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Fast Wireless Handoff in 802.11 Networks

Fast Wireless Handoff in 802.11 Networks. Sangho Shin Andrea G. Forte Anshuman S. Rawat Henning Schulzrinne. 802.11 Networks. A handoff occurs when a mobile station moves beyond the radio range of one AP and enters another BSS. Handoff delay. Mobile station. All APs.

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Fast Wireless Handoff in 802.11 Networks

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  1. Fast Wireless Handoff in 802.11 Networks Sangho Shin Andrea G. Forte Anshuman S. Rawat Henning Schulzrinne

  2. 802.11 Networks • A handoff occurs when a mobile station moves beyond the radio range of one AP and enters another BSS. Sangho Shin

  3. Handoff delay Mobile station All APs Probe request(broadcast) Probe response Probe delay Authentication request New AP Authentication delay Authentication response Reassocation request Reassociation delay Reassociation response Sangho Shin

  4. Handoff Delay Sangho Shin

  5. Problems • Handoff latency is too big for VoIP. • Seamless VoIP requires less than 90ms latency. • Handoff delay is from 200ms to 400msec. • The biggest component of handoff latency is probing (over 90%). Solutions • Selective Scanning • Caching Sangho Shin

  6. Selective Scanning • In most of the environments (802.11b & 802.11g), only channel 1, 6, 11 are used for APs. • Two APs that have the same channel are not adjacent (Co-Channel interference). • Scan 1, 6, 11 first !! Sangho Shin

  7. Selective Scanning - Algorithm Channel mask = 1, 6, 11 Scan channels using channel mask Found good AP ? Yes Join to the AP No Flip channel mask Set new channel mask New channel mask = 1,6,11 + scanned channels – current channel Sangho Shin

  8. Caching • Background • Spatial locality • Algorithm • After scanning, store the candidate AP info into cache (key=current AP) • Use the AP info in cache for association without scanning when handoff happens Sangho Shin

  9. Cache – Simulation Coverage area Detection area 1, 6 Channel mask AP1(11) Handoff !! AP3(1) AP2(6) Sangho Shin

  10. Cache – Simulation Coverage area Detection area 1, 6 Channel mask AP1(11) Handoff !! AP3(1) AP2(6) Cache miss! Selective Scanning AP2, AP3 Sangho Shin

  11. Cache – Simulation Coverage area Detection area 1, 6 1, 11 Channel mask AP1(11) Handoff !! AP3(1) AP2(6) Cache miss! Selective Scanning AP2, AP3 Connect AP2 Sangho Shin

  12. Cache – Simulation Coverage area Detection area 1, 11 Channel mask Handoff !! AP1(11) AP3(1) AP2(6) Sangho Shin

  13. Cache – Simulation Coverage area Detection area 1, 11 Channel mask Handoff !! AP1(11) Cache miss! AP3(1) AP2(6) Sangho Shin

  14. Cache – Simulation Coverage area Detection area 1, 11 Channel mask Handoff !! AP1(11) Cache miss! AP3(1) AP2(6) Selective Scanning AP1 Sangho Shin

  15. Cache – Simulation Coverage area Detection area 1, 11 1, 6 Channel mask Handoff !! AP1(11) Cache miss! AP3(1) AP2(6) Selective Scanning AP1 Connect AP1 Sangho Shin

  16. Cache – Simulation Coverage area Detection area 1, 6 Channel mask AP1(11) Handoff !! AP3(1) AP2(6) Sangho Shin

  17. Cache – Simulation Coverage area Detection area 1, 6 Channel mask AP1(11) Handoff !! AP3(1) AP2(6) Cache HIT! Sangho Shin

  18. Cache – Simulation Coverage area Detection area 1, 11 Channel mask AP1(11) Handoff !! AP3(1) AP2(6) Cache HIT! Connect AP2 Sangho Shin

  19. Cache – Simulation Coverage area Detection area AP1(11) 1, 11 Channel mask Handoff !! AP1(11) Cache Hit!! AP3(1) AP2(6) Sangho Shin

  20. Cache – Simulation Coverage area Detection area 1, 11 Channel mask Handoff !! AP1(11) Cache Hit!! AP3(1) AP2(6) Connect AP1 Sangho Shin

  21. Expreriment Result – Handoff time Sangho Shin

  22. Expreriment Result – Packet Delay Sangho Shin

  23. Expreriment Result – Packet Loss Sangho Shin

  24. Expreriment Result – Packet Loss Sangho Shin

  25. Conclusion • Fast MAC Layer handoff using selective scanning and caching • Selective Scanning : 100~130 msec • Caching : 2~4 msec • Don’t need to modify AP, infrastructure, or standard. Just need to modify wireless card driver! Sangho Shin

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