Demonstration of the highly reliable Hikari router network based on a newly developed disjoint path selection scheme

Integration of multiprotocol label switching functions and multiprotocol lambda switching functions can enhance the throughput of IP networks and remove bottlenecks that are derived from electrical packet processing. To enhance the packet forwarding capability, NTT proposed a photonic MPLS concept that includes MP/spl lambda/S, and demonstrated IP, MPLS, and photonic MPLS integrated router systems called the photonic MPLS router. This router system is now called the Hikari router. The word Hikari is Japanese meaning beam, light, lightwave, optical, photonic, and sunshine. The amount of IP data traffic has grown remarkably. Massive IP routers and flexible route control mechanisms are now required to cope with the increased amount of traffic. The Hikari router can offer two solutions utilizing photonic switching technologies, and photonic network operation and management technologies. The first solution is utilizing photonic switching technologies realized using optical-switch-based crossconnect systems. The other solution is realized using the MPLS and MP/spl lambda/S signaling protocol and photonic network protection functions. In this article we report on the implementation of the Hikari router systems, propose a newly developed disjoint path selection scheme for generalized MPLS networks with shared risk link group constraints, and demonstrate the signaling protocol and network protection functions. The demonstration system achieves a distributed optical path set-up/tear-down protocol with an extended constraint-based routing label distribution protocol. Fast self-healing through automatic protection switching and a new restoration scheme are also implemented. These functions are successfully implemented, and the performance is verified on a demonstration network. The protection switching scheme achieves protection in less than 20 ms, and the optical path restoration scheme achieves restoration in less than 500 ms.     

Optical digital cross-connect system using photonic switch matricesand optical amplifiers

This paper presents, for potential application to network failure restoration, an optical digital cross-connect system (DCS) which uses both a photonic switching network and an electric DCS. It is shown that a system constructed of LiNbO₃ 8×8 switch matrices and semiconductor traveling-wave optical amplifiers (TWA's) could be applied to metropolitan area networks. An experimental optical DCS system has been designed and fabricated which incorporates both LiNbO₃ switch matrices and TWA's, and with it, line-failure restoration, a fundamental operation of optical DCS, has been successfully demonstrated     

光环形网的光信噪比分析与系统设计

文章指出光环形网的设计中必须考虑最长环路保护时的光信噪比(OSNR)计算问题。导出了光分插复用／光交叉连接(OADM／OXC)节点级联的OSNR的计算公式。最后针对链路发生故障点不同的同一业务波长配置的保护倒换情况进行了OSNR的分析，给出了环路保护倒换情况下的OSNR最低条件的模型，并依据此模型建立了光环形网工程设计方法，简化了工程设计中OSNR验证的计算量。     

基于低串扰OXC的自动链路交换系统的设计与实现

介绍了基于低串扰OXC的自动链路交换系统的设计与实现,详细阐述了系统中OXC路由模块的硬件设计及实验方案.实验网络可以完成端到端光链路的自动建立.     

Broadband hitless bypass switch for integrated photonic circuits

A new microphotonic hitless switch is proposed. By enabling continuous, uninterrupted transition to a bypass path, it permits tuning of wavelength add-drop filters without disturbing intermediate channels. The scheme comprises two symmetrically actuated, 2 /spl times/ 2 /spl Delta//spl beta/-type optical switches, antisymmetrically cascaded in a balanced Mach-Zehnder configuration, and a /spl pi/ differential phase shift in the interferometer arms. By symmetry, it provides for wavelength-independent hitless operation before, during and after switch reconfiguration, permitting slow switching independent of bit rate. Compact implementations using high-index-contrast microelectromechanical-system (MEMS)-actuated switches are proposed.     

