Optimum Arrangement of Reliable Label-Switched Paths in MPLS Over Optical Networks

In MPLS (Multi-Protocol Label Switching) over optical networks, both the optical level and the MPLS level fault recovery can be considered. Generally, a more flexible path arrangement can be realized by the MPLS level recovery, while fast recovery can be achieved by the optical level recovery. When the optical level recovery is adopted, only normal traffic is carried through the working lightpaths and only recovered traffic is carried through the backup lightpaths. In contrast, the working LSPs (Label-Switched Paths) and the backup LSPs corresponding to other working LSPs can be accommodated into an identical lightpath when the MPLS level recovery is adopted. By such sophisticated accommodation of LSPs into the lightpaths, lightpath bandwidth can be utilized efficiently under the condition that the bandwidth utilization is restricted to attain the given objective of transfer quality for the MPLS packets in the normal state and unrestricted in a short time a failure occurs somewhere in the network. This paper proposes a simple mathematical programming model to obtain the optimum arrangement of the working and backup LSPs assuming the MPLS level recovery and a practical LSPs provisioning mode. By comparing the minimized network cost obtained from the optimum arrangement of the working and backup LSPs with the network cost resulting from the optical level recovery, this paper quantitatively evaluates the effectiveness of such bandwidth utilization improvement obtained from the MPLS level recovery and reveals that the MPLS level recovery can actually reduce the network cost due to its flexible arrangement of LSPs on the lightpaths.     

Generalized Sharing in Survivable Optical Networks

Shared path protection has been demonstrated to be a very efficient survivability scheme for optical networking. In this scheme, multiple backup paths can share a given optical channel if their corresponding primary routes are not expected to fail simultaneously. The focus in this area has been the optimization of the total channels (i.e., bandwidth) provisioned in the network through the intelligent routing of primary and backup routes. In this work, we extend the current path protection sharing scheme and introduce the Generalized Sharing Concept. In this concept, we allow for additional sharing of important node devices. These node devices (e.g., optical-electronic-optical regenerators (OEOs), pure all-optical converters, etc.) constitute the dominant cost factor in an optical backbone network and the reduction of their number is of paramount importance. For demonstration purposes, we extend the concept of 1:N shared path protection to allow for the sharing of electronic regenerators needed for coping with optical transmission impairments. Both design and control plane issues are discussed through numerical examples. Considerable cost reductions in electronic budget are demonstrated     

A Routing Algorithm Framework for Survivable Optical Networks Based on Resource Consumption Minimization

In this paper, we consider the problem of determining primary and backup paths for survivable optical wavelength-division multiplexed mesh networks. We propose a distributed routing mechanism, which is called Least Resource Consumption Routing, that tries to minimize the combined cost of the primary and the backup paths. The proposed cost model includes the effect of various factors such as mean load, variance of the load on the route, number of converters required by the route, and the length of the route. Further, we model the route cost in such a way that it is extensible to include any new parameters and vary their relative importance. The performance studies conducted for the 14-node National Science Foundation Network and a 30-node topology show that the proposed scheme leads to significant improvements in blocking probability at low and moderate loads. Further, the proposed cost model also reduces the number of converters required to obtain a target blocking performance as compared to some other techniques proposed in the literature.     

Survivable Passive Optical Networks Based on Arrayed-Waveguide-Grating Architectures

By arranging a small number of arrayed-waveguide gratings in survivable topologies with specific interconnection patterns, we can construct passive optical networks with a high degree of protection. A variety of designs are presented that differ in the level of survivability, the protection mechanism, and the amount of required end-user equipment.     

A Framework for Differentiated Survivable Optical Virtual Private Networks

Wavelength division multiplexed (WDM) networks are matured to provide, scalable data centric infrastructure, capable of delivering flexible, value added, high speed and high bandwidth services directly from the optical domain. Optical virtual private networks (OVPNs) make use of the concept of highly reconfigurable nature of lightpaths offered by WDM, to create secure tunnels of high bandwidth across the intelligent WDM optical transport network. An OVPN is a private connection between two or more edge devices (access nodes), that allows a group of clients to fully exploit the flexibility of the switched intelligent optical network. However, OVPNs will not be a viable alternative unless they can guarantee a predictable bandwidth, availability, response time, and fault-tolerance to users. In this paper, we study the problem of dynamically establishing lightpaths for OVPNs over intelligent optical transport networks to provide varying classes of service based on the type of primary and backup lightpaths and the number of backup lightpaths, when each OVPN is specified by the desired logical connectivity and Class of Service. The type of primary and backup lightpaths determines the QoS parameters such as response time and bandwidth. Whereas, the number of backup lightpaths determines the level of fault-tolerance and availability of OVPN. Based on the service classes, any OVPN in the network falls into one of the six classes viz. single dedicated primary and single dedicated backup (SDPSDB), single dedicated primary and multiple dedicated backups (SDPMDB), single dedicated primary and single shared backup (SDPSSB), single shared primary and single shared backup (SSPSSB), single shared primary and multiple shared backups (SSPMSB), and best-effort (BE). In BE, we consider two variations—(1) OVPN as dedicated logical ring topology (DLRT) and (2) OVPN as shared logical ring topology (SLRT). We conduct extensive simulation experiments to compare and evaluate the effectiveness of different classes of OVPNs for varying network configurations–varying number of fibers, wavelengths on physical links, and number of nodes in OVPN.     

