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

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Presentation on theme: "Video Streaming over 802.11b LAN Wireless channel unreliability : managing the starvation phenomenon Mohamed Ali Ben Abid Monday, 28 June 2004 Department."— Presentation transcript:

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

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

3 2 Actual Concept  b LAN: mobility, high data speed  Video Streaming: more and more expanded in the wired network  Video Streaming over b LAN, a promising combination.

4 3 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 4  Outline Background  The b LAN  Video Streaming The Study  Problem Setting  Scenario  Methodology  Results  Conclusion Project Presentation (2)

6 Background

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

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

9 8 CSMA/CA Access Mechanism (1) b LAN Access Mechanism Layers Architecture Background Errors  IFS  SIFS : separate transmissions, 28 μs  DIFS : station to start transmission, 128 μs  Positive Acknowledgement  Virtual Carrier Sense hidden node problem RTS/CTS

10 9 CSMA/CA Access Mechanism (2) The b LAN Access Mechanism Layers Architecture Background Errors  The access method is Distributed Coordination Function (DCF)

11 10 CSMA/CA Access Mechanism (3) The b LAN Access Mechanism Layers Architecture Background Errors The Backoff algorithm : Contention window from CW_min (16) to CW_max (1024). m = maximum transmissions times.

12 11 Errors in the channel The b LAN Access Mechanism Layers Errors Architecture Background  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)

13 Background

14 13 Video Structure Video Streaming Real-time Requirements Streaming principle Video structure Background Protocol Stack def: Video frame = Picture e.g. QCIF compression format : 1 picture = 176*144 pixels with YUV representation, 1 pixel : 3Bytes Gives frame size (Byte)

15 14 Streaming principle (1) Video Streaming Real-time Requirements Streaming principle Video Structure Background Protocol Stack Why is frame size variable ?

16 15 Streaming principle (2) Video Streaming Real-time Requirements Streaming principle Video Structure Background Protocol Stack Example of frame size PDF (Friends 2x16) here, the total number of frames is 32455

17 16 Video Requirements Burstiness of video + wireless channel unreliability Packet losses & delays Video Streaming Real-time Requirements Streaming principle Video Structure Background Protocol Stack Tradeoff : number of Data Link retransmission Nr / delay introduced. FER < 8/100 Nr_max = 4 (unicast) = 0 (multicast) UDP traffic (no layer 4 retransmission)

18 17 Protocol Stack Video Streaming Real - time Requirements Streaming principle Video Structure Background Protocol Stack

19 The Study

20 19 Problem Setting (1) Main Problem PBO constraints definitions ε dependences PBO/IBO The Study  Playout Buffer Occupancy (PBO) : Intitial Buffer Occupancy (IBO) = T_start(display) – T_start(buffer filling)

21 20 Problem Setting (2) Main Problem PBO constraints definitions ε dependences PBO/IBO The Study θ ? M ? Overflow ? T 0, T’ ? Starvation, interruption ? Playout Buffer Occupancy (PBO) free in an error free channel

22 21 Problem Setting (3) P9, P10…still not in buffer e.g. if F4 = P8, F4 displayed, buffer empty : starvation. Then, e.g. if F5 = (P9,P10) & if P9, P10 did not arrive  interruption in display Main Problem PBO constraints definitions ε dependences PBO/IBO The Study

23 22 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 = PBO free + ε < M+ ε < (b) S (a) = no interruption (b) = no buffer overflow Main Problem PBO constraints Variables definition ε dependences PBO/IBO The Study  Project focus : (a) given wireless scenario/ given video Chose an appropriate ε

24 23 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 Main Problem PBO constraints Variables definition ε dependences PBO/IBO The Study

25

26 25 Scenario (1) 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 4 scenariii Main features Experiment Scheme The Study

27 26 Scenario (2) layer 3 fragmentation threshold : 1475 B No L3 fragmentation layer 2 fragmentation threshold : 2346 B No L2 fragmentation UDP datagram size = 1460 B Scenario 4 scenariii Main features Experiment Scheme The Study

28 27 Scenario (3) Video modelized by the traffic (Friends 2x16) duration :1300 s mean rate : bit/s Iperf generated traffic is UDP traffic sent with a rate of bit/s for 1300s. Scenario 4 scenariii Main features Experiment Scheme The Study

29 28 Scenario (4) Scenario 4 scenariii Main features Experiment Scheme The Study Unicast / Multicast

30 29 Scenario (5) Channel :Non overlapping conditions Automatically choosed channel is number 10, but experiments made again with channel 1, 7, 13 (no difference / no interference problem) Scenario 4 scenariii Main features Experiment Scheme The Study

31 30 Scenario (6) 4 scenarii : Scenario 4 scenariii Main features Experiment Scheme The Study (*) UDP traffic sent at bps from time 0s to 1300s. & competing TCP traffic sent at 4.38 Mbps from time 360s to 960s.

