  Creol is an object-oriented modeling language in which inherently concurrent
objects exchange asynchronous method calls. The operational semantics of Creol
is written in an actor-based style, formulated in rewriting logic. The
operational semantics yields a language interpreter in the Maude system, which
can be used to analyze models. Recently, Creol has been applied to the modeling
of systems with radio communication, such as sensor systems. With radio
communication, messages expire and, if sent simultaneously, they may collide in
the air. In order to capture these and other properties of distributed systems,
we extended Creol's operational semantics with a notion of time. We exploit the
framework of a language interpreter to use a lightweight notion of time, in
contrast to that needed for a general purpose specification language. This
paper presents a timed extension of Creol, including the semantics and the
implementation strategy, and discusses its properties using an extended
example. The approach can be generalized to other concurrent object or
actor-based systems.
