An optimal protection and restoration scheme (OPARS) for optical networks

Protection and restoration are critical network design issues for optical networks since even a single failure for a short duration may result in huge data loss due to the large capacity of optical fibers. However, few studies have been done on these issues for optical burst switching (OBS) networks. Protection and restoration are essential mechanisms for guaranteeing more reliable traffic delivery services. But it is not easy to apply existing mechanisms to optical burst switching (OBS) networks due to its one-way reservation signaling and the statistical burst multiplexing. Thus, to achieve the high transmission performance and reliability simultaneously, unique properties of OBS must be considered in the design of protection scheme. In this paper, an optimal protection and restoration scheme (OPARS) has been introduced that not only optimizes the number of provisioned protection wavelengths adaptively based on the traffic load as well as the quality of service (QoS) requirements of bursts in high speed networks but also minimizes burst loss rates. In addition, the proposed scheme has been used as an efficient contention resolution technique. The simulation results verify that the proposed scheme improve the network resource and channel utilization while guaranteeing the targeted protection reliability and QoS requirements of bursts.     

Fast Restoration Based on Alternative Wavelength Paths in a Wide Area Optical IP Network

In this article we describe an experimental investigation of IP network restoration based on wavelength recovery. We propose a procedure for metro and wide area gigabit Ethernet networks that allows us to route the wavelength in case of link failure to another existing link by exploiting wavelength division multiplexing in the fiber. Such a procedure is obtained by means of an optical switch that is managed by a loss-of-light signal that is generated by a router in case of link failure. Such a method has been tested in an IP network consisting of three core routers with optical gigabit Ethernet interfaces connected by means of 50-km-long single-mode fibers between Rome and Pomezia. Compared with other conventional restoration techniques, such as OSPF and MPLS, our method -in very fast (20 ms) and is compatible with real-time TV services and low-cost chips.     

Fast Restoration Based on Alternative Wavelength Paths in a Wide Area Optical IP Network

Abstract

In this article we describe an experimental investigation of IP network restoration based on wavelength recovery. We propose a procedure for metro and wide area gigabit Ethernet networks that allows us to route the wavelength in case of link failure to another existing link by exploiting wavelength division multiplexing in the fiber. Such a procedure is obtained by means of an optical switch that is managed by a loss-of-light signal that is generated by a router in case of link failure. Such a method has been tested in an IP network consisting of three core routers with optical gigabit Ethernet interfaces connected by means of 50-km-long single-mode fibers between Rome and Pomezia. Compared with other conventional restoration techniques, such as OSPF and MPLS, our method -in very fast (20 ms) and is compatible with real-time TV services and low-cost chips.     

A Survivable Wavelength Division Multiplexing Passive Optical Network with Both Point-to-Point Service and Broadcast Service Delivery

Abstract

A survivable wavelength division multiplexing passive optical network enabling both point-to-point service and broadcast service is presented and demonstrated. This architecture provides an automatic traffic recovery against feeder and distribution fiber link failure, respectively. In addition, it also simplifies the protection design for multiple services transmission in wavelength division multiplexing passive optical networks.     

Agile protection based on network coding against key link failures

In order to provide cost-efficient and rapid protection against the key link failures dynamically, an intelligent p-cycle protection strategy based on network coding is proposed. Data units are combined from different links using network coding method at the on-cycle nodes, and then they are transmitted downstream for recovering data units lost due to failures. Under static traffic, an integer linear program (ILP) is formulated to provision the optimal p-cycles. Furthermore, according to the dynamic variation of the link importance degree, a heuristic cycle construction algorithm for generating, extending and contracting p-cycle is introduced to achieve intelligent and self-adaptive protection. The key of the proposed protection strategy is how to set the key link as a straddling link of the p-cycle as possible. The experiments demonstrate that the proposed strategy can guarantee instantaneous recovery of data units upon the failure of a key link with a low blocking rate and resource cost.     

An optimal network for passenger traffic

The optimal solution of an inter-city passenger transport network has been studied using Zipf’s law for the city populations and the Gravity law describing the fluxes of inter-city passenger traffic. Assuming a fixed value for the cost of transport per person per kilometer we observe that while the total traffic cost decreases, the total wiring cost increases with the density of links. As a result the total cost to maintain the traffic distribution is optimal at a certain link density which vanishes on increasing the network size. At a finite link density the network is scale-free. Using this model the air-route network of India has been generated and an one-to-one comparison of the nodal degree values with the real network has been made.     

Novel cobweb-topology WDM access network architecture featuring ultra-high reliability and easy scalability

A wavelength division multiplexing access network architecture with cobweb topology is proposed in this paper. It can be a candidate for metro access network with high reliability in the future. This architecture can provide two protection methods. The protection strategy which can maximize the protected traffic is elaborated in the context. Mathematical models of system performance such as network scale and link reliability are established and analyzed in this paper.     

