Mobile Computing –

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Mobile Computing –

Challenges and Contributions

Anregungen für Anwendungen, Projekte & mehr

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2 Prof. Dr. Thomas Schmidt http:/www.informatik.haw-hamburg.de/~schmidt

Arbeitsgruppe

o Arbeitsgebiete:

- IPv6, Mobiles Internet, Mobile Anwendungen, P2P Overlay

- Multimediakommunikation, Hypermedia, Semantic Web

o Sie finden uns in:

- Raum 580 & Raum 780

o Messen & Ausstellungen:

- CeBIT, LEARNTEC, NdW

o Auslandskooperationen

- Wir vermitteln gerne

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Mitarbeit in aktuellen Projekten

als studentischer Mitarbeiter, Bacheland, Masterand oder Doktorand …

Moviecast hylOs

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Overview

Challenges of Mobile Computing

Emerging Mobile Applications

Scalable, Mobility-Compliant Networks

Conclusions & Outlook

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Challenges of Mobile Computing

o Devices

- Capabilities: Processing, Power, …

- For Users: Interfaces, Design, Paradigm … - Immersive: How to embed and where?

o Mobility Middleware

- Service Discovery, Location, Configuration - Context Management & Transfer

- Scalability, Robustness, Security

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Challenges of Mobile Computing

o Mobile Applications

√ Communication & Infotainment

o M-Commerce, M-Learning, M-Web2.0

? Vehicular & Sensor Networks

? Ambient Intelligence, Location-based Services, …

o Mobility-Compliant Networks

- Wireless Transmission + Deployment - Scalable, Secure, Adaptive Routing - Multiservice Capabilities

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Application - Moviecast:

Mobile Video & Multicast

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Requirements

o Rigid real-time constraints - (50 – 100 ms) o Scalable, resource-adaptive video encoding o Mobility support on network layer

o Group communication enabled by network layer

o Encryption to secure all communication o Focus on standard compliant signalling +

communication

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Starting Point

o daViKo Video Conference Software

o H.264 Codec o Peer-to-Peer

Communication Model o Simple User Localisation o IPv4 & IPv6 –

Unicast & Multicast

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Moviecast Showcases

o Video from Train o Video on Handheld

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Building Blocks

o Scalable, highly optimised video codec:

Based on emerging SVC standard o Software stack:

Secure mobile group conferencing library o Network layer advancements:

P2P mobile group conferencing in real-time

o User interfaces

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Layered Software Stack

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DAVC Video Codec –

Optimized H.264/SVC

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SIP Group Communication Layer

o Critical: Determine device capabilities to build

optimized overlays

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SIP + Multicast (SSM):

Switch from Unicast to SSM

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SIP-SSM: Arrival of New Parties

Source – Schmidt, Wählisch, Cycon, Palkow: Scalable Mobile Multimedia Group Conferencing based on SIP initiated SSM, In: Proc. ECUMN’07, IEEE Press, February 2007.

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Mobile eLearning Objects

o eLO = eLearning Object

o Smallest self-consistent knowledge unit o eLOs aggregate

- Multimedia content entities - Meta data

- (Hyper-) Relations

o Meta data standard: IEEE LOM o Portability standard: SCORM

o Mobility: Transformation & Projection

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Introducing hylOs

hylOs = Hypermedia Learning Object System o eLearning content management system

o Implements rich eLO content modell o Fully LOM / SCORM compatible

o Rigorously XML

hylOs Components

o Presentation environment

o eLO instructional management o eLO authoring environment

o Semantic content augmentation

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hylOs Content Networks

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Application: Semantic Navigator

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Mobile Content on Demand

o Dynamic Content Adaptation to

- User Context

- Device Capabilities

- User Behavior & Preferences

o Content Delivery Just-in-Time

o Split Learning Objects into small Bricks

- Reduce Content Size per Learning Step

- Increase Attention between Learning Interruptions

o Reduction of complex Semantics to feasible Content Relations

- Decrease of Complexity according to the Mobile Context - Provide easy Understanding of Semantic Relations

Source – Hildebrand, Schmidt, Engelhardt: Mobile eLearning Content on Demand, In: International Journal of

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Use Case 1: iPod

Content Preparation:

o Publish Audio Material via RSS Feeds (Podcast)

o Export Course & related Content as Notes to the iPod:

- Provide Menu structure for seamless integration of iPod Click Wheel - Split Learning Objects into separate Content Bricks to meet iPod

capabilities

Content Usage & Navigation

o Obtain audible, textual and visual Information o Navigate directly on Course Content Outline

o Discover additional Information via reduced Semantic Relations o Return to Course Path from related Content

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Use Case 2: Playstation Portable

o Additional Support of:

- Wireless Network Access, web browser and flash player - Subscription access for Podcasts

- Specific haptic controls: Analogue Joystick, Keypad, Action Keys o Provide typical game play by:

- Build ‘Mission’-like Scenario from Course Content - Split Learning Objects to entertaining Mission-Steps - Use typical course-completing self test as ‘Final-Mission’

- Transfer Semantic related content navigation to Joystick

- Support Overview Maps by visualizing Semantics in Mind-Maps

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Use case 2: PSP - Sample

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Scalable, Mobility-Compliant Networks

o Threads & Challenges - The Pure Growth

- Multiple Attachments: Mobility Paging, Multihoming, … - Farewell from the Client-Server Paradigm

