Yuanjie Li
Postdoc at UCLA

3277 Boelter Hall
Department of Computer Science
University of California, Los Angeles
Los Angeles, CA 90095

Email: yuanjie.li [at] cs.ucla.edu

Google Scholar


I am a Postdoc Computer Science at University of California, Los Angeles. I did my Ph.D. from UCLA in June 2017. I was advised by Professor Songwu Lu. I am a member of the Wireless Networking Group (WiNG). Prior to UCLA, I received my bachelor degree from Tsinghua University in 2012.

My research interests are in the broad areas of networked systems, mobile computing and security. My recent focuses are on the 4G/5G mobile network architecture, protocols, network data analytics, network verification/diagnosis, demanding mobile applications, and mobile network/system security.


What's New

June 2017
MobileInsight 3.0 has been released! See our new website and GitHub repositories!
June 2017
I have successfully defended my Ph.D. thesis. See my Ph.D. thesis online. .
June 2017
Parallel control-plane latency reduction (DPCM) has been accepted to ACM MobiCom'17.
October 2016
MobileInsight won the MobiCom 2016 Best Community Paper Award.
July 2016
4G-SMS security has been accepted to ACM CCS'16.
June 2016
MobileInsight has been accepted to ACM MobiCom'16.

Previous news

April 2016
MobileInsight 2.0 has been released. Try our in-phone version of cellular network monitoring and analysis!
February 2016
Mobility misconfiguration analysis has been accepted to ACM SIGMETRICS'16.
August 2015
VoLTE security work has been accepted to ACM CCS'15.
April 2014
CNetVerifier has been accepted to ACM SIGCOMM'14.
December 2015
MMDiag and VoLTE* have been accepted to ACM HotMobile'16.
December 2015
iCellular has been accepted to USENIX NSDI'16.
November 2015
Femtocell work has been accepted to IEEE INFOCOM'16.
October 2015
Media coverage of our VoLTE work: TheVerge and RCRWireless News

Research Projects

MobileInsight
In-deivce runtime cellular network analytics [MobiCom'16] [Code release].
iCellular
Device-customized multi-carrier cellular network access [NSDI'16]
MMDiag
Mobility management analysis and diagnosis [SIGMETRICS'16] [INFOCOM'16] [HotMobile'16]
CNetVerifier
Cellular control-plane protocol verification [SIGCOMM'14] [IEEE/ACM ToN'16]

Publications

Conferences

A Control-Plane Perspective on Reducing Data Access Latency in LTE Networks MobiCom'17

Yuanjie Li, Zengwen Yuan, Chunyi Peng
The 23rd Annual International Conference on Mobile Computing and Networking (ACM MobiCom'17), acceptance rate: 35/186 = 18.8%

Control-plane operations are indispensable to providing data access to mobile devices in the 4G LTE networks. They provision necessary control states at the device and network nodes to enable data access. However, the current design may suffer from long data access latency even under good radio conditions. The fundamental problem is that, data-plane packet delivery cannot start or resume until all control-plane procedures are completed, and these control procedures run sequentially by design at the device and network nodes. In this work, we show both are more than necessary under popular usage cases. We design DPCM, which reduces data access latency through parallel processing approaches and exploiting device-side state replica. We implement DPCM and validate its effectiveness with extensive evaluations.

@inproceedings {li2017dpcm, author = {Yuanjie Li and Zengwen Yuan and Chunyi Peng}, title = {A Control-Plane Perspective on Reducing Data Access Latency in LTE Networks}, booktitle = {The 23rd ACM Annual International Conference on Mobile Computing and Networking (MobiCom'17)}, year = {2017}, month = Oct, address = {Snowbird, Utah, USA}}

The Tick Programmable Low-Latency SDR System MobiCom'17

Haoyang Wu, Tao Wang, Zengwen Yuan, Chunyi Peng, Zhiwei Li, Zhaowei Tan, Boyan Ding, Xiaoguang Li, Yuanjie Li, Jun Liu, Songwu Lu
The 23rd Annual International Conference on Mobile Computing and Networking (ACM MobiCom'17), acceptance rate: 35/186 = 18.8%

Tick is a new SDR system that provides programmability and low latency at both PHY and MAC. It supports modular design and element-based programming, similar to the Click router. It uses an accelerator-rich architecture, where an embedded processor executes control ows and handles various MAC events. User-defined accelerators o oad those computation-intensive, communication-heavy, fine-grained timing control tasks from the processor, and accelerate them in hardware. Tick applies a number of hardware and software co-design techniques to ensure low latency, includ- ing multi-clock-domain pipelining, field-based processing pipeline, separation of data and control flows, etc. We have implemented Tick and validated its effectiveness through extensive evaluations as well as two prototypes of 802.11ac SISO/MIMO and 802.11a/g full-duplex.

