Wavelength Division Multiplexing Optical Networks Research Articles

Opportunistic Optical Hyperchannel and Its Distributed QoS Assuring Access Control

Light-trail is proposed as a candidate to carry IP traffic over wavelength-division multiplexing optical networks given its capability of enabling high-speed provisioning and accommodating multigranularity traffic. In a light-trail, the optical shutters at the start node and the end node are configured to be in OFF state and the optical shutters at the intermediate nodes are configured to be in ON state. Thus, an optical bus is formed, allowing traffic multiplexing without the state change of any optical shutter. This, however, limits the system throughput and also makes it impossible to implement a fully distributed medium access control (MAC) protocol to assure quality of service (QoS) in a light-trail. With the recent development on ultrafast optical shutter, we propose an improved light-trail architecture, called opportunistic hyperchannel in this paper. In an opportunistic hyperchannel, an intermediate node can dynamically control its optical shutter which makes it possible to design a fully distributed QoS assuring MAC protocol. We then present a QoS assuring distributed dynamic scheduling protocol, namely, minimum source round robin (minSrcRR) protocol, for opportunistic hyperchannels. Theoretical analysis on the effectiveness of the proposed QoS assuring protocol and the worst-case delay bound are also derived in this paper. The simulation results quantitatively demonstrate the advantage of opportunistic hyperchannels and the effectiveness of minSrcRR protocol.

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.

Designs of high-performance multicast scheduling mechanisms in WDM networks

In this article, we propose three multicast scheduling mechanisms, lookback queue access, lookback ratio access, and double check head access, for the employment in the single-star Wavelength Division Multiplexing optical network. Each of the proposed scheduling schemes consists of two phases and is executed in real time. In general, the first phase is to search for a candidate multicast packet that can be sent, without partition, to all of its intended recipients. If phase 1 fails, the second phase is then activated to partition a multicast packet into multiple transmissions in accordance with specific criteria of each individual mechanism. These algorithms are designed to mitigate the head-of-line blocking effect, while at the same time achieving excellent network throughput levels and delay performance via the partitioning procedure. Performance results reveal the distinct features of each mechanism under various scenarios. For a wider range of networking environments, we further propose an interconnected dual-star structure and enhanced multicast scheduling algorithms. These enhanced schemes aim to exploit the inter-data channels efficiently and utilize the wavelength reuse property of the intra-data channels properly. Performance results have demonstrated the merits of deploying the proposed multicast algorithms in such a dual-star structure.

A novel multicast routing algorithm in sparse splitting WDM network with power attenuation constraint

With the increasing requirement for communication bandwidth, all-optical network has been more and more important owning to its large traffic capability. Multicasting is an important technology in wavelength division multiplexing (WDM) optical network, and has been studied in many works. In this paper, we consider the multicasting technology on all-optical metropolitan area network (MAN) with maximum power attenuation constraint. The objective is to minimize total cost of a multicasting request. This problem is NP-hard. We propose a heuristic, named Power-Constraint Fix-Destination-Path (PC-FDP) algorithm, to solve this maximal power-loss constrained minimizing cost multicasting problem. It means that, during the process of building a multicasting tree, when a destination is reached and its power satisfies the constraint, the path from source to it would be fixed in the tree. Simulation results show that, all multicasting trees building the proposed algorithm satisfy the power constraint, with slight increasing of the total cost.

Virtual topology design and flow routing in optical networks under multihour traffic demand

This article addresses the problem of finding a static virtual topology design and flow routing in transparent optical wavelength division multiplexing networks under a time-varying (multihour) traffic demand. Four variants of the problem are considered, using fixed or dynamically adaptable (meaning variable) flow routing, which can be splittable or unsplittable. Our main objective is to minimize the number of transceivers needed which make up for the main network cost. We formulate the problem variants as exact integer linear programs (ILPs) and mixed ILPs. For larger problem instances, we also propose a family of heuristics based on the concept of domination between traffic matrices. This concept provides the theoretical foundations for a set of techniques proposed to reduce the problem complexity. We present a lower bound to the network cost for the case in which the virtual topology could be dynamically reconfigured along time. This allows us to assess the limit on the maximum possible benefit that could be achieved by using optical reconfigurable equipment. Extensive tests have been conducted, using both synthetically generated and real-traced traffic demands. In the cases studied, results show that combining variable routing with splittable flows obtains a significant, although moderate, cost reduction. The maximum cost reduction achievable with reconfigurable virtual topologies was shown to be negligible compared to the static case in medium and high loads.

