Fast simulation of wavelength continuous WDM networks

This paper considers the estimation of blocking probabilities of circuit-switched WDM networks with no wavelength converters and with fixed routing. It presents an importance sampling simulation technique for determining whether or not such a network meets a specific grade of service requirement, in the sense of all routes having blocking below a given threshold. It is especially efficient for networks with high grades of service, which take a long time to simulate using conventional methods.     

WDM网络中的一种波长分配算法

本文研究了动态业务下，采用固定选路和备用选路的波分复用光传送网中的波长分配问题，提出了一种波长分配算法-相对最小影响算法。与己朋的利用全网信息分配波长的算法相比，该算法能更精确地描述波长分配对全网状态的影响，使网络资源的充分利用成为可能。计算机仿真表明，该波长分配算法性能较好。     

WDM网络中支持优先级的波长分配算法

本文提出了一种在WDM网络中支持优先级的波长分配算法,通过计算相对容量损失,力图在对较高优先级光路建立请求进行波长分配时,找到对较优先级请求影响最小的波长分配方案,这样,该算法既保证了较高优先级光路建立请求具有较低的阻塞率,同时又对较低优先级请求进行了优化,从而改善了全网的平均阻塞率。文中给出了计算机仿真结果。     

Efficient routing and wavelength assignment for reconfigurable WDM ring networks with wavelength converters

We consider the problem of wavelength assignment in reconfigurable WDM networks with wavelength converters. We show that for N-node P-port bidirectional rings, a minimum number of /spl lceil/PN/4/spl rceil/ wavelengths are required to support all possible connected virtual topologies in a rearrangeably nonblocking fashion, and provide an algorithm that meets this bound using no more than /spl lceil/PN/2/spl rceil/ wavelength converters. This improves over the tight lower bound of /spl lceil/PN/3/spl rceil/ wavelengths required for such rings given in if no wavelength conversion is available. We extend this to the general P-port case where each node i may have a different number of ports P/sub i/, and show that no more than /spl lceil//spl sigma//sub i/P/sub i//4/spl rceil/+1 wavelengths are required. We then provide a second algorithm that uses more wavelengths yet requires significantly fewer converters. We also develop a method that allows the wavelength converters to be arbitrarily located at any node in the ring. This gives significant flexibility in the design of the networks. For example, all /spl lceil/PN/2/spl rceil/ converters can be collocated at a single hub node, or distributed evenly among the N nodes with min{/spl lceil/P/2/spl rceil/+1,P} converters at each node.     

An evaluation of distributed wavelength provisioning in WDM optical networks with sparse wavelength conversion

Distributed wavelength provisioning is becoming one of the most important technologies for supporting next-generation optical networks. This paper describes the evaluation of the performance of distributed wavelength provisioning in wavelength-division-multiplexing (WDM) optical networks with sparse wavelength conversion (i.e., where wavelength conversion is available at only a subset of network nodes). Using the well-known destination-initiated reservation method as a case study, a highly accurate analytical model supported by comprehensive simulation validation is proposed. Both analytical and simulation results show that, in optical networks with distributed wavelength provisioning, sparse wavelength conversion still helps to significantly lower the connection-blocking probabilities. However, unlike that in centralized wavelength provisioning, sparse wavelength conversion may not easily achieve nearly the same performance as that of full wavelength conversion, especially under light traffic loads. This paper evaluates how the potential contribution of sparse wavelength conversion depends on different factors, such as the number of wavelength converters, the number of wavelength channels per fiber, the burstiness of traffic loads, and the network size, and discusses the influence of the signaling scheme.     

Nonblocking WDM switching networks with full and limited wavelength conversion

In previous years, with the rapid exhaustion of the capacity in wide area networks led by Internet and multimedia applications, demand for high bandwidth has been growing at a very fast pace. Wavelength-division multiplexing (WDM) is a promising technique for utilizing the huge available bandwidth in optical fibers. We consider efficient designs of nonblocking WDM permutation switching networks. Such designs require nontrivial extensions from the existing designs of electronic switching networks. We first propose several permutation models in WDM switching networks ranging from no wavelength conversion, to limited wavelength conversion, to full wavelength conversion, and analyze the network performance in terms of the permutation capacity and network cost, such as the number of optical cross-connect elements and the number of wavelength converters required for each model. We then give two methods for constructing nonblocking multistage WDM switching networks to reduce the network cost.     

Segment shared protection in WDM networks with partial wavelength conversion

In this paper, we propose a novel approach of survivable routing for segment shared protection (SSP) in mesh wavelength division multiplexing networks with partial wavelength conversion capability, with which spare capacity is allocated dynamically for a given working lightpath. The survivable routing process is formulated into a shortest path searching problem on the transferred graph of cycles (TGC) and wavelength graph of paths (WGP).     

