MobiShare: Sharing Context-Dependent Data

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MobiShare Sharing Context-Dependent Data
Services from Mobile Sources

• Efstratios Valavanis, Christopher Ververidis,
  Michalis Vazirgianis, George C. Polyzos, Kjetil
  Norvag
• Presented by Amy Sliva

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Introduction

• Connecting diverse resources under a common
  framework presents many challenges
• Uniform ubiquitous connectivity
• Heterogeneity of sources
• Effective and precise resource discovery
• Context awareness is an essential feature
• Sense dynamic information in real-time about the
  environment
• Position, orientation, lighting conditions,
  peoples identity, etc.

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Goals of MobiShare

• Provide a middleware system for managing
  resources
• Provide infrastructure architecture to offer
  ubiquitous connectivity to mobile devices
• Optimize a solution for data requested and shared
  by moving nodes
• Data-centric approach
• Service Oriented

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System Design

• Communication cell
• Area of coverage of a wireless network access
  point
• Mobile device connected to exactly one AP at any
  given time
• Cell Administration Server (CAS)
• Manage the area of coverage of an AP
• Responsible for maintaining list of devices and
  available services
• Provides service discovery capability
• Stores statistical info about users and devices

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System Design (cont.)

• Service discovery occurs through the CAS, data
  transfers are P2P

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Mobile Devices

• Assume one-to-one relationship between devices
  and users
• Hardware Requirements
• Digital Compass
• GPS receiver
• Wireless communication interface
• Software Requirements
• Request definition tool
• Service definition tool
• Application server (if the device can be a data
  source)
• Viewer applications (for documents, images, etc.)

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Central Application Servers

• Functionalities
• Assign addresses and ids to devices
• Perform authentication and access control
• Handle requests
• Publish services offered and host description
  files
• Maintain list of neighboring CASs, etc.
• Data Flows between CASs
• Extension of requests to neighbors
• Forwarding list of neighbors
• Request or deliver location information
• Push service description files

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Central Application Servers (cont.)

• Global service taxonomy of service categories
• Service directory of services offered by devices
  in the cell
• Service description repository of local services
• CAS directory of addresses of other CASs
• Device repository of devices in the cell
• Temporal profile manager for storing access
  patterns for devices

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Device Location Mechanism

• Upon entering a new cell a device reports its
  previous location and any services it hosts
• When a device leaves a cell, the previous cell
  stores the next location
• When a request for a devices service is
  received
• CAS returns the current IP if it is in the device
  repository
• If the device is not found locally, the request
  is forwarded to neighboring cells
• Follows chain of next cells for the device to
  locate it

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Service Description

• Always one CAS responsible for maintaining master
  copy of a service description
• Each new CAS that acquires the description has to
  notify the initial CAS
• If the description is updated, the local CAS
  takes ownership of the master copy
• When publishing a service
• Declare an initial area of availability
• Specify whether the service is fixed or mobile

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Service Submission

• Service definition tool helps user classify his
  service using a fixed service ontology
• Use WSDL to define the user interface
• Use RDF to store the semantic information
• Advertisement profile
• User-defined
• Mobility-based
• Request-based

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Service Discovery

• Locate services on-demand in reasonable time
• Retrieve all available resources and filter the
  results
• Refine the results by context
• Example Service Request
• Tourist with a mobile device submits a request to
  locate services that find taxis in his
  communication cell

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Request Process

• Request handler is initiated that stores metadata
  of the request
• Search string sent to the taxonomy module, and
  the set of services that semantically match are
  forwarded to the user
• Selected services are sent to the service handler
  which checks the service and device directories
  for availability
• User chooses a service to invoke
• Search can extend to adjacent cells

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Semantic Matching

• First we have to understand what the user is
  looking for
• WSDL and UDDI do not contain semantic information
• Exact matching is not good enough
• A service ontology is stored in RDF
• Use dictionary to match words to points in the
  service taxonomy
• Use distance measure to select part of the
  taxonomy
• Filter resulting set of services
• i.e., Exclude services that originate on
  non-local devices

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Taxonomy Path Example

• Request travel, book, taxi

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Context-awareness

• Two types of context
• Location (both requestor and source)
• Mobility parameters of the requestor
• All requests include location and orientation of
  requestor
• If user is located at the border between cells,
  the request is forwarded to the CAS in the
  neighboring cell
• Users can specify a request radius--helpful if
  the cell covers a large area

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Implementation

• Part of DBGlobe project
• Data-centric approach to global computing
• Prototype developed
• Uses IEEE 802.11b WLAN
• Cells managed by Microsoft Windows 2000 Servers
  running the MobiShare CAS module
• Software developed using C for .NET
• Metadata based on standards (XML, RDF, WSDL,etc.)
• CAS Modules
• Device Repository, Device Controller, Service
  Publisher, Service Request Handler, Service
  Description Repository, Service Directory
• Mobile Device Modules
• Request Definition Tool, Application Server,
  Viewer, and Service Definition Tool

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Preliminary Results

• Mobile devices take 2 seconds to detect they have
  entered a new cell
• 5 seconds for a newly published service to become
  available

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• Questions?