Research
My main research area is network services and protocols for cyber-physical systems, the Internet of Things (IoT), and multi-media network services. My research aims to enable self-managing IoT systems that automatically adapt to a changing environment and make automated decisions based on high-level programs and policies. I am also interested in developing programming abstractions for IoT applications that follow data, i.e., applications deployable to the network edge.
At Columbia, I supervise student projects at the undergraduate and graduate levels. I also occasionally mentor high-school students interested in computer science.
Selected Publications
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arXiv:2509.13724. September 2025
Mission-critical voice (MCV) communications systems have been a critical tool for the public safety community for over eight decades. Public safety users expect MCV systems to operate reliably and consistently, particularly in challenging conditions. Because of these expectations, the Public Safety Communications Research (PSCR) Division of the National Institute of Standards and Technology (NIST) has been interested in correlating impairments in MCV communication systems and public safety user quality of experience (QoE). Previous research has studied MCV voice quality and intelligibility in a controlled environment. However, such research has been limited by the challenges inherent in emulating real-world environmental conditions. Additionally, there is the question of the best metric to use to reflect QoE accurately.
This paper describes our efforts to develop the methodology and tools for human-subject experiments with MCV. We illustrate their use in human-subject experiments in emulated real-world environments. The tools include a testbed for emulating real-world MCV systems and an automated speech recognition (ASR) robot approximating human subjects in transcription tasks. We evaluate QoE through a Levenshtein Distance-based metric, arguing it is a suitable proxy for measuring comprehension and the QoE. We conducted human-subject studies with Amazon MTurk volunteers to understand the influence of selected system parameters and impairments on human subject performance and end-user QoE. We also compare the performance of several ASR system configurations with human-subject performance. We find that humans generally perform better than ASR in accuracy-related MCV tasks and that the codec significantly influences the end-user QoE and ASR performance.
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PhD Dissertation. Columbia University. 2023
Networked systems integrating software with the physical world are known as cyber-physical systems (CPSs). CPSs have been used in diverse sectors, including power generation and distribution, transportation, industrial systems, and building management. The diversity of applications and interdisciplinary nature make CPSs exciting to design and build but challenging to manage once deployed. Deployed CPSs must adapt to changes in the operating environment or the system's architecture, e.g., when outdated or malfunctioning components need to be replaced. Skilled human operators have traditionally performed such adaptations using centralized management protocols. As the CPS grows, management tasks become more complex, tedious, and error-prone.
This dissertation studies management challenges in deployed CPSs. It is based on practical research with CPSs of various sizes and diverse application domains, from the large geographically dispersed electrical grid to small-scale consumer Internet of Things (IoT) systems. We study the management challenges unique to each system and propose network services and protocols specifically designed to reduce the amount of management overhead, drawing inspiration from autonomic systems and networking research.
We first introduce PhoenixSEN, a self-managing ad hoc network designed to restore connectivity in the electrical grid after a large-scale outage. The electrical grid is a large, heterogeneous, geographically dispersed CPS. We analyze the U.S. electrical grid network subsystem, propose an ad hoc network to temporarily replace the network subsystem during a blackout, and discuss the experimental evaluation of the network on a one-of-a-kind physical electrical grid testbed. The novel aspects of PhoenixSEN lie in a combination of existing and new network technologies and manageability by power distribution industry operators.
Motivated by the challenges of running unmodified third-party applications in an ad hoc network like PhoenixSEN, we propose a geographic resource discovery and query processing service for federated CPSs called SenSQL. The service combines a resource discovery protocol inspired by the LoST protocol with a standard SQL-based query interface. SenSQL aims to simplify the development of applications for federated or administratively decoupled autonomous cyber-physical systems without a single administrative or technological point of failure. The SenSQL framework balances control over autonomous cyber-physical devices and their data with service federation, limiting the application's reliance on centralized infrastructures or services.
We conclude the first part of the dissertation by presenting the design and implementation of a testbed for usability experiments with mission-critical voice, a vital communication modality in PhoenixSEN, and during emergency scenarios in general. The testbed can be used to conduct human-subject studies under emulated network conditions to assess the influence of various network parameters on the end-user's quality of experience.
