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Proactive Context Transfer and Forced Handover in IEEE 802.11 Wireless LAN Based Access Networks

Proactive Context Transfer and Forced Handover in IEEE 802.11 Wireless LAN Based Access Networks. Mobile Computing and Communication Reviews, Volume 9, Number 3. Cheoleun Moon Computer Science Div. at KAIST. Contents. Motivation Overview of Handover Process Proposed Scheme

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Proactive Context Transfer and Forced Handover in IEEE 802.11 Wireless LAN Based Access Networks

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  1. Proactive Context Transfer and Forced Handover in IEEE 802.11 Wireless LAN Based Access Networks Mobile Computing and Communication Reviews, Volume 9, Number 3 Cheoleun Moon Computer Science Div. at KAIST

  2. Contents • Motivation • Overview of Handover Process • Proposed Scheme • Simulation Results • Conclusion

  3. Motivation • Mobility of wireless users has created many technological challenges • Mobile IP • IP mobility support • Also need to establish and keep service state information • QoS state • AAA(Authentication, Authorization and Accounting) state • Context Transfer Protocol (CTP) • Simple way to transfer context information from old AR to new AR • Some additional time will be required to re-establish service state after new AR receives context information

  4. Contributions • Propose a proactive scheme for CT • Attempts to estimate the best moment for proactive CT • Integration of Mobile IP, CTP, CARD protocol • Forced handover • Handover forced to occur at a “planned” moment

  5. Handover Process in IEEE 802.11 • AP • Link layer connectivity • AR • IP layer connectivity • Inter-AP handovers • Handover trigger • AP discovery/selection • Authentication • (Re-)association • Inter-AR handovers • Support routing process during handover between ARs • Mobile IP

  6. Handover Triggers and AP Discovery • Handover Triggers • Various different implementations • Include at least some link quality factors • Scanning cycle is repeated every Scanning Interval (TSI) • Probe Request/Probe Response • Until find new AP better than current one • Condition for inter-AP handover

  7. Mobile IP • Registration

  8. CTP and CARD • Context Transfer Protocol • Transfer service state between ARs to enable seamless mobility • Request-response mechanism • Insufficient in case of services involving network entities other than ARs (authentication servers, resource managers..)  Need proactive approach to CT • Candidate Access Router Discovery protocol • Discover IP addresses of candidate ARs for handovers and their capabilities

  9. Proposed Scheme • Estimation of proactive context transfer time • SNR is used for triggering and AP selection • Estimate the time until handover • If Tuntil_handover <= TSI, • Current scanning cycle is called scanning-to-CT • Next scanning cycle is called scanning-to-handover • MN identifies the scanning-to-CT by

  10. Forced Handover • There is not 100% guarantee that handover condition will be satisfied at the time of scanning-to-handover • Forced Handover • MN must make the handover after scanning-to-handover • Advantage • MN can set up an appropriate waiting time for transferred context at the new access network • MN may use Forced Handover as a trigger to send an Agent Solicitation message • Disadvantage • Unnecessary handovers

  11. Proactive Process • CARD Request • Address mapping • Identify inter-AP/inter-AR • CARD Reply • Handover type • Selected AP • Selected AR • Registration information (if inter-AR handover)

  12. Metrics for Performance Evaluation • Unnecessary Handovers • Handover that should not happen (but actually happened because of forcing) • Proactive Scheme Completion • Wasted bandwidth for sending Agent Solicitation message (if inter-AP handover) • Limited reduction of Agent Discovery delay (if inter-AR handover) • Reduction of Handover Latency • Latency of link switching + latency of network layer handover • Reduce Probe Delay (inter-AP) and Agent Discovery time (inter-AR)

  13. Simulation Results • Matlab • Probability of unnecessary handovers (Pun_HO) • Probability of proactive scheme completion (PPS_completion) • 61 APs distributed uniformly at a distance of 200m from each other • Radio propagation model • Path loss modelling (open outdoor environment) • Every AP has 6 neighbour APs • OPNET • Handover latency

  14. Unnecessary Handovers

  15. Proactive Scheme Completion

  16. Handover Latency Reduction S1: Active & Full Scan, Non-Forced Handover S2: Active & Selective Scan, Forced Handover, Incomplete CT S3: Active & Selective Scan, Forced Handover, Complete Proactive CT

  17. Conclusion • Presented a simple scheme for proactive CT with a new concept of Forced Handover • Predict the best moment in time to perform the CT • MN is forced to carry out handover • Proposed scheme • Reduce Probe delay, authentication delay and Agent Discovery delay • Improve handover latency • Small increase in the number of unnecessary handovers • This can be kept att a reasonably low level

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