@inproceedings {wu2017tick, author = {Haoyang Wu and Tao Wang and Zengwen Yuan and Chunyi Peng and Zhiwei Li and Zhaowei Tan and Boyan Ding and Xiaoguang Li and Yuanjie Li and Jun Liu and Songwu Lu}, title = {The Tick Programmable Low-Latency SDR System}, booktitle = {The 23rd ACM Annual International Conference on Mobile Computing and Networking (MobiCom'17)}, year = {2017}, month = Oct, address = {Snowbird, Utah, USA}}

Towards Automated Intelligence in 5G Systems ICCCN'17

Haotian Deng, Qianru Li, Yuanjie Li, Songwu Lu, Chunyi Peng, Taqi Raza, Zhaowei Tan, Zengwen Yuan, Zhehui Zhang
(In alphabetical order)
The 26th International Conference on Computer Communications and Networks (ICCCN 2017), invited paper

In this paper, we call for a paradigm shift away from the wireless-access focused research efforts on 5G networked systems. We believe that the architectural limitations should share equal blame on issues of performance, reliability, and security. We thus identify architectural weakness on both sides of the mobile clients and the 4G network infrastructure. Our recent findings show that, contrary to commonly held perceptions, many design and operational issues arise not due to poor wireless link qualities. Instead, they are rooted in such architectural downsides. To address these issues, we further propose a new approach of enabling automated intelligence inside the 4G/5G network systems. We next describe our ongoing efforts along two dimensions: empowering data-driven smart clients and constructing verifiable network infrastructure. We report some early results and discuss possible next steps.

@inproceedings {li17toward, author = {Haotian Deng and Qianru Li and Yuanjie Li and Songwu Lu and Chunyi Peng and Taqi Raza and Zhaowei Tan and Zengwen Yuan and Zhehui Zhang}, title = {Towards Automated Intelligence in 5G Systems}, booktitle = {The 26th International Conference on Computer Communications and Networks (ICCCN 2017)}, year = {2017}, month = Jul, address = {Vancouver, Canada}}

MobileInsight: Extracting and Analyzing Cellular Network Information on Smartphones MobiCom'16

Yuanjie Li, Chunyi Peng, Zengwen Yuan, Jiayao Li, Haotian Deng, Tao Wang
The 22nd Annual International Conference on Mobile Computing and Networking (ACM MobiCom'16), acceptance rate: 31/247 = 12.6%
Best Community Paper Award

We design and implement MobileInsight, a software tool that collects, analyzes and exploits runtime network information from operational cellular networks. MobileInsight runs on commercial off-the-shelf phones without extra hardware or additional support from operators. It exposes protocol messages on both control plane and (below IP) data plane from the 3G/4G chipset. It provides in-device protocol analysis and operation logic inference. It further offers a simple API, through which developers and researchers obtain access to low-level network information for their mobile applications. We have built three showcases to illustrate how MobileInsight is applied to cellular network research.

@inproceedings {li2016mobileinsight, author = {Yuanjie Li and Chunyi Peng and Zengwen Yuan and Jiayao Li and Haotian Deng and Tao Wang}, title = {MobileInsight: Extracting and Analyzing Cellular Network Information on Smartphones}, booktitle = {The 22nd ACM Annual International Conference on Mobile Computing and Networking (MobiCom'16)}, year = {2016}, month = Oct, address = {New York, USA}}

Instability in Distributed Mobility Management: Revisiting Configuration Management in 3G/4G Mobile Networks SIGMETRICS'16

Yuanjie Li, Haotian Deng, Jiayao Li, Chunyi Peng, Songwu Lu
The 42nd ACM International Conference on Measurement and Modeling of Computer Systems (SIGMETRICS), Antibes Juan-les-Pins, France, June 2016, acceptance rate: 28/208 = 13.4%

Mobility support is critical to offering seamless data service to mobile devices in 3G/4G cellular networks. To accommodate policy requests by users and carriers, micro-mobility management scheme among cells (i.e., handoff) is designated to be configurable. Each cell and mobile device can configure or even customize its own handoff procedure. In this paper, we examine the handoff miscon- figuration issues in 3G/4G networks. We show that they may incur handoff instability in the form of persistent loops, where the device oscillates between cells even without radio-link and location changes. Such instability is mainly triggered by uncoordinated parameter configurations and inconsistent decision logic in the handoff procedure. It can degrade user data performance, incur excessive signaling overhead, and violate network’s expected handoff goals. We derive the instability conditions, and validate them on two major US mobile carrier networks. We further design a software tool for automatic loop detection, and run it over operational networks. We discuss possible fixes to such uncoordinated configurations among devices and cells.

