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Towards the Quality of Service for VoIP Traffic in IEEE 802.11 Wireless Networks

Towards the Quality of Service for VoIP Traffic in IEEE 802.11 Wireless Networks. Sangho Shin PhD candidate Computer Science Columbia University. Internet. IP GW. WIFI. VoIP over WLANs. WIFI. Problems on VoIP in WLANs. User mobility: Handoff. Theater. Stadium. WIFI.

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Towards the Quality of Service for VoIP Traffic in IEEE 802.11 Wireless Networks

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  1. Towards the Quality of Service for VoIP Traffic in IEEE 802.11 Wireless Networks Sangho Shin PhD candidate Computer Science Columbia University

  2. Internet IP GW WIFI VoIP over WLANs

  3. WIFI Problems on VoIP in WLANs • User mobility: Handoff

  4. Theater Stadium WIFI Problems on VoIP in WLANs • User mobility: Handoff • Capacity

  5. Theater Stadium WIFI Problems on VoIP in WLANs • User mobility: Handoff • Capacity • Call admission

  6. Handoff Capacity Call Admission Control QoS problems on VoIP in WLANs QoS

  7. Outline • Layer 2 handoff • Layer 3 handoff • pDAD • Measurement • APC • DPCF Handoff Capacity QoS Call Admission Control • QP-CAT

  8. WIFI Handoff Handoff • Layer 2 handoff • Handoff between two APs • Layer 3 handoff • Handoff between two subnets

  9. Handoff Selective Scanning & Caching A layer 2 handoff algorithm to minimize the scanning time Sangho Shin, Andrea G. Forte, Anshuman Singh Rawat, and Henning Schulzrinne. ReducingMAC layer handofflatency in IEEE 802.11 wireless LANs. ACM MobiWac2004

  10. Mobile client All APs Probe request (broadcast) Probe response Probe delay New AP Authentication request Authentication response Authentication delay Association request Association response Association delay Handoff Layer 2 Handoff • Standard Layer 2 handoff procedure 500ms 2ms 2ms

  11. 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 7 7 7 8 8 8 9 9 9 10 10 10 11 11 11 1 1 1 AP2 AP4 AP1 AP3 WIFI Handoff Fast L2 Handoff • Selective Scanning • Scan the channels that APs are most likely installed on • Previously scanned APs’ channels • Non-overlapping channels • Do not scan the current channel Channel mask 6 1,11 11 Channel mask 11 1

  12. 2 3 4 5 6 7 8 9 10 11 1 Handoff Fast L2 Handoff • Selective Scanning • Scan the channels that APs are most likely installed on • Previously scanned channels • Non-overlapping channels • Do not scan the current channel • Caching • Locality • Store the scanned AP data to a cache • Perform handoff without scanning Channel mask

  13. WIFI Handoff Fast L2 Handoff AP2 • Caching • Locality • Store the scanned AP data to a cache • Perform handoff without scanning AP4 6 Cache 11 AP1 AP3 11 1

  14. ms US Patent Application No. 60/549,782 Handoff Fast L2 Handoff • Implementation • HostAP driver + Prism2 chipset • Requires changes only in the client wireless driver • Experimental results Experiments in 802.11b WLANs

  15. DHCP procedure DHCP Discover DAD DHCP Offer DHCP Request DHCP ACK DAD: Duplicate Address Detection WIFI Handoff Layer 3 Handoff • L3 handoff • Occurs when the subnet changes due to L2 handoff • Requires a new IP address • Problem of L3 handoff • Detection of subnet change • Long acquisition of a new IP address

  16. Handoff Seamless L3 handoff • Goal • Do not modify any standard or infrastructure • Fast subnet change detection • Subnet has each DHCP server or relay agent • Send a bogus DHCP request in the new subnet • Temp_IP • Scan unused IP address actively • Send APR requests to a range of IP addresses • Reduced the total L3 handoff to 180ms Andrea Forte, Sangho Shin, and Henning Schulzrinne. Improving Layer 3 Handoff Delay in IEEE 802.11 Wireless Networks. IEEE WICON, Aug 2006.

  17. Handoff pDAD Passive Duplicate Address Detection A real time DAD mechanism in the DHCP server Sangho Shin, Andrea Forte,and Henning Schulzrinne. Passive Duplicate Address Detection for Dynamic Host Configuration Protocol (DHCP). IEEEGLOBECOM, 2006.

