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

2. Outline Why VoIP ? Why 802.11 ? My research

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

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

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

6. My Research Quality of Service for VoIP in 802.11 WLANs

7. VoIP (SIP) Client in PDA SIP = Session Initiation Protocol (RFC 3261) SIP

8. VoIP Client in PDA SHARP Zaurus Prototype ARM chip + Linux

9. VoIP Client in PDA Final product

10. Handoff Handoff Time 500 ms ~ 1 s 4 ms ~ 100 ms Selective Scanning & Caching Layer 2 (MAC layer) Handoff ACM MobiWac’04

11. 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!

12. Handoff Selective Scanning & Caching US Patent Application No. 60/549,782 2004 Product of the Year Award INTERNET TELEPHONY ® magazine (www.itmag.com)www.itmag.com

13. Handoff Handoff Time 1 min 20 ms ~ 300 ms Fast L3 Handoff Passive DAD Layer 3 (IP layer) Handoff ACM WICON’06 IEEE Globcom’06

14. 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

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

16. Capacity 802.11 MAC PCFDCF DPCF APC VoIP Capacity 25%~30% Reduce polling overhead Fair resource distribution IEEE WCNC’05 ACM Qshine’06

17. Call Admission Control (CAC) WIFI QoS

18. Call Admission Control (CAC) WIFI QoS CAC

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

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

21. Experiments NJ Rutgers University

22. Capacity for VoIP traffic in 802.11 WLANs Experiments IEEE Infocom‘07 DPCF APCQP-CAT

23. Thank you !