On P2P Collaboration Infrastructures Manfred Hauswirth, Ivana Podnar, Stefan Decker Infrastructure for Collaborative Enterprise, th IEEE International Workshops on June 2005 Speaker : Ching-Chen Chang Date:2007/12/13

Overview The paper is about that how distributed mobile collaboration with P2P approaches could be applied.

Related Work(1/2) Three different collaboration scenarios  Ad-hoc offer temporary support possibly in a limited geographical area, and enable group members to flexibly interact and communicate with limited collaboration functionalities.  Short-term limited time spans, and enable virtual organizations and teams to collaborate in order to satisfy a mutual objective  Long-term set up by collaborating organizations and teams for longer time periods. Usually a centralized infrastructure is used for this type.

Related Work(2/2) Three technological strategies  A standard centralized solution It seems mainly adequate for long-term collaborations.  A pure P2P approach This approach would be suitable for ad-hoc and short- term collaborations, but presently can be considered for supporting ad-hoc scenarios which do not require high- reliability and availability of resources.  A mixed model Provides support for short-term and long-term collaborations.

Motivation Centralized systems require the setup and maintenance of the server. It requires the infrastructure to be in place and configured a-priori. It is costly in terms of hardware, software and time. The P2P approaches could be applied to remedy these shortcomings.

Introduction(1/2) Key characteristics of distributed mobile collaboration are the requirements for flexible interaction styles among users, and ubiquitous mobile access to resources and collaborators.

Introduction(2/2) Much of an overhead, and a more flexible support for short-term and ad-hoc collaboration is required that takes into account user mobility. The issue of possibly limited functionality of mobile devices

Requirements Users can find and access both required resources and available services. Efficient distributed search based on semantic descriptions of the involved data, users, services. Distributed storage, and secure and authenticated access to resources is needed. Group communication models. A team membership management service which should be augmented by a trust model.

Architecture(1/2) Device-dependent Presentation Higher-level services (e.g. instant messaging, white board, alerts) Distributed Storage TCP/UDP Distributed Trust Mng. Membership Mng. Presence Service Publish/ Subscribe Authenticated andSecure Access Mng. P2P Architecture for P2P collaboration systems.

Architecture(2/2) The transport layer provides the basic network communication between peers. The peer-to-peer overlay on top of this layer supports basic of nodes, indexing of data and efficient distributed search to increase resource availability. The five basic lower-level collaboration services which offer supporting services for building end services for mobile collaborators.

Distributed Search and Storage(1/4) Distributed search and replication mechanism  Discovering replicas and supporting up-to-date.  The consistency guarantees provided by the replication mechanism determine the freshness of the information. Distributed indexing system offers the replication and load-balancing for the index information. Resources may not be able to be accessed if the corresponding peer is offline. Replication is required to ensure available of the data.

Distributed Search and Storage(2/4) Distributed archival storage projects split resources into digestible pieces and distribute them. Coding strategies are needed, but the data manipulation operations are expensive. Updates in P2P system mean index updates. The key question for the distributed storage is which data should be replicated.

Distributed Search and Storage(1/4) It is the question whether complete consistency is required or some relaxed model would be tolerable.

Distributed Search and Storage(4/4) Relaxed consistency  When a peer downloads data, it becomes a replica.  In case of an update, all replicas would be informed.  Queries always include the version of the found data.  Conflicting updates require manual system.  If data is unavailable, the requester can subscribe to the system to be notified when the data becomes available.

Publish/Subscribe(1/2) A P/S system provides an efficient service which pushes the data at the time of its publication to interested subscribers. The major challenge for P/S in such environments is related to the design of efficient routing strategies that can deal with network changes (“churn”) while preserving high-expressiveness of subscriptions and low latency for delivered data.

Publish/Subscribe(2/2) How to match a published notification to the existing subscriptions in the index and how to build delivery trees based on P2P systems. These and related questions are subject of ongoing research.

Presence Presence service maintains and offers information on users’ presence and contact information. A user can define a default communication point which is activated in case the current presence information is unavailable. P/S is the natural interaction style for the presence service. Presence implementation can largely rely on an existing P/S implementation taking into account an extension related to user privacy.

Conclusion We are convinced that P2P-based collaboration is a paradigm that meets the requirements of users, but there is still a lack of enabling technologies which have to be researched and implemented.

Reference On P2P Collaboration Infrastructures &arnumber= &isnumber=33223 P2P 架構發展與議題 web.ydu.edu.tw/~hjw/course/p2p/ref01.ppt