1. NGMAST’08 – Jani Pellikkawww.mediateam.oulu.fi 1 Partially Decentralized Context Management for P2P Communities Jani Pellikka, Timo Koskela, Mika Ylianttila MediaTeam, University of Oulu 17th September, 2008 NGMAST’08

2. NGMAST’08 – Jani Pellikkawww.mediateam.oulu.fi 2 Outline Introduction of Concepts P2P Service Framework Community Context Context Management System Evaluation Discussion & Conclusions Future Work

3. NGMAST’08 – Jani Pellikkawww.mediateam.oulu.fi 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. NGMAST’08 – Jani Pellikkawww.mediateam.oulu.fi 4 P2P Service Framework Built on P2PSIP and Kademlia algorithm Architecture of three layers 1.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

5. NGMAST’08 – Jani Pellikkawww.mediateam.oulu.fi 5 P2P Service Framework

6. NGMAST’08 – Jani Pellikkawww.mediateam.oulu.fi 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. NGMAST’08 – Jani Pellikkawww.mediateam.oulu.fi 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. NGMAST’08 – Jani Pellikkawww.mediateam.oulu.fi 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. NGMAST’08 – Jani Pellikkawww.mediateam.oulu.fi 9 Context Management

10. NGMAST’08 – Jani Pellikkawww.mediateam.oulu.fi 10 Context Management

11. NGMAST’08 – Jani Pellikkawww.mediateam.oulu.fi 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. NGMAST’08 – Jani Pellikkawww.mediateam.oulu.fi 12 System Evaluation Community context VS. Individual subscriptions Is distributing context information in community context matrix form feasible in the terms of 1.generated network traffic overhead? 2.delay in time to obtain context of a whole community?

13. NGMAST’08 – Jani Pellikkawww.mediateam.oulu.fi 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. NGMAST’08 – Jani Pellikkawww.mediateam.oulu.fi 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 IndividualCommunity 1 member0.062 s0.095 s 20 members0.406 s0.125 s 40 members0.746 s0.171 s 100 members1.767 s0.322 s

15. NGMAST’08 – Jani Pellikkawww.mediateam.oulu.fi 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. NGMAST’08 – Jani Pellikkawww.mediateam.oulu.fi 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. NGMAST’08 – Jani Pellikkawww.mediateam.oulu.fi 17 Questions? Contact jani.pellikka@ee.oulu.fi