@inproceedings {li2016instability, title = {Instability in Distributed Mobility Management: Revisiting Configuration Management in 3G/4G Mobile Networks}, author = {Yuanjie Li and Haotian Deng and Jiayao Li and Chunyi Peng and Songwu Lu}, booktitle = {The 42nd ACM International Conference on Measurement and Modeling of Computer Systems (SIGMETRICS'16)}, year = {2016}, month = Jun, address = {Antibes Juan-les-Pins, France}, }

iCellular: Device-Customized Cellular Network Access on Commodity Smartphones NSDI '16

Yuanjie Li, Haotian Deng, Chunyi Peng, Zengwen Yuan, Guan-Hua Tu, Jiayao Li, Songwu Lu
The 13th USENIX Symposium on Networked Systems Design and Implementation (USENIX NSDI '16), acceptance rate: 45/228 = 19.7%

Exploiting multi-carrier access offers a promising direction to boost access quality in mobile networks. However, our experiments show that, the current practice does not achieve the full potential of this approach because it has not utilized fine-grained, cellular-specific domain knowledge. In this work, we propose iCellular, which exploits low-level cellular information at the device to improve multi-carrier access. Specifically, iCellular is proactive and adaptive in its multi-carrier selection by leveraging existing end-device mechanisms and standards-complaint procedures. It performs adaptive monitoring to ensure responsive selection and minimal service disruption, and enhances carrier selection with online learning and runtime decision fault prevention. It is readily deployable on smartphones without infrastructure/hardware modifications. We implement iCellular on commodity phones and harness the efforts of Project Fi to assess multi-carrier access over two US carriers: T-Mobile and Sprint. Our evaluation shows that, iCellular boosts the devices with up to 3.74x throughput improvement, 6.9x suspension reduction, and 1.9x latency decrement over the state-of-the-art selection scheme, with moderate CPU, memory and energy overheads.

@inproceedings {li2016icellular, title = {iCellular: Device-Customized Cellular Network Access on Commodity Smartphones}, author = {Yuanjie Li and Haotian Deng and Chunyi Peng and Zengwen Yuan and Guan-Hua Tu and Jiayao Li and Songwu Lu}, booktitle = {13th USENIX Symposium on Networked Systems Design and Implementation (NSDI 16)}, year = {2016}, month = Mar, address = {Santa Clara, CA}, url = {https://www.usenix.org/conference/nsdi16/technical-sessions/presentation/li-yuanjie}, publisher = {USENIX Association}, }

CAP on Mobility Control for 4G LTE Networks HotWireless '16

Yuanjie Li, Zengwen Yuan, Chunyi Peng, Songwu Lu
The 3rd ACM Workshop on Hot Topics in Wireless (HotWireless'16), invited paper

The CAP theorem exposes the fundamental tradeoffs among three key properties of strong consistency, availability and partition tolerance in distributed networked systems. In this position paper, we take the CAP perspective on 4G mobility control. We view the control-plane management for mobility support as a distributed signaling system. We show that the impossibility result of the CAP theorem also holds for mobility control: It is impossible for any mobility control to guarantee sequential consistency, high service availability, and partition tolerance simultaneously. Unfortunately, the current 4G system adopts its mobility scheme with the notion of sequential consistency. Our empirical study further confirms that, the incurred data unavailability (i.e., data service suspension) time is comparable to that induced by wireless connectivity setup. We argue that the desirable mobility control for the upcoming 5G networks should take a paradigm shift. We discuss our early effort on re-examining the consistency notion for higher availability and fault tolerance.
@inproceedings{li2016cap, title={CAP on Mobility Control for 4G LTE Networks}, author={Li, Yuanjie and Yuan, Zengwen and Peng, Chunyi and Lu, Songwu}, booktitle={The 3rd ACM Workshop on Hot Topics in Wireless (HotWireless'16)}, year={2016}, organization={ACM} }

A First Look at Unstable Mobility Management in Cellular Networks HotMobile '16

Yuanjie Li, Jiaqi Xu, Chunyi Peng, Songwu Lu
17th International Workshop on Mobile Computing Systems and Applications (ACM HotMobile 2016), acceptance rate: 18/55 = 32.7%

