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.     

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.     

Lightpath concentrators for all-optical networks

In some deployments of all-optical networks, it is necessary to concentrate the lightpaths from some fibers to fewer fibers. An N/spl times/M lightpath concentrator is an optical component for this purpose, and it concentrates the lightpaths from N incoming fibers to M outgoing fibers. In this paper, three designs of N/spl times/M lightpath concentrators are proposed. The first design is a generalization of optical crossconnects, and it requires M/spl times/M optical switches. The second design incorporates the concept of partial concentration so that it requires only m/spl times/m optical switches (where m相似文献   

Capacity performance of dynamic provisioning in optical networks

This paper describes an architecture and analyzes the performance of dynamic provisioning of lightpaths in an optical network. In dynamic provisioning, a lightpath is set up in real-time without rearranging the working and protection routes of existing lightpaths, and without the knowledge of future lightpath provisioning events. This paper develops a general model of the physical topology of the optical network, and outlines routing approaches for dynamic provisioning of lightpaths. It analyzes via simulations the performance of dynamically provisioned unprotected, 1+1 protected and mesh-restored lightpaths. The analysis of the efficiency of network utilization of dynamic provisioning focuses on the spare capacity needed for protection, and in particular focuses on the impact of sharing of wavelength channels for mesh-restored lightpaths. The main conclusion from the performance studies is that significant capacity gains are achieved with sharing of wavelength-channels for mesh-restored lightpaths with dynamic provisioning even for sparse topologies, and even at moderate loads     

Algorithms for Dynamic Routing in All-Optical Networks

In this paper, we have studied a number of algorithms for routing in all-optical wavelength routed networks. We have considered situations where a lightpath is dynamically created in response to a request for communication and the WDM channels constituting the lightpath are reclaimed when the communication is over. We have looked at two schemes for dynamic wavelength allocation. In the first scheme we have assumed the existence of a central agent to maintain a database of existing lightpaths where the central agent attempts to generate a new lightpath in response to a request for communication. In the second scheme, we attempt to generate a new lightpath using a distributed algorithm. In the first scheme we have exploited the existence of multiple paths between any pair of nodes in a network in order to reduce the blocking probability. For the second scheme, we have proposed three distributed strategies to determine, if possible, a lightpath when there is a request for communication. Each of these strategies have their advantages and disadvantages in terms of the expected blocking probability and the set-up time. We have studied the performances of both the schemes using Monte Carlo simulation.     

Lightpath Establishment Without Wavelength Conversion Based on Aggressive Rank Accounting in Multi-Domain WDM Networks

In multi-domain WDM networks, in order to establish inter-domain lightpaths across multiple domains without wavelength conversion, a lightpath establishment method based on rank accounting has previously been proposed. With the method, the inter-domain lightpaths are established with small blocking probability based on ranking databases for wavelengths; however, the performance of the method deteriorates when the ranking databases are not frequently updated. In this paper, we propose a lightpath establishment method based on aggressive rank accounting so that ranking databases are updated frequently. In the proposed method, border-node information is used in addition to wavelength usage information, and ranking databases for multiple nodes are updated simultaneously every time a lightpath establishment is processed. From the border-node information, accuracies of the wavelength usage information for each node are computed, and then the ranking database for each node is updated with the wavelength usage information and the computed accuracies. With the updated ranking database, each source node establishes an inter-domain lightpath without wavelength conversion to its destination node across multiple domains. We also present two implementations of the proposed method toward its practical use based on RSVP-TE signaling. We evaluate by simulation the performance of the proposed method, and we show that the proposed method provides smaller blocking probability than the conservative, conventional method when inter-domain lightpaths are not frequently established. We also show that the proposed method still provides smaller blocking probability even if routes of the inter-domain lightpaths change. Finally, we show that the performance of the proposed method is insensitive to the two implementations.     