Multicast routing and wavelength assignment with delay constraint in WDM networks with sparse wavelength conversions

With the developments in multimedia and other real-time group applications, the question of how to establish multicast trees satisfying Quality-of-Service (QoS) requirements is becoming a very important problem. In this paper, multicast routing and wavelength assignment with delay constraint (MCRWA-DC) in wavelength division multiplexing (WDM) networks with sparse wavelength conversions is studied. We propose a colored multigraph model for the temporarily available wavelengths. Based on this colored multigraph model, two heuristic algorithms are proposed to solve the MCRWA-DC problem. The proposed algorithms have the following advantages:(1) finish multicast routing and wavelength assignment in one step; (2) the total cost of the multicast tree is low; (3) the delay from the source node to any multicast destination node is bounded; and (4) locally minimize the number of wavelength conversions and the number of different wavelengths used to satisfy a multicast request. Simulation results show that the proposed algorithms work well and achieve satisfactory blocking probability.     

WDM光传送网中支持优先级的波长分配算法

文中提出了一种用于WDM光传送网的支持优先级的波长分配算法－动态门限法,该算法保证了较高优先级的光路建立请求具有较低的阻塞率,同时又考虑到较低优先级的光路建立请求的性能优化,从而很好地降低了全网的平均阻塞率。文中给出了计算机仿结果。     

Dynamic lightpath establishment in wavelength routed WDM networks

In wavelength-routed WDM networks, a control mechanism is required to set up and take down all-optical connections. Upon the arrival of a connection request, this mechanism must be able to select a route, assign a wavelength to the connection, and configure the appropriate optical switches in the network. The mechanism must also be able to provide updates to reflect which wavelengths are currently being used on each link so that nodes may make informed routing decisions. In this work, we review control mechanisms proposed in the literature. We also investigate and compare two different distributed control mechanisms for establishing all-optical connections in a wavelength-routed WDM network: an approach based on link-state routing, and one based on distance-vector routing     

Routing and wavelength assignment in WDM all-optical networks

A new mathematical formulation of the routing and wavelength assignment in wavelength division multiplexing (WDM) all-optical networks is proposed. Which yields tight linear programming lower bounds on the wavelength requirements both theoretically and computationally. An efficient procedure computing lower bounds is also presented together preliminary computational results.     

Multicast connection capacity of WDM switching networks with limited wavelength conversion

Currently, many bandwidth-intensive applications require multicast services for efficiency purposes. In particular, as wavelength division multiplexing (WDM) technique emerges as a promising solution to meet the rapidly growing demands on bandwidth in present communication networks, supporting multicast at the WDM layer becomes an important yet challenging issue. In this paper, we introduce a systematic approach to analyzing the multicast connection capacity of WDM switching networks with limited wavelength conversion. We focus on the practical all-optical limited wavelength conversion with a small conversion degree d (e.g., d=2 or 3), where an incoming wavelength can be switched to one of the d outgoing wavelengths. We then compare the multicast performance of the network with limited wavelength conversion to that of no wavelength conversion and full wavelength conversion. Our results demonstrate that limited wavelength conversion with small conversion degrees provides a considerable fraction of the performance improvement obtained by full wavelength conversion over no wavelength conversion. We also present an economical multistage switching architecture for limited wavelength conversion. Our results indicate that the multistage switching architecture along with limited wavelength conversion of small degrees is a cost-effective design for WDM multicast switching networks.     

WDM网络中波长信道的误码率估计

本文建立了完整的WDM光网络节点的同频串扰理论分析模型，考虑光放大器ASE噪声的影响，采用重要性采样技术进行数值仿真，得出某一波长信道中串扰导致的误码率，讨论波长个数、同源串扰数及消光比等因素对系统性能的影响，并与高斯近似法的结果进行了比较。     

Time-efficient optimal wavelength assignment in optical WDM networks with conversion capability

In wavelength-routed optical networks (WRONs), a wavelength assignment algorithm which can optimally utilize wavelength converters is strongly desired. In this letter, for the first time, we propose a novel graph constructed with groups of available wavelengths, called lambda-runs, to obtain the least-conversion lightpaths easily by applying the shortest-path routing Dijkstra's algorithm. Simulations show that our algorithm is much more scalable than an existing optimal algorithm, and significantly improves the blocking performance, compared to modified first-fit algorithm.     

