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Call Admission Control in IEEE 802.11 Wireless Networks using QP-CAT

Call Admission Control in IEEE 802.11 Wireless Networks using QP-CAT. Sangho Shin Henning Schulzrinne Department of Computer Science Columbia University. WIFI. WIFI. WIFI. WIFI. WIFI. WIFI. Call Admission Control (CAC) in IEEE 802.11 Wireless Networks. QoS. WIFI. WIFI. WIFI. WIFI.

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Call Admission Control in IEEE 802.11 Wireless Networks using QP-CAT

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  1. Call Admission Control in IEEE 802.11 Wireless Networks using QP-CAT Sangho Shin Henning Schulzrinne Department of Computer Science Columbia University

  2. WIFI WIFI WIFI WIFI WIFI WIFI Call Admission Control (CAC) in IEEE 802.11 Wireless Networks QoS

  3. WIFI WIFI WIFI WIFI WIFI WIFI Call Admission Control (CAC) in IEEE 802.11 Wireless Networks QoS CAC

  4. ADDTS Request ADDTS Response WIFI Framework of CAC • IEEE 802.11e Admission Control Category TSpec Min/Max MSDU Min/Max Service Interval Min/Avg/Max Data Rate ? Category TSpec Status

  5. Outline • CAC in 802.11 Wireless Networks • Related work • QP-CAT • Simulation results • Experimental results • Extension of QP-CAT • Conclusion

  6. CAC in 802.11 Wireless Networks • Problems • Difficult to estimate QoS of VoIP traffic from the channel status • Difficult to predict the impact of new VoIP calls • Keys • Accurate metric for QoS • Need to represent delay not throughput • Prediction algorithm • Need to accurately predict the impact of new calls on QoS of existing calls

  7. Related work • Model based • Build a theoretical model • Compute available bandwidth or delay • Monitoring based • Monitor the current transmissions • Compute a metric (channel usage ratio etc.) • Probing based • Metric: delay and packet loss • Used for wired networks • Very accurate and simple • Waste a certain amount of bandwidth • Virtual Probing based • QP-CAT

  8. QoS Metric in QP-CAT • Metric: Queue size of the AP • Strong correlation b/w the queue size of the AP and delay D=(Q+1)DT D=downlink delay DT=TXtime of a VoIP frame

  9. QoS Metric in QP-CAT Estimation error

  10. Emulate new VoIP traffic Compute Additional Transmission Decrease the queue size Predict the future queue size Additional transmission + Packets from a virtual new flow channel Actual packets additional packets current packets QP-CAT Algorithm (1/5) • Basic flow of QP-CAT

  11. QP-CAT Algorithm (2/5) • Emulation of VoIP flows • Two counters: DnCounter, UpCounter • Follow the same behavior of new VoIP flows • Increase the counters every packetization interval of the flows • Decrement the counters alternatively Example : 20ms packetization interval time 20ms 20ms DnCounter++ UpCounter++ DnCounter++ UpCounter++ DnCounter++ UpCounter++

  12. QP-CAT Algorithm (3/5) • Computation of Additional Transmission

  13. QP-CAT Algorithm (4/5) • Handling Tr • Virtual Collision

  14. QP-CAT Algorithm (5/5)

  15. 18 calls (actual) 16 calls + 1 virtual call (predicted by QP-CAT) 17 calls + 1 virtual call (predicted by QP-CAT) 17 calls (actual) 18th call starts QP-CAT Simulation results 16 calls + 1 virtual call (predicted by QP-CAT) 17 calls + 1 virtual call (predicted by QP-CAT) 17th call is admitted 16 calls (actual) 17 calls (actual)

  16. IEEE 802.11b client client client client client AP clients client client client client client client client client client Experiments • Linux, MadWifi, Atheros • ORBIT test-bed in Rutgers University • Experimental setup • Ethernet-to-Wireless • 11Mb/s data rate

  17. 11Mb/s 1 node - 2Mb/s 2 nodes - 2Mb/s 3 nodes - 2Mb/s QP-CAT • Experimental results (64kb/s 20ms PI)

  18. Multiple execution of QP-CAT • Parallel execution • Need to test various types of VoIP traffic • Run multiple QP-CAT using each type simultaneously • Serial execution • The longer we monitor, the better decision • Takes time for accurate decision • Run two QP-CAT serially

  19. TXOP D D D D D D TCP Tc QP-CATe CAC • QP-CAT with 802.11e • Emulate the transmission during TXOP TXOP D D D TCP

  20. Conclusion • QP-CAT uses the queue size of the AP as the metric for QoS of VoIP traffic • QP-CAT can accurately predict the impact of new VoIP calls using CAT • We can run QP-CAT in parallel or serially to handle multiple new VoIP flows • QP-CAT can handle background traffic in 802.11e using QP-CATe

  21. Thank you

  22. 1 2 Tr 1 2 Tr QP-CAT Algorithm (4/8) • Computation of Additional Transmission Tc = Tc2 + Tr - TDIFS • Tr > Tb • Tr < Tb Tc2 1 2 Tr

  23. 802.11 Frame Transmission DIFS DIFS SIFS Defer Data Node A ACK SIFS Data Node B ACK

  24. QP-CAT Algorithm (5/8) • Handling Tr : Tr > Tb

  25. QP-CAT Algorithm (6/8) • Handling Tr : Tr < Tb

  26. QP-CAT Algorithm (7/8) • Virtual collision

  27. TC Up Dn RX TX TC TT RX1 RX2 Implementation • Environment • Linux, MadWifi driver, Atheros chipset • Monitoring • Atheros chipset notifies RX timestamp in microsecond and TX timestamp in millisecond • Additional wireless card as monitor mode at the AP • Computing TC TC = RX2– RX1 - TT

  28. Related work (3/3) • Comparison

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