Large Optical Networks Research Articles

Large capacity optical networks applying multi-stage hetero-granular optical path routing

We propose a novel scalable large-scale OXC architecture with a two-stage hetero-granular optical path switching mechanism based on a combination of different granular optical selective switches and an appropriate network design algorithm that can make the best use of the proposed OXC architecture for building cost-effective large capacity optical networks. Simulation results verify that our proposed solution can offer a significant overall network cost reduction. The cost efficiency of networks based on the architecture is also investigated in relation to switching component cost and different network parameters.

One OCDMA PON System with 2D Multi-Length Two-Weight CHPCs

One OCDMA PON system is discussed in this paper. Multi-length Two-Weight Carrier Hopping Prime Codes is selected as encoder scheme, encoded information is transmitted through Optical fiber. Hard Limiter is utilized in receiver terminal to ensure lower bit error rate. Simulation shows that it can be used for large capacity optical networks.

Selfish routing and wavelength assignment strategies with advance reservation in inter-domain optical networks

The main challenge in developing large data network in the wide area is in dealing with the scalability of the underlying routing system. Accordingly, in this work we focus on the design of an effective and scalable routing and wavelength assignment (RWA) framework supporting advance reservation services in wavelength-routed WDM networks crossing multiple administrative domains. Our approach is motivated by the observation that traffic in large optical networks spanning several domains is not controlled by a central authority but rather by a large number of independent entities interacting in a distributed manner and aiming at maximizing their own welfare. Due to the selfish strategic behavior of the involved entities, non-cooperative game theory plays an important role in driving our approach. Here the dominant solution concept is the notion of Nash equilibria, which are states of a system in which no participant can gain by deviating unilaterally its strategy. On this concept, we developed a selfish adaptive RWA model supporting advance reservation in large-scale optical wavelength-routed networks and developed a distributed algorithm to compute approximate equilibria in computationally feasible times. We showed how and under which conditions such approach can give rise to a stable state with satisfactory solutions and analyzed its performance and convergence features.

A special issue on photonic signal processing

Photonic signal processing has been receiving increasing attention for about fifteen years. It would be enabling technology for next generation large capacity optical networks because it can avoid electronics bottleneck and decrease power consumption greatly. There are two main areas related to photonic signal processing. One topic is all-optical signal processing for digital bit sequence in optical network, such as all-optical wavelength conversion, alloptical logic operation, all-optical 3R regeneration, all-optical clock recovery, all-optical buffer, etc. The other topic is microwave photonic signal processing, such as microwave photonic filters, arbitrary waveform generation, RF signal generation, UWB signal generation, etc. However, there are still many problems to be solved before these functions could be used in optical networks. Researchers all over the world are concentrating on realizing photonic signal processing functions with some characteristics such as high operation speed and large bandwidth, flexible and multifunctional, potential integration. This special issue on photonic signal processing of Frontiers of Optoelectronics in China has collected review and research articles by a number of Chinese and international experts, especially from the research group sponsored by the National Basic Research Program of China (Grant No. 2011CB301700). There are seventeen excellent papers in this special issue including 4 review articles and 13 research articles. Prof. Yong Liu is a well known specialist in the field of photonic signal processing, and he reviewed some signal processing functions with nonlinear effects in semiconductor optical amplifiers. A wonderful review paper on slow light with silicon photonic crystals was given by Prof. Eric Cassan from University Paris-Sud, and he discussed the challenges, hot research topics and future trends in this field. Prof. Xinwan Li from Shanghai Jiao Tong University reviewed somemicro/nanostructure photonic devices for photonic signal processing, such as micro/nanofiber based devices and silicon waveguide based devices. Dr. Enming Xu reviewed some results on microwave photonic filters with semiconductor optical amplifiers. Moreover, there are 13 research articles focusing on photonic signal processing. An invited paper on compact silicon and hybrid plasmonic waveguides used for signal processing was presented by Prof. Yikai Su from Shanghai Jiao Tong University. Prof. Xianmin Zhang’s group presented a novel method for compensating dispersion effect in phase modulated radio over fiber links using an optical carrier Brillouin processing technique. Recent progress on slow light with cascaded microring resonators was reported by Prof. Jinzhong Yu’s group. Yu Ji from Prof. Jian Wu’s group demonstrated 40 GHz phase stable optical pulses with pulse-width of 1.88 ps, extinction ratio larger than 20 dB, the timing jitter of 57 fs and signal-to-noise ratio of 32.8 dB. Prof. Caiyun Lou and her colleagues also reported some research progress on optical signal processing functions with semiconductor optical amplifiers and delay interferometers. Some results on all-optical clock recovery with magnetically controllable fiber optical parametric oscillator were demonstrated by Prof. BaojianWu. Ping Zhao from Xinliang Zhang’s group presented a novel method for fabricating silica micro/nanofiber. Also, there are some theoretical simulation results in this special issue. Xinying Li from Prof. Nan Chi’s group analysed the impact of quadrature imbalance in the presence of frequency offset in an optical coherent offset quadrature phase-shift keying receiver. Prof. Guangqiong Xia and her colleagues analysed the impacts

