Limited Wavelength Conversion Research Articles

Simulation of Coherent Electromagnetic Waves in Wavelength Division Multiplexing (WDM) Transmission

This study analyzes the application of Wavelength Division Multiplexing (WDM) in fiber optic networks which aims to find the wavelength, WDM optical spectrum and modes, as well as the CPR estimated phase and modes. In this study WDM allows the simultaneous transmission of different data streams through a single optical fiber, using different wavelengths. This research was conducted using the python OptiCommPy module. This module is used to perform modeling of complex optical fiber transmission systems by considering the various parameters and disturbances involved in optical transmission. The results obtained from this study are that WDM networks can use full or limited wavelength conversion, depending on the wavelength conversion capability of each network node. Whereas multifiber networks use fiber pools between network nodes, and multifiber WDM networks can be implemented without or with full wavelength conversion. This research can be a guide for designing coherent electromagnetic waves in WDM transmissions using the OptiCommPy python module.

Joint Hybrid Wavelength Conversion and Fiber Delay Line for All-Optical Core Node Modeling and Optimization Using Dynamic QoS Support

All-optical networks (AON) assured a large bandwidth, high-speed switching, and QoS (Quality of Service) support. But due to the development of applications and services, new requirements are created in terms of, specifically resource utilization and QoS provision. To meet these demands, AON enabled core node architecture with multiple wavelength converters’ types involving full range wavelength converter (FRWC) having a significant cost. To reduce the cost, a hybrid AON with composite node architecture combining wavelength converters (WC), Fiber delay line (FDL), and wavelength range (WR) are introduced. In this architecture, fixed and limited wavelength converters (FXWC, LRWC) are utilized while the FRWC converter is replaced by FDL. The proposed architecture decreased the presence and usage of WC, FDL, and WR while assuring QoS support. A lightpath cost formulation is computed based on WR, WC, and FDL enabled in the proposed node architecture to decrease converter and FDL numbers. The cost also managed the wavelength availability to ensure lightpath control and QoS support using real-time requirements, especially loss and blocking delay. The obtained results in the comparative study, conducted in the simulation work, showed that the novel approach performed better than the existing approaches. Moreover, our proposal optimized AON resources, particularly node architecture design, while providing QoS support according to the traffic parameters and requirements.

Fast Service Recovery Under Shared Protection in WDM Networks

In this paper, we investigate the problem of survivable routing of static demands in connection-oriented WDM networks with shared protection. We first discuss conditions and characteristics of a typical backup path sharing approach with respect to the average length of backup paths, and the values of connection restoration time. Next we propose a new method of sharing the backup paths, called SPGC, which is the first one that does not increase the length of backup paths (thus providing fast restoration of broken connections). The respective ILP model has been introduced. Owing to the complexity of the SPGC problem, an efficient heuristic algorithm designed for the general case of limited wavelength conversion capability has been also proposed. Extensive numerical experiments have shown that the proposed backup path sharing approach provides values of service recovery time which are up to 50% shorter on average, compared to the typical sharing technique. These results were achieved together with a significant reduction of the total link capacity utilization ratio of up to 40%.

A wavelength assignment algorithm for de Bruijn WDM networks

This paper proposes an offline wavelength assignment technique for de Bruijn (d, k) optical wavelength division multiplexing (WDM) networks having nodal degree d and diameter k that can support lightpaths between pair of nodes. Each lightpath uses a channel (wavelength) along each link in its route. An efficient algorithm is proposed that can be used to assign wavelengths to lightpath requests in O(k|V|) time, where |V| represents the number of nodes of the de Bruijn network and V represents the set of nodes. The proposed algorithm can be efficiently used for wavelength assignment in de Bruijn WDM networks having limited wavelength conversion capabilities. This work shows that de Bruijn graph can be expressed as union of edge-disjoint rings. Wavelengths are assigned for the individual rings in the graph thus resulting in the assignment for the graph itself. Results are shown for a given de Bruijn graph and for an arbitrary request. The proposed algorithm is compared with two other algorithms, which use two other known works of wavelength assignment on ring topology. Comparisons of the time complexity and the type of wavelength conversion required for these algorithms clearly show that the proposed algorithm is a faster and more efficient way of assigning wavelengths.

