harmonization PHYs for other countries Published as IEEE Std 802 11d 2001 802 11e Quality of Service IEEE Std 802 11e 2005 802 11f Inter Access Point Protocol Published as IEEE Std Std 802 11F 2003 802 11h Dynamic Frequency Selection and transmit power control to satisfy 5GHz band operation in Europe Published as IEEE Std 802 11h 2003 802 11i MAC Enhancements for Enhanced Security Published as IEEE Std 802 11i 2004 802 11j 4 9 5 GHz operation in Japan IEEE Std 802 11j 2004 802 11k Radio Resource Measurement interface to higher layers Active Washington University in St Louis CSE574s 5 14 2006 Raj Jain IEEE 802 11 Activities Cont 802 11m Maintenance Correct editorial and technical issues in 802 11a b d g h Active 802 11n Enhancements for higher throughput 100 Mbps Active 802 11p Inter vehicle and vehicle road side communication at 5 8GHz Active 802 11r Fast Roaming Started July 2003 Active 802 11s ESS Mesh Networks Active 802 11T Wireless Performance Metrics Active 802 11u Inter working with External Networks Active 802 11v Wireless Network Management enhancements for interface to upper layers Extension to 80211 k Active Study Group ADS Management frame security Active Standing Committee Wireless Next Generation WNG Globalization jointly w ETSI BRAN and MMAC Active Washington University in St Louis CSE574s 5 15 2006 Raj Jain 802 11n Trend HDTV and flat screens are taking off Media Center Extenders from Linksys and other vendors Application HDTV and
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