Transcript ppt

NETWORK LAYER FEEDBACK ENABLED
ADAPTIVE APPLICATION-LEVEL REROUTE
by
Liping Guo
Gouri Landge
Agenda
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Motivation
Proposed NLFEALR-scheme
A simple simulation system
Realization of NLFEALR & MDC-PD
Results & Comparison
Conclusion
Q&A
Motivation
 Undesirable network condition:
 Two major causes for packet-loss over the
Internet: Congestion & Link/node failure.
 Link/node failure happens due to faulty
equipment, router misconfigurations, and fiber
cuts…
 Long transient period for link failure: single
domain-tens of seconds; inter-domain-several
minutes.
 What if nothing is done for the transient period?
Say 2 second-long transient period
Motivation (cont.)
 How to deal with it?
 Multiple Description Coding (MDC) with path
diversity (MDC-PD)
creates independently decodable representations of
the video and transmitting them on different routs.
 Tradeoff between compression performance and
error resilience
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What if link failure happens only infrequently?
“Overprotection” ! ! !
Motivation (cont.)
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Goal: avoid “overprotection” and achieve
efficient use of the network resources.
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How? Adaptive reroute “on the fly”
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Fast link failure feedback is essential!!!
Good news: Network Layer Feedback System
(NLFS) proposed in:
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R. Keralapura, C. N. Chuah, M. van der Schaar, C. Tillier, an B.
Pesquet-Popsecu, “Adaptive Multiple Descriptions Scalable Video
Coding Using Network Layer Feedback.”
Network Layer Feedback System
(NLFS) R. Keralapura et al.
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Video server needs to register with the nearest
“Overlay Broker” before starting a video session.
Synergy Layer is created on top of the IP layer and
deployed in every router in various domains to
provide feedback.
Link failure info (e.g. IP addr of failed node) is
passed to the server through the overlay broker.
The maximum feedback delay is approximately 0.26
second.
Adaptive Application-level Reroute
The idea
0.26s
Adaptive Application-level Reroute
(1) Routing components
- Routing table-like structure is maintained by each
media server; it contains info about all possible
backup paths.
- Loose Source Record Route (LSRR) is used to do
reroute.
(2) Rate adaptation component
The focus of our project !
Rate adaptation component
A simple video streaming system
Rate adaptation component
How did we look at the problem?
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Assume playback starts after 2 second buffering;
Once play back starts, buffer enters “equilibrium
status”: the number of frames in the buffer is constant
(avg);
Link failure breaks the buffer’s equilibrium status; in
worst case, buffer could be overplayed to empty;
severe video quality degradation at the receiver side.
Find a way to let the play out buffer recover its
equilibrium status fast…
How? Send more with less quality
Rate adaptation component
High quality to low quality switch
Synchronization control @ server
Rate adaptation component
What bit rate to switch to?
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Toc: buffer over-consume time includes failure feedback delay (max
0.26s), routing process time (Tp), and 1/2 RTT.
Rate adaptation component
Let’s do the math!
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(1)
Noc: number of over consumed frames during Toc (s).
Rn: newly adapted streaming bitrate. (kbps)
Bn: available bandwidth of the chosen backup path.
Rp: play rate at the receiver side.
