Pawel T. Wojciechowski

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We study the distributed infrastructures required for location-independent communication between migrating agents. These infrastructures are problematic: different applications may have very different patterns of migration and communication, and require different performance and robustness properties; algorithms must be designed with these in mind. To study(More)
We study communication primitives for interaction between mobile agents. They can be classified into two groups. At a low level there are location dependent primitives that require a programmer to know the current site of a mobile agent in order to communicate with it. At a high level there are location independent primitives that allow communication with a(More)
Summary form only given. We address programming abstractions for building protocols from smaller, reusable microprotocols. The existing protocol frameworks, such as Appia and Cactus, either restrict the amount of concurrency between microprotocols, or depend on the programmer, who should implement all the necessary synchronisation using standard language(More)
In this paper, we propose a new architecture for group communication middleware. Current group communication systems share some common features, despite the big differences that exist among them. We first point out these common features by describing the most representative group communication architectures implemented over the last 15 years. Then we show(More)
In this paper, we study dynamic protocol update (DPU). Contrary to local code updates on-the-fly, DPU requires global coordination of local code replacements. We propose a novel solution to DPU. The key idea is to add a level of indirection between the service callers and the service provider. This indirection level facilitates an implementation of simple(More)
In this paper we compare two approaches to the design of <i>protocol frameworks</i> -- tools for implementing modular network protocols. The most common approach uses events as the main abstraction for a local interaction between protocol modules. We argue that an alternative approach, that is based on service abstraction, is more suitable for expressing(More)
We propose a novel algorithm for hybrid transactional replication (HTR) of highly dependable services. It combines two schemes: a transaction is executed either optimistically by only one service replica in the deferred update mode (DU), or deterministically by all replicas in the state machine mode (SM); the choice is made by an oracle. The DU mode allows(More)
In this paper, we analyze and experimentally compare state-machine-based and deferred-update (or transactional) replication, both relying on atomic broadcast. We define a model that describes the upper and lower bounds on the execution of concurrent requests by a service replicated using either scheme. The model is parametrized by the degree of parallelism(More)
Mobile computation, in which executing computations can move from one physical computing device to another, is a recurring theme: from OS process migration, to language-level mobility, to virtual machine migration. This article reports on the design, implementation, and verification of overlay networks to support reliable communication between migrating(More)