Full Wavelength Conversion Capability Research Articles

PERFORMANCE ANALYSIS OF WSXC AND WIXC SSM OXC IN WDM OPTICAL NETWORKS

The impact of inband crosstalk on an optical signal passing through optical cross-connect nodes (OXC’s) in wavelength division multiplexing (WDM) optical network, is studied from the equation of electric field with crosstalk and the corresponding current. The analysis has been done for two SSM (space switching matrix) OXC architecture namely WSXC & WIXC where later one has full wavelength conversion capability. Although WIXC attenuates more crosstalk though it is found that depending on the values of optical propagation delay differences, coherent time of lasers and time duration of one bit of the signal, the required power penalty in WIXC may be greater than that of WSXC in some cases. The analysis has been performed on the measures of Bit Error Rate (BER) and Power Penalty.

Dynamic Routing and Wavelength Assignment in Multifiber WDM Networks with Wavelength Conversion Capability

This paper proposes a dynamic routing and wavelength assignment (RWA) scheme in multifiber WDM networks with wavelength conversion capability. In multifiber WDM networks, each link consists of multiple fibers. Thus, multiple lightpaths with the same wavelength can be established in the same link as long as they use different fibers. In WDM networks with wavelength conversion, the network nodes have wavelength conversion capability which can convert one wavelength to another. In order to efficiently utilize multifiber and wavelength conversion capability, an appropriate RWA scheme is necessary. The proposed scheme provides RWA for multifiber WDM networks with sparse and full wavelength conversion capability. In the proposed scheme, a route and wavelengths are selected for each lightpath based on wavelength availability and location of nodes with wavelength conversion capability. Through simulation experiments, we show that the proposed scheme reduces the blocking probability of lightpath establishment efficiently.

부분적 광파장 변환 노드를 이용한 광인터넷 복구

This paper studies the effects of wavelength conversion on self-healing optical networks. We examined the effects of wavelength conversion capability on the backup routing and the spare wavelength utilization. The efficiency of spare wavelength utilization is proportionally increased as the wavelength conversion capability increases, different from the call blocking probability for which about 30% of wavelength conversion capability shows nearly the same performance as full wavelength conversion capability. The spare resource utilization efficiency can be improved by using alternate routing and wavelength assignment algorithms.

Loss Differentiation in Full Wavelength Conversion Capable OBS Networks by Burst Cloning

Most of the QoS differentiation proposals for OBS are built upon a few traditional basic mechanisms. We propose a novel basic differentiation mechanism, Time domain Cloning Differentiation (TCD), based on the cloning concept. TCD evolves our previous QoS-MWST proposal, which was only applicable in limited and no wavelength conversion capable networks. TCD can also be used with full wavelength conversion capability. We also develop an analytical model of TCD in a single link, and present Proportional differentiation TCD, which provides edge-to-edge proportional loss differentiation based on TCD. We show that TCD outperforms other basic differentiation mechanisms.

Loss Differentiation in OBS Networks With Limited or No Wavelength Conversion

Quality of Service differentiation is an open research issue in optical burst switching (OBS) networks. Most proposals assume full wavelength-conversion, but wavelength converters are still very complex and expensive, and accordingly limited and no wavelength conversion OBS networks are likely to be the most common scenarios. In this paper, we define and analyze the QoS Multiple Wavelength Simultaneous Transmission technique (QoS-MWST), a novel method for providing loss differentiation in OBS networks with limited or no wavelength-conversion capability. In QoS-MWST, multiple copies of each burst are simultaneously sent on different wavelengths, so as to increase the chances of data delivery, and loss differentiation is achieved by properly sending more copies of the higher-priority bursts. Through analysis and extensive simulation experiments, we demonstrate that QoS-MWST can provide loss differentiation in OBS networks without full wavelength-conversion capability more efficiently than other differentiation techniques proposed in the literature.

Pre-planned optical burst switched routing strategies considering the streamline effect

Optical burst switching is a promising paradigm for the next IP over optical network backbones. However, due to its bufferless nature, it can be highly affected by burst contention. Several methods have been proposed to address this problem, most of them without considering a phenomenon unique to optical burst switched networks called streamline effect. Most of the reported studies also assume the existence of total wavelength conversion capacity on all nodes, presently a very expensive and somewhat unrealistic configuration, and additionally, the contention resolution schemes adopted increase in the complexity of the core nodes, hampering scalability. In this study, we present a traffic engineering approach for path selection with the objective of minimizing the contention considering the streamline effect and using only topological information. The main idea is to balance the traffic across the network in order to prevent congestion while keeping simple the architecture of the core nodes and without incurring into link state dissemination penalties. We propose and evaluate the path selection strategies in both networks with full wavelength conversion capability and networks with imposed wavelength continuity constraint. Results show that our strategies can outperform the traditionally used shortest path routing.