Dynamic routing and wavelength assignment in multi-granularity WDM networks

For the purpose of reducing the complexity and cost of optical large-scale cross-connect, wavelengths are grouped into wavebands or fiber to be switched as a single entity, which is called multi- granularity switching. However, it introduces more complexity into the routing and wavelength assignment problem. In this paper, we propose a novel graph model for describing the states of the multi-granularity switching WDM networks. Based on the model, the dynamic routing and wavelength assignment problems for multi-granularity traffic can be solved jointly, and different on-line wavelength grooming policies can be achieved simultaneously. By simulation, we compared the performance of our algorithms under different policy and different percent of fibers for fiber switching. The result proved that our algorithms yield better performance than those deal with the routing and wavelength assignment separately. This work was supported in part by NSFC Project No. 90104003, 60272023, 60372025 and National 863 project No. 2005AA122310.     

Performance modeling of bufferless WDM packet switching networks with limited-range wavelength conversion

All optical communication is attracting more and more attention because of the huge bandwidth of optics. In this paper, we study the performance of bufferless optical wavelength-division multiplexing (WDM) packet switching networks with limited-range wavelength conversion capabilities. We first introduce an optimal scheduling algorithm that maximizes the throughput of the switch. We then derive an analytical model to evaluate the performance of the switch in terms of packet-loss probability. Our model is the first accurate analytical model for a bufferless WDM packet switch with variable conversion distances, and can be used to quantitatively determine the maximum load for a given conversion distance or the minimum conversion distance for a given traffic load. We also conducted simulations to validate the analytical model. Both the analytical and simulation results reveal that limited-range wavelength conversion can achieve almost the same performance as full-range wavelength conversion.     

WDM网络中支持QoS的路由与波长分配算法

针对波分复用(wDM)网络中的路由与波长分配问题。提出了一种支持服务质量(QoS)的约束搜索算法。基于多目标规划模型,这种搜索算法可为网络各节点创建路由表,根据路由表信息求出非支配路径集合,从而一次性完成寻找路由和分配波长两项任务。仿真实例证明了该算法的有效性。     

WDM光网中的一种邻域加权累积的波长分配策略

针对光核心传送网中单纤场景下的路由选择与波长分配（Routing and Wavelength Assignment,RWA）问题,提出了一种邻域加权累积的波长分配策略。在一条路径上为一个连接请求选择波长时,将网络的所有链路归入当前路径的不同邻域中,然后根据与路径之间的距离为不同邻域赋予不同的权重,进而对每个波长在全网中被占用的个数进行加权累积,最后选择累积值最大的可用波长建立连接。仿真结果表明,相对于现有的阻塞率最低的最大使用（Most-Used）波长分配策略,所提策略具有更低的阻塞率。     

Study of multicast wavelength arrangement for maximizing network capacity in WDM networks with sparse wavelength converters

The issue of wavelength assignment is one of the most important factors that affect the capacity for the deployment of optical networks. This issue becomes more critical for multicast connections, especially when the network nodes have no wavelength conversion capability. Although the wavelength assignment can be more flexible if each node can perform wavelength conversion, the deployment cost increases accordingly. A compromise is to support a limited portion of conversion nodes in the WDM network. We propose a systematic approach for the wavelength assignment of multicast connections in WDM networks with sparse wavelength conversion nodes. The efficiency of the arrangement of wavelength is measured by its influences on the available capacity of the network and the consumption of wavelengths. By using the proposed approach, the Static Cost Greedy (SCG) algorithm [8] can be easily extended to be applicable in a Sparse Wavelength Conversion Network (SWCN). In addition, instead of SCG, the Minimum-Effect-First (MEF) algorithm is proposed to maximize the network capacity during wavelength assignment. We compare the performance of the proposed MEF methods with the extended SCG scheme through exhaustive simulations. The experimental results indicate that the proposed MEF schemes demonstrate much better performance than the SCG scheme. We also found that the performance is not always improved proportionally to the increment of the wavelength conversion nodes. The improvement reaches saturation when the number of conversion nodes is above 35% of the total number of nodes.

Lightpath (wavelength) routing in large WDM networks

We address the problem of efficient circuit switching in wide area optical networks. The solution provided is based on finding optimal routes for lightpaths and the new concept of semilightpaths. A lightpath is a fully optical transmission path, while a semilightpath is a transmission path constructed by chaining together several lightpaths, using wavelength conversion at their junctions. A fast and practical algorithm is presented to optimally route lightpaths and semilightpaths taking into account both the cost of using the wavelengths on links and the cost of wavelength conversion. We prove that the running time of the algorithm is the best possible in the wide class of algorithms allowing linear algebraic operations on weights. This class encompasses all known related practical methods. Additionally, our method works for any physical realization of wavelength conversion, independently whether it is done via optoelectronic conversion or in a fully optical way