Journal of Real-Time Systems, 12(3), pp.243-294, May 1997
In large-scale systems, such as Internet-based distributed systems, classical clock-synchronization solutions become impractical or poorly performing, due to the number of nodes and/or the distance among them. We present a global time service for world-wide systems, based on an innovative clock synchronization scheme, named CesiumSpray. The service exhibits high precision and accuracy; it is virtually indefinitely scalable; and it is fault-tolerant. It is deterministic for real-time machinery in the local area, which makes it particularly well-suited for, though not limited to, large-scale real-time systems.
The main features of our clock synchronization scheme can be summarized as follows: hybrid external/internal synchronization protocol improves effectiveness of synchronization; heterogeneous failure semantics for clocks and processors improves previous lower bounds on processors; two-level hierarchy improves scalability. The root of the hierarchy is the GPS satellite constellation, which ``sprays'' its reference time over a set of nodes provided with GPS receivers, one per local network. The second level of the hierarchy performs internal synchronization, further ``spraying'' the external time inside the local network.
@article{Verissimo:97a,
author = "Ver\'{\i}ssimo, Paulo and Rodrigues, Lu\'{\i}s and Casimiro, Ant\'{o}nio",
title = "CesiumSpray: a Precise and Accurate Global Time
Service for Large-scale Systems",
journal = "Journal of Real-Time Systems",
year = "1997",
abstractURL = "http://www.di.fc.ul.pt/~casim/papers/CesiumSpray/CesiumSpray.html",
documentURL = "http://www.di.fc.ul.pt/~casim/papers/CesiumSpray/CesiumSpray.pdf",
volume = "12",
number = "3",
pages = "243--294",
month = may,
keywords = "hybrid internal/external clock synchronization,
large-scale systems, global time, real-time
fault-tolerant systems, GPS"
}