Design of the optical path layer in multiwavelength cross-connectednetworks

We discuss the wavelength requirement for optical networks based on wavelength-division multiplexing (WDM). A mathematical model, to represent the routing and wavelength assignment in optical networks with or without wavelength conversion, is described, and metrics are defined to express the performance. A new heuristic for routing and wavelength assignment is proposed and compared with the Dijkstra algorithm and with a solution based on integer linear programming. The different techniques are applied to a variety of network examples with different traffic loads     

A novel dynamic survivable routing in WDM optical networks with/without sparse wavelength conversion

In this paper, we study the dynamic survivable routing problem, both in optical networks without wavelength conversion and in optical networks with sparse wavelength conversion, and propose a novel hybrid algorithm for it based on the combination of mobile agents technique and genetic algorithms (GA). By keeping a suitable number of mobile agents in the network to cooperatively explore the network states and continuously report cycles (that are formed by two disjoint-link routes) into the routing tables, our new hybrid algorithm can promptly determine the first population of cycles for a new request based on the routing table of its source node, without the time consuming process associated with current GA-based lightpath protection schemes. We further improve the performance of our algorithm by introducing a more advanced fitness function that is suitable for both the above networks. Extensive simulation studies on the ns-2 network simulator show that our hybrid algorithm achieves a significantly lower blocking probability than the conventional survivable routing algorithms for all the cases we studied.     

Link-State-Based Algorithms for Dynamic Routing in All-Optical Networks with Ring Topologies

The increased usage of large bandwidth in optical networks raises the problems of efficient routing to allow these networks to deliver fast data transmission with low blocking probabilities. Due to limited optical buffering in optical switches and constraints of high switching speeds, data transmitted over optical networks must be routed without waiting queues along a path from source to destination. Moreover, in optical networks deprived of wavelength converters, it is necessary for each established path to transfer data from source to destination by using only one wavelength. To solve this NP-hard problem, many algorithms have been proposed for dynamic optical routing like Fixed-Paths Least Congested (FPLC) routing or Least Loaded Path Routing (LLR). This paper proposes two heuristic algorithms based on former algorithms to improve network throughput and reduce blocking probabilities of data transmitted in all-optical networks with regard to connection costs. We also introduce new criteria to estimate network congestion and choose better routing paths. Experimental results in ring networks show that both new algorithms achieve promising performance.     

A next-generation optical regional access network

We describe an optical regional access network which combines electronic IP routing with intelligent networking functionality of the optical WDM layer. The optical WDM layer provides such networking functions as network logical topology reconfiguration, optical flow switching to offload traffic and bypass IP routers, wavelength routing of signals, protection switching and restoration in the optical domain, and flexible network service provisioning by reconfigurable wavelength connectivity. We discuss key enabling technologies for the WDM layer and describe their limitations. The symbiosis of electronic and optical WDM networking functions also allows support for heterogeneous format traffic and will enable efficient gigabit-per-second user access in next-generation Internet networks     

Virtual-node-based multicast routing and wavelength assignment in sparse-splitting optical networks

This paper investigates several problems associated with optical multicast routing and wavelength assignment in sparse-splitting optical networks for interactive real-time media distribution. Unfortunately, the constrained multicast routing with optimized wavelength assignment leads to NP-complete condition. Thus, in this paper, a virtual-node-based multicast routing algorithm is first proposed to satisfy the requirements of interactive real-time multicasting as well as the constraints from underlying optical networks. For the constructed multicast tree, we then associate an effective wavelength assignment algorithm. The experimental results show that the proposed algorithm combination performs well in terms of (1) the wavelength channel cost, (2) the maximum variation of inter-destination node delays, (3) the signal quality, and (4) the number of wavelength conversions.     

