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On Distributed Real-time Systems:

the mStar Environment,Net-based Learning and

Context-aware Applications

Kåre Synnes

Department of Computer Science and Electrical EngineeringCentre for Distance-spanning Technology

Luleå University of Technology

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Table of Contents

• Background

• Publications

• The mStar Environment– Robust Audio Transport

– Light-weight Application Level Tunneling

• Context-aware Applications– Privacy

• Net-based Learning

• Distributed Real-time Systems

• Conclusions

“ The best way to predict the future

is to invent it. ”- Alan Kay, 1971

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Background Distributed Real-time Systems

• Distributed– Internet (TCP, UDP, IP)– IP-Multicast, Peer-to-peer

• Real-time– Non-hard real-time characteristics– Synchronous

• Systems– From protocols to applications– Working prototypes– Feedback from real users

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BackgroundDistributed Real-time Systems

• Two frameworks for distributed real-time systems have been designed:– The mStar Environment

– The Alipes architecture

• The two frameworks are primarily discussed from two areas of usage:– Distributed Teamwork

– Net-based Learning

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Table of Contents

• Background• Publications• The mStar Environment

– Robust Audio Transport– Light-weight Application Level

Tunneling


• Net-based Learning• Distributed Real-time

Systems• Conclusions



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PublicationsThe mStar Environment

Paper APeter Parnes, Kåre Synnes, Dick Schefström, “The CDT mStar Environment: Scalable Distributed Teamwork in Action”.In the proceedings of Group 1997, Phoenix, Arizona, USA, November 1997.

Paper BPeter Parnes, Kåre Synnes, Dick Schefström, “Lightweight Application Level Multicast Tunneling using mTunnel”.In the Journal of Computer Communication, Volume 21, Issue 15, pp. 1295-1301, October 1998.

Paper CPeter Parnes, Kåre Synnes, Dick Schefström, “A Framework for Management and Control of Distributed Applications using Agents and IP-multicast”.In the proceedings of IEEE Infocom 1999, New York, USA, March 1999.

Paper DPeter Parnes, Kåre Synnes, Dick Schefström,“mStar: Enabling Collaborative Applications on the Internet”.In the Journal of Internet Computing, September/October 2000.

Paper EKåre Synnes, Peter Parnes, Dick Schefström, “Robust Audio Transport using mAudio”.Research Report 1999:04, ISSN 1402-1528, ISRN LTU-FR--99/04--SE, Luleå University of Technology, April 1999.

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PublicationsNet-based Learning

Paper FKåre Synnes, Serge Lachapelle, Peter Parnes, Dick Schefström,“Distributed Education using the mStar Environment”.Research Report 1997:25, ISSN 1402-1528, ISRN LTU-FR--97/25--SE, Luleå University of Technology,November 1997.In the proceedings of WebNet 1998 (Top Paper Award), Orlando, Florida, USA, November 1998. An extended version was also published in the Journal of Universal Computer Science, Vol. 4, Issue 10, pp. 807-823, October 1998.

Paper GKåre Synnes, Peter Parnes, Johnny Widén, Dick Schefström,“{Student 2000:} Net-based Learning for the Next Millennium”.Research Report 1999:05, ISSN 1402-1528, ISRN LTU-FR--99/05--SE, Luleå University of Technology, April 1999.In the proceedings of WebNet 1999, Honolulu, Hawai’i, USA, October 1999. Also presented in a shorter version at SCI/ISAS 1999, Orlando, Florida, USA, August 1999.

Paper HKåre Synnes, Tor Söderström, Peter Parnes, “Learning in Desktop Video-Conferencing Environments”.In the proceedings of WebNet 2001, Orlando, Florida, USA, October 2001.

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PublicationsContext-aware Applications

Paper IJames Nord, Kåre Synnes, Peter Parnes, “An Architecture for Location-aware Applications”.In the proceedings of HICSS-35 (Nominated for Best Paper), Big Island, Hawai’i, USA, January 2002.

Paper JKåre Synnes, James Nord, Peter Parnes, “Location Privacy in the Alipes Platform”.Research Report 2002:08, ISSN 1402-1528, ISRN LTU-SR--02/08--SE, Luleå University of Technology, April 2002.Submitted for review to HICSS-36.

