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1PV'2003, Nantes France, April 2003
Measurement of the Congestion Responsiveness
of RealPlayer Streaming Video Over UDP
Jae Chung, Mark Claypool, Yali Zhu
Computer Science DepartmentWorcester Polytechnic Institute
Worcester, MA, USA
http://www.cs.wpi.edu/~claypool/papers/h2h/
PV'2003, Nantes France, April 20032
The Hungry Wolf – Bandwidth Requirements for
Video•Voice uses 32-64 Kbps, but video has
broader range of data rates– Videoconference 0.1 Mbps (H.261, MPEG-4)– VCR 1.2 Mbps (MPEG-1)– Broadcast quality 2-4 Mbps (MPEG-2)– HDTV quality 25-34 Mbps (MPEG-2)
Thus, potential for more than network capacity
PV'2003, Nantes France, April 20033
The Wolf on the Prowl – Transport Protocols for Video
•Streaming video doesn’t always like TCP– Wants rate-based not window-based– Can tolerate some loss– AIMD causes rate fluctuationsSo, uses UDP where application controls
•But UDP has no built-in congestion control– Unfair, unfriendly, and even collapse!
•Approaches to have router detect and limit– Often model video as CBR “firehose” (is it?)
PV'2003, Nantes France, April 20034
The Wolf Pack – Commercial Video
•Commercial products have major impact
•Have been studies characterizing commercial traffic– Bandwidth use, frame rate, user use…
•But no work measuring responsiveness, or lack of it, of commercial video products
Measure responsiveness of RealPlayer over UDP
PV'2003, Nantes France, April 20035
Outline
•Introduction •Background •Experiments
•Analysis
•Conclusions
PV'2003, Nantes France, April 20036
RealVideo Network Characteristics
•SureStream (is it effective?)– Allows bandwidth scaling
•Buffer (how fast is it filled?)– Smoother playout
Server
RTSP
Data: TCP or UDP
-Choice automatic
-We force
PV'2003, Nantes France, April 20037
Outline
•Introduction •Background
•Experiments •Analysis
•Conclusions
PV'2003, Nantes France, April 20038
Responsiveness Measurement Environment
• Encoding rates RealTracker
• Data rates via tcpdump
• Loss rates and round-trip times via ping
• TBF to limit bandwidth– 75, 150, 300, 600 kbps
• 79 (of 100) Clips, 2 measurements per clip
Internet
Client
Hub
Router
10Mbps
DSL
700KbpsClient
Token Bucket Filter
UDP
TCPServer
PV'2003, Nantes France, April 20039
Outline
•Introduction •Background
•Experiments
•Analysis
– Bandwidth – TCP-Friendly– Media Scaling– Buffering Rate
•Conclusions
Head-to-Head Bandwidth
0
50
100
150
200
250
300
350
400
0 50 100 150 200 250 300 350 400
Ave
rag
e B
and
wid
th fo
r U
DP
(K
bps
)
Average Bandwidth for TCP (Kbps)
75 Kbps150 Kbps300 Kbps600 Kbps
PV'2003, Nantes France, April 200311
A Sheep in Wolf’s Clothing?
•Remove low bandwidth (36%)
•Then remove unscalable (14%)
[PFTK98]
Media Scaling Distribution
0
0.1
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0.3
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0.5
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0.8
0.9
1
1 2 3 4 5 6 7 8 9
Cum
ula
tive
Den
sity
Number of Scales (Coded-Bandwidth)
Media Scaling Dynamics
0
50000
100000
150000
200000
250000
0 50 100 150 200 250 300 350
Co
ded-
Ban
dw
idth
(bp
s)
P layout + Buffereing Tim e (sec)
local bw lim it (35 kbps)Scale (Coded-BW ) Movement for C lip-65 TCPScale (Coded-BW ) Movement for C lip-65 UDP
Media Scaling Adaptation Speed
0
0.1
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0.9
1
0 10 20 30 40 50 60 70 80
Cum
ula
tive
Den
sity
E laps Time in Seconds: 0 to tim e(Coded-BW < 35kbps)
Scale Adaptation Speed for TCPScale Adaptation Speed for UDP
Buffering Rate to Playout Rate
0
1
2
3
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5
6
7
0 50 100 150 200 250 300 350 400
Ave
rage
Buf
feri
ng R
ate
/ A
vera
ge S
tead
y P
layo
ut R
ate
Average Steady Playout Rate (Kbps)
TCP (A ll DSL-TBF Runs)UDP (All DSL-TBF R uns)
PV'2003, Nantes France, April 200316
Summary
•No concrete incentives to respond to congestion– In fact, may be “rewarded” for not
•However, RealVideo clearly adjusts– Often TCP-Friendly
•Content providers need to provide chance for scalability– Scaling levels
•Buffering at higher rate is bad for network since bursty
•Why not TCP? API is limiting
PV'2003, Nantes France, April 200317
Future Work
•Other commercial Players– Microsoft Media Player
•Perceptual quality of video over TCP versus UDP
•Characterization of clips on Internet– So can examine “typical” clips
18PV'2003, Nantes France, April 2003
Measurement of the Congestion Responsiveness
of RealPlayer Streaming Video Over UDP
Jae Chung, Mark Claypool, Yali Zhu
Computer Science DepartmentWorcester Polytechnic Institute
Worcester, MA, USA
http://www.cs.wpi.edu/~claypool/papers/h2h/