Scott Burleigh

New opportunities in ecological sensing using wireless sensor networks

Measuring environmental variables at appropriate temporal and spatial scales remains an important challenge in ecological research. New developments in wireless sensors and sensor networks will free ecologists from a wired world and revolutionize our ability to study ecological systems at relevant scales. In addition, sensor networks can analyze and manipulate the data they collect, thereby moving data processing from the end user to the sensor network itself. Such embedded processing will allow sensor networks to perform data analysis procedures, identify outlier data, alter sampling regimes, and ultimately control experimental infrastructure. We illustrate this capability using a wireless sensor network, the Sensor Web, in a study of microclimate variation under shrubs in the Chihuahuan Desert. Using Sensor Web data, we propose simple analytical protocols for assessing data quality “on-the-fly” that can be programmed into sensor networks. The ecological community can influence the evolution of environmental sensor networks by working across disciplines to infuse new ideas into sensor network development.

The interplanetary internet: A communications infrastructure for Mars exploration☆

A strategy is being developed whereby the current set of internationally standardized space data communications protocols can be incrementally evolved so that a first version of an operational Interplanetary Internet is feasible by the end of the decade. This paper describes its architectural concepts, discusses the current set of standard space data communications capabilities that exist to support Mars exploration and reviews proposed new developments. We also speculate that these current capabilities can grow to support future scenarios where human intelligence is widely distributed across the Solar System and day-to-day communications dialog between planets is routine.

WWWorkflow: World Wide Web based workflow

The paper describes WWWorkflow, a system developed at the Jet Propulsion Laboratory for the computer mediation of work through an organization. WWWorkflow exploits an opportunity created by organizational intranets to provide a common user interface across heterogeneous platforms. A distinctive feature of WWWorkflow is the careful separation of process mediation from product data management. WWWorkflow supports many types of workflow and is not focused on any single information structure. Three major components of the system are presented: a relational database approach to process definition and management, process initiation and event response software used to drive the flow of work through the organization, and a World Wide Web (WWW) based user interface and mechanism for integrating workflow with existing data management services. Lessons learned from its deployment at the Johnson Space Center, Houston are discussed.

Delivery Time Estimation for Space Bundles

We present a method for predicting delivery time of bundles in space internetworks. The bundle delivery time estimation (BDTE) tool exploits contact graph routing (CGR), predicts bundle route, and calculates plausible arrival times along with the corresponding probabilities. Latency forecasts are performed in an administrative node with access to an instrumentation database (DB) appropriate for statistical processing. Through both analysis and experimentation, we demonstrate that estimates of bundle earliest plausible delivery time and destination arrival probabilities can be provided.

The Deep Impact Network Experiments - Concept, Motivation and Results

The first Deep Impact Network Experiment (DINET I) was performed by personnel at the Jet Propulsion Laboratory with the cooperation of the EPOXI project on the Deep Impact (DI) spacecraft. Using nine ground-based computers controlled from the Experiment Operations Center (EOC) in JPL’s Protocol Technology Lab (PTL) and the DI spacecraft, all connected via JPL’s interplanetary overlay network (ION) disruption-tolerant network (DTN) protocol implementation, the DINET I experiment successfully integrated and tested the first link of the interplanetary internet over the course of 27 days in 2008. The DTN concept allows for automated scheduling and routing of data through an overlay network that bridges smaller local networks. The accomplished technical goal of DINET I was to prove the capabilities of delay-tolerant networking protocols – specifically the Licklider transmission protocol (LTP) and bundle protocol (BP) – in an interplanetary operational environment. The accomplished strategic goal of DINET I was to provide a venue in which to simultaneously raise the JPL technology readiness level of ION and encourage mission project acceptance of DTN technology in space operations communications. A follow-on experiment with the Deep Impact spacecraft, DINET II, is planned by JPL and funded by NASA. DINET II has developed and will test new DTN capabilities such as key-based authentication, mixed-route file delivery, and improvements to DINET I software on the EPOXI ground-based testbed system with the addition of network nodes at JHU-APL, CU Boulder and the International Space Station.

