Topic-based Delivery of Event Messages in Peer-to-Peer Publish/Subscribe Systems

An event-driven publish/subscribe (PS) model of a distributed system is used in various applications.In this paper, we discuss a peer-to-peer (P2P) model of a topic-based PS system (P2PPS model) where each peer process (peer) can both subscribe interesting topics and publish event messages with topics. In our previous studies, we propose the TBC (topic-based-causally delivery) protocol a homogeneous networkswhere maximum delay time between every pair of peers is same. Here, a pair of event messages are checked if the event messages are related in the topic vector and are causally delivered by takingadvantage of physical time and linear time. In this paper, we consider a system where peers are interconnectedin heterogeneous networks. Here, maximum delay time between every pair of peers is not same.We propose a heterogeneous TBC (HTBC) protocol where event messages are TBC-causally delivered to target peers in heterogeneous network. We evaluate the HTBC protocol and show the number of pair of event messages unnecessarily ordered is reduced in the HTBC protocol.Key Words : Publish/subscribe (PS) systems, Peer-to-peer (P2P) model, Topic-based causal dependency, Topic vectors, Heterogeneous TBC (HTBC) protocol, Linear clock, Physical clock, Heterogeneous networks

Object-based Information Flow Control in Peer-to-peer Publish/Subscribe Systems

Distributed systems are getting so scalable like IoT (Internet of Things) and P2P (Peer-to-Peer) systems that millions of devices are connected and support various types of applications. Here, distributed systems are required to be secure in addition to increasing the performance, reliability, and availability and reducing the energy consumption. In distributed systems, information in objects flows to other objects by transactions reading and writing data in the objects. Here, some information of an object may illegally flow to a subject which is not allowed to get the information of the object. Especially, a leakage of sensitive information is to be prevented from occurring. In order to keep information systems secure, illegal information flow among objects has to be prevented. Types of synchronization protocols are so far discussed based on read and write access rights in the RBAC (Role-Based Access Control) model to prevent illegal information flow.In this thesis, we newly propose a P2PPSO (P2P type of topic-based PS (Publish/Subscribe) with Object concept) model and discuss the models and protocols for information flow control. A P2PPSO model is composed of peer processes (peers) which communicate with one another by publishing and subscribing event messages. Each peer can both publish and receive event messages with no centralized coordinator compared with traditional centralized PS models. Each event message published by a source peer carries information to a target peer. The contents carried by an event message are considered to be composed of objects. An object is a unit of data resource. Objects are characterized by topics, and each event message is also characterized by topics named publication topics.In order to make a P2PPSO system secure, we first newly propose a TBAC (Topic-Based Access Control) model. Here, an access right is a pair ⟨t, op⟩ of a topic t and a publish or subscribe operation op. A peer is allowed to publish an event message with publication topics and subscribe interesting topics only if the publication and subscription access rights are granted to the peer, respectively. Suppose an event message e_j published by a peer p_j carries an object on some topics into a target peer p_i. Here, information in the peer p_j illegally flows to the peer p_i if the target peer p_i is not allowed to subscribe the topics. An illegal object is an object whose topics a target peer is not allowed to subscribe. Even if an event message is received by a target peer by checking topics, objects carried by the event message may be illegal at the target peer. Hence, first, we propose a TOBS (Topics-of-Objects-Based Synchronization) protocol to prevent target peers from being delivered illegal objects in the P2PPSO system. Here, even if an event message is received by a target peer, illegal objects in the event message are not delivered to the target peer.In the TOBS protocol, every event message is assumed to be causally delivered to every common target peer in the underlying network. Suppose an event message e_2 is delivered to a target peer p_i before another event message e_1 while the event message e_1 causally precedes the event message e_2 (e_1 →_c e_2). Here, the event message e_2 is premature at the peer p_i. Hence, secondly, we propose a TOBSCO (TOBS with Causally Ordering delivery) protocol where the function to causally deliver every pair of event messages is added to the TOBS protocol. Here, we assume the underlying network supports reliable communication among every pair of peers, i.e. no event message loss, no duplicate message, and the sending order delivery of messages. Every pair of event messages received by using topics are causally delivered to every common target peer by using the vector of sequence numbers.In the TOBS and TOBSCO protocols, objects delivered to target peers are held as replicas of the objects by the target peers. If a peer updates data of an object, the peer distributes event messages, i.e. update event messages, to update every replica of the object obtained by other peers. If a peer updates an object without changing topics, the object is referred to as altered. Here, an update event message for the altered object is meaningless since peers check only topics to exchange event messages. Hence, thirdly, we propose an ETOBSCO (Efficient TOBSCO) protocol where update event messages of objects are published only if topics of the objects are updated to reduce the network overhead.In the evaluation, first, we show how many numbers of event messages and objects are prevented from being delivered to target peers in the TOBS protocol. Next, we show every pair of event messages are causally delivered but it takes longer to deliver event messages in the TOBSCO protocol than the TOBS protocol. Finally, we show the fewer number of event messages are delivered while it takes longer to update replicas of altered objects in the ETOBSCO protocol than the TOBSCO protocol.博士(工学)法政大学 (Hosei University