MEMS: the path to large optical crossconnects

Continuous growth in demand for optical network capacity and the sudden maturation of WDM technologies have fueled the development of long-haul optical network systems that transport tens to hundreds of wavelengths per fiber, with each wavelength modulated at 10 Gb/s or more. Micro-electromechanical systems devices are recognized to be the enabling technologies to build the next-generation cost-effective and reliable high-capacity optical crossconnects. While the promises of automatically reconfigurable networks and bit-rate-independent photonic switching are bright, the endeavor to develop a high-port-count MEMS-based OXC involves overcoming challenges in MEMS design and fabrication, optical packaging, and mirror control. Due to the interdependence of many design parameters, manufacturing tolerances, and performance requirements, careful trade-offs must be made in MEMS device design as well as system design. We provide an overview of the market demand, various design trade-offs, and multidisciplinary system considerations for building reliable and manufacturable large MEMS-based OXCs     

OA&M framework for multiwavelength photonic transport networks

Photonic networks based on wavelength division multiplexing (WDM) and optical path technologies are expected to realize flexible, transparent, and cost-effective transport networks with a large transmission capacity. This paper explores the design framework of photonic transport networks taking into consideration the operation administration and maintenance (OA&M) functions required for the successful introduction of WDM systems based on the optical path concept. From the view point of network maintenance, clear distinction is made between the optical path layer and the optical section layer to facilitate accurate and smooth failure localization. The digital multiplexing span between physical multiplexing interfaces at the end-to-end digital nodes should have the same maintenance span as the corresponding optical path. We argue that cooperative maintenance by OA&M functions at both the digital and optical layers can be a practical way of network supervision. A supervisory (SV) signal transfer method and a configuration that is suitable for the terrestrial trunk network are also indicated. As an example, a practical SV system design methodology and an actual procedure developed for a single channel optical transmission system based on optical in-line amplifiers are introduced. Furthermore, application of the developed SV system and network restoration schemes is discussed for future WDM-based photonic networks. The OA&M aspects introduced will be valuable for creating future photonic network systems     

Robust photonic transport network implementation with optical crossconnect systems

We adopt the optical path concept to develop a photonic transport network. Because robustness is critical in a nationwide backbone network, we implement, as a first step, digital frame-based optical path network systems. NTT has developed several types of photonic transport systems. They are an optical path cross-connect system which has little quality of service monitoring large-scale integration circuit for each wavelength; a photonic transport payload assembler-disassembler, which accommodates client signals into optical path payloads and vice versa; and a repeater. The implementation of a PTS is depicted. A network-element-level operating system and an optical-network-level operating system are required to operate the WDM photonic transport network. We introduce a TMN-based network operating system. Finally, an overview of NTT's photonic transport network trial is presented     

Virtual path recovery switching and hitless reversion switching in180 km ATM self-healing ring

The feasibility of virtual path switching for recovery and hitless reversion switching is demonstrated using a 180 km 2.4 Gbit/s ATM self-healing ring. Results confirm rapid and highly-reliable recovery switching on line failure, and hitless reversion switching on demand     

Intelligent and Reliable Photonic Cross-Connect System Based on Overlay Model

We developed a carrier-based photonic cross-connect (PXC) system based on an optical switch, which provides wavelength-division-multiplexing transmission, generalized multiprotocol label switching, and optical-transport-network management. This system uses an overlay model in which the administrative authority between the client-network-element (NE) layer and the carrier's PXC layer is completely separated. The PXC system provides user-network interface signaling between the client NEs and the PXCs, which enables automatic optical path setting between the two client NEs through a PXC network. We considered new protection schemes for the PXC system and successfully carried out an experiment in a testbed network using one of the discussed schemes. The new concept of policy control in the control-plane management is introduced, and the feasibility of our PXC system is demonstrated. This system is promising as a prototype for a next-generation optical transport system. Furthermore, the PXC system will enable the creation of a new type of optical transport layer service, accommodate increased Internet traffic demand, and reduce network operation loads and costs for Internet service providers and carriers in the near future.     

