Recovery in multilayer optical networks

The integration of different network technologies into a multilayer network, as in Internet-based networks carried by optical transport networks (OTNs), creates new opportunities but also challenges with respect to network survivability. In different network layers, recovery mechanisms that are active can be exploited jointly to reach a more efficient or faster recovery from failures. This interworking is also indispensable in order to overcome the variety of failure scenarios that can occur in the multilayer-network environment. A well-considered coordination between the different layers and their recovery mechanisms is crucial in order to attain high performance recovery. This paper provides an overview of multilayer recovery issues and solutions in an Internet protocol (IP)-over-optical-network environment, which is illustrated by quantitative case studies.     

采用多层恢复机制的IP over WDM网络生存性研究

IP over WDM网络是下一代网络的核心,生存性则是保证服务质量(QoS)的关键要素.当网络中出现故障时,选择在IP层还是光层进行保护和恢复是非常重要的课题.文章在论述IP层和光层的保护和恢复机制的基础上,提出了多层联合恢复机制的思想,针对多层联合恢复机制中各层之间如何协调进行了仔细的分析,并提出了自己的见解.     

ATM网络业务恢复机制研究

提出了基于网管控制下的层次化ATM网络业务恢复管理机制，指出了在网络维护管理过程中采用多种恢复机制并进行层次化技术处理的重要性。ATM网络的正常可靠运行需要从网络各个层次，运用各种恢复管理机制对业务进行管理维护。在网络实际运行过程当中，联合应用网络各层次上的恢复管理机制是非常重要的。描述了该技术具体应用以及基于网管控制的业务恢复策略。     

Integrated Survivability Strategies of IP/GMPLS/Optical Multi-layer Network

In last decade,due to that the popularity of the internet, data-central traffic kept growing,some emerging networking requirements have been posed on the todays telecommunication networks,especially in the area of network survivability.Obviously,as a key networking problem,network reliability will be more and more important.The integration of different technologies such as ATM,SDH,and WDM in multilayer transport networks raises many questions regarding the coordination of the individual network layers.This problem is referred as multilayer network survivability.The integrated multilayer network survivability is investingated as well as the representation of an interworking strategy between different single layer survivability schemes in IP via generalized multi-protocol label switching over optical network.     

Integrated Survivability Strategies of IP／GMPLS／Opticai Multi——layer Network

In last decade,due to that the popularity of the internet, data--central traffic kept growing, some emerging networking requirements have been posed on the today‘s telecommunication networks,especially in the area of network survivability. Obviously, as a key networking problem, network reliability will be more and more important. The integration of different technologies such as ATM, SDH, and WDM in multilayer transport networks raises many questions regarding the coordination of the individual network layers.This problem is referred as multilayer network survivability. The integrated multilayer network survivability is investingated as well as the representation of an interworking strategy between different single layer survivability schemes in IP via generalized multiprotocol label switching over ootical netwnrk     

Is multilayer networking feasible?

IP traffic has been growing every year, bringing the need for deploying an IP backbone interconnected by links provided by the transport network. Thus, network operators have had traditionally divided their core network in two, the IP network and the transport network. Network planning and engineering tasks have been performed independently in both domains. Traditionally, the transport network has been quite inflexible, and changes have often required a long time to occur. However, recent developments in the control plane allow flexibility in the transport network, making it possible to set up and tear down circuits on demand. In this light, multilayer traffic engineering has been proposed to jointly manage both IP and transport layers, with the aim of optimizing the use of resources. This paper aims to describe the rationale behind multilayer traffic engineering, demonstrate its feasibility and quantify its advantages in terms of cost effectiveness. Also, this work takes a look at the different choices in performing the multilayer operation, in terms of control plane implementation and equipment integration. Finally, the paper presents a report on multilayer traffic engineer experimentation which proves its feasibility and show a preliminary techno-economic case study of the multilayer operation.     

