Distributed control based routing and wavelength assignment strategy for WDM optical networks

Wavelength-division-multiplexing (WDM) is emerging as the dominant technology for the next generation optical networks. The control strategy can be either centralized or distributed. In centralized control, there is a central controller to keep track of the state of the network. It is also responsible for selecting the path for data transmission. Most of the work done in this field is based on centralized control. For large networks, distributed control is preferred over centralized control because of low control overhead. Distributed control strategy requires exchange of control messages among nodes. The distributed control generally results in the possibility of resource reservation conflicts among simultaneous path establishments and poor resource utilization. In this paper, we have proposed one distributed control based routing and wavelength assignment strategy that avoids the problem of resource reservation conflicts along with the efficient utilization of resources.     

Effects of structure-dynamics correlation on hierarchical transitions in heterogeneous oscillatory networks

The impact of frequency-degree and amplitude-degree correlation is studied for heterogeneous networks of coupled Stuart–Landau oscillators. It is shown that increasing coupling strength gives rise to hierarchical processes of oscillation quenching. In case of frequency-degree correlated networks, higher-frequency oscillators gradually become almost quenched while low-frequency ones still remain oscillating. In case of amplitude-degree correlated networks, there appear three distinct domains, two contain low-amplitude oscillations with positive and negative means, and the third includes high-amplitude oscillations around the origin.     

All-optical code routing in interconnected optical CDMA and WDM ring networks

We propose an all-optical hybrid network composed of optical code division multiple access (CDMA) rings interconnecting through a reconfigurable wavelength division multiplexing (WDM) metro area ring. This network retains the advantages of both the optical CDMA and WDM techniques, including asynchronous access and differentiated quality of service, while removing the hard limit on the number of subscribers and increasing network flexibility. The all-optical network is enabled by using nonlinear optical loop mirrors in an add/drop router (ADR) that performs code conversion, dropping, and switching asynchronously. We experimentally demonstrate the functionalities of the ADR in the proposed scheme asynchronously and obtain error-free performance. The bit-error rate measurements show acceptable power penalties for different code routes.     

Survivable routing and spectrum allocation algorithm based on p-cycle protection in elastic optical networks

With the number of large capacity applications in core network increasing, the bandwidth requirement of optical connections in conventional Wavelength Division Multiplexing (WDM) networks keeps enhancing, so that the Orthogonal Frequency Division Multiplexing (OFDM) technology is adopted to provide higher spectrum efficiency and flexibility in the future elastic optical networks. Meanwhile, survivability in the conventional WDM optical networks has been widely studied as an important issue to ensure the service continuity. However, survivability in OFDM-based elastic optical networks is more challenging than that in conventional WDM optical networks because each fiber usually carries even more connections. Therefore, it is necessary to study the new lightpath protection algorithm in elastic optical networks. Since p-cycle protection scheme has short restoration time and simple protection switching procedure, in this paper, we study the static Survivable p-Cycle Routing and Spectrum Allocation (SC-RSA) problem with providing an Integer Linear Programming (ILP) formulation. Since RSA is a NP-hard problem, we propose a new heuristic algorithm called Elastic p-Cycle Protection (ECP) to tolerate the single-fiber link failure. For each demand, ECP scheme can compute highly-efficient p-cycles to provide protection for all of the on-cycle links and the straddling links. We also consider the load balancing and choose the proper working path for each demand. Simulation results show that the proposed ECP scheme achieves better performances than traditional single-line-rate survivable schemes.     

Power control of optical CDMA star networks

In this paper, we apply the power control concept to optical CDMA star networks. Two approaches are considered, namely, centralized and distributed power control. Both approaches are used to optimize the optical transmit power and to maximize network capacity in terms of the number of users satisfying a target signal to interference (SIR) ratio. Centralized algorithms result in the optimum power vector while distributed algorithms are more suitable for practical system implementation and eliminate the need for a centralized control node. Both analytical and simulation results show significant improvement in the performance of the power controlled optical CDMA system. For instance, in a network of 31 nodes, a doubling of the capacity as compared to the non power control case is obtained. Furthermore, we show in the interference-limited case that the network performance is upper bounded by the number of nodes and the correlation properties of the employed code rather than network attenuation and optical fiber lengths. The concept of network partitioning is then introduced to simplify optimum power calculations. Using network partitioning, we find in the interference-limited case that the optical fibers after the star coupler are irrelevant to the optimum power evaluation.     

Blocking probability analysis of survivable routing in WDM optical networks with/without sparse-wavelength conversion

In this paper, a new algorithm for wavelength assignment has been proposed and its performance is evaluated in terms of blocking probability and fairness. It has been shown that the proposed algorithm offers the least blocking probability. The blocking performance of wavelength division multiplexing (WDM) network has been analyzed for the network having 10 nodes and for varying loads. As the load per link (in Erlangs) increases, the blocking probability increases. The result shows that the performance of first-fit algorithm is better than random algorithm whereas the proposed algorithm offers the least blocking.     

