Simultaneous OCDM signal transmission over multiple WDM channels using Mach-Zehnder interferometric selector

Proposed is an easy technique for overlaying multiple wavelength division multiplexing (WDM) signals on optical code division multiplexing (OCDM) signals. The approach results in a broad coding spectrum for OCDM signals, and thus provides highly secure services in WDM-based networks. The technique is validated experimentally using an OCDM signal and two WDM signals.     

Fault management in IP-over-WDM networks: WDM protection versus IPrestoration

We consider an IP-over-WDM network in which network nodes employ optical crossconnects and IP routers. Nodes are connected by fibers to form a mesh topology. Any two IP routers in this network can be connected together by an all-optical wavelength-division multiplexing (WDM) channel, called a lightpath, and the collection of lightpaths that are set up form a virtual topology. In this paper, we concentrate on single fiber failures, since they are the predominant form of failures in optical networks. Since each lightpath is expected to operate at a rate of few gigabits per second, a fiber failure can cause a significant loss of bandwidth and revenue. Thus, the network designer must provide a fault-management technique that combats fiber failures. We consider two fault-management techniques in an IP-over-WDM network: (1) provide protection at the WDM layer (i.e., set up a backup lightpath for every primary lightpath) or (2) provide restoration at the IP layer (i.e., overprovision the network so that after a fiber failure, the network should still be able to carry all the traffic it was carrying before the fiber failure). We formulate these fault-management problems mathematically, develop heuristics to find efficient solutions in typical networks, and analyze their characteristics (e.g., maximum guaranteed network capacity in the event of a fiber failure and the recovery time) relative to each other     

Priority-based Dynamic Lightpath Allocation for Survivable WDM Networks

In recent years, there has been considerable research interest in the design of survivable wavelength division multiplexing (WDM) networks. Many papers have proposed mixed-integer linear program (MILP) formulations as well as heuristics to optimally allocate lightpaths, using protection based schemes. Such schemes provide quick and guaranteed recovery, but do not use resources efficiently. About 50% of allocated resources remain idle, under fault-free conditions. If these “idle” resources were used for low-priority connections (which could be pre-empted if necessary), the resource utilization would improve significantly. This paper introduces two MILP formulations for priority-based dynamic lightpath allocation in survivable WDM networks. We define three different levels of service and allocate resources based on the requested service level. An important advantage of our approach is that while we can handle multiple levels of service, the traditional (single level) shared and dedicated path protection schemes can be treated simply as a special case of the proposed formulations. The first formulation solves the problem optimally, but is quite time consuming. The second formulation makes some simplifications, and is more efficient. The results demonstrate that our approach can significantly improve resource utilization and is feasible for practical sized networks, particularly under low- to medium-traffic load. For large networks and high traffic conditions, simpler heurtistic algorithms are more appropriate. In such cases, the proposed MILP formulation can be a useful tool to validate the performance of the heuristics.     

On the performance of distributed lightpath provisioning with dynamic routing and wavelength assignment

Distributed lightpath provisioning in wavelength-division multiplexing (WDM) networks has gained wide research interests. In this article, we study the performance of distributed lightpath provisioning in WDM networks with dynamic routing and wavelength assignment (RWA). Specifically, we consider the case where routing of each lightpath is calculated based on globally flooded link-state information, and wavelength assignment is decided through local information exchanges. Simulation results show that such schemes steadily outperform those schemes with only global flooding or only local information exchanges. More significantly, the impacts of various factors on the proposed scheme, including RWA algorithm, network topology, number of wavelengths per fiber, global flooding interval, and traffic load, have been evaluated. Such evaluations help to achieve some insights useful for the future developments of efficient lightpath provisioning schemes.

A computational model for estimating blocking probabilities of multifiber WDM optical networks

In this letter, we propose a computational model for calculating blocking probabilities of multifiber wavelength division multiplexing (WDM) optical networks. We first derive the blocking probability of a fiber based on a Markov chain, from which the blocking probability of a link is derived by means of conditional probabilities. The blocking probability of a lightpath can be computed by a recursive formula. Finally, the network-wide blocking probability can be expressed as the ratio of the total blocked load versus the total offered load. Simulation results for different fiber-wavelength configurations conform closely to the numerical results based on our proposed model, thus demonstrating the feasibility of our proposed model for estimating the blocking performance of multifiber WDM optical networks.     

