Availability analysis of span-restorable mesh networks

The most common aim in designing a survivable network is to achieve restorability against all single span failures, with a minimal investment in spare capacity. This leaves dual-failure situations as the main factor to consider in quantifying how the availability of services benefit from the investment in restorability. We approach the question in part with a theoretical framework and in part with a series of computational routing trials. The computational part of the analysis includes all details of graph topology, capacity distribution, and the details of the restoration process, effects that were generally subject to significant approximations in prior work. The main finding is that a span-restorable mesh network can be extremely robust under dual-failure events against which they are not specifically designed. In a modular-capacity environment, an adaptive restoration process was found to restore as much as 95% of failed capacity on average over all dual-failure scenarios, even though the network was designed with minimal spare capacity to assure only single-failure restorability. The results also imply that for a priority service class, mesh networks could provide even higher availability than dedicated 1+1 APS. This is because there are almost no dual-failure scenarios for which some partial restoration level is not possible, whereas with 1+1 APS (or rings) there are an assured number of dual-failure scenarios for which the path restorability is zero. Results suggest conservatively that 20% or more of the paths in a mesh network could enjoy this ultra-high availability service by assigning fractional recovery capacity preferentially to those paths upon a dual failure scenario     

Locally reconfigurable p-cycle networks for dual-failure restoration

p-Cycle reconfiguration methods (for instance complete, incremental, or dynamic-repair) based on the first event adaptive restoration model provide a promising approach for improving the dual-failure restorability characteristics of static p-cycle methods based on the static preplanned restoration model. However, if the reconfiguration process triggered by the first failure is not completed before a second failure occurs, p-cycle reconfiguration methods fail to achieve 100% dual-failure restorability and reduce to the static p-cycle methods which do not take advantage of the spare capacity to be reconfigured. In this study, we propose to use a new restoration model designated as first event locally adaptive restoration model with a coordinated re-restoration effort. This model is aimed to limit the reconfiguration scope to a local p-cycle where the spare capacity is only reconfigured on its straddling links for reducing the reconfiguration overhead (i.e., the average number of reconfigured links during the reconfiguration time.) According to this model, a two-phase locally reconfigurable p-cycle method is proposed. Only the straddling links of the local p-cycle affected by the first failure are reconfigured in the first phase. The second phase is not initialized until the second failure really occurs in the affected local p-cycle. The second phase is to enable the dual-failure restorations with a coordinated re-restoration effort for the first failed link from its original end nodes for any damage that the second failure causes to previously deployed restoration paths. The objective of the proposed method is to maximize the dual-failure restorability within a limited reconfiguration scope. We evaluate the correlation between the normalized spare capacity cost and the dual-failure restorability. The results show that the proposed local reconfiguration heuristic method improves the average dual-failure restorability of the 9n17s and Cost 230 networks by 45.1% and 20.1%, respectively, relative to the static p-cycles method and achieves closely the optimal value obtained using integer linear programming (ILP). Additionally, the spare capacity cost of the proposed local reconfiguration method is smaller than that of previous p-cycle reconfiguration methods in the two test networks.

Automatic protection switching for p-cycles in WDM networks

p-Cycle recovery relies on a protection switching protocol. We detail several issues for such a protocol taking the evolution from ring networks to p-cycles into account. In particular, we propose and evaluate a protocol enhancement to provide means for node failure protection. For the evaluation, we describe an integer linear program, which is applied to network design case studies, and formulate availability models for p-cycles. The case studies show that the protocol enhancement improves availability at marginal additional design cost.     