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Table of Contents




– Robust Audio Transport– Light-weight Application

Level Tunneling




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The mStar EnvironmentResearch Issues

• What does the new generation of Internet-based real-time applications and systems require of a framework to allow distributed clients to act as autonomous entities with individual control, while at the same time allowing these clients to share information and control to jointly work as one system?

• How can real-time communication be made robust and adaptable to handle lossy and congested network conditions in general? How can an audio agent be designed to handle delay, delay variation and packet loss in particular?

• How can agents (modules) be designed for reuse and adaptation when implementing aggregated clients and systems?

• How should frameworks be designed to allow usage by mobile users, who inherently have limited terminal and network capacities?

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’Better-than-being-there’

The mStar EnvironmentmStar -> Marratech

• mDesk (WebDesk)• mWhiteBoard• mAudio• mWeb• mChat• mVote• mWave• mIR• mRadio• mTunnel• mGW• mSD• mSP• mPortal

• mVCR• mMOD• mIndex• mEdit• mVideo• SlideBurster• Director

Most tools start with a small m, thus the mStar (m*) name.

Most tools start with a small m, thus the mStar (m*) name.

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The mStar EnvironmentRobust Audio Transport

• Audio is the most important real-time media– Packet Loss

• Mostly 1-5%• Occasionally higher

• mAudio

• Audio Quality Tool– 3 sample technique

• Up to 20% loss can be repaired using fairly simple techniques– substitution

• silence• noise

– self-similarity• repetition• mixing

– redundancy

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The mStar EnvironmentRobust Audio Transport

• The phrase ‘Hello World!’ (40% loss)

• The three waveforms:– original– mixing– redundancy/repetition

• Combining methods for recovery are very effective!

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7The mStar Environment

Light-weight Application Level Tunneling

• Many networks lack support for multicast– Tunneling!

• Some networks cannot support high bandwidths– Bandwith reduction!

• mTunnel– web interface

– inter-domain

• mGW– mobile applications

– intra-domain

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• Saving bandwidth– Transcoding of data

– Statistical compression by grouping packets together

– 5-14% gain depending on traffic type

• Advanced measures to save bandwidth– mixing audio sources

– switching video source depending on current speaker

– lowering the frame rate

The mStar EnvironmentLight-weight Application Level

Tunneling

Yields extra delay!

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Table of Contents



Level Tunneling






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Context-aware ApplicationsResearch Issues

• What distinguishes a mobile application from its ‘stationary’ counterpart? Are they identical, or is it rather a question of the client and terminal capacities? Is location the primary distinguishing factor, in other words using context information to enhance usability and other factors in mobile terminals?

• How could seamless selection between alternative positioning techniques be achieved? Could alternative positioning techniques be used in conjunction and thus serve as additive techniques? Could position information be exchanged between nearby portable devices?

• How can access to location and context information be restricted to ensure the privacy of a user of a framework for distributed real-time applications? What criteria are important and how could usability be considered from the very start?

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Context-aware ApplicationsThe Alipes Platform

Applications

Positioning platform

Priv

acy

/ Sec

urity

Map Service

ServiceInfobase

GP

S

GS

M/G

PR

S

Blu

etoo

th

Wav

eLA

N

RF

ID

IRD

A

SB

Map

-ser

vice

Yel

low

Pag

es

Loca

tion

DB

Web

Sea

rch

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Context-aware ApplicationsPeer-to-Peer Position Exchange

PlatformM

PS

Blu

etoo

th

Carol

Platform

Blu

etoo

th

Wav

eLA

N

Dave

MPS ±ε

WaveLAN ±ε

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Context-aware ApplicationsTracker and GeoNotes

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Context-aware ApplicationsPrivacy

• The user owns and controls his own position information!

• The user decides who is allowed to access his position by granting a contract– Period in time– Number of queries– Granularity– Delegation rights

• A contract can be set up between the user’s client and...– A client application

– A location server

• The user can choose to delegate the right to set up contracts to a location server

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Table of Contents



Level Tunneling






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Net-based LearningResearch Issues

• What are the effects of using the frameworks for distributed teamwork in general and net-based learning in particular?

• What services and applications could best exemplify the future use of an integrated framework for distributed real-time applications with support for context-awareness and conferencing for distributed teamwork and net-based learning?

