An efficient Fault Localization Algorithm for IP/WDM Networks

We propose an algorithm for localizing multiple failures in an IP/WDM network. They can be either hard failures (unexpected events that interrupt suddenly the established channels) or soft failures (events that progressively degrade the quality of transmission). Hard failures are detected at the WDM layer, whereas soft failures can be detected at the optical layer if proper testing equipment is deployed, and/or by performance monitoring at a higher layer, which is here IP. The algorithm also tolerates missing and false alarms. Even without missing and false alarms, multiple fault localization is NP-hard. The diagnosis phase (i.e., the localization of the faulty components upon reception of the alarms) can however remain very fast, but at the expense of a very complex precomputation phase, carried out whenever the optical channels are set up or cleared down. We show how the algorithm performs on an example of an IP/WDM network

Fault location algorithms for optical networks

Today, there is no doubt that optical networks are the solution to the explosion of Internet traffic that two decades ago we only dreamed about. They offer high capacity with the use of Wavelength Division Multiplexing (WDM) techniques among others. However, this increase of available capacity can be betrayed by the high quantity of information that can be lost when a failure occurs because not only one, but several channels will then be interrupted. Efficient fault detection and location mechanisms are therefore needed. Our challenge is to identify and locate failures (single or multiple) at the physical layer of an optical network in the presence of some lost and/or false alarms. After briefly introducing optical networks and the multiplexing techniques that can be used, we study the most common components and their most usual failures. We propose a classification of all the network components based on their behaviour when failures occur. This classification gives an abstract model of the optical network, which is appropriate for developing algorithms to locate faulty elements. Two algorithms that solve the fault location problem are proposed. Both algorithms cope with existence of false and missing alarms when locating single and multiple failures. The problem of locating multiple failures already in the absence of false or missing alarms, has been shown to be NP-complete. The first algorithm, which is called Alarm Filtering Algorithm (AFA) is based on the combination of two approaches: forward and backward. The forward approach returns for each network element, their domain, which is the set of network elements that will send an alarm when the considered element fails. The backward approach returns the set of elements that are directly related to the received alarms. In this approach, the alarms that are considered to provide redundant information, are discarded. The combination of the results given by both approaches allows the location of multiple failures, given an allowed number of false and missing alarms. However, this algorithm does not minimize the complexity when new alarms are received. Hence, a second algorithm, which is called Fault Location Algorithm (FLA), is proposed. The FLA concentrates the complexity in ,a pre-computation phase, so that when new alarms are received, the result of the algorithm is rapidly displayed. The FLA algorithm is based on the construction of a binary tree that realizes a non linear error correcting code. The FLA has also been extended to locate soft failures in addition to hard failures. Hard failures are unexpected failures, whereas soft failures are progressive failures due to equipment aging, misalignments or external factors such as temperature or pressure. Both algorithms are compared on some simulated networks using different network topologies and failure cases. The comparison has also be done on the basis of their worst case complexity. Some conclusions indication with which settings each algorithm perform the best, were obtained

Monitoring of dynamic all-optical network.

