DEPT. OF INFO. & COMM., GIST

Network-Adaptive Video Streaming over Wireless Mesh Networks

SangHoon Park

October 25th, 2007

Networked Media Laboratory, Department of Information and Communication

School of Information & MechatronicsGwangju Institute of Science & Technology (GIST)

shpark@nm.gist.ac.kr

http://nm.gist.ac.kr/~shpark

Lab SeminarLab Seminar

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Presentation Outline

Introduction & Motivation

Problem Description

Proposed System Architecture & Scheme

Implementation

Experimental Results

Conclusions & Future Work

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Video Streaming over Wireless Mesh Networks (WMNs) WMNs

A cheap and efficient method for providing network connectivity

Providing real-time multimedia service over WMNs VoD (Video on Demand) or Video broadcasting services in WMNs-based ubiquitous

environment

Video receivers: Multimedia communication with Internet servers

<Video service infrastructure in Wireless Mesh Networks> VoD Server

Video broadcasting

server

Video receivers

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Challenges in Video Streaming over WMNs

Higher bit error rate (BER) than that in wired-line links

Packet losses caused by many reasons Congestion, Random channel error, Route change/break, …

Scarce and time-varying network available bandwidth Dynamic channel capacity due to various kinds of interference

As increasing hop-count, end-to-end throughput is severely degraded

Lack of QoS support mechanism e.g., IEEE 802.11 has serious deficiencies in multi-hop environment due to hidden

terminal effects and contention from neighbor traffic

< Link-throughput > < End-to-end throughput >

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Considerable Solution Approaches To handle the impact of channel error

Efficient and resilient video coding and protection (e.g., FEC, delay-constrained ARQ, link-layer

retransmission, …)

To handle scarce and dynamic network available bandwidth Scalable video transmission using scalable video coding

Network-adaptive video rate control using network monitoring

Multi-path video transmission

QoS-supporting in layer MAC-layer service differentiation (e.g., IEEE 802.11e)

Cross-layer approach (Cross-layer optimization or interaction) Jointly consider different layers, including multimedia application, routing and transporting protocol, link

layer scheduling, and physical layer power control

We are focusing on the problem: Scarce and dynamic network available

bandwidth

How to effectively dynamically adapt video stream? End-to-end video quality improvement

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Problem Description

Basic Assumptions A video flow can be transmitted in scalable fashion (e.g., temporal scalability)

Base layer: l1, enhancement layers: l2, l3, …, ln

After video rate adaptation, k video layers are transmitted

A video flow use a single path in WMNs

S RN1 N2 N3

N5

N7N6

N4

Source video stream

3l2l1l

nl

1l

2l

kl

Adapted video stream

Video adaptation

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Problem Description (Cont.)

Interference due to competing flow Network available bandwidth for video flow is fluctuating

Arbitrary Intra-/Inter-background flow

For the given assumptions, How to adapt scalable video according to time-varying network available bandwidth to

improve end-to-end video quality?

Assumption: There is no greedy background flow. To cover this issue, multiple flow

scheduling algorithm or congestion control is required

S RN1 N2 N3

B1

Be

video flow

background flow

time-varying network available bandwidth

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Video Adaptation: End-to-End Vs Hop-by-Hop Rate Adaptation

End-to-end Video Rate Adaptation End-to-end statistics (e.g., loss rate, quality) monitoring at receiver

Sender adapt video based on feedback from receiver

Main drawbacks Reliability of feedback will be decreased as the congestion is increased

To guarantee reliable feedback, an additional back channel for feedback is needed

Delay of feedback makes that video adaptation reacts slowly to time-varying channel

condition

S RN1 N2 N3

end-to-end feedback

video adaptation

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Video Adaptation: End-to-End Vs Hop-by-Hop Rate Adaptation

Hop-by-hop Video Rate Adaptation Link statistics monitoring (e.g., MAC-layer loss rate) at each intermediate hop

Intermediate hop adapt video based on own monitoring information

Advantages The problems raised in the end-to-end approach can be solved

Overhead & Challenges Cross-layer design is required

Monitoring & rate adaptation module should be deployed at each intermediate hop

Prioritized packetization at sender is needed

S RN1 N2 N3

monitoring& adaptation

monitoring& adaptation

monitoring& adaptation

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Proposed System Architecture: Preliminary Design

Internet

video streams

Access pointMesh routers

< WMN Backbone> < WLAN>

Video Server

WMN gateway

Video receiver

Real-time parsing &prioritized

packetization

Intermediate node QoS control

playoutPlayout

buffering

Gateway architecture Video receiver architectureIntermediate node architecture

Packet droppingfor rate

adaptation

Wirelesschannel

monitoring

Packetdiscarding

Networkmonitoring

(multiple flow)