VCube-PS: A Causal Broadcast Topic-based Publish/Subscribe System

In this work we present VCube-PS, a topic-based Publish/Subscribe system built on the top of a virtual hypercube-like topology. Membership information and published messages are broadcast to subscribers (members) of a topic group over dynamically built spanning trees rooted at the publisher. For a given topic, the delivery of published messages respects the causal order. VCube-PS was implemented on the PeerSim simulator, and experiments are reported including a comparison with the traditional Publish/Subscribe approach that employs a single rooted static spanning-tree for message distribution. Results confirm the efficiency of VCube-PS in terms of scalability, latency, number and size of messages.Comment: Improved text and performance evaluation. Added proof for the algorithms (Section 3.4

A Publish/Subscribe System Using Causal Broadcast Over Dynamically Built Spanning Trees

International audienceIn this paper we present VCube-PS, a topic-based Publish/Subscribe system built on the top of a virtual hypercube-like topology. Membership information and published messages to subscribers (members) of a topic group are broadcast over dynamically built spanning trees rooted at the message's source. For a given topic, delivery of published messages respects causal order. Performance results of experiments conducted on the PeerSim simulator confirm the efficiency of VCube-PS in terms of scalability, latency, number, and size of messages when compared to a single rooted, not dynamically, tree built approach

ZeroComm: Decentralized, Secure and Trustful Group Communication

In the context of computer networks, decentralization is a network architecture that distributes both workload and control of a system among a set of coequal participants. Applications based on such networks enhance trust involved in communication by eliminating the external author- ities with self-interests, including governments and tech companies. The decentralized model delegates the ownership of data to individual users and thus mitigates undesirable behaviours such as harvesting personal information by external organizations. Consequently, decentral- ization has been adopted as the key feature in the next generation of the Internet model which is known as Web 3.0. DIDComm is a set of abstract protocols which enables secure messaging with decentralization and thus serves for the realization of Web 3.0 networks. It standardizes and transforms existing network applications to enforce secure, trustful and decentralized com- munication. Prior work on DIDComm has only been restricted to pair-wise communication and hence it necessitates a feasible strategy for adapting the Web 3.0 concepts in group-oriented networks. Inspired by the demand for a group communication model in Web 3.0, this study presents Zero- Comm which preserves decentralization, security and trust throughout the fundamental opera- tions of a group such as messaging and membership management. ZeroComm is built atop the publisher-subscriber pattern which serves as a messaging architecture for enabling communi- cation among multiple members based on the subjects of their interests. This is realized in our implementation through ZeroMQ, a low-level network library that facilitates the construction of advanced and distributed messaging patterns. The proposed solution leverages DIDComm protocols to deliver safe communication among group members at the expense of performance and efficiency. ZeroComm offers two different modes of group communication based on the organization of relationships among members with a compromise between performance and security. Our quantitative analysis shows that the proposed model performs efficiently for the messaging operation whereas joining a group is a relatively exhaustive procedure due to the es- tablishment of secure and decentralized relationships among members. ZeroComm primarily serves as a low-level messaging framework but can be extended with advanced features such as message ordering, crash recovery of members and secure routing of messages

