Cornell CS Logo
Starting October, 2012: Assistant Professor (tenure-track “Lecturer” in their British-style) at Technion Electrical Engineering. From December, 2011: Visiting Professor in School of Electronics Engineering and Computer Science at Peking University.
Daniel A. Freedman

Daniel A. Freedman


Department of
Computer Science

Cornell University

email: dfreedman@[see-ess cornell edu]
work: 607-255-[zeero won won zeero]
office: Cornell University
Department of Computer Science
4119C Upson Hall
Ithaca, NY 14853


My research agenda spans distributed systems and networking.

As a reflection of my academic upbringing, I draw inspiration from physics to address questions in computer science and engineering.

In this vein, my recent work pushes the state-of-the-art in precision and reproducibility of network measurements, which ultimately reveals insights into distributed-systems behavior, informs architecture design, and leads to more dependable systems.

I also pursue separate, more traditional, distributed-systems projects, building systems for wide-area collaboration that integrate server-hosted data with edge content, and that optimize wide-area communication via multicast overlays on complex heterogeneous networks.

Academic background

In Fall, 2008, I joined the Computer Science Department at Cornell University as a Post-Doctoral Research Associate, where I work with Ken Birman on (distributed) systems and networking.

Prior, I received my M.S. and Ph.D. in theoretical physics, also from Cornell, and my S.B. in physics from MIT. Professor Tomás Arias served as my advisor for the former graduate degrees, and Prof. Dr. Uwe-Jens Wiese (now at the Albert Einstein Center for Fundamental Physics at the University of Bern) for the latter undergraduate one.

My doctoral work in condensed-matter physics involved computational studies, both empirical and ab initio, of the growth of crystalline oxides.


As a post-doc (and a graduate student before), I’ve supervised a significant number of both M.Eng. students and undergraduates:

Computer Science (M.Eng.): Jared Cantwell (2008-10), Petko Nikolov (2008-9), Yilin Qin (2009), Mihir Patel (2009-10), Michael Ryan (2010), Matt Pearson (2010), Matthew Mukerjee (2010-11), Samarth Lad (2011), Ansu Abraham (2011), Hee Jung Ryu (2011), Kaushik Nataraj (2011-12), Scott Phung (2011-12), Abdelrahman Kamel (2012), Shivendra Singh (2012)

Computer Science (U.Grad.): Chuck Sakoda (2008-9), Revant Kapoor (2009)

Computer Science (H.S. [Outreach]): Theo Jepsen (2009), Nadia Kiamilev (2010), Jed Thompson (2011)

Electrical and Computer Engineering (M.Eng.): Hera Li (2010-11)

Electrical Engineering (Visiting U.Grad.): Sushobhan Nayak (2010, IIT-Kanpur)

Physics (U.Grad.): Anselm Levskaya (2002-3), Carlos Ramirez (2006-8)

I welcome students to contact me regarding research possibilities. I have opportunities not only for folks from Computer Science, but also from Cornell’s Electrical and Computer Engineering and Applied and Engineering Physics departments.

Spring get-together in April 2011 with current students in then-research group: Hera Li, Samarth Lad, Daniel Freedman, Kyle Hsu (Kyle left shortly thereafter, without participating in group research), Matt Mukerjee (L to R).

Spring get-together in April, 2011, with current students in then-research group: Hera Li, Samarth Lad, Daniel Freedman, Kyle Hsu (Kyle left shortly thereafter, without participating in group research), Matt Mukerjee (L to R). (Earlier group photo from December, 2010.)

Current projects

Instrumentation for exact network timings:

I invented and implemented BiFocals instrumentation to provide the first-ever exact measurement of timings of network packets in flight. My team deployed BiFocals to empirically characterize 10 Gbps Ethernet (10GbE) optical wide-area networks (see below), both in the wild and in the lab.

BiFocals substantially departs from typical network-timing techniques that use measurement software running on endpoint computers attached to the network under test; these invariably introduce non-deterministic timing errors. BiFocals instead directly taps the network fiber. It leverages common physics test equipment — oscilloscopes, pattern generators, frequency synthesizers, lasers, etc. — as well as numerical methods to deliver provably exact timings. It records a contiguous portion of the entire physical-layer symbol stream in real-time. Software post-processing utilizes Fast Fourier Transforms for clock recovery, protocol knowledge for packet extraction, and symbol-stream timebase information to assign the final time-stamps. Our precision is significantly better than the width of a single 10GbE symbol (~100 picoseconds), hence our timings are exact, even at the highest deployed data rates.