部分共享波长转换光网络动态路由的改进算法

提出了一种应用于部分共享波长转换（PWC）的波长路由光网络（WRON）中的基于节点阻塞的动态路由算法,它不需要共享复杂的波长转换信息,而是将各节点的阻塞特性考虑到路由过程中。为评价算法性能,在14节点的国家科学基金网（NSFNET）拓扑中进行了仿真。结果表明,新的路由算法显著改善了网络的阻塞性能和建路失败的概率,尤其是随着网络负载的降低,网络性能的改善更显著。     

Routing and Wavelength Assignment in Multi-Segment WDM Optical Networks using Clustering Techniques

This paper studies the routing and wavelength assignment (RWA) problem in multi-segment optical networks. The notion of network segment is referred to any part of the network that requires special consideration of wavelength routing such as separate administrative domains in a large scale optical network, sub-networks run by various service providers, etc. In multi-segment optical networks, each segment has different resource availability or hardware characteristics. The differences between multi-segment optical networks and homogeneous optical networks are discussed. We then present a resource abstraction technique called blocking island and define a multi-segment blocking island graph (BIG) network model. Using a minimum splitting routing heuristic introduced in the context of the blocking island paradigm in conjunction with the multi-segment BIG model, we propose a general RWA algorithm that takes a combined view of the network resource to integrate routing, wavelength assignment and gateway selection in a single routing framework. In the simulation, we demonstrate the effectiveness of our proposed algorithm by comparing it with other state-of-the-art heuristics in this area.     

Computing approximate blocking probabilities for a class ofall-optical networks

We study a class of all-optical networks using wavelength-division multiplexing (WDM) and wavelength routing, in which a connection between a pair of nodes in the network is assigned a path and a wavelength on that path. Moreover, on the links of that path no other connection can share the assigned wavelength. Using a generalized reduced load approximation scheme we calculate the blocking probabilities for the optical network model for two routing schemes: fixed routing and least loaded routing     

一种改进遗传算法在WDM光网络中的应用

在波长路由光网(WRON)中,波长转换对提高网络性能、减少阻塞率起着重要的作用.但由于目前全光波长转换器非常昂贵,因而如何最优利用波长转换是配置光网络的一个重要问题.文中利用遗传算法很好地解决了这一问题,并且利用数值模拟的方法,计算了美国自然科学基金网(NSFnet)网络中最优配置下网络的阻塞情况.然后针对普通遗传算法的缺点,提出了一种改进遗传算法.最后利用数值模拟的方法,比较了两种算法的性能.     

Dynamic Routing and Wavelength Assignment in Survivable WDM Networks

Dense wavelength division multiplexing (DWDM) networks are very attractive candidates for next generation optical Internet and intelligent long-haul core networks. In this paper we consider DWDM networks with wavelength routing switches enabling the dynamic establishment of lightpaths between each pair of nodes. The dynamic routing and wavelength assignment (RWA) problem is studied in multifiber networks, assuming both protection strategies: dedicated and shared. We solve the two subproblems of RWA simultaneously, in a combined way using joint methods for the wavelength selection (WS) and wavelength routing (WR) tasks. For the WS problem in contrast to existing strategies we propose a new, network state based selection method, which tries to route the demand on each wavelength, and selects the best one according to different network metrics (such as available channels, wavelengths per fiber and network load). For the WR problem we propose several weight functions for using in routing algorithms (Dijkstra or Suurballe), adapting dynamically to the load of the links and to the length of the path. The combination of different wavelength selection and routing (WS&WR) methods enables wide configuration opportunities of our proposed algorithm allowing good adaptation to any network state. We also propose the extension of the RWA algorithm for dedicated and shared protection and a new method for applying shared protection in dynamic WDM environment. The detailed analysis of the strategies demonstrate that our RWA algorithm provides significantly better performance than previous methods in terms of blocking probability whether with or without protection methods.     