Defining Tolerance: Impacts of Delay and Disruption when Managing Challenged Networks

Challenged networks exhibit irregularities in their communication performance stemming from node mobility, power constraints, and impacts from the operating environment. These irregularities manifest as high signal propagation delay and frequent link disruption. Understanding those limits of link disruption and propagation delay beyond which core networking features fail is an ongoing area of research. Various wireless networking communities propose tools and techniques that address these phenomena. Emerging standardization activities within the Internet Research Task Force (IRTF) and the Consultative Committee for Space Data Systems (CCSDS) look to build upon both this experience and scalability analysis. Successful research in this area is predicated upon identifying enablers for common communication functions (notably node discovery, duplex communication, state caching, and link negotiation) and how increased disruptions and delays affect their feasibility within the network. Networks that make fewer assumptions relating to these enablers provide more universal service. Specifically, reliance on node discovery and link negotiation results in network-specific operational concepts rather than scalable technical solutions. Fundamental to this debate are the definitions, assumptions, operational concepts, and anticipated scaling of these networks. This paper presents the commonalities and differences between delay and disruption tolerance, including support protocols and critical enablers. We present where and how these tolerances differ. We propose a set of use cases that must be accommodated by any standardized delay-tolerant network and discuss the implication of these on existing tool development.

Congestion control in disruption-tolerant networks: A comparative study for interplanetary and terrestrial networking applications

Abstract Controlling congestion is critical to ensure adequate network operation and performance. That is especially the case in networks operating in challenged- or extreme environments where episodic connectivity is part of the network’s normal operation. Consequently, the “pure” end-to-end congestion control model employed by the Internet is not adequate. Our goal is to study congestion control mechanisms that have been proposed for these so-called disruption tolerant networks, or DTNs. In this paper, we conduct a performance study comparing existing DTN congestion control mechanisms for two main application domains, namely: inter-planetary (IPN) and terrestrial networking applications. Our results confirm that congestion control helps increase message delivery ratio, even in highly congested network scenarios. Furthermore, the results show that existing DTN congestion control mechanisms do not perform well in IPN scenarios. Our study also suggests that good design principles for congestion control in DTN scenarios include: combining reactive and proactive control, using local information instead of global knowledge, and employing mechanisms that are routing protocol independent. One important conclusion from our quantitative study is that there is currently no universal congestion control mechanism that fits all DTN scenarios and applications.

Enabling Autonomous Exploration via the Solar System Internet

A summary of recent networking and autonomy technology developments within NASA that can enable new types of space exploration and more effective interaction with space assets.

Moving toward space internetworking via DTN: its operational challenges, benefits, and management

The international space community has begun to recognize that the established model for management of communications with spacecraft ‐ commanded data transmission over individual pair-wise contacts ‐ is operationally unwieldy and will not scale in suppor t of increasingly complex and sophisticated mission s such as NASA’s Constellation project. Accordingly, the i nternational Inter-Agency Operations Advisory Group (IOAG) i chartered a Space Internetworking Strategy Group (SISG), which released its initial recommendations in a November 2008 report. The report includes a recommendation that the space flight community adopt Delay-Tolerant Networking (DTN) to address the problem of interoperability and communication scaling, especially in mission environments where there are multiple spacecraft operating in concert. This paper explores some of the issues th at must be addressed in implementing, deploying, and operating DTN as part of a multi-mission, multi-age ncy space internetwork as well as benefits and future operational scenarios afforded by DTN-based space internetworking.

An environment for incremental development of distributed extensible asynchronous real-time systems

Incremental, parallel development of distributed real-time systems is difficult. Architectural techniques and software tools developed at the Jet Propulsion Laboratorys (JPLs) Flight System Testbed (FST) make feasible the integration of complex systems in various stages of development. In particular, two techniques are used: a strict layering architecture for organization of independent subsystems, and a distributed, low-overhead, asynchronous messaging system. These techniques were developed in a few user-months and have proven their usefulness in a spacecraft integration test and simulation environment.