Dynamic resource allocation with service guarantees over large scale optical networks

The lack of effective contention resolution mechanisms in the optical domain presents dynamic optical switching architectures with a hard dilemma between high loss (when adopting one-way reservations) and high delay (when using two-way reservations). In this work we evaluate an alternative hierarchical network architecture, which achieves a satisfactory compromise by partitioning the network into a number of geographically limited domains operating in slot and frame synchronous mode where two-way reservations are effective.

An improved lightpath allocation for grade of services in survivable WDM mesh networks

A large optical network may carry multiple traffic with different grade of services. Several previous papers suggest a preemptive multi-class routing scheme: (1) low grade of services’ primary path can share resources with high grade of services’ backup path; (2) low grade of services can be preempted by high grade of services in case of a failure. However, they just optimize the network resources without considering the high grade of services’ failure state. In this paper, we propose an improved lightpath allocation for grade of services to implement in single-link failure WDM mesh networks. The main advantages are to consider Grade 3 (the highest level) lightpath’s failure state when a link fault happens and to make the best of Grade 1(the lowest level) lightpaths working resources as the backup resources of Grade 3 lightpaths. Compared to the previous work, it can obtain better performances in resource utilization ratio, lightpath establishment and the number of average interrupted lightpaths.

Video Service Delivery Over a Repeater-Based Optical Access Network

A low-cost and bandwidth-efficient scheme for delivering video services to customers over a long reach, large split repeater-based optical access network is proposed and experimentally demonstrated. Video channels that are on radio-frequency subcarriers are electrically combined with regenerated downstream data at the repeater and delivered to the customers on a single wavelength channel. Experimental results show that error-free transmission can be obtained for all channels with adequate power budget to support a split ratio more than 64.

Computational intelligence in photonics technology and optical networks: A survey and future perspectives

The continuous growth of broadband communications, multimedia services and Internet is absolutely related to the deployment and operation of optical networks. Despite optical fibers’ enormous physical bandwidth the development of optical networks for today’s advanced, reliable and guaranteed-type services, require an efficient management of the bandwidth together with an orthological and careful use of optical components given their high manufacturing cost. These requirements have lead to the need for sophisticated photonic devices and to optical networks’ implementations of increased functionality and associated thus complexity. For the efficient consideration of those problems different design and optimization techniques have been applied to date. However, as the complexity increases, the use of computational intelligence (CI) in those problems is becoming a unique tool of imperative value. In this paper we review in a unified approach the applications of CI starting from the physical layer and ending to services layer, given that here there is a strong relation and unique interplay between components’ technology and network issues, being sharing the common target of physical bandwidth’s efficient utilization. The applicability of different CI classes (genetic algorithms and evolution strategies, fuzzy systems, and artificial neural networks) in optical wavelength division multiplexing (WDM) networks is identified and evaluated. Furthermore specific optical networks’ optimization problems are categorized. Being a rapidly growing area, new trends, such as evolutionary game theory, in understanding and design of large scale Optical Network are also identified and discussed. The paper seeks to review the aforementioned areas, identify new problems and trends, triggering this way new research efforts for interdisciplinary cooperation between researchers.