Performance evaluation of p-cycle based protection methods for provisioning of dynamic multicast sessions in mesh WDM networks

Network survivability is crucial to both unicast and multicast traffic. Up to now, extensive research has been done on unicast traffic protection. Recently, due to the rapid growth of multicast applications, such as video-conferencing, high definition television (HDTV), distance learning, and multi-player on-line gaming, the problem of multicast traffic protection has started to draw more research interests. The preconfigured protection cycle (p-cycle) method proposed by Grover offers fast speed in restoration (because p-cycles are pre-cross-connected) and high efficiency in resource utilization (because p-cycles protect both on-cycle and straddling links). So far p-cycles based protection approaches have been intensively studied for unicast traffic protection, but have been rarely investigated for multicast traffic. We propose to apply p-cycles to dynamic protection provisioning of multicast traffic, and evaluate the blocking performance in comparison to other existing multicast protection schemes. We consider three different p-cycle based multicasting protection methods, namely dynamic p-cycle (DpC) design, p-cycle based protected working capacity envelope (PWCE) design, and hybrid DpC and PWCE design. We show that p-cycle-based multicast protection approaches offer much better blocking performance, as compared with other existing multicast protection schemes. The main reasons for the much better blocking performance are attributed to the facts that (i) the selection of p-cycles is independent of the routing of the multicast light trees, (ii) there are no path/segment disjoint constraints between the selected p-cycles and the multicast light trees to be protected, (iii) the selected p-cycles are the most efficient p-cycles.

An overview of p-cycle based optical multicast protection approaches in mesh WDM networks

This paper provides an overview of p-cycle based optical multicast protection approaches for link failure recovery, combined node and link failure recovery, and source failure recovery on top of combined node and link failure recovery. We discuss several recently proposed p-cycle based optical multicast protection approaches, including the link-protecting p-cycle based optical multicast protection approach, the tree-protecting p-cycle based optical multicast protection approach, node-and-link protecting p-cycle based optical multicast protection approach, and flow p-cycle based optical multicast protection approach. They outperform other existing optical multicast protection approaches in both capacity efficiency and recovery speed.     

论BSC/RNC与MGW双联在现网中的应用

根据在现网中出现的故障,深入分析移动通信网络中核心网设备MGW与无线侧设备BSC/RNC的连接现状,针对现网中存在的问题,通过介绍双联技术的优点,提出对现网MGW双联改进方案。     

Comparison of <Emphasis Type="Italic">p</Emphasis>-cycles and <Emphasis Type="Italic">p</Emphasis>-trees in a unified mathematical framework

As high-speed networks grow in capacity, network protection becomes increasingly important. Recently, following interest in p-cycle protection, the related concept of p-trees has also been studied. In one line of work, a so-called “hierarchical tree” approach is studied and compared to p-cycles on some points. Some of the qualitative conclusions drawn, however, apply only to p-cycle designs consisting of a single Hamiltonian p-cycle. There are other confounding factors in the comparison between the two, such as the fact that, while the tree-based approach is not 100% restorable, p-cycles are. The tree and p-cycle networks are also designed by highly dissimilar methods. In addition, the claims regarding hierarchical trees seem to contradict earlier work, which found pre-planned trees to be significantly less capacity-efficient than p-cycles. These contradictory findings need to be resolved; a correct understanding of how these two architectures rank in terms of capacity efficiency is a basic issue of network science in this field. We therefore revisit the question in a definitive and novel way in which a unified optimal design framework compares minimum capacity, 100% restorable p-tree and p-cycle network designs. Results confirm the significantly higher capacity efficiency of p-cycles. Supporting discussion provides intuitive appreciation of why this is so, and the unified design framework contributes a further theoretical appreciation of how pre-planned trees and pre-connected cycles are related. In a novel further experiment we use the common optimal design model to study p-cycle/p-tree hybrid designs. This experiment answers the question “To what extent can a selection of trees compliment a cycle-based design, or vice-versa?” The results demonstrate the intrinsic merit of cycles over trees for pre-planned protection.     

