Overlay Topology Design Tradeoffs

Transcript

QoE in Pull Based P2P-TV Systems:
R. Fortuna, E. Leonardi, M. Mellia, M. Meo, S. Traverso
IEEE International Conference on Peer-to-Peer Computing
August 2010
S. Traverso (Politecnico di Torino)
August 2010
Outline
Outline
August 2010
1 / 29
Outline
Outline
1
Introduction
Motivations
Definitions
2
Overlay Topology Design
The Strategy
Chunk Signaling and Scheduling
Performance Evaluation Model
Network Scenario
Video Parameters
Results
3
Video-Aware Schedulers
The Strategy
Results
4
Conclusions
5
Q&A
August 2010
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Introduction
Introduction
August 2010
3 / 29
Introduction
Motivations
Why this work?
P2P-TV is a promising technology to reduce the cost of streaming
content over the Internet, while offering a world-wide service...
... but many issues about how to improve the user perceived video
quality are still open.
The “Network-Aware P2P-TV Application over Wise Networks” FP7
project aims at developing an application to broadcast high definition
video.
We focused our attention on
i) the design of the overlay topology, i.e. the network built by peers
at application layer;
ii) exploiting properties of encoded videostream to improve users’
QoE.
August 2010
4 / 29
Introduction
Motivations
Why this work?
P2P-TV is a promising technology to reduce the cost of streaming
content over the Internet, while offering a world-wide service...
... but many issues about how to improve the user perceived video
quality are still open.
The “Network-Aware P2P-TV Application over Wise Networks” FP7
project aims at developing an application to broadcast high definition
video.
We focused our attention on
i) the design of the overlay topology, i.e. the network built by peers
at application layer;
ii) exploiting properties of encoded videostream to improve users’
QoE.
August 2010
4 / 29
Introduction
Definitions
Basic concepts
A source peer splits the video streams in small chunks that are
injected inside the overlay.
Peers start exchanging chunks according to some scheduling scheme.
Chunks are exchanged among peers that are neighbors of each others.
P2P streaming systems, differently from file sharing, have to face with
the real-time constraint!
I
Every chunk must be received within a deadline Dmax also called
playout delay.
August 2010
5 / 29
Introduction
Definitions
Assumptions
Peers are Internet nodes and tipically their upload bandwidth is much
lower than the downlink one.
Peers upload bandwidth and latencies between peers are supposed to
be known somehow.
We neglect the effect of churning since scheduling dynamics are much
faster.
Peers exchange signaling information to trade chunks.
August 2010
6 / 29
Introduction
Definitions
Assumptions
be known somehow.
faster.
August 2010
6 / 29
Introduction
Definitions
Assumptions
be known somehow.
faster.
August 2010
6 / 29
Introduction
Definitions
Assumptions
be known somehow.
faster.
August 2010
6 / 29
August 2010
7 / 29
The Strategy
Intuition
To avoid long trading phases, peers with short end-to-end latencies
should be connected to each other.
To speed up chunk replication, high bandwidth peers should be well
connected to each other (to the source).
The number of neighbors of a peer have to choose, should be related
to its upload bandwidth.
August 2010
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The Strategy
Intuition
August 2010
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The Strategy
Intuition
August 2010
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The Strategy
The Strategy
How many neighbors?
Being Kp the number of neighbors of a peer p chooses, we set
Kp = max(3, 10 dBp /rs e) where Bp is the upload bandwidth of peer and rs
is the average video rate of the stream.
How to choose neighbors?
Given peer p, all peers q such that Bq > 1/2Bp and lpq < 1/2E [lpq ] are
marked as desired peers. Given the size of Kp , αKp peers are randomly
selected and (1 − α)Kp peers are selected within a set of desired peers of
p.
The neighborood size
The resulting size of the neighborood of a peer is Cp > Kp (edges are
bidirectional).
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A pull mechanism
Every peer periodically generates offer messages to publish the list of
its useful chunks.
Neighbors reply to each offer with a select message in which they
specify the chunk they need.
Once the select message is received, the chunk is then transmitted.
When the chunk is received, an acknoledgement message is sent back
to the trasmitter.
P5
P1
P7
P2
OFFERS
P4
P2
SELECTS
Np
Np
OFFERS
SELECTS
time
Chunk #1
to Peer 2
Chunk #1
to Peer 5
Chunk #2
to Peer 1
Chunk #2
to Peer 2
Chunk #2
to Peer 7
Chunk #3
to Peer 4
August 2010
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Peer and Chunk Selections
The Peer Selection
Np neighbors are contacted by a peer in every offer session. Np is a
fraction of the total neighborood Cp . In our tests, neighbors to contact
with offer messages are chosen uniformly at random.