New and improved approaches for wavelength assignment in wavelength-continuous optical burst switching networks

Considering the economic and technical aspects of wavelength converters, full wavelength conversion capability will not be available throughout optical networks in the foreseeable future. This letter investigates the wavelength assignment problem in wavelength-continuous optical burst switching (OBS) networks. First, we develop a novel static approach, termed balanced static wavelength assignment (BSWA), which outperforms all other static strategies, and achieves almost the same performance as dynamic strategies with the advantage that no extra dynamic information is needed. Then, we apply BSWA to a dynamic approach to accelerate network convergence and reduce the initial burst loss. Numerical results show that our approaches make significant improvements in the burst loss probability in OBS networks.

A novel optical burst switching scheme—logical cascaded private subnet with start wavelength assignment policy

Many recent studies have convincingly demonstrated that network traffic exhibits a noticeable self-similar nature, which has a considerable impact on network performance, and most studies of optical burst switching (OBS) networks are under a fundamental assumption that full wavelength conversion is available throughout the network. In practice, however, economic and technical considerations are likely to dictate a more limited and sparse deployment of wavelength converters in the optical network. Therefore, we present a novel scheme for OBS networks, called logical cascaded private subnet (LCPN) with start wavelength assignment policy. We define the concept of canoe relative to cluster in self-similar traffic, and introduce a new device named payload segregator at the edge node as a gateway to the core node in OBS Networks. According to the changes in the edge node framework, we put forward the concept of cluster private subnet and canoe private subnet in the core node correspondingly. A new start wavelength assignment policy is proposed for the absence of (full) wavelength conversion capabilities in the core node of OBS Networks. The performance study indicates that, our new scheme is robust under self-similar traffic and wavelength continuity constraint.

A, new multicast wavelength assignment algorithm in wavelength-routed WDM networks

This paper addresses the multicast wavelength assignment (MC-WA) problem in wavelength-routed WDM networks with full light splitting and wavelength conversion capabilities. Current approaches are based on the multicast switch model that supports only split-convert (S-C) switch scheme. This scheme leads to redundant wavelength conversions for a given multicast request. In this paper, we propose a new split-convert-split (S-C-S) switch scheme capable of eliminating the redundant wavelength conversions. In order to implement this new switch scheme, we develop a new multicast switch model based on the concept of sharing of light splitters and wavelength converters. Furthermore, existing multicast wavelength assignment algorithm allows only one wavelength to carry the light signal on a fiber link, the so-called single-wavelength assignment strategy. In this paper, we explore the advantages of a new multi-wavelength assignment strategy which allows multiple available wavelengths in a link to carry the multicast signal. This will reduce the number of wavelength conversions required for the multicast request. Consequently, based on the new S-C-S multicast switch model and the new multi-wavelength assignment strategy, we generalize the existing algorithms to produce a new Multicast 'Wavelength Assignment Algorithm (MWAA) to support both the new switch model and the new wavelength assignment strategy. Compared with the existing algorithm, our new algorithm is a more general one which makes the multicast wavelength assignment more flexible, covering different switch schemes and different assignment strategies. In addition, it delivers good performance in term of minimizing the number of wavelength conversions. The improvement percentage is sensitive to the maximum out-degree value of a node, D. For a 100-node multicast tree, the improvement percentage increases from 38% at D = 3 to about 73% at D = 16. This is highly significant.

Semi-Dynamic Protection Path Configuration for Hybrid Optical Cross-Connect Networks

In this paper, a semi-dynamic protection path configuration method is proposed for WDM optical networks. In the method, the protection path is established by connecting several sub-lightpaths from the source node to the destination node of the original working lightpath, as opposed to conventional path restoration method where a single protection lightpath between the source-destination pair performs restoration. The proposed method provides enhanced flexibility in protection path configuration and relieves the cost of spare capacity reservation. This paper also studies the effects of wavelength conversion capability of intermediate optical cross-connect nodes on protection path routing and spare capacity utilization. In terms of spare capacity utilization, the proposed method shows substantial reduction of spare capacity overhead compared with dedicated path restoration in all optical networks without wavelength conversion, and shows similar capacity efficiency compared with shared path restoration in opaque networks with full wavelength conversion capability. In terms of robustness, the proposed method shows nearly the same restoration ratio for double-link failure as that of dynamic restoration method.

