|System installed inside a UMass Amherst PVTA bus.|
Despite the proliferation of inexpensive mobile computing devices that can be carried on our person or in our vehicles, ubiquitous computing environments are far from common. Although many wireless networking technologies are available, including cell towers, WiFi access points, and mobile ad hoc networks, all expect stable, contemporaneous paths across the Internet.
Wireless network paths can become unstable for several reasons, including high node mobility, low node density, and short radio range; intermittent power from energy management schemes; environmental interference and obstruction; equipment failure; and malicious intent. These problems are common in practice, and especially so in undeveloped areas or when a stable infrastructure is destroyed by natural disaster or war.
Overcoming these problems has been the focus of some of Associate Professor Brian Levine’s research over the last several years. Disruption tolerant networks (DTNs) allow for routing in networks where contemporaneous end-to-end paths are unstable or unlikely. Nodes in a DTN might include moving vehicles, pedestrians or kiosks.
Levine’s DTN research has been focused on building a fully operational testbed called UMass DieselNet. “Simulations and analysis are important for predicting performance trends,” Levine said, “but real systems expose problems that may not be obvious on paper.” DieselNet currently consists of computers on 30 buses that roam the UMass Amherst campus and surrounding county. Each vehicle powers a small Linux-based computer with an attached WiFi access point to provide wireless access to passengers and passersby (The WiFi standard, based on IEEE 802.11b, is the most common form of wireless networking on laptops.). A second wireless card constantly scans the surrounding area for open WiFi networks and other buses. Each bus also has a GPS device attached to record its current location. The network has been operational since May 2004.
From the beginning, DieselNet has been the result of student efforts. John Burgess is a graduate student in Levine’s lab and has been working on DieselNet since he was an undergraduate at UMass Amherst. “While many students have spent time on the project, our progress on DieselNet is primarily due to John’s hard work and the quality of his design,” Levine said.
The custom software Levine’s students have deployed allows the buses to transfer data between each other as they pass on the road and to connect to open wireless access points along the bus roads in the surrounding county. The buses use access points to “check in” whenever possible to a main site that contains software updates and doubles as a monitoring site. At that time a bus provides its current GPS location and MAC address, and it uploads logs of its performance during the day. All routes intersect in Amherst, Massachusetts; Fig. 1 shows the density of bus-to-bus connection opportunities during a one-month period in that geographic area. The current status of the Diesel DTN and statistics like those shown in the figure are available on the web at prisms.cs.umass.edu/diesel.
|Figure 1: Density of bus-to-bus connection opportunities|
The project is part of a larger effort by Levine and Assistant Professor Mark Corner. Levine is working with Corner on the next stage of the research, and he credits the partnership for their success with funding agencies. The pair (together with partners Mostafa Ammar and Ellen Zegura from Georgia Tech) have received over 1.5 million dollars in funding from the National Science Foundation (NSF) and the Defense Advanced Research Projects Agency (DARPA) to research DTNs and related technologies. Corner’s work focuses on building a novel mobile platform for the DTN, incorporating energy management techniques that will allow stationary nodes to operate for months at a time on battery and solar power. These nodes will expand the DieselNet testbed by allowing buses that pass through the same area to exchange data even if they do not pass through at the same time.
Levine plans to offer a few novel services to bus passengers. “We are working with the great folks at the Pioneer Valley Transit Authority (PVTA), Adam Shearson and Tom Caron, who have been supportive of the project since the beginning, to do something different for bus riders,” said Levine. Soon, each bus’s web server will provide cached web pages, including news and sports information, podcasts of free radio shows, and a community bulletin board. “We are also trying to get a Risk-like board-game played across buses and across days. We want a trace of the communication load it generates between players,” Levine said, “It will be very unique.”
Professor Levine received a Ph.D. and a Masters degree in Computer Engineering
from the University of California, Santa Cruz in 1999 and 1996, respectively.
His research interests in general include network privacy and security,
peer-to-peer networking, and mobility. He joined the Department of Computer
Science in 1999 as an assistant professor. This year, he was tenured
and promoted to associate professor. He is Director of the Center for
Academic Excellence in Information Assurance Education at UMass Amherst,
as designated by the National Security Agency in 2003. He was awarded
an NSF CAREER grant in 2001 for work in peer-to-peer networking. In 2004,
he was awarded a Lilly teaching fellowship from UMass Amherst. Levine
is an associate editor of the IEEE/ACM Transactions on Networking, and
is co-chair of Intl. Workshop on Network and Operating Systems Support
for Digital Audio and Video (NOSSDAV) in 2006 along with Prof. Mark Claypool
at WPI. He lives in Northampton with his wife Amy, an English teacher
at Amherst Regional High School.