A novel fault management approach for DWDM optical networks

Connection availability is considered as a critical metric when providing differentiated services in Wavelength‐Division Multiplexing mesh networks. Indeed, one of the major concerns of optical network operators is related to improving the availability of services provided to their highest‐class clients. Achieving this objective is possible through managing faults using the different classical protection schemes, namely the so‐called dedicated and shared protection schemes. However, the majority of the work concerning protection schemes has considered the primary connections as equally important when contending for the use of the backup resources. As a main contribution in this paper, we therefore propose an improvement of the existing protection schemes through the introduction of relative priorities among the different primary connections contending for the access to the protection path. To evaluate numerically the benefits of the service differentiation feature introduced in our proposal, we first develop a mathematical model, based on which we derive explicit expressions for the average connection availabilities that result from both the classical protection schemes and the proposed priority‐aware one. Through this model, we show how the availability of the highest‐class clients is improved when deploying the proposed priority‐aware protection scheme. Finally, with the same objective in mind, we develop a simulation study, where a given set of connection demands with predefined availability requirements is provisioned using different protection strategies. Through this study, we show that the priority‐aware protection strategy satisfies service‐availability requirements in a cost‐effective manner compared with the classical protection schemes.Copyright © 2006 John Wiley & Sons, Ltd.     

Improved EDF-based management of the setup of connections in opaque and transparent optical networks

The need to support the diverse quality-of-service (QoS) requirements of the ever-emerging Internet applications is a major challenge for optical network operators. This paper tackles such a challenge through the definition of a QoS-aware optical connection setup management scheme. The proposed scheme utilizes the Earliest Deadline First (EDF) queueing discipline to schedule the setup of optical connections that cannot be established due to lack of optical resources. The EDF-based approach aims at minimizing blocking probability while realizing QoS differentiation. Blocking probability reduction is realized through the insertion of blocked connection requests into a queue giving them thus a second chance with respect to network access. QoS differentiation on the other hand is achieved as follows. The blocked connection requests are ranked in the EDF queue according to their connection setup requirements, which are viewed as deadlines during connection setup. In this way, pending connection requests having shorter setup time requirements are guaranteed to experience better QoS compared to the ones having longer setup time requirements. The performance of the EDF-based strategy is analyzed through extensive simulations in the context of both opaque and transparent NSFNET network topologies. The reported results show that the proposed strategy yields remarkable reduction in terms of blocking probability while effecting QoS differentiation.     

A Simple Priority Mechanism for Shared-Protection Schemes

One of the major challenges of optical network operators is ensuring the stringent levels of availability required by their highest-class clients. To achieve this, we introduce relative priorities among the different primary connections contending for access to the protection paths. In this letter, we propose an analytical model for the proposed priority-enabled scheme. As a key distinguishing feature from existing literature, we derive explicit analytic expressions for the average availability and service disruption rate for the different priority classes     

A generalized protection framework using a new link-State availability model for reliable optical networks

This paper investigates a generalized protection framework for availability-guaranteed connection provisioning in an optical wavelength-division-multiplexed (WDM) network. Reliability is a crucial concern in high-speed optical networks. A service level agreement (SLA), which mandates high service availability even in the face of network failures must be met in provisioning a reliable connection. In this study, a new link-state-modeling mechanism is developed to form a dynamic link-state parameter called link and resource availability (LRA), which represents physical-layer availability and resource status for an optical link. Such up-to-date link-state information can be used by a standard link-state routing protocol to efficiently provision reliable connections. Based on the link-state availability model, LRA, a connection-provisioning algorithm is then proposed which can guarantee customers' availability requirements. A new generalized protection model is developed through dynamic LRA-based provisioning. Numerical results demonstrate the performance of the proposed provisioning approach to be promising.     

Availability analysis under multiple link failures in WDM networks with shared-link connections

In optical Wavelength Division Multiplexing (WDM) networks, different protection schemes have been proposed in the literature, namely, dedicated protection and shared protection. Shared protection techniques significantly reduce the required spare capacity by providing the same level of availability as dedicated protection. However, current mission critical applications (which heavily depend on the availability of communication resources) require connection availability in the order of 99.999% or higher, which corresponds to a downtime of almost 5 min a year on the average. Therefore, in order to satisfy a connection serviceavailability requirement defined by the users Service Level Agreement in a cost-effective and resource-efficient way, network operators need a systematic mechanism to evaluate the network availability under multiple failure scenario to ensure that current network configuration can meet the required availability degree; otherwise, a network upgrade is required. Unfortunately, under multiple failure scenario, traditional availability analysis techniques based on reliability block diagrams are not suitable for survivable networks with shared spare capacity. Therefore, a new concept is proposed to facilitate the calculations of network availability. In this paper, we propose an analytical model for evaluating the availability of a WDM network with shared-link connections under multiple link failures. The analytical model is also verified using Monte Carlo simulation. The proposed model significantly contributes to the related areas by providing network operators with a quantitative tool to evaluate the system availability and, thus, the expected survivability degree of WDM optical networks with shared connections under multiple link failures.     