Traffic grooming in an optical WDM mesh network

In wavelength-division multiplexing (WDM) optical networks, the bandwidth request of a traffic stream can be much lower than the capacity of a lightpath. Efficiently grooming low-speed connections onto high-capacity lightpaths will improve the network throughput and reduce the network cost. In WDM/SONET ring networks, it has been shown in the optical network literature that by carefully grooming the low-speed connection and using wavelength-division multiplexer (OADM) to perform the optical bypass at intermediate nodes, electronic ADMs can be saved and network cost will be reduced. In this study, we investigate the traffic-grooming problem in a WDM-based optical mesh topology network. Our objective is to improve the network throughput. We study the node architecture for a WDM mesh network with traffic-grooming capability. A mathematical formulation of the traffic-grooming problem is presented in this study and several fast heuristics are also proposed and evaluated     

Performance and testbed study of topology reconfiguration in IP over optical networks

With the widespread deployment of Internet protocol/wavelength division multiplexing (IP/WDM) networks, it becomes necessary to develop traffic engineering (TE) solutions that can effectively exploit WDM reconfigurability. More importantly, experimental work on reconfiguring lightpath topology over testbed IP/WDM networks is needed urgently to push the technology forward to operational networks. This paper presents a performance and testbed study of topology reconfiguration for IP/WDM networks. IP/WDM TE can be fulfilled in two fashions, overlay vs. integrated, which drives the network control software, e.g., routing and signaling protocols, and selects the corresponding network architecture model, e.g., overlay or peer-to-peer. We present a traffic management framework for IP over reconfigurable WDM networks. Three "one-hop traffic maximization"-oriented heuristic algorithms for lightpath topology design are introduced. A reconfiguration migration algorithm to minimize network impact is presented. To verify the performance of the topology design algorithms, we have conducted extensive simulation study. The simulation results show that the topologies designed by the reconfiguration algorithms outperform the fixed topology with throughput gain as well as average hop-distance reduction. We describe the testbed network and software architecture developed in the Defense Advanced Research Projects Agency (DARPA) Next Generation Internet (NGI) SuperNet Network Control and Management project and report the TE experiments conducted over the testbed.     

Dynamic connection provisioning with shared protection in IP/WDM networks

Internet protocol (IP) traffic connections arrive dynamically at wavelength‐division multiplexing (WDM) network edges with low data rates compared with the wavelength capacity, availability, and quality‐of‐service (QoS) constraints. This paper introduces a scheme to be integrated into the control and management plane of IP/WDM networks to satisfy the availability and QoS required for IP traffic connections bundled onto a single wavelength (lightpath) in WDM networks protected by shared‐backup path protection (SBPP). This scheme consists of two main operations: (i) routing multi‐granular connections and traffic grooming policies, and (ii) providing appropriate shared protection on the basis of subscribers’ service‐level agreements in terms of data rate, availability, and blocking probability. Using the Markov chain process, a probabilistic approach is developed to conceive connection blocking probability models, which can quantify the blocking probability and service utilization of M:N and 1:N SBPP schemes. The proposed scheme and developed mathematical models have been evaluated in terms of bandwidth blocking ratio, availability satisfaction rate, network utilization, and connection blocking probability performance metrics. The obtained research results in this paper provide network operators an operational setting parameter, which controls the allocation of working and backup resources to dynamic IP traffic connections on the basis of their priority and data rate while satisfying their requirements in terms of bandwidth and availability. Copyright © 2013 John Wiley & Sons, Ltd.     

QoS aware traffic grooming and integrated routing on IP over WDM networks

In this article, we consider traffic grooming and integrated routing in IP over WDM networks. The challenges of this problem come from jointly considering traffic grooming, IP routing, and lightpath routing and wavelength assignment (RWA). Due to the high bandwidth of optical fiber, there exists a mismatch between the capacity needed by an IP flow and that provided by a single lightpath. Traffic grooming is therefore used to increase the network utilization by aggregating multiple IP flows in a single lightpath. However, traffic grooming incurs additional delays that might violate Quality-of-Service (QoS) requirements of IP users. In this work, the tradeoff between traffic grooming and IP QoS routing is well-formulated as a mixed integer and linear optimization problem, in which the revenue from successfully provisioning IP paths is to be maximized. Problem constraints include IP QoS, routing, optical RWA, and the WDM network capacity. We propose a novel Lagrangean relaxation (LGR) algorithm to perform constraint relaxation and derive a set of subproblems. The Lagrangean multipliers are used in the proposed algorithm to obtain a solution in consideration of grooming advantage and resource constraints simultaneously. Through numerical experiments and comparisons between the proposed algorithm and a two-phase approach, LGR outperforms the two-phase approach under all experimental cases. In particular, the improvement ratio becomes even more significant when the ratio of IP flow to the wavelength capacity is smaller.     

