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Mobile computing research has often focused on untethering an in-use computing device, rather than enabling the mobility of the computation task itself. This paper presents an architecture, implementation, and experimental evidence that together validate a new continuous computing concept, application session handoff. The iMASH architecture leverages previous work on proxies, content adaptation, and client awareness to provide a unique, middleware-enable capability for continuous computing. Implementation in both socket- and RPC-based environments shows that very fast, secure session handoff of non-trivial client/server applications across heterogeneous client devices and network is feasible: experiments on a number of applications yielded handoff latencies ranging from 0.5s to 2s.

Ubiquitous computing across a variety of wired and wireless connections still lacks an effective security architecture. In our research work, we address the specific issue of designing and building a security architecture for application session handoff, a functionality which we envision will be a key component enabling ubiquitous computing. Our architecture incorporates a number of proven approaches into the new context of ubiquitous computing. We employ the Bell-LaPadula (1976) and capability models to realise access control and adopt public key infrastructure (PKI)-based approaches to provide efficient and authenticated end-to-end security. To demonstrate the effectiveness of our design, we implemented an application enabled with this security architecture and showed that it incurred low latency.

Personal computing on mobile platforms such as laptops and personal digital assistants, rather than in a traditional desktop environment, is becoming increasingly more common. We address the issue of application session transfer for uninterrupted data access across this diverse range of platforms. This work is part of the iMASH project, a multi-year, multi-discipline collaborative effort focused on enabling mobile client platforms and incorporating them into existing legacy networked systems for use by medical practitioners. We have developed a tiered architecture that includes a middleware server layer positioned between existing application servers and multiple clients to make session transfer transparent to the user. Any client application executing our middleware-aware remote code library can save and restore its session by interacting with a middleware server. As a proof of concept, we have implemented the transfer of bookmarks, history, Web cache, and user preferences with the Mozilla open source Web browser, from this effort we have established baseline performance metrics and have found that the overhead is within reasonable bounds of just a few seconds of latency.

This research proposes and tests an approach to engineering distributed file systems that are aimed at wide-scale, Internet-based use. The premise is that replication is essential to deliver performance and availability, yet the traditional conservative replica consistency algorithms do not scale to this environment. Our Ficus replicated file system uses a single-copy availability, optimistic update policy with reconciliation algorithms that reliably detect concurrent updates and automatically restore the consistency of directory replicas. The system uses the peer-to-peer model in which all machines are architectural equals but still permits configuration in a client-server arrangement where appropriate. Ficus has been used for six years at several geographically scattered installations. This paper details and evaluates the use of optimistic replica consistency, automatic update conflict detection and repair, the peer-to-peer (as opposed to client-server) interaction model, and the stackable file system architecture in the design and construction of Ficus. The paper concludes with a number of lessons learned from the experience of designing, building, measuring, and living with an optimistically replicated file system. © 1998 John Wiley & Sons, Ltd.

This paper presents a practical set of algorithms for maintaining the consistency of a replicated file system with an optimistic update policy. These algorithms permit a system which allows updates to an object so long as any copy is available; the algorithms then return the various copies to consistency at their first opportunity. These algorithms have been used to build the Ficus replicated file system.>