Availability-Aware Provisioning Strategies for Differentiated Protection Services in Wavelength-Convertible WDM Mesh Networks

In an optical WDM mesh network, different protection schemes (such as dedicated or shared protection) can be used to improve the service availability against network failures. However, in order to satisfy a connections service-availability requirement in a cost-effective and resource-efficient manner, we need a systematic mechanism to select a proper protection scheme for each connection request while provisioning the connection. In this paper, we propose to use connection availability as a metric to provide differentiated protection services in a wavelength-convertible WDM mesh network. We develop a mathematical model to analyze the availabilities of connections with different protection modes (i.e., unprotected, dedicated protected, or shared protected). In the shared-protection case, we investigate how a connection's availability is affected by backup resource sharing. The sharing might cause backup resource contention between several connections when multiple simultaneous (or overlapping) failures occur in the network. Using a continuous-time Markov model, we derive the conditional probability for a connection to acquire backup resources in the presence of backup resource contention. Through this model, we show how the availability of a shared-protected connection can be quantitatively computed. Based on the analytical model, we develop provisioning strategies for a given set of connection demands in which an appropriate, possibly different, level of protection is provided to each connection according to its predefined availability requirement, e.g., 0.999, 0.997. We propose integer linear programming (ILP) and heuristic approaches to provision the connections cost effectively while satisfying the connections' availability requirements. The effectiveness of our provisioning approaches is demonstrated through numerical examples. The proposed provisioning strategies inherently facilitate the service differentiation in optical WDM mesh networks.     

Joint wireless and optical resources allocation for availability-guaranteed service in survivable fiber-wireless access network

The fiber-wireless (FIWi) access network not only leverages the technical merits of wireless and optical access networks, but also provides a potential opportunity for the design of survivable access networks. Previous works have studied the survivability of FiWi access network against network component failure by means of backup fiber deployment and wireless rerouting. However, most of these works put less attention on the connection availability and ignore the joint allocation of wireless and optical resources, which plays an important role in improving the global network performance gain. In this paper, we consider a notable failure scenario in FiWi access network but less mentioned in previous works, i.e., single shared-risk link group failure. We first propose a model for FiWi network to estimate the connection availability of service demand. Then, a novel resource allocation approach is proposed to provide the availability-guaranteed service. Under the requirements of bandwidth and connection availability, we deal with the optimal allocation of joint wireless and optical resources with the objective of minimum resource consumption. Numerical results demonstrate that the proposed scheme can reduce the resource consumption significantly compared to the resource allocation without considering connection availability.     

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.     

一种基于类矩形分布模型结合热力图的市区政企传输网络规划设计方法

政企集团客户专线业务的电路局向、业务接入点均为客户自行决定，业务开通存在极大的不可预见性。为有效解决政企客户业务开通的主观性强、调整难度大、周期长及效率低等问题，搭建典型仿真环境，构筑类矩形分布模型，结合热力图提出两种部署策略。仿真分析可知，相同条件下，满足覆盖的需求VC-OTN （VC cross-connecting function with optical transport network）点数随最大接入距离增大而减小，客户点覆盖率随部署VC-OTN点位增大而增大，策略2（根据成熟度分组覆盖）部署效益高于策略1（优先覆盖热点区域）。满足覆盖率需求时，理论最小、策略1和策略2所需VC点位数分别为26个、58个和50个。为网络系统精准快速建设提供可靠理论指导，避免盲目部署，提升部署规划精度，为后续搭建市区VC-OTN节点提供建设参考思路。     

Mesh光网络基于有向P圈的保护配置策略

文章针对波分复用(WDM)光网络的工作机制,提出了有向P圈的概念和WDM网络基于有向P圈的保护机制及配置策略.同时,提出了对偶圈合并法则和以此为基础的P圈生成和网络保护资源配置启发式算法.为了验证配置方案的有效性,利用OPNET Modeler搭建了自动交换光网络(ASON)-WDM仿真平台,在泛欧COST239网络拓扑和北美NSFnet网络拓扑上进行了大量仿真.仿真结果证明了P圈生成算法和有向P圈配置策略的有效性和可行性.     