Simulation tools for multilayer fault restoration - [Modeling and simulation: a practical guide for network designers and developers]

The complexity of networks today makes it difficult to handle fault restoration by means of human intervention. Future network architectures are expected to be self-protecting and, more generally, self-organizing. In this article we describe the modeling methods and simulation tools we have used for the analysis of a new integrated restoration scheme operating at multiple layers/networks. The networks over which we have performed the analysis are ATM and SDH, but the methodology could be applied to other multilayer architectures too. A network model has been created that consists of both ATM and SDH layers. Using this network model, we have seen how the new scheme explores the free bandwidth over both layers. The multilayer bandwidth exploration was modeled using Microsoft Visual C++. Using OPNET Modeler, a node model was created to analyze the restoration message processing within it and the interaction with other nodes for the purpose of simulating the restoration delay. The article emphasizes the simulation methodology rather than the results of the simulation. Among others, we describe which additional functionalities a simulation tool is necessary to have in order to simulate multilayer networks. A comparison of OPNET and Microsoft Visual C++ is made, describing their advantages and the reasons we found it necessary to use both.     

Impedance characteristics of power distribution grids in nanoscale integrated circuits

The essential design characteristic of nanoscale integrated circuits is increased interconnect complexity. Conductors at different levels of the interconnect hierarchy have highly different physical and, consequently, electrical characteristics. These interconnect lines also exhibit inductive behavior due to enhanced switching speed of nanoscale devices, making interconnect design and analysis difficult. The design of robust and area efficient power distribution networks for high-speed integrated circuits has therefore become a challenging task. The impedance characteristics of multilayer power distribution grids and the relevant design implications are the subject of this paper. The power distribution network spans many layers of interconnect with disparate electrical properties. Unlike single-layer grids, the electrical characteristics of multilayer grids vary significantly with frequency. As the frequency increases, a large share of the current flow is transfered from the low-resistance upper layers to the low-inductance lower layers. The inductance of a multilayer grid therefore decreases with frequency, while the resistance increases with frequency. The lower layers of multilayer power grids provide a low-inductance current path, significantly reducing the grid impedance at high frequencies. Multilayer power distribution grids extend to the lower interconnect layers, exhibiting superior high-frequency impedance characteristics as compared to power distribution grids built exclusively within the upper, low-resistance metal layers. A significant share of metal resources to distribute the global power should therefore be allocated to the lower metal layers. An analytic model is also presented to determine the impedance characteristics of a multilayer grid from the inductive and resistive properties of the comprising individual grid layers.     

IP over WDM的多层生存性

在论述IP层和光层的保护和恢复机制的基础上,提出了多层联合恢复机制的思想,针对多层联合恢复机制中各层之间如何协调进行了分析,为了获得优化的多层网络故障恢复能力,提出了利用GMPLS的基于层间协调机制的集成多层网络生存方案.     

A vertical Path Computation Element (PCE) based path provisioning scheme in multilayer optical networks

The explosive growth of Internet traffic has led to a dramatic increase in demand for data transmission capacity, which requires high transmission rates beyond the conventional transmission capability. This demand has spurred tremendous research activities in new high-speed transmission and switching technologies. As optical transmission technology keeps maturing, next generation optical networks are expected to be controlled by Generalized Multiprotocol Label Switching (GMPLS) protocol suite and operating at multiple switching layers. In order to ensure the most efficient utilization of multilayer network resources, and to maximize revenue from existing capacity, effective global provisioning solution that providing the network with the possibility of reacting in advance to traffic changes should be provided. This paper proposes a new path provisioning scheme in multilayer optical networks based on the vertical Path Computation Element (PCE) architecture to efficiently exploit multiple PCE cooperation. This paper also investigated the problem of how network nodes overcome limited visibility of network resources. Unlike most of the previous studies, the topology of the upper switching layer is not always equal to the physical topology of lower switching layer.     

BFD‐based failure detection and localization in IP over OBS/WDM multilayer network