Optimal Packet Scheduling in WDM Optical Switches With Output Buffer and Limited Wavelength Conversion

All-optical packet switching is a promising candidate for future high-speed switching. However, due to the absence of optical random access memory, the traditional Virtual Output Queue (VOQ) based input-queued switches are difficult to implement in the optical domain. In this paper we consider output-buffered optical packet switches. We focus on packet scheduling in an output-buffered optical packet switch with limited-range wavelength conversion, aiming at maximizing throughput and minimizing average queuing delay simultaneously. We show that this problem can be converted to a minimum cost maximum network flow problem. To cope with the high complexity of general network flow algorithms, we present an algorithm that can efficiently find an optimal schedule in O(min{NW,BW}) time, where <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> is the switch size, W is the number of wavelength channels per fiber and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> is the length of the longest FDL at the output of the switch. The complexity of the new algorithm asymptotically matches the lower bound of the scheduling problem. We also conduct extensive simulations to test the performance of the proposed scheduling algorithm under different traffic models.

Performance analysis of optical burst switching node with limited wavelength conversion capabilities

The systematical and scalable frameworks were provided for estimating the blocking probabilities under asynchronous traffic in optical burst switching (OBS) nodes with limited wavelength conversion capability (LWCC). The relevant system architectures of limited range and limited number of wavelength converters (WCs) deployed by a share-per-fiber (SPF) mode were developed, and the novel theoretical analysis of node blocking probability was derived by combining the calculation of discouraged arrival rate in a birth-death process and two-dimensional Markov chain model of SPF. The simulation results on single node performance verify the accuracy and effectiveness of the analysis models. Under most scenarios, it is difficult to distinguish the plots generated by the analysis and simulation. As the conversion degree increases, the accuracy of the analysis model worsens slightly. However, the utmost error on burst loss probability is far less than one order of magnitude and hence, still allows for an accurate estimate. Some results are of actual significance to the construction of next-generation commercial OBS backbones.

Wavelength conversion in multihop wavelength division multiplexed transport networks

In this paper, we have analyzed the wavelength conversion for a multihop wavelength division multiplexed (WDM) transport networks to minimize the blocking probability. The analytical model is presented for a static-routing for a multihop paths wavelength conversion. The results have been validated for three cases, without wavelength conversion, with wavelength conversion and limited wavelength conversion. We show that by using wavelength conversion, there is significant improvement in performance of these transport networks. Each of the three cases of wavelength conversion is discussed for different degrees of conversions. It is observed that the higher the degree of conversion is, the lower is the blocking probability. Also as the degree of conversion is increased further, the curve for limited range conversion moves towards the no conversion.

Fixed point analysis of limited range share per node wavelength conversion in asynchronous optical packet switching systems

In this article, we study an asynchronous optical packet switch equipped with a number of wavelength converters shared per node. The wavelength converters can be full range or circular-type limited range. We use the algorithmic methods devised for Markov chains of block-tridiagonal type in addition to fixed-point iterations to approximately solve this relatively complex system. In our approach, we also take into account the finite number of fiber interfaces using the Engset traffic model rather than the usual Poisson traffic modeling. The proposed analytical method provides an accurate approximation for full range systems for relatively large number of interfaces and for circular-type limited range wavelength conversion systems for which the tuning range is relatively narrow.

Reservation signalling mechanism for reducing blocking probability in optical burst switching networks with limited wavelength conversion capabilities

First, the optical burst switching (OBS) network with limited wavelength conversion capability (LWCC) is decomposed into multiple wavelength continuous segments according to the position of wavelength converters. Based on the decomposed network model, two reservation signalling mechanisms for OBS-LWCC networks, namely wavelength-amend-on-demand (WAoD) and contention-based limited signalling protocol (CLSP), are proposed to reduce the blocking probability in the OBS-LWCC networks. In WAoD, the congested node sends a feedback message to the closest upstream switch with wavelength conversion capability. The notified switch will change the burst wavelength to the one assigned by the congested node to avoid collision in advance. Extensive simulation results indicate that by applying the wavelength reconfiguration method to the core nodes without wavelength conversion capability, the proposed WAoD scheme can improve the blocking performance in the OBS-LWCC networks significantly. Furthermore, CLSP, which combines the burst time-slot reconfiguration with the wavelength reconfiguration of WAoD, always has the lowest burst loss probability when compared with both the conventional and the proposed reservation mechanisms.

