Kejie Lu

Analysis of blocking probability for distributed lightpath establishment in WDM optical networks

In this paper, we analyze the blocking probability of distributed lightpath establishment in wavelength-routed WDM networks by studying the two basic methods: destination-initiated reservation (DIR) and source-initiated reservation (SIR). We discuss three basic types of connection blocking: 1) blocking due to insufficient network capacity; 2) blocking due to outdated information; and 3) blocking due to over-reservation. It is shown that the proposed models are highly accurate for both the DIR and the SIR methods, in both the regular and irregular network topologies, under the whole range of traffic loads.

A Survey on Platoon-Based Vehicular Cyber-Physical Systems

Vehicles on the road with some common interests can cooperatively form a platoon-based driving pattern, in which a vehicle follows another vehicle and maintains a small and nearly constant distance to the preceding vehicle. It has been proved that, compared with driving individually, such a platoon-based driving pattern can significantly improve road capacity and energy efficiency. Moreover, with the emerging vehicular ad hoc network (VANET), the performance of a platoon in terms of road capacity, safety, energy efficiency, etc., can be further improved. On the other hand, the physical dynamics of vehicles inside the platoon can also affect the performance of a VANET. Such a complex system can be considered a platoon-based vehicular cyber-physical system (VCPS), which has attracted significant attention recently. In this paper, we present a comprehensive survey on a platoon-based VCPS. We first review the related work of a platoon-based VCPS. We then introduce two elementary techniques involved in a platoon-based VCPS, i.e., the vehicular networking architecture and standards, and traffic dynamics, respectively. We further discuss the fundamental issues in a platoon-based VCPS, including vehicle platooning/clustering, cooperative adaptive cruise control, platoon-based vehicular communications, etc., all of which are characterized by the tightly coupled relationship between traffic dynamics and VANET behaviors. Since system verification is critical to VCPS development, we also give an overview of VCPS simulation tools. Finally, we share our view on some open issues that may lead to new research directions.

Shared fiber delay line buffers in asynchronous optical packet switches

Packet contention is a major issue in asynchronous optical packet switching networks. Optical buffering, which is implemented by fiber delay lines (FDLs), is fundamental to many optical switch implementations for resolving contention. Most existing optical buffering implementations are output-based and require a huge amount of FDLs as well as larger switch sizes, which impose extra cost on the overall system. In this paper, we consider a shared optical buffering architecture which can reduce the buffer size at a switch. We propose an analytical model to evaluate the packet loss probability and the average delay For shared buffers at a single switch. We then compare the performance of output buffers to shared buffers under different granularities of FDLs. We observe that, by choosing an appropriate granularity, the shared buffering scheme can significantly reduce packet loss with much smaller switch sizes and fewer FDLs than the output buffering architecture. The accuracy of the analytical model is also confirmed by extensive simulation

WIRELESS BROADBAND ACCESS: WIMAX AND BEYOND - A Secure and Service-Oriented Network Control Framework for WiMAX Networks

WiMAX, worldwide interoperability for microwave access, is an emerging wireless communication system that can provide broadband access with large-scale coverage. As a cost-effective solution, multihop communication is becoming more and more important to WiMAX systems. To successfully deploy multihop WiMAX networks, security is one of the major challenges that must be addressed. Another crucial issue is how to support different services and applications in WiMAX networks. Since WiMAX is a relatively new standard, very little work has been presented in the literature. In this article we propose a secure and service-oriented network control framework for WiMAX networks. In the design of this framework we consider both the security requirements of the communications and the requirements of potential WiMAX applications that have not been fully addressed previously in the network layer design. The proposed framework consists of two basic components: a service-aware control framework and a unified routing scheme. Besides the design of the framework, we further study a number of key enabling technologies that are important to a practical WiMAX network. Our study can provide a guideline for the design of a more secure and practical WiMAX network

A framework for a distributed key management scheme in heterogeneous wireless sensor networks

Key management has become a challenging issue in the design and deployment of secure wireless sensor networks. A common assumption in most existing distributed key management schemes is that all sensor nodes have the same capability. However, recent research works have suggested that connectivity and lifetime of a sensor network can be substantially improved if some nodes are given greater power and transmission capability. Therefore, how to exploit those heterogeneity features in design of a good distributed key management scheme has become an important issue. This paper proposes a unified framework for distributed key management schemes in heterogeneous wireless sensor networks. Analytical models are developed to evaluate its performance in terms of connectivity, reliability, and resilience. Extensive simulation results show that, even with a small number of heterogeneous nodes, the performance of a wireless sensor network can be improved substantially. It is also shown that our analytical models can be used to accurately predict the performance of wireless sensor networks under varying conditions.

