Transcript 為無線網路視訊單播傳送而設計之動態多通道複製機制

Adaptive MPEG-4 Video Streaming
with Bandwidth Estimation: Journal
Version
指導老師：童曉儒
報告人：張益瑞
2015/4/9
教授
1
Outline
• Introduction
• Related Work
• MPEG-4 Background
• The Video Transport Protocol
• VTP Implementation
• Experimental Evaluation
• Conclusion
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Introduction
• Video streams are usually delivered via UDP with no
transport layer congestion control.
• Video streams are loss tolerant and delay sensitive.
• TCP involves the repeated halving and growth of its
congestion window, following Additive
Increase/Multiplicative Decrease (AIMD) algorithm.
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Introduction
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Introduction
• We design and implement a protocol that
attempt to maximize the quality of real-time
MPEG-4 video streams while simultaneously
providing basic end-to-end congestion control.
• Video Transport Protocol (VTP) delivers
consistent quality video in moderately
congested networks and fairly shares
bandwidth with TCP.
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Introduction
• Primary goal of adapting video stream to the
characteristics of the network path between
sender and receiver.(VTP sends packets using
UDP, adding congestion control at the
application layer.)
• Secondary goal of VTP is the minimal use of
network and computer resources.(bandwidth
and memory)
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Related Work
• Service model for multimedia streaming fall
into two categories:
1. Modifications or enhancements to AIMD congestion
control to better accommodate streaming
applications.
2. Model-based flow control based primarily on TCPFriendly Rate Control (TFRC)
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Related Work
• Rate Adaptation Protocol (RAP) :rate based protocol,
receiver feedback , no fairness with TCP.
• Stream Control Transmission Protocol (SCTP)
:multi-streaming, congestion control in SCTP is
identical to TCP.
• TCP-Friendly Rate Control (TFRC) : maintain the
sending rate at the level of a TCP flow under the
same conditions.
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Related Work
• TCP’s behaviors of poor link utilization in high-loss
environments and unfairness.
• VTP aims to be adaptive and flexible by making
minimal assumptions about the network and using
network feedback as a indicator, not as rigorous set of
input parameters.
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MPEG-4 Background
• High bitrate scalability and compression efficiency
• Spatial and temporal redundancy in individual frames
• Object-based encoding
▫ Video objects (VOs)
▫ Video object planes (VOPs)
▫ Group of Video Object Planes (GOV)
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MPEG-4 Background
• (I-VOPs)
• (P-VOPs)
• (B-VOPs)
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MPEG-4 Background
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MPEG-4 Background
• Macroblock
• Slice
• Quantization
Parameters(QPs):
量化參數較高就
是較高的壓縮率
與low quality。
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MPEG-4 Background/ VTP policy
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The Video Transport Protocol
• Sender and Receiver Interaction
• Bandwidth Estimation and Rate Adjustment
• Rate Based Congestion Control
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The Video Transport Protocol(concept)
• Communication between sender and receiver is a
“closed loop,” the receiver sends acknowledgments to
the sender at regular intervals.
• The bandwidth of the forward path is estimated and
used by the sender to determine the sending rate.
• VTP is rate based. There is no congestion window or
slow start phase.
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Sender and Receiver Interaction
RTT
measurement
& bandwidth
computation
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RTT
measurement
& bandwidth
computation
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Bandwidth Estimation and Rate Adjustment
b: rate sample
d: data bytes
t: time
B: bandwidth estimate
α : weighting factor
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Bandwidth Estimation and Rate Adjustment
(Finite State Machine, FSM)
Q: video encoding levels
IR: increase rate states
DR: decrease rate states
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Rate Based Congestion Control
• VTP is to adapt the outgoing video stream so
that, in times of network congestion, less video
data is sent into the network and consequently
fewer packets are lost and fewer frames are
discarded.
• VTP performs a type of congestion avoidance:
it increases its rate by a small amount on every
estimated RTT.
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VTP Implementation
• Software Architecture
• Transmission Schedules for Variable Bitrate Video
• Minimizing Client Buffer Requirements
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Software Architecture
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Software Architecture
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Transmission Schedules for Variable
Bitrate Video
V(t): the cumulative amount of
bytes consumed by the client from
the start of the streaming session to
time t
C(t): CBR schedule
ν(τ): the video is encoded at a
variable rate
U(t): Utilization
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Transmission Schedules for Variable
Bitrate Video
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Minimizing Client Buffer Requirements
Buffer 沒
有使用過
多或不足
的情形
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Minimizing Client Buffer Requirements
Quantization parameters(QPs): 量化參數高就是較高的壓縮率與low
quality。(DivX)
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Minimizing Client Buffer Requirements
Quantization parameters(QPs): 量化參數高就是較高的壓縮率與low
quality。(FFMpeg)
FFmpeg are smaller and
use less bandwidth than
DivX for the
same QPs
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Experimental Evaluation
•
•
•
•
•
Basic Protocol Behavior
Fairness with TCP
Random Link Errors
Comparison with TFRC
Video Quality
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Basic Protocol Behavior
• One of the main goals of VTP is to fairly share
network resources with other traffic.
• VTP attempts to achieve fairness with TCP by
reducing its sending rate whenever the bandwidth
estimate indicates that the current rate cannot be
supported.
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Basic Protocol Behavior
理想的sending rate：依估計的bandwidth調整sending rate。
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Fairness with TCP
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Fairness with TCP
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Random Link Errors
從random error的角度來看，VTP不因TCP發生大量error而快速搶占
TCP的頻寬，只是平緩的增加traffic。
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Comparison with TFRC
s: packet size
R: RTT
p: the steady state loss event rate
tRTO: the value of the TCP retransmit timeout
T: transmit rate
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Comparison with TFRC
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Video Quality
Quantization parameters(QPs): 量化參數高就是較高的壓縮率與low
quality。
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Video Quality
從Frame rate的角度來看，使用VTP可達到較穩定的Frame rate。
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Video Quality
從Frame rate的角度來看，使用VTP可達到較穩定的Frame rate。
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Video Quality
QPs 減低 3 ~ 5 可維持略高的影片品質。
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Conclusion
• VTP is the use of bandwidth estimation to adapt the
sending rate and the video encoding in response to
changes in network conditions
• We found that VTP fairness toward TCP is vulnerable
if the lowest video bitrate is higher than the average
link fair share available to VTP.
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