# Sitemap

A list of all the posts and pages found on the site. For you robots out there is an XML version available for digesting as well.

## Future Blog Post

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## Blog Post number 4

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## Blog Post number 3

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## Blog Post number 2

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## Blog Post number 1

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## Portfolio item number 1

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## Efficient reliable opportunistic network coding based on hybrid flow in wireless network

Published in China Communications, 2011

Although the wireless network is widely used in many fields, its characteristics such as high bit error rate and broadcast links may block its development. Network coding is an artistic way to exploit its intrinsic characteristics to increase the network reliability. Some people research network coding schemes for inter-flow or intra-flow, each type with its own advantages and disadvantages. In this paper, we propose a new mechanism, called MM-NCOPE, which integrates the idea of interflow and intra-flow coding. On one hand, MM-NCOPE utilizes random liner coding to encode the NCOPE packets while NCOPE is a sub-protocol for optimizing the COPE algorithm by iteration. In NCOPE, packets are automatically matched by size to be coded. As a result, it improves the coding gain in some level. On the other hand, we adopt the partial Acknowledgement retransmission scheme to achieve high compactness and robustness. ACK is an independent packet with the highest priority rather than a part of the data packets. Compared with existing works on opportunistic network coding, our approach ensures the reliability of wireless links and improves the coding gain. Read more

Recommended citation: Jing Chen, Tong Li, Ruiying Du, Jianming Fu, Jianwei Liu. "Efficient reliable opportunistic network coding based on hybrid flow in wireless network." China Communications, vol. 8, no. 4, pp. 125-131, 2011. PDF

## The 2ACT Model-based Evaluation for In-network Caching Mechanism

Published in IEEE ISCC, 2013

With the popularity of information and content items that can be cached within ISP networks, developing high-quality and efficient content distribution approaches has become an important task in future internet architecture design. As one of the main techniques of content distribution, in-network caching mechanism has attracted attention from both academia and industry. However, the general evaluation model of in-network caching is seldom discussed. The trade-off between economic cost and the deployment of in-network caching still remains largely unclear, especially for heterogeneous applications. We take a first yet important step towards the design of a better evaluation model based on the Application Adaptation CapaciTy (2ACT) of the architecture to quantify the trade-off in this paper. Based on our evaluation model, we further clarify the deployment requirements for the in-network caching mechanism. Based on our findings, ISPs and users can make their own choice according to their application scenarios. Read more

Recommended citation: Ke Xu, Min Zhu, Ning Wang, Song Lin, Haiyang Wang and Tong Li, "The 2ACT Model-based Evaluation for In-network Caching Mechanism." IEEE Symposium on Computers and Communications (ISCC), pp. 636-641, 2013. PDF

## Achieving Optimal Traffic Engineering Using a Generalized Routing Framework

Published in IEEE TPDS, 2015

The open shortest path first (OSPF) protocol has been widely applied to intra-domain routing in today's Internet. Since a router running OSPF distributes traffic uniformly over equal-cost multi-path (ECMP), the OSPF-based optimal traffic engineering (TE) problem (i.e., deriving optimal link weights for a given traffic demand) is computationally intractable for large-scale networks. Therefore, many studies resort to multi-protocol label switching (MPLS) based approaches to solve the optimal TE problem. In this paper we present a generalized routing framework to realize the optimal TE, which can be potentially implemented via OSPFor MPLS-based approaches. We start with viewing the conventional optimal TE problem in a fresh way, i.e., optimally allocating the residual capacity to every link. Then we make a generalization of network utility maximization (NUM) to close this problem, where the network operator is associated with a utility function of the residual capacity to be maximized. We demonstrate that under this framework, the optimal routes resulting from the optimal TE are also the shortest paths in terms of a set of non-negative link weights that are explicitly determined by the optimal residual capacity and the objective function. The network entropy maximization theory is employed to enable routers to exponentially, instead of uniformly, split traffic over ECMP. The shortest-path penalizing exponential flow-splitting (SPEF) is designed as a link-state protocol with hop-by-hop forwarding to implement our theoretical findings. An alternative MPLS-based implementation is also discussed here. Numerical simulation results have demonstrated the effectiveness of the proposed framework as well as SPEF. Read more

