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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 - PowerPoint PPT Presentation
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Video Streaming over 802.11b LANWireless channel unreliability : managing the
starvation phenomenon
Mohamed Ali Ben Abid
Monday, 28 June 2004
Department of Communication Technology
Supervisors CensorsSupervisors Censors
Frank H.P. Fitzek Karsten ThygesenHans 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 StudyProblem SettingScenarioMethodologyResultsConclusion
Project Presentation (2)
Background The 802.11b LANThe 802.11b LAN
Video StreamingVideo Streaming
7
802.11b LAN - Architecture
• different BSS, different MN
• 1 BSS controlled by 1 AP
The 802.11b LANThe 802.11b LAN
Access Mechanism
Layers
Errors
Architecture
Background
8
802.11 layers
• PHY layer : data transmission
• 802.11 MAC : fragmentation, Ack
• 802.2 : packets retransmission
The 802.11b LANThe 802.11b LAN
Access Mechanism
Layers
Errors
Architecture
Background
9
CSMA/CA Access Mechanism (1)
802.11b LAN802.11b 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
CSMA/CA Access Mechanism (2)
The 802.11b LANThe 802.11b LAN
Access Mechanism
Layers
Architecture
Background
Errors
The access method is Distributed Coordination Function (DCF)
11
CSMA/CA Access Mechanism (3)
The 802.11b LANThe 802.11b 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
Errors in the channel
The 802.11b LANThe 802.11b 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)
BackgroundThe 802.11b LANThe 802.11b LAN
Video StreamingVideo Streaming
14
Video Structure
Video StreamingVideo 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
Streaming principle (1)
Video StreamingVideo Streaming
Real-time Requirements
Streaming principle
Video Structure
Background
Protocol Stack
Why is frame size variable ?
16
Streaming principle (2)
Video StreamingVideo 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
Video Requirements
• Burstiness of video + wireless channel unreliability Packet losses & delays
Video StreamingVideo 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
Protocol Stack
Video StreamingVideo Streaming
Real - time Requirements
Streaming principle
Video Structure
Background
Protocol Stack
The Study Problem Setting
ScenarioScenario
MethodologyMethodology
ResultsResults
ConclusionConclusion
20
Problem Setting (1)
Main ProblemMain 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
Problem Setting (2)
Main ProblemMain Problem
PBO constraints
definitions
ε dependences
PBO/IBO
The Study
• θ ?
• M ? Overflow ?
• T0, T’ ?
• Starvation, interruption ?
Playout Buffer Occupancy
(PBO)free in an error free channel
22
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 ProblemMain Problem
PBO constraints
definitions
ε dependences
PBO/IBO
The Study
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
Main ProblemMain Problem
PBO constraints
Variables definition
ε dependences
PBO/IBO
The Study
Project focus : (a)
given wireless scenario/ given video
Chose an appropriate ε
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 Main ProblemMain Problem
PBO constraints
Variables definition
ε dependences
PBO/IBO
The Study
The StudyProblem SettingProblem Setting
ScenarioScenario
MethodologyMethodology
ResultsResults
ConclusionConclusion
26
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
ScenarioScenario
4 scenariii
Main features
Experiment Scheme
The Study
27
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
ScenarioScenario
4 scenariii
Main features
Experiment Scheme
The Study
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.
ScenarioScenario
4 scenariii
Main features
Experiment Scheme
The Study
29
Scenario (4)
ScenarioScenario
4 scenariii
Main features
Experiment Scheme
The Study
• Unicast / Multicast
30
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)
ScenarioScenario
4 scenariii
Main features
Experiment Scheme
The Study
31
Scenario (6)
• 4 scenarii :
ScenarioScenario
4 scenariii
Main features
Experiment Scheme
The Study
(*) UDP traffic sent at 759486 bps from time 0s to 1300s.
& competing TCP traffic sent at 4.38 Mbps from time 360s to 960s.
