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Document D4 1 POPEYE lower level Design Document
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Executive Summary, The purpose of this deliverable document D4 1 entitled POPEYE lower level Design Document is. to provide a first architectural view of the network abstraction architecture and middleware services. addressed by WP4, This document was developed taking the following documents as references. Milestone M4 1 entitled POPEYE P2P over MANET State Of The Art Analysis Report. which provides an overview of unicast and multicast routing protocols in a MANET in order. to select the most appropriate ones to POPEYE architecture This document also showed. some middleware services just as several simulation environments. Milestone M4 2 entitled Draft POPEYE Lower Level Architecture Description Report. which provides a draft of the network abstraction architecture and middleware services. addressed by WP4 This Milestone document is the start point of the Deliverable D4 1. Another important document used as a reference to this Deliverable is an internal document. entitled POPEYE Module Interface Description written with the cooperation of all the. partners of POPEYE and which lists all the modules that are going to be developed. organized by Work Packages and which gives details of every module like the functions or. methods provided by each module a brief definition of the method and the complements. that need to be developed, This document follows the table of contents established during the POPEYE Technical Meeting that. took place in Genoa on January 18th 19th 2007 D4 1 is organized through the following sections. 1 Introduction,2 Functional Description,3 Architecture. 4 Relationship with other modules, The first section of the document provides a brief introduction considering the conclusions of the.
previous documents and explaining the motivation behind the lower level architecture design. The second section of this document presents the functional description of each module within the. scope of WP4 namely Peer Discovery Services Communication Services Naming. Services Publish Subscribe Services and Group Management Services. The document then presents an architectural view of the different modules describing both their. static architecture and their dynamic behaviour UML class diagrams and sequence diagrams are. included to describe the internal architecture and the dynamic behaviour respectively. The last section of the document provides a description of the relationships between WP4 modules. and other POPEYE modules, Furthermore this document describes and illustrates the achievements made in the first year of the. project The first two phases have concluded specification and state of the art analysis phase and. design research phase and the key achievements of these phases are the following. Specification and state of the art analysis, o We have evaluated state of the art solutions for P2P over MANET taking into. account MANET routing alternatives and existing middleware approaches. o We have identified several protocols that must be considered for routing issues and. P2P services, o We have produced the aforementioned Milestone M4 1 which provides an overview. of unicast and multicast routing protocols as well as middleware services and. simulation environments,Design research phase, o We have identified performance limitations that require cross layer communication. between routing protocols and the P2P layer, o We have explored several interactions between WP4 components ad hoc routing.
overlay routing multicast communication group management. o We have produced a Milestone document M4 2 which presents a first draft. proposed architecture for WP4, o We have identified specified designed and started developing several modules in. both Middleware Layer and Network Abstraction Layer. o The specification and design of these modules include a functional description of. each module and a global architectural view of WP4. o We also produced a first prototype of Middleware Layer services that provides basic. communication mechanisms to the upper layer applications. o And finally we have refined the milestone M4 2 to produce the Deliverable. document D4 1 which presents the first architectural view of the network abstraction. architecture and middleware services addressed by WP4. Revision history,Version Date Description Editors,Contributors. First Name Last Name Company Email,Acronym Meaning. CSCW Computer Supported Cooperative Work,CWE Collaborative Working Environments. DHT Distributed hash table,DRM Delete Replicated Messages.
DYMO Dynamic MANET On Demand Routing Protocol, DYMOUM DYMO implementation of University of Murcia. GM Group Manager,JMS Java Message Service,JNDI Java Naming and Directory Interface. MANET Mobile Ad hoc Network,MMARP Multicast MANET Routing Protocol. MP2P Mobile Peer to Peer,PDS Peer Discovery Services. P2P Peer to Peer,WP Work Package, The present document has been produced in consistence with the definition of terms described.
in the POPEYE Glossary v1 0 accessible on the POPEYE web site. Table of Contents,Executive Summary 2,Revision history 4. Contributors 5,Acronyms 6,Table of Contents 7,1 Introduction 9. 2 Functional description 12,2 1 WP4 Functionalities overview 12. 2 2 Peer Discovery Services 12,2 3 Communication Services 13. 2 4 Publish Subscribe Services 14,2 5 Group Management Services 15.
