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

In progress

http://grouper.ieee.org/groups/802/11/

Approved External

802.11 MAC Standards

In progress Approved External

http://grouper.ieee.org/groups/802/11/

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

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

BSS

IBSS

BSS

BSS

Distribution

System

http://wireless.ictp.trieste.it/school_2002/lectures/ermanno/802.11_Architecture.ppt

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

wireless.ictp.trieste.it/school_2002/lectures/ermanno/System_Performance.ppt http://www.cs.tut.fi/kurssit/TLT-6556/Slides/Lecture4.pdf

Past dates are standards approval dates. Future dates from 802.11 working group timelinesLetters 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 maintenance802.11o “typologically unsound”802.11q too close to 802.1q802.11x generic 802.11 standard

802.11t (test) will produce 802.11.2

Jun 1997 802.11 2 Mbps ISMSep 1999 802.11a 54 Mbps UNIISep 1999 802.11b 11 Mbps ISMOct 2001 802.11d global roamingJun 2003 802.11f interoperabilityJun 2003 802.11g 54 Mbps ISMOct 2003 802.11h spectrum managementJun 2004 802.11i securityOct 2004 802.11j Japanese spectrumSep 2005 802.11e real time QoSDec 2007 802.11k RRM measurementsMar 2008 802.11r fast roamingMar 2008 802.11y US 3.65 GHzSep 2008 802.11n 100 MbpsJan 2009 802.11u external networksFeb 2009 802.11w packet securityMar 2009 802.11p vehicular (5.9)Aug 2009 802.11s mesh networksAug 2009 802.11.2 test recommendationsSep 2009 802.11v network management

802.11 Alphabet Soup

http://grouper.ieee.org/groups/802/11/Reports/802.11_Timelines.htm

• Common MAC– RTS/CTS scheme to handle hidden nodes– Random backoffs to handle collisions

802.11b PHY2.4 GHz (ISM)14 overlapping channels

802.11g PHY2.4 GHz (ISM)14 overlapping channels

802.11a 5 GHz (UNII)23 orthogonal channels

802.11 a/b/g

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

• 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

Lower Upper

U.S. 2.402 2.48Europe 2.402 2.48Japan 2.473 2.495Spain 2.447 2.473France 2.448 2.482

2.4 GHz

USUNII Low 5.15 – 5.25 (4) 50 mWUNII Middle 5.25 – 5.35 (4) 250 mWUNII Upper 5.725-5.825 (4) 1 W5.47 – 5.725 GHz released in Nov 2003

Europe5.15-5.35 200 mW5.47-5.725 1 W

Japan4.9-5.0915.15-5.25 (10 mW/MHz) unlicensed

5 GHz

802.11j and spectrum (Oct 2004)

• 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/pres

s_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/ne

ws/st/showArticle.jhtml?articleID=16503607

802.11h (Oct 2003)

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)