Barbara Pfarr

An optimization framework for dynamic, distributed real-time systems

The paper presents a model that is useful for developing resource allocation algorithms for distributed real-time systems that operate in dynamic environments. Interesting aspects of the model include dynamic environments, utility and service levels, which provide a means for graceful degradation in resource-constrained situations and support optimization of the allocation of resources. The paper also provides an allocation algorithm that illustrates how to use the model for producing feasible, optimal resource allocations.

Proven and Robust Ground Support Systems - GSFC Success and Lessons Learned

Over the past fifteen years, Goddard Space Flight Center has developed several successful science missions in-house: the Wilkinson Microwave Anisotropy Probe (WMAP), the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE), the Earth Observing 1 (EO-1), and the Space Technology 5 (ST-5) missions, several Small Explorers, and several balloon missions. Currently in development are the Solar Dynamics Observatory (SDO) and the Lunar Reconnaissance Orbiter (LRO). What is not well known is that these missions have been supported during spacecraft and/or instrument integration and test, flight software development, and mission operations by two in house satellite Telemetry and Command (T&C) systems, the Integrated Test and Operations System (ITOS) and the Advanced Spacecraft Integration and System Test (ASIST). The advantages of an in- house satellite Telemetry and Command system are primarily in the flexibility of management and maintenance - the developers are considered a part of the mission team, get involved early in the development process of the spacecraft and mission operations control center, and provide on-site, on-call support that goes beyond Help Desk and simple software fixes. On the other hand, care must be taken to ensure that the system remains generic enough for cost effective re-use from one mission to the next. The software is designed such that many features are user-configurable. Where user- configurable options were impractical, features were designed so as to be easy for the development team to modify. Adding support for a new ground message header, for example, is a one-day effort because of the software framework on which that code rests. This paper will discuss the many features of the Goddard satellite Telemetry and Command systems that have contributed to the success of the missions listed above. These features include flexible user interfaces, distributed parallel commanding and telemetry decommutation, a procedure language, the interfaces and tools needed for a high degree of automation, and instantly accessible archives of spacecraft telemetry. It will discuss some of the problems overcome during development, including secure commanding over networks or the Internet, constellation support for the three satellites that comprise the ST-5 mission, and geographically distributed telemetry end users.

Collaborative problem solving agent for on-board real-time systems

Breakthrough in Earth Science Observing will occur when constellations of Earth observing satellites are able to fully collaborate together and collectively monitor the conditions of our planet through a vast array of instruments. These satellites form a network that consists of distributed processes that need to respond to perceived scientific events, the spacecraft environment, spacecraft anomalies and user commands. The requests and responses exhibit dynamic behavior. In order to handle such dynamic environments, a method is needed to guarantee the real-time quality of service constraints. The DeSiDeRaTa resource management approach is being enhanced to characterize the dynamic aspects of intraconstellation topologies and to accommodate the concept of service levels and utility. This paper presents a design model of cooperative problem solving to show how the solution approach addresses the key challenges presented in the problem and specifies how the agent, resource manager and satellite constellations would operate correctly and interact in complex, dynamic and unpredictable environments. It extends the system model of DeSiDeRaTa to accommodate the concepts of utility, service levels and planning. The system model for the IPA is presented to show the proof of concept.

Monitoring network QoS in a dynamic real-time system

This paper presents our design and tests of a realtime network monitoring program for DeSiDeRaTa, an existing resource management system. This monitor will assist DeSiDeRaTa in maintaining an acceptable Quality of Service (QoS) for groups of real-time applications by reporting the communication delays caused by inadequate network bandwidth. The network monitoring application we developed uses SNMP and network topology information gleaned from the DeSiDeRaTa application specification files. Network bandwidth utilization of each real-time communication path is computed, and experiments have been run to demonstrate the accuracy of these measurements.

Wearable computers for NASA applications

At the Goddard Space Flight Center, members of the Real-Time Software Engineering Branch are developing a wearable, wireless, voice-activated computer using many off-the-shelf components. This will be used in a wide range of crosscutting space applications that would benefit from having instant internet, network, and computer access with complete mobility and hands-free operations. These applications can be applied across many fields and disciplines including spacecraft fabrication, integration and testing (including environmental testing), and astronaut on-orbit control and monitoring of experiments with ground based experimenters. To satisfy the needs of NASA customers, this wearable computer needs to be connected to a wireless network, to transmit and receive real-time video over the network, and to receive updated documents via the Internet or NASA servers. The voice-activated computer, with a unique vocabulary, will allow the users to access documentation in a hands-free environment and interact in real-time with remote users. We will discuss wearable computer development, hardware and software issues, wireless network limitations, video/audio solutions and difficulties in language development.

A dynamic, real-time testbed for resource management technology

This paper describes a test-bed for technology that unifies agent based computing and adaptive resource management for dynamic real-time systems. We describe a unified framework that combines a hybrid agent based architecture with explicit resource adapting mechanisms.

An efficient schedulability analysis policing technique for periodic, dynamic real-time applications

Schedulability Analysis (SA) approaches that are based on a priori information and use fixed execution times with constant workloads work well in many application domains and allow pre-deployment guarantees of real-time performance such as Rate Monotonic Analysis (RMA). However, certain realtime applications must operate in highly dynamic environments, thereby precluding accurate characterization of workloads by static models. This leads to the notion that a new SA trigger for dynamic environments, in which applications experience large variations in the workload, needs to guarantee real-time performance during run-time. This paper examines the case of periodic, dynamic real-time systems, and describes an efficient SA policing technique which can trigger SA appropriately, and uses a dynamic threshold which becomes sensitive when the quality of service (QoS) of the dynamic real-time application approaches its deadline.

Worst-Case Analysis for Real-Time Processes in Time-Sharing Environments.

This paper presents a technique for predicting response times of real-time tasks that operate in a time-sharing environment that also has priority classes (as in the real-time priority class paradigm of the Solaris operating system). Response time prediction is accomplished by a worst-case approach for calculating the queuing delay that a process will experience. Experimental results show that the predicted response times for actual programs provide feasible upper bounds, making the prediction technique suitable for hard real-time environments.