Conflict-Free Replicated Data Types in Dynamic Environments

Over the years, mobile devices have become increasingly popular and gained improved computation capabilities allowing them to perform more complex tasks such as collaborative applications. Given the weak characteristic properties of mobile networks, which represent highly dynamic environments where users may experience regular involuntary disconnection periods, the big question arises of how to maintain data consistency. This issue is most pronounced in collaborative environments where multiple users interact with each other, sharing a replicated state that may diverge due to concurrency conflicts and loss of updates. To maintain consistency, one of today’s best solutions is Conflict-Free Replicated Data Types (CRDTs), which ensure low latency values and automatic conflict resolution, guaranteeing eventual consistency of the shared data. However, a limitation often found on CRDTs and the systems that employ them is the need for the knowledge of the replicas whom the state changes must be disseminated to. This constitutes a problem since it is inconceivable to maintain said knowledge in an environment where clients may leave and join at any given time and consequently get disconnected due to mobile network communications unreliability. In this thesis, we present the study and extension of the CRDT concept to dynamic environments by introducing the developed P/S-CRDTs model, where CRDTs are coupled with the publisher/subscriber interaction scheme and additional mechanisms to ensure users are able to cooperate and maintain consistency whilst accounting for the consequent volatile behaviors of mobile networks. The experimental results show that in volatile scenarios of disconnection, mobile users in collaborative activity maintain consistency among themselves and when compared to other available CRDT models, the P/S-CRDTs model is able to decouple the required knowledge of whom the updates must be disseminated to, while ensuring appropriate network traffic values

Distributed aop middleware for large-scale scenarios

En aquesta tesi doctoral presentem una proposta de middleware distribuït pel desenvolupament d'aplicacions de gran escala. La nostra motivació principal és permetre que les responsabilitats distribuïdes d'aquestes aplicacions, com per exemple la replicació, puguin integrar-se de forma transparent i independent. El nostre enfoc es basa en la implementació d'aquestes responsabilitats mitjançant el paradigma d'aspectes distribuïts i es beneficia dels substrats de les xarxes peer-to-peer (P2P) i de la programació orientada a aspectes (AOP) per realitzar-ho de forma descentralitzada, desacoblada, eficient i transparent. La nostra arquitectura middleware es divideix en dues capes: un model de composició i una plataforma escalable de desplegament d'aspectes distribuïts. Per últim, es demostra la viabilitat i aplicabilitat del nostre model mitjançant la implementació i experimentació de prototipus en xarxes de gran escala reals.In this PhD dissertation we present a distributed middleware proposal for large-scale application development. Our main aim is to separate the distributed concerns of these applications, like replication, which can be integrated independently and transparently. Our approach is based on the implementation of these concerns using the paradigm of distributed aspects. In addition, our proposal benefits from the peer-to-peer (P2P) networks and aspect-oriented programming (AOP) substrates to provide these concerns in a decentralized, decoupled, efficient, and transparent way. Our middleware architecture is divided into two layers: a composition model and a scalable deployment platform for distributed aspects. Finally, we demonstrate the viability and applicability of our model via implementation and experimentation of prototypes in real large-scale networks