Recommended citation: Ke Xu, Meng Shen, Hongying Liu, Jiangchuan Liu, Fan Li and Tong Li, "Achieving Optimal Traffic Engineering Using a Generalized Routing Framework." IEEE Transactions on Parallel and Distributed Systems (TPDS), vol. 27, no. 1, pp. 51-65, 2015. PDF

## Research on Mobile Data Subsidy Model and Case Study

Published in Journal of Computer Research and Development, 2016

This is a paper written in Chinese, please refer to the original website for details. Read more

Recommended citation: Hui Su, Ke Xu, Meng Shen, Yong Wang, Yifeng Zhong, Tong Li. "Research on Mobile Data Subsidy Model and Case Study." Journal of Computer Research and Development (in Chinese), vol. 53, no. 4, pp. 861-872, 2016. PDF

## Modeling, Analysis, and Implementation of Universal Acceleration Platform Across Online Video Sharing Sites

Published in IEEE TSC, 2016

User-generated video sharing service has attracted a vast number of users over the Internet. The most successful sites, such as YouTube and Youku, now enjoy millions of videos being watched every day. Yet, given limited network and server resources, the user experience of existing video sharing sites (VSSes) is still far from being satisfactory. To mitigate such a problem, peer-to-peer (P2P) based video accelerators have been widely suggested to enhance the video delivery on VSSes. In this paper, we find that the interference of multiple accelerators will lead to a severe bottleneck across the VSSes. Our model analysis shows that a universal video accelerator can naturally achieve better performance with lower deployment cost. Based on this observation, we further present the detailed design of Peer-to-Peer Video Accelerator (PPVA), a real-world system for universal and transparent P2P accelerating. Such a system has already attracted over 180 million users, with 48 million video transactions every day. We carefully examine the PPVA performance from extensive measurements. Our trace analysis indicates that it can significantly reduce server bandwidth cost and accelerate the video download speed by 80 percent. Read more

Recommended citation: Ke Xu, Tong Li*, Haiyang Wang, Haitao Li, Wei Zhu, Jiangchuan Liu and Song Lin. "Modeling, Analysis, and Implementation of Universal Acceleration Platform Across Online Video Sharing Sites." IEEE Transactions on Services Computing (TSC), vol.11, no.3, pp. 534-548, 2016. (*Corresponding author) PDF

## Towards Minimal Tardiness of Data-intensive Applications in Heterogeneous Networks

Published in IEEE ICCCN, 2016

The increasing data requirement of Internet applications has driven a dramatic surge in developing new programming paradigms and complex scheduling algorithms to handle data-intensive workloads. Due to the expanding volume and the variety of such flows, their raw data are often processed on intermediate processing nodes before being sent to servers. The intermediate processing constraints are however not yet considered in existing task and flow computing models. In this paper, we aim to minimize the total tardiness of all flows in the presence of intermediate processing constraints. We build a model to consider Tardiness-aware Flow Scheduling with Processing constraints (TFS-P), which is unfortunately NP-Hard. Hence, we propose a heuristic Routing and Scheduling duplex MATching (RSMAT) framework based on the classic Gale-Shapley Matching Theory. We find that the problem can be well-addressed by classic Deferred Acceptance (DA) algorithm, in which the match is stable but inefficient for the model. We therefore propose the Tardiness-aware Deferred Acceptance algorithm with Dynamical Quota (TDA-DQ). This algorithm is enhanced by overcoming the inefficient stability and smartly considering the dynamical quota in the system. The evaluation compares TDA-DQ to the lower bound obtained by a modified subgradient optimization algorithm. The result indicates that TDA-DQ can achieve near-optimal performance for data-intensive applications. Read more

Recommended citation: Tong Li, Ke Xu, Meng Shen, Haiyang Wang, Kun Yang, and Yuchao Zhang. "Towards Minimal Tardiness of Data-intensive Applications in Heterogeneous Networks." IEEE International Conference on Computer Communication and Networks (ICCCN), pp. 1-9, 2016. PDF

