Wavelength Conversion In Networks Research Articles

Performance Analysis of WSS-Based ROADM With Shared-Per-Group Tunable Wavelength Converters

We propose a flexible shared-per-group (SPG) architecture for wavelength selective switch (WSS)-based reconfigurable optical add/drop multiplexers (ROADMs) to support dynamic datacenter wavelength-convertible networks. The key components of this module are grouping installed tunable wavelength converter (TWCs) and tunable filter (TFs). Using the SPG architecture, the demands that collide among different outputs will be all-optically resolved by a combination of TWCs and TFs without installing any switch matrix devices. Thus, the proposed SPG architecture may produce better blocking performance than the conventional shared-per-link, shared-per-wavelength architectures consuming lower costs. Meanwhile, analytical model is proposed to evaluate the SPG blocking probability by means of the self-constrained iteration method. Accurate results showed that SPG architecture requires the number of groups larger than the number of ports to produce the optimal blocking performance, saving 50% of TWCs under high and moderate traffic loads.

Blocking RWA Model Analysis in Irregular OTN Topology

Wavelength converters (WC) that configured on the nodes can make the same wavelength optical channel from the continuity constraints, if it is configured suitable, it will effectively reduce the network congestion ratio. In this paper, we investigate the sub graph algorithm with blocking RWA model for the large capacity optical transport. Because the price is more expensive WC, it can not be deployed in all nodes considering the increasing costs and maintenance complexity. We investigated is the WC configuration during network construction, with only part of the network node configuration. The studies show that the rational allocation of part of the WC can get nearly the same performance as the full wavelength conversion network.

Performance analysis of topologies for optical wavelength convertible networks

An architecture of wavelength converters shared per-node wavelength cross-connects is proposed to function the optical node in simulation. And first-fit wavelength allocation algorithm and Dijkstra shortest path routing algorithm are used. It is shown that star topology performs the best on blocking probability, average hop count and average packet delay, but it is unfavorable on link utilization. Furthermore, wavelength conversion is not ideal for the star topology. However, the ring topology network is the cost-optimal one if the appropriate wavelength conversion capability in network is to be considered.

Stable Logical Topologies for Survivable Traffic Grooming of Scheduled Demands

There has been considerable research interest in the area of traffic grooming for WDM mesh networks. The vast majority of the current work can be classified into one of two categories, either static grooming or dynamic grooming. In many situations, the individual traffic demands require bandwidth at certain predefined intervals, and resources allocated to nonoverlapping demands can be reused in time. In this paper, we propose a new traffic grooming technique that exploits knowledge of the connection holding times of traffic demands to lead to more efficient resource utilization. We consider wavelength-convertible networks as well as networks without any wavelength conversion capability and implement survivability using dedicated and shared path protection. Although individual demands may be short lived, it is desirable to have a logical topology that is relatively stable and not subject to frequent changes. Therefore, our objective is to design a stable logical topology that can accommodate a collection of low-speed traffic demands with specified setup and teardown times. Our approach results in lower equipment cost and significantly reduced overhead for connection setup/teardown. We present efficient integer linear program (ILP) formulations that address the complete traffic grooming problem, including logical topology design, routing and wavelength assignment, and routing of traffic demands over the selected topology. The primary focus of our ILP formulations is to minimize the resource requirements. However, it is possible to modify our formulations to maximize the throughput, if necessary.

Blocking in wavelength-routed all-optical WDM network with wavelength conversion

The blocking probability in wavelength-routed all optical networks is very important measure of performance of the network, which can be affected by many factors such as network topology, traffic load, number of links, algorithms employed and whether wavelength conversion is available or not. In this paper, we have proposed a mathematical model to reduce the blocking probability of the WDM optical network for wavelength-convertible networks. The model can be used to evaluate the blocking performance of any network topology also it can be useful to improve its blocking performance of the given network topology. The blocking probability variation of the network for a particular load (per link) has been studied based on the load variation and total number of wavelengths used in the network. This model gives good results for high load (per link).

Blocking in wavelength-routed all-optical WDM network with or without wavelength conversion

The blocking probability in wavelength-routed all-optical networks is a very important measure of performance of the network. This blocking probability can be affected by many factors such as network topology, traffic load, number of links, algorithms employed and whether wavelength conversion is available or not. In this paper we have proposed a mathematical model to reduce the blocking probability of the WDM optical network for both wavelength convertible networks as well as for wavelength non-convertible networks. The model is can be used to evaluate the blocking performance of any network topology also it can be useful to improve its performance of the given network topology.