Shared-p-cycles method for design of survivable WDM networks

In future high-capacity wavelength division multiplexed (WDM) optical networks, the failure of a network component such as a fiber link can lead to severe disruption in the networks’ traffic. Hence, it is imperatively important to provide fast and full protection in WDM optical networks. In this paper, we propose a new approach, called shared preconfigured protection cycles (shared-p-cycles), for the design of survivable WDM networks. We develop an integer linear program (ILP) formulation to solve the problem of shared-p-cycles design for WDM networks with and without wavelength conversion. Numerical results show that the shared-p-cycles design is more efficient in the use of spare capacity and requires much less spare capacity than the conventional p-cycles design.

Integrated Scheduling of Grid Applications in WDM Optical Light-Trail Networks

A novel task graph model, flexible task model (FTM), is proposed for modeling the grid computing tasks and the relationships among the tasks. In this model, a task may generate output before the task completes whereas previous work assumes that no output is available until the task is completed. In addition, a task in FTM can start to execute when it has collected a minimum amount of required input from its predecessors. FTM is more general and flexible than the conventional task graph model considered in previous work. Based on FTM, we investigate the problem of scheduling grid applications that integrates the resource allocation for task execution and service provisioning for subwavelength data communication between the tasks. Data communication between grid tasks under the FTM model is better supported using light-trails in wavelength division multiplexing (WDM) networks, than lightpaths. The objective is to minimize the total amount of time for task completion or makespan. Simulation results show that our proposed scheduling algorithm under FTM significantly reduces the total task completion time compared with that under the conventional task graph model. Moreover, the communication service provisioning using light-trails is very resource efficient.

Wavelength assignment for all-to-all broadcast in WDM optical ring with limited drops

All-to-all broadcast communication is to disseminate a unique message from each node to every other node in a network. This is a fundamental problem in multiprocessor systems and telecommunication networks that need to collect information about other nodes in the network regularly in order to manage network resources efficiently. It is known that in wavelength division multiplexing (WDM) optical networks with single hop routing, the number of wavelengths needed for realizing all-to-all broadcast is quite large, even for a moderately sized network. One possible method to reduce the number of wavelengths is to adopt a network with drop-and-continue capable nodes. In such networks, a message from a source node can be dropped only at a limited number of destination nodes along a light path due to power loss of the dropping optical signals at the destination nodes. In this paper, a new wavelength assignment method is proposed to establish all-to-all broadcast in unidirectional ring and bi-directional ring networks which contain drop-and-continue capable nodes. An upper bound on the number of wavelengths required to establish all-to-all broadcast is also derived for unidirectional ring and bi-directional ring.

Tunable Optical Filter by Thermal Effect Based on MEMS Technology

In the broadband communication network, the wavelength-division-multiplexed (WDM) system is widely used to maximize the information that the signals can carry. As a result, the number of channels which are carried by different optical wavelengths in the WDM optical fiber network also keeps increasing. To separate the huge number of different wavelength signals, optical filter is required. The optical filter based on semiconductor has been widely studied due to the maturation of semiconductor fabrication technology and that it is possible to integrate the filter with the stable semiconductor devices such as laser diodes and MOSFETS. The tunable optical filter is basically a selective optical resonator that only allows the resonant modes passing through. Various mechanical methods are studied to achieve the tunable effect by tuning the physical structure of the filter; however, there is not much research on how the semiconductor material will affect the tuning function. In this paper, the author studied the influence of refractive index of the multi-silicon-slabs on the filter, whereby the tuning of refractive index is reached by thermal effect. It is found by simulation that when heating the silicon slabs, the increasing refractive index of silicon will lead to a shift of the resonant mode wavelength. This shift is almost linear with the change of the temperature, which is about 1nm with every 20K temperature increase. For certain devices, the result of the simulation showed it is possible to tune the resonant mode from C band to L band in the Fiber Optical Communication.

Dynamic virtual topology reconfiguration algorithms for WDM optical networks

Aiming at the problem of the traffic changing dynamically in a Wavelength Division Multiplexing (WDM) optical network, the virtual topology designed for an old traffic set needs to be reconfigured to route more connections. Based on maximum link load and the average packet hop distance for increasing network throughput, an adaptive topology reconfiguration algorithm, which determined the change in the virtual topology with a corresponding change in the demand set, was proposed by formulating the reconfiguration problem as mixed-integer linear program in the paper. The performance of the proposed algorithm was studied through extensive simulation experiments. The simulation results show that the network performance can be improved significantly by the proposed algorithm.