Capacity Planning of Survivable Mesh-based Transport Networks under Demand Uncertainty

Almost all existing work on the design of survivable networks is based on a specific demand forecast to which one optimizes routing and transport capacity assignment for a single target planning view. In practice these single-forecast models may be used repetitively by a planner to consider a range of different scenarios individually, hoping to develop intuition about how to proceed. But this is not the same as having a planning method that can inherently and quantitatively consider a range of possible futures all at once. Our approach considers both the cost of initial design construction and the expected cost of possible augmentations or “recourse” actions required in the future, adapting the network to accommodate different actual future demands. In practice, these recourse actions might include lighting up a new DWDM channel on an existing fiber or pulling-in additional cables, or leasing additional capacity from third party network operators, and so on. A stochastic linear programming approach is used to achieve designs for which the total cost of current outlays plus the expected future recourse costs is minimized. Realistic aspects of optical networking such as network survivability based on shared spare capacity and the modularity and economy-of-scale effects are considered. These are not only important practical details to reflect in planning, but they give the “future-proof” design problem for such networks some unique aspects. For instance, what is the working capacity under one future scenario that may not waste capacity if that demand scenario does not materialize, because the same channels may be used as shared spare capacity under other future scenarios. Similarly economy-of-scale effects bear uniquely on the future-proof planning problem, as the least-cost strategy on a life-cycle basis may actually be to place more capacity today than current requirements would suggest. This is of obvious relevance to planners given the recent hard times in the telecommunications industry, causing a tendency to minimize costs now regardless of the consequences.     

QoS Based Survivable Logical Topology Design in WDM Optical Networks

The need to establish wavelength-routed connections in a service differentiated manner is becoming increasingly important. In the backbone network, support of quality of service (QoS) capabilities at the lightpath level will have to be addressed in the optical domain. Providing a service differentiated connection on an arbitrary virtual topology which does not support any differentiated services will lead to the misuse of network resources. We address the virtual topology design and routing problem, where we minimize congestion in the network. In our work, the service differentiating parameter is bit error rate (BER) in the optical domain. We present a mixed integer linear programming (MILP) formulation for the above problem. We also propose a heuristic based approach to minimize the congestion in the network while satisfying the QoS constraints. These QoS constraints in our case are the differing BER requirements for each connection between each (source, destination) pair. We then present different methods of providing survivability for the virtual topology and compare the performance of these methods.     

Performance Analysis of WDM Optical Networks with Wavelength Usage Constraint

Due to power considerations, it is possible that not all wavelengths available in a fiber can be used at a given time. In this paper, an analytical model is proposed to evaluate the blocking performance of wavelength-routed optical networks with and without wavelength conversion where the usable wavelengths in a fiber is limited to a certain maximum number, referred to as wavelength usage constraint. The effect of the wavelength usage constraint is studied on ring and mesh-torus networks. It is shown that the analytical model closely approximates the simulation results. We also evaluate the performance of the first-fit wavelength assignment algorithm and compare its performance with the random wavelength assignment algorithm through simulation. It is observed that increasing the total number of wavelengths in a fiber is an attractive alternative to wavelength conversion when the number of usable wavelengths in a fiber is maintained the same.     

光传送网的生存技术

 生存技术作为光传送网体系演进中最为重要的组成部件,受到学术界和工业界广泛而持久的关注.论文回顾和总结光传送网生存技术的重要研究成果及若干最新进展,内容包括:光网络的连接恢复技术、可生存光网络的资源优化与服务质量、两层网络的连接恢复技术以及透明光网络的故障定位技术.     

OTN承载以太网业务方式的探讨

以太网技术的应用正在由局域网延伸到城域网甚至广域网中,相应的以太网带宽也逐渐增加,40 GE/100 GE标准都已在进行讨论.本文首先简单介绍了OTN技术,然后讨论并比较了已有GE/10 GE业务映射到0TN净荷中的可行方式及未来出现的40 GE/100 GE业务映射到OTN净荷中的可能方式.     

