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Department of Communication Technology

Department of Communication Technology. Video Streaming over 802.11b LAN Wireless channel unreliability : managing the starvation phenomenon Mohamed Ali Ben Abid Monday, 28 June 2004. Supervisors Censors

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Department of Communication Technology

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  1. Department of Communication Technology Video Streaming over 802.11b LANWireless channel unreliability : managing the starvation phenomenonMohamed Ali Ben AbidMonday, 28 June 2004

  2. Supervisors Censors Frank H.P. Fitzek Karsten Thygesen Hans Peter Schwefel Thomas Toftegaard Nielsen

  3. Actual Concept 802.11b LAN: mobility, high data speed Video Streaming: more and more expanded in the wired network Video Streaming over 802.11b LAN, a promising combination.

  4. Project Presentation (1) Goal : Optimizing the video client’s resources while maintaining a good video quality. Means : Managing the Playout Buffer of the video. Estimating a buffer compensation for the wireless channel unreliability.

  5. Outline Background The 802.11b LAN Video Streaming The Study Problem Setting Scenario Methodology Results Conclusion Project Presentation (2)

  6. Background • The 802.11b LAN • Video Streaming

  7. 802.11b LAN - Architecture different BSS, different MN 1 BSS controlled by 1 AP Background The 802.11b LAN Architecture Layers Access Mechanism Errors

  8. 802.11 layers PHY layer : data transmission 802.11 MAC : fragmentation, Ack 802.2 : packets retransmission Background The 802.11b LAN Architecture Layers Access Mechanism Errors

  9. CSMA/CA Access Mechanism (1) • IFS • SIFS : separate transmissions, 28 μs • DIFS : station to start transmission, 128 μs • Positive Acknowledgement • Virtual Carrier Sense • hidden node problem • RTS/CTS Background 802.11b LAN Architecture Layers Access Mechanism Errors

  10. CSMA/CA Access Mechanism (2) • The access method is Distributed Coordination Function (DCF) Background The 802.11b LAN Architecture Layers Access Mechanism Errors

  11. CSMA/CA Access Mechanism (3) • The Backoff algorithm : Background The 802.11b LAN • Contention window from CW_min (16) to CW_max (1024). • m = maximum transmissions times. Architecture Layers Access Mechanism Errors

  12. Errors in the channel • Main Types of errors : frame loss / erroneous frames. • Causes of errors due to the channel : • Shadowing • Multipath fading • PHY layer adjusting the sending rate. • Detection/Correction Mechanisms : • if CRC failed, frame discarded • each MAC frame ACKnowledged (unicast) • ARQ (Send and Wait) • FEC (adds redundant bits) Background The 802.11b LAN Architecture Layers Access Mechanism Errors

  13. The 802.11b LAN Video Streaming Background

  14. Video Structure • def: Video frame = Picture • e.g. QCIF compression format : 1 picture = 176*144 pixels • with YUV representation, 1 pixel : 3Bytes Background Gives frame size (Byte) Video Streaming Video structure Streaming principle Real-time Requirements Protocol Stack

  15. Streaming principle (1) Background Video Streaming Video Structure • Why is frame size variable ? Streaming principle Real-time Requirements Protocol Stack

  16. Streaming principle (2) • Example of frame size PDF (Friends 2x16) • here, the total number of frames is 32455 Background Video Streaming Video Structure Streaming principle Real-time Requirements Protocol Stack

  17. Video Requirements Burstiness of video + wireless channel unreliability Packet losses & delays Tradeoff : number of Data Link retransmission Nr / delay introduced. • FER < 8/100 • Nr_max = 4 (unicast) = 0 (multicast) Background Video Streaming • UDP traffic (no layer 4 retransmission) Video Structure Streaming principle Real-time Requirements Protocol Stack

  18. Protocol Stack Background Video Streaming Video Structure Streaming principle Real - time Requirements Protocol Stack

  19. The Study • Problem Setting • Scenario • Methodology • Results • Conclusion

  20. Problem Setting (1) • Playout Buffer Occupancy (PBO) : The Study Main Problem • Intitial Buffer Occupancy (IBO) = T_start(display) – T_start(buffer filling) PBO/IBO definitions PBO constraints ε dependences

  21. Problem Setting (2) • θ ? • M ? Overflow ? • T0, T’ ? • Starvation, interruption ? The Study Main Problem PBO/IBO definitions Playout Buffer Occupancy (PBO)free in an error free channel PBO constraints ε dependences

  22. Problem Setting (3) • P9, P10…still not in buffer • e.g. if F4 = P8, F4 displayed, buffer empty : starvation The Study • . Then, e.g. if F5 = (P9,P10) & if P9, P10 did not arrive • interruption in display Main Problem PBO/IBO definitions PBO constraints ε dependences

  23. Problem Setting (4) θ = Initial buffer occupancy (error free channel) ε = Buffer compensation to the wireless channel unreliability Initial_Buffer = θ + ε 0 <(a) PBO = PBOfree + ε < M+ ε <(b)S (a) = no interruption (b) = no buffer overflow The Study Main Problem • Project focus : (a) given wireless scenario/ given video Chose an appropriate ε PBO/IBO Variables definition PBO constraints ε dependences

  24. Problem Setting (5) ε depends on the following parameters : Wireless conditions N = number of MNs Distance(s) laptop(s)/AP Competing traffic(s) FER (must be < 8%) NLoS Interference (neglected) Handovers (not here) Video Features Θ, T’ A priori estimation : ε < 5%* Θ The Study Main Problem PBO/IBO Variables definition PBO constraints ε dependences

