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!
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