Mobile Context Handoff in Distributed IEEE 802.11 Systems

1
Mobile Context Handoff inDistributed IEEE 802.11
Systems

• Jidong Wang and Lichun Bao
• Bren School of Information and Computer Sciences
• Presented by Lichun Bao

2
Introduction

• The need for mobility management
• Service provisions require consistent network
  connection
• VoIP over WLAN system requires low disruptions
  and low latency to ongoing traffic.
• Multimedia streaming to handsets

3
Solutions

• Mobility management systems
• Application layer SIP
• Transport layer Indirect TCP, Freeze TCP,
  improved TCP (NewReno, SACK, ELN)
• Network layer Mobile IP
• Data link layer IAPP, Snooping (TCP)
• Problems identified
• Data plane issues
• Control plane mechanisms
• Management of resources

4
Date link layer solutions

• Access points (APs)
• Logical functional entity in networking
• Data link layer services (MAC, addressing,
  errors)
• Differentiate from WTP wireless terminal point
• Physical device interfacing with the end-systems.
• Architecture of the AP implementations
• Autonomous regular IEEE 802.11 APs
• Centralized Aruba Networks APs, Cellular
  basestations
• Distributed ad hoc and mesh networks

5
Centralized AP Architecture

• Depends on the AP function placements
• Local MAC completing the whole MAC functions
• Split MAC separating MAC functions
• Remote MAC moving the MAC functions completely
  to remote central controllers

6
Our Approach

• Autonomous AP architecture
• Each AP is self-managing entity
• APs exchange control information such as host
  mobility, and other association states.
• Local AP implementation
• APs implements the whole set of MAC functions,
  including channel access, and station management.

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IEEE 802.11 System Architecture
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IEEE 802.11 Mobility Support
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Assumptions

• A single subnet supported by switches and hubs
• Access point functions are completely implemented
  on WTPs,
• WTPs are attached to hubs and switches

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Mobile AP Protocol

• Traffic monitoring
• Each AP monitors the RSSI values of all MS around
  it, no matter associated or not. Exponential
  averaging is used for simplicity.
• Each AP broadcast in layer-2 a MAC frame telling
  all the MS with the highest RSSI values among the
  subnet.
• Handoff Decision
• The AP with current association state determines
  whether it is a smart move to start handoff

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Mobile AP (cont.)

• Handoff
• Once a currently associated AP decides to move, a
  mobile context is transferred to the new AP.
• Messages used
• WATCH monitoring
• HO_START initiate HO
• HO_ACK agree to HO
• HO_DONE indicate completion

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Mobile AP Message Format

• Based on IAPP
• Mobile AP context information
• MAC address, associated AP BSSID, association ID,
  sequence numbers of MS and associated AP,
  buffered data frames.

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The End Result

• The associated AP seems following the MS in the
  subnet.

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Other Considerations

• Data link layer routing
• The new AP fake a dataframe from the MS.
• Switches self-learn the current location of the
  mobile station
• Beacons from the old AP
• No need to send again at the new AP
• If MS depends on beacons from old AP, Mobile AP
  does not work.

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Performance Evaluation

• Simulation
• Tools NCTUns 2.0 over Linux Fedora 2.0
• Setup
• IEEE 802.11b, 1Mbps as the base rate for control
  signals, and uses probing and re-association for
  mobility
• TCP traffic
• CBR UDP traffic 1024B/packet, 100 packet /
  second.
• Compare
• Delay of UDP traffic
• Sequence number growth of TCP traffic.

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UDP Performance
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TCP Performance
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Conclusion

• Mobile AP can be incorporated into IAPP.
• Mobile AP can work in other types of WLAN systems
  as well.
• Mobile AP support seamless mobility management.
• Key idea transfer the complete association
  context information for the mobile station.

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Questions????

• Happy surfing ?