Assuring Resilient Time Synchronization

In many distributed and pervasive systems the clocks of nodes are required to be synchronized to a unique global time. Due to unpredictable system and environment characteristics, the distance of a local clock from global time is a variable factor very hard to predict. Systems usually adopt measures to guarantee an upper bound on such distance from global time that are very often quite far from typical execution scenarios and thus are of practical little use. This paper describes the Reliable and Self-Aware Clock (R&SAClock), a low-intrusive software service that is able to compute a conservative estimation of distance from an external global time. R&SAClock acts as a new clock that couples information gained from synchronization mechanisms with information collected from the local clock to provide both current time and a self-adaptive reliable estimation of distance from global time. This paper describes the main functions, services and time-related mechanisms of R&SAClock and an implementation for the NTP synchronization mechanism and Linux OS. 1

A self-aware clock for pervasive computing systems

The paper addresses the challenges and opportunities of instrumenting pervasive computing systems with a logical clock, aware of the quality of synchronization with respect to a time reference. Pervasive computing systems are i) mobile, ii) dynamic and iii) composed of a large number of distributed components; in systems with these characteristics the availability of a ”smart ” clock that is i) capable to use different mechanisms for the synchronization with the global distributed time reference and ii) aware of the current quality of synchronization with such time reference, can be very useful in order to build dependable middleware services and applications.

Quantitative Evaluation of Distributed Algorithms Using the Neko Framework: the NekoStat Extension

In this paper we present NekoStat, an extension of the Neko tool. Neko is a Java framework and a communication platform that permits rapid prototyping of distributed applications; it provides tools to organize the applications using a layered architecture, with the network(s) at the bottom of the architecture. Neko is also a communication platform that allows sending and receiving of generic Java objects. Distributed systems realized within the Neko framework can be exercised both on real networks and on simulated ones, without changes in the application code. We constructed an extension to plain Neko, called NekoStat; it permits attainment of quantitative evaluations of distributed systems. In the paper we describe this extension; we motivate the development of NekoStat, we describe the design and finally we illustrate its usage through a case study, which highlights the usefulness of NekoStat