Multiple-Constraint-Aware RWA Algorithms Based on a Comprehensive Evaluation Model： Use in Wavelength-Switched Optical Networks

Because of explosive growth in Internet traffic and high complexity of heterogeneous networks,improving the routing and wavelength assignment (RWA) algorithm in underlying optical networks has become very important.Where there are multiple links between different the node pairs,a traditional wavelength-assignment algorithm may be invalid for a wavelength-switched optical networks (WSON) that has directional blocking constraints.Also,impairments in network nodes and subsequent degradation of optical signals may cause modulation failure in the optical network.In this paper,we propose an RWA algorithm based on a novel evaluation model for a WSON that has multiple constraints.The algorithm includes comprehensive evaluation model (CEM) and directional blocking constraint RWA based on CEM (DB-RWA).Diverse constraints are abstracted into various constraint conditions in order to better assign routing and wavelength.We propose using the novel CEM to optimize routing according to an assessed value of constraints on transmission performance.This eliminates the effects of physical transmission impairments in a WSON.DB-RWA based on CEM abstracts directional blocking conditions in multiple links between network nodes into directional blocking constraints.It also satisfies rigorous network specifications and provides flexibility,scalability,and first-fit rate for the backbone,especially in multiple links between WSON nodes.     

Efficient routing and wavelength assignment for reconfigurable WDMnetworks

Through the use of configurable wavelength-division-multiplexing (WDM) technology including tunable optical transceivers and frequency selective switches, next-generation WDM networks will allow multiple virtual topologies to be dynamically established on a given physical topology. For N node P port networks, we determine the number of wavelengths required to support all possible virtual topologies (PN lightpaths) on a bidirectional ring physical topology. We show that if shortest path routing is used, approximately N wavelengths are needed to map N lightpaths. We then present novel adaptive lightpath routing and wavelength assignment strategies that reduce the wavelength requirements to [(N/2)] working wavelengths per port for protected networks and [(N/3)] wavelengths in each direction per port for unprotected networks. We show that this reduced wavelength requirement is optimal in the sense that it is the minimum required to support the worst case logical topology. Furthermore, we prove that a significant number of logical topologies require this minimum number of wavelengths. We also develop joint routing and wavelength assignment strategies that not only minimize the number of wavelengths required to implement the worst case logical topologies but also reduce average wavelength requirements. Finally, methods for extending these routing and wavelength assignment results to general two-connected and three-connected physical topologies are presented     

Performance Evaluations for Dynamic Wavelength Routed All-Optical Multifiber Networks

This paper presents a study on dynamic wavelength routed all-optical networks by simulating traffic on all-optical networks. A performance study is carried out on dynamic all-optical networks for fixed and free routing. It is explained how multiple fibers correspond to limited wavelength conversion, and it is explained why the presence of wavelength converters increase the complexity of optical cross connects. We find that both free routing and wavelength conversion lowers the blocking probability significantly. The new contribution is that we determine the gain in blocking probability as function of the number of fibers per link and the offered load. We find that multiple fibers reduce the effect of wavelength converters significantly.     

On Multicast Routing for Wavelength-Routed WDM Networks with Dynamic Membership

Future broadband networks must support integrated services and offer flexible bandwidth usage. In our previous work in [1], we explored the optical link control (OLC) layer on the top of optical layer that enables the possibility of bandwidth on-demand (BoD) service directly over wavelength division multiplexed (WDM) networks. Today, more and more applications and services such as video-conferencing software and Virtual LAN service require multicast support over the underlying networks. Currently, it is difficult to provide wavelength multicast over optical switches without optical/electronic conversions although the conversion takes extra cost. In this paper, based on the proposed wavelength router architecture (equipped with ATM switches to offer O/E and E/O conversions when necessary), a dynamic multicast routing algorithm is proposed to furnish multicast services over WDM networks. The goal is to join a new group member into the multicast tree so that the cost, including the link cost and the optical/electronic conversion cost, is kept as low as possible. The same algorithm can be applied to other wavelength routing architectures with redefinition of electronic copy cost. The effectiveness of the proposed wavelength router architecture as well as the dynamic multicast algorithm is evaluated by simulation.     

