Development of a Multipurpose Audio Transmission System on the Internet

8/14/2019 Development of a Multipurpose Audio Transmission System on the Internet

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Development of aMultipurpose Audio

Transmission Systemon the Internet

Takashi Kishida

Graduate School of Information Sciences,

Hiroshima City University, Japan


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2003.6.19 Human.Society@Internet Conference 2

Overview

Introduction Purpose

Audio communication scenes Implementation Evaluations

Conclusion


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Background

Spreading Broadband networks Real-time audio transmission ispopular

Various types of audiocommunications have beenattempted.

Distance lecture, Distancechorus etc.

We should consider requirements dependingon each scene.


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A problem in the Audio

Transmission Considerations in audio communication scenes

Robustness Reliability audio transmission An ability to recover packet losses on networks

Short delay End-to-end delays include processing delays of an

end node and transfer delays on a network

Trade-off between robustness and delays

Difficulty to realize both requirements at thesame time

Ex.) the case of about 150 ms

delays


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Purpose

Consideration on conditions ofrequirements for each audio

communication scenes

Development of a multipurpose

audio transmission system toadapt to various scenes


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Classification

LowHighVery HighSynchronization

Reliable

transmission

Smoothinteraction

Audiosynchronizati

onShort dela

Mainrequirement

HighMiddleLowRobustness

AnyLess than

400msITU-T G.114

Less than

100 ms

Allowable

delay

One to

many

Many to

many

Many to

many

Direction

Distance

lecture

Audioconference

Distancechorus

Scenes

Requirements


7/332003.6.19 Human.Society@Internet Conference 7

Audio Communication Scenes

DistanceChorus

Distance Lecture

Audio conferenceConversation

100ms

400ms

End-to-end delay

Low High0ms

Robustness



MRATMultipurpose RAT)

MRAT was developed onthe basis of RAT RAT(Robust Audio Tool) is

one of mbone tools. MRAT has three modes

to adapt to variousscenes

Chorus mode

shorter delays Conversation mode Broadcast mode

high



Communication Scenes andmodes of MRAT

DistanceChorus

Distance Lecture

Audio conferenceConversation

100ms

400ms

End-to-end Delay

Low High0ms

Robustness

Original RAT

Shorter delays

High robustness

Chorusmode

Conversationmode

Broadcastmode

These twomodes areadded.



Chorus mode

We tuned buffering parameters ofan audio device.

To realize delays less than about100ms

This mode is set up as to achieve shorterdelay



Read length variation

This elapsed time related to delays.

The longer elapsed time is, the longer delays are.



Evaluation of cushion

Cushion is close related to buffering time anddefined by elapsed time.

Cushion was decreased

to about 26 ms from 90ms by changingparameters.

MRAT realizes delays of70ms.(Cushion + An additional processing delay =



We use Reed-Solomon block codeReed-Solomon block code has advantagein burst errors

Broadcast mode

To achieve robustness

Advantage in a real-time application

FEC Forward Error

Correctionsenderreceiver

generating redundant packet each somepacketsrecovery from redundant packets in thecase of packet losses

Broadcast mode is set up as to achieve robustness.


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State of Implementation

All modes are completed Almost all audio codec are

implemented in Broadcast mode

Confirmation of implementation

SoundBlaster Live! ValueSoundcard

Vine Linux 2.1,Vine Linux2.1.5,VineLinux2.5

OS

Pentium 1.0GHz Pentium300MHzCPU


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Evaluations of MRAT

Measurement of delays on eachmode

FEC Performance measurement ofBroadcast mode Practical experiments

Distance Chorus using Chorus mode Distance seminar using Broadcast

mode


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Experimental environment ondelays

Ethernet100Mbps

Host A Host B

Transmit

Recording PC

Record Record

Metronom

e

CPU Pentium

600MHz

CPU Pentium

1GHz

We measured thedifference of delaysbetween (a) and (b).

