Multicast protection scheme in survivable WDM optical networks

The protection design is a key issue in survivable wavelength division multiplexing (WDM) optical networks. Most researches focused on protecting unicast traffic against the failure of a single network component such as a link or a node. In this paper, we investigate the protection scheme for multicast traffic in meshed WDM optical networks under dual-link failure consideration, and propose a novel protection algorithm called shared segment protection with reprovisioning (SSPR). Through dynamically adjusting link-cost according to the current network state, SSPR establishes a primary light-tree and corresponding link-disjoint backup segments for each multicast connection request. A backup segment can efficiently share wavelength capacity of its working tree or the common resource of other backup segments. Capacity reprovisioning establishes new segments for the vulnerable connections after a link failure and tolerates following link failures. The simulation results show that SSPR not only can make good use of wavelength resources and protect multicast sessions against any single-link failure, but also can greatly improve the traffic restorability in the event of dual-link breakdown.     

Applying tabu search to backup path planning for multicast networks

More and more multimedia applications rely on the ability of networks to provide multicast communications. Network survivability becomes a critical issue in network planning, design, and operation to reduce the impacts of failures in high-speed networks. A rapid and cost-effective restorable network must be planned to maintain network survivability and use network bandwidth effectively. This paper considers the problem of preplanning delay-constrained backup path for multicast networks to minimize the total cost of all the backup paths. Based on the path restoration scheme, a tabu search (TS) algorithm is proposed to find a near optimal solution for the problem under investigation. Diversification and intensification strategies are suggested. The computational experiments are conducted to demonstrate the performance of the proposed TS algorithm. The results show that it offers high-quality solutions within a short amount of time.     

Particle swarm optimization-based DRWA for wavelength continuous WDM optical networks using a novel fitness function

Greater demand of bandwidth and network usage flexibility from customers along with new automated means for network resource management has led to the concept of dynamic resource provisioning in WDM optical networks where unlike the traditional static channel assignment process, network resources can be assigned dynamically. This paper examines a novel particle swarm optimization (PSO)-based scheme to solve dynamic routing and wavelength assignment (dynamic RWA) process needed to provision optical channels for wavelength continuous Wavelength Division Multiplexed (WDM) optical network without any wavelength conversion capability. The proposed PSO scheme employs a novel fitness function which is used during quantization of solutions represented by respective particles of the swarm. The proposed fitness function takes into account the normalized path length of the chosen route and the normalized number of free wavelengths available over the whole route, enabling the PSO-based scheme to be self-tuning by minimizing the need to have a dynamic algorithmic parameter ‘α’ needed for better performance in terms of blocking probability of the connection requests. Simulation results show better performance of the proposed PSO scheme employing novel fitness function for solving dynamic RWA problem, not only in terms of connection blocking probability but also route computation time as compared to other evolutionary schemes like genetic algorithms.     

Traffic grooming, routing, and wavelength assignment in WDM transport networks with sparse grooming resources

While a single fiber strand in wavelength division multiplexing (WDM) has over a terabit-per-second bandwidth and a wavelength channel has over a gigabit-per-second transmission speed, the network may still be required to support traffic requests at rates that are lower than the full wavelength capacity. To avoid assigning an entire lightpath to a small request, many researchers have looked at adding traffic grooming to the routing and wavelength assignment (RWA) problem. In this work, we consider the RWA problem with traffic grooming (GRWA) for mesh networks under static and dynamic lightpath connection requests. The GRWA problem is NP-Complete since it is a generalization of the RWA problem which is known to be NP-Complete. We propose an integer linear programming (ILP) model that accurately depicts the GRWA problem. Because it is very hard to find a solution for large networks using ILP, we solve the GRWA problem by proposing two novel heuristics. The strength of the proposed heuristics stems from their simplicity, efficiency, and applicability to large-scale networks. Our simulation results demonstrate that deploying traffic grooming resources on the edge of optical networks is more cost effective and results in a similar blocking performance to that obtained when distributing the grooming resources throughout the optical network domain.     

