1. VoIP over Wireless LANs Sangho Shin Ph.D. Candidate Department of Computer Science Columbia University

2. Why VoIP? Personalized Service Location-based Service Emergency Service IP Voice Service

3. Why 802.11? Unlicensed channels Easy to install High speed Widely deployed Cheap

4. VoIP over 802.11 WLANs PBX Internet WIFI AP (Access Point)

5. QoS of VoIP in Wireless LANs Handoff Capacity Call Admission Control QoS

6. Handoff Handoff Time 500 ms ~ 1 s 4 ms ~ 100 ms Selective Scanning & Caching Layer 2 (MAC layer) Handoff

7. 1 2 3 4 5 6 7 89 10 11 2.402 GHz2.468 GHz 22 MHz ► Selective Scanning ► Caching  Locality  Store the scanned AP information to a cache Layer 2 Handoff 802.11b channels Only clients (driver) need to be modified!

8. Handoff Handoff Time 1 min 20 ms ~ 300 ms Fast L3 Handoff Passive DAD Layer 3 (IP layer) Handoff

9. Layer 3 Handoff ► Fast L3 Handoff (Client side)  Fast subnet discovery using a DHCP query  Scan unused IPs in a new subnet ► Passive DAD (Server side) 160.123.234.31 160.123.231.32 160.123.235.35 160.123.232.36 160.123.238.38 160.123.234.32 160.123.234.35 160.123.234.36 160.123.234.31 160.123.234.38 V V V V Request Response Monitor Collect IPs Update IP list Fast Response

10. Capacity Theater Stadium More simultaneous calls Low VoIP capacity in WLANs Low bandwidth Low utilization of VoIP traffic

11. Capacity 802.11 MAC PCFDCF DPCF APC VoIP Capacity 25%~30% Reduce polling overhead Fair resource distribution

12. Call Admission Control (CAC) WIFI QoS

13. Call Admission Control (CAC) WIFI QoS CAC

14. Call Admission Control (CAC) CAC QoSUtilization 90% 80%

15. CAC with QP-CAT QoSUtilization Call Admission Control (CAC) CAC QoSUtilization 90% 80% 100%98%

16. QP-CAT ? QoS Delay Predicted delay with QP-CAT Queue size Prediction (QP) Computation of Additional Transmission (CAT) MAC

17. Experiments NJ Rutgers University

18. Capacity for VoIP traffic in 802.11 WLANs Experiments DPCF APCQP-CAT

19. Thank you !