Survivability Strategy for Large and Scalable WDM Optical Networks

The restoration 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 strategy that avoids the problem of resource reservation conflicts along with the efficient utilization of resources. The resource utilization is enhanced by using backup multiplexing technique i.e. there can be resource sharing between backup light-paths. The proposed strategy is based on proactive approach i.e. the backup lightpath is established along with primary lightpath to avoid time delay in searching the alternate path for affected traffic after failure to avoid data loss.

Design of virtual topologies for large optical networks through an efficient MILP formulation

In this paper we propose a Mixed-Integer Linear Programming (MILP) formulation for designing virtual topologies of wavelength-routed optical networks, considering as objective function the minimization of the traffic electronically forwarded at the network nodes. Our goal is twofold. Firstly, to reduce packet router processing requirements of the electronic routers, and secondly, to get the most transparent traffic distribution for a given traffic matrix, using the available optical resources at the nodes. The proposed formulation was applied successfully to reasonable sized networks yielding optimal solutions in a few minutes. To the best knowledge of the authors, this is the first report on optimizing virtual topology and traffic routing of large optical networks with a low computational cost MILP formulation.

Subpath Protection for Scalability and Fast Recovery in Optical WDM Mesh Networks

This paper investigates survivable lightpath provisioning and fast protection switching for generic mesh-based optical networks employing wavelength-division multiplexing (WDM). We propose subpath protection, which is a generalization of shared-path protection. The main ideas of subpath protection are: 1) to partition a large optical network into smaller domains and 2) to apply shared-path protection to the optical network such that an intradomain lightpath does not use resources of other domains and the primary/backup paths of an interdomain lightpath exit a domain (and enter another domain) through a common domain-border node. We mathematically formulate the routing and wavelength-assignment (RWA) problem under subpath protection for a given set of lightpath requests, prove that the problem is NP-complete, and develop a heuristic to find efficient solutions. Comparisons between subpath protection and shared-path protection on a nationwide network with dozens of wavelengths per fiber show that, for a modest sacrifice in resource utilization, subpath protection achieves improved survivability, much higher scalability, and significantly reduced fault-recovery time.

Routing and Wavelength Assignment in Multi-Segment WDM Optical Networks using Clustering Techniques

This paper studies the routing and wavelength assignment (RWA) problem in multi-segment optical networks. The notion of network segment is referred to any part of the network that requires special consideration of wavelength routing such as separate administrative domains in a large scale optical network, sub-networks run by various service providers, etc. In multi-segment optical networks, each segment has different resource availability or hardware characteristics. The differences between multi-segment optical networks and homogeneous optical networks are discussed. We then present a resource abstraction technique called blocking island and define a multi-segment blocking island graph (BIG) network model. Using a minimum splitting routing heuristic introduced in the context of the blocking island paradigm in conjunction with the multi-segment BIG model, we propose a general RWA algorithm that takes a combined view of the network resource to integrate routing, wavelength assignment and gateway selection in a single routing framework. In the simulation, we demonstrate the effectiveness of our proposed algorithm by comparing it with other state-of-the-art heuristics in this area.