Mobility management is a prominent feature in cellular networks. In this paper, we examine the (in)stability of mobility management. We disclose that handoff may never converge in some real-world cases. We focus on persistent handoff oscillations, rather than those transient ones caused by dynamic networking environment and user mobility (e.g., moving back and force between two base stations). Our study reveals that persistent handoff loops indeed exist in operational cellular networks. They not only violate their design goals, but also incur excessive signaling overhead and data performance degradation. To detect and validate instability in mobility management, we devise MMDIAG, an in-device diagnosis tool for cellular network operations. The core of MMDIAG is to build a handoff decision automata based on 3GPP standards, and detect possible loops by checking the structural property of stability. We first leverage device-network signaling exchanges to retrieve mobility management policies and configurations, and then feed them into MMDIAG, along with runtime measurements. MMDIAG further emulates various handoff scenarios and identifies possible violations (i.e., loops) caused by the used policies and configurations. Finally, we validate the identified problems through real measurements over operational networks. Our preliminary results with a top-tier US carrier demonstrate that, unstable mobility management indeed occurs in reality and hurts both carriers and users. The proposed methodology is effective to identify persistent instabilities and pinpoint their root causes in problematic configurations and policy conflicts.
@inproceedings{li2016first, title={A First Look at Unstable Mobility Management in Cellular Networks}, author={Li, Yuanjie and Xu, Jiaqi and Peng, Chunyi and Lu, Songwu}, booktitle={Proceedings of the 17th International Workshop on Mobile Computing Systems and Applications}, pages={15--20}, year={2016}, organization={ACM} }

Understanding and Diagnosing Real-World Femtocell Performance Problems INFOCOM'16

Chunyi Peng, Yuanjie Li, Zhuoran Li, Jie Zhao, Jiaqi Xu
IEEE International Conference on Computer Communications (INFOCOM'16), acceptance rate: 18.3%

Femtocells (small cells) augment the current mobile network by providing users short-range radio access at home and small-business settings. They have rapidly emerged as a promising scheme to alleviate capacity and coverage shortage by offloading traffic from the conventional Macrocells (large cells). Despite its increasing popularity, the real-world Femtocell performance has remained largely unexplored. In this paper, we conduct an in-depth study to assess Femtocell performance and diagnose identified issues in operational carrier networks. We focus on user-deployed Femtocells in a top-tier US mobile network. While the Femtocell generally works well, unanticipated performance degradations and even failures still occur. Contrary to conventional wisdom in the research community, we find that, radio link quality and interference is not the main bottleneck of Femtocells in many real-life usage scenarios. For instance, while Femtocell deployment at blind-zones with no radio coverage is desirable, not all deployments have succeeded; Compared with their Macrocell counterparts, Femtocells exhibit lower speed and larger speed variations, and induce larger delay for data services. Moreover, mobility support for femtocells is incomplete and no seamless migration is available under certain usage scenarios. We pinpoint their root causes, quantify the potential impacts,and share the learned lessons.
@inproceedings{li16-infocom, title = {{Understanding and Diagnosing Real-World Femtocell Performance Problems}}, author = {Chunyi Peng and Yuanjie Li and Zuoran Li and Jie Zhao and Jiaqi Xu}, booktitle = {INFOCOM}, month = {April}, year = {2016}, }

New Security Threats Caused by IMS-based SMS Service in 4G LTE Networks CCS'16

Guan-Hua Tu, Chi-Yu Li, Chunyi Peng, Yuanjie Li, Songwu Lu,
The 23rd ACM Conference on Computer and Communications Security (CCS'16), acceptance rate: 137/837=16.3%

SMS (Short Messaging Service) is a text messaging service for mobile users to exchange short text messages. It is also widely used to provide SMS-powered services (e.g., mobile banking). With the rapid deployment of all-IP 4G mobile networks, the underlying technology of SMS evolves from the legacy circuit-switched network to the IMS (IP Multimedia Subsystem) system over packet-switched network. In this work, we study the insecurity of the IMS-based SMS. We uncover its security vulnerabilities and exploit them to devise four SMS attacks: silent SMS abuse, SMS spoofing, SMS client DoS, and SMS spamming. We further discover that those SMS threats can propagate towards SMS-powered services, thereby leading to three malicious attacks: social network account hijacking, unauthorized donation, and unauthorized subscription. Our analysis reveals that the problems stem from the loose security regulations among mobile phones, carrier networks, and SMS-powered services. We finally propose remedies to the identified security issues.
@inproceedings{tu16-ccs, author = {Guan-Hua Tu and Chi-Yu Li and Chunyi Peng and Yuanjie Li and Songwu Lu}, title = {{New Security Threats Caused by IMS-based SMS Service in 4G LTE Networks}}, booktitle = {ACM CCS} month = {October}, year = {2016}, location = {Hofburg Palace, Vienna, Austria}, }

VoLTE*: A Lightweight Voice Solution to 4G LTE Networks HotMobile '16

Guan-Hua Tu, Chi-Yu Li, Chunyi Peng, Zengwen Yuan, Yuanjie Li, Songwu Lu
The 17th International Workshop on Mobile Computing Systems and Applications (ACM HotMobile 2016), acceptance rate: 18/55 = 32.7%