Dynamic waveband grooming based on hierarchical integrated grooming auxiliary graph in multi-domain mesh optical networks

With the number of wavelengths in fibers increasing, the number of optical switching ports in conventional Optical Cross-Connect (OXC) keeps enhancing, so that waveband grooming technique is proposed to save the switching ports in OXC. Most of previous works focused on waveband grooming in single-domain optical network. Since the current optical backbone is actually divided to multiple domains according to the different network providers, it is necessary to study the waveband grooming in multi-domain optical networks. However, waveband grooming in multi-domain optical networks is more challenging than that in single domain networks because of the routing scalability and security issues. Therefore, in this paper, we propose a new heuristic Hierarchical Multi-domain Waveband Grooming (HMWG) algorithm based on Hierarchical Integrated Grooming Auxiliary Graph (H-IGAG) to reduce the total number of optical switching ports. The H-IGAG is compared of the Intra-domain Waveband Integrated Auxiliary Graph (Intra-WIAG) and the Inter-domain waveband Virtual Topology Graph (Inter-VTG). For the demand in single-domain, HMWG directly computes the route from the source node to destination node in the single-domain with waveband grooming on Intra-WIAG. For the demand spanning different domains, HMWG first computes the route from the source node to the selected border node in source domain and computes the route from the selected border node to the destination node in destination domain with waveband grooming on Intra-WIAG, respectively. Then, HMWG computes the route from the selected border node in source domain to the selected border node in destination domain with waveband grooming on Inter-VTG. Simulation results show that, compared with previous grooming algorithm, HMWG can obtain better performance.     

Experimental validation for time-domain fluorescence diffuse optical tomography of linear scheme

We present a full three-dimensional, featured-data algorithm for time-domain fluorescence diffuse optical tomography that inverts the Laplace-transformed time-domain coupled diffusion equations and employs a pair of appropriate transform-factors to effectively separate the fluorescent yield and lifetime parameters. By use of a time-correlation single-photon counting system and the normalized Born formulation, we ex-perimentally validate that the proposed scheme can achieve simultaneous reconstruction of the fluorescent yield and lifetime distributions with a reasonable accuracy.     

Data center application oriented control architecture in multi-domain optical networks

With the rapid development of cloud computing, data center application based on considerable storage and computing has become one of the most important service types. Currently the high performance computing facilities and large-capacity storage devices are highly distributed in different locations. Then how to make full use of the current data center mainly depends on the effective joint scheduling of application layer and network layer resources. According to the rigid requirement of data center application, a novel convergence control architecture, i.e. Service-Oriented Group Engine (SOGE) framework is proposed in multi-domain optical networks based on DREAM architecture, and also the corresponding resource demand model (RDM) is built. A resource joint scheduling algorithm (RJSA) for application layer and network layer resource is proposed and implemented based on SOGE framework. Moreover, the SOGE framework and resource joint scheduling algorithm are validated and demonstrated on the test-bed based on DREAM architecture.     

Detect overlapping and hierarchical community structure in networks

Clustering and community structure is crucial for many network systems and the related dynamic processes. It has been shown that communities are usually overlapping and hierarchical. However, previous methods investigate these two properties of community structure separately. This paper proposes an algorithm (EAGLE) to detect both the overlapping and hierarchical properties of complex community structure together. This algorithm deals with the set of maximal cliques and adopts an agglomerative framework. The quality function of modularity is extended to evaluate the goodness of a cover. The examples of application to real world networks give excellent results.     

Experimental study of sweep control in e-beam evaporated optical coatings

<正>High performance optical coating requires excellent uniformity of thin-film.Keeping the surface of evaporation material flat is propitious for the stability of vapor plume,and can improve the uniformity of thin-film.Based on the principle of electron beam spot sweep,a pattern controller in domestic coater is designed.For the purpose of even evaporation during auto-sweep,the influence of the depth of material surface in the crucible on the evaporation characteristic is considered.Pre-melting and evaporation experiments are performed on melting material(Ti_3O_5),subliming material(SiO_2),and semi-melting, semi-subliming material(HfO_2).The sweeping experimental results show that using the designed sweep controller can make good performance on evaporation and pre-melting for the above materials.     

The hierarchical backbone of complex networks

Given any complex directed network, a set of acyclic subgraphs can be extracted that will provide valuable information about its hierarchical structure. This Letter presents how the interpretation of the network weight matrix as a transition matrix allows the hierarchical backbone to be identified and characterized in terms of the concepts of hierarchical degree, which expresses the total weights of virtual edges established along successive transitions. The potential of the proposed approach is illustrated with respect to simulated random and preferential-attachment networks as well as real data related to word associations and gene sequencing.     

