Fred Kuhns

An overview of the Real-Time CORBA specification

A growing class of real-time systems require end-to-end support for various quality-of-service (QoS) aspects, including bandwidth, latency, jitter and dependability. Applications include command and control, manufacturing process control, videoconferencing, large-scale distributed interactive simulation, and testbeam data acquisition. These systems require support for stringent QoS requirements. To meet this challenge, developers are turning to distributed object computing middleware, such as the Common Object Request Broker Architecture, an Object Management Group (OMG) industry standard. In complex real-time systems, DOC middleware resides between applications and the underlying operating systems, protocol stacks and hardware. CORBA helps decrease the cycle time and effort required to develop high-quality systems by composing applications using reusable software component services rather than building them entirely from scratch. The Real-Time CORBA specification includes features to manage CPU, network and memory resources. The authors describe the key Real-Time CORBA features that they feel are the most relevant to researchers and developers of distributed real-time and embedded systems.

Supercharging planetlab: a high performance, multi-application, overlay network platform

In recent years, overlay networks have become an important vehicle for delivering Internet applications. Overlay network nodes are typically implemented using general purpose servers or clusters. We investigate the performance benefits of more integrated architectures, combining general-purpose servers with high performance Network Processor (NP) subsystems. We focus on PlanetLab as our experimental context and report on the design and evaluation of an experimental PlanetLab platform capable of much higher levels of performance than typical system configurations. To make it easier for users to port applications, the system supports a fast path/slow path application structure that facilitates the mapping of the most performance-critical parts of an application onto an NP subsystem, while allowing the more complex control and exception-handling to be implemented within the programmer-friendly environment provided by conventional servers. We report on implementations of two sample applications, an IPv4 router, and a forwarding application for the Internet Indirection Infrastructure. We demonstrate an 80x improvement in packet processing rates and comparable reductions in latency.

The design and performance of a real-time I/O subsystem

The paper describes the design and performance of a real time I/O (RIO) subsystem that supports real time applications running on off-the-shelf hardware and software. The paper provides two contributions to the study of real time I/O subsystems. First it describes how RIO supports end-to-end, prioritized traffic to bound the I/O utilization of each priority class and eliminates the key sources of priority inversion in I/O subsystems. Second, it illustrates how a real time I/O subsystem can reduce latency bounds on end-to-end communication between high-priority clients without unduly penalizing low priority and best-effort clients.

The Design and Performance of a Pluggable Protocols Framework for Object Request Broker Middleware

To be an effective platform for performance-sensitive real-time and embedded applications, off-the-shelf CORBA middleware must preserve communication-layer quality of service (QoS) properties to applications end-to-end. However, the standard CORBA’s GIOP/IIOP 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 communication middleware. First, we outline the key design challenges faced by pluggable protocols developers. Second, we describe how TAO, our high-performance, real-time CORBAcompliant ORB, addresses these challenges in its pluggable protocols framework. Third, we present the results of benchmarks that pinpoint the impact of TAO’s OO design on its endto-end efficiency, predictability, and scalability. Our results demonstrate how applying optimizations to communication middleware can yield highly flexible/reusable designs and highly efficient/predictable implementations. In particular, the overall round-trip 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 125 secs. The ORB middleware accounts for approximately 48% or 60 secs of the total round-trip latency. These results illustrate that (1) communication middleware performance is largely This work was supported in part by Boeing, DARPA contract 9701516, GDIS, NSF grant NCR-9628218, Nortel, Siemens, and Sprint. an implementation detail and (2) the next-generation of optimized, standards-based CORBA middleware can replace ad hoc and proprietary solutions. Subject areas: Frameworks; Design Patterns; Distributed and Real-Time Systems

The open network laboratory

The Open Network Laboratory (ONL) is a remotely accessible network testbed of high performance routers which has been designed with an eye towards ease of use for users from the naïve to the expert. The system is built around a set of high-performance routers that are extendible and easily configurable through the Remote Laboratory Interface (RLI), an intuitive graphical interface. The RLI also makes it easy to configure packet filters in the routers, assign flows or flow aggregates to separate queues with configurable QoS and attach hardware monitoring points to real-time charts. The RLIs real-time charts and user data facility make it easy to directly view the effects of traffic as it moves through a router, allowing the user to gain better insight into system behavior and create compelling demonstrations. Each port of the router is equipped with an embedded processor that supports software plugins which allow users to extend the systems functionality. This paper describes the ONL and how it can be used in networking education. Our web site onl.arl.wustl.edu includes a short video and a tutorial.

Design and evaluation of a high-performance dynamically extensible router

This paper describes the design, implementation and performance of an open, high performance, dynamically extensible router under development at Washington University in St. Louis. This router supports the dynamic installation of software and hardware plug-ins in the data path of application data flows. It provides an experimental platform for research on programmable networks, protocols, router software and hardware design, network management, quality of service and advanced applications. It is designed to be flexible without sacrificing performance. It supports gigabit links and uses a scalable architecture suitable for supporting hundreds or even thousands of links. The systems flexibility makes it an ideal platform for experimental research on dynamically extensible networks that implement higher level functions in direct support of individual application sessions.

Developing next-generation distributed applications with QoS enabled DPE middleware

This article describes how recent advances in distributed object computing middleware are enabling the creation of common quality-of-service capabilities that support next-generation distributed applications. DOC middleware helps to simplify and coordinate applications in order to leverage the underlying network and end-system QoS architectures more effectively. This article also describes a QoS-enabled middleware framework used to customize the CORBA audio/video streaming service for applications on multiple operating system platforms.

Evaluating policies and mechanisms for supporting embedded, real-time applications with CORBA 3.0

To be an effective platform for performance-sensitive real time systems, commercial-off-the-shelf (COTS) distributed object computing (DOC) middleware must support application quality of service (QoS) requirements end-to-end. However, conventional DOC middleware does not provide this support, which makes it unsuited for applications with stringent latency, determinism, and priority preservation requirements. It is essential, therefore, to develop standards based, COTS DOC middleware that permits the specification, allocation, and enforcement of application QoS requirements end-to-end. The Real-time CORBA and Messaging specifications in the forthcoming CORBA 3.0 standard are important steps towards defining standards based COTS DOC middleware that can deliver end-to-end QoS support at multiple levels in distributed and embedded real time systems. However these specifications still lack sufficient detail to portably configure and control processor, communication, and memory resources for applications with stringent QoS requirements. The paper provides four contributions to research on real time DOC middleware. First, we show how the CORBA 3.0 Real-time and Messaging specifications provide a starting point for addressing the needs of an important class of applications with stringent real time requirements. Second, we show how the CORBA 3.0 specifications are not sufficient to solve all the issues within this application domain. Third, we describe how we have implemented portions of these specifications, as well as several enhancements, using TAO, which is our open-source real time CORBA ORB. Finally, we empirically evaluate the performance of TAO to illustrate how its features address the QoS requirements of certain types of real time applications.

Evaluating policies and mechanisms to support distributed real‐time applications with CORBA

To be an effective platform for performance‐sensitive real‐time systems, commodity‐off‐the‐shelf (COTS) distributed object computing (DOC) middleware must support application quality of service (QoS) requirements end‐to‐end. However, conventional COTS DOC middleware does not provide this support, which makes it unsuited for applications with stringent latency, determinism, and priority preservation requirements. It is essential, therefore, to develop standards‐based, COTS DOC middleware that permits the specification, allocation, and enforcement of application QoS requirements end‐to‐end.

The design and performance of a pluggable protocols framework for real-time distributed object computing middleware

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 TAOs 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.