Optical burst switching (OBS), which takes advantage of both high capacity of optical fiber and sophisticated control of electronics, has been considered as a promising paradigm for the modern Internet. In this paper, the recovery procedures for IP over OBS/WDM multilayer network are addressed, which focus on the failure detection and failure localization. Bidirectional forwarding detection (BFD) mechanism which provides low‐overhead, short‐duration detection of failures in the path between adjacent forwarding engines, including the interfaces, data link(s) is introduced for the failure detection and localization in the IP over OBS/WDM multilayer network, especially at the OBS/WDM layer. The unique feature of OBS and the easy‐to‐implement merit of BFD make it feasible for BFD adopted at OBS/WDM layer. Besides, BFD is a highly cost effective method when compared with traditional methods such as detecting the Loss of Light of each wavelength. Not only the implementation details of BFD‐based failure detection for the OBS/WDM layer are demonstrated in this paper, but also how the BFD localizes failures such as fiber failure, link failure and node failure. Moreover, extensive simulations have been done at different scenarios such as single failure and multiple failures. And the numerical results concerning the performance of BFD‐based failure detection and localization in terms of failure detection and localization time and BDP lost rate verified the proposed solution. Copyright © 2011 John Wiley & Sons, Ltd.     

多层前向网络的逼近机理与拓扑结构学习方法

对多层前向网络的最小二乘逼近机理进行了系统的分析，指出隐层节点函数特性的特定选择是构成网络有效逼近能力最关键的因素。分析了增加隐层数和增加隐节点数在改进网络逼近效果方面不同的作用机理，给出了前向网络拓扑结构学习的通用算法和其对应的神经生物学机制。     

An effective network congestion control method for multilayer network

The congestion control problem in a single node network has been solved by the nonlinear feedback control method,which has been proven to be effective and robust for different router’s queue size.However,these control models are based on the single layer network architecture,and the senders and receivers are directly connected by one pair of routers.With the network architecture being more and more complex,it is a serious problem how to cooperate many routers working in the multilayer network simultaneously.In this paper,an effective Active Queue Management（AQM）scheme to guarantee the stability by the nonlinear control of imposing some restrictions on AQM parameter in multilayer network is proposed.The nonlinear control can rely on some heuristics and network traffic controllers that appear to be highly correlated with the multilayer network status.The proposed method is based on the improved classical Random Early Detection（RED）differential equation and a theorem for network congestion control.The theorem proposed in the paper proved that the stability of the fluid model can effectively ensure the convergence of the average rate to its equilibrium point through many routers in multilayer network.Moreover,when the network capacity is larger,the proposed scheme can still approach to the fullest extensibility of utilization and ensure the stability of the fluid model.The paper reveals the reasons of congestion control in multilayer network,provides a theorem for avoiding network congestion,and gives simulations to verify the results.     

Optimized design of survivable MPLS over optical transport networks

In this paper we study different options for the survivability implementation in MPLS over Optical Transport Networks (OTNs) in terms of network resource usage and configuration cost. We investigate two approaches to the survivability deployment: single-layer survivability, where some recovery mechanism (e.g. protection or restoration) is implemented in a single network layer and multilayer survivability, where recovery is implemented in multiple network layers. The survivable MPLS over OTN design is implemented as a static network optimization problem and incorporates various methods for spare capacity allocation (SCA) to reroute disrupted traffic.The comparative analysis between the single layer and the multilayer survivability shows the influence of the traffic granularity on the survivability cost: for high-bandwidth LSPs, close to the optical channel capacity, the multilayer survivability outperforms the single layer one, whereas for low-bandwidth LSPs the single-layer survivability is more cost-efficient. For the multilayer survivability we demonstrate that by mapping efficiently the spare capacity of the MPLS layer onto the resources of the optical layer one can achieve up to 22% savings in the total configuration cost and up to 37% in the optical layer cost. Further savings (up to 9%) in the wavelength use can be obtained with the integrated approach to network configuration over the sequential one; however, this is at the increase in the optimization problem complexity. These results are based on a cost model with current technology pricing and were obtained for networks targeted to a nationwide coverage.     

Reliability of Pb(Mg,Nb)O3–Pb(Zr,Ti)O3 multilayer ceramic piezoelectric actuators by Weibull method

Expected lifetime and reliability of multilayer ceramic actuators were considered. 5 × 5 × 5 mm³ sized multilayer ceramic actuators with 60 ceramic sheet layers embedded internal electrodes were selected in this experimental analysis. Specially selected rectified AC bias was applied to the multilayer ceramic actuators to remove heating during charging and discharging process. Sixteen sets of multilayer ceramic actuators under the different experimental conditions were tested for statistical analysis. Weibull function method was employed to calculate mean time to failure. Arrhenius model and power law model were considered to simulate experimental data. From the experimental data and theoretical consideration, equation of expected lifetime was estimated.     