Perfect quantum routing in regular spin networks

Motivated by the need for quantum computers to communicate between multiple, well separated qubits, we introduce the task of quantum routing for distributing quantum states, and generating entanglement, between these sites. We describe regular families of coupled quantum networks which perfectly route qubits between arbitrary pairs of nodes with a high transmission rate. The ability to route multiple states simultaneously and the regularity of the networks vastly improve the utility of this scheme in comparison to the task of state transfer, leading us to propose an implementation in optical lattices.     

Efficient and robust routing on scale-free networks

Information routing is one of the most important problems in large communication networks. In this paper we propose a novel routing strategy in which the optimal paths between all pairs of nodes are chosen according to a cost function that incorporates degrees of nodes in paths. Results on large scale-free networks demonstrate that our routing strategy is more efficient than the shortest path algorithm and the efficient routing strategy proposed by Yan et al. [Phys. Rev. E 73, 046108 (2006)]. Furthermore our routing strategy has strong robustness against cascading failure attacks on networks.     

Modular and hierarchical structure of social contact networks

Social contact networks exhibit overlapping qualities of communities, hierarchical structure and spatial-correlated nature. We propose a mixing pattern of modular and growing hierarchical structures to reconstruct social contact networks by using an individual’s geospatial distribution information in the real world. The hierarchical structure of social contact networks is defined based on the spatial distance between individuals, and edges among individuals are added in turn from the modular layer to the highest layer. It is a gradual process to construct the hierarchical structure: from the basic modular model up to the global network. The proposed model not only shows hierarchically increasing degree distribution and large clustering coefficients in communities, but also exhibits spatial clustering features of individual distributions. As an evaluation of the method, we reconstruct a hierarchical contact network based on the investigation data of a university. Transmission experiments of influenza H1N1 are carried out on the generated social contact networks, and results show that the constructed network is efficient to reproduce the dynamic process of an outbreak and evaluate interventions. The reproduced spread process exhibits that the spatial clustering of infection is accordant with the clustering of network topology. Moreover, the effect of individual topological character on the spread of influenza is analyzed, and the experiment results indicate that the spread is limited by individual daily contact patterns and local clustering topology rather than individual degree.     

Avalanche transmission and critical behaviour in load-bearing hierarchical networks

The strength and stability properties of hierarchical load-bearing networks and their strengthened variants have been discussed in a recent work. Here, we study the avalanche time distributions on these load-bearing networks. The avalanche time distributions of the V-lattice, a unique realization of the networks, show power-law behaviour when tested with certain fractions of its trunk weights. All other avalanche distributions show Gaussian peaked behaviour. Thus the V-lattice is the critical case of the network. We discuss the implications of this result.     

Experimental implementation of optical clockwork without carrier-envelope phase control

We demonstrate optical clockwork without the need for carrier-envelope phase control by use of sum-frequency generation between a continuous-wave optical parametric oscillator at 3.39 microm and a femtosecond mode-locked Ti:sapphire laser with two strong spectral peaks at 834 and 670 nm, a spectral difference matched by the 3.39-microm radiation.     

Velocity and hierarchical spread of epidemic outbreaks in scale-free networks

We study the effect of the connectivity pattern of complex networks on the propagation dynamics of epidemics. The growth time scale of outbreaks is inversely proportional to the network degree fluctuations, signaling that epidemics spread almost instantaneously in networks with scale-free degree distributions. This feature is associated with an epidemic propagation that follows a precise hierarchical dynamics. Once the highly connected hubs are reached, the infection pervades the network in a progressive cascade across smaller degree classes. The present results are relevant for the development of adaptive containment strategies.     

Comparison and performance of routing protocols in SONET based networks

In this paper, comparison of various protocols used in the SONET based networks has been investigated in terms of the performance characteristics like end-to-end queuing delay, end-to-end link throughput, link utilization, etc. By creating a model to simulate the packet flow within a SONET DCC network characteristics of two routing protocols, the RIP (routing information protocol) and OSPF (open shortest path first) defined in the G.7712 standard are analyzed. Finally on comparing all the performance characteristics of the two routing protocol it is observed that OSPF protocol achieves better performance and is the least obtrusive on network operations.     

Feed-forward control of SOA gain for power equalization in optical burst switching networks

We evaluate the performance of a novel technique to equalize power variation between optical bursts using feed-forward control of semiconductor optical amplifier gain. The technique enables large dynamic range power equalization of incoming optical bursts with up to 10 dB power difference. Moreover, the technique can remove SOA-induced waveform distortion. We achieve more than 4 dB sensitivity improvement with equalized burst power.