Ben Y. Zhao

Packet-Level Telemetry in Large Datacenter Networks

By: 
Yibo Zhu, Nanxi Kang, Jiaxin Cao, Albert Greenberg, Guohan Lu, Ratul Mahajan, Dave Maltz, Lihua Yuan, Ming Zhang, Ben Y. Zhao, Haitao Zheng
Appears in: 
CCR August 2015

Debugging faults in complex networks often requires capturing and analyzing traffic at the packet level. In this task, datacenter networks (DCNs) present unique challenges with their scale, traffic volume, and diversity of faults. To troubleshoot faults in a timely manner, DCN administrators must a) identify affected packets inside large volume of traffic; b) track them across multiple network components; c) analyze traffic traces for fault patterns; and d) test or confirm potential causes. To our knowledge, no tool today can achieve both the specificity and scale required for this task.

Papyrus: A Software Platform for Distributed Dynamic Spectrum Sharing Using SDRs

By: 
Lei Yang, Zengbin Zhang, Wei Hou, Ben Y. Zhao, and Haitao Zheng
Appears in: 
CCR January 2011

Proliferation and innovation of wireless technologies require significant amounts of radio spectrum. Recent policy reforms by the FCC are paving the way by freeing up spectrum for a new generation of frequency-agile wireless devices based on software defined radios (SDRs). But despite recent advances in SDR hardware, research on SDR MAC protocols or applications requires an experimental platform for managing physical access. We introduce Papyrus, a software platform for wireless researchers to develop and experiment dynamic spectrum systems using currently available SDR hardware.

Public Review By: 
D. Wetherall

Dynamic spectrum sharing has become increasingly important. In the US, for example, the FCC has allowed unlicensed use of spectrum white spaces unused by TV around 700 MHz, giving final rules for access as recently as September 23. More work is needed to understand what strategies will be most valuable to let different devices access and share this spectrum without stepping on the primary users or each other. To see how those designs work in practice, researchers need an experimental platform. That is where Papyrus comes in. It is just such a platform, built on the USRP software-defined radio and providing two primitives for spectrum sharing. The first primitive is wideband spectrum sensing using power spectral density edge detection instead of energy detection for better accuracy. The second primitive is flexible selection of bandwidth for transmit and receive operations using a distributed version of OFDMA over non-contiguous frequency bands. Both of these primitives are generally useful and a strength of the work.
What is new here? That is the question the reviewers asked, given that the two key features of Papyrus were unveiled as part of the authors' work on the Jello system presented at NSDI 2010. The answer is that Papyrus has been crystallized as a separate core from the broader Jello system based on experience. This core is the widely reusable portion that other researchers will want most, and it has now been released and is available to the research community. The paper provides an API for the core along with other key parameters. To illustrate the API, it describes how Papyrus is used by Jello, as well as by Ganache, another system the authors have built using Papyrus for intelligent guardband configuration that appeared in Mobicom 2010. All of which should be good news for wireless researchers.

AirLab: Consistency, Fidelity and Privacy in Wireless Measurements

By: 
Vinod Kone, Mariya Zheleva, Mile Wittie, Ben Y. Zhao, Elizabeth M. Belding, Haitao Zheng, and Kevin Almeroth
Appears in: 
CCR January 2011

Accurate measurements of deployed wireless networks are vital for researchers to perform realistic evaluation of proposed systems. Unfortunately, the difficulty of performing detailed measurements limits the consistency in parameters and methodology of current datasets. Using different datasets, multiple research studies can arrive at conflicting conclusions about the performance of wireless systems. Correcting this situation requires consistent and comparable wireless traces collected from a variety of deployment environments.

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