In cognitive radio networks (CRNs), primary users (PUs) can leverage secondary users (SUs) as cooperative relays to increase their transmission rates, while SUs will in return obtain more spectrum access opportunities, leading to cooperative CRNs (CCRNs). Prior research works in CCRNs mainly focus on providing ubiquitous access and high throughput for users, but have rarely taken energy efficiency into consideration. Besides, most existing works assume that the SUs are passively selected by PUs regardless of SUs' willingness to help, which is obviously not practical. To address energy issue, this paper proposes an energy-efficient cooperative strategy by leveraging temporal and spatial diversity of the primary network. Specifically, SUs with delay-Tolerant packets can proactively make the cooperative decisions by jointly considering primary channel availability, channel state information, PUs' traffic load, and their own transmission requirements. We formulate this decision-making problem based on the optimal stopping theory to maximize SUs' energy efficiency. We solve this problem using a dynamic programming approach and derive the optimal cooperative policy. Extensive simulations are then conducted to evaluate the performance of our proposed strategy. The results show significant improvements of SUs' energy efficiency compared with existing cooperative schemes, which demonstrate the benefits of our proposed cooperative strategy in conserving energy for SUs.

Jianqing Liu;Haichuan Ding;Ying Cai;Hao Yue;玉光 方;式刚 陈

IEEE Journal on Selected Areas in Communications

2016-12

Most existing P2P networks route requests in O( kN ^1/k ), O(log N), O(log N/log k) hops, where N is the number of participating nodes and k is an adjustable parameter. Although some can achieve O(d)-hop routing for a constant d by tuning the parameter k, the neighbor locations however become a function of N, causing considerable maintenance overhead if the user base is highly dynamic as witnessed by the deployed systems. This paper explores the design space using the simple uniformly-random neighbor selection strategy, and proposes a random peer-to-peer network that is the first of its kind to resolve requests in d hops with a chosen probability of 1 - c, where c is a constant. The number of neighbors per node is within a constant factor from the optimal complexity O(N ^1/d ) for any network whose routing paths are bounded by d hops.

Shiping Chen;Yuan Li;Kaihua Rao;Lei Zhao;Tao Li;式刚 陈

2008

We demonstrate that CSMA/CA networks, including IEEE 802.11 networks, exhibit severe fairness problem in many scenarios, where some hosts obtain most of the channel's bandwidth while others starve. Most existing solutions require nodes to overhear transmissions made by contending nodes and, based on the overheard information, adjust local rates to achieve fairness among all contending links. Their underlying assumption is that transmissions made by contending nodes can be overheard. However, this assumption holds only when the transmission range is equal to the carrier sensing range, which is not true in reality. As our study reveals, the overhearing-based solutions, as well as several non-overhearing AIMD solutions, cannot achieve MAC-layer fairness in various settings. We propose a new rate control protocol, called PISD (Proportional Increase Synchronized multiplicative Decrease). Without relying on overhearing, it provides fairness in CSMA/CA networks, particularly IEEE 802.11 networks, by using only local information and performing localized operations. It combines several novel rate control mechanisms, including synchronized multiplicative decrease, proportional increase, and background transmission. We prove that PISD converges and achieves (weighted) fairness.

Ying Jian;式刚 陈

2008

Distributed denial of service (DDoS) has long been an open security problem of the Internet. Most proposed solutions require the upgrade of routers across the Internet, which is extremely difficult to realize, considering that the Internet consists of a very large number of autonomous systems with routers from different vendors deployed over decades. A promising alternative strategy is to avoid the universal upgrade of router infrastructure and instead rely on an overlay of end systems. The prior anti-DoS overlays were designed to protect emergency services for authorized clients. They assume that trust exists between authorized clients and a private server. Only authenticated traffic can pass through the overlay network to reach the server, while the attack traffic is not admitted without passing the authentication. The follow-up extension of the anti-DoS overlays for web service has other serious limitations. This paper attempts to solve an important problem. How to design an anti-DoS overlay service (called AID) that protects general-purpose public servers while overcoming the limitations of the existing systems? Anyone, including the attackers, should be able to access the server. Authentication can no longer be the means of defense. While both normal and malicious clients are given the access, AID is designed to fend off attack traffic while letting legitimate-traffic through. Its operations are completely transparent to the users (humans or hosts), the client/server software, and the internal/core routers. To connect the AID service nodes (which are end systems), we choose a random overlay network for its rich, unpredictable connectivity, short diameter, and ease of management. We use a distributed virtual-clock packet scheduling algorithm to restrict the amount of data any client can impose on AID. We analyze the properties of the AID service based on probabilistic models. Our simulations demonstrate that AID can effectively protect legitimate-traffic from attack traffic. Even when 10% of all clients attack, just 1.4% of legitimate-traffic is mistakenly blocked, no matter how aggressive the attackers are.