Intelligent shared-segment protection

Progress in network technologies and protocols is paving the road towards flexible optical transport networks, in which dynamic leasable circuits could be set up and released on a short-term basis according to customers’ requirements.Recently, new solutions for automatized network management promise to allow customers to specify the terms of the service level agreement (SLA) to be guaranteed (with different price range) by the service provider. In this paper we consider that these service level specifications (SLS), since they are now made available on-demand during the connection request, could be exploited to retrieve useful information able to improve the routing efficiency.In particular, we propose to exploit the knowledge of connection holding time, among the other SLS, to develop a novel intelligent approach for shared-segment protection (SSP).We will exploit the knowledge of the holding-time of connection requests to minimize resource overbuild due to backup capacity and hence to achieve resource-usage efficiency. For a typical US nationwide network, we compare our two proposed holding-time aware approaches to the respective two holding-time-unaware approaches: both of them, even in their holding-time unaware version, have been shown to be very efficient solutions for shared-segment protection. Nonetheless, we have obtained additional savings on resource overbuild of up to 11% for practical scenarios exploiting holding-time knowledge.     

Protection based on backup radios and backup fibers for survivable Fiber-Wireless (FiWi) access network

In Fiber-Wireless (FiWi) access network, the optical back-end is vulnerable to the network component failure due to its tree topology. Any failure at the optical back-end may cause huge data loss. Thus, the survivability in FiWi is an important issue, especially the protection for the optical back-end. Some works propose to protect the optical back-end in FiWi by means of the wireless rerouting in the wireless front-end. However, these works cannot guarantee that there are always the available wireless paths for the traffic rerouting. In this paper, we divide the failures at the optical back-end into ONU-level failure and OLT-level failure according to the failure severity. To tolerate the ONU-level failure, we allocate each ONU a partner ONU and establish the wireless-backup-path between them by deploying backup radios on the traversed wireless routers. To tolerate the OLT-level failure, we cluster all segments in the network and place the backup fibers among the segments in each cluster to establish the protection ring. Thus, each pair of segments in the same cluster can backup for each other along the optical-backup-paths on the protection ring. We propose the heuristic algorithms to minimize the cost of backup radios and the cost of backup fibers. The simulation results demonstrate that the proposed algorithms are effective in enhancing the survivability of FiWi, while requiring less cost than the previous works.     

Cost Efficient Fault Tolerant Design in Mesh Optical Networks with the Load Aware Method

With increasing wavelength capacity, the fault tolerant policy of the mesh optical network becomes much more important. To meet the survivability requirement, a set of cost efficient fault tolerant mechanisms are designed in this paper. The main objective is the minimization of the total number of required wavelengths. Furthermore, based on the method of the Integer Linear Program (ILP), shared-path protection and shared-link protection strategies are achieved, respectively. Moreover, the objective of minimizing the load imbalance is used to ensure the network resources utilized efficiently, and then the wavelength contention can be mitigated by selecting the working path and backup path reasonably. The results show that the survivability of the optical network can be guaranteed in a cost efficient manner.     

Topological network design for SONET ring architecture

Service restoration and survivability have become increasingly important in telecommunications network planning with the introduction of fiber-optic high-speed networks. Synchronous optical network (SONET) technology promotes the use of interconnected rings in designing reliable networks. We describe a heuristic approach for designing networks comprised of interconnected rings. Our approach is particularly attractive for relatively sparse networks in which the set of all cycles (constituting the potential rings) can be determined at a reasonable computational effort. Most networks fall into this category. Given a set of nodes, with demand among all possible node-pairs, and a set of available links that connect the nodes, the problem is to select an optimal subset of rings, utilizing only allowable links, such that each node is included in at least one ring and each ring is connected to at least one other ring at two or more nodes. Such a multiple ring network ensures instantaneous restoration of service in case of a single link or node failure. We first generate a large set of candidate rings and approximate the cost of each ring based on the nodes that are served by the ring and based on the demands. We then apply a set covering algorithm that selects a (minimum cost) subset of the candidate rings such that each node is included on at least one ring. Finally, we select a few additional rings in order to achieve the required connectivity among the rings. We present computational results for realistic-size (e.g., 500 nodes) telecommunication networks     