  18. Request Response V 160.123.234.32 V 160.123.234.32 V 160.123.234.35 V 160.123.234.36 160.123.234.31 160.123.234.38 Handoff Passive DAD • Server side solution for seamless L3 handoff • Eliminate the DAD procedure in the DHCP server when assigning new IP addresses Monitor the network Collect IP addresses Update IP list Respond quickly to the request 160.123.234.31 160.123.231.32 160.123.235.35 160.123.232.36 160.123.238.38

  19. 1.1.1.1 AA-BB-CC Handoff Passive DAD • Architecture Address Usage Collector (AUC) DHCP server Lease table IP MAC IP MAC Expire Router

  20. 1.1.1.1 AA-BB-CC 1.1.1.1 AA-BB-CC 100 Handoff Passive DAD • Example 1: IP address collection DHCP server IP MAC Expire AUC Lease table IP:1.1.1.1 MAC:AA-BB-CC IP MAC Web server Router ARP query IP:1.1.1.1 IP:1.1.1.1 MAC:AA-BB-CC

  21. 1.1.1.2 1.1.1.1 DD-EE-FF AA-BB-CC 1.1.1.2 1.1.1.1 DD-EE-FF AA-BB-CC 100 100 Handoff Passive DAD • Example 2: Malicious user detection DHCP server IP MAC Expire AUC Lease table IP:1.1.1.2 MAC:DD-EE-FF IP MAC Web server Bad IP table IP MAC Router ARP query IP:1.1.1.1 MAC:AA-BB-CC IP:1.1.1.2 MAC:DD-EE-FF

  22. 1.1.1.1 1.1.1.2 1.1.1.1 AA-BB-CC AA-BB-CC DD-EE-FF 1.1.1.1 1.1.1.2 1.1.1.1 AA-BB-CC AA-BB-CC DD-EE-FF 100 100 100 Handoff Passive DAD • Example 3: IP collision detection DHCP server IP MAC Expire AUC Lease table IP:1.1.1.1 MAC:00-00-00 IP MAC Web server Bad IP table IP MAC Router Block 00-00-00 Forward HTTP traffic FORCE RENEW IP:1.1.1.3 ARP query IP:1.1.1.1 MAC:AA-BB-CC IP:1.1.1.2 IP:1.1.1.1 MAC:DD-EE-FF MAC:00-00-00

  23. Call Admission Control Outline Handoff Capacity • Layer 2 handoff • Layer 3 handoff • pDAD • Measurement • APC • DPCF QoS • QP-CAT

  24. End-to-end < 150ms [ITU-G] Internet < 60ms 30ms 30ms 30ms Threshold Capacity WIFI Capacity VoIP Capacity • Definition • The number of VoIP calls whose uplink and downlink delay are less than 60ms Experimental result 64kb/s 20ms PI 802.11b 11Mb/s

  25. Capacity VoIP Capacity • Experimental measurement in the ORBIT test-bed • ORBIT test-bed (Rutgers Univ. NJ) • Open-Access Research Test-bed for Next-Generation Wireless Networks Sangho Shinand Henning Schulzrinne. Experimental measurement of the capacity for VoIP traffic in IEEE 802.11 Wireless Networks. IEEE INFOCOM, 2007.

  26. Capacity VoIP Capacity Experimental results in the ORBIT test-bed Downlink delay Downlink delay Uplink delay Uplink delay CBR VBR with 0.39 activity ratio 64kb/s VoIP traffic 20ms packetization interval 11Mb/s data rate

  27. PLCP MAC IP payload 802.11 frame Packetization interval 1 2 3 4 5 1 2 3 4 5 offset Capacity VoIP Capacity • Factors that affects the VoIP capacity • Preamble size • ACK data rate • 11Mb/s (QualNet)  16 calls • 2 Mb/s (MadWifi driver, NS-2)  15 calls • Offset among VoIP packets of other clients • Simulator  Synchronized  high collision rate • Experiments  Randomized  lower collision rate • ARF (Auto Rate Fallback) • Simulator Fixed rate15 calls • Experiments ARF enabled by default14 calls

  28. Capacity VoIP Capacity • Factors that affects the experimental results • Scanning • Scanning related frames delays VoIP packets • Simulator No scanning • Experiments  Scan APs due to retransmissions • Retry limit • Long retry limit (4)  short transmission time, high packet loss • Short retry limit (7)  long transmission time, low packet loss • Network buffer size • Buffer size ↑  packet loss ↓ delay ↑ • Buffer size ↓  packet loss ↑ delay ↓

  29. Capacity DPCF Dynamic Point Coordination Function An improved polling based PCF MAC protocol Takehiro Kawata, Sangho Shin, Andrea G. Forte, and Henning Schuzrinne. Improving The Capacity for VoIP Traffic in IEEE 802.11 Networks with Dynamic PCF. IEEE WCNC2005.

