António Casimiro

CesiumSpray: A Precise and Accurate Global Clock Service for Large-Scale Systems

Paulo Veríssimo, Luís Rodrigues and António Casimiro

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.


  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  = "",
  documentURL  = "",
  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"


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