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\begin{abstract}

Fault tolerance is a crucial design consideration for mission-critical
distributed real-time and embedded (DRE) systems, such as avionics
mission computing systems, and supervisory control and data
acquisition systems.  Increasingly more 
of these systems are created using emerging middleware standards, such
as publish-subscribe communication services and component based
architectures. Most previous R\&D efforts in fault tolerance
middleware has focused on client-server object systems. Application of
this research to concrete domains frequently requires specialization,
hand-tailoring, and customization to accommodate for the real world
challenges of these systems, including nondeterminism, scale, and
interaction patterns.

This paper describes our current applied R\&D efforts to develop fault
tolerance technology for a specific piece of mission critical DRE
infrastructure, a dynamic resource manager, built using CORBA
components and exhibiting characteristics representative of real-world
DRE systems. This paper makes three contributions to the design and
implementation of fault tolerant support in DRE system. First, we
describe the fault tolerance challenges presented by these systems,
including support for component infrastructure, mixed mode  FT
techniques (supporting active and passive fault tolerance), support
for nondeterminism, issues of scale (limiting the spread of the FT
infrastructure to those elements that require it), and the need for
predictable and bounded recovery times.  Second, we describe the
design of our fault tolerant DRE architecture.  Finally, we illustrate
the fault recovery times in our FT DRE infrastructure in the presence
of faults for a representative domain, a mission critical computing
environment. 

{\bf Keywords:} Fault tolerance, Mission-critical Middleware

\end{abstract}

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