The Study Problem SettingProblem Setting
ScenarioScenario
MethodologyMethodology
ResultsResults
ConclusionConclusion
33
Methodology (1)
Data is sent by the server with the CBR : λArrival Times delivered by Ethereal
cumulative data volume V(t) can be plotted:
MethodologyMethodology
Deducing ε
Plotting the margin
Definitions
The Study
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)MethodologyMethodology
Deducing ε
Plotting the margin
Definitions
The Study
35
Methodology (3)
the difference gives μ(t)
MethodologyMethodology
Deducing ε
Plotting the margin
Definitions
The Study
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
MethodologyMethodology
Deducing ε
Plotting the margin
Definitions
The Study
37
Methodology (5) – deducing ε
• Also, using the PBO of the video (during the time T’
MethodologyMethodology
Deducing ε
Plotting the margin
Definitions
The Study
38
Methodology (6) – deducing ε
MethodologyMethodology
Deducing ε
Plotting the margin
Definitions
The Study
39
Methodology (7) – deducing ε
• Choosing an appropriate ε ?Simple method : (e.g) ε = μ / CDF(μ) =0.9More 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
MethodologyMethodology
Deducing ε
Plotting the margin
Definitions
The Study
40
The Study
Problem SettingProblem Setting
ScenarioScenario
MethodologyMethodology
ResultsResults
ConclusionConclusion
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
ResultsResults
Problems Managing
SEQuence number
Found ε /scenario
The Study
43
Results (2)
• Ethereal : IP ID field SEQ numbers of missing packets
ResultsResults
Problems Managing
SEQuence number
Found ε /scenario
The Study
44
Results (3)
ResultsResults
Problems Managing
SEQuence number
Found ε /scenario
The Study
45
Results (4)
ResultsResults
Problems Managing
SEQuence number
Found ε /scenario
The Study
46
Results (5)
ResultsResults
Problems Managing
SEQuence number
Found ε /scenario
The Study
47
Results (6)
• Pb 1 : μ(t) sometimes negative ?!?
μ(t) = = λ*t – V(t) > 0 ; (t>0)
e.g : scenario 2
ResultsResults
Problems Managing
SEQuence number
Found ε /scenario
The Study
48
Results (7)
Choice of origin !!
ResultsResults
Problems Managing
SEQuence number
Found ε /scenario
The Study
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)ResultsResults
Problems Managing
SEQuence number
Found ε /scenario
The Study
50
Results (9)
• Future possible corrections: study λAP (Sniffer near AP)
Suppress the time in the wired network
• Ter (wired) = Temission-reception
Temission = 1460*8/10*106 (10Mbps) =1.17ms
Tpropag = 5*2/200000 = 0.085 ms (neglected)
T traitment , Tqueues (negleted)
ResultsResults
Problems Managing
SEQuence number
Found ε /scenario
The Study
51
Results (10)
• Ter (wired) ~ 1.17 ms
• mean IAT = 1460*8/ λ = 15 ms
ResultsResults
Problems Managing
SEQuence number
Found ε /scenario
The Study
52
The Study
Problem SettingProblem Setting
ScenarioScenario
MethodologyMethodology
ResultsResults
ConclusionConclusion
53
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
Conclusion (2)
• Video features :PBOfree , 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
Conclusion (3)
• ε is deduced from the PBOfree (video features) and μ (wireless conditions)
e.g : ε / ( CDF [PBOfree(x - )] * PDF [(x)]. dx < 10-4
ε ~ 5% θ (unicast)
ε ~ 20% θ !! (multicast) to be reviewed
56
Conclusion (4)
• Future work : solve origin problems consider λAP instead of λ
(use of sniffer in air interface)mobility/handoversDifferent laptops with different traffics at
different starting times
57
THANK YOU
Mohamed Ali Ben Abid
Supervisors
Frank H. P. Fitzek
Hans Peter Schwefel
Censors
Karsten Thygesen
Thomas Toftegaard Nielsen