The Chunk Selection
Chunks requested in select messages are randomly chosen over the the list
of useful ones proposed in offer messages.
This is commonly known as Random Peer, Random Useful Chunk
scheduling policy.
August 2010
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Nework Scenario
Our simulation involved 2000 peers partitioned in four classes according to
their upload capacity:
Class 1: 5.0Mb/s ± 10%;
Class 2: 1.6Mb/s ± 10%;
Class 3: 0.64Mb/s ± 10%;
Class 4: 0Mb/s.
We consider 4 scenarios, with increasing heterogeneity. The average
upload bandwidth is E [Bp ] = 1.3Mb/s in all cases.
Class
H = 0.01
H = 0.05
H = 0.10
H = 0.15
1
1
5
10
15
2
76.7
58.5
35.8
13.2
3
2.3
16.5
34.2
51.8
4
20
20
20
20
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The Transport Network
The transport network introduces a latency lpq to all the datagrams
sent from peer p to q.
Peers are distributed over the Earth surface and scattered over
domains representing continents.
Then, latencies are proportional to the geodetical distance between
peers.
1
80
40
20
PDF
Latitude [Deg]
60
0
-20
-40
-60
-80
-150 -100
-50
0
50
Longitude [Deg]
100
150
Figure: Peers distribution over Earth
surface.
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.05
0.1
0.15 0.2
Latency [s]
0.25
0.3
0.35
Figure: Latency frequencies,
E [lpq ] = 96ms.
August 2010
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Real video sequences
Three well-known video sequences have been considered as benchmarks.
Pink of the Aerosmith
Paris
Foreman
Length
40s
33.3s
40s
Spatial Res.
352 × 240
352 × 288
352 × 288
Frame/sec
25
30
25
The videos consists of 1000 frames ≈ 40s of visualization.
H.264/AVC codec has been adopted for encoding sequences.
Hierarchical structure of GOP: frames can be IDR, P, B or b.
Intra frames (IDR) carry valuable information (bigger), inter frames
(P,B or b) carry differential information (and are much smaller).
August 2010
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Results
The Impact of α
45
PSNR [dB]
40
35
30
25
EVQ
Dmax=6s
Dmax=5s
Dmax=4s
Dmax=3s
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
α
1
Average PSNR for different values of α for ρ = 0.9 (ρ = E [Bp ]/rs ).
August 2010
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Results
80
80
60
60
60
40
40
40
20
0
-20
-40
20
0
-20
-40
-60
-60
-80
-80
-150 -100
-50
0
50
Longitude [Deg]
100
150
Latitude [Deg]
80
Latitude [Deg]
Latitude [Deg]
The Impact of α II
20
0
-20
-40
-60
-80
-150 -100
-50
0
50
Longitude [Deg]
100
Figure: α = 0.0
Figure: α = 0.1
150
-150 -100
-50
0
50
Longitude [Deg]
100
150
Figure: α = 1.0
August 2010
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Results
80
60
60
40
40
40
20
0
-20
-40
20
0
-20
-40
-60
-60
-80
-80
-150 -100
-50
0
50
Longitude [Deg]
100
Latitude [Deg]
80
60
Latitude [Deg]
80
150
Figure: α = 0.0
20
0
-20
-40
-60
-80
-150 -100
-50
0
50
Longitude [Deg]
100
150
Figure: α = 0.1
-150 -100
-50
0
50
Longitude [Deg]
100
150
Figure: α = 1.0
46
44
PSNR [dB]
Latitude [Deg]
The Impact of α II
42
40
EVQ
α=0.0 Dmax=5s
α=0.1 Dmax=5s
α=1.0 Dmax=5s
38
36
1
6
11
16
21 26
Peers ID
31
36
41
α = 0.0 can lead to disconnected topologies!
August 2010
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Results
45
45
40
40
PSNR [dB]
PSNR [dB]
Adapting Kp to the upload capacity
35
30
25
EVQ
Dmax=6s
Dmax=5s
35
30
Dmax=4s
Dmax=3s
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
α
1
25
EVQ
Dmax=6s
Dmax=5s
Dmax=4s
Dmax=3s
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
α
1
Fixed Kp = 20 (left) and variable Kp = max(3, 10 dBp /rs e) (right) for
ρ = 0.9.
