Kam S. Tso

Cluster-based failure detection service for large-scale ad hoc wireless network applications

The growing interest in ad hoc wireless network applications that are made of large and dense populations of lightweight system resources, calls for scalable approaches to fault tolerance. Moreover, the nature of these systems creates significant challenges for the development of failure detection services (FDSs), because their quality often depends heavily on reliable communication. In particular, ad hoc wireless networks are notoriously vulnerable to message loss, which precludes deterministic guarantees for the completeness and accuracy properties of FDSs. To meet the challenges, we propose an FDS based on the notion of clustering. Specifically, we use a cluster-based communication architecture to permit the FDS to be implemented in a distributed manner via intra-cluster heartbeat diffusion and to allow a failure report to be forwarded across clusters through the upper layer of the communication hierarchy. In doing so, we extensively exploit the message redundancy that is inherent in ad hoc wireless settings to mitigate the effects of message loss on the accuracy and completeness properties of failure detection. As shown by our mathematical analysis, the resulting FDS is able to provide satisfactory probabilistic guarantees for the desired properties.

Robot geometry calibration

Autonomous robot task execution requires that the end effector of the robot be positioned accurately relative to a reference world-coordinate frame. The authors present a complete formulation to identify the actual robot geometric parameters. The method applies to any serial link manipulator with arbitrary order and combination of revolute and prismatic joints. A method is also presented to solve the inverse kinematic of the actual robot model which usually is not a so-called simple robot. Experimental results performed by utilizing a PUMA 560 with simple measurement hardware are presented. As a result of this calibration a precision move command is designed and integrated into a robot language, RCCL, and used in the NASA Telerobot Testbed.<<ETX>>

UMI: an interactive supervisory and shared control system for telerobotics

An interactive user interface, UMI (User-Macro-Interface), and its complete task execution system have been developed and implemented for use by an operator to describe, simulate, and execute tasks on a multiarm telerobot. The operator interactively sets up the execution environment and specifies input parameters for a variety of available task primitives. Several task primitives can be stored together as a task sequence for later sequence execution. The primitives or sequences can be executed on a graphics simulator or on the JPL Telerobot, which includes two task execution manipulators, one manipulator used for positioning cameras, and two six-degree-of-freedom force reflecting hand controllers used for shared and teleoperation modes of execution. In supervisory control, the operator sets up a task primitive or a sequence of primitives and executes the task autonomously. In teleoperation, the user specifies desired initialization parameters and controls the arms with the hand controllers. In shared control, teleoperated inputs from the operator hand controllers are merged during task execution with inputs from user parameterized autonomous primitives. In all modes of operation, UMI allows the operator to stop execution at any time. The UMI interface is intended as the operator interface at a local command site to prepare and send commands to a remote space telerobot.<<ETX>>

Mars pathfinder mission Internet-based operations using WITS

The Web Interface for Telescience (WITS) is an Internet-based tool that the Mars Pathfinder mission used for both mission operations at JPL and public outreach. WITS enables the viewing of downlinked images and results in various ways, terrain feature measurement and annotation, and planning of daily mission activities. WITS is written in the Java language and is accessible by mission scientists and the general public via a web browser. The public can use WITS to plan and simulate their own rover missions. WITS will also be used in the 1998 lander and 2001, 2003, and 2005 rover missions to Mars.

Internet-based operations for the Mars Polar Lander mission

The Mars Polar Lander (MPL) mission was the first planetary mission to use Internet-based distributed ground operations where scientists and engineers collaborate in daily mission operations from multiple geographically distributed locations via the Internet. This paper describes the operations system, the Web interface for telescience (WITS), which was used by the MPL mission for Internet-based operations. WITS was used for generating command sequences for the landers robotic arm and robotic arm camera, and as a secondary tool for sequence generation for the stereo camera on the lander. WITS was also used as a public outreach tool. Results are shown from the January 2000 field test in Death Valley, California.