OCDM/WDM多跳光网络及其端到端误码率性能研究

采用码分复用与波分复用相结合的技术可以构成基于波长和码字转换的多跳光网络。只考虑码字转换,首先给出了光码分复用/波分复用多跳光网络的构成方法和码字转换器的一般结构,然后分析了网络中端到端的误码率性能。计算结果表明:码字转换次数的增加对端到端误码率的影响较小;当接收端的干扰信道数小于前一码字转换阶段的干扰信道数时,端到端误码率与判决阈值的关系曲线在最小值附近出现一近水平区间。     

Experimental GMPLS-based provisioning for future all-optical DPRing-based MAN

Given the abundance and strategic importance of ring fiber plants in metropolitan area networks (MANs), and the accelerating growth of Internet traffic, it is crucial to extend the existing Internet protocol (IP)-based generalized multiprotocol label switching (GMPLS) framework to provision dynamic wavelength division multiplexing (WDM) optical rings. Nevertheless, the emerging GMPLS-based lightpath provisioning does not cover the intricacies of optical rings. No GMPLS standard exists for optical add-drop multiplexer (OADM) rings, relying instead upon proprietary static solution. The objective of this paper is to propose and evaluate novel GMPLS-based lightpath signaling and wavelength reservation schemes specifically designed for dedicated protection ring (DPRing)-based MANs. Performance evaluation has been carried out in a GMPLS-based testbed named ADRENALINE.     

Performance of Single-Hop WDM LANs Supporting Real-Time Services

Optical wavelength division multiplexing (WDM) local area networks are capable of fulfilling the enormous bandwidth demands of present and future applications. Up to now, the WDM LAN world is primarily dominated by the passive-star coupler (PSC) based architectures, for which many medium access control (MAC) protocols have been proposed. However, an arrayed waveguide grating multiplexer (AWGM)-based single-hop WDM network seems to be a very promising alternative. One of the most critical issues in designing next generation photonic LANs is the support of real-time services for applications with different time constraints. In this paper, different basic access protocols for the PSC as well as AWGM-based single-hop WDM LANs are considered and their performance in supporting real-time traffic is analyzed by means of extensive computer simulations. For evaluation of real-time performance, packet drop rates and deadline missing rates are taken as performance measures. Furthermore, new real-time message scheduling schemes are proposed which improve the performance of protocols accommodating mixed traffic. They can be differentiated between message scheduling at the source nodes transmit queues and scheduling based upon control information from a control channel. It is shown that both types of priority scheduling significantly improve the overall real-time performance.     

波分复用网络的保护方式

首先介绍了在WDM网络中常用的光通道保护、光复用段保护方式及其实际使用方案,然后对WDM网络中采用不同保护方式的优缺点进行了分析,并对WDM网络中保护方案的设计提出了建议.     

Application of Raman-distributed amplification to WDM transmissionsystems using 1.55-μm dispersion-shifted fiber

A numerical design method for wavelength division multiplexing (WDM) transmission systems employing distributed Raman amplification (DRA) is proposed. This method evaluates fiber nonlinear effects by considering the equivalent fiber loss with DRA. The method is used to evaluate the performance of WDM transmission systems in which DRA is employed in a 1.55-μm dispersion-shifted fiber (DSF) transmission line. Transmission limit and the optimum fiber input powers for 1550-nm band (C-band) and 1580-nm band (L-band) transmission are investigated. Results show that bidirectional pumping is the best approach to extending transmission distance. Furthermore, the transport limits of optical transport networks that use DRA and optical add/drop multiplexers are analyzed     

Optical satellite networks

Several nongeosynchronous satellite constellation networks providing broad-band access to end-users are currently under development. The use of multigigabit laser intersatellite links (ISLs) is the enabling factor for routing traffic through the spare segment and creating a global space-based optical backbone network. Optical networking techniques based on wavelength division multiplexing (WDM) ISLs and wavelength routing can allow by-pass of the transit traffic significantly simplifying routing decisions and minimizing processing delays. The paper examines the characteristics of these networks and investigates the applicability of various optical networking schemes based on single hop and multihop approaches. Single hop can be adopted in medium earth orbit (MEO) systems consisting of 10 to 15 satellites whereas double-hop schemes based on the matrix lightpath allocation approach are suited for constellations up to 100 satellites, covering the requirements of most of the proposed low earth orbit (LEO) systems. Multihop will be required for some of the very large in number of satellites constellations. Statistical multiplexing of the transported traffic over the ISLs appears to be a necessary condition to achieve an efficient utilization of the satellite resources. Traffic routing has to take into account the impact of the varying range of the interorbit ISLs on the propagation delays. Although maximum leverage of the technologies developed for fiber optic WDM networks should be made, the technologies to be employed on board the satellites have to be space-qualified that may limit the applicability of some otherwise high-efficiency components     