Signaling Schemes for Distributed Connection Management in Wavelength-Routed Optical Mesh Networks

The next-generation optical transport network will evolve from point-to-point connectivity to mesh networking, which can provide fast and automatic provisioning with enhanced flexibility and survivability. Signaling is used to support connection setup, maintenance, and teardown in such a network. In this paper, we study the performance of two hop-by-hop and one parallel signaling schemes in wavelength-routed optical mesh networks. Based on the sequence between optical crossconnect (OXC) switching and signaling message processing, we classify hop-by-hop signaling into two types that comply with the requirements of GMPLS signaling protocols. These two types are forward before switching configuration (FBSC) and forward after switching configuration (FASC). Also, we propose a parallel signaling scheme that is different from the existing hop-by-hop GMPLS signaling protocols. Considering OXC architectures and traffic patterns, we compare the FBSC, FASC, and parallel signaling schemes using simulation experiments, in terms of network blocking probability and reservation time. The simulation data reveal that the performance of a signaling scheme depends on the nature of the signaling as well as the network setting (e.g., the OXC architecture and traffic pattern). We analyze reasons for this result and discuss tradeoffs between these signaling schemes. This work offers some insight into designing an efficient signaling protocol for wavelength-routed optical mesh networks.     

用于ASON中的光交叉连接设备

光交叉连接(OXC)技术是光节点的关键技术,OXC是自动交换光网络(ASON)的核心,为此阐述了ASON的基本概念和特点,以及OXC的结构和工作原理,讨论了目前实现智能OXC的关键技术:智能光MEMS(微电子机械系统)技术和通用多协议标签交换技术.     

智能OXC在ASON中的应用

IP与光技术的融合要求底层光网络具有高度的灵活性和可扩展性，产生了全新的ASON（自动交换光网络），智能OXC（光交叉连接）设备是ASON中的最关键的设备。文中简单介绍了智能自动交换光网络的概念、网络结构，详细分析了ASON中智能OXC矩阵硬件结构和OXC控制平面信令路由功能，最后讨论了智能OXC相关协议及扩展的GMPLS技术。智能OXC强大的光交换能力结合智能信息路由协议，必将与现有网络融合向全智能光网络发展。     

Dynamic provisioning of availability-constrained optical circuits in the presence of optical node failures

This paper investigates what impact optical node failures may have on wavelength-division-multiplexed networks, in which reliable end-to-end optical circuits are provisioned dynamically. At the node level, the optical cross-connect (OXC) equipment availability measure is estimated using proven component level availability models. At the network level, end-to-end optical circuits are provisioned only when the level of connection availability required by the application can be guaranteed. With the objective of yielding efficient utilization of the network resources, i.e., fibers and OXCs, circuit redundancy is achieved by means of shared path protection (SPP) switching, in combination with differentiated reliability (DiR). The resulting optimal routing and wavelength assignment problem is proven to be NP-complete. To produce suboptimal solutions in polynomial time, a heuristic technique is presented, which makes use of a time-efficient method to estimate the end-to-end circuit availability in the presence of multiple (link and node) failures. Using the proposed heuristic, a selection of representative OXC architectures and optical switching technologies is examined to assess the influence of the node equipment choice on the overall network performance.     

High-dimensionality shared-medium photonic switch

A space-division photonic switch which has the potential to achieve high dimensionality is presented. The proposed switch, which resembles a collapsed network, does not use optical crosspoints; rather a dedicated path is provided for all input/output port connections on a common high-bandwidth transmission medium. This eliminates the restrictions imposed by 2×2 switching elements in classical space-division switching fabrics. The demonstration of a fully connected 120×120 space-division time-multiplexed photonic switch is reported. The dimensionality and blocking performance of a shared-medium photonic switch that uses time-multiplexing is analyzed     

A photonic wavelength-division switching system using tunable laserdiode filters

A photonic wavelength-division switching system using semiconductor tunable wavelength filters is proposed. A switching system using wavelength switches and multistage switching networks is discussed. A crucial point in developing this switching system is to achieve a large number of wavelength-division channels. The potential of 100 wavelength-division channels in such switching systems is estimated, based on InP optical integrated circuits. A wavelength network synchronization which permits the network to utilize such a large number of wavelength-division channels without wavelength misalignment and drift is proposed. An eight-channel wavelength-division switching experiment, using phase-shift-controlled distributed feedback laser diodes as tunable wavelength filters, is reported     