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Net-based Learning

• One of the primary usages of the mStar environment– Lectures

– Seminars

– Groupwork

– Presence (Corridor)

• Interactivity!• Independence

– Space & Time

Tutored groupwork for language learning

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Net-based LearningLessons Learned

• Students view the recorded lectures– Evenings

– Days before exams

– Partial replay, finding something in particular

– Possibility to pause and study base or in-depth material

• Side conversations– chat

• Social clustering– students help out

– group assignments

– changes the burden of the teacher, instead of a lecturer he will become a tutor

• Complexity!– A/V hardware

– Tools (usability)

– Time (isolation)

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Net-based LearningLessons Learned

• To support presence and improvisation in static lectures– Electronic whiteboard– Sensor-switched

cameras– Multiple projectors

• New pedagogical approaches is needed!– Problem-based learning– Project-based learning

• Bring the conferencing tools into a face-to-face situation– Best of two worlds!

• Mobile learning - find learning objects while moving around

• Recorded media

• Assignments

• Tutors

• Context dependent

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Table of Contents



Level Tunneling






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Distributed Real-time SystemsSymmetry

• Equal access and control of media involved– Interactivity!!

• No centrally stored shared state

• Loosely coupled autonomous client applications

• mStar– IP Multicast

• Alipes– Peer-to-peer– SIP server topology

• IP Multicast• Mobile IP

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Distributed Real-time SystemsRobustness

• A symmetric design means few or no dependencies on central servers– No bottleneck– No shared state

• Handle freely leaving and joining clients

• ’Best-effort’ local states– No guarantee that all users

see an identical view at all times

• mStar– IP Multicast

• Reliable/Unreliable– Loss recovery

• Repair schemes• Redundancy

– Bandwidth adaptation and management

• Alipes– Peer-to-peer– Multiple positioning

sources• Redundancy

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Distributed Real-time SystemsAdaptiveness

• Clients need to adapt to heterogeneous networks

• Other types of heterogeneity needs also to be considered– Terminals– Users– Context/Usage

• mStar– Bandwidth adaptation– Tunnels and gateways

• Recoding• Mixing• Scaling• Switching

• Alipes– Multiple positioning

sources

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Distributed Real-time SystemsScalability

• Scalability is imortant from multiple perspectives– Heterogenous

• Terminals

• Networks

– Number of simultaneous

• Users

• Sessions

• mStar– IP Multicast (?)

• Alipes– Peer-to-peer

– SIP server topology• IP Multicast

• Mobile IP

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Distributed Real-time SystemsReusability

• Standard components used in different ways– A/synchronously– Stand alone– Integrated– Different scenarios

• Net-based learning• Collaborative teamwork

• Special purpose clients are quickly developed

• mStar– Agent architecture

• Control Bus

• Alipes– Modular positioning

techniques• Platform

(Multiple techniques)• Single technique

– Modular map services

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Distributed Real-time SystemsUsability

• Distributed real-time systems may be quite complex to use

• Not an add-on, it needs to be considered from scratch

• Tight-loop iterative or cyclic design that involves users!

• mStar– Reuse of agents

• Stand-alone/Integrated• Different contexts

• Alipes– Allows for

differentiation of privacy management

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Table of Contents



Level Tunneling






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ConclusionsContributions

The principal contributions made by the author of this thesis are:

– The design and implementation of the mStar environment for distributed real-time applications based on IP-multicast and agent components.

– The design, implementation and evaluation of the audio agent component in the mStar environment.

– The design and implementation of the audio transcoding and video-by-audio switching mechanisms in the mTunnel application.

– The application and study of net-based learning using the mStar environment.

– The design and implementation of the Alipes architecture for location-aware applications, including the privacy management.

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ConclusionsNovelty

The novelty of this work lies in the ways in which the mStar environment and the Alipes architecture support the creation

of symmetric, robust, modular and interactive real-time applications for distributed teamwork and net-based learning

scenarios using heterogeneous networks and terminals.

The novelty of this work lies in the ways in which the mStar environment and the Alipes architecture support the creation

of symmetric, robust, modular and interactive real-time applications for distributed teamwork and net-based learning

scenarios using heterogeneous networks and terminals.

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ConclusionsBetter-than-(only-)being-there

• The original vision was that remote users would find using the tools ’better-than-being-there’.

• Now people are becoming highly mobile and are bringing the tools to face-to-face meetings...

• ...what if context-awareness, wearable computing and enhanced reality is added to the equation?

• Could it even be ’better-than-only-being-there’?

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Questions?

That’s all.Thank you for your attention!

