Future applications running on mobile platforms will sometimes need to query sensors and track sensor data over time. This paper uses the publish-subscribe paradigm as a natural solution to querying sensors from mobile platforms, and proposes a scalable approach to implement publish-subscribe, driven by the querying application. Our approach is evaluated by simulation, focusing on scalability

Flooding is an important communication primitive in mobile ad-hoc networks and also serves as a building block for more complex protocols such as routing protocols. In this paper, we propose a novel approach to flooding, which relies on proactive compensation packets periodically broadcast by every node. The compensation packets are constructed from dropped data packets, based on techniques borrowed from forward error correction. Since our approach does not rely on proactive neighbor discovery and network overlays it is resilient to mobilit.We evaluate the implementation of Mistral through simulation and compare its performance and overhead to purely probabilistic flooding. Our results show that Mistral achieves a significantly higher node coverage with comparable overhead.

We present DRIFT - a total order multicast algorithm for ad hoc networks with mobile or static nodes. Due to the ad hoc nature of the network, DRIFT uses flooding for message propagation. The key idea of DRIFT is virtual flooding - a way of using unrelated message streams to propagate message causality information in order to accelerate message delivery. We describe DRIFT in detail. We evaluate its performance in a simulator and in a wireless sensor network. In both cases our results demonstrate that the performance of DRIFT exceeds that of the simple total order multicast algorithm designed for wired networks, on which it is based. In simulation at scale, for certain experiment settings, DRIFT achieved speedup of several orders of magnitude

Datacenters are complex environments consisting of thousands of failure-prone commodity components connected by fast, high capacity interconnects. The software running on such datacenters typically uses multicast communication patterns involving multiple senders. We examine the problem of time-critical multicast in such settings, and propose Slingshot, a protocol that uses receiver-based FEC to recover lost packets quickly. Slingshot offers probabilistic guarantees on timeliness by having receivers exchange FEC packets in an initial phase, and optional complete reliability on packets not recovered in this first phase. We evaluate an implementation of Slingshot against SRM, a well-known multicast protocol, and show that it achieves two orders of magnitude faster recovery in datacenter settings

With the widespread availability of wireless technology and the deployment of an increasing variety of sensors, information generated by sensors is becoming available to applications running on mobile nodes. Retrieving this information in a reliable, efficient manner will be an important building block for many applications. However, unreliable, low bandwidth communication links and node mobility make efficient, reliable, and scalable information retrieval a challenge.

We propose a novel approach to the composition of group communication protocols. In this approach, components are modelled as finite state machines communicating via signals. We introduce two building blocks, called adaptor and adaplexor, that ease the development and the composition of group communication protocol stacks, and we discuss how isolation can be achieved in this setting. To validate our architectural concepts, we have implemented the proposed group communication architecture in SDL.

Group communication provides communication primitives with various semantics and their use greatly simplifies the development of highly available services. However, despite tremendous advances in research and numerous prototypes, group communication stays confined to small niches and academic prototypes. In contrast, message-oriented middleware such as the Java message service (JMS) is widely used, and has become a de-facto standard. We believe that the lack of a well-defined and easily understandable standard is the reason that hinders the deployment of group communication systems. Since JMS is a well-established technology, an interesting solution is to extend JMS adding group communication primitives to it. Foremost, this requires extending the traditional semantics of group communication in order to take into account various features of JMS, e.g., durable/nondurable subscriptions and persistent/non-persistent messages. The resulting new group communication specification, together with the corresponding API, defines group communication primitives compatible with JMS.

In today's systems, applications are composed from various components that may be located on different machines. The components (acting as servers) may have to collaborate in order to service a client request. More specifically, a client request to one component may trigger a request to another component. To ensure fault-tolerance, components are generally replicated. Replicated components lead to the problem of a replicated server invoking another replicated server. We call this the problem of replicated invocation. Replicated invocation has been considered in the context of deterministic servers. However, the problem is more difficult to address when servers are non-deterministic. In this context, work has been done to enforce deterministic execution. In this paper, we consider a different approach: instead of preventing non-deterministic execution of servers we discuss how to handle it. We present the problem of non-deterministic replicated invocation. Our solution then consists of sharing sufficient undo information among the replicas of the server invoking another server.

Mobile agents have attracted considerable interest in recent years. In the context of mobile agents, fault tolerance is crucial to enable the integration of mobile agent technology into today's business applications. This article identifies two important properties for fault-tolerant mobile agent execution: nonblocking and exactly-once. Nonblocking ensures that the agent execution can proceed despite a single failure of the agent or the machine, for instance. Replication is the generally adopted mechanism to prevent blocking, but may lead to multiple executions of the agent (i.e., a violation of the exactly-once property), which is undesirable with operations that have side effects. Hence, we propose that fault-tolerant mobile agent execution be modeled as a sequence of agreement problems. Our approach is nonblocking and ensures exactly-once execution. FATOMAS, our prototype fault-tolerant mobile agent system, implements our approach. Its performance evaluation illustrates the overhead of the replication mechanisms.

Mobile agents are computer programs that act autonomously on behalf of a user and travel through a network of heterogeneous machines. To enable mobile agent technology for e-business, transaction support needs to be provided, in particular execution atomicity. Execution atomicity ensures that either all operations of the agent succeed, or none at all, and needs to be ensured also in the face of infrastructure failures. We distinguish between blocking and non-blocking solutions for transactional mobile agents, i.e., mobile agents, that execute as a transaction. The approach presented in the paper is non-blocking. A non-blocking transactional mobile agent execution has the important advantage, that it can make progress despite failures.

Fault tolerance is fundamental to the further development of mobile agent applications. In the context of mobile agents, fault-tolerance prevents a partial or complete loss of the agent, i.e., it ensures that the agent arrives at its destination. We present FATOMAS, a Java-based fault-tolerant mobile agent system based on an algorithm presented in an earlier paper (2000). Contrary to the standard "place-dependent" architectural approach, FATOMAS uses the novel "agent-dependent" approach. In this approach, the protocol that provides fault tolerance travels with the agent. This has the important advantage to allow fault-tolerant mobile agent execution without the need to modify the underlying mobile agent platform (in our case ObjectSpace's Voyager). In our performance evaluation, we show the costs of our approach relative to the single, non-replicated agent execution. Pipelined mode and optimized agent forwarding are two optimizations that reduce the overhead of a fault-tolerant mobile agent execution.

Fault tolerance is fundamental to the further development of mobile agent applications. In the context of mobile agents, fault tolerance prevents a partial or complete loss of the agent, i.e. ensures that the agent arrives at its destination. Simple approaches such as checkpointing are prone to blocking. Replication can in principle improve solutions based on checkpointing. However existing solutions in this context either assume a perfect failure detection mechanism (which is not realistic in an environment such as the Internet), or rely on complex solutions based on leader election and distributed transactions, where only a subset of solutions prevents blocking. The paper proposes a novel approach to fault tolerant mobile agent execution, which is based on modeling agent execution as a sequence of agreement problems. Each agreement problem is one instance of the well understood consensus problem. Our solution does not require a perfect failure detection mechanism, while preventing blocking and ensuring that the agent is executed exactly once.