Models of Restoration Probability in WDM Networks Employing Active Restoration

The ever-increasing demand for network bandwidth makes network survivability an issue of great concern. Lightpath restoration is a valuable approach to guaranteeing an acceptable level of survivability in WDM optical networks with better resource utilization than that of its protection counterpart. Active restoration (AR) is a newly proposed lightpath restoration scheme [M. Mostafa et al. OSA Journal of Optical Networking, vol. 3, no. 4, pp. 247–260] that combines the best of protection and reactive restoration while avoiding their shortcomings. In this paper, we conduct detailed performance analysis on the restoration probability of AR-based WDM networks. In particular, analytical models of restoration probability are developed respectively for networks with full-wavelength conversion capability and for networks without wavelength conversion capability under different backup path searching schemes. Based on the new models, we investigate the effects of wavelength availability, wavelength conversion capability, path length as well as backup path seeking methods on the restoration probability.

On Trading Wavelengths With Fibers: A Cost-Performance Based Study

We consider the effect of multiple fibers on wavelength division multiplexing networks without wavelength conversion. We study networks with dynamic wavelength routing and develop accurate analytical models to compare various possible options using single- and multiple-fiber networks. We use results of an analytical model and simulation-based studies to evaluate the blocking performance and cost of multifiber networks. The number of fibers required providing high performance in multifiber networks and their costs are compared. A case is made for using multiple fibers in each link with fewer wavelengths instead of using a single fiber with many wavelengths. In particular, we show that a network with four fibers per link and with four wavelengths on each fiber without any wavelength conversion on any node yields similar same performance as the networks with one fiber per link and 16 wavelengths per fiber on each link and with full wavelength conversion capability on all nodes. In addition, the multifiber network may also offer the cost advantage depending on the relative cost of components. We develop a parametric cost model to show that multiple fibers in each link are an attractive option. Finally, such multifiber networks also has fault tolerance, with respect to a single fiber failure, already built into the system.

Design and Performance Analysis of a Simple OXC

Optical cross-connects are expected to be the key element in future optical transport networks. In this paper, a simple OXC architecture is proposed and its performance evaluated by means of simulations. The main advantage of the proposed design in front of previously reported structures consists in the absence of any tunable component. Obtained results show that the proposed device performance is close to that given by an OXC with full wavelength conversion capability.

Optimal wavelength converter placement in arbitrary topology wavelength-routed networks

This paper describes an algorithm for optimally placing a given number of wavelength converters in all-optical networks with arbitrary topologies. We first introduce the simple network model upon which the algorithm is based. We provide a formulation of the overall network blocking probability when a given number of nodes in the network, is provided with full wavelength conversion capability. We then present our optimal converter placement algorithm and illustrate its working using a simple example. The savings offered by our algorithm in the calculation of blocking performance are analyzed. The benefits of our optimal converter placement algorithm are studied through network examples such as the path, NSFnet and the mesh-torus. Finally, some heuristics for converter placement are presented.

A new approach to dimensioning optical networks

A network dimensioning method allocates appropriate capacities to the links based on the network topology and traffic requirements. We introduce the concept of absorption probability instead of blocking probability which is a more appropriate measure to express the grade of service of an optical network, in many cases. Absorption probability can be obtained from transient analysis of a Markov chain. Computation of exact absorption probabilities requires large computing resources and is thus feasible only for small networks. We present a method to approximate the absorption probability of a wavelength-routed network with arbitrary topology and traffic patterns assuming the nodes have full wavelength conversion capability. We show that the approximation method performs well especially in the desired range of absorption probabilities and it is computationally efficient.

Optimal Routing for Protection and Restoration in an Optical Network

In this paper we provide a centralized method for optimally selecting the set of active and backup paths in an optical transport network in the cases of shared-path restoration and 1:1 protection schemes. We provide novel mixed integer linear programming (MILP) formulations for both the schemes, for a network with full wavelength conversion capability. The given formulations are not restricted to consider single link failures: the concept of fault event is introduced to handle the possibility that multiple links go simultaneously under fault. The optimization objective includes the total capacity requirement plus an additional term related to the active paths reliability. We use a simple decomposition heuristic to support the resolution process. The optimization is solved for various sample scenarios in order to evaluate the resource saving achieved with the shared-path restoration scheme. The impact of different factors such as topology, traffic demand and structure of failures on the resource saving is analyzed. Also, we provide guidelines about handling differentiated levels of protection within the framework of the proposed formulations.