An Ant-Based Approach for Dynamic RWA in Optical WDM Networks

In this paper, we propose a new ant-based algorithm for the dynamic routing and wavelength assignment (RWA) problem in optical WDM networks under the wavelength continuity constraint. Unlike conventional approaches, which usually require centralized global network information, our new RWA algorithm constructs the routing solution in a distributed manner by means of cooperative ants. To facilitate the ants’ foraging task, we adopt in our algorithm a probabilistic routing table structure for route selection. The new algorithm is highly adaptive in that it always keeps a suitable number of ants in the network to cooperatively explore the network states and continuously update the routing tables, so that the route for a connection request can be determined promptly by the current states of routing tables with only a small setup delay. Some new schemes for path scoring and path searching are also proposed to enhance the performance of our ant-based algorithm. Extensive simulation results upon three typical network topologies indicate that the proposed algorithm has a very good adaptability to traffic variations and it outperforms both the fixed routing algorithm and the promising fixed–alternate routing algorithm in terms of blocking probability. The ability to guarantee both a low blocking probability and a small setup delay makes the new ant-based routing algorithm very attractive for both the optical circuit switching networks and future optical burst switching networks     

Hybrid-hierarchical optical path network design algorithms utilizing ILP optimization

In this paper, we present design algorithms for the hierarchical optical path networks that utilize hybrid-hierarchical optical cross-connects (hybrid-HOXCs). The hybrid-HOXCs employ a waveband cross-connect for routing waveband paths and an electrical cross-connect for grooming wavelength paths. We first develop an integer linear programming model to solve the network design problem. We then propose a 2-stage ILP-based design algorithm for hierarchical optical path networks that utilize the hybrid-HOXCs. Its effectiveness is evaluated through numerical experiments. Impact of the critical parameter, electrical/optical port cost ratios, on total network cost is also investigated.     

Lightpath routing for intelligent optical networks

An overview of current issues and challenges in lightpath routing for optical networks is given. An architecture is presented in which optical switches are deployed, usually in the core, to interconnect IP routers at the edges. Lightpath routing within this architecture follows the framework of generalized multiprotocol label switching. Our discussion pays particular attention to the aspects of optical routing that differ from routing in irrational IP networks. Such aspects include physical layer constraints, wavelength continuity, the decoupling of the control network topology from the data network topology, explicit routing with wavelength assignment, and diversity routing for fast protection. We also present an algorithmic framework for lightpath computation, highlighting the issue of wavelength continuity and the differences between lightpath computation and traditional IP route computation     

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.     

Distributed dynamic grooming routing and wavelength assignment in WDM optical mesh networks

The bandwidth of a wavelength channel in WDM optical networks is very high compared to the user’s requirements for various applications. Therefore, there is a scope for better utilization of channel bandwidth by traffic grooming, in which several user’s channels are multiplexed for transmission over a single channel. Several research works have been reported on traffic grooming routing and wavelength assignment (GRWA) for static and dynamic traffic pattern under centralized environment. Distributed dynamic grooming routing and wavelength assignment (DDGRWA) is a new and quite unexplored area in WDM optical mesh networks. This article introduces the concept of distributed traffic grooming in WDM mesh networks which also includes virtual topology construction, reconfiguration, routing and wavelength assignment in the distributed environment assuming incoming traffic to be dynamic in nature. We have also presented simulation results of our algorithm on dynamically generated traffic under various network topologies.     

Path selection methods with multiple constraints in service-guaranteed WDM networks

We propose a new approach to constraint-based path selection for dynamic routing and wavelength allocation in optical networks based on WDM. Our approach considers service-specific path quality attributes, such as physical layer impairments, reliability, policy, and traffic conditions, and uses a flooding-based transfer of path information messages from source to destination to find multiple feasible paths. It is fully decentralized, as it uses local network state information. To better understand how multiple constraints impact the efficiency of wavelength routing, and consequently provision the service guarantees, we specifically focus on electronic regenerators that, while being widely considered as the basic building blocks for optical switching nodes, are likely to impose conflicting constraints on routing. For example, electronic regenerators extend the optical reach and could perform wavelength shifting, but also induce impairments, such as delays and operational costs. The question for constraint-based routing is how to account for these conflicting effects. To validate the network modeling, a wide range of networking scenarios are simulated, such as ring, mesh and interconnections of all-optical networks with electronic gateways. For all these scenarios, our approach is shown to efficiently accommodate multiple, conflicting routing metrics related to different services and network architectures.