Published in IEEE ICDCS, 2017

Recommended citation: Tong Li, Chathura Sarathchandra Magurawalage, Kezhi Wang, Ke Xu, Kun Yang, Haiyang Wang. "On efficient offloading control in cloud radio access network with mobile edge computing". IEEE International Conference on Distributed Computing Systems (ICDCS), pp. 2258-2263, 2017. PDF

## Going Fast and Fair: Latency Optimization for Cloud-Based Service Chains

Published in IEEE Network, 2017

State-of-the-art microservices have been attracting more attention in recent years. A broad spectrum of online interactive applications are now programmed to service chains on the cloud, seeking better system scalability and lower operating costs. Different from the conventional batch jobs, most of these applications consist of multiple stand-alone services that communicate with each other. These step-by-step operations unavoidably introduce higher latency to the delay-sensitive chained services. In this article, we aim at designing an optimization approach for reducing the latency of chained services. Specifically, presenting the measurement and analysis of chained services on Baidu's cloud platform, our real-world trace indicates that these chained services are suffering from significantly high latency because they are mostly handled by different queues on cloud servers for multiple times. However, such a unique feature introduces significant challenges to optimize a microservice's overall queueing delay. To address this problem, we propose a delay-guaranteed approach to accelerate the overall queueing of chained services while obtaining fairness across all the workloads. Our evaluations on Baidu servers shows that the proposed design can successfully reduce the latency of chained services by 35 percent with minimal impact on other workloads. Read more

Recommended citation: Yuchao Zhang, Ke Xu, Haiyang Wang, Qi Li, Tong Li, and Xuan Cao. "Going Fast and Fair: Latency Optimization for Cloud-Based Service Chains". IEEE Network, pp. 138-143, 2017. PDF

## Social Account Linking via Weighted Bipartite Graph Matching

Published in Wiley IJCS, 2017

Along with the increasing popularity of online social network (OSN), it is common that the same user holds many accounts among different OSNs (eg, Facebook, Twitter, WeChat, QQ). In this scenario, an interesting and challenging problem arises: how to link accounts among OSNs belonged to a natural person, which is also known as a graph matching problem. The solution helps understand user behaviors and offer better services. To solve the account linking problem, various techniques for OSNs have been proposed. However, most existing methods assume specific OSN features impractical in general OSNs and unscalable to large_scale OSNs. To address these shortcomings, in this paper, we remodel the account linking problem into maximum matching on weighted bipartite graphs and utilize the Kuhn_Munkres algorithm to solve it. In our solution, we capture user profile, user online time distribution, and user interest as features to describe user accounts and measure account similarity, which is used as weight of edge in bipartite graphs. Then, the maximum matching on weighted bipartite graphs is solved with the Kuhn_Munkres algorithm. The experiments conducted on the real datasets show that our solution outperforms the baseline methods with 11%, 17%, and 29% on average in precision, recall, and F1 score, respectively. Read more

Recommended citation: Jiangtao Ma, Yaqiong Qiao, Guangwu Hu, Tong Li, Yongzhong Huang, Yanjun Wang, Chaoqin Zhang. "Social Account Linking via Weighted Bipartite Graph Matching". International Journal of Communication Systems (IJCS), vol.31, no.7, pp. 1-17, 2017. PDF

## A Measurement Study on Multi-path TCP with Multiple Cellular Carriers on High-speed Rails

Published in ACM SIGCOMM, 2018

Recent advances in high speed rails (HSRs) are propelling the need for acceptable network service in high speed mobility environments. However, previous studies show that the performance of traditional single-path transmission degrades significantly during high speed mobility due to frequent handoff. Multi-path transmission with multiple carriers is a promising way to enhance the performance, because at any time, there is possibly at least one path not suffering a handoff. In this paper, for the first time, we measure multi-path TCP (MPTCP) with two cellular carriers on HSRs with a peak speed of 310 km/h. We find a significant difference in handoff time between the two carriers. Moreover, we observe that MPTCP can provide much better performance than TCP in the poorer of the two paths. This indicates that MPTCP's robustness to handoff is much higher than TCP's. However, the efficiency of MPTCP is far from satisfactory. MPTCP performs worse than TCP in the better path most of the time. We find that the low efficiency can be attributed to poor adaptability to frequent handoff by MPTCP's key operations in sub-flow establishment, congestion control and scheduling. Finally, we discuss possible directions for improving MPTCP for such scenarios. Read more