Dynamic circuit provisioning in all-optical WDM networks using lightpath switching

In this paper we investigate the problem of provisioning holding-time-aware (HTA) dynamic circuits in all-optical wavelength division multiplexed (WDM) networks. We employ a technique called lightpath switching (LPS) wherein the data transmission may begin on one lightpath and switch to a different lightpath at a later time. Lightpath switches are transparent to the user and are managed by the network. Allowing LPS creates a number of segments that can use independent lightpaths. We first compare the performance of traditional routing and wavelength (RWA) assignment to routing and wavelength assignment with LPS. We show that LPS can significantly reduce blocking compared to traditional RWA. We then address the problem of routing dynamic anycast HTA dynamic circuits. We propose two heuristics to solve the anycast RWA problem: anycast with continuous segment (ACS) and anycast with lightpath switching (ALPS). In ALPS we exercise LPS, and provision a connection request by searching for the best candidate destination node is such a way that the network resources are utilized efficiently. In ACS we do not allow a connection request to switch lightpaths. The lightpaths to each candidate destination node of a request are computed using traditional RWA algorithms. We first compare the performance of ACS to ALPS and observe that ALPS achieves better blocking than ACS. Furthermore, we also compare the performance of these two anycast RWA algorithms to the traditional unicast RWA algorithm. We show that the anycast RWA algorithms presented here significantly outperform the traditional unicast RWA algorithms.     

Multicast wavelength assignment with sparse wavelength converters to maximize the network capacity using ILP formulation in WDM mesh networks

In general, multicast routing and wavelength assignment (MC-RWA) can be subdivided in routing and wavelength assignment issues in wavelength-division multiplexing (WDM) mesh networks. Previous studies on WDM multicast have mainly focused on WDM multicast routing. The multicast wavelength assignment problem is studied in this paper. A unicast routing path can be established by a lightpath in an all-optical network. However, in the multicasting case, a multicast routing tree can be established by a single light-tree or several lightpaths, or a combination of several light-trees and lightpaths. We propose a wavelength assignment algorithm for finding an optimal combination of lightpaths and light-trees to construct a newly required multicast session. First of all, two cost functions are given to evaluate the establishing cost for each feasible wavelength, and then find a set of wavelengths that covers all destinations with the minimal cost using Integer Linear Programming (ILP) formulation. We focus on maximizing the total number of users served in a multicast session and the network capacity. The simulation results show that the proposed algorithm can improve system resource utilization and reduce the blocking probability compared with the First-Fit algorithm.This research was partially supported by the Grant of National Science Council, R.O.C. (NSC 94-2745-E-155-007-URD).     

Dynamic lightpath establishment considering four-wave mixing in multifiber WDM networks

This paper proposes a dynamic lightpath establishment scheme considering four-wave mixing (FWM) in multifiber wavelength-division multiplexed (WDM) all-optical networks. The FWM is one of the most important physical impairments to be resolved in WDM networks because the FWM induces nonlinear inter-channel crosstalk and decays the performance of WDM networks. In WDM networks, data are transmitted via lightpaths. When the effect of FWM crosstalk is large, it is highly possible that data transmission fails even if lightpaths are correctly established. The proposed scheme aims to avoid not only the blocking of lightpath establishment but also the accumulation of FWM crosstalk by means of ingenious selection of routes, wavelengths, and fibers for lightpath establishment. In the proposed scheme, a route and a wavelength are selected for each lightpath based on wavelength availability and wavelength placement of established lightpaths. Furthermore, fibers on the route are selected based on estimated FWM power. In this paper, we show the effectiveness of the proposed scheme through simulation experiments.     

A novel survivable routing algorithm for shared segment protection in mesh WDM networks with partial wavelength conversion

In this paper, a survivable routing algorithm is proposed for shared segment protection (SSP), called optimal self-healing loop allocation (OSHLA), which dynamically allocates spare capacity for a given working lightpath in mesh wavelength-division-multiplexing (WDM) networks with partial wavelength conversion capability. Two novel graph transformation approaches, namely graph of cycles and wavelength graph of paths, are introduced to solve this problem, in which the task of survivable routing is formulated as a series of shortest path searching processes. In addition to an analysis on the computation complexity, a suite of experiments is conducted to verify OSHLA on four networks with different topologies and traffic loads. We find that the blocking probability and computation complexity are dominated by the upper bound on the length of the working and protection segments. Comparison is made between OSHLA and four other reported schemes in terms of blocking probability. The results show that OSHLA can achieve the lowest blocking probability under the network environment of interest. We conclude that OSHLA provides a generalized framework of survivable routing for an efficient implementation of SSP in mesh WDM partial wavelength convertible networks. With OSHLA, a compromise is initiated by manipulating the upper bound on the length of working and protection segments such that the best performance-computation complexity gain can be achieved.     