式刚 陈;Yibei Ling;Randy Chow;Ye Xia

Computer Networks

2007-10-24

Yi Cui;Ben Y. Zhao;式刚 陈

Advances in Multimedia

2007

Today's peer-to-peer networks are designed based on the assumption that the participating nodes are cooperative, which does not hold in reality. Incentive mechanisms that promote cooperation must be introduced. However, the existing incentive schemes (using either reputation or virtual currency) suffer from various attacks based on false reports. Even worse, a colluding group of malicious nodes in a peer-to-peer network can manipulate the history information of its own members, and the damaging power increases dramatically with the group size. Such malicious nodes/collusions are difficult to detect, especially in a large network without a centralized authority. In this paper, we propose a new distributed incentive scheme, in which the amount that a node can benefit from the network is proportional to its contribution, malicious nodes can only attack others at the cost of their own interests, and a colluding group cannot gain advantage by cooperation regardless of its size. Consequently, the damaging power of colluding groups is strictly limited. The proposed scheme includes three major components: a distributed authority infrastructure, a key sharing protocol, and a contract verification protocol.

Zhan Zhang;式刚 陈;Zhen Mo;Myungkeun Yoon

Journal of Parallel and Distributed Computing

2012-12

Persistent spread measurement is to count the number of distinct elements that persist in each network flow for predefined time periods. It has many practical applications, including detecting long-term stealthy network activities in the background of normal-user activities, such as stealthy DDoS attack, stealthy network scan, or faked network trend, which cannot be detected by traditional flow cardinality measurement. With big network data, one challenge is to measure the persistent spreads of a massive number of flows without incurring too much memory overhead as such measurement may be performed at the line speed by network processors with fast but small on-chip memory. We propose a highly compact Virtual Intersection HyperLogLog (VI-HLL) architecture for this purpose. It achieves far better memory efficiency than the best prior work of V-Bitmap, and in the meantime drastically extends the measurement range. Theoretical analysis and extensive experiments demonstrate that VI-HLL provides good measurement accuracy even in very tight memory space of less than 1 bit per flow.

You Zhou;Yian Zhou;Min Chen;式刚 陈

Performance Evaluation Review

2017-6-5

This paper formulates a bi-objective optimization model to determine timing plans for coordinated traffic signals along arterials to minimize traffic delay and the risk associated with human exposure to traffic emissions. Based on a cell-transmission representation of traffic dynamics, a modal sensitive emission approach is used to estimate the tailpipe emission rate for each cell of a signalized arterial. A cell-based Gaussian plume air dispersion model is then employed to capture the dispersion of air pollutants and compute the roadside pollutant concentrations. A measure of mean excess exposure is further defined to represent the risk associated with human exposure to traffic pollutants under the wind uncertainty. A signal timing optimization model is formulated to optimize the cycle length, offsets, green splits and phase sequences to minimize the total system delay and the mean excess exposure simultaneously. The bi-objective optimization model is solved via a simulation-based genetic algorithm to find a set of Pareto optimal solutions. A numerical example is presented to demonstrate the model.

Lihui Zhang;Yafeng Yin;式刚 陈

Transportation Research Part C: Emerging Technologies

2013-4

This chapter discusses the measurement of per-flow sizes for high-speed links. It is a particularly difficult problem because of the need to process and store a huge amount of information, which makes it difficult for the measurement module to fit in the small but fast SRAM space (in order to operate at the line speed). We provide a novel measurement function that estimates the sizes of all flows. It delivers good performance in tight memory space where other approaches no longer work. The effectiveness of the online per-flow measurement approach is analyzed and confirmed through extensive experiments based on real network traffic traces.The rest of this chapter is organized as follows: Sect. 2.1 discusses the performance metrics. Section 2.2 gives an overview of the system design. Section 2.3 discusses the state of the art. Section 2.4 presents the online data encoding module. Sections 2.5–2.6 present two offline data decoding modules. Section 2.7 discusses the problem of setting counter length. Section 2.8 addresses the problem of collecting flow labels. Section 2.9 presents the experimental results. Section 2.10 extends the estimators for large flow sizes. Section 2.11 gives the summary.

Tao Li;式刚 陈

2013

For data-collection applications in sensor networks, it is important to ensure all data sources have equal (or weighted) access to network bandwidth so that the base stations receive a complete picture about the monitored area. We point out the fairness problem in the current design of sensor networks, which may cause extremely biased bandwidth allocations. It is a challenge to design a fully distributed fairness solution due to the lack of global knowledge about the distribution of data sources and their routing paths. This paper proposes a new aggregate fairness model and a localized algorithm (called AFA) that implements the model. AFA is designed to work with any routing protocol. In particular, it allows the packets from a data source to follow an arbitrary set of forwarding paths to the base stations. This flexibility makes it considerably harder to allocate bandwidth fairly among different data sources. AFA solves the problem with only localized operations at the sensors. It is easy to implement, which is an attractive property for sensor networks. Moreover, the algorithm automatically adjusts a sensor's forwarding rate to avoid packet drops due to downstream congestion, which helps improve energy efficiency. We perform extensive simulations, demonstrating that the proposed algorithm can effectively improve end-to-end fairness.

式刚 陈;Zhan Zhang

2006