A testbed for a unified teleoperated-autonomous dual-arm robotic system

A description is given of a complete robot control facility built at the CIT Jet Propulsion Laboratory as part of a NASA telerobotic program to develop a state-of-the-art robot control environment for laboratory-based spacelike experiments. This system has the following features: separation of the computing facilities into local and remote sites, autonomous motion generation in joint or Cartesian coordinates, dual-arm force reflecting teleoperation with voice interaction between the operator and the robots, shared control between the autonomously generated motions and operator controlled teleoperation, and dual-arm coordinated trajectory generation. The system has been used to carry out realistic experiments such as the exchange of an orbital replacement unit, bolt turning, and door opening, using a mixture of autonomous actions and teleoperation, with either a single arm or two cooperating arms.<<ETX>>A description is given of a complete robot control facility built as part of a NASA telerobotics program to develop a state-of-the-art robot control environment for performing experiments in the repair and assembly of spacelike hardware to gain practical knowledge of such work and to improve the associated technology. The basic architecture of the manipulator control subsystem is presented. The multiarm Robot Control C Library, a key software component of the system, is described, along with its implementation on a Sun-4 computer. The systems simulation capability is also described, and the teleoperation and shared control features are explained.<<ETX>>

The Web Interface for Telescience (WITS)

The Web Interface for Telescience (WITS) has been developed to enable scientists to participate in planetary rover missions from their home institutions, rather than having to travel to JPL as has been required in the past. A scientist accesses WITS via a commercial web browser. WITS provides various views of the scene: including a descent image view which allows the user to see where the rover has been and currently is in a global perspective, a panoramic view which is an overhead view of the area immediately around the rover, and a wedge view which is an image from a rover-mounted camera. Scientists can select science targets in a wedge image and science subtasks to perform at those targets. A mission planner can select rover waypoints to traverse between science targets, and waypoint subtasks to perform at those locations. A public version allows the general public to view the same information and plan their own simulated missions.

A unified teleoperated-autonomous dual-arm robotic system

A description is given of a complete robot control facility built as part of a NASA telerobotics program to develop a state-of-the-art robot control environment for performing experiments in the repair and assembly of spacelike hardware to gain practical knowledge of such work and to improve the associated technology. The basic architecture of the manipulator control subsystem is presented. The multiarm Robot Control C Library, a key software component of the system, is described, along with its implementation on a Sun-4 computer. The systems simulation capability is also described, and the teleoperation and shared control features are explained. >

A performability-oriented software rejuvenation framework for distributed applications

While inherent resource redundancies in distributed applications facilitate gracefully degradable services, methods to enhance their dependability may have subtle, yet significant, performance implications, especially when such applications are stateful in nature. In this paper, we present a performability-oriented framework that enables the realization of software rejuvenation in stateful distributed applications. The framework is constructed based on three building blocks, namely, a rejuvenation algorithm, a set of performability metrics, and a performability model. We demonstrate via model-based evaluation that this framework enables error-accumulation-prone distributed applications to deliver services at the best possible performance level, even in environments in which a system is highly vulnerable to failures.

On low-cost error containment and recovery methods for guarded software upgrading

To assure dependable onboard evolution, we have developed a methodology called guarded software upgrading (GSU). We focus on a low-cost approach to error containment and recovery for GSU. To ensure low development cost, we exploit inherent system resource redundancies as the fault tolerance means. In order to mitigate the effect of residual software faults at low performance cost, we take a crucial step in devising error containment and recovery methods by introducing the confidence-driven notion. This notion complements the message-driven (or communication-induced) approach employed by a number of existing checkpointing protocols for tolerating hardware faults. In particular, we discriminate between the individual software components with respect to our confidence in their reliability and keep track of changes of our confidence (due to knowledge about potential process state contamination) in particular processes. This, in turn, enables the individual processes in the spaceborne distributed system to make decisions locally at run-time, on whether to establish a checkpoint upon message passing and whether to roll back or roll forward during error recovery. The resulting message-driven confidence-driven approach enables cost-effective checkpointing and cascading-rollback free recovery.