Post‐Disaster least loaded lightpath routing in elastic optical networks

Disaster events directly affect the physical topology of core networks and may lead to simultaneous failure of multiple lightpaths leading to massive service outages for network operators. To recover from such a failure scenario, the existing routing algorithms running on network nodes (routers or switches) typically attempt to reestablish the connections over new routes with shortest distances and hop count approach. However, this approach may result in congestion on some links, while other links may have the unutilized capacity. Hence, intelligent lightpath computing techniques are required to efficiently route network traffic over the new routes by considering traffic load of each link in addition to distance and hop count to minimize network congestion. In this paper, we have proposed a capacity‐constrained maximally spatial disjoint lightpath algorithm to tackle the provisioning and restoration of disrupted lightpaths in a postdisaster scenario in the context of elastic optical networking. This algorithm computes an alternate least loaded lightpath for disrupted primary lightpath using capacity‐constrained shortest lightpath. Alternate lightpath selection is based on a criteria parameter for a lightpath to be least loaded and constrained by either the length or the spatial distance between primary and alternate lightpaths. The spatial distance between lightpaths enables to reestablish the disrupted connection request away from disaster proximity. The performance of the proposed algorithm is evaluated through simulation for several parameters like blocking probability, network utilization, connection success rates, and minimum spatial distance.     

A dynamic hop count shifting RWA algorithm for wavelength routed optical networks

In this article, we find that the limiting hop count in a lightpath impacts on the performance of optical networks. Based on this observation, we propose a dynamic hop count shifting (DYHOS) algorithm that limits the hop count of lightpaths dynamically, depending on the traffic load. The proposed algorithm searches an available route, while minimizing the waste of network resources and limiting excessive traffic on the network. Hence, the proposed algorithm increases the network throughput and reduces the blocking probability. Comparing with shortest path routing and adaptive path routing algorithms, we show the performance of the proposed algorithm has the lowest blocking probability influenced by the hop count of lightpaths for a given routing algorithm.

Dynamic light trail routing in WDM optical networks

Fiber optics have replaced copper as the primary transmission medium. Wavelength Division Multiplexing (WDM) networks effectively increase single-link bandwidth from 10 Mbps to over 160 Gbps, and have been considered as a promising candidate for the next-generation backbone network. All optical circuits each on a separate wavelength called lightpaths represent the first major method for optical communication. The granularity provided between a source and destination node is that of a complete wavelength. Once a lightpath is set up, the entire wavelength is used exclusively by the connection’s source and destination node-pair. No sub-wavelength sharing between nodes along the lightpath is allowed. However, it is often observed that the bandwidth requirement in today’s network is often dynamically varying and does not justify the need for allocating an entire wavelength. Therefore, the wavelength capacity may be underutilized. A new technology termed light trail was proposed to avoid the inability of intermediate nodes to use a connection wavelength, and the constant reconfiguration of switches. In this article, we study dynamic light trail routing in a WDM optical network. We present an efficient algorithm for establishing a light trail routing for a new connection request, while using minimum network resources. We also study survivable network routing using the proposed light trail technology. We present an efficient heuristic for computing a pair of working and protection light trails for a dynamic incoming connection request. Simulation results are presented which demonstrate the advantages of our routing schemes.     

Performance analysis of multicast routing and wavelength assignment protocol with dynamic traffic grooming in WDM networks

The need for on‐demand provisioning of wavelength‐routed channels with service‐differentiated offerings within the transport layer has become more essential because of the recent emergence of high bit rate Internet protocol (IP) network applications. Diverse optical transport network architectures have been proposed to achieve the above requirements. This approach is determined by fundamental advances in wavelength division multiplexing (WDM) technologies. Because of the availability of ultra long‐reach transport and all‐optical switching, the deployment of all‐optical networks has been made possible. The concurrent transmission of multiple streams of data with the assistance of special properties of fiber optics is called WDM. The WDM network provides the capability of transferring huge amounts of data at high speeds by the users over large distances. There are several network applications that require the support of QoS multicast, such as multimedia conferencing systems, video‐on‐demand systems, real‐time control systems, etc. In a WDM network, the route decision and wavelength assignment of lightpath connections are based mainly on the routing and wavelength assignment (RWA). The multicast RWA's task is to maximize the number of multicast groups admitted or minimize the call‐blocking probability. The dynamic traffic‐grooming problem in wavelength‐routed networks is generally a two‐layered routing problem in which traffic connections are routed over lightpaths in the virtual topology layer and lightpaths are routed over physical links in the physical topology layer. In this paper, a multicast RWA protocol for capacity improvement in WDM networks is designed. In the wavelength assignment technique, paths from the source node to each of the destination nodes and the potential paths are divided into fragments by the junction nodes and these junction nodes have the wavelength conversion capability. By using the concept of fragmentation and grouping, the proposed scheme can be generally applied for the wavelength assignment of multicast in WDM networks. An optimized dynamic traffic grooming algorithm is also developed to address the traffic grooming problem in mesh networks in the multicast scenario for maximizing the resource utilization and minimizing the blocking probability. Copyright © 2011 John Wiley & Sons, Ltd.     