多层网络结构系统安全的几个关键技术

多层网络结构系统增加了系统的扩展性能的同时，也因为其运行环境复杂，用户众多，并且存放、处理的数据非常重要，所以多层网络结构系统的安全设计非常重要。一个系统存在的安全问题可能主要来源于两方面：安全控制机构的故障及系统安全定义的缺陷。作者在深入了解当今网络安全技术及各类解决方案的同时，本文重点介绍多层网络结构系统中几种常用的网络安全关键技术，并采用了分层解决方案的思想以确保整个系统的安全。     

片式多层电容电阻复合元件的研制

采用低温共烧陶瓷(LTCC)技术将电容、电阻元件集成在多层陶瓷基板里,构成了一种新型的片式多层复合元件,并研究了其制造工艺性能和频率特性。结果表明,片式多层电容电阻复合元件制造工艺适合批量化生产,并为片式多层LC滤波器、LTCC基板及器件的研发提供了极好的参考价值。     

特殊场景的LTE覆盖技术

文章首先介绍了 LTE异构网和 LTE立体组网技术,在此基础上,重点研究高铁和密集城区的 LTE覆盖技术。讨论了如何应对高铁 LTE覆盖的多普勒频移效应问题,并给出了高铁沿线覆盖和隧道两种环境下的组网方式建议。最后,探讨了如何采用 LTE异构网和立体组网技术,通过合理的网络布局来解决密集城区的容量和深度覆盖问题。     

Data-centric optical networks and their survivability

The explosive growth of data traffic-for example, due to the popularity of the Internet-poses important emerging network requirements on today's telecommunication networks. This paper describes how core networks will evolve to optical transport networks (OTNs), which are optimized for the transport of data traffic, resulting in an IP-directly-over-OTN paradigm. Special attention is paid to the survivability of such data-centric optical networks. This becomes increasingly crucial since more and more traffic is multiplexed onto a single fiber (e.g., 160×10 Gb/s), implying that a single cable cut can affect incredible large traffic volumes. In particular, this paper is tackling multilayer survivability problems, since a data-centric optical network consists of at least an IP and optical layer. In practice, this means that the questions "in which layer or layers should survivability be provided?" and "if multiple layers are chosen for this purpose, then how should this functionality in these layers be coordinated?" have to be answered. In addition to a theoretical study, some case studies are presented in order to illustrate the relevance of the described issues and to help in strategic planning decisions. Two case studies are studying the problem from a capacity viewpoint. Another case study presents simulations from a timing/throughput performance viewpoint     

A Delivery System for Self‐Healing Inorganic Films

Multilayer composites that utilize polymeric and brittle inorganic films are essential components for extending the lifetimes and exploiting the flexibility of many electronic devices. However, crack formation within the brittle inorganic layers that arise from defects as well as the flexing of these multilayer composite materials allows the influx of atmospheric water, a major source of device degradation. Thus, a composite material that can initiate self‐healing upon the influx of environmental water through defects or stress‐induced cracks would find potential applications in multilayer composite materials for permeation barriers. In the present study, the reactive metal oxide precursor TiCl₄ is encapsulated within the pores of a degradable polymer, poly(lactic acid) (PLA). Electrospun PLA fibers are found to be reactive to atmospheric water leading to the hydrolysis of the degradable polymer shell and subsequent release of the reactive metal oxide precursor. Release of the reactive TiCl₄ from the pores results in hydrolysis of the metal oxide precursor, forming solid titanium oxides at the surface of the fibers. The efficacy of this self‐healing delivery system is also demonstrated by the integration of these reactive fibers in the polymer planarization layer, poly(methyl methacrylate), of a multilayer film, upon which an alumina barrier layer is deposited. The introduction of nanocracks in the alumina barrier layer lead to the release of the metal oxide precursor from the pores of the fibers and the formation of titanium dioxide nanoparticles within the crack and upon the thin film surface. In this study the first delivery system that may find utility for the self‐healing of multilayer barrier films through the site‐specific delivery of metal oxide nanoparticles through smart reactive composite fibers is established.