  30. Contention Free Repetition Interval Contention Period (CP) Contention Free Period (CFP) Beacon CF-End DCF poll poll Poll+data poll poll data data data Null Null Capacity Dynamic PCF • PCF (Point Coordination Function) • Polling based media access • No contention, no collision • Polling overhead • No data to transmit  Unnecessary polls waste bandwidth • Big overhead, considering the small VoIP packet size Polling overhead

  31. Talking period Silence period Talking period poll voice Null send in CP 1 2 1 1 2 1 2 1 1 2 Set more data bit Dynamic PCF • Dynamic Polling List • Keeps the talking nodes only • More Data bit • Set the More Data bit, then the AP polls the node again • Synchronization • Synchronize the polls with data

  32. Capacity Simulation results • VoIP capacity • Increased from 30 calls to 37 calls • Polls decreased by 50%, Null Functions by 90% • 760 frames / second = 7.29 VBR Calls

  33. Capacity APC Adaptive Priority Control A new packet scheduling algorithm at the AP in DCF Sangho Shin and Henning Schulzrinne. Balancing uplink and downlink delay of VoIP traffic in IEEE 802.11 Wireless Networks using Adaptive Priority Control (APC).ACM QShine2005.

  34. Capacity APC • Big gap between uplink and downlink delay Unfair resource distribution between uplink and downlink in DCF Solution  High priority to AP How? How much?

  35. Capacity APC • How? • Contention Free Transmission (CFT) • Transmit P packets contention free (w/o backoff) • How much? (Optimal P) • P QAP/QC • QAP is the number of packets in the queue of the AP • QC is the average number of packets in the queue of all clients • Adapts to instant change of uplink and downlink traffic volume P=3 P=4 D D D U U D D D D backoff

  36. Capacity APC • Example Downlink volume > Uplink volume QAP =12, QC=2, P=6 QAP =6, QC=1, P=6

  37. Threshold Capacity Capacity APC Simulation results 802.11b 11Mb/s 64kb/s VBR traffic 20ms pkt intvl 0.39 activity ratio 28 Calls  35 calls (25%)

  38. Call Admission Control Outline Handoff Capacity • Layer 2 handoff • Layer 3 handoff • pDAD • Measurement • APC • DPCF QoS • QP-CAT

  39. CAC QP-CAT Queuesize Prediction using Computation of Additional Transmissions A novel call admission control algorithm Sangho Shin and Henning Schulzrinne.Call Admission Control in IEEE 802.11 Wireless Networks using QP-CAT.IEEE INFOCOM2008.

  40. CAC Admission Control using QP-CAT • QP-CAT • Metric: Queue size of the AP • Strong correlation between the queue size of the AP and delay • Key idea: predict the queue size increase of the AP due to new VoIP flows, by monitoring the current packet transmissions Correlation between queue size of the AP and delay (Experimental results with 64kb/s VoIP calls)

  41. 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 CAC QP-CAT • Basic flow of QP-CAT

  42. CAC QP-CAT • Computation of Additional Transmission • Virtual Collision • Deferrals of virtual packets

  43. 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 CAC 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)

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

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

  46. Conclusion • Reduced the layer 2 handoff time using Selective Scanning and Caching • Achieved the seamless layer 3 handoff using Temp IP and pDAD • Measured the VoIP capacity in wireless networks via experiments and identified the factors that affect the VoIP capacity • Improved the VoIP capacity using DPCF and APC • Can perform call admission control with fully utilizing the channel bandwidth, using QP-CAT

  47. Other research • Implementation of SIP Servlet • Development of a SIP client in a PDA (SHARP Zaurus) • Soft Handoff using dual wireless cards • Measurement of usage of IEEE 802.11 wireless networks in an IETF meeting

  48. Thank you!

  49. VoIP Capacity in IEEE 802.11e Experimental results using AC_VO and AC_VI Experimental results with TCP traffic using AC_VO

  50. Comparison b/w poll and VoIP frame • Poll size • 28B (MAC header + CRC) • Total TX time = PHY (128 us) + MAC (26 us) = 154 us • Data • 28B + 160B • Total TX time = PHY (128 us) + MAC (26 us) + VoIP data (116 us) = 270 us • A Poll = 154/270 = 60% of a VoIP frame

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