Recommended citation: Li Li, Ke Xu, Tong Li, Kai Zheng, Chunyi Peng, Dan Wang, Xiangxiang Wang, Meng Shen, Rashid Mijumbi. "A Measurement Study on Multi-path TCP with Multiple Cellular Carriers on High-speed Rails." Proceedings of the 2018 Conference of the ACM Special Interest Group on Data Communication (ACM SIGCOMM), pp. 161-175, 2018. PDF

## Towards Cloud-Based Distributed Interactive Applications: Measurement, Modeling, and Analysis

Published in ACM/IEEE TON, 2018

With the prevalence of broadband network and wireless mobile network accesses, distributed interactive applications (DIAs) such as online gaming have attracted a vast number of users over the Internet. The deployment of these systems, however, comes with peculiar hardware/software requirements on the user consoles. Recently, such industrial pioneers as Gaikai, Onlive, and Ciinow have offered a new generation of cloud-based DIAs (CDIAs), which shifts the necessary computing loads to cloud platforms and largely relieves the pressure on individual user's consoles. In this paper, we aim to understand the existing CDIA framework and highlight its design challenges. Our measurement reveals the inside structures as well as the operations of real CDIA systems and identifies the critical role of cloud proxies. While its design makes effective use of cloud resources to mitigate client's workloads, it may also significantly increase the interaction latency among clients if not carefully handled. Besides the extra network latency caused by the cloud proxy involvement, we find that computation-intensive tasks (e.g., game video encoding) and bandwidth-intensive tasks (e.g., streaming the game screens to clients) together create a severe bottleneck in CDIA. Our experiment indicates that when the cloud proxies are virtual machines (VMs) in the cloud, the computation-intensive and bandwidth-intensive tasks may seriously interfere with each other. We accordingly capture this feature in our model and present an interference-aware solution. This solution not only smartly allocates workloads but also dynamically assigns capacities across VMs based on their arrival/departure patterns. Read more

Recommended citation: Haiyang Wang, Tong Li*, Ryan Shea, Xiaoqiang Ma, Feng Wang, Jiangchuan Liu, Ke Xu*. "Towards Cloud-Based Distributed Interactive Applications: Measurement, Modeling, and Analysis." ACM/IEEE Transactions on Networking (TON), vol.26, no.1, pp. 3-16, 2018. (*Corresponding author) PDF

## Communication and Computation Cooperation in Cloud Radio Access Network with Mobile Edge Computing

Published in CCF TON, 2018

Recommended citation: Tong Li, Kezhi Wang, Ke Xu, Kun Yang, Chathura Sarathchandra Magurawalage, Haiyang Wang. "Communication and Computation Cooperation in Cloud Radio Access Network with Mobile Edge Computing." CCF Transactions on Networking (CTON), pp. 43-52, 2018. PDF

## A Hierarchical Cooperative Caching Strategy for Mobile Content Delivery Network

Published in Chinese Journal of Computers, 2018

This is a paper written in Chinese, please refer to the original website for details. Read more

Recommended citation: Zhicheng Ge, Ke Xu, Liang Chen, Tong Li, Long Yao, and Meng Shen. "A Hierarchical Cooperative Caching Strategy for Mobile Content Delivery Network." Chinese Journal of Computers (in Chinese), vol.41, no.12, pp. 2769-2786, 2018. PDF

## ABQ: Active Buffer Queueing in Datacenters

Published in IEEE Network, 2019

Congestion control is always an active research field for guaranteeing the Quality of Services (QoS) of datacenter networks (DCNs). However, the current end-to-end TCP design enables both senders and receivers not to directly and precisely obtain the congestion information, incurring inaccurate or non-real-time adjustments. Moreover, switches that act as fundamental primitives in DCN are usually used for reactive congestion feedbacks (e.g., Ack and ECN), leading to underused for proactive congestion control. In this article, we propose a novel active queue management (AQM) scheme called Active Buffer Queueing (ABQ) which leverages active buffer queueing of DCN switches to achieve both high-throughput and loss-free transmissions. When the traffic pattern in DCN is changed intensely in flow size, number and interval, the feedback information to TCP end hosts are imprecise. Unlike other AQMs, the key idea of ABQ is to adjust the flow rate (or packet pace) directly in the switch according to the real-time congestion state. We explain the design rationale behind ABQ and present simulation results of its performance. Finally, we discuss the implementation on the NetFPGA. Read more