VoLTE is the designated voice solution to the LTE network. Its early deployment is ongoing worldwide. In this work, we report an assessment on VoLTE. We show that VoLTE offers no categorically better quality than popular VoIP applications in all tested scenarios except some congested scenarios. Given the high cost on infrastructure upgrade, we argue that VoLTE, in its current form, might not warrant the deployment effort. We sketch VoLTE*, a lightweight voice solution from which all parties of users, LTE carriers, and VoIP service providers may benefit.
@inproceedings{tu2016volte, title={VoLTE*: A Lightweight Voice Solution to 4G LTE Networks}, author={Tu, Guan-Hua and Li, Chi-Yu and Peng, Chunyi and Yuan, Zengwen and Li, Yuanjie and Zhao, Xiaohu and Lu, Songwu}, booktitle={Proceedings of the 17th International Workshop on Mobile Computing Systems and Applications}, pages={3--8}, year={2016}, organization={ACM} }

Demystify Undesired Handoff in Cellular Networks ICCCN '16

Chunyi Peng, Yuanjie Li
To appear in the 25th International Conference on Computer Communication and Networks (ICCCN 2016), acceptance rate: 30%

Handoff is critical to providing seamless network access to mobile devices in cellular networks. To accommodate diverse requirements by users and operators, micro-mobility management scheme among cells (i.e., handoff) is designated to be configurable. Each cell and mobile device can configure or even customize its own handoff procedure which likely results in inconsistent among their handoffs. In this paper, we examine the current design and practice of handoff in desired reachability. We show that handoff misconfigurations exist and they make the device stuck in an undesired target cell (e.g., 2G when 4G available). We model the distributed mobility management as an iterative process and use analysis to classify the causes. We further design a software tool for automatic loop detection, and run it over operational networks. We validate the identified issues on two major US mobile carrier networks.
@inproceedings{peng16-icccn, author = {Chunyi Peng and Yuanjie Li}, title = {{Demystify Undesired Handoff in Cellular Networks}}, booktitle = {ICCCN}, month = {August}, year = {2016}, }

Insecurity of Voice Solution VoLTE in LTE Mobile Networks CCS '15

Chi-Yu Li, Guan-Hua Tu, Chunyi Peng, Zengwen Yuan, Yuanjie Li, Songwu Lu, Xinbing Wang
The 22nd ACM Conference on Computer and Communications Security (CCS '15), acceptance rate: 128/646 = 19.8%

VoLTE (Voice-over-LTE) is the designated voice solution to the LTE mobile network, and its worldwide deployment is underway. It reshapes call services from the traditional circuit-switched telecom telephony to the packet-switched Internet VoIP. In this work, we conduct the first study on VoLTE security before its full rollout. We discover several vulnerabilities in both its control-plane and data-plane functions, which can be exploited to disrupt both data and voice in operational networks. In particular, we find that the adversary can easily gain free data access, shut down continuing data access, or subdue an ongoing call, etc. We validate these proof-of-concept attacks using commodity smartphones (rooted and unrooted) in two Tier-1 US mobile carriers. Our analysis reveals that, the problems stem from both the device and the network. The device OS and chipset fail to prohibit non-VoLTE apps from accessing and injecting packets into VoLTE control and data planes. The network infrastructure also lacks proper access control and runtime check.
@inproceedings{Li:2015:IVS:2810103.2813618, author = {Li, Chi-Yu and Tu, Guan-Hua and Peng, Chunyi and Yuan, Zengwen and Li, Yuanjie and Lu, Songwu and Wang, Xinbing}, title = {Insecurity of Voice Solution VoLTE in LTE Mobile Networks}, booktitle = {Proceedings of the 22nd ACM SIGSAC Conference on Computer and Communications Security}, series = {CCS '15}, year = {2015}, isbn = {978-1-4503-3832-5}, location = {Denver, Colorado, USA}, pages = {316--327}, numpages = {12}, url = {http://doi.acm.org/10.1145/2810103.2813618}, doi = {10.1145/2810103.2813618}, acmid = {2813618}, publisher = {ACM}, address = {New York, NY, USA}, keywords = {LTE, attack, cellular networks, defense, volte},}

Control-Plane Protocol Interactions in Cellular Networks SIGCOMM'14

Guan-Hua Tu†, Yuanjie Li(: co-primary), Chunyi Peng, Chi-Yu Li, Hongyi Wang, Songwu Lu
ACM SIGCOMM'14, acceptance rate: 45/237 = 18.9%