The second dissertation part focuses on network enrollment of IoT devices, a management process that is often complicated, frustrating, and error-prone, particularly in consumer-oriented systems. We motivate the work by reverse-engineering and analyzing Amazon Echo's network enrollment protocol. The Echo is one of the most widely deployed IoT devices and, thus, an excellent case study. We learn that the process is rather complicated and cumbersome.
We then present a systematic study of IoT network enrollment with a focus on consumer IoT devices in advanced deployment scenarios, e.g., third-party installations, shared physical spaces, or evolving IoT systems. We evaluate existing frameworks and their shortcoming and propose WIDE, a network-independent enrollment framework designed to minimize user interactions to enable advanced deployment scenarios. WIDE is designed for large-scale or heterogeneous IoT systems where multiple independent entities cooperate to set the system up. We also discuss the design of a human-subject study to compare and contrast the usability of network enrollment frameworks.
A secure network must authenticate a new device before it can be enrolled. The authentication step usually requires physical device access, which may be impossible in many advanced deployment scenarios, e.g., when IoT devices are installed by a specialist in physically unreachable locations. We propose Lighthouse, a visible-light authentication protocol for physically inaccessible IoT devices. We discuss the protocol's design, develop transmitter and receiver prototypes, and evaluate the system. Our measurements with off-the-shelf components over realistic distances indicate authentication times shorter or comparable with existing methods involving gaining physical access to the device. We also illustrate how the visible-light authentication protocol could be used as another authentication method in other network enrollment frameworks.
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2021 IEEE Global Communications Conference: IoT and Sensor Networks (Globecom2021 IoTSN). Madrid, Spain. December 2021
With over 20 million units sold since 2015, Amazon Echo, the Alexa-enabled smart speaker developed by Amazon, is probably one of the most widely deployed Internet of Things consumer devices. Despite the very large installed base, surprisingly little is known about the device's network behavior. We modify a first generation Echo device, decrypt its communication with Amazon cloud, and analyze the device pairing, Alexa Voice Service, and drop-in calling protocols. We also describe our methodology and the experimental setup. We find a minor shortcoming in the device pairing protocol and learn that drop-in calls are end-to-end encrypted and based on modern open standards. Overall, we find the Echo to be a well-designed device from the network communication perspective.
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2021 IEEE International Conference on Communications, Control, and Computing Technologies for Smart Grids (SmartGridComm) (IEEE SmartGridComm'21). Aachen, Germany. October 2021
When the electrical grid in a region suffers a major outage, e.g., after a catastrophic cyber attack, a "black start" may be required, where the grid is slowly restarted, carefully and incrementally adding generating capacity and demand. To ensure safe and effective black start, the grid control center has to be able to communicate with field personnel and with supervisory control and data acquisition (SCADA) systems. Voice and text communication are particularly critical. As part of the Defense Advanced Research Projects Agency (DARPA) Rapid Attack Detection, Isolation, and Characterization Systems (RADICS) program, we designed, tested and evaluated a self-configuring mesh network prototype called the Phoenix Secure Emergency Network (PhoenixSEN). PhoenixSEN provides a secure drop-in replacement for grid's primary communication networks during black start recovery. The network combines existing and new technologies, can work with a variety of link-layer protocols, emphasizes manageability and auto-configuration, and provides services and applications for coordination of people and devices including voice, text, and SCADA communication. We discuss the architecture of PhoenixSEN and evaluate a prototype on realistic grid infrastructure through a series of DARPA-led exercises.
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TPRC48: The 48th Research Conference on Communication, Information, and Internet Policy. February 2021
The COVID-19 pandemic and related restrictions forced many to work, learn, and socialize from home over the internet. There appears to be consensus that internet infrastructure in the developed world handled the resulting traffic surge well. In this paper, we study network measurement data collected by the Federal Communications Commission's Measuring Broadband America program before and during the pandemic in the United States (US). We analyze the data to understand the impact of lockdown orders on the performance of fixed broadband internet infrastructure across the US, and also attempt to correlate internet usage patterns with the changing behavior of users during lockdown. We found the key metrics such as change in data usage to be generally consistent with the literature. Through additional analysis, we found differences between metro and rural areas, changes in weekday, weekend, and hourly internet usage patterns, and indications of network congestion for some users.
