TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 1

Design and Evaluation of a Multi-User Virtual Audio Chat

Lea Skorin-Kapov

R&D Center, Ericsson Nikola Tesla,

Zagreb, Croatia

Maja Matijašević

FER, University of Zagreb, Croatia

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 2

Presentation Outline

• Introduction

• Research issues

• Development of Virtual Audio Chat (VAC)

• Performance evaluation

• Conclusions

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 3

Introduction

• Virtual Reality (VR): interactive, immersive, multisensory, 3D synthetic environment

• VR service issues that dictate QoS requirements:– Rich VR/multimedia content– Perceived “real-time” interactivity– Multiple users

• Problem: different representations of QoS at user/application level and at communication level

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 4

• Research has mainly progressed in two complementary directions:– Performance of virtual reality end systems– Virtual reality communications

• Limited research on relating user perceived system performance with quantitative network parameters in distributed VEs

• Our Goal: address relationship between network and application level parameters

• Interconnection model used for reference

Research issues

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 5

• Attempts to present common issues in different VR

applications• User view: seamless virtual world, composed of shared

virtual objects and media streams (“trans(ient) objects”),

and modified by simulation and/or user interactions• Spatial composition: objects’ media components• Distribution/synchronisation: replication of distributed

objects and synchronisation for streams• Media connectivity: different media profiles - mapping to

transport level QoS parameters

NVR Interconnection Model (1)

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 6

NVR Interconnection Model (2)ObjectUV

Replicationprofile

a v

MC Media profile Media profile

(QoS) Media connectivity (best effort)

Stream mapping

SharedObject

Audiocont.

Videocont.

Textcont.

Media containerGeometry3D graphics2D graphics

audio video textcombined

SC

TransObject

Data,graphics

Replication Stream synchronization (inter-stream)

Media synchronization (intra-stream)DS

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 7

Development of Virtual Audio Chat

• Audio conference with (desktop) virtual reality interface

Three basic components:

• VRML mobile phone model

• Java applet opening RTP based audio conference

– Java Media Framework (JMF) API used

• Modified Session Directory (sdr) tool – enables user to

schedule and announce multimedia session

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 8

VRML mobile phone model

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 9

Virtual bufferInteraction with mobile keys

Animation

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 10

Real-time data transfer using RTP/RTCP

Application A Application B

Decoding Encoding

RTP RTCP

UDP/IP (multicast)

Figure adapted from “Internet Protocols for Multimedia Communications”, T. Braun , IEEE MultiMedia, 1997

DecodingEncoding

RTPRTCP

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 11

Modified session directory (sdr) tool• Sdr – scheduling/announcing multimedia sessions on the

MBone

• Modified by enabling new media type: vrml_audio

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 12

VAC interconnection model

graphics

ReplicationDS

MCMedia connectivity

SharedObject

Geometry3D graphicsSC

Profile 1

Stream synchronization (inter-stream)

Profile 2

TransObject

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 13

Performance Evaluation

• RTP/RTCP packet throughput

• Interactivity

– quantitative interactivity parameters

• Immersion

– quantitative immersion parameters

– jitter and packet loss

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 14

RTP/RTCP packet throughput

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 15

Interactivity

• Relating to scope and extend of user interactions in a VE

• Empirical approach using a questionnaire used to obtain user evaluation

• Can be quantified as combination of sensory support, navigation, and user representation

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 16

Object selection and manipulation

Interactions

None (viewer)User appearance (avatar quality)

Examine, fly, walkNavigation technique

Pointer (2D) recognitionCommand input

Mouse trackingVirtual controls

Tracking

ValueParameter

Quantitative interactivity parameters

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 17

Immersion

• Presentation quality of (multi) sensory information that user perceives as a 3D synthetic environment

• Quantified as combination of visual, auditory, and haptic immersion

No spatializationSound spatialization

Phone quality    (8000 Hz, 8 bit/sample)

Sound quality

ValueParameter

Quantitative immersion parameters

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 18

• Measurements of jitter and packet loss using rtpmon tool – reads RTCP packets generated by users

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 19

Conclusions

• A simple multi-user interactive VR/Web application has

been designed and developed

• The overall approach, from model to implementation, is

general and may be applied to a wide range of virtual

reality applications

• Performance results may be used for application

improvements (as perceived by the user) as well as for

resource reservation

TERENA NETWORKING CONFERENCE 2002 03. - 06.2002., Limerick Ireland 20

DEMO!