Multiple-wavelength transmitter for WDM optical network

Optical network based on wavelength-division multiplexing (WDM) technology will be a most active research topic in the 21st century. This paper describes a WDM multiple-wavelength transmitter and several key corresponding devices for optical network, including amplified spontaneous emission (ASE) spectrum-sliced multiple-wavelength optical source, optical add/drop multiplexer (OADM), semiconductor optical amplifier (SOA), as well as the spectrum noise suppression scheme. The new research results are reported, and the applications of these developed devices are also introduced.

LSP partial spatial-protection in MPLS over WDM optical networks

We consider Label Switched Path (LSP) protection for connections with various protection grade requirements in multi-protocol label switching (MPLS) over wavelength division multiplexing (WDM) optical networks. In full protection, bandwidth needs to be reserved for the backup LSP to protect the failure of any fiber along the primary LSP. In this paper, we study the problem of partial spatial-protection (PSP) where bandwidth is reserved for the backup LSP to protect the failure of a subset of fibers traversed by the primary LSP to satisfy the specified protection grade. We formulate the optimal LSP PSP problem as an ILP and identify three suboptimal problems. For each suboptimal problem, an exhaustive search algorithm and a heuristic are developed. We analyze the probability that a connection can be restored upon a fiber failure and find that it is higher than or equal to the protection grade specified. We also develop a failure recovery protocol which specifies recovery operations upon failure and determines whether a connection can be recovered if the failed fiber is one of its unprotected fibers. Through extensive simulation experiments, we demonstrated that the proposed LSP PSP algorithms perform better than shared LSP protection in blocking probability and resource efficiency.

Resource Planning for Dynamic Traffic Grooming in WDM Optical Networks

Dynamic traffic grooming in wavelength division multiplexing (WDM) optical networks refers to consolidating dynamically arriving subwavelength connections onto lightpaths. Most studies on dynamic traffic grooming focused on designing effective algorithms to achieve better performance (typically blocking probability) with given resources such as wavelengths and transponders. In this paper, we study the reverse problem: given the blocking requirement in dynamic traffic grooming, how to determine the resources needed to meet this requirement. We call it resource planning for dynamic traffic grooming. It is raised in a situation that after the initial deployment of optical networks, service providers often need to upgrade resources to accommodate increasing traffic demands. We formulate it as an ILP problem, and developed heuristics to solve this problem for large networks. Numerical results show that the heuristics can achieve good performance, and network resources increase slowly when requiring lower client call blocking probability.

Fractional Path Coloring in Bounded Degree Trees with Applications

This paper studies the natural linear programming relaxation of the path coloring problem. We prove constructively that finding an optimal fractional path coloring is Fixed Parameter Tractable (FPT), with the degree of the tree as parameter: the fractional coloring of paths in a bounded degree trees can be done in a time which is linear in the size of the tree, quadratic in the load of the set of paths, while exponential in the degree of the tree. We give an algorithm based on the generation of an efficient polynomial size linear program. Our algorithm is able to explore in polynomial time the exponential number of different fractional colorings, thanks to the notion of trace of a coloring that we introduce. We further give an upper bound on the cost of such a coloring in binary trees and extend this algorithm to bounded degree graphs with bounded treewidth. Finally, we also show some relationships between the integral and fractional problems, and derive a 1+5/3e≈1.61—approximation algorithm for the path coloring problem in bounded degree trees, improving on existing results. This classic combinatorial problem finds applications in the minimization of the number of wavelengths in wavelength division multiplexing (wdm) optical networks.

Distributed control based routing and wavelength assignment strategy for WDM optical networks

Wavelength-division-multiplexing (WDM) is emerging as the dominant technology for the next generation optical networks. The control strategy can be either centralized or distributed. In centralized control, there is a central controller to keep track of the state of the network. It is also responsible for selecting the path for data transmission. Most of the work done in this field is based on centralized control. For large networks, distributed control is preferred over centralized control because of low control overhead. Distributed control strategy requires exchange of control messages among nodes. The distributed control generally results in the possibility of resource reservation conflicts among simultaneous path establishments and poor resource utilization. In this paper, we have proposed one distributed control based routing and wavelength assignment strategy that avoids the problem of resource reservation conflicts along with the efficient utilization of resources.