本文提出一种新颖的动态全光网络监控分布式算法，该算法可估计光网络中光纤链路上的误码率，在不需要额外光监控元件的情况下同时监控，检测和定位多处光纤链路损坏。在光网络传输过程中，各个终端结点的接受机可以时时地估计出收到光流的误码率，这些误码率信息可以通过扩展OSPF-TE协议在全网共享。基于这些共享的误码率信息，我们将光纤损坏检测问题抽像成一个线性编程（LP）算法，其中每一个误码率信息代表一个限制条件。我们之后运用一些算法优化技巧将这个问题的维度和复杂度大大地降低，以便可以直接嵌入到每个网络结点可能自带的微处理器单元中进行实时计算运用。本文提出的算法同时适用于没有光波长转换器的光网络和配备光波长转换器的光网络。 通过沿用OSPF协议的分层多域思想，大规模网络可以分化成小的域和连接各域的主干网络，从而可以将一个复杂的大规模网络检错问题转化成一系列简单小网络检错问题。通过将该算法在一个由408 节点组成，支持40波长的大规模GMPLS 网络仿真平台上仿真，算法的有效性得到了验证。为了保证用于仿真的网络流量模型合理且符合实际，本文也对动态全光网络流量模型做了一定研究。在自相似网络流量模型下，我们发现长短光流的不公平性问题可以给动态全光网络带来很大问题，会大大地降低网络的吞吐率。我们运用一种截短长光流的方法可以将这个问题很有效地解决。据我们所知，这是目前唯一的一个能运用于现实中超大规模光网络的低成本可实现且可以作到波长级监控和同时监控多个链路错误的算法。该方法可以不用额外添加昂贵的光监控元件就可实现对动态全光网络的监控，并且该方法同时适用于透明，半透明及配置波长转换器的光网络。A new and efficient distributed algorithm for estimating the bit-error-rate (BER) of links in dynamic optical networks is proposed. The method can be used to monitor, detect and localize multiple soft link-failures without incurring any additional optical monitoring equipment. During the transmission of each optical flow the end node’s receiver can estimate the digital BER information, and the BER information can be shared among the network by extending the Open Shortest Path First-Traffic Engineering Extension (OSPF-TE) protocol easily. We model the faults localization problem as a linear programming (LP) algorithm, where each BER information measured from a flow serves as a constraint. Optimization techniques are applied to significantly simplify the complexity of the LP algorithm in order to make it solvable in real time by an integrated processor attached to the network node. The proposed algorithm is capable of monitoring networks with or without wavelength converters. A large scale network can be divided into several layers according to the OSPF protocol, thus the algorithm can be applied to large networks in the real world similar to OSPF. The monitoring algorithm is demonstrated by network simulations over a 408-node, 40-wavelength network test-bed where up to twenty faulty links are identified.To make sure the traffic generator model is reasonable, the traffic model for dynamic all-optical network is also studied in this work. Under self-similar traffic, we found that the dynamic optical networks suffer from the long flow short flow unfairness problem, which would reduce the throughput as well. So a segmentation strategy is proposed to solve this problem.To the best of our knowledge, this is the first realistic and low-cost framework which can monitor channel level BER changes to identify multi-link-failures efficiently for large scale dynamic all-optical WDM networks, without using expensive optical monitors or additional supervisory channels. The approach proposed is applicable to transparent, translucent and wavelength-converted optical networks.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Li, Huadong.Thesis (M.Phil.)--Chinese University of Hong Kong, 2012.Includes bibliographical references (leaves 64-66).Abstracts also in Chinese.Chapter Chapter 1 --- Introduction --- p.1Chapter Chapter 2 --- Backgrounds --- p.11Chapter 2.1 --- ROADMs, Dynamic networks --- p.11Chapter 2.1 --- Types of failures considered: --- p.13Chapter 2.2 --- Brief review of OSPF routing protocol --- p.15Chapter Chapter 3 --- Traffic model used --- p.16Chapter 3.1 --- Introduction --- p.16Chapter 3.2 --- LFSF unfairness problem --- p.19Chapter 3.3 --- Flow segmentation strategy --- p.23Chapter 3.4 --- Simulation results --- p.24Chapter 3.5 --- Summary and Conclusion --- p.29Chapter Chapter 4 --- Estimated digital BER monitoring and faults diagnosis algorithm --- p.31Chapter 4.1 --- Intra-domain faults diagnosis algorithm --- p.31Chapter 4.2 --- Hierarchically layering scheme for inter-domain network monitoring --- p.37Chapter Chapter 5 --- Simulation results and analysis --- p.40Chapter 5.1 --- Simulation set up --- p.40Chapter 5.1.1 --- 100Gbps simulation set up --- p.40Chapter 5.1.2 --- 10Gbps simulation set up --- p.42Chapter 5.2 --- Simulation results --- p.44Chapter 5.2.1 --- 100Gbps simulation results: --- p.44Chapter 5.2.2 --- 10Gbps simulation: --- p.51Chapter 5.3 --- Conclusion --- p.61Chapter Chapter 6 --- Conclusion --- p.62Reference --- p.6

