%  $Id: conclusions.tex,v 1.4 2004/05/16 15:29:18 gokhale Exp $

\section{Conclusions}
\label{conclusion}

R\&D over the past decade on object-oriented standards middleware,
such as CORBA, has demonstrated its effectiveness in developing
and supporting QoS requirements of large-scale distributed and real-time
systems. Over the past few years, OO middleware has been evolving into
component-oriented middleware. Component-based software development
has already received widespread acceptance in the enterprise business
and desktop application domains. However, developers of distributed
real-time and embedded (DRE) systems have encountered limitations with
the available component middleware platforms, such as the CORBA
Component Model (CCM) and the Java 2 Enterprise Edition (J2EE).  These
limitations often preclude developers of DRE systems from fully
exploiting the benefits of component software.  In particular,
component middleware platforms lack standards-based
publisher/\-subscriber communication mechanisms 
that support key quality-of-service (QoS) requirements of DRE systems,
such as low latency, bounded jitter, and end-to-end operation priority
propagation.  QoS-enabled publisher/\-subscriber services are available
in object middleware platforms, such as Real-time CORBA, but such
services have not been integrated into component middleware due to a
number of development and configuration challenges.

This paper provides three approaches to integrating real-time
publisher/\-subscriber services within QoS-enabled component
middleware. The pros and cons of individual integration approaches are
described. We also provide performance evaluation for the
container-based integration approach, which provides the least
intrusive and most standards-conforming approach. The collocated case
results, which demonstrate event dispatching overhead, provides
sufficient guidance to indicate that all the real-time properties of
real-time event channels is preserved. The distributed case reveals
the performance continues to remain predictable, however, with the
additional cost of network latencies, which is expected.

Our ongoing R\&D in this field involves the evaluation of the remaining design
choices and application of this technology in the context of a variety of DRE
domains, including telecom, avionics mission computing, software radio
and industrial process control.
The software described in this paper is available for download from
\url{www.dre.vanderbilt.edu/CIAO} (for the CIAO QoS-enabled component
middleware) and \url{www.dre.vanderbilt.edu/cosmic} (for the CoSMIC
modeling tools we used for configuring and deploying event channels
within CIAO).