High-speed data transmission over a 1 km broad wavelength window multimode fiber

For cost and design simplicity, various optical network architectures have been proposed in which downstream traffic from the optical line terminal to the optical networking unit is transmitted by carriers in the 1550 nm window, and upstream traffic by those in the 1300 nm window. A new generation of multimode fiber (MMF) has been designed to accommodate this requirement and to address technical challenges associated with fiber coupling. By restricting the number of modes at both fiber input and output, using off-the-shelf single-mode transceivers, single-wavelength 40 Gbit/s data transmission over a 1 km broad wavelength window multimode fiber has been demonstrated with only a 1.5 dB power penalty. The capacity in this new class of MMF is expected to increase with conventional technologies in single-mode fiber such as wavelength-division multiplexing and polarization multiplexing.     

Maximum covering planning of survivable Fiber-Wireless access network considering network connectivity

Fiber-Wireless (FiWi) access network is now becoming a promising architecture for access networks. Survivability is one of the key issues in the planning of FiWi access network because many high-rate traffic flows may be interrupted in case of a single fiber failure, which can cause a huge traffic loss. In addition, the users need ubiquitous broadband access that can be provided by FiWi access network. In this paper, we propose the protection approach called Maximum Covering Planning with Survivability (MCPS), including Integer Linear Programming (ILP) solution and heuristic solution, for the planning of survivable FiWi access network against single distribution fiber failure. The proposed approach aims at maximum coverage under the constraints of network connectivity. When a distribution fiber is broken, the interrupted Optical Network Unit (ONU) can transmit traffic to its backup ONU through the wireless paths between them. Simulation results show the network coverage of clients for different number of ONUs in different urban areas, and demonstrate the relationship between network coverage and the cost represented by the number of WiFi routers.     

Self-healing ring-based WDM-PON

In this paper, a survivable ring-based wavelength-division-multiplexing (WDM)-passive optical network (PON) for fiber protection is proposed. Protections for feeder fiber and distributed fiber are independent in the scheme. Optical line terminal (OLT) and optical network units (ONUs) can automatically switch to protection link when fiber failure occurs. Protection distributed fiber is not required in the scheme. Cost-effective components are used in ONUs to minimize costs of network. A simulation study is performed to demonstrate the scheme. Its result shows good performance of upstream and downstream signals.     

中国铁路客运网网络性质的研究

中国铁路客运系统可以采用两种不同的网络构建方式来描述. 一种是以铁路的站点作为“节点”，并以轨道作为“边”，这样生成的网络称为铁路地理网. 统计显示该网络的平均群聚系数〈C〉近似为零，故该网络为树状网络. 另一种是以站点作为“节点”，任意两个站点间只要有同一列车在这两个站点停靠，就可以认为这两个站点间有连线，这样生成的网络称为车流网. 统计显示该网络有较大的平均群聚系数和较小的平均网络距离〈d〉，而且该网络节点的度分布基本上服从无标度幂律分布，故车流网为具有无标度性质的小世界网络. 关键词： 铁路地理网 车流网 小世界 无标度分布     

Survivable routing and spectrum allocation algorithm based on p-cycle protection in elastic optical networks

With the number of large capacity applications in core network increasing, the bandwidth requirement of optical connections in conventional Wavelength Division Multiplexing (WDM) networks keeps enhancing, so that the Orthogonal Frequency Division Multiplexing (OFDM) technology is adopted to provide higher spectrum efficiency and flexibility in the future elastic optical networks. Meanwhile, survivability in the conventional WDM optical networks has been widely studied as an important issue to ensure the service continuity. However, survivability in OFDM-based elastic optical networks is more challenging than that in conventional WDM optical networks because each fiber usually carries even more connections. Therefore, it is necessary to study the new lightpath protection algorithm in elastic optical networks. Since p-cycle protection scheme has short restoration time and simple protection switching procedure, in this paper, we study the static Survivable p-Cycle Routing and Spectrum Allocation (SC-RSA) problem with providing an Integer Linear Programming (ILP) formulation. Since RSA is a NP-hard problem, we propose a new heuristic algorithm called Elastic p-Cycle Protection (ECP) to tolerate the single-fiber link failure. For each demand, ECP scheme can compute highly-efficient p-cycles to provide protection for all of the on-cycle links and the straddling links. We also consider the load balancing and choose the proper working path for each demand. Simulation results show that the proposed ECP scheme achieves better performances than traditional single-line-rate survivable schemes.     