Pan-European Optical Transport Networks: An Availability-based Comparison

The traffic to be carried by today's European backbone networks increases very rapidly. An important portion of this traffic consists of data traffic (mainly IP-related). In the future data traffic is expected to become the abundantly dominant traffic type, while voice traffic will only account for a very small portion of the total traffic volume. In this paper, some network topologies for such a pan-European fiber-optic backbone network are presented (more details can be found in [1]). These topologies are compared in terms of the efficiency of the network design both from a cost and capacity point of view and in terms of the availability of the connections routed over this network. In order to be able to assess the network topologies under realistic circumstances, the expected traffic demand is forecasted. This enables to make the comparison for the current traffic volume as well as for the traffic patterns of the future. As not all types of (data) traffic require the same degree of survivability and in order to leverage the total capacity cost of the network design, a distinction is made between different recovery options in the optical layer for the different traffic types considered.     

以太无源光网络生存性分析

参考FSAN/ITU-TG.983.1标准和SDH的APS协议原理,探讨了EPON的四种树形自愈结构和两种E-PON自愈环网络结构,并分别对树形自愈结构中的节点光纤备份和自愈环光纤备份方式的保护倒换机制和生存能力进行详细的分析。     

光传送网的一体化网管研究

光传送网技术可望成为下一代的主导传送网技术。详细讨论了光传送网（ＯＴＮ）和光传送网的管理技术。结合ＴＭＮ、ＳＮＭＰ和ＣＯＲＢＡ，着重研究了ＯＴＮ的一体化网管。一种Ｑ－Ａｄａｐｔｅｒ被提出来用于集成ＴＭＮ和ＳＮＭＰ，一种直接的ＣＯＲＢＡ／ＳＮＭＰ接口被用来实现ＣＯＲＢＡ和ＳＮＭＰ的集成。最后简要分析了几个和ＯＴＮ一体化网管相关的问题：ＩＰ层和光层的联合路由，多层保护以及ＯＴＮ的ＯＡＭ技术。     

移动城域光传送网发展探讨

本文对光传送网技术发展趋势,ASON(自动交换光网络)的优点,以及引入ASON的可行性、必要性、引入的时机和方法等问题提出了合理性建议.并对网络转型需求和光传送网技术发展的共同驱动下,未来几年光传送网的目标网络架构进行了全面的分析和阐述.     

Availability Design of Optical Transport Networks

A design technique for reliable optical transport networks is presented. The network is first dimensioned in order to carry a given set of static protected optical connections, each one routed maximizing its availability. The network can be further optimized by minimizing the number of fibers to be installed, while keeping a control on connection availability, which can remain the same or decrease by a prefixed margin factor. Design and optimization algorithms are provided for networks adopting dedicated and shared path-protection. The optimization approach is heuristic. Results obtained by applying the proposed technique to two case-study networks are shown and discussed. These two case-study experiments are carried out exploiting a realistic model to evaluate terrestrial and submarine optical link availability.     

OBT: Optical Burst Transport in Metro Area Networks

For the past few years, the evolution of electro-optical technology has driven change in optical networks in the access and backbone areas. Optical bypassing and traffic aggregation mitigate the scalability problem in backbone networks, and burst mode transmission can provide a cost-efficient solution for access networks. Using those technologies, a new solution can be found for metro area networks, which interconnect access and backbone networks. In this article, we introduce a new solution for metro area networks, called optical burst transport (OBT). OBT is designed to use the promising technologies of backbone and access networks so that it provides all benefits, such as dynamic bandwidth provisioning, scalability, and robustness for unbalanced traffic. The performance evaluation of OBT also is verified by means of a testbed implementation.     

光联网中的光开关器件

光联网是当前光网络的发展趋势,光联网的实现主要依赖于光开关、光滤波器、光放大器等关键光电子器件和密集波分复用等系统技术的进展。光开关是实现光交换的关键元器件,被广泛应用于光层的路由选择、波长选择、光交叉互连以及自愈保护等功能,主要应用包括:     

光传送网中光开关器件的进展

随着波分复用技术的广泛应用和光联网的发展,光开关将成为组建未来光网络的关键器件。光开关的类型有光微电机械开关、马赫-曾德干涉仪型开关、热光效应光开关、液晶光开关、喷墨气泡光开关、光栅开关和声光开关等。文章概述了这些光开关的原理,并进而介绍了光开关器件的最新进展。