kutscher / ott / bartsch 2007-05-23 1 supporting network access and service location in dynamic...
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Kutscher / Ott / Bartsch
2007-05-23 1
Supporting Network Access and Service Locationin Dynamic Environments
Dirk Kutscher <[email protected]>
Jörg Ott <[email protected]>
Steffen Bartsch <[email protected]>
TNC 20072007-05-23
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Trends Service location and selection a major issue
for WLAN service providers
Different use cases Information about general coverage, roaming possibilities
and tariffs Facilitating automated access Providing information for diagnosis and maintenance
Existing ways for service location and selection insufficient for mobile users Fragmented information services (per provider) Inadequate solutions for automated access
(Google Maps mesh-ups etc.) no offline usage! Information often outdated
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Example: FON Community WLAN Approach
Web-based information service with Google Maps-based visualization
Informational only Information cannot be used for
automated client device configuration
No relation to user’s current context Position, required services
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Selected Recent Developments FON Connection Manager
Locate and automatically connect to FON Hotspots (Symbian S60)
DeviceScape Centralized connectivity management approach Mobile clients access DeviceScape information database through DNS
requests Providing WISP-specific information (how to log on) Mainly targeting automated log-on
iPass Hotspot Finder Offline hotspot finder for Windows XP, Vista Pre-downloadable maps Offline search based on different criteria
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Shortcomings
Many provider-specific solutionsNot useful for general network service location
No structured update mechanismsUsers have to manually update the application/database
Focusing on WLAN network accessOther (related) services not coveredVoIP access, multimedia resources etc.
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Service Maps: Main Concepts
Network Information Service for Heterogeneous networks Challenged environments Large scale deployment
Different take on network service location Receiver- and infrastructure-based filtering Accommodate different network architectures
Main concept Mobile nodes receive/request service information from different sources and
construct network service map according to MN requirements Support offline usage Leverage locality of distribution networks (e.g., WLAN) and service scope
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Service Map Distribution Architecture
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Data Model
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Filtering and Aggregation
Aggregation E.g., provider-independent aggregators
can combine Service Maps from multiple providers
Filtering Different types of filter operations
Tag filter: specify service tags that have to be present in a service description
Location filter: Filter services relevant to a specific region
XPath filter: filter based on arbitrary XML content in service descriptions and refinements
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Service Map URNs Motivation: Transport-independent distribution can generate multiple
copies
Globally unique identification for service maps required
Uniform Resource Name (URN) as an identification mechanism for service maps, fragments and refinements
Comparison rules (subset predicate)
Resolution Mechanism based onDynamic Delegation Discovery System (DDDS) Obtain specific URI through domain-specific translation rules
urn:svcmap:example.org:20061028:campus-wlan#coord=53.10663,8.852487;range=100
urn:svcmap:example.org:20061028:campus-wlan?6453#refinement-2343
urn:svcmap:example.org:20061128:wlan#xpath=//tariff[@type='volume']
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Bootstrapping
Automating access to Service Map information in foreign networks Identify active Service Map service, i.e., in a
foreign hotspot Obtain basic configuration information, e.g.,
Service Map URIs
Bootstrapping defined for different environments Broadcast/Multicast: FLUTE session on
standardized multicast address; simpler variant (no FLUTE) as a fallback
Unicast-only: IP-auto-configuration, resolving standardized bootstrapping URN through local DNS
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Security Authenticity and integrity fundamental Service Map properties
Have to preclude denial-of-service attacks by forged service information
Challenge: transceiver-model is based on changes to the information base by intermediaries Filtering and aggregation must still be possible Still, receivers cannot establish trust-relationship with every possible transceivers
(scalability, operational issues)
Service Map approach:maintaining security propertiesof Service Maps fragmentsacross the distribution chain Authenticated data structures
based on Merkle hash trees Implemented with XML Digital Signatures
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Implementation
InfrastructureService Map
distribution servers
Client softwareWeb-based client
Browser-based Service Map interface for online usage
Mobile client Offline client for
smaller devices, mobile phones
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Experiences
Larger-scale campus WLAN applicationSetup, operations, measurements
Enhancing connectivity in mobile scenariosEmploying service maps for scheduling network accessSimulations
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Campus Scenario
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Bootstrapping in campus environment
Using FLUTE via IP-Multicast Providing data on 400 APs Reasonable bandwidths: 1kB – 64kB Good performance:
about 2 – 16s
Campus Evaluation
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Mobile Scenario Evaluation
Mobile user connectivity WLAN emulation Either with acquiring data on
APs in proximity or with sensing and probing
Relatively simple connectivity algorithmStill 10% increase in Internet
connectivity
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Uploadserver
U U U U
HT
TP
S
Access control +anonymization
Incomingdatabase
Aggregator
Data set matching +freshness handling
Dynamicdatabase
Integrator
Providerdatabase
Mapping reportsto known hotspots
ServiceMaps
Service MapSender
Distribution
U U U U
Ser
vice
Map
Tra
nsp
ort
Contribution
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http://service-maps.net/spot-3faed
Hotspot DisplaysRevisited
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Conclusions
Automating access to WLAN hotspots is a major challenge for making evolving WLAN-based applications usable
First developments are becoming eminent
But: no provider-independent approach available today
Network Service Maps as a general approach:Application- and provider-independent, supporting different transport services and organizational configurations
Recent results: Large-scale operation
Leveraging community contributions through contribution interface for user-observed hotspots