Blocking probability analysis of survivable routing in WDM optical networks with/without sparse-wavelength conversion

In this paper, a new algorithm for wavelength assignment has been proposed and its performance is evaluated in terms of blocking probability and fairness. It has been shown that the proposed algorithm offers the least blocking probability. The blocking performance of wavelength division multiplexing (WDM) network has been analyzed for the network having 10 nodes and for varying loads. As the load per link (in Erlangs) increases, the blocking probability increases. The result shows that the performance of first-fit algorithm is better than random algorithm whereas the proposed algorithm offers the least blocking.

A novel domain-by-domain survivable mechanism in multi-domain wavelength-division-multiplexing optical networks

In multi-domain wavelength-division-multiplexing (WDM) optical networks, the inter-domain routing is a challenge since each single-domain cannot view the full network topology. At the same time, survivability is also an important issue in optical networks since the failures of fiber links or network nodes may lead to a lot of traffic being blocked. In this paper, we study the survivability in multi-domain WDM optical networks, and propose a new survivable mechanism called load balanced domain-by-domain routing (LBDDR). In LBDDR, in order to obtain the efficient inter-domain survivable routes, we present the domain-by-domain routing (DDR) method which can find the intra-domain sub-working path and sub-backup path in each single-domain to form the inter-domain working path and backup path for each demand. In order to reduce the blocking probability, we present the load balanced routing method which can encourage the traffic to be uniformly distributed on the links with more free wavelengths. Simulation results show that, compared with conventional mechanism, LBDDR can obtain better performances.

On Hierarchical Traffic Grooming in WDM Networks

The traffic grooming problem is of high practical importance in emerging wide-area wavelength division multiplexing (WDM) optical networks, yet it is intractable for any but trivial network topologies. In this work, we present an effective and efficient hierarchical traffic grooming framework for WDM networks of general topology, with the objective of minimizing the total number of electronic ports. At the first level of hierarchy, we decompose the network into clusters and designate one node in each cluster as the hub for grooming traffic. At the second level, the hubs form another cluster for grooming intercluster traffic. We view each (first- or second-level) cluster as a <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">virtual</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">star</i> , and we present an efficient near-optimal algorithm for determining the logical topology of lightpaths to carry the traffic within each cluster. Routing and wavelength assignment is then performed directly on the underlying physical topology. We demonstrate the effectiveness of our approach by applying it to two networks of realistic size, a 32-node, 53-link topology and a 47-node, 96-link network. Comparisons to lower bounds indicate that hierarchical grooming is efficient in its use of the network resources of interest, namely, electronic ports and wavelengths. In addition to scaling to large network sizes, our hierarchical approach also facilitates the control and management of multigranular networks.

An improved shared-path protection algorithm for double-link failures in meshed WDM optical networks

In this paper, we investigate survivability in wavelength division multiplexing (WDM) mesh networks and propose a new algorithm called improved shared-path protection (ISPP) to completely tolerate the double-link failures. Compared with previous algorithms for protecting double-link failures, i.e., shared-path protection (SPP) and shared-link protection (SLP), the advantage of ISPP is to allow primary paths and backup paths to share the mixed wavelength-links based on the proposed new rules in which some primary wavelength-links can be changed to mixed wavelength-links, which can be shared by primary paths and backup paths. In addition, some mixed wavelength-links also can be shared by different backup paths for saving resources. Simulation results show that ISPP algorithm performs better in resource utilization ratio and blocking probability than conventional SPP and SLP algorithms.

Determining the maximum signal power in 10 Gbit/s WDM optical networks

Nowadays in optical networks there is a trend line to extend the maximum transmission distance. Several techniques are known; however, the simplest one is to increase the signal power in the optical fiber. The task of minimizing the number of inline amplifiers in order to increase the deployed system’s cost effectiveness leads to increasing the signal power. The only problem is the nonlinear behavior of the optical fiber which limits the signal power to be inserted into the optical fibers. In this paper, we present a model to calculate analytically the signal quality deterioration due to nonlinear effects at the receiver point. As a result, we give the exact value of the optimal signal power at the transmitter point or at the output of the inline amplifiers for 10 Gbit/s wavelength division multiplexed (WDM) systems.