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Towards Pervasive Connectivity in Mobile
ComputingFrank Siegemund
European Microsoft Innovation Center
November 2006
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Outline Motivation Related Work System Architecture Implementation Application Conclusions
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Motivation Most middleware assumes basic connectivity
– Web Services– Jini– Corba
Problematic in mobile scenarios– Mobile P2P systems– Mobile CSCW
Heterogeneity– Bluetooth, WLAN, IrDA, GPRS– IPv4 vs. IPv6– NATs and firewalls
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Mobile P2P Bootstrapping problem Establish connectivity
between mobile users Mobile devices as first-
class citizens in P2P applications
Exploit knowledge about connectivity in the group
More reliable/robust group establishment
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Scenario Content sharing
between mobile users Conference scenario Skiing trip Existing group collects
connectivity parameters Sharing by means of
visual tags/glyphs Handheld-embedded
cameras for capturing tags
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Outline Motivation Related Work System Architecture Implementation Application Conclusions
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Related Work Capturing visual tags with handheld
devices and low-cost cameras– Rekimoto et al.
Visual tags in Pervasive Computing– Rohs and Zweifel– Many interesting scenarios
Visual tags to bypass Bluetooth device discovery– Scott et al.
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Related Approaches Out-of-band discovery for Bluetooth
– IrDA– RFID
Collaborative approaches for device discovery– Siegemund and Rohs
Manual configuration Send SMS with information about group
– Complicated from user perspective
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Outline Motivation Related Work System Architecture Implementation Application Conclusions
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System Architecture
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Collecting Connectivity Data Overlay between group members Exploit heterogeneity
– Various communication technologies in group– Different security constraints
Construct group connectivity profile Create tags to transmit connectivity profile Candidate group member captures tags Simplified user interaction
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Group Overlay Overlay can contain both mobile and stationary
nodes Overlay provides multicast group Nodes in group have synchronized state Connectivity properties of nodes shared between
group members NATs can be dealt with via different group peers Direct connections not always possible Group used to circumvent connectivity
constraints
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Visual Tags Tags captured from
video stream Captured by handheld-
embedded digital cameras
Direct user feedback about detected tags possible
Small video resolution requires displaying multiple tags
Concrete tag layout unimportant
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Outline Motivation Related Work System Architecture Implementation Application Conclusions
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Implemenation Heterogeneous environment
– Windows Mobile 5.0 smartphones– Window XP/Vista desktops
Implementation on desktops using Windows P2P Infrastructure
Mobile devices join/create P2P overlay– Socket interface – Lightweight database for data synchronization
Native implementation
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Visual Tags Tag detection in
DirectShow Analyze single video
frames Basic algorithm
– Black and white conversion
– Region detection– Identify guide bars– Decode tags– Determine tag index– Finish if all tags have
been decoded– Join group
Similar to Rekimoto
et al.
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Improvements Determine threshhold for black/white conversion
in feedback loop– Different lightning conditions
Mark tag in video frame to provide feedback to users – Tag detected or not
Synchronization– Tag contains time a single tag is displayed– Capturing device can calculate schedule for reading
tags
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Evaluation 240 x 320 video frame resolution Implementation on 195 Mhz smartphone
– State of the art (no high-end model) 400 ms per frame
– Can be improved significantly !!!– Copy filter
90 ms for thresholding 250 ms for region detection Algorithm deals with small rotations of the tag More sophisticated tag detection systems
available
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Outline Motivation Related Work System Architecture Implementation Application Conclusions
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Example Application Mobile P2P chat
application Messaging for user
groups on mobile devices
Overlay to distribute connectivity parameters
Tags to exchange connectivity profiles
Deal with NATs and connectivity constraints
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Outline Motivation Related Work System Architecture Implementation Application Conclusions
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Conclusions Basic connectivity problematic in mobile scenarios Current middleware solutions insufficiently address
this problem Facilitate groups to establish connectivity in mobile
scenarios Groups create finger print of network environment NATs and security constraints can be dealt with Visual tags user friendly way to communicate
connection properties Useful for mobile P2P and CSCW scenarios Real-life applications
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Contact
Frank SiegemundEuropean Microsoft Innovation CenterRitterstrasse 23, 52072 [email protected]