An improved scheme for self-healing in ATM networks

Broadband networks based on ATM technology can carry a large volume of data and can support diverse services like audio, video, and data uniformly. The reliability and availability levels provided by such networks should be very high. Self-healing is an elegant concept in this direction to provide highly reliable networks. A self-healing network can detect failures such as link/node failures and reroute the failed connections automatically using distributed control mechanisms. In this paper, we consider link and node failures including the VP terminating nodes unlike Kawamura and Tokizawa (Self-healing in ATM networks based on virtual path concept, IEEE Journal on Selected Areas in Communications 12 (1) (1994) 120–127). We present here an improved scheme for self-healing in ATM networks based on the concept of backup VPs. The problems we address are: (i) self-healing scheme; and (ii) backup VP routing. Two issues are addressed in the self-healing scheme: (i) backup VP activation protocol; and (ii) dynamic backup VP routing. We propose a new backup VP activation protocol which uses a VC packing strategy which allows the fast and prioritized restoration of critical VCs that were carried by failed VPs. We also propose a distributed dynamic backup VP routing algorithm which reduces the resource contention that may occur when multiple source–destination pairs contend for the routes simultaneously. The objective of the backup VP routing problem is to find a backup VP for each of the working VPs so that the cost of providing the backup is minimized. We propose a heuristic based solution for the backup VP routing problem using the concept of minimum cost shortest paths. We conducted simulation experiments to evaluate the performance of the proposed schemes. The results show that the proposed schemes are effective. Comparison of the results with those of the earlier schemes (R. Kawamura, I. Tokizawa, Self-healing in ATM networks based on virtual path concept, IEEE Journal on Selected Areas in Communications 12 (1) (1994) 120–127; C.J. Hou, Design of a fast restoration mechanism for virtual path-based ATM networks, Proceedings of IEEE INFOCOM’97, Kobe, Japan, April 1997) shows that the proposed schemes perform better.     

Building Edge-Failure Resilient Networks

We consider the design of resilient networks that are fault tolerant against link failures. Resilience against link failures can be built into the network by providing backup paths, which are used in the eventuality of an edge failure occurring on a primary path in the network. We consider several network design problems in this context; these problems are motivated by the requirements of current high-speed optical networks. In all the following problems the objective is to provide resilience in networks while minimizing the cost incurred. The main problem under consideration in this paper is that of backup allocation: this problem takes as its input an already provisioned primary network and a parameter k, and allocates backup capacity on the edges of the underlying network so that all the demand can be routed even in the presence of k edge failures. We also consider a variant of this problem where the primary network has a tree topology, and it is required that the restored network retains a tree topology. We then address the problem of simultaneous primary and backup allocation: we are given specifications of the traffic to be handled, and the goal is to provision both the primary as well as the backup network. Finally, we investigate a single-commodity problem motivated by a pragmatic scenario in which the primary network is not known in advance and demands between source--sink pairs arrive online.     

An efficient link allocation algorithm for survivable ATM-based personal communication networks

The integration of the issue of survivability of wireless networks in the design process of the backbone network is addressed in this paper. The effectiveness of this integration plays a critical role in the success of the wireless network and the satisfaction of its mobile users. In this paper, we consider the design problem of allocating the backbone links in ATM-based personal communication networks (PCNs) that are survivable under single backbone link failures. Survivability is achieved by selecting two link-disjoint routes in the backbone network between every pair of ATM switches. We also take the novel approach of not only minimizing the diameter of the network as a primary objective but also minimizing the total length of the network as a secondary objective. We propose a new heuristic algorithm to optimize the design of the network based on both objectives. We report the results of an extensive simulation study that show that our algorithm generates backbone networks that can withstand single link failures, have shorter average diameters and smaller total lengths and achieve a higher percentage of admitted calls under a mobile environment.     

