IEEE 802'11r

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• (IEEE 802.11r)
• Presenter
• Reima Soikkeli
• Tampere University of Technology
• reima.soikkeli(at)tut.fi

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Outline

• Definitions Terms
• Operation modes
• Examples
• 802.11r Motivations
• 802.11r Timeline
• Hidden node
• Expedited Handoff Packet Delivery
• The Mobility Concepts in WLAN
• Conclusion
• References
• Questions

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Definitions Terms

• IEEE 802.11r defines the Mobility in WLAN
• 802.11r - Standard will address fast roaming
  among access points
• 802.11r will support faster handoffs, improving
  application performance for mobile devices
• Faster handoffs will be critical to meet the
  real-time requirements of delay-sensitive
  applications, e.g. VoIP
• 802.11 Groups related to 802.21
• 802.11r Fast BSS Transition
• Between BSSes within the same ESS
• Improvements on MAC-layer

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Operation modes

• Infrastructure mode
• At least one Access Point (AP)
• Wireless end stations
• Basic Service Set (BSS)
• One AP
• Extended Service Set (ESS)
• Multiple APs

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802.11r Mobility Examples
b) ESSWLAN
a) Roaming Station
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802.11r Motivations

• Transitions between 802.11-1999 BSSes are hard
  enough task
• Many additions to 802.11 are making transitions
  much harder
• All proposals require 802.11i (802.1x) and
  802.11e support
• Need to minimize the time required to move
  between BSSs
• Goal anything that will speed transitions
• VoIP is primary application target
• For 802.21 what 802.11r creates might be used
  by 802.21
• 802.21 might have to use 802.11r facilities for
  roaming between 802.11 domains. (Similar to
  using 802.11u facilities for roaming between
  802.11 and external domains.)

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802.11r Timeline

• November 2004, Preliminary presentations of
  proposals
• 8 proposals received
• December 15 Preliminary draft text on 802
  server
• January 2005 Extensive presentations
• February 2005 Final draft text on server
• March 2005 Final proposals selections begin
  Draft 0
• May 2005 Task Group internal Letter Ballot
• Should be complete before 802.21 ends
• 802.11r support may become de-facto requirement
  for 802.21

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Expedited Handoff Packet Delivery

• Packet delivery latency in a BSS depends heavily
  on the network load (number of users, traffic
  pattern, etc.)
• Handoff packets must contend for the medium just
  like other contention based packets
• Due to the variability of the packet delivery
  delay, even with the proposed shortened handoff
  signaling protocol sequence, it is very difficult
  to have a bounded delay for fast BSS handoff
• To reach the goal of less than 50ms handoff
  latency, a method for expediting the delivery of
  fast BSS handoff protocol packets must be
  provided by Task Group

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Hidden node

• C cannot hear A
• If A is transmitting to B, then C cannot hear
  this
• If then C is trying to transmit to B, there will
  be a collision at B
• Only the receiver can help avoid collisions
• Busy tone, Request To Send (RTS), Clear To Send
  (CTS)

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Link Layer Mobility (BSS Transition, MAC Layer
Mobility)

• 802.11 provides MAC layer mobility within an
  Extended Service Set
• Stations continuously monitor the signal strength
  and quality from all access points
• Link layer mobility provides a seamless
  transition from one AP to another
• Station in the distribution system can send out
  frames addressed to the MAC address of the other
  mobile station, Access Points take care of the
  final hop to the Mobile Stations
• Link layer mobility requires co-operation of the
  Access Points
• A Standardized Inter-Access Point Protocol (IAPP)
  is likely to provide standardized method for the
  link layer mobility

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Network Layer Mobility (ESS Transition)

• When Mobile Station moves from one ESS to
  another, the seamless transition is not supported
  without suitable protocol support
• Mobile IP is considered to provide network layer
  mobility in WLAN networks
• Software client in the terminals are needed for
  mobility, which slows down the wide deployment
• The implementation differs between vendors

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Network Layer Mobility (ESS Transition) Mobile IP

• Two IP addresses are allocated for the Mobile
  Station Home Address and so called care of
  Address
• Mobile IP is based on the idea that the visited
  network informs the home network the care of
  IP address where the visiting mobile station can
  be found
• IP Mobility support is described in RFC 2002
• Additional support and system components are
  needed a Home Agent and a Foreigner Agent

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Application Layer Mobility (User Mobility,
Personal Mobility, Session Mobility)

• Application Layer Mobility provides mobility of
  users instead of mobility of terminals or IP
  addresses
• Users can use different terminals
• Application Layer Mobility is based on SIP
  (Session Initiation Protocol)
• SIP is designed by IETF and defined in RFC3261
• SIP resembles HTTP

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Conclusion

• Bigger challenges arise when a MS move from an
  ESS to the next one
• To achieve the goal of seamless mobility in
  WLAN, a fast Mobile IP handover is the solution
• Mobile IP serves as a base to realize mobility
• Mobile IP alone is insufficient to handle fast
  handover
• Performance of delay-sensitive applications like
  Voice over IP would not be compromised even if a
  MS is crossing a boarder between two WLAN networks

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References

• A study of mobility in WLAN www.tml.hut.fi/Studi
  es/T-110.551/2004/papers/Li.pdf
• IEEE Group Homepage http//groupee.ieee.org/grou
  ps/802/11
• Liaison Report IEEE 802.11 work related to
  802.21 www.drizzle.com/aboba/IEEE/ 11-05-
  0024-00-0000-january-05-ieee802-11-ietf-liaison-re
  port.ppt
• The Mobility Concepts is WLAN www.comlab.hut.fi/
  opetus/333/2004slides/topic42.pdf
• 83180 Wireless LANs Home page http//www.cs.tut.
  fi/kurssit/83180/

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Questions?
Thank You!