Control-plane protocols are complex in cellular networks. They communicate with one another along three dimensions of cross layers, cross (circuit-switched and packet-switched) domains, and cross (3G and 4G) systems. In this work, we propose signaling diagnosis tools and uncover six instances of problematic interactions. Such control-plane issues span both design defects in the 3GPP standards and operational slips by carriers. They are more damaging than data-plane failures. In the worst-case scenario, users may be out of service in 4G, or get stuck in 3G. We deduce root causes, propose solutions, and summarize learned lessons.
@inproceedings{tu2014control, title={Control-plane protocol interactions in cellular networks}, author={Tu, Guan-Hua and Li, Yuanjie and Peng, Chunyi and Li, Chi-Yu and Wang, Hongyi and Lu, Songwu}, booktitle={ACM SIGCOMM Computer Communication Review}, volume={44}, number={4}, pages={223--234}, year={2014}, organization={ACM} }

Scalable Opportunistic VANET Content Routing With Encounter Information VCA'13

Yu-Ting Yu, Yuanjie Li, Xingyu Ma, Wentao Shang, MY Sanadidi, Mario Gerla
The 2nd International Workshop on Vehicular Communications and Applications (VCA), 2013

Recently, Information Centric Networking (ICN) has attracted much attention also for mobiles. Unlike host-based communication models, ICN promotes data names as the first-class citizen in the network. However, the current ICN name-based routing requires Interests be routed by name to the nearest replica, implying the Interests are flooded in VANET. This introduces large overhead and consequently degrades wireless network performance. In order to maintain the efficiency of ICN implementation in VANET, we propose an opportunistic geo-inspired content based routing method. Our method utilizes the last encounter information of each node to infer the locations of content holders. With this information, the Interests can be geo-routed instead of being flooded to reduce the congestion level of the entire network. The simulation results show that our proposed method reduces the scope of flooding to less than two hops and improves retrieval rate by 1.42 times over flooding-based methods.
@inproceedings{yu2013scalable, title={Scalable opportunistic vanet content routing with encounter information}, author={Yu, Yu-Ting and Li, Yuanjie and Ma, Xingyu and Shang, Wentao and Sanadidi, MY and Gerla, Mario}, booktitle={Network Protocols (ICNP), 2013 21st IEEE International Conference on}, pages={1--6}, year={2013}, organization={IEEE} }

Journals

MobileInsight: Extracting and Analyzing Cellular Network Information on Smartphones GetMobile

Yuanjie Li, Chunyi Peng, Zengwen Yuan, Jiayao Li, Haotian Deng, Tao Wang
ACM GetMobile: Mobile Computing and Communications, Volume 21 Issue 1 (March 2017): 39--42.

MobileInsight is a software tool that collects, analyzes and exploits runtime, fine-grained cellular network information over commodity phones. It is our first step to help developers and researchers understand the closed, large-scale cellular network system. It exposes the below-IP protocol messages to the user space, provides protocol analysis, and offers APIs for mobile applications to obtain low-level network information. We have built showcases to illustrate how MobileInsight can be applied to cellular network research.

@article{li2017mobileinsight, title={MobileInsight: Analyzing Cellular Network Information on Smartphones}, author={Li, Yuanjie and Peng, Chunyi and Yuan, Zengwen and Deng, Haotian and Li, Jiayao and Wang, Tao}, journal={GetMobile: Mobile Computing and Communications}, volume={21}, number={1}, pages={39--42}, year={2017}, publisher={ACM} }

Detecting Problematic Control-Plane Protocol Interactions in Mobile Networks ToN'16

Guan-Hua Tu†, Yuanjie Li(: co-primary), Chunyi Peng, Chiyu Li, Songwu Lu
IEEE/ACM Transactions on Networking (ToN), 24(2): 1209-1222, April 2016

The control-plane protocols in 3G/4G mobile networks communicate with each other, and provide a rich set of control functions, such as radio resource control, mobility support, connectivity management, to name a few. Despite their significance, the problem of verifying protocol correctness remains largely unaddressed. In this paper, we examine control-plane protocol interactions in mobile networks. We propose CNetVerifier, a two-phase signaling diagnosis tool to detect problematic interactions in both design and practice. CNetVerifier first performs protocol screening based on 3GPP standards via domain-specific model checking, and then conducts phone-based empirical validation in operational 3G/4G networks. With CNetVerifier, we have uncovered seven types of troublesome interactions, along three dimensions of cross (protocol) layers, cross (circuit-switched and packet-switched) domains, and cross (3G and 4G) systems. Some are caused by necessary yet problematic cooperation (i.e., protocol interactions are needed but they misbehave), whereas others are due to independent yet unnecessary coupled operations (i.e., protocols interactions are not required but actually coupled). These instances span both design defects in 3GPP standards and operational slips by carriers and vendors. They all result in performance penalties or functional incorrectness. We deduce root causes, present empirical results, propose solutions, and summarize learned lessons.
@article{tudetecting, title={Detecting Problematic Control-Plane Protocol Interactions in Mobile Networks}, author={Tu, Guan-Hua and Li, Yuanjie and Peng, Chunyi and Li, Chi-Yu and Lu, Songwu}, publisher={IEEE} }