Qn: quality of the newly adapted video stream. (kbpf)
Rn = Rp * Qn
Assume refill buffer overrun portion within 1 second
(2) Qn = Bn / (Rp *1s + Noc)
(3) Noc = Rp * Toc
(4) Toc = 0.26s + Tp + ½ RTT
Rate adaptation component
An example bitrate switch table
Server maintains the bitrate switch table
Quality of video
(consumption rate in bits)
A simple simulation system
Codec: IBMCTF
Hinting file parser
Hinting file modifier
A simple simulation system
An example packet description in a hinting file
% PACKET_NUM=20
6
% TRANSMIT_SUCCESS
1
% IDENTIFICATION_TAGS
# Type GOPnum Fr_Typ Tlev
0 1
0
4
0
% DEPENDENCIES
4~5
% PACKET_SIZE
762
% IN_STREAM_POS
2000
Pos
Res
0
Ch
0
Chunk SubChunk
0
2
Simulation System
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Assumptions
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Link Bandwidth: 768 kbps
Average Link Failure Feedback Delay: 0.26 Sec
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Routing process time: 0.04 Sec
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Round trip time (RTT): 150 m Sec
Video Playback Rate: 30 Frames/Sec
Buffering time: 2s * 30f/s= 60 frames
Input
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288 Frames of Akiyo Sequence at cif
resolution
Realization of Rate Adaptation
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Assumption
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Available Bandwidth of Backup Path: 768 kbps
The Over Consumed Frames Refilled in 1 Sec
Toc = Tfb+ Tp+ ½ RTT
= 0.26s + 0.04s + ½(0.15s) = 0.38s
Noc = Rp * Toc = 30fps * 0.38s = 11 frames
Qn = Bn / (Rp * 1 + Noc)
=768kbps/(30+11) frames = 18.73 kbpf
Rn = Rp * Qn = 30 fps * 18.73kbpf = 562 (kbps)
Realization of Rate Adaptation (cont.)
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PSNR at 562 kbps is calculated while
decoding
To illustrate the effect of the quality
adaptation, we simply replace the PSNR
values of affected 41 frames, with new
PSNR.
Feature can be added to the codec to be
able to decode bit stream with switched
bit rate. In fact, this will be needed at the
receiver side, to use Rate Adaptation.
Realization of MDC-PD
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Codec generated Hinting File:
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Attributes:
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The packet attributes
The status of packet transmission as seen by
the receiver.
Texture or Motion Vector
I Frame or H Frame
Sub chunk, the packet dependency
Transmission Status
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Success or Fail
Realization of MDC-PD (cont.)
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Multiple Independently Decodable
Descriptions
Redundant information along with each
description
Error Resilience but lower quality
To achieve unequal protection
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Prioritize packets by assigning different
weights based on their attributes
Put most significant packets in all descriptions
Discard least significant ones to maintain BW
Realization of MDC-PD (cont.)
Weight Assignment
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I-Frame (Intra-coded Frame) : 400
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spatial redundancy within the frame
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Independent of any other frame
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Referenced by several other inter-coded frames
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Loss can cause catastrophe to the decoded video
H-Frame (Inter-coded Frame) : 100
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Temporal redundancy among neighboring frames
Motion vector information
Dependent on I frame and other H frames
Realization of MDC-PD (cont.)
Weight Assignment (cont.)
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Temporal Level : 80 to 10
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I Frames and H Frames are further classified based on
their temporal level.
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Temporal levels 4 through 1 are assigned weights 80,
40, 20 and 10.
Sub Chunk Number: variable
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Sub chunk number indicates the packet dependency.
Higher sub chunk number, lower significance
Realization of MDC-PD (cont.)
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If cumulative weight of a packet is greater than
the high threshold, add the packet to both
descriptions
Equal number of packets with weight less than
the low threshold is discarded.
Packets with weight between the higher and low
thresholds are evenly distributed between the two
descriptions such that both the streams can be
decoded independently.
RESULTS & ANALYSIS
RESULTS & ANALYSIS (cont)
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Both MDC-PD and our application-level reroute
scheme improve video performance in the
event of link failure.
Under normal condition MDC performance is
about 1dB below the performance of Feedback
Method due to Redundancy.
MDC experiences the lower PSNR for the entire
duration of the transient period
Using feedback enabled reroute method, the
lower PSNR is experienced only for a short
duration which is independent of the transient
period
CONCLUSIONS
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MDC-PD provides good error
resiliency
But has drawback of overprotection
when network conditions are fairly
stable
Feedback enabled application-level
reroute scheme can be used as
complementary solution for
bandwidth efficiency