Tom Callahan

Email: tom at lastname dot us

Current Status:	Senior Director of Engineering at Elastic, where I lead the Elasticsearch development team
Previous:	Senior Director of Platform Engineering at Explorys, an IBM Company (Part of Watson Health)
	Software Architect at Heureka
	Senior Software Engineer at Explorys
Education:	Ph.D., Computer Science, Case Western Reserve University, 2013. (dissertation) M.S., Computer Science, Case Western Reserve University, 2012. (thesis) B.S., Computer Science, Miami University (Ohio), 2008.
Research Advisers:	Prof. Michael Rabinovich and Prof. Mark Allman

Research Projects

Active DNS Measurement
This project probes over 1 million devices providing recursive DNS service
on the Internet. We analyze the devices to describe aspects of the client-side
DNS system, including topology, security, and protocol compliance.
Passive DNS Measurement
In this project we examine packet-traces of client DNS traffic from a small
community of users. We study both the behavior of clients as they interact
with the DNS, as well as the behavior of the services clients interact with.
Communicating without Fixed Infrastructure
Transactions on today's Internet require some sort of fixed infrastructure to
commence -- usually a DNS hostname or an IP address. In this project, we
implement a system of communication that requires no fixed infrastructure. Based
upon a secret key, we enable users to scan for and discover a common set of open
recursive DNS servers. Further, we describe a several methods for storing
arbitrary data in DNS caches using the secret key, without using any predefined
domain name.
Metadata Information Storage System (MISS)
The Metadata Information Storage System is a new foundational naming service for the
Internet centered around users. Users and their applications may name content,
configuration items, and other computer objects, which the user may then make
available to other users or on other devices. We explore the design and security
requirements of the system and explore new functionality available to applications.
HTTP Measurement (M.S. Research)
In this work we provide a long-term characterization of web traffic using four years
of HTTP traffic from a small research institute. We study characteristics of the
traffic from client and server behavior to object and connection characteristics.

Publications

Kyle Schomp, Tom Callahan, Michael Rabinovich, Mark Allman. On Measuring the Client-Side DNS Infrastructure, ACM Internet Measurement Conference, October 2013. (To appear) (PDF)
Tom Callahan, Mark Allman, Michael Rabinovich. On Modern DNS Behavior and Properties, ACM SIGCOMM Computer Communication Review, February 2013. (PDF)
Tom Callahan, Mark Allman, Michael Rabinovich. Pssst, Over Here: Communicating Without Fixed Infrastructure, IEEE InfoCom Mini-Conference, March 2012. (PDF)
Tom Callahan, Mark Allman, Michael Rabinovich. Pssst, Over Here: Communicating Without Fixed Infrastructure. Technical Report 12-002, International Computer Science Institute, January 2012. (PDF)
Tom Callahan, Mark Allman, Michael Rabinovich, Owen Bell. On Grappling with Meta-Information in the Internet. ACM SIGCOMM Computer Communication Review, 41(5), October 2011. (PDF)
Tom Callahan, Mark Allman, Vern Paxson. A Longitudinal View of HTTP Traffic. Passive and Active Measurement Conference, April 2010. (PDF)