Restoration in all-optical GMPLS networks with limited wavelength conversion

A new generation of optical components and the advance of the Generalized Multi-Protocol Label Switching (GMPLS) control plane supporting dynamic provisioning and restoration of optical connections (i.e., lightpaths), brings the vision of the dynamic all-optical network closer to reality. An emerging technology is the conversion between wavelengths, which removes the wavelength continuity constraint, thus allowing an easier and more flexible connection allocation. A limitation in the number of wavelength converters impairs their benefits especially during the restoration phase, when many simultaneous recovery attempts must share residual resources. This paper investigates the restoration performance of GMPLS-controlled all-optical networks with limited wavelength converter deployment. We investigate how different restoration methods, namely span restoration, segment restoration, and end-to-end restoration are affected by the availability of a limited number of wavelength converters at each node. For this purpose an enhanced wavelength assignment scheme compliant with GMPLS signaling is exploited, aiming at saving converters by assigning a higher preference to wavelengths not requiring conversion. An extensive simulation study has been conducted comparing the performance of this scheme to the most advanced scheme based on standard GMPLS signaling for the three restoration methods. Simulation results show that the enhanced wavelength assignment scheme significantly reduces the number of wavelength converters (WCs) necessary to achieve good recovery performance. The enhanced scheme especially improves span restoration performance, where the matching between the stubs' and recovery segment wavelength may require a WC. End-to-end restoration is the least affected, due to a higher degree of freedom in the route choice, while segment restoration performance lies in between.

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.

Multi-wavelength multicast wavelength assignment algorithm for limited wavelength conversion in wavelength-division multiplexing networks

The multicast wavelength assignment problem in wavelength-routed wavelength- division multiplexing networks with limited wavelength conversions is addressed. A new multi- wavelength multicast wavelength assignment (MMWA) algorithm has been developed based on the multi-wavelength assignment strategy, by allowing multiple available wavelengths in a link to carry the multicast signal. This new multicast wavelength algorithm provides advantages for the network with limited wavelength conversions, by accommodating more multicast requests and providing good trade-off between wavelength cost and wavelength conversion cost. Simulation results show that the MMWA algorithm can satisfy more multicast requests in comparison with the previous single-wavelength assignment strategy. The improvement can be as high as 50-80%. This is highly significant. The MMWA algorithm also provides a good cost trade-off by making significant reduction of wavelength conversion cost (over 50%) while keeping the additional wavelength usage within a reasonable range (around 15%).

A Node-level Blocking Probability Analysis for WRON

This work presents the blocking performance of the individual node with (full or limited) wavelength conversion in wavelength routed optical networks (WRON) based on the theory of probability. And a blocking probability model is proposed. Particularly, we pay more attention to investigate wavelength routing node performance improvement by using more feasible limited wavelength conversion. Based on our analytical model, we calculate the blocking probability for individual wavelength routing node and then make a simulation to validate it. It is seen that the node with low conversion degrees has small number of fiber link ports and large number of wavelength per link is more realistic choice.

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.

Multicasting for all-optical multifiber networks

All-optical wavelength-routed WDM WANs can support the high bandwidth and the long session duration requirements of the application scenarios such as interactive distance learning or on-line diagnosis of patients simultaneously in different hospitals. However, multifiber and limited sparse light splitting and wavelength conversion capabilities of switches result in a difficult optimization problem. We attack this problem using a layered graph model. The problem is defined as a k-edge-disjoint degree-constrained Steiner tree problem for routing and fiber and wavelength assignment of k multicasts. A mixed integer linear programming formulation for the problem is given, and a solution using CPLEX is provided. However, the complexity of the problem grows quickly with respect to the number of edges in the layered graph, which depends on the number of nodes, fibers, wavelengths, and multicast sessions. Hence, we propose two heuristics layered all-optical multicast algorithm [(LAMA) and conservative fiber and wavelength assignment (C-FWA)] to compare with CPLEX, existing work, and unicasting. Extensive computational experiments show that LAMA's performance is very close to CPLEX, and it is significantly better than existing work and C-FWA for nearly all metrics, since LAMA jointly optimizes routing and fiber-wavelength assignment phases compared with the other candidates, which attack the problem by decomposing two phases. Experiments also show that important metrics (e.g., session and group blocking probability, transmitter wavelength, and fiber conversion resources) are adversely affected by the separation of two phases. Finally, the fiber-wavelength assignment strategy of C-FWA (Ex-Fit) uses wavelength and fiber conversion resources more effectively than the First Fit.

