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Partially Decentralized Context Management for P2P Communities

Partially Decentralized Context Management for P2P Communities. Jani Pellikka , Timo Koskela, Mika Ylianttila MediaTeam, University of Oulu 17th September, 2008 NGMAST’08. Outline. Introduction of Concepts P2P Service Framework Community Context Context Management System Evaluation

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Partially Decentralized Context Management for P2P Communities

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  1. Partially Decentralized Context Management forP2P Communities Jani Pellikka, Timo Koskela, Mika Ylianttila MediaTeam, University of Oulu 17th September, 2008 NGMAST’08

  2. Outline • Introduction of Concepts • P2P Service Framework • Community Context • Context Management • System Evaluation • Discussion & Conclusions • Future Work

  3. Introduction 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)

  4. P2P Service Framework • Built on P2PSIP and Kademlia algorithm • Architecture of three layers • P2PSIP Layer – provides network access as well as resource publishing and discovery • Management Layer – provides higher level functionalities (e.g. community and context management) through an API • Application/service Layer – consists of both Web-based and native mobile applications and services

  5. P2P Service Framework

  6. Community 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

  7. Community 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

  8. Context 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

  9. Context Management

  10. Context Management

  11. Context 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)

  12. System Evaluation • Community context VS. Individual subscriptions • Is distributing context information in community context matrix form feasible in the terms of • generated network traffic overhead? • delay in time to obtain context of a whole community?

  13. System 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

  14. System 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

  15. Discussion & 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

  16. Future 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

  17. Questions? Contact jani.pellikka@ee.oulu.fi

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