With the popularity of wireless networking and mobile devices, mobile computing has changed the way we live and work. The special characteristics of mobile environments, such as highly variable connectivity, disconnection, location-dependency and energy and resource sensitivity and the diversity and flexibility introduced by mobile systems have new challenges for research in distributed systems. Mobile distributed computing represents a discipline of distributed systems research and practice towards support for mobility. It is concerned with creating solutions to enable the sharing of distributed resources/services and to facilitate remote collaborations while people work away from the fixed, wired facilities.
This special issue is devoted to distributed algorithms, systems and applications for mobile computing environments. It contains five papers, selected from the program of the 3rd International Workshop on Mobile Distributed Computing (MDC'05), in conjunction with IEEE International Conference on Distributed Computing Systems, June 8–10, 2005, Columbus, Ohio, USA.
The first paper, “Consistency of cooperative caching in mobile peer-to-peer systems over MANET” by Cao et al. revisits an important caching consistency problem in mobile environments. It proposes a novel RPCC approach based on relay peers between the source host and the cache nodes. The layer of relay peers facilitates the implementation of both push-based and pull-based strategies, which helps to reduce the communication overhead and query latency. The push and pull operations can be performed asynchronously and simultaneously. Moreover, the proposed RPCC approach is flexible in that it can deal with three kinds of consistency requirements (strong and weak consistency) adaptively.
The paper “Context adaptation of the communication stack”, by Mocito et al. presents a middleware framework, called Morpheus, to support the development of context-aware adaptive communication protocols stacks. The protocol stacks can be reconfigured according to the local context and the context of the remaining remote participants. The context information and the current node configuration feed a Markov decision process for the derivation of appropriate reconfigurations.
In the paper “A middleware architecture for mobile 3D graphics”, Agu et al. describe a graphics-aware middleware architecture, called the mobile adaptive distributed graphics framework (MADGRAF), for running complex 3D graphics applications on low end mobile devices over wireless networks. In MADGRAF, a server can perform mobile device-optimized pre-processing of complex graphics scenes in order to speed up run time rendering, scale high-resolution meshes using polygon or image-based simplification, progressively transmit compressed graphics files, conceal transmission errors by including redundant bits or perform remote execution, all tailored to the client's capabilities.
The paper “On mobile transaction processing in dynamically configurable mobile database communities” by Brayner and de Aguiar Moraes Filho describes an approach for controlling concurrency of mobile transactions executed in mobile database communities (MDBCs). The proposed approach is based on the use of semantic knowledge to relax the notion of absolute transaction atomicity. Supported by this new concept of atomicity, the authors propose a new correctness criterion, denoted mobile semantic serializability, for the execution of concurrent transactions in MDBCs. The proposed correctness criterion provides a high degree of inter-transaction parallelism and ensures consistency of the mobile database.
The last paper, “Path-history-based access control for mobile agents” by Cao and Lu is devoted to trusted computing based on mobile agents. In mobile agent environments, agents' authorization and access control should be adaptive to their path history. In this regard, the authors propose two concepts of path pattern and host patch as conceptual components to declare a dynamic trust relationship with migrating agents in a flexible and fine-grained manner. These two components are integrated with the RBAC model, leading to a new phRBAC model. The new model preserves the advantages of the original RBAC and facilitates the enforcement of this unique security policy in mobile agent systems.
I want to thank all the submission authors for their contributions to this special issue and the MDC'05 program committee and external reviewers for their in-depth and timely comments. I am also grateful to Dr Ivan Stojmenovic, the Editor-in-Chief of this journal for his encouragement, support, and guidance throughout this project. I hope that you will find this special issue interesting and useful.