2 6 Naming Services 15,2 6 1 Search Mechanism 16,3 Architecture 18. 3 1 WP4 Architecture overview 18,3 2 Peer Discovery Services 18. 3 2 1 Peer Discovery Service static view 18,3 2 2 Peer Discovery Service dynamic view 19. 3 2 3 Superpeer Architecture Description 24,3 3 Communication Services Architecture 25. 3 3 1 JGroups Protocol Stack modifications 26,3 3 2 Communication Services static view 28.
3 3 3 Communication Services dynamic view 28,3 4 Publish Subscribe Services Architecture 29. 3 4 1 Publish Subscribe Services static view 29,3 4 2 Publish Subscribe Services dynamic view 30. 3 5 Group Management Services Architecture 32,3 5 1 Group Management Services static view 32. 3 5 2 Group Management Services dynamic view 33,3 6 Naming Services Architecture 34. 3 6 1 Naming Services static view 34,3 6 2 Naming services dynamic view 36.
3 6 3 Search Mechanism Architecture 37,4 Relationship with other modules 39. 4 1 WP4 Dependencies Overview 39,4 2 Peer Discovery Services 39. 4 2 1 Relationship with security modules 39,4 2 2 Relationship with communication service 39. 4 2 3 Context delivery module 39,4 3 Communication Services 39. 4 3 1 Context delivery module 39,4 3 2 Plugin based Framework module 39.
4 4 Publish Subscribe Services 40,4 4 1 Workspace management 40. 4 4 2 Plugin based Framework module 40,4 5 Group Management Services 40. 4 5 1 Workspace management 40,4 5 2 Relationship with security modules 40. 4 6 Naming Services 40,4 6 1 Data sharing persistence modules 40. 4 6 2 Plugin based Framework module 40,4 6 3 Search Mechanism 40.
5 Conclusion 41,6 References 42,APPENDIX A Module Interface Description 43. 1 INTRODUCTION, The POPEYE objectives are to provide a simple and reliable computing environment for group. collaboration over mobile ad hoc networks, The POPEYE infrastructure integrates a communication platform and context aware secure and. personalised core services to enable the design and the usability of collaborative applications in. such mobile environments This platform must offer services in different areas such as group. management basic communication and naming services while considering flexibility and. spontaneous character of mobile ad hoc networks These services rely on multicast communication. since it stands as the most efficient way to perform synchronous group communication and they. will provide the foundations to build higher layer functionalities for the core services level. In order to provide these services the integrated platform should meet several requirements First of. all due to MANET characteristics mobile and multi hop scenario must be supported Also. scalability and low traffic overhead are key features that must be included to provide an efficient. communication platform Therefore network topology awareness allows benefiting from peer. locality and avoids generating extra routing traffic a main concern in mobile networks Therefore. group communication will be based on this topology awareness to achieve an effective and scalable. messaging system, The purpose of this document is in first place to show the functional description and the. architecture of the WP4 modules in terms of dynamic and static behaviour Besides different. relationships with other modules are expounded Before further explanation of these topics the rest. of the introduction will present the state of the art on MANET collaboration middleware. Afterwards JGroups is presented as the foundation of the middleware that will provide all. communication layer functionalities together with an introduction to the specific overlay topology. State of the art, Previous to design and development process study on current middleware for MANET.
