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

2. 2 VoIP over WLANs Internet IP GW WIFI

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

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

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

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

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

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

9. 9 Selective Scanning & Caching A layer 2 handoff algorithm to minimize the scanning time Sangho Shin, Andrea G. Forte, Anshuman Singh Rawat, and Henning Schulzrinne. Reducing MAC layer handoff latency in IEEE 802.11 wireless LANs. ACM MobiWac 2004 Handoff

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

11. 11 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 11 6 1 WIFI 1,11 Channel mask 1 234657891011 1 234657891011 AP1 AP2 AP3 AP4 1 234657891011 Handoff

12. 12 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 1 234657891011 Handoff

13. 13 Caching –Locality –Store the scanned AP data to a cache –Perform handoff without scanning Fast L2 Handoff 11 6 1 Key12 WIFI AP1 AP2 AP3 AP4 Cache Key12 AP1AP2AP3 Key12 AP1AP2AP3 AP2AP3AP4 Key12 AP1AP2AP3 AP2AP3AP4 Key12 AP1AP2AP3 AP2AP3AP4 Handoff

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

15. 15 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 Layer 3 Handoff WIFI DHCP Discover DHCP Offer DHCP Request DHCP ACK DAD DHCP procedure DAD: Duplicate Address Detection Handoff

16. 16 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. Handoff

17. 17 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). IEEE GLOBECOM, 2006. Handoff

18. 18 Passive DAD Server side solution for seamless L3 handoff –Eliminate the DAD procedure in the DHCP server when assigning new IP addresses 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 the network Collect IP addresses Update IP list Respond quickly to the request Handoff

19. 19 Passive DAD DHCP server Router Lease table IPMACExpire IPMAC AA-BB-CC1.1.1.1 Architecture Address Usage Collector (AUC) Handoff

20. 20 Passive DAD AUC DHCP server Router IP:1.1.1.1 MAC:AA-BB-CC Lease table ARP query Web server MAC:AA-BB-CC IPMACExpire 1.1.1.1AA-BB-CC100 IPMAC AA-BB-CC1.1.1.1 Example 1: IP address collection Handoff

21. 21 Passive DAD AUC DHCP server Router IP:1.1.1.1 IP:1.1.1.2 MAC:DD-EE-FF Lease table Web server MAC:AA-BB-CC IPMACExpire 1.1.1.1AA-BB-CC100 IPMAC AA-BB-CC1.1.1.1 IP:1.1.1.2 MAC:DD-EE-FF ARP query 1.1.1.2DD-EE-FF100 Bad IP table IPMAC DD-EE-FF1.1.1.2 Example 2: Malicious user detection Handoff

22. 22 Passive DAD AUC DHCP server Router IP:1.1.1.1 MAC:00-00-00 Lease table ARP query Web server Block 00-00-00 Forward HTTP traffic MAC:AA-BB-CC IPMACExpire 1.1.1.1AA-BB-CC100 IPMAC AA-BB-CC1.1.1.1 IP:1.1.1.2 MAC:DD-EE-FF IP:1.1.1.1 MAC:00-00-00 1.1.1.2DD-EE-FF1001.1.1.1AA-BB-CC100 Bad IP table IPMAC DD-EE-FF1.1.1.2AA-BB-CC1.1.1.1 FORCE RENEW IP:1.1.1.3 Example 3: IP collision detection Handoff

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

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

25. 25 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 Shin and Henning Schulzrinne. Experimental measurement of the capacity for VoIP traffic in IEEE 802.11 Wireless Networks. IEEE INFOCOM, 2007. Capacity

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

27. 27 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 PreamblePLCP header TX time VoIP Capacity sizeratesizerate Long144b1Mb/s48b2Mb/s192μs12 calls Short72b1Mb/s48b1Mb/s96 μs15 calls 12345 Packetization interval 12345 offset PLCPMACIPpayload 802.11 frame Capacity

28. 28 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 ↓ Capacity

29. 29 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 WCNC 2005. Capacity

30. 30 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 Contention Free Period (CFP) Contention Period (CP) Contention Free Repetition Interval DCF poll Poll+datapoll BeaconCF-End data Null Polling overhead Capacity

31. 31 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 Dynamic PCF Silence period poll Null Talking period voice Talking period send in CP 1 1 2 2 1 12 12 1 Set more data bit