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Proceedings of the 2nd International Workshop on Edge Systems, Analytics and Networking. New York, NY, USA. 2019
The serverless and functions as a service (FaaS) paradigms are currently trending among cloud providers and are now increasingly being applied to the network edge, and to the Internet of Things (IoT) devices. The benefits include reduced latency for communication, less network traffic and increased privacy for data processing. However, there are challenges as IoT devices have limited resources for running multiple simultaneous containerized functions, and also FaaS does not typically support long-running functions. Our implementation utilizes Docker and CRIU for checkpointing and suspending long-running blocking functions. The results show that checkpointing is slightly slower than regular Docker pause, but it saves memory and allows for more long-running functions to be run on an IoT device. Furthermore, the resulting checkpoint files are small, hence they are suitable for live migration and backing up stateful functions, therefore improving availability and reliability of the system.
Teaching
- ENGI E1006 Introduction to Computing for Engineers and Applied Scientists
Spring 2023 - COMS W3132 Intermediate Computing in Python
Spring and Summer 2024
Awards
- Davide Giri Memorial Prize
The Fu Foundation School of Engineering and Applied Science, Columbia University
May 2023 - Best Educational Paper Award
The 2nd GENI Research and Educational Experiment Workshop, Salt Lake City
March 2013
Posters
- A Platform for Experimental Research in Critical Voice Communications, NIST PSCR 2022 Annual Stakeholder Meeting, San Diego, CA, June 2022
- Naming, Twinning, and Observing--Towards Cyber-Physical Systems Spanning Administrative and Geographical Boundaries, 2021 NSF CPS Principal Investigators' Meeting, June 2021
- Towards Scalable, Reliable, and Resilient IoT Systems for Smart Cities [video], Smart Cities Center Poster Session, Columbia University Data Science Institute, November 6, 2020
- Alexa, How Secure Are You?, Summer Research Institute Poster Session, Barnard College, August 2018
- Smartlock: Senior Design Expo Project, Senior Design Expo, Columbia University, May 2015
Talks
- A Platform for Experimental Research in Critical Voice Communications [video], NIST PSCR 2022 Annual Stakeholder Meeting, San Diego, CA, June 2022
- An Analysis of Amazon Echo's Network Behavior [video], IEEE GLOBECOM, Madrid, Spain, December 2021
- Talking After Lights Out: An Ad Hoc Network for Electric Grid Recovery, IEEE SmartGridComm21, Aachen, Germany, October 2021
- Naming, Twinning, and Observing--Towards Cyber-Physical Systems Spanning Administrative and Geographical Boundaries [video], 2021 NSF CPS Principal Investigators' Meeting, June 2021
- Social Distancing and the Internet: What Can Performance Measurements Tell Us?, TPRC 48, Washington, D.C., February 2021
- Prototyping Distributed IoT Applications With WebRTC, IPTComm 2016, Chicago, October 2016
- Access Control for Smart Objects, IAB Workshop on Smart Object Security, Paris, March 2012
- SIP Express Router, FOSDEM, Brussels, February 2006
Service
- IoT 2024 TPC Member
- ACM SIGCOMM'23 Local Arrangements Chair
- IoT 2023 TCP Member
Software
- lora-modem-abz: Open LoRaWAN firmware for Murata Type ABZ wireless module [Python library]
- py-mjpeg: Python library for working with MJPEG streams
- AMBE: A library for working with DVSI's vocoder chips
- PulseAudio.js: PulseAudio client for NodeJS
- mcv-testbed: Testbed for experiments with mission-critical voice
- autoprov: Auto-provisioning server for Yealink W52P phones
- dns2avahi: A DNS to Avahi (multicast DNS) gateway