collaboration has been required In this case the evaluated middleware approaches are divided in. two different groups a first one including overlay topology related proposals and a second one. embracing programming abstractions and P2P layer basic services Besides other more complex. CSCW systems have been considered, Current investigation on P2P middleware is based on two different scopes regarding overlay. topology On the one hand several unstructured overlays have been adapted to fit MANET. requirements On the other hand structured overlays like distributed hash tables DHTs have. proven to be an efficient platform for building distributed applications Therefore distributed. applications and network services in mobile ad hoc networks MANETs could potentially benefit. from the deployment of a DHT over the ad hoc network. However most of the evaluated middleware do not have a real implementation since they are just. implemented for testing purposes in simulators like ns 2 Tuple spaces implementations PMR99. as well as other middleware solutions not directly addressed to MANET JXTA p2pCM PGM05. do not consider the multi hop scenario and lack communication efficiency In terms of portability. adaptations of well known and successful Internet systems like XL Gnutella CGT05 BTM. RaS06 and DHT implementations for MANET ZaS05 PDH04 rely on a specific routing. protocol thus making them not suitable for our purposes. Secondly and after analyzing the different approaches we state that there is no mature middleware. for P2P over MANET neither at overlay level nor at collaborative level Mature P2P middleware. like JXTA cannot be directly applied in MANETs due to its excessive communication overhead. TCP connections XML based protocols In terms of mobility most of the approaches being. evaluated consider the existence of certain network infrastructure Furthermore current. collaborative middleware does not fulfil all CSCW requirements like asynchronous and. synchronous communication global virtual data structures or ordered communication channel. among others However JGroups toolkit stands as a good alternative since it provides most of the. CSCW required functionalities such as group membership and communication over a secure and. ordered multicast channel and offers a flexible and extensible implementation. In terms of communication in collaborative systems multicast seems the most natural way to. perform group collaboration However IP multicast unreliable nature is not sufficient to guarantee. most of the desired functionalities To cope with these needs JGroups JGroups appears to be the. most suitable and robust solution JGroups is a reliable group communication toolkit based on IP. multicast but extended with reliability and group membership It provides a protocol stack. architecture in order to suit each application with its specific needs Moreover JGroups supports. group creation and deletion joining or leaving the groups membership detection and notification. detection and removal of crashed members Group members can send member to group messages. or member to member messages, The key characteristic of JGroups is that reliability of multicast communication is a deployment. issue and does not have to be implemented by the developer of the application The protocol stack. can be extended with protocols that handle transport fragmentation failure detection lost messages. retransmission ordering membership and encryption It is also possible to add a new protocol in. order to implement a desired functionality JGroups also provides high level abstractions called. building blocks such as a Replicated Hash Table a Message Dispatcher to provide synchronous. communication or an RPC Dispatcher to invoke remote methods in all group members. Furthermore Jgroups has two ports for the J2ME architecture JGroups ME and JGroups CDC. Although JGroups is not designed for high churn rate networks its layered protocol stack permits to. replace components to adapt to specific requirements In this line we aim to develop a generic. collaboration middleware that can transparently work on top of different network infrastructures. Wifi AP Infrastructure Ad hoc network Multi hop networks By replacing lower level layers we. will for example provide specific solutions for a MANET network using the unicast DYMO. protocol and MMARP manet multicast protocol, In fact we propose to create a lower level layer based on dynamic super peers in order to support. the MANET scenarios presented in the POPEYE project. Superpeer overlay topology, Besides considering the best way to perform collaboration for the purpose of building a sound. collaboration architecture MANET constraints should also be considered Since performance is a. critical issue on multihop networks communication must be minimized and enhanced between. groups members, Taking this as a basis in first place we must say that most collaborative applications chat shared.