ESM: Efficient and Scalable Data Center Multicast Routing ToN'13

Dan Li, Yuanjie Li, Jianping Wu, Sen Su, Jiangwei Yu
IEEE/ACM Transactions on Networking (ToN), 20(3): 944-955, 2013

Multicast benefits group communications in saving network traffic and improving application throughput, both of which are important for data center applications. However, the technical trend of data center design poses new challenges for efficient and scalable multicast routing. First, the densely connected networks make traditional receiver-driven multicast routing protocols inefficient in multicast tree formation. Second, it is quite difficult for the low-end switches widely used in data centers to hold the routing entries of massive multicast groups. In this paper, we propose ESM, an efficient and scalable multicast routing scheme for data center networks. ESM addresses the challenges above by exploiting the feature of modern data center networks. Based on the regular topology of data centers, ESM uses a source-to-receiver expansion approach to build efficient multicast trees, excluding many unnecessary intermediate switches used in receiver-driven multicast routing. For scalable multicast routing, ESM combines both in-packet Bloom Filters and in-switch entries to make the tradeoff between the number of multicast groups supported and the additional bandwidth overhead. Simulations show that ESM saves 40%-50% network traffic and doubles the application throughputs compared to receiver-driven multicast routing, and the combination routing scheme significantly reduces the number of in-switch entries required. We implement ESM on a Linux platform. The experimental results further demonstrate that ESM can well support online tree building for large-scale groups with churns, and the overhead of the combination forwarding engine is light-weighted.
@article{li2012esm, title={ESM: efficient and scalable data center multicast routing}, author={Li, Dan and Li, Yuanjie and Wu, Jianping and Su, Sen and Yu, Jiangwei}, journal={IEEE/ACM Transactions on Networking (TON)}, volume={20}, number={3}, pages={944--955}, year={2012}, publisher={IEEE Press} }

Photon induced tunneling in optomechanical systems PRA'13

Xun-Wei Xu, Yuanjie Li, Yu-xi Liu
Physical Review A (PRA), 87.025803, 2013

In contrast to recent studies [Rabl, Phys. Rev. Lett. 107, 063601 (2011); Nunnenkamp et al., Phys. Rev. Lett. 107, 063602 (2011)] on photon blockade that prevents subsequent photons from resonantly entering the cavity in optomechanical systems, we study the photon-induced tunneling that increases the probability of admitting subsequent photons in those systems. In particular, we analytically and numerically show how two- or three-photon tunneling can occur by avoiding single-photon blockade. Our study provides another way on photon control using a single mechanical resonator in optomechanical systems.
@article{xu2013photon, title={Photon-induced tunneling in optomechanical systems}, author={Xu, Xun-Wei and Li, Yuan-Jie and Liu, Yu-xi}, journal={Physical Review A}, volume={87}, number={2}, pages={025803}, year={2013}, publisher={APS} }

Antibunching photons in a cavity coupled to an optomechanical system JPB'13

Xun-Wei Xu, Yuanjie Li
Journal of Physics B (JPB), 2013

We study the photon statistics of a cavity linearly coupled to an optomechanical system via second order correlation functions. Our calculations show that the cavity can exhibit strong photon antibunching even when optomechanical interaction in the optomechanical system is weak. The cooperation between the weak optomechanical interaction and the destructive interference between different paths for two-photon excitation leads to the efficient antibunching effect. Compared with the standard optomechanical system, the coupling between a cavity and an optomechanical system provides a method to relax the constraints to obtain single photon by optomechanical interaction.
@article{xu2013antibunching, title={Antibunching photons in a cavity coupled to an optomechanical system}, author={Xu, Xun-Wei and Li, Yuan-Jie}, journal={Journal of Physics B: Atomic, Molecular and Optical Physics}, volume={46}, number={3}, pages={035502}, year={2013}, publisher={IOP Publishing} }

Thesis

Augmenting Intelligence in Mobile Networked System

Yuanjie Li
Ph.D. Thesis, UCLA 2017
UCLA Dissertation Year Fellowship

@article{li2017augmenting, title={Augmenting Intelligence in Mobile Networked System}, author={Li, Yuanjie}, year={2017} }

The ongoing revolution in the mobile networked system (consisting of mobile clients, and the 4G/5G network infrastructure) is reaching a critical stage. On one hand, it has been operational for years, resulting in billions of users and tens of petabytes per month for mobile data traffic. On the other hand, users today regularly complain about network failures, unsatisfactory performance, and security threats with alarming frequency. The impact of such problematic issues may further exaggerate, as the emerging next-generation applications (such as interactive virtual/augmented reality, self-driving cars, telemedicine, and drone-based delivery, etc.) pose more stringent requirements. The convention wisdom seems to attribute most of these issues to the poor wireless channel quality, thus motivating a range of new access technologies to mitigate them.