Subpath protection for scalability and fast recovery in optical WDM mesh networks

This paper investigates survivable lightpath provisioning and fast protection switching for generic mesh-based optical networks employing wavelength-division multiplexing (WDM). We propose subpath protection, which is a generalization of shared-path protection. The main ideas of subpath protection are: 1) to partition a large optical network into smaller domains and 2) to apply shared-path protection to the optical network such that an intradomain lightpath does not use resources of other domains and the primary/backup paths of an interdomain lightpath exit a domain (and enter another domain) through a common domain-border node. We mathematically formulate the routing and wavelength-assignment (RWA) problem under subpath protection for a given set of lightpath requests, prove that the problem is NP-complete, and develop a heuristic to find efficient solutions. Comparisons between subpath protection and shared-path protection on a nationwide network with dozens of wavelengths per fiber show that, for a modest sacrifice in resource utilization, subpath protection achieves improved survivability, much higher scalability, and significantly reduced fault-recovery time.     

Rerouting technique with dynamic traffic in WDM optical networks

In this paper, we have proposed an efficient wavelength rerouting algorithm for dynamic provisioning of lightpath. In wavelength division multiplexed (WDM) networks rerouting of lightpath can be used to improve throughput and to reduce blocking probability. We have proposed a shortest path wavelength rerouting (SPWRR) algorithm for dynamic traffic in WDM optical networks. The results have shown that SPWRR algorithm can improve blocking performance of the network. In this paper, low complexity algorithm has been developed which is used for the calculation of blocking probability of network. The proposed algorithm has also been applied on the realistic network such as NSFnet for calculation and optimization of blocking probability of the network.     

WDM光网络中的业务量疏导

波分复用（WDM）技术在主干传送网中巳广泛应用，WDM光网络的研究进展也非常迅速，光网络中的业务量疏导定义为复用、解复用和交换低速率业务流到大容量的光路中的行为。介绍了WDM光网络的业务量疏导的重要性，研究方法及其最新研究进展情况。     

A novel generic graph model for traffic grooming in heterogeneous WDM mesh networks

As the operation of our fiber-optic backbone networks migrates from interconnected SONET rings to arbitrary mesh topology, traffic grooming on wavelength-division multiplexing (WDM) mesh networks becomes an extremely important research problem. To address this problem, we propose a new generic graph model for traffic grooming in heterogeneous WDM mesh networks. The novelty of our model is that, by only manipulating the edges of the auxiliary graph created by our model and the weights of these edges, our model can achieve various objectives using different grooming policies, while taking into account various constraints such as transceivers, wavelengths, wavelength-conversion capabilities, and grooming capabilities. Based on the auxiliary graph, we develop an integrated traffic-grooming algorithm (IGABAG) and an integrated grooming procedure (INGPROC) which jointly solve several traffic-grooming subproblems by simply applying the shortest-path computation method. Different grooming policies can be represented by different weight-assignment functions, and the performance of these grooming policies are compared under both nonblocking scenario and blocking scenario. The IGABAG can be applied to both static and dynamic traffic grooming. In static grooming, the traffic-selection scheme is key to achieving good network performance. We propose several traffic-selection schemes based on this model and we evaluate their performance for different network topologies.     

Dynamic lightpath provisioning in optical WDM mesh networks with asymmetric nodes

The wavelength selective switch-based reconfigurable optical add/drop multiplexers is a promising switching equipment for future reconfigurable wavelength-division multiplexing (WDM) mesh networks. However, its asymmetric switching property complicates the optimal routing and wavelength assignment problem. In an asymmetric switching scenario, using the classic Dijkstra’s algorithm can lead to invalid paths traversing unconnected ports of an asymmetric node. To solve this problem, we propose both link-state (LS) and distance vector (DV) schemes for dynamic lightpath provisioning in optical WDM mesh networks with asymmetric nodes. The proposed LS schemes include the asymmetric switching-aware (ASA) Dijkstra’s algorithm, the $K$ -shortest path-based algorithm, and the entire path searching (EPS) algorithm. Simulation results show that the ASA-Dijkstra’s algorithm will bring notable improvement of the blocking performance with low computational complexity, while the EPS algorithm has much higher complexity and is not suitable to be employed in large-scale networks. On the other hand, our proposed DV solution, i.e., the information diffusion-based routing (IDBR), can achieve the lowest blocking probability with the lowest computational complexity. Moreover, IDBR does not require the distribution of local asymmetric switching information like the LS schemes, thus having a high level of topology confidentiality.