whiteboards and other need messages to be received by different members of a group at the same. time In order to avoid sending the same message several times through the network hence lower. network performance multicast messaging stands as a good option to cope with group collaboration. necessities In the POPEYE architecture MMARP RSG03 routing protocol provides this. multicast functionality at network level Although it is also possible to provide multicast delivery at. application level its complexity and overhead make network protocol implementation much more. efficient than application level multicast Nevertheless multicast communication needs of tree. maintenance and advertisement messages which may cause excessive message propagation. throughout the whole network consuming bandwidth and battery from resource constrained. Collaboration on POPEYE is more probable to be performed between collocated peers since. groups tend to be formed in a nearby area Thus most multicast messages will be exchanged. between close peers making unnecessary the construction of full multicast maintenance structures. For this reason we try to benefit from this behaviour and optimize network traffic by exploiting. cross layer functionalities Therefore we propose a superpeer overlay based on cluster. communication Multicast messages will be sent only inside a cluster in order to minimize. propagation of multicast maintenance messages Then if multicast messages must be sent to farther. locations in the network i e a member of the group is located outside the cluster the superpeer. which is the responsible of a cluster will send the message transparently to the other interested. Superpeer selection will be dynamic self adjusting and sensitive to device characteristics such as. connectivity reliability bandwidth and battery power Superpeer selection algorithms will manage. this procedure and in consequence will define cluster size and the precise number of superpeers in. order to maximize multicast performance,2 FUNCTIONAL DESCRIPTION. This section describes the functionality of each of the WP4 modules. 2 1 WP4 FUNCTIONALITIES OVERVIEW, This section provides a brief description of each WP4 module focusing on the module. functionality, Firstly this work package provides communication mechanisms to achieve an effective and. scalable messaging over a mobile ad hoc network Communication Service module is. responsible for offering such communication primitives to middleware services and. applications Since collaborative applications are tightly related to group communication. reliable multicast messaging is proposed to perform 1 to many communications Moreover. unicast communication is also supported in order to provide 1 to 1 messaging. Secondly taking into account MANET constraints and collaborative applications scenario. an overlay architecture based on clusters and superpeers is proposed The goal of this. overlay is to reduce multicast communication by limiting multicast forwarding within the. scope of the cluster Superpeers retransmit multicast traffic between clusters and are in. charge of managing cluster information Peer Discovery Service module is in charge of. maintaining the clusters and the superpeers, Finally WP4 provides a basic support of core collaborative services Basic services like a. naming service and a publish subscribe service provide the basis to develop upper layer. services and simple final applications The lower layer of the POPEYE middleware is. constituted by these services along with the group management service which deals with. creation and deletion of groups and user membership information. Network Abstraction Layer Modules,2 2 PEER DISCOVERY SERVICES.
Peer Discovery Service will be responsible for the organization of the network This service. is also used among superpeers to share information about services enabled in the whole. Superpeers periodically transmit messages SP INFO to a well known multicast address. 228 8 8 8 announcing their presence to other nodes which wants to join the network A. new becoming peer with an IP network address and running DYMOUM and MMARP. routing protocols first of all will establish thereby the aforementioned multicast address in. order to receive the messages sent by the superpeers Once the node receives the message he. checks the distance TTL i e Time to live in hops to the superpeer so as to compare it. lately to the distance to other reachable superpeers. Once the node has checked the distance to the superpeer he will send an acknowledge. message SP OK to the nearest superpeer and will wait for a confirmation to join a cluster. and thus became a peer of the network If a peer wants to leave a cluster he will send a. SP KO message to the superpeer address to let the superpeer update his cluster information. Afterwards the superpeer will send a confirmation message to the peer. Superpeers do not only participate in the network as normal peers but they are also. responsible for managing a cluster and thereby superpeers need to communicate each other. changes in their clusters, Among other functionalities of a superpeer as we have shown in above paragraphs he has. to send messages to announce his presence to peers to provide them mechanisms to join his. cluster However a superpeer also has to establish a different multicast address 224 0 0 8. in order to receive updated information of the network from other superpeers Information. about groups and services available in other clusters will be sent to this address. Figure 1 shows an example of the proposed architecture In this case the network is divided. into three clusters with their corresponding superpeers. Super peer,10 Standar peer,M1 Multicast participant. Figure 1 Proposed network architecture, Another important issue carried out by this service is the group management which will be. described below in the architecture section, This service provides the next primitive functions. Create a group in the network,Delete a group in the network.