Fast-Unreserved Failure Restoration for Meshed Intelligent Photonic Networks

In this article, an unreserved restoration solution for fast failure restoration in intelligent photonic networks is proposed. The unreserved restoration scheme is a real-time restoration technique that allows for utilizing network capacity dynamically and with full flexibility. However, it has the disadvantage of having a long restoration time as real-time redials are required after a failure is detected. The restoration time is crucial because long restoration times can result in data loss that is not expected, especially in high-speed networks. The proposed method targets reducing the aggregated optical cross-connect switching time to minimize real-time failure restoration time. With the proposed solution, in an event of failure, the restoration time can be reduced to times that are similar to those achieved in the reserved schemes. Common unreserved schemes have an inherent need for retries because the first try after failure detection and notification cannot always be guaranteed due to lack of network resource. In this paper, an enhanced implementation for the proposed solution is designed and described, which allows the features of the proposed solution to be fully realized and overcomes the inherent drawback of redundant OXC switching events for retries in common unreserved schemes. Through simulation experiments, it is shown that under a given network condition, the real-time path setup time for failure restoration required in the proposed solution can be improved by 68% compared with the common unreserved schemes.     

P比特光交换节点研究

光网络中引入全光交换技术可以无需进行光电光转换和电信号处理,使网络具备透明性,大大降低节点的复杂性和节点成本。多粒度交换节点减小了交换矩阵的规模,降低了交换矩阵的复杂性,是波分复用（WDM）网络节点发展的一个方向。随着正交频分复用（OFDM）技术的引入,带宽可变的节点技术得到了越来越广泛的关注。文章介绍了传统的基于波长的光交叉连接器（OXC）交换结构、多粒度交换结构,以及基于正交频分复用/单载波频分复用（OFDM/SCFDM）的节点交换结构,并通过实验对基于带宽可变的可重构的光分插复用器（ROADM）、OXC节点技术进行了验证。在实验中提出的基于子波带的交换结构中,节点容量达到了P比特量级。     

Waveband Grooming based on Layered Auxiliary Graph in multi-domain optical networks

With the number of wavelengths on fibers keeps increasing, the size and the cost of Optical Cross-Connect (OXC) are greatly enhanced and then the control and management of optical switches become more and more complicated. Therefore, the technique called waveband switching is proposed to reduce the size and the cost of OXC; that is, to save the All-Optical (OOO) switching ports in OXC. However, the existing waveband switching algorithms are all limited in single-domain optical networks. Actually, with the scale of optical backbone keeps enlarging, the network is divided to multiple independent domains to perform the hierarchy routing for achieving the scalability. In order to reduce the size and the cost of OXC meanwhile to achieve the scalability in multi-domains, in this paper we propose a new heuristic algorithm called Waveband Grooming with Layered Auxiliary Graph (WGLAG) since the waveband grooming problem is the NP-hard to perform the inter-domain routing based on the virtual topology of multi-domain network and the intra-domain routing based on the physical topology of single-domain network. In intra-domain routing with waveband grooming of each single-domain, we propose the Layered Auxiliary Graph (LAG) that includes one virtual topology layer and multiple waveband-plane layers to compute a single-hop, or multi-hop or hybrid waveband route for each connection request based on the sub-path waveband grooming scheme. Simulation results show that, WGLAG not only can effectively save more switching ports to reduce the cost of OXC but also can obtain lower blocking probability than other algorithm.     

A novel IP with MPLS over WDM-based broad-band wavelength switchedIP network

This paper presents a new technology for constructing IP over photonic systems. An IP with multiprotocol label switching (MPLS) over wavelength division multiplexing (WDM)-based broad-band IP network architecture and protocol is proposed and analyzed in this paper, which supports variable-length IP-like optical packet label switching and optical virtual path routing. This system tries to merge into one layer the functionalities of the wavelength switching, SONET mux/demux, and IP routing, and is sometimes known as the concept of optical MPLS. The label banding, forwarding/switching process, and node architecture of the proposed network are discussed and studied. A unique as well as important function of a lambda/label edge router (LER) is a flow assembly device that can encompass MPLS' forward equivalence classes, label stacking, and label switching path aggregation function. At the same time, a particular function of the core label switching router is wavelength merging. A fiber delay line is used to delay the data stream in order to process the label information and resolve contention. Transmission bit error rate measurements of the baseband data stream and back-to-back is also demonstrated to show its feasibility