Recommended citation: Lei Xu, Ke Xu, Tong Li, Kai Zheng, Meng Shen, Xiaojiang Du and Xinle Du. "ABQ: Active Buffer Queueing in Datacenters." IEEE Network, pp. 232-237, 2019. PDF

## Minimizing Tardiness for Data-intensive Applications in Heterogeneous Systems: A Matching Theory Perspective

Published in IEEE TPDS, 2020

The increasing data requirements of Internet applications have driven a dramatic surge in developing new programming paradigms and complex scheduling algorithms to handle data-intensive workloads. Due to the expanding volume and the variety of such flows, their raw data are often processed on Intermediate Processing Nodes (IPNs) before being sent to servers. However, the intermediate processing constraint is rarely considered in existing flow computing models. This paper aims to minimize the tardiness of data-intensive applications in the presence of intermediate processing constraint. Motivating cases show that the tardiness is affected by both IPN locations and flow dispatching strategies. Based on the observation that dispatching flows to IPNs is essentially building a matching between flows and IPNs, a novel solution is proposed based on matching theory. In the deployment phase, a tardiness-aware deferred acceptance algorithm is developed to optimize IPN locations. In the operation phase, the Power-of-D paradigm and matching theory are combined together to dispatch flows efficiently. Evaluation results show that our solution effectively minimizes the total tardiness of data-intensive applications in heterogeneous systems. Read more

Recommended citation: Ke Xu, Liang Lv, Tong Li*, Meng Shen, Haiyang Wang, Kun Yang. "Minimizing Tardiness for Data-intensive Applications in Heterogeneous Systems: A Matching Theory Perspective." IEEE Transactions on Parallel and Distributed Systems (TPDS), vol.31, no.1, pp. 144-158, 2020. (*Corresponding author) PDF

## TACK: Improving Wireless Transport Performance by Taming Acknowledgments

Published in ACM SIGCOMM, 2020

The shared nature of the wireless medium induces contention between data transport and backward signaling, such as acknowledgement. The current way of TCP acknowledgment induces control overhead which is counter-productive for TCP performance especially in wireless local area network (WLAN) scenarios. In this paper, we present a new acknowledgement called TACK ("Tame ACK"), as well as its TCP implementation TCP-TACK. TCP-TACK works on top of commodity WLAN, delivering high wireless transport goodput with minimal control overhead in the form of ACKs, without any hardware modification. To minimize ACK frequency, TACK abandons the legacy received-packet-driven ACK. Instead, it balances byte-counting ACK and periodic ACK so as to achieve a controlled ACK frequency. Evaluation results show that TCP-TACK achieves significant advantages over legacy TCP in WLAN scenarios due to less contention between data packets and ACKs. Specifically, TCP-TACK reduces over 90% of ACKs and also obtains an improvement of ~28% on goodput. We further find it performs equally well as high-speed TCP variants in wide area network (WAN) scenarios, this is attributed to the advancements of the TACK-based protocol design in loss recovery, round-trip timing, and send rate control. Read more

Recommended citation: Tong Li, Kai Zheng, Ke Xu, Rahul Arvind Jadhav, Tao Xiong, Keith Winstein, and Kun Tan. "TACK: Improving Wireless Transport Performance by Taming Acknowledgments." Proceedings of the 2020 Conference of the ACM Special Interest Group on Data Communication (ACM SIGCOMM), pp. 15-30, 2020. PDF

## Talk 1 on Relevant Topic in Your Field

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## Conference Proceeding talk 3 on Relevant Topic in Your Field

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## Teaching experience 1

Undergraduate course, University 1, Department, 2014

This is a description of a teaching experience. You can use markdown like any other post. Read more

## Teaching experience 2

Workshop, University 1, Department, 2015

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