Cluster-based Method for Eavesdropping Identification and Localization in Optical Links

We propose a cluster-based method to detect and locate eavesdropping events in optical line systems characterized by small power losses. Our findings indicate that detecting such subtle losses from eavesdropping can be accomplished solely through optical performance monitoring (OPM) data collected at the receiver. On the other hand, the localization of such events can be effectively achieved by leveraging in-line OPM data.Comment: 4 pages, 6 figures, Asia Communications and Photonics Conference (ACP) 202

Failure Localization Aware Protection in All-Optical Networks

The recent development of optical signal processing and switching makes the all-optical networks a potential candidate for the underlying transmission system in the near future. However, despite its higher transmission data rate and efficiency, the lack of optical-electro-optical (OEO) conversions makes fault management a challenge. A single fiber cut can interrupt several connections, disrupting many services which results in a massive loss of data. With the ever-growing demand for time-sensitive applications, the ability to maintain service continuity in communication networks has only been growing in importance. In order to guarantee network survivability, fast fault localization and fault recovery are essential. Conventional monitoring-trail (m-trail) based schemes can unambiguously localize link failures. However, the deployment of m-trail requires extra transceivers and wavelengths dedicated to monitoring the link state. Non-negligible overhead makes m-trail schemes neither scalable nor practicable. In this thesis, we propose two Failure Localization Aware (FLA) routing schemes to aid failure localization. When a link fails, all traversing lightpaths become dark, and the transceiver at the end node of each interrupted ligthpath issues an alarm signal to report the path failure. By correlating the information of all affected and unaffected paths, it is possible to narrow down the number of possible fault locations to just a few possible locations. However, without the assistance of dedicated supervisory lightpaths, and based solely on the alarm generated by the interrupted lightpaths, ambiguity in failure localization may be unavoidable. Hence, we design a Failure Localization Aware Routing and Wavelength Assignment (FLA-RWA) scheme, the Least Ambiguous Path (LAP) routing scheme, to dynamically allocate connection requests with minimum ambiguity in the localization of a link failure. The performance of the proposed heuristic is evaluated and compared with traditional RWA algorithms via network simulations. The results show that the proposed LAP algorithm achieves the lowest ambiguity among all examined schemes, at the cost of slightly higher wavelength consumption than the alternate shortest path scheme. We also propose a Failure Localization Aware Protection (FLA-P) scheme that is based on the idea of also monitoring the protection paths in a system with path protection for failure localization. The Least Ambiguous Protection Path (LAPP) routing algorithm arranges the protection path routes with the objective of minimizing the ambiguity in failure localization. We evaluate and compare the ambiguity in fault localization when monitoring only the working paths and when monitoring both working and protection paths. We also compare the performance of protection paths with different schemes in regards to fault localization

Cloud RAN for Mobile Networks - a Technology Overview

Cloud Radio Access Network (C-RAN) is a novel mobile network architecture which can address a number of challenges the operators face while trying to support growing end-user’s needs. The main idea behind C-RAN is to pool the Baseband Units (BBUs) from multiple base stations into centralized BBU Pool for statistical multiplexing gain, while shifting the burden to the high-speed wireline transmission of In-phase and Quadrature (IQ) data. C-RAN enables energy efficient network operation and possible cost savings on base- band resources. Furthermore, it improves network capacity by performing load balancing and cooperative processing of signals originating from several base stations. This article surveys the state-of-the-art literature on C-RAN. It can serve as a starting point for anyone willing to understand C-RAN architecture and advance the research on C-RA