Cross-layer design

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Prioritized Packetization for Temporal Scalability

<Simple packetization>NOL= number of layers

TSpacket

RTPheader

TSpacket

TSpacket

TSpacket

TSpacket

TSpacket

TSpacket

Priorityfield

188*7=1316 12

1500

1

NOL+2

NOLRate

profileCurrent

layer

1NOL

We assume Profile: MPEG-2 TS over RTP

Priority field Each RTP packet contain additional fields in application layer

Frame indexing (may not need) Priority (layering information)

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Experimental Results: WMN Testbed

Deployed in GIST DIC 2nd floor

1 Gateway (N1), 6 Intermediate

nodes (N2~N7)

IEEE 802.11a-based

Single Interface

< Base-line throughput test (static routing): N1->N6>Link-throughput End-to-end throughput

N1 (gateway)

N2

KOREN

N3

N4

N5

N6N7

static routing path for throughput test

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Video format MPEG-2 TS

Resolution: 30fps 720x480

Bitrate: 4Mbps CBR

GOP: IBBPBB

Interference by background traffic N3 -> N2: 2~4Mbps Pareto UDP traffic

N4 -> N3: 2~4Mbps Pareto UDP traffic

N5 -> N4: 2~4Mbps Pareto UDP traffic

N6 -> N5: 2~4Mbps Pareto UDP traffic

N7 -> N6: 2~4Mbps Pareto UDP traffic

Single video streaming service N1 -> N2 -> N3 -> N4 -> N5 -> N6 -> video

receiver using static routing

N1 (gateway)

N2

KOREN

N3

N4

N5

N6N7

video receiver

video traffic

background traffic

Experimental Setup

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Temporal scalability of experimental video

stream Clip length: 2 minutes

GOP: IBBPBB, 30fps, 4Mbps

4 Temporal layers (l1, l2, l3, l4)

Rate profile of each temporal layer

l1: 1.52Mbps, l2: 0.86Mbps, l3: 0.8Mbps, l4: 0.8Mbps

Frame rate profile of each temporal layer

l1: 5fps, l2: 5fps, l3: 10fps, l4: 10fps

< Source video stream traffic characteristic >

I0 B1 B2 P3 B5 B6 Original GOP

I0

B1

B2

P3

B5

B6

l1: Base layer

l2

l3

l4

Enhancement layers

< Temporal layering of experimental video stream>

Experimental Video Specification

Time (s)

0 50 100 150 200 250 300

Kbp

s

3800

3850

3900

3950

4000

4050

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Experimental Results: Preliminary Results

< Background traffic pattern >

Experiment 1: 10 times According to the background traffic load

< Background traffic characteristic: 2M pareto >

Experiment

Index

Dst->Src Traffic pattern

Peak sending

rate

1 N3->N2 Pareto 2M

2 N3->N2 Pareto 3M

3 N3->N2 Pareto 4M

4 N4->N3 Pareto 2M

5 N4->N3 Pareto 3M

6 N4->N3 Pareto 4M

Time(s)

0 50 100 150 200 250

Bitr

ate

0.0

5.0e+5

1.0e+6

1.5e+6

2.0e+6

2.5e+6

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Experimental Results Methodology for end-to-end video quality measurement

Receiving stage: Received packet ratio per frame, Discarded frame ratio

Displayed Frame rate

Discontinuity, Variance of Discontinuity (VoD), Autocorrelation of

Discontinuity (AoD)

Demuxing Decoding RenderingReceiving < th

Y

Frame discarding

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Preliminary Experimental Results: N4->N3 background flow

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Preliminary Experimental Results with No Background

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Conclusions & Future Work Network-Adaptive

End-to-End Vs Hop-by-hop Video Adaptation in WMNs

Preliminary Architecture & Scheme are proposed

Future WorkPerformance Evaluation through extensive experiments

Hop-by-hop scheme needed to be improved

There is still video distortion before video adaptation starting due to

reactive reponse

To solve this problem, error recovery and adaptive playout can be

incorporated (preliminary idea!)

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References[1] J. Jun and M. L. Sichitiu, “The nominal capacity of wireless mesh networks,” IEEE Wireless

Communications Magazine, Oct. 2003.

[2] Q. Zhang, “Video delivery over wireless multp-hop networks,” in Proc. ISPCS, Dec. 2005

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Thanks ! Q & A