Analytic approximation of the jitter incurred by CBR traffics in IP networks

In this paper, an analytic approximation is derived for the end-to-end delay-jitter incurred by a periodic traffic with constant packet size. The single node case is considered first. It is assumed that the periodic traffic is multiplexed with a background packet stream under the FCFS service discipline. The processes governing the packet arrivals and the packet sizes of the background traffic are assumed to be general renewal processes. A very simple analytical approximation is derived and its accuracy is assessed by means of event-driven simulations. This approximation is then extended to the multiple node case yielding a simple analytical approximation of the end-to-end jitter. This approximation is shown to be fairly accurate in the light to moderate traffic conditions typically encountered in IP core networks.     

Hall effect analysis of high purity p-type GaAs grown by metalorganic chemical vapor deposition

Variable temperature Hall effect and low temperature photoluminescence measurements have been performed on high purityp- andn-type GaAs grown at atmospheric pressure by metalorganic chemical vapor deposition. These high purity epitaxial GaAs layers were grown as a function of the arsine (AsH₃) to trimethylgallium (TMG) ratio (V/III ratio). The accurate quantitative assessment of the electronic properties of thep-type layers was emphasized. Analysis of the material focussed on the variation of the concentration of the shallow impurities for different V/III ratios. Surface and interface depletion effects are included to accurately estimate the concentration of impurities. The model of the merging of the excited states of the acceptor with the valence band is used to include the dependence the activation energy of the impurity on the acceptor concentration as well as on acceptor species identity. The characteristicp- ton-type conversion with increasing V/III ratio was observed in these samples and the reason for thep- ton-type conversion is that the background acceptor concentration of carbon decreases and the germanium donor concentration increases as the V/III ratio is increased.     

P-cycle Protection in multi-domain optical networks

Providing resilient inter-domain connections in multi-domain optical GMPLS networks is a challenge. On the one hand, the integration of different GMPLS domains to run traffic engineering operations requires the development of a framework for inter-domain routing and control of connections, while keeping the internal structure and available resources of the domains undisclosed to the other operators. On the other hand, the definition of mechanisms to take advantage of such automatically switched inter-domain connectivity is still an open issue. This article focuses on the analysis of applicability of one of these mechanisms: P-cycle-based protection. The proposed solution is based on the decomposition of the multi-domain resilience problem into two sub-problems, namely, the higher level inter-domain protection and the lower level intra-domain protection. Building a P-cycle at the higher level is accomplished by certain tasks at the lower level, including straddling link connection, capacity allocation and path selection. In this article, we present several methods to realize inter-domain P-cycle protection at both levels and we evaluate their performance in terms of availability and spent resources. A discussion on a proposal of implementation of signalling based on extensions of existing protocols such as RSVP-TE and the PCE architecture illustrates the practical viability of the approach.

节点失效对无线传感器网络覆盖与连通可靠性影响的模型研究

针对节点失效引起无线传感器网络监测性能下降的问题,该文以节点随机均匀部署的网络为研究对象,从节点失效的角度提出了评价网络覆盖与连通两个基本监测性能的量化指标,建立了评价模型,通过设计节点失效算法对随机失效与恶意入侵两种节点失效类型进行了计算机模拟,利用仿真结果比较了网络监测性能在不同失效类型时的变化情况,总结出经验公式,为网络参数的选取提供了依据。     

5G超密集组网关键技术与组网架构探讨

5G超密集组网是建设绿色、高效、灵活部署5G网络的关键技术。也是应对未来1000倍流量增长的必然要求。随着大量低功率站点部署,虽然提升了系统容量,但面临因站间距太小带来了干扰和频繁切换问题,影响用户体验,以及大量低功率站点部署需要消耗大量的传输资源。本文重点讨论了解决这三个问题的关键技术：虚拟小区技术、双连接技术、CoMP干扰协调技术、无线回传技术。探讨了5G超密集组网架构实现。     

A neural-based nonlinear L 1-norm optimization algorithm for diagnosis of networks