Call Admission Control Optimization in WiMAX Networks

Worldwide interoperability for microwave access (WiMAX) is a promising technology for last-mile Internet access, particularly in the areas where wired infrastructures are not available. In a WiMAX network, call admission control (CAC) is deployed to effectively control different traffic loads and prevent the network from being overloaded. In this paper, we propose a framework of a 2-D CAC to accommodate various features of WiMAX networks. Specifically, we decompose the 2-D uplink and downlink WiMAX CAC problem into two independent 1-D CAC problems and formulate the 1-D CAC optimization, in which the demands of service providers and subscribers are jointly taken into account. To solve the optimization problem, we develop a utility- and fairness-constrained optimal revenue policy, as well as its corresponding approximation algorithm. Simulation results are presented to demonstrate the effectiveness of the proposed WiMAX CAC approach.

Robust and efficient detection of DDoS attacks for large-scale internet

In recent years, distributed denial of service (DDoS) attacks have become a major security threat to Internet services. How to detect and defend against DDoS attacks is currently a hot topic in both industry and academia. In this paper, we propose a novel framework to robustly and efficiently detect DDoS attacks and identify attack packets. The key idea of our framework is to exploit spatial and temporal correlation of DDoS attack traffic. In this framework, we design a perimeter-based anti-DDoS system, in which traffic is analyzed only at the edge routers of an internet service provider (ISP) network. Our framework is able to detect any source-address-spoofed DDoS attack, no matter whether it is a low-volume attack or a high-volume attack. The novelties of our framework are (1) temporal-correlation based feature extraction and (2) spatial-correlation based detection. With these techniques, our scheme can accurately detect DDoS attacks and identify attack packets without modifying existing IP forwarding mechanisms at routers. Our simulation results show that the proposed framework can detect DDoS attacks even if the volume of attack traffic on each link is extremely small. Especially, for the same false alarm probability, our scheme has a detection probability of 0.97, while the existing scheme has a detection probability of 0.17, which demonstrates the superior performance of our scheme.

Integrated Downlink Resource Management for Multiservice WiMAX Networks

In this paper, we propose a novel downlink resource management framework for multiservice WiMAX (worldwide interoperability for microwave access) networks. Our framework consists of two major components: adaptive power allocation (APA) and call admission control (CAC). We formulate each of them as an optimization problem, where the demands of both WiMAX service providers and subscribers are taken into account. To solve the optimization problems, we develop a fairness-constrained greedy revenue algorithm for downlink APA optimization and a utility-constrained greedy approximation algorithm for downlink CAC optimization. Our simulation results show that, when combining the APA and CAC optimization methods together, the proposed resource management framework can meet the expectations of both service providers and subscribers

Performance Analysis of Wireless Sensor Networks With Mobile Sinks

In wireless sensor networks (WSNs), one major challenge is how to prolong the network lifetime while maintaining a certain data collection rate for resource-limited static sensors. To achieve this goal, many mobility-assisted data collection (MADC) schemes have been proposed in the literature. However, there is a lack of systematic analysis on the behaviors of the MADC models in terms of both throughput capacity, which is defined as the maximal data collection rate, and lifetime, which will be associated with a specific data collection rate. In this paper, we address this issue in a large-scale WSN with mobile sinks from a theoretical perspective, which has not yet been studied. In particular, we first propose a general MADC model that includes many important parameters such as the number of mobile sinks, the velocity of a mobile sink, and the traveling path of a mobile node. We then develop a comprehensive theoretical approach to obtain the achievable throughput capacity and lifetime. By applying the proposed approach, we investigate the behaviors of WSNs with one or more mobile sinks. Our analysis not only shows how a WSN with mobile sinks can outperform a static WSN but also provides insights on how we can adjust the MADC parameters to improve the data collection rate and to maximize the lifetime. Finally, our analysis is validated through extensive simulations.

A Secure VANET MAC Protocol for DSRC Applications

Vehicular ad hoc networking is an important component of Intelligent Transportation Systems. The main benefit of vehicular ad hoc network (VANET) communication is seen in active safety systems that increase passenger safety by exchanging warning messages between vehicles. Other applications and private services are also permitted in order to lower the cost and to encourage VANET deployment and adoption. Dedicated Short Range Communications (DSRC) is a key enabling technology for VANET applications and services. There are many challenges that must be addressed before VANETs can be successfully deployed. Among these challenges is designing of security mechanisms to secure VANETs against abuse, and designing of efficient medium access control (MAC) protocols so that safety related and other application messages can be timely and reliably disseminated through VANETs. In this paper we propose a secure MAC protocol for VANETs, with different message priorities for different types of applications to access DSRC channels. Our simulations and analysis show that the proposed MAC protocol can provide secure communications while guarantee the reliability and latency requirements of safety related DSRC applications for VANETs.