The BiFocals software components are released under an open-source BSD license and available through

High-speed WAN measurement and protocol design:

Using the precision afforded by BiFocals, I discovered a novel class of packet burstiness on wide-area network (WAN) paths. (A public dataset of the captured traces is available.) We identified the formation of packet chains as traffic transits WANs, even with the network amply over-provisioned. We measured endpoint packet loss, induced by such burstiness, and found it to be far more severe than expected from packet-chain lengths. We recognized this as deriving from an underlying impedance mismatch between ever-increasing raw network data rates and constrained endpoint single-core processing power. We are now designing new end-to-end parallel-stream data-transfer protocols to prevent such endpoint loss upon exposure to packet chains and to harness modern commodity multi-core architectures.

Systems for wide-area collaboration:

Kevlar optimizes group-based communication across qualitatively different network environments, by federating multiple application- and physical-layer multicast protocols. In doing so, it provides a feasible and deployable “narrow waist” for large-scale multicast. It delivers the first practical multicast across realistic WAN deployments that combine backbone transit segments (generally without any physical-layer multicast) with extensive local topologies, themselves supporting various flavors of multicast and burdened with firewalls, bottleneck links, and other local network-policy impediments. Due to its decentralized membership state, Kevlar provides resilience to churn and efficiency of recovery, critical for real deployments in non-trivial applications and settings. Kevlar builds atop our Live Objects platform for distributed programming.

Our Live Objects platform allows novice programmers to create complex distributed systems, just as conceptually simple markup languages lowered barriers to create web sites and applications. Live Objects extends the ideas of language-based composition to include communication channels: It replicates objects on multiple nodes in a distributed system, synchronizes state across the network, and forms compositions on each node that interact via event-based interfaces. This facilitates combination of server-hosted data with edge content, using both peer-to-peer and client-server technologies.

Selected publications

Overcoming CAP with Consistent Soft-State Replication

Kenneth P. Birman, Daniel A. Freedman, Qi Huang, and Patrick Dowell.

IEEE Computer 45, 50-58 (2012).

(Cover feature of Special Issue on CAP.)

Instrumentation for exact packet timings in networks.

Daniel A. Freedman, Tudor Marian, Jennifer H. Lee, Ken Birman, Hakim Weatherspoon, Chris Xu.

Proceedings of the 2011 IEEE International Instrumentation and Measurement Technology Conference (I2MTC ’11). Binjiang, Hangzhou, China. May 10-12, 2011.

Exact temporal characterization of 10 Gbps optical wide-area network.

Daniel A. Freedman, Tudor Marian, Jennifer H. Lee, Ken Birman, Hakim Weatherspoon, Chris Xu.

Proceedings of the 10th ACM SIGCOMM Conference on Internet Measurement (IMC ’10). Melbourne, Australia. November 1-3, 2010.

(Early-Accept Paper; one of three.)

Empirical Characterization of Uncongested Lambda Networks and 10GbE Commodity Endpoints.

Tudor Marian, Daniel A. Freedman, Hakim Weatherspoon, Ken Birman.

Proceedings of the 40th Annual IEEE / IFIP International Conference on Dependable Systems and Networks (DSN ’10), Performance and Dependability Symposium (PDS). Chicago, IL, USA. June 28-July 1, 2010.

Kevlar: A Flexible Infrastructure for Wide-area Collaborative Applications.

Qi Huang, Daniel A. Freedman, Ymir Vigfusson, Ken Birman, Bo Peng.

Proceedings of the ACM / IFIP / Usenix 11th International Middleware Conference (Middleware ’10). Bangalore, India. November 29-December 3, 2010.

Enabling Tactical Edge Mashups with Live Objects.

Daniel Freedman, Ken Birman, Krzys Ostrowski, Mark Linderman, Robert Hillman, Albert Frantz

Proceedings of the 15th International Command and Control Research and Technology Symposium (ICCRTS ’10), Information Sharing and Collaboration Processes and Behaviors Track. Santa Monica, CA, USA. June 22-24, 2010.

(Best Paper in Track; Best Paper in Conference.)

Elastic effects of vacancies in strontium titanate: Short- and long-range strain fields, elastic dipole tensors, and chemical strain.

Daniel A. Freedman, D. Roundy, T. A. Arias.

Physical Review B 80, 064108 (2009).

(Selected by American Physical Society journal editors for inclusion in Physical Review B’s Kaleidoscope Images for August, 2009.)


The National Defense Science and Engineering Graduate (NDSEG) Fellowship, awarded by the United States Department of Defense, provided a measure of independence for the start of my doctoral program.

My research funding continued through the Cornell Center for Materials Research (CCMR) and, specifically, its Interdisciplinary Research Group (IRG) on the Dynamics of Growth of Complex Materials.

Within the Computer Science department, much of my recent funding is provided by the Directorate for Computer & Information Science & Engineering (CISE) of the National Science Foundation (NSF), the Information Directorate of the Air Force Research Laboratory (AFRL), and the Air Force Office of Warfighting Integration (AF/XC).


I am a passionate (yet quite) amateur photographer (with focus on portraiture and macro work), Free Software proponent, and horology enthusiast...