My research interests span many aspects of systems. In my past life as a Masters student at Utah, I focused on mobile, wireless sensor networks and applications and tools for embedded systems. As a staff member, I get to explore my other interests, including wired and wireless network protocols, network managment, distributed systems of many sorts, virtualization, etc. I really like building real systems that do cool stuff.

• Emulab
I do lots of hacking and some sysadmin stuff within the context of Emulab. Specifically, I maintain our wireless testbeds, stuff to do with Linux, our PlanetLab portal, and lots of other interesting things that come up from time to time.

• Mobile Emulab: A Mobile, Wireless Sensor Network Testbed
Although network simulation continues to be the dominant method of experimental evaluation in wireless networking, much research has established the failure of simulator models to adequately express wireless signal propagation. These shortcomings can lead to incomplete evaluation of routing protocols and applications. When mobility is added to the research, real evaluation becomes still more difficult due to the difficulty of creating and controlling mobile nodes in a real environment.

In response to these problems, and with the hope of encouraging real mobile wireless research, I have helped to create a remotely-accessible mobile wireless network testbed. The testbed consists of several robots, each with a small computer and small wireless devices called motes, manueverable in an area surrounded by fixed motes. Through a variety of interfaces, remote researchers can control these robots interactively over the Web. An overhead tracking system localizes the robots to within 1cm, providing repeatable positioning and valuable knowledge to researchers studying how signal propagation affects their experiments.

Status: working system available to researchers.

• mobiQ: Improving Quality of WSNs Through Mobility
mobiQ is an WSN application designed to improve quality of a sensor network using mobile base stations as sinks. In a sensor network, quality consists of primarily network lifetime and quality of sensed data. End of life of a deployed sensor network occurs when enough nodes have failed so that useful sensing is no longer possible. With current routing protocols, some nodes may end up routing significantly more packets than others, and thus fail sooner than others, due to battery expiration. Furthermore, if nodes die, fail due to hardware, or expire due to environmental effects, the network's sensing ability is decreased.

mobiQ uses mobile sinks to equalize the number of messages sent by each node, investigate event hotspots, and detect fixed node failures and obtain event data on their behalf when possible. Each mobile sink is restricted to its own sector of the network, but fixed nodes may connect to whichever sink is "closest" (in terms of routing). Mobile sinks autonomously move based on the output of several estimators, which use a combination of current fixed node state and location data.

Status: under heavy development; hopefully, papers soon!

• SNAP-M
I developed SNAP-M to provide a generic interface for communicating with WSNs from a PC. SNAP-M provides a GUI, plugin-based interface through which users interface with WSNs. Several plugins are already supplied, and should be generally useful. They provide support for connecting to Emulab motes and TinyOS SerialForwarder sources, monitoring incoming packets, sending packets and scripting sends, and managing mobility in Mobile Emulab. A set of libraries parses user-supplied Java Active Message wrappers (generated by mig from C structures) and helps users easily construct and view packets by transforming message fields into human-readable formats instead of raw bytes. Users may add their own Java plugins for any specific application control required.

Status: in development; contact me if you want to use it.

• (defended, nearing completion) D. Johnson. Design and Implementation of a Mobile Wireless Sensor Network Testbed. Masters Thesis, University of Utah, expected October 2007.
• D. Johnson, T. Stack, R. Fish, D. Flickinger, L. Stoller, R. Ricci, J. Lepreau. Mobile Emulab: A Robotic Wireless and Sensor Network Testbed. Proc. of IEEE INFOCOM 2006, April 2006. [ link ]
• D. Johnson, D. Flickinger, T. Stack, R. Ricci, L. Stoller, R. Fish, K. Webb, M. Minor, J. Lepreau. Poster Abstract: Robot Couriers: Precise Mobility in a Wireless Network Testbed (also Demo Abstract: Emulab's Wireless Sensor Net Testbed: True Mobility, Location Precision, and Remote Access). In Proc. of ACM SenSys 2005. San Diego, CA, Nov 2-4 2005.
• A. Tripathi, M. Koka, S. Karanth, I. Osipkov, H. Talkad, T. Ahmed, D. Johnson. Robustness and Security in a Mobile-Agent based Network Monitoring System. University of Minnesota Tech Report, May 2004.

• D. Johnson, T. Stack, R. Fish, D. Flickinger, L. Stoller, R. Ricci, J. Lepreau. Mobile Emulab: A Robotic Wireless and Sensor Network Testbed. IEEE INFOCOM 2006, Barcelona, April 2006. [ ppt, 6-up pdf ]
• Mobile Emulab Testbed Demo. TinyOS Tech Exchange III, Stanford University. Feb 2006.
• Mobile Emulab Testbed Demo/Poster. ACM SenSys 2005. San Diego, CA, Nov 2-4 2005.
• Mobile Emulab Testbed Demo. IEEE SECON 2005. Santa Clara, CA, Sep 2005.
• Mobile Emulab Poster Presentation. ACM MobiSys, Seattle, WA, June 6-8 2005.

I like hacking, listening to psychedelic rock (and humming and whistling, according to colleagues!), and reading (especially anthropology novels). I also enjoy exploring remote areas, especially ghost towns, when I have time.

I've taken lots of pictures around Utah and on conference trips; view the gallery.