Based on exact penalty function, a new neural network for solving the L ₁-norm optimization problem is proposed. In comparison with Kennedy and Chua’s network(1988), it has better properties.Based on Bandler’s fault location method(1982), a new nonlinearly constrained L ₁-norm problem is developed. It can be solved with less computing time through only one optimization processing. The proposed neural network can be used to solve the analog diagnosis L ₁ problem. The validity of the proposed neural networks and the fault location L ₁ method are illustrated by extensive computer simulations. Supported by Doctoral Special Fund of State Education Commission and the National Natural Science Foundation of China, Grant No.59477001 and No.59707002     

The role of outdiffusion in the activation of high dose Mg implantations in InP

We have studied the annealing behaviour of magnesium implanted in indium phosphide. The activated fraction of dopants was found to depend strongly on implanted dose and substrate temperature during implantation. Low activation for high dose (10¹⁵ cm⁻²) implantations was found to be a result of pronounced outdiffusion (80%). We also found a large variation in the apparent activation energy for implantation temperatures between room temperature and 300° C.     

Overlay multicast for MANETs using dynamic virtual mesh

Overlay multicast protocol builds a virtual mesh spanning all member nodes of a multicast group. It employs standard unicast routing and forwarding to fulfill multicast functionality. The advantages of this approach are robustness and low overhead. However, efficiency is an issue since the generated multicast trees are normally not optimized in terms of total link cost and data delivery delay. In this paper, we propose an efficient overlay multicast protocol to tackle this problem in MANET environment. The virtual topology gradually adapts to the changes in underlying network topology in a fully distributed manner. To save control overhead, the participating nodes only keep a fisheye view of the dynamic mesh. The multicast tree is progressively adjusted according to the latest local topology information. Simulations are conducted to evaluate the tree quality. The results show that our approach solves the efficiency problem effectively. This research was supported in part by the National Science Foundation under the grants CCR-0296070 and ANI-0296034. The preliminary results of this work is presented in “Efficient Overlay Multicast in Mobile Ad Hoc Networks,” Proc. IEEE WCNC 2003. Chao Gui is a Technical Research Staff at Kiyon Inc (www.kiyon.com). His research interests include wireless networking and mobile computing. His current efforts are on industrial implementation of wireless mesh networks and embedded systems. Dr. Gui has received Ph.D. in Computer Science from University of California at Davis in 2005. Prasant Mohapatra is currently a Professor in the Department of Computer Science at the University of California, Davis. He has also held various positions at Iowa State University, Michigan State University, Intel Corporation, Panasonic Technologies, Institute of Infocomm Research, Singapore, and the National ICT, Australia. Dr. Mohapatra received his Ph.D. in Computer Engineering from the Pennsylvania State University in 1993. He was/is on the editorial boards of the IEEE Transactions on computers, ACM/Springer WINET, and Ad hoc Networks Journal. He has served on numerous technical program committees for international conferences, and served on several panels. He was the Program Vice-Chair of INFOCOM 2004, and the Program Co-Chair of the First IEEE International Conference on Sensor and Ad Hoc Communications and Networks, (SECON-2004). Dr. Mohapatra’s research interests are in the areas of wireless networks, sensor networks, Internet protocols and QoS.     

基于GMPLS的动态分布式WDM网状网恢复路由选择算法研究

提出了一种在GMPLS体系下的分布式业务路径和恢复路径在线选路算法，以使光网络在动态业务请求下能有效的利用波长资源。由于该算法对业务路径和恢复路径的选择进行了联合优化，其性能更优于独立业务路径恢复算法(SSPR)。仿真结果表明，利用该算法时业务路径和恢复路径占用的网络总资源明显小于SSPR算法，而恢复时间只比SSPR算法略有增加。     

Mesh结构P/G布线网络层次化快速分析方法

本文提出了一个基于网络划分的P／G布线网络层次化快速分析方法。其中，对于子网运算，通过对Cholesky分解法三角化对称正定阵的图模型分析，并基于Mesh结构网络的自身特点，提出了一个基于图顶点排序的加速子网分析运算策略；并用基于MPI的并行结构实现了P／G布线网络分析的并行运算。     