August 2010
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Results
Network stress
0.1
Network stress [ms]
0.09
0.08
0.07
0.06
0.05
Dmax=3s
Dmax=4s
Dmax=5s
Dmax=6s
0.04
0.03
0.02
0
0.2
0.4
0.6
0.8
1
α
Figure: The network stress index, i.e. the average distance covered by chunks
expressed it terms of the corresponding latency (ρ = 0.9).
August 2010
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Results
Robustness
46
H=0.01
H=0.05
H=0.10
H=0.15
EVQ
44.5
44
43.5
43
42.5
42
41.5
41
0.025
45
PSNR [dB]
PSNR [dB]
45.5
45
40
35
30
25
0.22
0.415
0.61
α
0.805
1
Paris
Foreman
Pink
Paris EVQ
Foreman EVQ
Pink EVQ
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
α
1
Figure: Average PSNR versus α for
Figure: Average PSNR versus α for
different degrees of heterogeneity H with different video sequences with ρ = 0.9,
H = 0.10 and variable Kp .
Dmax = 5s and ρ = 0.9.
August 2010
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August 2010
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PSNR [dB]
PSNR [dB]
Different frame types and losses
55
50
45
40
35
30
25
20
15
55
50
45
40
35
30
25
20
15
0
5
10
15
20 25
Time [s]
30
35
40
0
5
10
15
20 25
Time [s]
30
35
40
Figure: PSNR variation of a random peer versus time. ρ = 0.6 (rs = 780kb/s,
top) and ρ = 1.0 (rs = 1290kb/s, bottom).
August 2010
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The Strategy
Improving chunk selection
Different frame types have different importance in a video stream.
A frame loss may cause very different levels of degradation of the
reconstructed video quality:
I
I
missing an IDR frame impairs the video decoding until the next IDR;
missing a b frame impairs only the decoding of one single frame.
We can assign priority to chunks transporting precious frames.
To avoid chopping frames into several chunks, we set one frame per
chunk.
Priority is assigned to frames based on the amount of degradation
they might induce if lost: q is the number of subsequent frames that
would be affected by the lost of that frame.
A weight q ω is given to every chunk encapsulating a frame.
With ω > 0 we assign a larger weight to more important frames.
August 2010
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The Strategy
Improving chunk selection
Different frame types have different importance in a video stream.
A frame loss may cause very different levels of degradation of the
reconstructed video quality:
I
I
missing an IDR frame impairs the video decoding until the next IDR;
missing a b frame impairs only the decoding of one single frame.
We can assign priority to chunks transporting precious frames.
To avoid chopping frames into several chunks, we set one frame per
chunk.
Priority is assigned to frames based on the amount of degradation
they might induce if lost: q is the number of subsequent frames that
would be affected by the lost of that frame.
A weight q ω is given to every chunk encapsulating a frame.
With ω > 0 we assign a larger weight to more important frames.
August 2010
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Results
Slight Improvements
42
Pink
PSNR [dB]
40
38
36
34
ω=0.0
ω=0.5
ω=1.0
ω=2.0
32
5
10
15
20 25
PeerID
30
35
40
45
Figure: PSNR for different peers and values of ω with ρ = 1.1, Dmax = 5s and
H = 0.10. Pink by Aerosmith video sequence.
August 2010
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Results
Slight Improvements II
40
38
Paris
PSNR [dB]
36
34
32
30
ω=0.0
ω=0.5
ω=1.0
ω=2.0
28
26
5
10
15
20 25
PeerID
30
35
40
45
H = 0.10. Paris video sequence.
August 2010
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Results
Slight Improvements III
38
PSNR [dB]
36
Foreman
34
32
30
ω=0.0
ω=0.5
ω=1.0
ω=2.0
28
26
5
10
15
20 25
PeerID
30
35
40
45
H = 0.10. Foreman video sequence.
August 2010
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Conclusions
Conclusions
August 2010
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Conclusions
Conclusions
We provided guidelines for the design of the overlay topology and the
chunk scheduling algorithm.
By carefully designing the overlay topology we can partially localize the
traffic and improve the user QoE.
By prioritizing chunks that encapsulate valuable pieces of information at
the scheduler level, system performance can be slightly improved in
overloaded conditions.
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Conclusions
Conclusions
August 2010
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Conclusions
Conclusions
August 2010
27 / 29
Q&A
Q&A
August 2010
28 / 29
Q&A
Thank you for your attention!
August 2010
29 / 29

Overlay Topology Design Tradeoffs

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