NGMAST’08 – Jani Pellikka www.mediateam.oulu.fi 1

Partially Decentralized Context Management for

P2P Communities

Partially Decentralized Context Management for

P2P Communities

Jani Pellikka, Timo Koskela, Mika YlianttilaMediaTeam, University of Oulu

17th September, 2008NGMAST’08

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OutlineOutline

• Introduction of Concepts

• P2P Service Framework

• Community Context

• Context Management

• System Evaluation

• Discussion & Conclusions

• Future Work

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Introduction of ConceptsIntroduction of Concepts

• Context - information that is used to characterize the situation of an entity

• A P2P System - P2P overlay network that resides in the OSI application layer

• A Community - a group of a limited number of people held together by shared interests (rather than all users of the whole system)

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P2P Service FrameworkP2P Service Framework

• Built on P2PSIP and Kademlia algorithm

• Architecture of three layers1. P2PSIP Layer – provides network access as well

as resource publishing and discovery

2. Management Layer – provides higher level functionalities (e.g. community and context management) through an API

3. Application/service Layer – consists of both Web-based and native mobile applications and services

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P2P Service FrameworkP2P Service Framework

P2PSIP Network

Infrastructure-based Wireless (UMTS)

Application LayerNetwork Layer

Near-field Communication

Wireless LAN

P2PSIP NetworkAccess

Service Discovery and Publishing

CommunityManagement

ContextManagement

ResourceManagement

Usage RightsManagement

Application Programming Interface

Applications / Services

ManagementLayer

ServiceLayer

P2PSIPLayer

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Community ContextCommunity Context

• Distribution is optimized for transferring the context information of communities

• Community Context• A collection of the context information of individual

community members

• Includes all context information of a single member

• Utilized by services and applications to determine the situation for a whole community

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Community ContextCommunity Context

• Community Context Matrix• Context information of a single member can be

broken into several context types (location, time, identity, activity, …)

• Community context can then be thought as a matrix, where the members reside on the vertical axis, and their context types on the horizontal axis

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N

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c

CCC

CCC

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21

22221

11211

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Context ManagementContext Management

• Architecture based on ’Model for Presence and Instant Messaging’ (RFC2778) by IETF

• Context Service, a centralized server component• Mobile devices (community members) publish their

context information to the context service

• Applications and services request (subscribe) to be notified on changes in community context or in the context information of individual members

• No information which users constitute a community: the context service has to obtain this piece of information from the P2P overlay

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Context ManagementContext Management

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Context ManagementContext Management

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Context ManagementContext Management

• Context distribution using IETF standards• Context information of a member is represented

using Presence Information Data Format (PIDF)

• Community context matrix is represented as a resource list, where the PIDF documents of single members are collected inside a multipart/related document stucture

• Context information is transferred over Session Initiation Protocol (SIP)

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System EvaluationSystem Evaluation

• Community context VS. Individual subscriptions

• Is distributing context information in community context matrix form feasible in the terms of1. generated network traffic overhead?

2. delay in time to obtain context of a whole community?

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System EvaluationSystem Evaluation

• Network Traffic Analysis• More beneficial to use community context subscriptions• With large communities, network traffic gain exceeds 60 %• In individual subscriptions, most of the network traffic was due to

overhead of SIP headers

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System EvaluationSystem Evaluation

• Delay Analysis• More benficial to use community context

subscriptions (although additional overhead is caused by P2P lookups for community members)

• With large communities, community context subscriptions are over five times faster

Individual Community

1 member 0.062 s 0.095 s

20 members 0.406 s 0.125 s

40 members 0.746 s 0.171 s

100 members 1.767 s 0.322 s

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Discussion & ConclusionsDiscussion & Conclusions

• Using community context outperforms individual subscriptions to single members in terms of both network traffic and context retrieval delay

• Benefits: substantially reduced network traffic overhead and context subscription delay

• Context management is suitable for resource limited devices

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Future WorkFuture Work

• Evaluate our context management solution in real-life application scenarios with application/service pilots

• Detailed delay analysis on different phases in context subscription

• More compact representations for community context will be studied as well

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Questions?Questions?

Contact

jani.pellikka@ee.oulu.fi