Traffic Engineering in the Wavelength Domain for Optical Burst-Switched Networks

This paper addresses the possibility of using traffic engineering in the wavelength domain as a way to improve the performance of optical burst-switched (OBS) networks. With that aim, we detail a heuristic traffic engineering strategy that determines the order by which the ingress nodes of the network should search for an available wavelength for burst transmission, in order to minimize the probability that data bursts going through overlapping paths reach a common fiber link using the same wavelength. By means of network simulation, it is shown that the proposed traffic engineering strategy outperforms the existing strategies in reducing burst loss in OBS networks. This trend holds for core nodes with different degrees of wavelength conversion, ranging from the absence of wavelength converters to the use of dedicated full-range wavelength converters. More specifically, it is shown that using only traffic engineering in the wavelength domain can dramatically reduce burst loss in networks without wavelength conversion or alternatively it can reduce the number of wavelength converters in networks based on shared wavelength conversion. The simulation results also show that by combining traffic engineering in the wavelength domain with the use of the inexpensive electronic buffers at the ingress nodes, the performance of OBS networks with dedicated full-range wavelength converters can be further improved at the expense of a slight increase in the burst transfer delay.

Dynamic Versus Static Wavelength-Routed Optical Networks

It is widely believed that dynamic operation of wavelength-routed optical networks will help overcome the inefficiencies of static allocation in terms of wavelength utilization. In this paper, this hypothesis is reviewed. The wavelength requirements of dynamic wavelength-routed optical networks are quantified and compared to static routing. To do so, new analytical and algorithmic lower bounds for the wavelength requirements of dynamic networks are proposed. They are used to evaluate the optimality of the already proposed algorithms whose wavelength requirements are quantified - by means of simulation- with and without the wavelength continuity constraint, as well as for uniform and nonuniform traffic demand. Results show that, without wavelength conversion capability, the benefit of dynamic wavelength-routed optical networks is not significant: lower wavelengths requirements than static networks are achieved only at low traffic loads (< 0.3 - 0.4). In wavelength convertible networks instead, dynamic operation leads to lower wavelength requirements than static operation over a wide traffic load range (< 0.7 - 0.8), making dynamic operation attractive in this type of network. Under nonuniform traffic it was found that dynamic operation achieves slightly higher wavelength savings than in the uniform traffic case. But the savings were not high enough as to impact on results of the uniform traffic case. These results can aid network operators in the design and optimization of optical WDM networks.

Re-Routing at Critical Nodes to Enhance Performance of Wavelength Reassignment in All-Optical WDM Networks Without Wavelength Conversion

Reassignment of calls to different wavelengths on blocking can be used in WDM networks without wavelength conversion to get almost the same performance as that of WDM networks with wavelength conversion for circuit switched traffic . However, in a few networks, we did find that while the reassignment on blocking does improve the performance of WDM networks without wavelength conversion, the performance falls short of that of wavelength conversion networks. In this paper, we analyze the reasons for this behavior in these networks. On identifying certain critical nodes as a cause of this behavior, we propose a rerouting technique around the critical node. With a small amount of rerouting, this bottleneck can be removed and the performance of WDM networks without wavelength conversion becomes almost equal to that of networks with wavelength conversion, thus making the wavelength conversion (costly) feature, as redundant. In this paper, we also propose a technique to carry out seamless wavelength reassignment so as not to disrupt traffic during the wavelength reassignment process.

A novel online wavelength assignment algorithm in wavelength-convertible multi-granular optical networks

As industrial technology gets more mature, a single fiber can offer more and more wavelengths. However, it also results in a large amount of switching ports at optical cross-connects (OXCs). Certainly, it is expected that higher and higher complexity is inevitable to control and manage such large OXCs. In this paper, we study the dynamic wavelength assignment problem in waveband switching (WBS) networks composed of multi-granular OXCs (MG-OXCs). Moreover, in order to relax the wavelength continuity constraint on lightpath establishments, each MG-OXC node is equipped with a certain number of converters. To efficiently minimize the extra port consumption and utilize wavelength converters, we proposed an online wavelength assignment algorithm named Least Weighted Configuration Cost (LWCC). For a new request, LWCC first adopts fixed routing and then exploits the layered-graph approach and a new cost function for edge weight assignment to determine adequate wavelength(s). The performance metrics of interest include both blocking performance and converter utilization. Numerical results show that LWCC is superior in waveband grouping and therefore results in significant performance gain in terms of blocking probability.

