Efficient Reliable Group Communication for Distributed Systems

Many applications can profit from broadcast communication, but few operating systems provide primitives that make broadcast communication available to user applications. In this paper we introduce primitives for broadcast communication that have been integrated with the Amoeba distributed operating system. The semantics of the broadcast primitives are simple, powerful, and easy to understand. Our primitives, for example, guarantee total ordering of broadcast messages. The proposed primitives are also efficient: if a network supports physical multicast, a reliable broadcast can be done in just slightly more than two messages on the average, so, the performance of a reliable broadcast is roughly comparable to that of a remote procedure call. In addition, the primitives are flexible: user applications can, for example, trade performance against fault tolerance. 1

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

Client-access protocols for replicated services

Published versio

A middleware service for fault-tolerant group communications

PhD ThesisMany distributed applications require multicast group communication services, enabling an entity to interact with a group of other entities. Providing the reliability and ordering guarantees required by group based applications is not a trivial task in distributed systems where computation and communication delays might not be known accurately. Furthermore, the approaches available to support these guarantees are diverse. The choice of approach may significantly effect the performance of an application and/or may not be suitable for some application types. Nowadays, distributed applications are frequently built as a Middleware service. The Thesis develops techniques for providing group communication support in Middleware environments. A group communication service has been designed and implemented in such a way as not to hinder the interoperability/portability of applications built using it. The service provides a variety of functions that may be tailored to suit many different types of applications. Group communication protocols are presented that ensure reliability and ordering guarantees. Furthermore, the reliability and ordering guarantees of such protocols may be tailored to suit a wide variety of applications. Mechanisms that provide a variety of approaches to inter-member and inter-group interactions that are suitable for satisfying the requirements of many different types of applications (e.g., fault- tolerant, collaborative) are also supported. The service can work over local and wide area networks (Internet).Hewlett Packard laboratories Engineering and Physical Science Research Counci

Secure Group Communication in Delay Tolerant Mobile Ad-Hoc Network

Delay-tolerant networks (DTNs) are well-known for delivering various types of information from different senders in a multicast manner, both in centralised and decentralised networks. Wireless mobile nodes form small networks in which one or more senders transmit data to one or more destinations through intermediate nodes. DTN routing protocols differ from traditional wireless routing protocols. There are security threats in DTNs, such as blackhole attackers dropping data, jamming attacks consuming bandwidth, and Vampire attacks depleting battery power and available bandwidth. This paper proposes a prevention scheme to detect and mitigate all three types of attackers in multicast communication. These attackers can impact performance by generating false replies, flooding with redundant information, and wasting communication power. The primary focus of this paper is on security issues related to DTN routing protocols. In order to counter malicious nodes, a blacklist is maintained, and if a neighbour identifies a node as malicious, it excludes packets from that node. Meanwhile, the neighbour continues sending packets to the malicious node, except for broadcast packets, which are dropped. If a node is found to forward no packets or only some packets by all its neighbours, any reply it gives to route requests is disregarded, and any request it initiates is ignored. Successful data reception at the destination indicates that hop-based data delivery maintains a record of successful transmissions. The proposed security scheme demonstrates improved performance

Middleware for transparent TCP connection migration : masking faulty TCP-based services

Masteroppgave i informasjons- og kommunikasjonsteknologi 2004 - Høgskolen i Agder, GrimstadMission critical TCP-based services create a demand for robust and fault tolerant TCP communication. Sense Intellifield monitors drill operations on rig sites offshore. Critical TCP-based services need to be available 24 hours, 7 days a week, and the service providers need to tolerate server failure. How to make TCP robust and fault tolerant without modifying existing infrastructure like existing client/server applications, services, TCP stacks, kernels, or operating systems is the motivation of this thesis. We present a new middleware approach, first of its kind, to allow TCP-based services to survive server failure by migrating TCP connections from failed servers to replicated surviving servers. The approach is based on a proxy technique, which requires modifications to existing infrastructure. Our unique middleware approach is simple, practical, and can be built into existing infrastructure without modifying it. A middleware approach has never been used to implement the proxy based technique. Experiments for validation of functionality and measurement of performance of the middleware prototype are conducted. The results show that our technique adds significant robustness and fault tolerance to TCP, without modifying existing infrastructure. One of the consequences of using a middleware to make TCP communication robust and fault tolerant is added latency. Another consequence is that TCP communication can survive server failure, and mask it. Companies providing robust and fault tolerant TCP, is no longer dependant of third party hardware and/or software. By implementing our solution, they can gain economical advantages. A main focus of this report is to present a prototype that demonstrates our technique and middleware approach. We present relevant background theory which has lead to the design architecture of a middleware approach to make TCP communication fault tolerant. Finally we conduct experiments to uncover the feasibility and performance of the prototype, followed by a discussion and conclusion

Design, Implementation, and Verification of the Reliable Multicast Protocol

This document describes the Reliable Multicast Protocol (RMP) design, first implementation, and formal verification. RMP provides a totally ordered, reliable, atomic multicast service on top of an unreliable multicast datagram service. RMP is fully and symmetrically distributed so that no site bears an undue portion of the communications load. RMP provides a wide range of guarantees, from unreliable delivery to totally ordered delivery, to K-resilient, majority resilient, and totally resilient atomic delivery. These guarantees are selectable on a per message basis. RMP provides many communication options, including virtual synchrony, a publisher/subscriber model of message delivery, a client/server model of delivery, mutually exclusive handlers for messages, and mutually exclusive locks. It has been commonly believed that total ordering of messages can only be achieved at great performance expense. RMP discounts this. The first implementation of RMP has been shown to provide high throughput performance on Local Area Networks (LAN). For two or more destinations a single LAN, RMP provides higher throughput than any other protocol that does not use multicast or broadcast technology. The design, implementation, and verification activities of RMP have occurred concurrently. This has allowed the verification to maintain a high fidelity between design model, implementation model, and the verification model. The restrictions of implementation have influenced the design earlier than in normal sequential approaches. The protocol as a whole has matured smoother by the inclusion of several different perspectives into the product development