Analysis of OBS Networks With Limited Wavelength Conversion

Presented herein is a scalable framework for estimating path blocking probabilities in optical burst switched (OBS) networks where limited wavelength conversion is possible. Although presented under the guise of OBS, it is pertinent to a broader class of optical networks based on the principle of bufferless unacknowledged switching. By applying the framework to the NSFNET topology, it is shown that even the most limited conversion range may reduce path blocking probabilities by several orders of magnitude, compared with no wavelength conversion. Moreover, contrary to previous results derived for all-optical non-OBS networks with acknowledgement, OBS with full wavelength conversion achieves significantly lower blocking probabilities than OBS with limited wavelength conversion when the conversion range is small. Underpinning the framework is a generalization of the classical reduced load approximation. Assuming links evolve independently of each other allows decoupling of the network into its constituent links. A set of fixed-point equations describing the evolution of each conversion range are then solved by successive substitution to estimate link blocking probabilities. Having these link blocking probabilities, path blocking probabilities are evaluated. The complexity of the framework is dominated by the wavelength conversion range and is independent of the number of wavelengths per link under certain symmetry conditions. Both just-in-time (JIT) and just-enough-time (JET) scheduling are considered. Simulations are implemented to corroborate the accuracy of the framework

OBS contention resolution performance

In this paper, a performance comparison of resolution policies specific to optical burst switching is presented. A framework, based on a reduced-load approximation, is developed to estimate path blocking probabilities in an optical burst switched network of arbitrary topology, in which any combination of the following resolution policies is applied in a specific order: limited wavelength conversion, burst deflection and burst segmentation. Our framework is used to compare the relative performance of each resolution policy for two sets of ingress and egress router pairs defined on the NSF network. With respect to the assumptions considered, it is shown that limited wavelength conversion is more effective in reducing blocking relative to burst deflection if the maximum wavelength conversion radius is sufficiently large, otherwise burst deflection is more effective. Furthermore, limited wavelength conversion or burst deflection are more effective in reducing blocking relative to burst segmentation. Burst segmentation is justified as a stand alone resolution policy; however, using burst segmentation to complement another resolution policy offers only a marginal reduction in blocking. Both just-in-time and just-enough-time scheduling is analyzed. Simulations are implemented to corroborate the accuracy of our framework and extensions.

Blocking probability of asynchronous optical burst/packet switches with limited range wavelength conversion

A theoretical analysis of the performance of asynchronous bufferless optical burst/packet switch with limited range wavelength conversion is proposed. We analyze the problem using a queuing model of birth-death process with discouraged arrivals. To calculate the discouraged arrival rate, a theorem about the average number of circular runs is introduced and proved. The effectiveness and advantage of the method is verified by simulation and comparison

WDM optical interconnects with recirculating buffering and limited range wavelength conversion

All-optical communication, in particular, wavelength-division-multiplexing (WDM) technique, has been proposed as a promising candidate to meet the ever-increasing demands on bandwidth from emerging bandwidth-intensive computing/networking applications. However, with current technology, the cost of optical communication, especially the cost of optical buffering and wavelength conversion, remains a major concern for such applications. In this paper, we study WDM optical interconnects that utilize low cost recirculating buffering and limited range wavelength conversion. We first consider the packet scheduling problem in this type of interconnect, and formalize the problem of maximizing throughput and minimizing packet delay as a matching problem in a bipartite graph. We give an optimal parallel algorithm for this problem that runs in O(Bk/sup 2/) time, compared to O((N+B)/sup 3/k/sup 3/) time if directly applied to existing matching algorithms for general bipartite graphs, where N is the number of input/output fibers of the interconnect, B is the number of fiber delay lines, and k is the number of wavelengths. We also consider efficient switching fabric designs for this type of interconnect. We distinguish between the switching fabric connecting the input fibers to the output fibers and the switching fabric connecting the input fibers to the delay lines and show that by adopting the idea of concentration, the cost of the latter can be reduced significantly in terms of the number of crosspoints.

Ant Colony Optimization for Dynamic RWA in WDM Networks with Partial Wavelength Conversion

Dynamic routing and wavelength assignment (RWA), which supports request arrivals and lightpath terminations at random times, is needed for rapidly changing traffic demands in wavelength division multiplexed, (WDM) networks. In this paper, a new distributed heuristic algorithm based on ant colony optimization for dynamic RWA is put forward. We consider the combination of route selection and wavelength assignment as a whole using a multilayer-graph model. Therefore, an extended multilayer-graph model for WDM networks with limited wavelength conversion is presented. Compared with other RWA methods, the Ant Colony heuristic algorithm can achieve better global network optimization and can reduce communication overhead cost of the networks. Simulation showed that a lower blocking probability and a more rational wavelength resource assignment can be achieved.