Discussion by Angela Sasse, PhD.

Questions by the examination board and the audience.

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Seminars today

13.15-13.55 Angela Sasse (30+10 minutes)

13.55-14.20 Coffee

14.20-15.00 Björn Pehrson (30+10 minutes)

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BackgroundUnicast

• The sender duplicates the traffic once per additional receiver– This leads to a waste of

bandwidth!

• An alternative is to use replication servers in the network.– Points of failure

– Bottle-necks

The sender sends 3 identical copiesof the data (one for each receiver).

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BackgroundMulticast

• Traffic is duplicated when necessary– a single copy of the

data will travel on each connection

– the sender does not need to keep track of the receivers

– not relying on a central server

– MBone

The sender sends 1 copy which isduplicated by the network.

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BackgroundUnicast versus Multicast

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BackgroundPeer-to-peer

• Clients talk directly between each other without any servers in between

• This is typically used by loosely-coupled autonomous clients using ad-hoc networking

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Future Work

• mStar– Ubiquitous multicast

• Unicast/multicast• Tunnels/gateways

– Layered media (video)– Reduce complexity

• Net-based learning– Pedagogy– Technology

• Special client

• Alipes– Study the privacy

mechanisms– Prototype applications– Sound positioning– Non-users– Context

• Combining mStar and Alipes– Mobile Learning

(Mole)

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The mStar EnvironmentOverview

• It all began in 1995– VIC, video

– VAT, audio

• The Tunable Multicast Platform (/TMP)– a software library

for developing and integrating distributed applications

• The main choice of technology:– Java and IP Multicast

• The original usage:– Electronic Education

(Net-based Learning)

– Electronic Meetings(Collaborative Teamwork)

– Electronic Corridor(Virtual Corridor)

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The mStar Environment Management and Control of Distributed Applications

• There is a need to control the use of applications within an organization– avoiding flooding

– remote support and maintenance

• Agent-based design– Control Bus, CB

• Resource Discovery– finding the agents in a

group

– identify points of control

• mManager

• Also, bandwidth management in clients based on policies

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Context-aware ApplicationsResearch Issues

• What criteria should be used for seamless selection between alternative positioning techniques?

• Could alternative positioning techniques be used in conjunction and serve as additive techniques? – Could these be different peoples portable devicees?

• How could privacy be kept intact?

• What services and applications could best examplify future usage of such a platform?

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Context-aware ApplicationsThe Privacy Mechanism

Check party id

versus ban rules

Verify party id and key

Check contracts

Check general criteria

Check on/off

rule

Deny access

Grant access

Query

Deny

Negotiate contract

Grant

Off

Banned!

Unknown key

Matching denycriterion

No contract

Matching grantcriterion

Valid contract found

New contract

On

Ok

Ok

Ok

Ok

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Context-aware ApplicationsLocating a user using peer-to-peer technologies

[email protected]

GPS WLAN MPSBT

WLANd

BTd

MPSd

SIPd

Dave

2. Lookup Carol

3. Query Position

1. Locate Carol’s SIPd

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Context-aware ApplicationsLocating a user using a location server

[email protected]

GPS LOC

WLANd

BTd

MPSdSIPd

Dave

2. Lookup Carol

3. Query Position

1. Locate Carol’s SIPd

LOCd

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Net-based LearningWhy Net-based learning?

• Location independence

• Time efficiency– less traveling

– searchable content

• Decrease cost

• Increase quality

The Vision:An environment fornet-based learning and collaborative teamwork that offers a ‘better-than-being-there’experience for people not able to attend lectures, seminars or meetings physically.

The Vision:An environment fornet-based learning and collaborative teamwork that offers a ‘better-than-being-there’experience for people not able to attend lectures, seminars or meetings physically.

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Net-based LearningDistributed Lectures and Seminars

• HTML slides are prepared in advance

• Symmetric tools

– Audio/Video

– Web

– Whiteboard

– Chat

• Recording

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BackgroundProjects and Courses

• MATES(EU - Esprit 20598)

• Education Direct(Foundation for Knowledgeand Competence Development)

• Roxy(EU - Esprit 8410)

• MediaSite(EU - IA 1012 UR)

• Multimedia Systems

• Object-oriented Programming and Design

• Software Engineering

• EMC Technology

• Graduate StudentCourses and Seminars

• Seminars and Presentations

“Live as you teach.”