生存光传输网络的交叉连接模块结构

基于波分复用技术的光传输网络在克服当前网络容量瓶颈的同时又面临网络生存的挑战,它必须快速、有效地恢复因网络故障而受损的工作光路。该文分析了四种基本网络恢复技术以及与之相对应的OXC节点模块结构,即:保留光纤链路方式、保留波长链路方式、保留波长路径方式以及动态波长路径方式;并从光连接恢复时间、网络资源效率和控制复杂度三个侧面比较了不同OXC结构对于网络生存的影响。     

Reconfiguration for service and self-healing in ATM networks based on virtual paths

This paper presents a reconfiguration scheme resulting in capacity efficiency and fast restoration by utilizing the inherent benefits of Virtual Paths in ATM networks. The unified optimization of bandwidth reconfiguration is addressed so that switched ATM networks can support both service and survivability from a common pool of network spare capacity at a given time. The spare capacity is composed of idle bandwidth and freed up bandwidth from the switch pairs which have a surplus bandwidth. Fast restoration can be achieved by using the pre-optimized network spare bandwidth and preplanned backup Virtual Paths based on the link and node disjoint path routing scheme. The overall operation of the proposed self-healing strategy can be consolidated into distributed fault management functions at ATM layer based on Virtual Paths. The scheme enables a logical Virtual Paths ring protection switching in ATM networks.     

New insights on survivability in multi-domain optical networks

With the development of intelligent optical networks and the general multi-protocol label switching (GMPLS) technique, the seamless convergence between IP network and optical network is no longer be a dream but a practical reality. Similar to the Internet, current optical networks have been divided into multiple domains each of which has its own network provider and management policy. Therefore, the development of multi-domain optical networks will be the trend of new-generation intelligent optical networks, and GMPLS-based survivability for multi-domain optical networks will become a hot topic of research in the future. This paper provides a comprehensive review of the existing survivable schemes in multi-domain optical networks and analyzes the shortcomings of current research. Based on previous studies, we present possible challenges and propose new ideas to design efficient survivable schemes to guide the future work of researchers in multi-domain optical networks.     

Dynamic routing and spectrum (re)allocation in future flexgrid optical networks

Future flexible-grid elastic optical networks are very promising due to their higher spectrum efficiency and flexibility comparing to the rigid spectrum grid optical networks realized with the traditional wavelength division multiplexing (WDM) technology. The maturity of key system components enabling flexgrid optical networks, such as advanced modulation techniques and multi-granular switching, is already high enough and thus their deployment is expected in the near future. The main feature of such networks is the removal of fix grid-space assignment (in general 50 GHz) to the optical connections independently of the required bandwidth. In fact, the available optical spectrum in flexgrid network is divided into frequency slots of a fixed spectrum width and an optical connection can be allocated into the number of slots that better matches the actual bandwidth of the connection demand. Nonetheless, such allocation must satisfy two constraints, i.e. the slots must be (i) contiguous in the spectrum domain and (ii) continuous along the links on the routing path. These constraints result in a need for dedicated Routing and Spectrum Allocation (RSA) algorithms able to operate under dynamic traffic conditions. From the network design perspective, an important issue is the selection of the frequency slot width which may have an impact on the network performance. Last but not least, network dynamicity entails spectrum fragmentation, which significantly reduces the network performance. In this paper we address these topics and, in particular: (1) we present an RSA algorithm to be used in dynamic network scenarios, (2) we study the optimal slot width as a function of the foreseen traffic to be served, and (3) we propose an algorithm to reallocate already established optical connections so that to make room in the spectrum for the new ones. Exhaustive simulation results reveal that the proposed approach improves the blocking probability performance in flexgrid optical networks.     

