Gaoxi Xiao

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discuss three basic types of connection blocking: 1) blocking due to insufficient network capacity; 2) blocking due to outdated information; and 3) blocking due to over-reservation.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.

Algorithms for allocating wavelength converters in all-optical networks

In an all-optical wide area network, some network nodes may handle heavier volumes of traffic. It is desirable to allocate more full-range wavelength converters (FWCs) to these nodes, so that the FWCs can be fully utilized to resolve wavelength conflict. We propose a set of algorithms for allocating FWCs in all-optical networks. We adopt the simulation-based optimization approach, in which we collect utilization statistics of FWCs from computer simulations and then perform optimization to allocate the FWCs. Therefore, our algorithms are widely applicable and they are not restricted to any particular model or assumption. We have conducted extensive computer simulations on regular and irregular networks under both uniform and nonuniform traffic. Compared with the best existing allocation, the results show that our algorithms can significantly reduce: (1) the overall blocking probability (i.e., better mean quality of service) and (2) the maximum of the blocking probabilities experienced at all the source nodes (i.e., better fairness). Equivalently, for a given performance requirement on blocking probability, our algorithms can significantly reduce the number of FWCs required.

Clustering algorithms for maximizing the lifetime of wireless sensor networks with energy-harvesting sensors

Motivated by recent developments in Wireless Sensor Networks (WSNs), we present several efficient clustering algorithms for maximizing the lifetime of WSNs, i.e., the duration till a certain percentage of the nodes die. Specifically, an optimization algorithm was proposed for maximizing the lifetime of a single-cluster network, followed by an extension to handle multi-cluster networks. Then we study the joint problem of prolonging network lifetime by introducing energy-harvesting (EH) nodes. An algorithm is proposed for maximizing the network lifetime where EH nodes serve as dedicated relay nodes for cluster heads (CHs). Theoretical analysis and extensive simulation results show that the proposed algorithms can achieve optimal or suboptimal solutions efficiently, and therefore help provide useful benchmarks for various centralized and distributed clustering scheme designs.

An adaptive routing algorithm for wavelength-routed optical networks with a distributed control scheme

For a wavelength-routed network in which connection requests are arriving and departing at high rates, an appropriate control scheme must be implemented to set up light paths for each request in a fast and efficient manner. The control scheme, which includes routing and wavelength assignment algorithms, must also be scalable, and should attempt to minimize the number of blocked connections. In this paper, we consider a distributed control scheme which utilizes a new adaptive routing approach called alternate-link routing. In the proposed approach, routing decisions for a light path are made adaptively on a hop-by-hop basis by individual nodes in a distributed manner. The scheme does not require the maintenance of any global information. A simulation is developed to analyze blocking performance, and it is shown that the proposed approach outperforms fixed routing and, under certain conditions, also outperforms fixed alternate-path routing.

Fast Distributed Demand Response With Spatially and Temporally Coupled Constraints in Smart Grid

As the next generation power grid, smart grid is characterized as an informationized system, and demand response is one of its important features to deal with the ever-increasing peak energy usage. However, the supply capacity and required demand make the demand response problem with both spatially and temporally coupled constraints, which, to the best of our knowledge, has not been thoroughly investigated in a distributed manner. The complexity lies in how to guarantee privacy and convergence of distributed algorithms. Aiming at this challenge, in this paper, we first propose a distributed algorithm, which is based on dual decomposition and does not require each user to reveal his/her private information. Then, the convergence analysis is conducted to provide guidance on how to choose the proper step size; through which, we notice that the convergence speed of the subgradient projection method is not fast enough and it is highly dependent on the choice of the step size. Therefore, to increase the convergence rate of the distributed algorithm, we further propose a fast approach based on binary search. Finally, the distributed algorithms are illustrated by numerical simulations and the extensive comparison results validate the better performance of the fast approach.

System crash as dynamics of complex networks

Significance System crash, as an essential part of system evolution, sometimes happens in peculiar manners: Weakened systems may survive for a surprisingly long time before suddenly meeting their final ends, whereas seemingly unbeatable giants may drastically crash to virtual nonexistence. We propose a model that describes system crash as a consequence of some relatively simple local information-based individual behaviors: Individuals leave networks according to some most straightforward assessment of current and future benefits/risks. Of note, such a simple rule may enable a single push/mistake to cause multistage-style system crash. Our study helps to make sense of the process where complex systems go into unstoppable cascading declines and provides a viewpoint of predicting the fate of some social/natural systems. Complex systems, from animal herds to human nations, sometimes crash drastically. Although the growth and evolution of systems have been extensively studied, our understanding of how systems crash is still limited. It remains rather puzzling why some systems, appearing to be doomed to fail, manage to survive for a long time whereas some other systems, which seem to be too big or too strong to fail, crash rapidly. In this contribution, we propose a network-based system dynamics model, where individual actions based on the local information accessible in their respective system structures may lead to the “peculiar” dynamics of system crash mentioned above. Extensive simulations are carried out on synthetic and real-life networks, which further reveal the interesting system evolution leading to the final crash. Applications and possible extensions of the proposed model are discussed.

Intermediate-node initiated reservation (IIR): a new signaling scheme for wavelength-routed networks

A problem of many distributed lightpath provisioning schemes is wavelength contention, which occurs when a connection request attempts to reserve a wavelength channel that is no longer available. This situation results from the lack of updated global link-state information at every node. In networks with highly dynamic traffic loads, wavelength contention may seriously degrade the network performance. To overcome this problem, we propose a new framework for distributed signaling and introduce a class of schemes referred to as intermediate-node initiated reservation. In the new scheme, reservations may be initiated at any set of nodes along the route; in contrast, reservations can only be initiated by the destination node in the classic destination initiated reservation (DIR) scheme. As a result, the possibility of having outdated information due to propagation delay is significantly lowered. Specifically, we consider two schemes within this framework, for networks with no wavelength conversion and for networks with sparse wavelength conversion, respectively. Theoretical and simulation results show that, compared with the classic DIR scheme, the new schemes can significantly improve the network blocking performance. The accuracy of the analytical models is also confirmed by extensive numerical simulations.

Analysis of blocking probability for connection management schemes in optical networks

We develop a model for evaluating the blocking probability of various connection management protocols for wavelength-routed optical networks with dynamic lightpath establishment. The model characterizes both blocking due to insufficient resources and blocking due to multiple interfering connection requests. We then use the analytical model to compare two connection management schemes, one which utilizes source-initiated reservation, and another which utilizes destination-initiated reservation.

Tolerance of intentional attacks in complex communication networks

Motivated by recent developments in the theory of complex networks, we examine the tolerance of communication networks for intentional attacks that aim to crash the network by taking down network hubs. In addition to providing a brief survey of key existing results, we investigate two different effects that largely have been ignored in past studies. Many communication networks, such as the Internet, are too large for anyone to have global information of their topologies, which makes accurate, intentional attacks virtually impossible; most attacks in communication networks must propagate from nodes to adjacent nodes, utilizing local-network topology information only. We show that incomplete global information has a different impact on intentional attacks in different circumstances, and local information-based attacks can actually be highly efficient. Such insights will be helpful for the future development of efficient protection schemes against network attacks.

Blocking analysis of dynamic lightpath establishment in wavelength-routed networks

In this paper, we analyze the blocking probability of dynamic lightpath establishment in wavelength-routed networks. By using the destination-initiated reservation (DIR) method as a case study, we analyze traffic blocking occurring due to insufficient network capacity as well as traffic blocking caused by outdated information. Simulation results show the proposed models to be highly accurate.