32 The Study

33 32 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: Methodology Deducing ε Plotting the margin Definitions The Study

34 33 Methodology (2) The Cumulative (receiving) throughput, Λ(t) = V(t)/t 0) The margin function μ(t) : μ(t) = [ λ - Λ(t) ]*t = λ*t – V(t) > 0 ; (t>0) Methodology Deducing ε Plotting the margin Definitions The Study

35 34 Methodology (3) the difference gives μ(t) Methodology Deducing ε Plotting the margin Definitions The Study

36 35 Methodology (4) – deducing ε then, plotting : the Probability Density Function (PDF) of the margin μ the Cumulative Distribution Function (CDF) of the margin μ Methodology Deducing ε Plotting the margin Definitions The Study

37 36 Methodology (5) – deducing ε Also, using the PBO of the video (during the time T’ Methodology Deducing ε Plotting the margin Definitions The Study

38 37 Methodology (6) – deducing ε Methodology Deducing ε Plotting the margin Definitions The Study

39 38 Methodology (7) – deducing ε Choosing an appropriate ε ? Simple method : (e.g) ε = μ / CDF(μ) =0.9 More judicuous: Pstarvation =  (Pr (B  +  < x). f μ (x). dx < where, B  = PBO free and x from  to infinity  (F B  (x -  ). f μ (x). dx <  ( CDF [PBO free (x -  )] * PDF [  (x)]. dx < Methodology Deducing ε Plotting the margin Definitions The Study

40 39 The Study

41 40 Remembering Scenarii

42 41 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 Results Problems Managing SEQuence number Found ε /scenario The Study

43 42 Results (2) Ethereal : IP ID field SEQ numbers of missing packets Results Problems Managing SEQuence number Found ε /scenario The Study

44 43 Results (3) Results Problems Managing SEQuence number Found ε /scenario The Study

45 44 Results (4) Results Problems Managing SEQuence number Found ε /scenario The Study

46 45 Results (5) Results Problems Managing SEQuence number Found ε /scenario The Study

47 46 Results (6) Pb 1 : μ(t) sometimes negative ?!? μ(t) = = λ*t – V(t) > 0 ; (t>0) e.g : scenario 2 Results Problems Managing SEQuence number Found ε /scenario The Study

48 47 Results (7) Choice of origin !! Results Problems Managing SEQuence number Found ε /scenario The Study

49 48 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 λ AP < λ & λ AP is variable (VBR) Results Problems Managing SEQuence number Found ε /scenario The Study

50 49 Results (9) Future possible corrections: study λ AP (Sniffer near AP) Suppress the time in the wired network Ter (wired) = Temission-reception Temission = 1460*8/10*10 6 (10Mbps) =1.17ms Tpropag = 5*2/ = ms (neglected) T traitment, Tqueues (negleted) Results Problems Managing SEQuence number Found ε /scenario The Study

51 50 Results (10) Ter (wired) ~ 1.17 ms mean IAT = 1460*8/ λ = 15 ms Results Problems Managing SEQuence number Found ε /scenario The Study

52 51 The Study

53 52 Conclusion (1) Tradeoff between wireless channel unreliability and Video Streaming stringent QoS requirements ε defined as buffer compensation to manage the starvation phenomenom ε depends both on the wireless conditions and the video features

54 53 Conclusion (2) Video features :PBO free, T’ and θ Wireless parameters : distance AP/laptop, Mode, traffic duration, datagram lengths, mean rate, competing traffic, NloS… CBR λ, volume V(t) Margin function defined : μ(t) = λ*t – V(t) > 0 ; (t>0)

55 54 Conclusion (3) ε is deduced from the PBO free (video features) and μ (wireless conditions) e.g : ε /  ( CDF [PBO free (x -  )] * PDF [  (x)]. dx < ε ~ 5% θ (unicast) ε ~ 20% θ !! (multicast) to be reviewed

56 55 Conclusion (4) Future work :  solve origin problems  consider λ AP instead of λ (use of sniffer in air interface)  mobility/handovers  Different laptops with different traffics at different starting times

57 56 THANK YOU Mohamed Ali Ben Abid Supervisors Frank H. P. Fitzek Hans Peter Schwefel Censors Karsten Thygesen Thomas Toftegaard Nielsen


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