32. 32 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 Capacity

33. 33 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 QShine 2005. Capacity

34. 34 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? Capacity

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

36. 36 APC Q AP =12, Q C =2, P=6 Downlink volume > Uplink volume Q AP =6, Q C =1, P=6 Example Capacity

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

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

39. 39 QP-CAT Queue size 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 INFOCOM 2008. CAC

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

41. 41 Emulate new VoIP traffic Packets from a virtual new flow QP-CAT Basic flow of QP-CAT Compute Additional Transmission channel Actual packets Additional transmission Decrease the queue size Predict the future queue size + current packets additional packets CAC

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

43. 43 QP-CAT 16 calls (actual) 17 calls + 1 virtual call (predicted by QP-CAT) 16 calls + 1 virtual call (predicted by QP-CAT) 17 calls (actual) 17th call is admitted 17 calls + 1 virtual call (predicted by QP-CAT) 16 calls + 1 virtual call (predicted by QP-CAT) 18th call starts 17 calls (actual) 18 calls (actual) Simulation results CAC

44. 44 QP-CAT Experimental results (64kb/s 20ms PI) 11Mb/s1 node - 2Mb/s 2 nodes - 2Mb/s3 nodes - 2Mb/s CAC

45. 45 QP-CAT QP-CATe –QP-CAT with 802.11e –Emulate the transmission during TXOP DDDTCP TXOP TcTc DDDTCP TcTc DDD TXOP CAC

46. 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. 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. 48 Thank you!

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

50. 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

51. 51 Development of SIP VoIP Client SIP

52. 52 Development of SIP VoIP Client SHARP Zaurus Prototype

53. 53 Development of SIP VoIP Client

54. 54 Layer 2 Handoff Handoff process Associate 6 Association Request Association Response WIFI Authenticate 6 New AP Authentication Request Authentication Response WIFI Scan APs 3 2 1 4 5 6 7 8 9 10 11Channels 1 6 11 APs Probe Request Probe Responses …… WIFI 500ms 2ms

55. 55 APC Q AP =8, Q C =2, P=4 Q AP =4, Q C =2, P=2 Q AP =12, Q C =2, P=6 Downlink == Uplink Downlink < Uplink Downlink > Uplink Q AP =4, Q C =1, P=4 Q AP =6, Q C =1, P=6 Q AP =2, Q C =1, P=2

56. 56 Seamless L3 handoff Goal –Do not modify any standard or infrastructure Fast subnet change detection –Idea: Subnet has each DHCP server or relay agent –Broadcast a bogus DHCP request The DHCP server responds with DHCP NACK Check the IP address of the DHCP server –Extension of L2Cache Stores the subnet ID –IP address of DHCP or relay agent Temp IP –Idea: Unused IPs every 5 IPs used –Scan potentially unused IP addresses in the new subnet Transmit multiple ARP packets –Pick a non-responded IP address as a temporary IP address Use it until a new IP address is assigned by the DHCP server ARP DHCP Discover timeout Update sessions DHCP Offer DHCP Request Update sessions DHCP Ack DHCP Request DHCP NACK Detect subnet change L2handoff Determine Temp IP 128.59.17.1 128.59.17.2 128.59.17.3 128.59.17.4 128.59.17.5 128.59.17.6 128.59.17.7 128.59.17.8 128.59.17.9 128.59.17.10 128.59.17.11 128.59.17.12

57. 57 Total handoff time ms Seamless L3 handoff Implementation –Linux, HostAP driver, SIP client Experiments 180 30 CU WLANCS LAN WIFI Experiments in 802.11b

58. 58 Problems of PCF in VBR VoIP traffic –Polling during silence periods –Synchronization problem –Multiple packetization intervals Silence period Dynamic PCF poll Null Talking period voice Example : 64kb/s 20ms PI with 0.39 AR Total waste = 9 VBR calls sent in CP APP MAC 121 111122 12112 111122 12 APP MAC CFP Interval = 10msCFP Interval = 20ms Node 1: 10ms, Node 2: 20ms

59. 59 Dynamic Polling List –Keeps the talking nodes only More Data bit –Set the More Data bit, then APs polls the node again Synchronization Dynamic PCF Silence period poll Null Talking period voice Talking period send in CP 12 111122 121 APP MAC CFP Interval = 20ms Set more data bit APP MAC cannot be in CPSet more data bit