Resource provisioning for survivable WDM networks under a sliding scheduled traffic model

Resource allocation in WDM networks, under both the static and dynamic traffic models have been widely investigated. However, in recent years there has been a growing number of applications with periodic bandwidth demands. Resources for such applications can be scheduled in advance, leading to a more efficient utilization of available network capacity. The setup and teardown times of the scheduled demands may be fixed, or may be allowed to slide within a larger window. A number of optimal integer linear program (ILP) solutions for the first problem (fixed setup/teardown times) have been presented in the literature. In this paper we present two new ILP formulations for the more general sliding scheduled traffic model, where the setup and teardown times may vary within a specified range. We first consider wavelength convertible networks and then extend our model to networks without wavelength conversion. Our ILP formulations jointly optimize the problem of scheduling the demands (in time) and allocating resources for the scheduled lightpaths. The fixed window model can be treated as a special case of our formulations. Our formulations are able to generate optimal solutions for practical sized networks. For larger networks, we have proposed a fast two-step optimization process. The first step schedules the demands optimally in time, so that the amount of overlap is minimized. The second step uses a connection holding time aware heuristic to perform routing and wavelength assignment for the scheduled demands.

Reduction of Blocking Probability in Restricted Shared Protected Optical Network using Alternate Path Routing and Wavelength Converter Placement

In this paper, we have proposed a restricted shared protection scheme in wavelength convertible optical network. In our proposed approach, we have included both alternate path routing and partial placement of wavelength converter for reduction of blocking probability. With computer simulation, we have evaluated the performance of our proposed approach, by comparing it with the existing shared protection.

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.

Performance analysis of multi-fiber WDM network with limited-range wavelength conversion

Wavelength routed optical networks have emerged as a technology that can effectively utilize the enormous bandwidth of the optical fiber. Wavelength conversion technology and wavelength converters play an important role in enhancing fiber utilization and in reducing the overall call blocking probability of the network. In this paper, we develop a new analytical model to calculate the average blocking probability in multi-fiber link networks using limited range wavelength conversion. Based on the results obtained, we conclude that the proposed analytical model is simple and yet can effectively analyze the impact of wavelength conversion ranges and number of fibers on network performance. Also a new heuristic approach for placement of wavelength converters to reduce blocking probabilities is explored. Finally, we analyze network performance with the proposed scheme. It can be observed from numerical simulations that limited range converters placed at a few nodes can provide almost the same blocking probability as full range wavelength converters placed at all the nodes. We also show that being equipped with a multi-fiber per-link has the same effect as being equipped with the capability of limited range wavelength conversion. So a multi-fiber per-link network using limited range wavelength conversion has similar blocking performance as a full wavelength convertible network. Since a multi-fiber network using limited range wavelength conversion could use fewer converters than a single-fiber network using limited range wavelength conversion and because wavelength converters are today more expensive than fiber equipment, a multi-fiber network in condition with limited range wavelength conversion is less costly than a single fiber network using only limited range wavelength conversion. Thus, multi-fiber per-link network using limited range wavelength conversion is currently a more practical method for all optical WDM networks. Simulation studies carried out on a 14-node NSFNET, a 10-node CERNET (China Education and Research Network), and a 9-node regular mesh network validate the analysis.

Framework for waveband switching in multigranular optical networks: part II--wavelength/waveband conversion and survivability [Invited

&lt;p&gt;&lt;a href="http://www.osa-jon.org/virtual_issue.cfm?vid=22"&gt;Feature Issue on Waveband Switching, Routing, and Grooming&lt;/a&gt;&lt;/p&gt;We consider multigranular optical networks using waveband switching (WBS) technology. The use of advanced WDM has significantly increased the available bandwidth in backbone networks by increasing the number of wavelengths. As the number of wavelengths in a fiber is increased, the number of ports or the size of the optical cross connects increases rapidly. Using WBS, wavelengths are grouped into bands and switched as a single entity thus reducing the cost and control complexity of switching nodes by minimizing the port count. Part I of our study [J. Opt. Netw.5, 1043-1055 (2006)] compared the various cross-connect architectures for WBS including the three-layer and single-layer multigranular cross connects. It also discussed various issues relating to waveband switching networks that are different from traditional wavelength routing networks (WRNs), for example, traffic grooming, and it showed why techniques developed for WRNs cannot be simply applied to WBS networks. We study the effect of wavelength and waveband conversion on the performance of WBS networks with reconfigurable multigranular optical cross connects. We present an algorithm for waveband grouping in wavelength convertible networks and evaluate its performance with full, limited, and intraband wavelength conversion. We then focus on survivability in WBS networks and show how waveband and wavelength conversion can be used effectively to recover from failures in WBS networks.