A novel multi-link fault-tolerant algorithm for survivability in multi-domain optical networks

With the large-scale deployment of optical network equipments, the problems of separated domains management and the multi-domain-based survivability have become the primary challenge in new generation intelligent optical networks. Aimed at resisting multi-link failures in multi-domain optical networks (MDON), a heuristic multi-link fault-tolerant (MLFT) algorithm for survivability in MDON is proposed in this article, which applied Hamiltonian cycle protection and segment-shared protection to establish a novel survivability strategy for either intra-domain??s or inter-domain??s multiple links, respectively. Furthermore, a new virtual-link mapping scheme and link-cost formulas are presented to encourage the appropriate routing selection and load balancing, which can also contributed to better resource utilization ratio and blocking ratio. Simulation results show that MLFT realizes the multi-link fault-tolerant survivability at a lower cost with better performances in redundancy ratio, blocking ratio, and computation complexity.     

Performance evaluation of the survivability schemes in WOBAN: a quality of recovery (QoR) method

The hybrid wireless optical broadband access network (WOBAN) is a combination of an optical backhaul and a wireless front‐end, which combine the huge amount of available bandwidth of optical networks and the ubiquity and mobility of wireless access networks with the objective of reducing their cost and complexity. Survivability is one of the most important issues in WOBAN. In this paper, the survivability schemes in WOBAN are addressed from a particular point of view of the quality of recovery (QoR) method. The QoR is a comprehensive measure to evaluate the survivability schemes in terms of availability, recovery time, redundancy, and bandwidth of backup path. The specific procedures to set up the analytical models for the survivability schemes in WOBAN are given based on the QoR concept, including abstract, normalization, and application. Besides, the weights assignment is provided to calculate the QoR value for the operators, home users, or business users with different requirements, which in turn offers the user‐perceptive quality of service. To verify the performance of the survivability schemes by the QoR method, extensive simulations are made under different WOBAN configurations. Numerical results show that for the intra‐domain survivability schemes, the wireless and optical mixed protection scheme is the best choice for failure recovery in WOBAN. The wireless scheme is the second choice for the solution, which emphasizes cost control, while for the solution that emphasizes the network performance, the 1:1 scheme is the second choice. The 1:N scheme obtains the worst QoR value as the splitter ratios increase. For the inter‐domain survivability schemes, optimizing backup optical networking units selection and backup fibers deployment scheme outperforms maximum protection with minimum cost scheme from the point of view of QoR. Copyright © 2013 John Wiley & Sons, Ltd.     

抗毁WDM网中支持QoS的选路和波长分配算法

该文首先探讨了抗毁WDM网中支持QoS的分层图模型,在此基础上提出一种抗毁WDM网中支持QoS的选路和波长分配算法。该算法根据上层业务不同的QoS要求,对其光路建立请求区别对待,以满足它们不同的阻塞率和恢复率要求。计算机仿真结果表明该算法既满足了上层业务不同的QoS要求,同时又充分利用了有限的网络资源,使全网的平均阻塞率降低。     

A multilayer differentiated protection services architecture

Metropolitan area and long-haul networks are migrating toward the deployment of optical mesh technologies. This requires, among other things, a new generation of highly intelligent protection and restoration mechanisms to perform functions of protection and bandwidth management. We introduce an architecture that provides differentiated protection services across multiple layers of network hierarchy. A connection at any client layer can request a protection against resource failures at any lower layer. A key aspect of the architecture is the hierarchical tree organization of shared risk link group (SRLG) resources. They represent routing-related failures across all layers of protocol stack. The architecture is very scalable in terms of communicating link-state and bandwidth information between adjacent layers. SRLG trees are used to aggregate this information and provide a summary to the client layer. We discuss the requirements and challenges for routing and signaling mechanisms in order to support the proposed architecture. The complexity of this architecture is evaluated and compared with the complexity of a nonhierarchical alternative.     

