Wireless LANs

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/
In progress
Approved
External
5
802.11 MAC Standards
http//grouper.ieee.org/groups/802/11/
In progress
Approved
External
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/lectur
es/ermanno/802.11_Architecture.ppt
8
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

9
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 lt PIFS lt 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

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/Lectu
re4.pdf
wireless.ictp.trieste.it/school_2002/lectures/erma
nno/System_Performance.ppt
11
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 int
eroperability 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

• 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
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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
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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

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802.11j and spectrum (Oct 2004)
2.4 GHz

• 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 2.48
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
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802.11h (Oct 2003)

• 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/ne
  tqa0900aecd802570a1.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
  ?articleID16503607

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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)

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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)