  25. The Study • Problem Setting • Scenario • Methodology • Results • Conclusion

  26. Scenario (1) The Study • Server : desktop, P3-800MHz, 256MB RAM, 100Mbps Ethernet Card, 10/100 BaseT cable • AP is Nokia A032 and cards are Nokia C110 • MN = 1 laptop P4-2.2GHz, 256MB RAM, WinXP Scenario Experiment Scheme Main features 4 scenariii

  27. Scenario (2) • UDP datagram size = 1460 B The Study • layer 3 fragmentation threshold : 1475 B No L3 fragmentation • layer 2 fragmentation threshold : 2346 BNo L2 fragmentation Scenario Experiment Scheme Main features 4 scenariii

  28. Scenario (3) Video modelized by the traffic (Friends 2x16) duration :1300 s mean rate : 759486 bit/s Iperf generated traffic is UDP traffic sent with a rate of 759486 bit/s for 1300s. The Study Scenario Experiment Scheme Main features 4 scenariii

  29. Scenario (4) • Unicast / Multicast The Study Scenario Experiment Scheme Main features 4 scenariii

  30. Scenario (5) • Channel : Non overlapping conditions The Study Scenario Automatically choosed channel is number 10, but experiments made again with channel 1, 7, 13 (no difference / no interference problem) Experiment Scheme Main features 4 scenariii

  31. Scenario (6) • 4 scenarii : The Study Scenario (*) UDP traffic sent at 759486 bps from time 0s to 1300s. & competing TCP traffic sent at 4.38 Mbps from time 360s to 960s. Experiment Scheme Main features 4 scenariii

  32. The Study • Problem Setting • Scenario • Methodology • Results • Conclusion

  33. Methodology (1) Data is sent by the server with the CBR : λ Arrival Times delivered by Ethereal cumulative data volume V(t) can be plotted: The Study Methodology Definitions Plotting the margin Deducing ε

  34. Methodology (2) The Cumulative (receiving) throughput, Λ(t) = V(t)/t < λ ; (t>0) The margin function μ(t) : μ(t) = [ λ - Λ(t) ]*t = λ*t – V(t) > 0 ; (t>0) The Study Methodology Definitions Plotting the margin Deducing ε

  35. Methodology (3) The Study Methodology Definitions the difference gives μ(t) Plotting the margin Deducing ε

  36. Methodology (4) – deducing ε then, plotting : the Probability Density Function (PDF) of the margin μ the Cumulative Distribution Function (CDF) of the margin μ The Study Methodology Definitions Plotting the margin Deducing ε

  37. Methodology (5) – deducing ε Also, using the PBO of the video (during the time T’ The Study Methodology Definitions Plotting the margin Deducing ε

  38. Methodology (6) – deducing ε The Study Methodology Definitions Plotting the margin Deducing ε

  39. Methodology (7) – deducing ε Choosing an appropriate ε ? Simple method : (e.g) ε = μ / CDF(μ) =0.9 More judicuous: Pstarvation =  (Pr (B+  < x) . fμ(x). dx < 10-4 where, B=PBOfree and x from  to infinity  (FB(x -  ) . fμ (x). dx < 10-4  ( CDF [PBOfree(x -  )] * PDF [(x)]. dx < 10-4 The Study Methodology Definitions Plotting the margin Deducing ε

  40. The Study Problem Setting Scenario Methodology Results Conclusion

  41. Remembering Scenarii

  42. Results (1) For Friends 2x16, θ = 6.79 Mbyte 5 % * θ ~ 0.3 MByte Using the simple method: Scenario 1 : ε = 0.25 MByte Scenario 2 : ε = 0.30 MByte Scenario 3 : ε = 2.75 Mbyte !!! (need to use the second method found 1.4 Mbyte with method 2) Scenario 4 : ε = 0.31 MByte The Study Results Found ε /scenario SEQuence number Problems Managing

  43. Results (2) Ethereal : IP ID field SEQ numbers of missing packets The Study Results Found ε /scenario SEQuence number Problems Managing

  44. Results (3) The Study Results Found ε /scenario SEQuence number Problems Managing

  45. Results (4) The Study Results Found ε /scenario SEQuence number Problems Managing

  46. Results (5) The Study Results Found ε /scenario SEQuence number Problems Managing

  47. Results (6) Pb 1 : μ(t) sometimes negative ?!? μ(t) = = λ*t – V(t) > 0 ; (t>0) e.g : scenario 2 The Study Results Found ε /scenario SEQuence number Problems Managing

  48. Results (7) The Study Results Found ε /scenario Choice of origin !! SEQuence number Problems Managing

  49. Results (8) Pb2 : Why cumulative loss data is different from the maximum value of μ ? e.g. (scenario 2) respectively 0.17 Mbit & 2.4 Mbit AP adjusting the sending rate : AP sends with λAP < λ & λAP is variable (VBR) The Study Results Found ε /scenario SEQuence number Problems Managing

  50. Results (9) Future possible corrections: study λAP (Sniffer near AP) Suppress the time in the wired network Ter (wired) = Temission-reception The Study Temission = 1460*8/10*106 (10Mbps) =1.17ms Tpropag = 5*2/200000 = 0.085 ms (neglected) T traitment , Tqueues (negleted) Results Found ε /scenario SEQuence number Problems Managing

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