Causal Delivery Protocols in Real-time Systems: a Generic Model
Paulo Veríssimo.
From the Journal of Real-Time Systems, vol 10, n 1, pp.45-73, 1996.
Kluwer Academic Publishers
Abstract
The objective of this paper is to introduce a model for causal
delivery protocols in real-time systems. We start by showing that
temporal order properties of real-time protocols are independent of
whether they are timer-driven or clock-driven, being instead related
to their degree of synchronism, that we call steadiness. Then, we
derive a set of correctness conditions for such protocols to secure
causal delivery order. To achieve this objective, we use an extension
of Lamport's model of time-stamp based order. We show that both timer-
and clock-driven protocols have order correctness limits dictated by
the environment and the target applications, and define those limits,
through a set of working formulas. We show that in extremely adverse
cases, timer-driven protocols will perform as well as clock-driven
ones, due to the restrictions imposed on the operation of the latter,
which is perhaps surprising. These results open the door to exploring
new forms of communication in time-critical systems, for example,
supporting clock- and time-driven communication, and event- and
time-triggered operation. We expect that the results of this paper
will give insight to that problem, and will be useful in real-life
systems, such as distributed computer control.
Also available
extended report (gzip postscript).