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BackgroundNetworks

• Campus network– ~2000 students

• County network– to most municipalities

in Norrbotten

• City network– Gigabit bandwidth

• Connections to homes– ADSL/Cable/Ethernet

• Most people in Norrbotten will have high bandwidth access within a few years

• This will impact how people live!

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Net-based LearningSeminars and Lectures

• The traditional lecture is the ‘pulse’ of the course– giving the pace

– check point

– questions

• Student seminars for information sharing:– the student present

topics

– the topic is then discussed in class

– excellent way to share knowledge

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Net-based LearningThe board

• A touch-sensitive board, onto which the whiteboard or slide viewer is projected

• Used instead of mouse

• The speaker is more free to move around

• Easier to draw pictures freehand

• Direct manipulation

• Enables a higher degree of freedom and improvisations!

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Net-based LearningThe Virtual Corridor

• A collection of low bit-rate video flows

• Presence– during lectures

– always on (home), a place for quick help

• Visibility might remedy shyness

• A differentiation of the sound sources during lectures– lecturer

– remote attendants

• Enables a higher degree of presence and location!

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Net-based LearningThe Future Lecture Hall

A Whiteboard (Touch Sensitive - SmartBoard)

B Web Slides

C Virtual Corridor

D Lecturer Station

• Spatialized Audio– Front, Lecturer

– Side, Network

• Multiple Camera Angles

A

C

D

B

Control Booth

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Net-based LearningVirtual group room

• Group discussions

• With or without a supporting teacher

• Can be used to replay and discussion of recordings– enables interactivity

even to fairly static recordings

• Additional tools can be used– whiteboard

• Builds group awareness among remote students– lessens isolation

• Virtual Teachers Room

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Net-based LearningThe Digital Library

• The library is central to most universities

• Now also lectures and learning content can be stored Information can be

retrieved independent of time and space.

Everyone have equal access to information.

• CDT mMOD server– 3 years

– numerous courses, seminars and presentations

– daily use

• Life-long-learning– modularized courses

– searchable content

– put pedagogy first

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Net-based LearningTutored Groupwork

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Position Types

• Two primitives– Circle (Sub) Sector

– Rectangle

• A position can consist from any combination of these– Can both include and

exclude another primitives

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MPS

Position Merging

Combined Position

WaveLAN

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Location Aware Applications

• Map Navigator

• FriendFinder (TRAB)

• Messenger (MRC/eStreet)

• GeoNotes (SICS)

• WaveView (MRC/Radiosphere)

• Mole (CDL)

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Example

A simple example of two users movingaround...

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Future research questions

• How do users of mobile applications feel about that they may be positioned? (Under different levels of access to and control of the privacy mechanisms.)

• Is the management of privacy rules simple and understandable enough for the average user?

• What level of management of the rules is necessary and used? (Is nested rules really necessary as they add a lot of complexity?)

• How many rules will a user define generally and in contrast to how much the applications are used?

• How do the users’ rules generally interact?

• How can the management of position information be extended to also include context information in general.

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Service Infobase

• The inherent structure of the web is a loosely coupled information database

• How can we search this sphere of information to look for positioned services?

• ”Look for all restaurants within a 1000 m range that have meatballs for lunch.”– Electronic menu– Table reservation– Electronic ordering

• HTML meta-tags• XML databases

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Map Service

• Coordinate Systems– WGS84 (degrees or minutes)

– RT90

• Image Size– up to 1280x1024

• Image Formats– gif, ping, jpeg, bmp, wbmp, svg

• Scale– meters per pixel

• Orientation– freely from 0 to 360 degrees

Map DBPDAURL

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Simple WaveLan Positioning

• Each basestation stores their position and a list of connected MAC addresses

• The MAC database queries all basestations via SNMP

• The PDA queries the MAC database for their position

MAC DBPDA(MAC)

URL

BS BS BS

SNMP

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Advanced WaveLan Positioning

Method 1: Signal Map

1. Signal strengths are premeasured or estimated and stored in a database per location

2. The signal strength are then compared to find the location

Method 2: Triangulation

1. Signal strenghts are measured from atleast three (or four) basestations

2. The signal strengths are triangulated to find the most accurate location

1/38 [email protected] 2002-06-07 On Distributed Real-time Systems: the mStar Environment,...

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Transcript of 1/38 [email protected] 2002-06-07 On Distributed Real-time Systems: the mStar Environment,...