(a) Sound ofmetronome

(b) Soundvia Host B


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FEC Performance measurement ofBroadcast mode

Ethernet100Mbps

Lossgenerator

Host A Host BCPU Pentium 600MHz

OS Vine Linux2.5

CPU Pentium 1GHz

OS Vine Linux2.1

CPU Pentium 300MHz

OS Vine Linux2.1

Packet lossgenerated

1,2,4,6,8,10%

Measure after

decoding RScodes

We compared the experimental values and

the theoretical values

Experimentalvalues


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Result

0

1

2

3

4

5

0 2 4 6 8 10 12

Packet loss rate before applying FEC (%)

Packetlossrateafterap

plyingFE

(15,13)Experimental value

(15,13)Theoretical value





(1513)

(15

12)

(1511)

The theoretical values and the experimental valuesare almost the same.Packet loss rate can be decreased from 11% to less than 1% by using FEC.


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Di t S i i


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Hiroshima City Univ.

Hiroshima Univ.

SagaUniv.

Experimen

tal IPNetwork(ATM

45Mbps)

Jitter 4ms

Avg. packet loss

0.000058 %

RTT 14.8ms

Hiroshima City Univ. SagaUniv.

Jitter 6ms

Avg. packet loss0.120%

RTT 8.5ms

Hiroshima-city Univ.

-- Hiroshima Univ.Audio MRAT(160Kbps)

Movie Mpeg2ts(5Mbps)

Requirementbandwidth

Distance Seminar usingBroadcast mode


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The results of error recovery for only 100 seconds

as a typical part during the seminar

Error recovery of packetlosses using Broadcast mode

0.0%

1.0%

2.0%

3.0%4.0%

5.0%

6.0%

7.0%

0 20 40 60 80 100Time (sec)

Packetloss

rate(%)

Before applying FEC

After applying FEC

Packet losses are almost recovered by usingbroadcast mode


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Hiroshima City Uni

akushima Elementary School(Main melody)

inami-Kanon Elementary(Sub melody)

Experimental IPnetwork

10Mbps, widearea Ethernet

7075ms

DistanceChorus

Accompaniment

Accompaniment

Accompaniment

Submelod

y

Main+Sub

melody

Accompaniment

+Sub melody

Accompaniment

+Main melody

Mainmelody

7 msJitter

2.1 msTransfer delay

512 kbpsRequirementbandwidth


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Conclusion Classification of audio communication

scenes Development of a multipurpose audio

transmission system, MRAT, and itsevaluation Some practical experiments such as a

distance chorus at multi-points and

distance seminars

Our system can be used in multipleaudio communication scenes.


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Future Problems New applications using each mode Dynamic and adaptive changing of

three modes depending on therequirements


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Scalability of Distance Chorus

How wide area torealize distancechorus?

Light propagation:21000km in 70ms

We think practicalchorus is inMetropolitan networkwithin an area of afew hundreds

kilometers.

Considering this restriction, distance chorusis not realized in the worldwide on theInternet

The mostideal

situation

Its realizable as a regionalnetwork


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Bandwidth of MRAT

6652.8GSM

160128VDVI

160128DVI

8064G726-40

12096G726-40

160128G726-40

200160G726-40320256A-law

320256-law

640512Linear-16

Bandwidth ofAfter RS encode[kbps]

RS encodeBandwidth[kpbs]

Encoding

h li f d


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The quality of soundcomparison of MRAT and RAT

36.4RAT

3.4MRAT(Broadcast mode)

The detected number of

noise

This is the result that the noise of MRAT and RAT

was measured.FFT was used for the measurement.

li h i


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To realize the DistanceChorus

70ms

accompaniment

Mainmelody

Submelody

Ideal tolerant delay


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End-to-end delay bounds

150ms

Delay not Perceived

In most cases

400ms

Natural

Interaction

ITU-T G.114 ITU-T G.114

150m

s

400m

s

Best medium


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Development of a Multipurpose Audio Transmission System on the Internet

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