The Design and Performance of a Pluggable Protocols Framework for Real-Time Distributed Object Computing Middleware

Abstract

To be an effective platform for performance-sensitive real-time and embedded applications, off-the-shelf CORBA middleware must preserve the communication-layer quality of service (QoS) properties of applications end-to-end. However, the standard CORBA GIOP/HOP interoperability protocols are not well suited for applications that cannot tolerate the message footprint size, latency, and jitter associated with general-purpose messaging and transport protocols. It is essential, therefore, to develop standard pluggable protocols frameworks that allow custom messaging and transport protocols to be configured flexibly and used transparently by applications.This paper provides three contributions to research on pluggable protocols frameworks for performance-sensitive distributed object computing (DOC) middleware. First, we outline the key design challenges faced by pluggable protocols developers. Second, we describe how we resolved these challenges by developing a pluggable protocols framework for TAO, which is our high-performance, real-time CORBA -compliant ORB. Third, we present the results of benchmarks that pinpoint the impact of TAO's pluggable protocols framework on its end-to-end efficiency and predictability.Our results demonstrate how the application of optimizations and patterns to DOC middleware can yield both highly flexible/reusable designs and highly efficient/predictable implementations. In particular, the overall roundtrip latency of a TAO two-way method invocation using the standard inter-ORB protocol and using a commercial, off-the-self Pentium II Xeon 400 MHz workstation running in loopback mode is ~189 µsecs. The ORB middleware accounts for approximately 48% or ~90 µsecs of the total roundtrip latency. Using the specialized POSIX local IPC protocol reduces roundtrip latency to ~125 µsecs. These results illustrate that (1) DOC middleware performance is largely an implementation detail and (2) the next-generation of optimized, standards-based CORBA middleware can replace ad hoc and proprietary solutions.