Join a group in the network,Leave a group in the network. Obtain the list of members of a selected group,2 3 COMMUNICATION SERVICES. The Communication Services module is a network abstraction layer module which provides. basic communication mechanisms to the middleware layer Besides interaction with physical. network this module provides the Communication Channel a component that offers unicast. and multicast communication between members of a group A member of the group can. send a message to a specific member or to all members of the group The user of a. communication channel can receive messages by invoking blocking calls or by managing. message events that are fired whenever a message is received. It is also possible to use a communication channel with a specific identifier that restricts the. communication between channels with the same identifier used by different peers These. special channels are called Named Communication Channels Messages that contain. identifiers are filtered on reception and are delivered to the applications or services that have. registered a listener with the specified identifier. Provided functions, Create a default communication channel a channel is created with a default name. Create a named communication channel a channel is created with a specific name. Send a message a message is delivered to the recipient member. Send a message to the group a message is delivered to all the members of the group. Asynchronous receive an event is fired when a message is received. Synchronous receive blocking call The application blocks until a message is. Middleware Layer Modules,2 4 PUBLISH SUBSCRIBE SERVICES. In every group different publish subscribe channels are available In this way users can. create topics and then assign subscriptions to them Subscriptions are needed to receive. messages published under a certain topic To be able to retrieve messages after network. disconnection durable subscriptions are also available. The publish subscribe mechanism uses the multicast capability of the JChannel to send a. message to all members of a group If a peer is not interested in receiving messages from a. certain topic messages will be automatically discarded Messages are not sent via the. communication channel since this channel is intended to be used just by higher level. Durable subscriptions persist to network disconnection so that if a peer leaves the network. due to disconnection or mobility issues messages published on that topic are delivered. automatically to the subscriber when rejoining the group This can be achieved because all. members with a durable subscription on a topic keep all received messages for a certain. time Then lost messages or previously posted messages can be recovered by asking one of. the members of the group, This publish subscribe functions are implemented as a subset of the JMS specification Only.
the multicast model is implemented which means that the point to point model is not. Provided functions, Create a topic allows to send receive messages on a topic. Publish a message under a topic sends a multicast message to all group members. Create a subscription to a topic allows a member to receive messages published. under a certain topic, Create a durable subscription to a topic allows a member to receive messages. published under a certain topic and to keep them for a certain period of time. Register a listener to process messages defines how messages will be processed. when they are received under a certain topic,2 5 GROUP MANAGEMENT SERVICES. Group management services support multiple group creation Groups are essential for. collaboration in POPEYE since all actions are performed inside the scope of a group. Groups are created by providing the group name and then multicast address and port. mapping are provided from the underlying services Each member can join several groups at. the same time and they will be notified about event generation whenever other groups are. created or deleted Membership on each group is provided as a list of members that currently. belong to the group together with notification about member join departure events. Furthermore reconciliation after network merge will be available for services such as. naming and publish subscribe,Provided functions, Get group members returns a list with all the members in the current group. Add listener for membership changes allows registering a listener into a group that. notifies changes whenever a members joins or leaves the group These listener. methods will be invoked when a Join Leave event is produced. Remove a listener for membership changes remove one of the previously registered. Add listener for group membership changes allows registering a listener that notifies. changes whenever a group is created or deleted These listener methods will be. invoked when a groupCreated or groupDeleted event is produced. 2 6 NAMING SERVICES, Each group in the POPEYE network maintains a decentralized Naming Service which binds.
names with resources and locations These resources can be context information sources. registered plug ins or other available objects and services The Naming Service is based on. a Replicated Hashtable i e a replicated structure provided by JGroups which replicate each. entry of a hash table to all members of the group The naming service contents are replicated. among all members of the group therefore these contents are automatically available to all. members of the same group whenever they are generated. The Naming Service provides an implementation of a subset of the JNDI specification. which offers the following functionalities over a flat namespace. Bind a name to an object, Bind a name to an object overwriting any existing binding. Unbind a specific object,Retrieve the named object. Enumerate the names bound in the named context along with the objects bound to.

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