This dissertation demonstrates that, besides the wireless link, the architectural limitation should share equal responsibility. The fundamental problem is that, the entire networked system does not possess sufficient intelligence on what problems may arise, why such issues occur under the given scenarios, and how to react. The mobile clients lack runtime infor- mation on the underlying “black-box” network operations, whereas the infrastructure suffers from the complex interplays of protocol functions among distributed nodes. Both again are rooted in the basic design tenet of “smart core, dumb terminal” adopted by the current mobile networked systems. Our study has uncovered a range of real issues incurred by the architectural limitations (rather than the poor wireless link), including handoff instability, suboptimal roaming, and long data access latency perceived by both the client and the infrastructure. Most of the current solutions are piecemeal efforts without looking into the core system architecture designs.

This dissertation thus explores a new dimension in mobile networked systems. We seek to augment the system intelligence on verifying the baseline designs a priori, detecting problematic scenarios based on runtime information feedback, understanding their root causes, and taking smart actions. To this end, we propose a new knowledge plane for the system software stack, which offers a novel primitive for the mobile networked system that helps to unleash its architectural limitations. The knowledge plane follows the “smart client, simple infras- tructure” principle but leaps one step forward. On one hand, it explores the “data-driven approach to smart clients” by exposing rich network information at runtime and leveraging some recent results on data sciences and machine learning. On the other hand, it seeks to devise simple, yet verifiable protocol solutions with provable properties by applying techniques on network verification and distributed computing. In this way, we enable a simpler and more open networked system for the mobile devices.

The main contribution of this dissertation is the design, instantiation, analysis, and vali- dation of the knowledge plane and its benefits on performance and reliability. The concrete results cover on both the client device and the network infrastructure. On the mobile client side, we construct the knowledge plane using the “bottom-up” data-driven system design, by enabling the client-side access to rich network data at runtime. It thus opens access to the typically “closed” network operations without infrastructure changes. We build MobileInsight, the first tool that opens up the runtime, fine-grained cellular network data and offers protocol analytics (using AI-based inference) on commodity phones; it has been used by 247 universities and companies during its first-year release so far. As a showcase application, we develop iCellular, an enhanced client-centric, multi-carrier roaming service. By leveraging low-level network data analytics, iCellular boosts the device with up to 3.74× throughput improvement, 1.9× latency reduction over the state-of-the-art solution from Google Project Fi.

On the infrastructure side, we enable the knowledge plane with the “top-down” approach. We treat the infrastructure as a distributed system, define the structural properties (stability, availability, consistency, etc.) that capture the high-level demands, apply verification and distributed computing techniques to reason about them, and enforce provable reliability and efficiency. At the management plane, we conduct the first study on the stability of the distributed mobility management. We show that, policy/configuration conflicts exist in reality, and force the device to oscillate among base stations permanently. We prove the necessary/sufficient conditions for the stability, and create MMDiag that detects and resolves the policy/configuration conflicts. At the control plane, we build DPCM, the first paradigm in the mobile network that parallelizes the control plane procedures for low-latency data access. It is inspired by the generalized CAP theorem, and leverages the device-side state replica achieve 2.1×–11.5× latency reduction on average in different scenarios.

These results show that, augmenting the future mobile networked system with intelli- gence can benefit both the client and the infrastructure. The knowledge plane presented in this dissertation provides a viable solution to move one step closer toward a future mobile networked system (5G and beyond) with Intelligence-as-a-Service.


Teaching Experience

CS211:
Wireless and Mobile Network (graduate course), Fall 2015, Spring 2015
CS118:
Computer Network Fundamentals, Fall 2013, Fall 2014
CS31:
Introduction to Computer Science, Winter 2014
CS33:
Introduction to Computer Organization, Spring 2014

Awards

October 2016
MobiCom’16 Best Community Paper Award
July 2016
Outstanding Chinese Oversea Graduate Student Award
June 2016
UCLA Dissertation Year Fellowship
March 2015
Finalist Award for Qualcomm Innovation Fellowship (QINF)
December 2012
Best Student Research Training (SRT) Award, Tsinghua University
December 2011
Qianheng Huang Scholarship, Tsinghua University

Academic Activities