- Cognitive Networks & Context Transfer - Group Communication Services

o Trade-off between Management Areas - Network Core

- Access Networks - End-Nodes

o Scalability Constraint: ≤ Logarithmic Resource Expansion

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Im gegenwärtigen Internet sind nur Vorwärtsmessungen möglich:

o Mehrfache traceroute Scans von unterschiedlichen Quellen o Errechnung der jeweiligen

Pfade zwischen Routern o Zwei große Projekte

- Skitter (CAIDA, San Diego) - DIMES (Tel Aviv University) Ê Quellpunkte kritisch

Abenteuer:

Die Entdeckung des Internets

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Ist das Internet ein Zufallsgraph?

o Strukturuntersuchung: Knotengrade o Ein Maß für

- Konnektivität - Robustheit - Verkehrs-

ströme - Bildungs-

mechanismen

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Gradkorrelation

Skitter DIMES

Assortativity Coefficients Skitter: 0,011

DIMES: 0,091

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Räumliche Grad-Autokorrelation

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Diskussion: Entdeckung des Internets

o Das Internet hat viele regionale Vermaschungen

- Nur durch viele, global verteilte Monitorpunkte sichtbar

o Es hat beinahe skaleninvariante Eigenschaften

- Potenzgesetze gelten nicht uneingeschränkt

o Das Internet ist kein Zufallsgraph

- Korrelationen mittlerer Reichweite

- Schwach abhängige Knotengradveränderungen:

Ähnliche Vermaschung nächster Nachbarn

Antikorrelation zwischen Autonomen Systemen

o Was bedeutet dies für Internetmobilität?

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Mobilität - Schnelles Handover:

Fast MIPv6 (RFC 4068)

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FMIPv6 Performanz:

Packetverlust in realistischer Simulation

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Handover-Verhalten zwischen Access-Routern

Problem:

Wie korreliert geographische Nachbarschaft mit topologischer Distanz an den Rändern des

Internets?

Methode:

- Bildung von regionalen Clustern im Zugangsbereich - Evaluiere Access-Router Abstände durch Scanning

in den traceroute Metriken RTT und Hops

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Vorgehen

o Cluster mithilfe von GeoIP Datenbank (MaxMind) o Scans von Quellen in Berlin, Hamburg, San Diego,

Shanghai und öffentlichen traceroute Angeboten o Zufallsmengen von 500 IP-Bereichen aus jedem

regionalen Cluster

o Vergleich mit geographisch unkorrelierten Mengen o Vergleich mit CAIDA Daten:

- Vom gleichen Zeitraum (Oktober 2006)

- Tracepaths minimiert über alle 18 Monitorpunkte (CAIDA Scan-Quellen)

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RTT Verteilung - Scans

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RTT Verteilung - Caida

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Folgerungen für die

Handover Performanz

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Zwischenresümee

o FMIPv6 beschleunigt Netzwechsel

o Prädiktive verlustlose Handovers sind realitätsfern o An den Rändern des Internets sind geographische

und topologische Distanz korreliert

o Ein ‚walking User‘ kann in seiner Umgebung ein beschleunigtes Handover-Verhalten erwarten o Generalitätsvermutung:

- 25 ms in 802.11 (= ½ Layer 2 Handoff) ist a priori beste Handover Antizipationszeit

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Mobile Multicast Senders

Need to Change Routing (Source Filters):

- Extend (CoA,G) states to (CoA,HoA,G)

Need to Preserve Previous Trees:

- Keep contact subsequent to handover

Idea: Morph Previous into Next Tree:

- Elongate root (modify RPF Check) - Discover shortcuts

- Dismiss unneeded branches

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Tree Morphing

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Root Elongation Phase

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First Shortcut

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Optimized Tree

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Implementation & Analysis

Source – Christ, Schmidt & Wählisch: A Light-Weight Implementation Scheme of the Tree Morphing Protocol for Mobile Multicast Sources, In: Proceedings of the 33rd EUROMICRO Conference, IEEE Computer Society Press, August 2007.

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Overlay Service Networks

o Distributed Indexing (DHTs)

- Global Routing with overall Logarithmic Scaling - Deployable on the Overlay / Application Layer - Allows for Scalable Adaptive Services:

- Mobility Resilience - Context Provisioning

- Group Communication Services

o But: Performance Degradation beyond Underlay

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Hybrid Shared Tree Architecture

Source – Wählisch, Schmidt: Between Underlay and Overlay: On Deployable Efficient Mobility-agnostic Group Communication Services,, In: Internet Research, Vol. 17, No. 5, Emerald Insight, November 2007.

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Multicast on Hybrid Shared Trees

o Unmodified Layer2/3 Multicast in End System Domains o Prefix-base Distribution Tree on Top of DHT

- HST inherits Pastry’s proximity selection benefits

- Replication load on forwarders limited by size of prefix alphabet

- Strictly predictable per packet processing costs

o No Dedicated Overlay Nodes (e.g., Rendezvous Point)

- Advoids bottlenecks and single points of failure

o In Combination with Bidir–PIM: Mobility-Agnostic Routing

- Prefix tree will be built only receiver-based

- Decouples group and state management from forwarding plane

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Conclusions & Outlook

o Mobile Computing Today

- Open for Several Directions

o Mobile Applications

- Moviecast – Pushing Performance Limits - hylOs – Exploring the Mobile Paradigm

o Mobility-Compliant Networking

- Discovering the Internet Impact

- Evolving the Internet Core Capabilities - Complementing IP in Hybrid Approaches

Mobile Computing –