Electrical Characteristics of <Emphasis Type="Italic">n</Emphasis>-ZnO/<Emphasis Type="Italic">p</Emphasis>-Si Heterojunction Diodes Grown by Pulsed Laser Deposition at Different Oxygen Pressures

Heterojunction diodes of n-type ZnO/p-type silicon (100) were fabricated by pulsed laser deposition of ZnO films on p-Si substrates in oxygen ambient at different pressures. These heterojunctions were found to be rectifying with a maximum forward-to-reverse current ratio of about 1,000 in the applied voltage range of −5 V to +5 V. The turn-on voltage of the heterojunctions was found to depend on the ambient oxygen pressure during the growth of the ZnO film. The current density–voltage characteristics and the variation of the series resistance of the n-ZnO/p-Si heterojunctions were found to be in line with the Anderson model and Burstein-Moss (BM) shift.     

基于Markov过程的渲染集群可用性分析

在考虑到多个集群节点存在着CMF(共模失效)情形下研究了系统的可用性。分别提出了由2个集群节点组成的系统在"单步修复"和"整体修复"方案下的CTMC(连续时间Markov链),得出了2种不同方案的优劣比较结论,同时采用SRN(随机回报网)仿真工具进行了验证;并进一步研讨了n(n>2)个集群节点组成系统的情形。     

Connectivity in one-dimensional ad hoc networks: A queueing theoretical approach

In this paper we analyze connectivity issues in one-dimensional ad hoc networks. Starting with a deterministic channel model, we show how an equivalent GI|D|∞ queueing model may be used to address network connectivity. In this way, we obtain exact results for the coverage probability, the node isolation probability and the connectivity distance for various node placement statistics. We then show how a GI|G|∞ model may be used to study broadcast percolation problems in ad hoc networks with general node placement in the presence of fading channels. In particular, we obtain explicit results for the case of nodes distributed according to a Poisson distribution operating in a fading/shadowing environment. In the latter case, heavy traffic theorems are applied to derive the critical transmission power for connectivity and broadcast percolation distance in highly dense networks. The impact of signal processing schemes able to exploit the diversity provided by small-scale fading by means of multiple antennas is considered. The analysis is then extended to the case of unreliable ad hoc networks, with an in-depth discussion of asymptotic results. This work was partially supported by the EURO NGI Network of Excellence. The work of D. Miorandi was partially supported by Fond. A. Gini. This work has been done while D. Miorandi, at that time with University of Padova (Italy), was visiting the MAESTRO project at INRIA Sophia Antipolis. Daniele Miorandi received his “Laurea” (summa cum laude) and Ph.D. degrees from Univ. of Padova (Italy) in 2001 and 2005, respectively. He currently holds a post-doc position at CREATE-NET, Trento (Italy). In 2003/04 he spent 12 months of his doctoral thesis visiting the MAESTRO team at INRIA Sophia Antipolis (France). His research interests include stochastic modelling, performance evaluation and protocols design for wireless networks. Eitan Altman received the B.Sc. degree in electrical engineering (1984), the B.A. degree in physics (1984) and the Ph.D. degree in electrical engineering (1990), all from the Technion-Israel Institute, Haifa. In (1990) he further received his B.Mus. degree in music composition in Tel-Aviv university. Since 1990, he has been with INRIA (National research institute in informatics and control) in Sophia-Antipolis, France. His current research interests include performance evaluation and control of telecommunication networks and in particular congestion control, wireless communications and networking games. He is in the editorial board of several scientific journals: Stochastic Models, JEDC, COMNET, SIAM SICON and WINET. He has been the (co)chairman of the program committee of several international conferences and workshops (on game theory, networking games and mobile networks). More informaion can be found at http://www.inria.fr/mistral/personnel/Eitan.Altman/me.html