A hybrid fiber-optic/electrical network for launch vehicles

The proposed use of fiber-optic networks in launch vehicles is examined. A data bus architecture is defined, which would replace the mesh network connecting major second-stage avionic packages, in addition to one replacing the take-off minus zero umbilical link from the vehicle to the launch complex. The analysis for a Delta, including bus traffic, cost, and risk factors, led to the selection of n hybrid fiber/electrical network. Candidate termini were tested.     

A hybrid fiber-optic/electrical network for launch vehicles

The proposed use of fiber-optic networks in launch vehicles is examined. A data bus architecture is defined, which would replace the mesh network connecting major second-stage avionic packages, in addition to one replacing the take-off minus zero umbilical link from the vehicle to the launch complex. The analysis for a Delta, including bus traffic, cost, and risk factors, led to the selection of n hybrid fiber/electrical network. Candidate termini were tested.     

Blocking in wavelength-routed all-optical WDM network with wavelength conversion

The blocking probability in wavelength-routed all optical networks is very important measure of performance of the network, which can be affected by many factors such as network topology, traffic load, number of links, algorithms employed and whether wavelength conversion is available or not. In this paper, we have proposed a mathematical model to reduce the blocking probability of the WDM optical network for wavelength-convertible networks. The model can be used to evaluate the blocking performance of any network topology also it can be useful to improve its blocking performance of the given network topology. The blocking probability variation of the network for a particular load (per link) has been studied based on the load variation and total number of wavelengths used in the network. This model gives good results for high load (per link).     

一种新的格状波分复用光网络保护方法

在P圈法和哈密顿环保护法的基础上,提出了一种新的适用于格状波分复用光网络的基于资源的环保护方法,我们称之为RP圈法.与其他基于环的格状光网络保护方法相比,RP圈法具有配置方式简单、与业务模型不相关以及圈具有长度限制等许多特点.文中给出了RP圈法的一种启发式算法,仿真结果表明此算法具有较高的容量效率,是一种可适用于动态业务的实用化光网络保护方法.     

A Single-Star Multi-Ring Structure of Self-Healing Wavelength Division Multiplexing Optical Access Network

Abstract

A simple single-star multi-ring structure of multi-wavelength optical access network for enlarging network scale and protecting distribution fiber is presented. In this scheme, the ring structure enables optical network units to switch automatically to a protection link when the distribution fiber fails, and a star structure is adopted to weaken the sphere of the distribution fiber failure's influence. The simple combination of these two structures greatly increases the number of subscribers and minimizes costs of network. The network's survivability can also be better than that of a star network or ring network. In addition, it can easily be upgraded from an existing star network, so this article also proposes a method to update the existing star network. The simulation result shows the structure is of good performance.     

Hybrid multiplexed OFDM-DWDM-EPON access network

For bottleneck problem of the broadband access networks, Ethernet-PON comes out as a striking and promising solution. Even though, EPON nodes necessitate a cost-effective up-gradation, WDM based topology proves to be a vigilant up-grading approach that deals with the deployment of multiple wavelengths in the upstream/downstream directions. Furthermore, only EPON nodes with privileged traffic can be WDM-upgraded. Accordingly, we propose and demonstrate a hybrid multiplexed OFDM/DWDM-EPON access network employing OSSB modulation scheme. Case A demonstrates a single channel OFDM-OSSB-EPON system and achieves a fiber link of 27 km with split ratio of 16. Afterwards, a contrast between OFDM-EPON and conventional EPON (C-EPON) after a fiber link of 20 km with split ratio of 16 is carried out. Case B targets the transmission of two channels with channel spacing of 0.1 nm to realize OFDM-DWDM-OSSB-EPON system and achieves a fiber link of 20 km with split ratio of 32.     

A weighted network evolution with traffic flow

In this paper, we propose a simple weighted network model that generalizes the complex network model evolution with traffic flow previously presented to investigate the relationship between traffic flow and network structure. In the model, the nodes in the network are represented by the traffic flow states, the links in the network are represented by the transform of the traffic flow states, and the traffic flow transported when performing the transform of the traffic flow states is considered as the weight of the link. Several topological features of this generalized weighted model, such as the degree distribution and strength distribution, have been numerically studied. A scaling behavior between the strength and degree s∼klogk is obtained. By introducing some constraints to the generalized weighted model, we study its subnetworks and find that the scaling behavior between the strength and degree is conserved, though the topology properties are quite sensitive to the constraints.     

一种新型光分插复用器及其在WDM自愈环网中的应用

提出了一种新型的基于FBG和光环形器的双向光分插/复用器结构.它的结构简单,网络配置灵活,而且可实现单纤双向环网中功率放大.结合该OADM,首次给出了在单纤双向DNI环网实现保护的策略,指出此结构在各种WDM网络中实现单纤环网保护的可行性.