On burst rescheduling in OBS networks with partial wavelength conversion capability

The core nodes in an optical burst switching (OBS) network are normally equipped with wavelength converters (WCs) to reduce the burst loss probability. Since WCs are expensive and still immature technologically, it is desirable to reduce the number of WCs in the network and to have partial wavelength conversion capability at the core nodes. Nevertheless, a majority of algorithms in the literature are proposed under the full wavelength conversion assumption. As a result, they do not consider the burst loss caused by insufficient WCs, i.e., bursts dropped due to the unavailability of free WCs to convert them to unused wavelengths. In this paper, we demonstrate how to use burst rescheduling to decrease the burst loss due to insufficient WCs and hence cut down on the overall burst loss probability in OBS networks. Two burst rescheduling algorithms are proposed. Their effectiveness in reducing the overall burst loss probability is verified through simulation experiments.     

ATM网络中关键服务生存性保证机制

生存性是ＡＴＭ网络中亟待解决的问题,文中在介绍了当前ＡＴＭ网络中基于ＶＰ层的故障恢复机制后,引入生存重要性因子表征网络中不同服务的生存重要性,定义了加权恢复率;基于关键服务生存性保证的要求,提出了关键ＶＣ预建立保证连接和关键ＶＣ优先的实时恢复两种解决方式,并综合形成了关键服务生存性的保证机制。     

WDM网状网中基于树路由的鲁棒抗毁算法研究*

研究了波分复用（WDM）网状网在软管不确定业务量模型下的鲁棒抗毁问题,提出一种新的基于树路由机制的共享分段保护算法——TSSP (tree-based shared-segment protection) 算法。利用软管模型下树路由机制的基本特征,TSSP算法首先计算出一个具有最小叶子节点数的工作树,然后根据恢复时间的要求为树上所有的叶子节点对寻找保护路径,最后借助共享保护的思想进行波长配备,从而达到优化网络性能的目的。仿真结果表明,相对于现有的鲁棒抗毁算法,TSSP不仅具有较小的全网代价,其恢复速度也较     

All-to-All Optical Routing in Chordal Rings of Degree 4

We consider the problem of routing in networks employing all-optical routing technology. In such networks, information between nodes of the network is transmitted as light on fiber-optic lines without being converted to electronic form in between. We consider switched optical networks that use the wavelength-division multiplexing (or WDM) approach. A WDM network consists of nodes connected by point-to-point fiber-optic links, each of which can support a fixed number of wavelengths. The switches are capable of redirecting incoming streams based on wavelengths, without changing the wavelengths. Different messages may use the same link concurrently if they are assigned distinct wavelengths. However, messages assigned the same wavelength must be assigned edge-disjoint paths. Given a communication instance in a network, the optical routing problem is the assignment of {routes} to communication requests of the instance, as well as wavelengths to routes so that the number of wavelengths used by the instance is minimal. We focus on the all-to-all communication instance I _A in a widely studied family of chordal rings of degree 4, called optimal chordal rings . For these networks, we prove exact bounds on the optimal load induced on an edge for I _A , over all shortest-path routing schemes. We show an approximation algorithm that solves the optical routing problem for I _A using at most 1.006 times the lower bound on the number of wavelengths. The previous best approximation algorithm has a performance ratio of 8. Furthermore, we use a variety of novel techniques to achieve this result, which are applicable to other communication instances and may be applicable to other networks. Received July 22, 1998; revised October 14, 1999.     

光纤Mesh网络动态组播业务疏导算法

针对当前低速组播业务请求与光网络高速波长传输容量的问题,基于光网络组播业务疏导模型,提出动态组播业务疏导算法,将新的组播业务请求疏导到已建立的光组播树上,达到提高网络资源的利用率、降低组播业务连接阻塞概率的目的。仿真结果表明,该算法可有效地改善网络性能。