Accounting for Shared Regenerators in GMPLS-Controlled Translucent Optical Networks

In translucent optical networks, the usage of sparse opto-electronic regenerators permits to overcome optical signal quality degradations. In dynamic translucent optical networks, where lightpaths are established upon request, regenerators can be effectively time shared. However, the current generalized multiprotocol label switching (GMPLS) protocol suite does not consider how to dynamically reserve and release shared regenerators and how to distribute regenerator availability information to network nodes. In this paper, four Translucent Lightpath Dynamic Provisioning (TLDP) schemes are proposed to establish lightpaths in dynamic distributed translucent optical networks. TLDP schemes differently combine the utilization of specific open shortest path first-traffic engineering (OSPF-TE) or resource reservation protocol-traffic engineering (RSVP-TE) extensions and shared regenerator availability information. Simulation results show that TLDP scheme based on OSPF-TE extensions obtains lower lightpath setup time, but higher control plane load than TLDP schemes based on RSVP-TE extensions. Moreover, schemes based on RSVP-TE extensions or on OSPF-TE extensions obtain the same lowest blocking probability.      

Waveband Switching for Dynamic Traffic Demands in Multigranular Optical Networks

Waveband switching (WBS) in conjunction with multigranular optical cross-connect (MG-OXC) architectures can reduce the cost and complexity of OXCs. In this paper, we study the performance of different MG-OXC architectures under dynamic traffic. In the case with online incremental traffic, we compare two MG-OXC architectures in terms of the blocking probability of new lightpath requests and study the impact of port counts and traffic loads. We develop an online integer linear programming model (On-ILP), which minimizes the number of used ports and the request blocking probability, given a fixed number of wavelengths and MG-OXC architecture. The On-ILP optimizes the routing of new lightpaths so as to maximize lightpath grouping and reduce the port count given that existing traffic cannot be rearranged. We also propose a new efficient heuristic algorithm, called maximum overlap ratio (MOR) to satisfy incremental traffic and compare it with the On-ILP, first-fit, and random-fit algorithms. Our results and analysis indicate that using WBS with MG-OXCs can reduce the size (and, hence, the cost) of switching fabrics compared to using ordinary OXCs. Based on the results and observations in the incremental traffic case, we further study the performance of a particular MG-OXC architecture under fully dynamic or fluctuating traffic. Our simulations show that the proposed heuristic algorithm waveband assignment with path graph, which groups wavelengths to bands and uses wavelength converters efficiently under fluctuating traffic, significantly outperforms other heuristic algorithms.     

Rerouting technique with dynamic traffic in WDM optical networks

In this paper, we have proposed an efficient wavelength rerouting algorithm for dynamic provisioning of lightpath. In wavelength division multiplexed (WDM) networks rerouting of lightpath can be used to improve throughput and to reduce blocking probability. We have proposed a shortest path wavelength rerouting (SPWRR) algorithm for dynamic traffic in WDM optical networks. The results have shown that SPWRR algorithm can improve blocking performance of the network. In this paper, low complexity algorithm has been developed which is used for the calculation of blocking probability of network. The proposed algorithm has also been applied on the realistic network such as NSFnet for calculation and optimization of blocking probability of the network.     

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).     

Dither-free low-bias controller for deeply modulated Mach-Zehnder modulators

We have recently proposed and demonstrated, by means of simulation, the benefits of a simple yet effective cognitive technique to enhance stateless Path Computation Element algorithms with the aim of reducing the connection blocking probability when relying on a potentially non-up-to-date traffic engineering database. In this paper, we employ that technique, called elapsed time matrix (ETM), in the framework of the CHRON (Cognitive Heterogeneous Reconfigurable Optical Network) architecture and, more importantly, validate and analyze its performance in an emulation environment (rather than in a simulation environment) supporting impairment-aware lightpath establishment. Not only dynamic lightpath establishment on demand has been studied, but also restoration processes when facing optical link failures. Emulation results demonstrate that ETM reduces the blocking probability when establishing lightpaths on demand, and increases the percentage of successful restorations in case of optical link failure. Moreover, the use of that technique has little impact on lightpath setup time and lightpath restoration time, respectively.