A decentralized framework for cross administrative domain data sharing

Federation of messaging and storage platforms located in remote datacenters is an essential functionality to share data among geographically distributed platforms. When systems are administered by the same owner data replication reduces data access latency bringing data closer to applications and enables fault tolerance to face disaster recovery of an entire location. When storage platforms are administered by different owners data replication across different administrative domains is essential for enterprise application data integration. Contents and services managed by different software platforms need to be integrated to provide richer contents and services. Clients may need to share subsets of data in order to enable collaborative analysis and service integration. Platforms usually include proprietary federation functionalities and specific APIs to let external software and platforms access their internal data. These different techniques may not be applicable to all environments and networks due to security and technological restrictions. Moreover the federation of dispersed nodes under a decentralized administration scheme is still a research issue. This thesis is a contribution along this research direction as it introduces and describes a framework, called \u201cWideGroups\u201d, directed towards the creation and the management of an automatic federation and integration of widely dispersed platform nodes. It is based on groups to exchange messages among distributed applications located in different remote datacenters. Groups are created and managed using client side programmatic configuration without touching servers. WideGroups enables the extension of the software platform services to nodes belonging to different administrative domains in a wide area network environment. It lets different nodes form ad-hoc overlay networks on-the-fly depending on message destinations located in distinct administrative domains. It supports multiple dynamic overlay networks based on message groups, dynamic discovery of nodes and automatic setup of overlay networks among nodes with no server-side configuration. I designed and implemented platform connectors to integrate the framework as the federation module of Message Oriented Middleware and Key Value Store platforms, which are among the most widespread paradigms supporting data sharing in distributed systems

A Network-Agnostic and Cheat-Resistant Framework for Multiplayer Online Games

"Video games are kids' stuff" may be still in the minds of many people. But the video games industry is far beyond its infancy and has already grown into a multi-billion dollar business. The NPD Group reports that in 2007 the revenues generated in the U.S. with video game soft- and hardware for consoles and personal computers reached a total of 18.8 billion dollars, a 40 percent increase over 2006. According to PricewaterhouseCoopers, the global sales will even surpass those of the music industry within the next years. With the success of the Internet, online games are a constantly increasing part of these sales. According to DFC Intelligence, the worldwide online game market will grow to over 13 billion dollars in 2011. The probably most successful online game genre today is that of the so-called Massively Multiplayer Online Games (MMOGs). This kind of games provides vast virtual worlds, where thousands of players can meet and interact simultaneously. Most of these worlds are persistent, i.e. they may be online for years. They are hosted on Internet servers which are online 24/7 and players can join and leave the game whenever they like to. The persistence of the game world allows for long-term development of virtual avatars with individual characteristics and possessions. The leader of the MMOG market today is Blizzard Entertainment with the title World of Warcraft. In the beginning of 2008, World of Warcraft had 10 million subscribers (each paying up to 15 dollars per month) and a market share of 62 percent. Developing todays video games is a complex and cost-intensive task and multiplayer online functionality has a significant share in this. In 2008, the first video game hit the 100 million dollar mark for development costs. In addition to that, publishers of online games need to provide the necessary services to allow their customers to play the game over the Internet. Traditionally, most online games and nearly all MMOGs are built relying on the Client/Server architecture. The client software runs on the player's computers and shows only an audio-visual representation of the game world. It accepts commands issued by the player and transmits them to the server. Processing the commands and managing the state of the game is completely done on the server-side. Thus, to be able to handle hundreds or thousands of players simultaneously, large amounts of computing power and network bandwidth are required. Additionally, the service requires a large staff for server maintenance, software updates, billing and customer services. The provision of the World of Warcraft service did cost about 200 million dollars since its launch in November 2004. In addition to the effort of maintaining a multiplayer online game service after its launch there arises another challenge: keeping the game free of cheaters. A cheater may be defined as a user that performs an action that gives an advantage over his opponents that is considered unfair by the game developer. One must be aware that cheating is a major concern in multiplayer games as it seriously affects the game experience of honest players. Especially for subscription-based online games this is fatal, since customers will cancel their subscriptions if the experience doesn't meet their expectations. Game publishers usually do not hesitate to close the accounts of players that they believe to have cheated. For example, in 2006 Blizzard Entertainment announced in their forums that they have banned 59,000 players from World of Warcraft within a single month