Efficient algorithms for wavelength rerouting in WDM multi-fiber unidirectional ring networks

In this article, we consider wavelength rerouting in wavelength-routed Wavelength-Division Multiplexed (WDM) multi-fiber unidirectional ring networks with circuit switching. The wavelength continuity constraint imposed by WDM networks leads to poor blocking performance. Wavelength rerouting is a viable and cost effective mechanism that can improve the blocking performance by rearranging certain existing lightpaths to accommodate a new request. Recently, in Ref. [1], a rerouting scheme called ‘Parallel Move-To-Vacant Wavelenth Retuning (MTV-WR)’ with many attractive features such as shorter disruption period and simpler switching control has been proposed. A polynomial time rerouting algorithm has also been proposed in Ref. [1] to minimize the weighted number of rerouted lightpaths in WDM networks with the parallel MTV-WR rerouting scheme. However, this algorithm is not time optimal and works correctly when the fiber links, wavelength channels, and lightpaths are all bidirectional. We present here a time-optimal rerouting algorithm to minimize the number of rerouted lightpaths in wavelength-routed WDM multi-fiber unidirectional ring networks with parallel MTV-WR rerouting scheme. This algorithm requires only O( NFW) time units, where N is the number of nodes in the network, F is the number of fiber links between two consecutive nodes, and W is the number of wavelength channels available on a fibre link. We also present on O( NF 2 W) time rerouting algorithm to minimize the weighted number of rerouted lightpaths. The simulation results show that the rerouting algorithms improve the blocking performance considerably and only very few lightpaths are required to be rerouted per rerouting. The results also show that, for a given network load per wavelength per fiber, increasing the number of wavelengths or the number of fibers, leads to an improved performance by the networks with rerouting, without any rerouting and with full wavelength conversion capability at the routing nodes.

Sparse Wavelength Conversion in Wavelength-Routed WDM Optical Networks*

A wavelength-routed optical network can suffer inefficiencies due to the wavelength-continuity constraint (under which a signal has to remain on the same wavelength from the source to the destination). In order to eliminate or reduce the effects of this constraint, a device called a wavelength converter may be utilized. Due to the high cost of these wavelength converters, many studies have attempted to determine the exact benefits of wavelength conversion. However, most of these studies have focused on optical networks that implement full wavelength conversion capabilities. An alternative to full wavelength conversion is to employ only a sparse number of wavelength converters throughout the network, thereby reducing network costs. This study will focus on different versions of sparse wavelength conversion--namely, sparse nodal conversion, sparse switch-output conversion, and sparse (or limited) range conversion--to determine if most of the benefits of full conversion can be obtained using only sparse conversion. Simulation and analytical results on these three different classes of sparse wavelength conversion will be presented. In addition, this study will present heuristic techniques for the placement of sparse conversion facilities within an optical network.

Multiwavelength optical networks with limited wavelength conversion

This paper proposes optical wavelength division multiplexed (WDM) networks with limited wavelength conversion that can efficiently support lightpaths (connections) between nodes. Each lightpath follows a route in a network and must be assigned a channel on each link along the route. The load /spl lambda//sub max/ of a set of lightpaths is the maximum over all links of the number of lightpaths that use the link. At least /spl lambda//sub max/ wavelengths will be needed to assign channels to the lightpaths. If the network has full wavelength conversion capabilities, then /spl lambda//sub max/ wavelengths are sufficient to perform the channel assignment. Ring networks with fixed wavelength conversion capability within the nodes are proposed that can support all lightpath sets with load /spl lambda//sub max/ at most W-1, where W is the number of wavelengths in each link. Ring networks with a small additional amount of wavelength conversion capability within the nodes are also proposed that allow the support of any set of lightpaths with load /spl lambda//sub max/ at most W. A star network is also proposed with fixed wavelength conversion capability at its hub node that can support all lightpath sets with load /spl lambda//sub max/ at most W. These results are extended to tree networks and networks with arbitrary topologies. This provides evidence that significant improvements in traffic-carrying capacity can be obtained in WDM networks by providing very limited wavelength conversion capability within the network.