Prsentation Slides
Transcript of Prsentation Slides
Video Streaming Over Wireless: Video Streaming Over Wireless: Where TCP is Not Enough Where TCP is Not Enough
Xiaoqing Zhu, Jatinder Pal Singh and Bernd GirodXiaoqing Zhu, Jatinder Pal Singh and Bernd Girod
Information Systems LaboratoryInformation Systems Laboratory
Stanford UniversityStanford University
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Wireless Home NetworkingWireless Home Networking
54 Mbps
6 Mbps
24 Mbps
12 Mbps
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• TCP throughput over wireless• Demo: video streaming vs. file transfer• Comparison with ideal solution• What’s missing in TCP?
OutlineOutline
X. Zhu et al: Video Streaming over Wireless April 1, 2008 4
Heterogeneity in Wireless Link SpeedsHeterogeneity in Wireless Link Speeds
C1Cl
CN
Channel Time
…
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UDP Throughput over WirelessUDP Throughput over Wireless
10 20 30 40 500
5
10
15
20
25
30
Nominal Speed of Second Link (Mbps)
Thr
ough
put
(Mbp
s)
Simulation in NS2, for 802.11a network
Stream 1, alone
Stream 2, alone
Stream 1, shared
Stream 2, shared
54Mbps
) ) ) ) )
) ) ) ) )
Stream 2
Stream 1
6 ~ 54 Mbps
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TCP Throughput over WirelessTCP Throughput over Wireless
10 20 30 40 500
5
10
15
20
Nominal Speed of Second Link (Mbps)
Thr
ough
put (
Mbp
s)
54Mbps
) ) ) ) )
) ) ) ) )
Stream 2
Stream 1
6 ~ 54 Mbps
Simulation in NS2, for 802.11a network
Stream 1, alone
Stream 2, alone
Stream 1, shared
Stream 2, shared
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Overhead of TCP ACKOverhead of TCP ACK
6 9 12 18 24 36 48 540
20
40
60
80
100
Nominal Link Speed (Mbps)
Pe
rce
nta
ge
of
Ch
an
ne
l Tim
e (
%)
Data ACK
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Demo: Two NodesDemo: Two Nodes
Link Speed: 11 Mbps
Throughput : 4.4 MbpsShared : 1.0 Mbps (~ 20 % channel time)
Link Speed: 2 Mbps
Throughput : 1.4 Mbps
Shared : 1.0 Mbps (~ 70% channel time)
Video Source @ 2Mbps
File Transfer Source: 3.7MB
Scenario AScenario A
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TCP PerformanceTCP Performance
Video Streaming @ 2 Mbps
Time
Ra
te
…
File Transfer @ 1.0 Mbps
Share of Channel Time
23%
71%
6%
Video Streaming
File Transfer
ContentionOverhead
~ 30 s
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What Could Have Happened …What Could Have Happened …
Share of Channel Time
45%
50%
5%
Video Streaming
File Transfer
ContentionOverhead
Ra
te
Time
…
Video Streaming @ 2 Mbps
File Transfer @ 0.7 Mbps
~ 42 s
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Scenario BScenario B
Link Speed: 54 Mbps
Throughput : 20 Mbps
Shared : 1.2 Mbps(~ 6% Channel Time)
Link Speed: 2 Mbps
Throughput : 1.4 Mbps
Shared : 1.2 Mbps(~ 85% Channel Time)
Video Source @ 3 Mbps
File Transfer Source: 3.7MB
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TCP PerformanceTCP Performance
Time
Video Streaming @ 3 Mbps
File Transfer @ 1.2 Mbps
~ 25 s
Share of Channel Time6%
86%
8%
Video Streaming
File Transfer
ContentionOverhead
Ra
te …
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What Could Have Happened …What Could Have Happened …
Ra
te
Time
Video Streaming @ 3 Mbps
File Transfer @ 1.2 Mbps
…
~ 27 s
Share of Channel Time
15%
79%
6%
Video Streaming
File Transfer
ContentionOverhead
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What’s Missing in TCP?What’s Missing in TCP?
• Awareness of application’s utility function– For file transfer, aggregate rate matters– For video streaming, instantaneous rate matters– Video streams differ in their rate-quality tradeoffs
Utility function only needed at the source
• Knowledge of wireless link heterogeneity– Channel time shared among competing links– Congestion due to neighboring transmissions– High rate over a fast link vs. low rate over a slow link
End-to-end measurement no longer suffices
Notion of fairness should be revisited
Clean Slate Design Clean Slate Design or or
Evolution? Evolution?
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TCP Throughput over WirelessTCP Throughput over Wireless
1.22 MTUR
RTT p
1.22 MTUR
RTT p
packet size
roundtrip time
packetloss rate
data rate
[Mahdavi, Floyd 1997]
[Floyd et al. 2000]
• Per-packet fairness at the MAC layer
• Similar end-to-end observations of p, and RTT for competing wireless links
• Approximately equal rate, regardless of link speed
[Heusse et al. 2003]
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TCP Throughput over WirelessTCP Throughput over Wireless
54Mbps
) ) ) ) )
) ) ) ) )
Stream 2
Stream 1
6 ~ 54 Mbps
Simulation in NS2, for 802.11a network