supporting network access and service location in dynamic environments

Kutscher / Ott / Bartsch

2007-05-23 1

Supporting Network Access and Service Locationin Dynamic Environments

Dirk Kutscher <dku@tzi.org>

Jörg Ott <jo@netlab.hut.fi>

Steffen Bartsch <sbartsch@tzi.org>

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 Information often outdated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

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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

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Map

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nsp

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Contribution

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2007-05-23 21

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

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2007-05-23 23

Dirk Kutscher <dku@tzi.org>

http://service-maps.net/