一种新的对称CDMA系统中非对称业务下的呼叫允许控制策略

未来无线多媒体网络将以分组技术为基础,支持多种业务的传输,业务的QoS保证将受到一定的挑战.各运营商也将针对自己所服务的对象特点,定义各类业务的QoS等级,来提供具有不同QoS要求的业务.因此,呼叫允许控制(Call Admission Control,CAC)策略将要以分组业务为主要对象,即既要在充分利用系统资源的基础上保证各业务的QoS要求,又要适应各运营商之间的不同需求.因此本文提出一种新的对称CDMA系统中非对称业务下基于动态QoS保证的CAC策略.各运营商可根据自己的要求定义各业务的QoS等级.由于业务的不同特性,使得网络中上行链路和下行链路的业务呈现不对称性,为避免资源的浪费,将根据网络中的资源占有情况动态的地分配上行和下行链路中的资源.仿真结果表明,该策略可以自适应地保证各业务的QoS要求,提高了业务间的公平性和系统资源的利用率.     

FSAN OAN-WG and future issues for broadband optical access networks

Network operators are aiming to provide a broadband access network to facilitate the next-generation telecom services. They have established the Full Services Access Networks (FSAN) group in order to find the best way to achieve early and cost-effective deployment of broadband optical access systems. They concluded that a single worldwide broadband access system should be investigated in the FSAN and then standardized in the international standards bodies such as the ITU-T. This article outlines the FSAN organization and the study targets for its Optical Access Network working group, and some key future study issues in terms of optical distribution network requirements and the required system functionalities of the B-PON system. It also describes its standardization strategy and the interaction between the FSAN and ITU-T     

Enhanced Dynamic Segment Protection in WDM Optical Networks under Reliability Constraints

In this letter, we study the protection problem in wavelength division multiplexing (WDM) optical networks, and propose a novel dynamic heuristic algorithm called differentiated reliable segment protection (DRSP). Differing from previous work, DRSP can effectively avoid the trap problem and is able to find a feasible solution for each connection request. Therefore, DRSP outperforms the previous work. Simulation results have shown to be promising.     

Service-Centric Provisioning in WDM Backbone Networks for the Future Internet

A service level agreement (SLA) is a formal contract between the service provider (SP) and the customer. Among various specifications, the SLA states an availability requirement and a penalty the SP pays if this requirement is violated. Traditional approaches to protection use a fixed deployment of backup resources, or do not consider the status of a service. As more heterogeneous applications use optical wavelength-division multiplexing (WDM) backbone network services of the future internet, these service-agnostic approaches are unable to accommodate the differentiated availability requirements. This results in substantial revenue loss either by refusing requests, or by accepting them and then violating their SLAs. In this paper, we propose and investigate the characteristics of a centralized control and management framework for service-aware, admission, and re-provisioning (SAR) in WDM backbone networks of the future internet. Our framework aggressively admits service requests, and dynamically reprovisions existing services by exploiting knowledge of their status. We first propose a GMPLS-based architecture and a revenue model for our analysis. Then we introduce a priority index, called urgency level (UL). An UL is assigned to an existing service indicating its status and relative importance, technically and economically. We reprovision resources by shifting them from low-UL services to provide backups for higher-UL services, which are more at risk of violating their SLAs or which have higher penalties. Our framework increases the revenue for the SP by creating more sales revenue and reducing potential penalties. Numerical results show improved performance in terms of 1) lower resource overbuild; 2) lower bandwidth blocking ratio; 3) higher SLA satisfaction ratio; 4) more balanced SLA violations; and 5) higher overall net revenue. Our framework is also shown to be effective for a range of failure models and penalty strategies.      

Dynamic Routing and Wavelength Assignment in Optical Networks by Means of Genetic Algorithms

We propose a novel genetic algorithm for solving the dynamic routing and wavelength assignment (DRWA) problem in wavelength-routed optical networks. The algorithm not only obtains low call blocking probability, but it also employs a very short computation time. Moreover, it is capable of providing fairness among connections, that is, to offer approximately the same quality of service (in terms of blocking probability) for all source-destination node pairs. Since requirements on optical network availability are highly severe, we also propose an extension of the algorithm to provide fault-tolerance capability at the optical layer. It is achieved by means of protection, where each optical connection request is provided with a pair of lightpaths (a primary and a backup lightpath). Again, the genetic algorithm proves to be highly efficient, in this case, at performing routing and wavelength assignment of pairs of lightpaths.     

4G与5G网络互操作部署策略研究

未来4G与5G网络将会长期共存,共同发展,运营商在整个网络建设过程中需重点考虑4G与5G制式共存下的系统间的互操作。因此,本文根据3GPP Rel-15标准要求,讨论了融合网元部署策略、N26接口开启策略、语音方案选择、切换方案选择等4G/5G互操作过程中面临的关键问题, 分析出4/5G网络共存下互操作关键部署策略,为后续运营商在网络演进中选择部署策略提供参考。