Wavelength assignment with sparse wavelength conversion for optical multicast in WDM networks

This paper addresses the problem of multicast wavelength assignment for sparse wavelength conversion (MWA-SWC) in wavelength-routed wavelength-division-multiplexing (WDM) networks. It aims to optimally allocate the available wavelength for each link of the multicast tree, given a sparse wavelength conversion network and a multicast request. To our knowledge, little research work has been done to address this problem in literature.In this paper, we propose a new technique called MWA-SWC algorithm to solve the problem. The algorithm first maps the multicast tree from the sparse conversion case to the full conversion case by making use of a novel virtual link method to carry out the tree mapping. The method provides a forward mapping to generate an auxiliary tree as well as a reverse mapping to recover the original tree. Applying the auxiliary tree, we propose a dynamic programing algorithm for the wavelength assignment (WA) aiming to minimize the number of wavelength converters (NWC) required. Simulation results show that our new algorithm outperforms both random and greedy algorithms with regard to minimizing the NWC. Testing on various scenarios by varying the number of wavelength conversion nodes in the tree has confirmed the consistency of the performance. The primary use of the MWA-SWC algorithm is for static traffic. However, it can also serve as a baseline for dynamic heuristic algorithms. Typically, the MWA-SWC algorithm will provide great benefit when the number of available wavelengths on each link of the multicast tree is relatively large and the performance advantage is significant.

Framework for waveband switching in multigranular optical networks: part I-multigranular cross-connect architectures [Invited

Feature Issue on Waveband Switching, Routing, and GroomingOptical networks using wavelength-division multiplexing (WDM) are the foremost solution to the ever-increasing traffic in the Internet backbone. Rapid advances in WDM technology will enable each fiber to carry hundreds or even a thousand wavelengths (using dense-WDM, or DWDM, and ultra-DWDM) of traffic. This, coupled with worldwide fiber deployment, will bring about a tremendous increase in the size of the optical cross-connects, i.e., the number of ports of the wavelength switching elements. Waveband switching (WBS), wherein wavelengths are grouped into bands and switched as a single entity, can reduce the cost and control complexity of switching nodes by minimizing the port count. This paper presents a detailed study on recent advances and open research issues in WBS networks. In this study, we investigate in detail the architecture for various WBS cross-connects and compare them in terms of the number of ports and complexity and also in terms of how flexible they are in adjusting to dynamic traffic. We outline various techniques for grouping wavelengths into bands for the purpose of WBS and show how traditional wavelength routing is different from waveband routing and why techniques developed for wavelength-routed networks (WRNs) cannot be simply applied to WBS networks. We also outline how traffic grooming of subwavelength traffic can be done in WBS networks. In part II of this study [Cao , submitted to J. Opt. Netw.], we study the effect of wavelength conversion on the performance of WBS networks with reconfigurable MG-OXCs. We present an algorithm for waveband grouping in wavelength-convertible networks and evaluate its performance. We also investigate issues related to survivability in WBS networks and show how waveband and wavelength conversion can be used to recover from failures in WBS networks.

An Inter-domain Routing and Signaling Scheme for Optical Mesh Networks

An inter-domain routing and signaling scheme based on the OBGP protocol for WDM networks with a mesh topology is proposed in the paper. For mesh networks with wavelength conversion, inter-domain routing and signaling are realized by introducing a new message based on an optimal path identifier (OPI) and by establishing the corresponding message-exchange procedures. Considering the wavelength continuity constraint, a strategy called improved destination wavelength assignment (IDWA) combined with the OPI-based message is presented to establish a lightpath dynamically. The scheme is verified on the NSFNET and the CERNET by simulation. Results show that the blocking performance of a non-wavelength-conversion network is even a little lower than that of a wavelength-conversion network.

Analytical model of sparse-partial wavelength conversion in wavelength-routed WDM networks

Wavelength conversion is one of the key techniques to improve the blocking performance in wavelength-routed WDM networks. Given that wavelength converters nowadays remain very expensive, how to make effective use of wavelength converters becomes an important issue. In this letter, we analyze the sparse-partial wavelength conversion network architecture and demonstrate that it can significantly save the number of wavelength converters, yet achieving excellent blocking performance. Theoretical and simulation results indicate that, the performance of a wavelength-routed WDM network with only 1-5% off wavelength conversion capability is very close to that with full-complete wavelength conversion capability.

New strategy for optimizing wavelength converter placement

This paper proposes a new strategic alternate-path routing to be combined with the particle swarm optimization (PSO) algorithm to better solve the wavelength converters placement problem. The strategic search heuristic is designed to provide network connectivity topologies for the converters to be placed more effectively. The new strategy is applied to the 14-node NSFNET to examine its efficiency in reducing the blocking probability in sparse wavelength conversion network. Computed results show that, when applied to the identical optimization framework, our search method outperforms both the equal-cost multipath routing and traffic-engineering-aware shortest-path routing.