Architecture and sparse placement of limited-wavelength converters for optical networks

Equipping all nodes of a large optical network with full conversion capability is prohibitively costly. To improve performance at reduced cost, sparse converter placement algorithms are used to select a subset of nodes for full-conversion deployment. Further cost reduction can be obtained by deploying only limited conversion capability in the selected nodes. We present a limited wavelength converter placement algorithm based on the k-minimum dominating set (k-MDS) concept. We propose three different cost-effective optical switch designs using the technologically feasible nontunable optical multiplexers. These three switch designs are flexible node sharing, strict node sharing, and static mapping. Compared to the full search heuristic of O(N 3 ) complexity based on ranking nodes by blocking percentages, our algorithm not only has a better time complexity O(RN 2 ), where R is the number of disjoint sets provided by k-MDS, but also avoids the local minimum problem. The performance benefit of our algorithm is demonstrated by network simulation with the U.S Long Haul topology having 28 nodes (R is 5) and the National Science Foundation (NSF) network having 16 nodes (R is 4). Our simulation considers the case when the traffic is not uniformly distributed between node pairs in the network using a weighted placement approach, referred to as k-WMDS. From the optical network management point of view, our results also show that the limited conversion capability can achieve performance very close to that of the full conversion capability, while not only decreasing the optical switch cost but also enhancing its fault tolerance.

Routing and dimensioning in optical networks under traffic growth models: an asymptotic approach

We consider the problem of routing and dimensioning in a large optical network where traffic is growing over time. A model of traffic in optical network lightpaths is presented. Lightpaths arrive randomly according to a time-varying Poisson process and hold for a random time with a general distribution. We propose a wavelength division multiplexing network that requires no capacity upgrading in a given time period T while allowing the operator to accommodate all the lightpath requests. We obtain an exact solution of the routing and dimensioning problem under an asymptotic regime where both the capacities and the arrival rates are large. For moderate link capacities, we propose a method to dimension the links so that the first lightpath request rejection occurs, with high probability, after the specified time T. This involves the computation of capacity-exhaustion probability $the probability that at least one lightpath request is rejected in the time period (0, T) due to lack of bandwidth/capacity on some link. Computation of the exact capacity-exhaustion probability is possible for a few specific holding time distributions (e.g., exponential). Since this requires large computing resources, it is feasible only for small networks. We propose a method to estimate the capacity-exhaustion probabilities for a large optical network with general holding time distribution based on the results of an asymptotic analysis. We show that this method has a low computational complexity and is quite accurate in the desired range of low capacity-exhaustion probabilities.

Dominating set algorithms for sparse placement of full and limited wavelength converters in WDM optical networks

Optical wavelength converters are expensive, and their technology is still evolving. Deploying full conversion capability in all nodes of a large optical network would be prohibitively costly. We present a new algorithm for the sparse placement of full wavelength converters based on the concept of a k-minimum dominating set (k-MDS) of graphs. The k-MDS algorithm is used to select the best set of nodes that will be equipped with full-conversion capability. To allow placement of full wavelength conversion at any arbitrary number of nodes, we introduce a HYBRID algorithm and compare its performance with the simulation-based k-BLK approach. We also extend the k-MDS algorithm to the case of limited conversion capability by using a scalable and cost-effective node-sharing switch design. Compared with full search algorithms previously proposed in the literature our algorithm has better blocking performance, has better time complexity, and avoids the local minimum problem. The performance benefit of our algorithms is demonstrated by simulation.

Multilayer optical filters with random errors

Optical structures consisting of multiple dielectric layers are used as filters in many applications, including wavelength division multiplexing (WDM), in optical networking. The desired frequency response in transmittance or reflectance of the device is obtained by proper design of the thickness and refractive index of each of the different layers. Random deviations from the design parameters will cause the transfer functions to exhibit random departures from the ideal design. Frequently, multilayer devices are targeted for use in large optical networks in which signals will traverse a cascade of such devices. The end-to-end transfer functions seen by these signals (the product of the individual transfer functions) become narrower in bandwidth as the number of transfer functions increases. For a given tolerance on the wavelength drift of each signal laser, the tolerances placed on filter shapes become tighter as the optical network becomes larger, and this can present significant system design and performance issues. Previously, Monte Carlo analysis was used to study random transfer-function errors. This paper discusses an analytical method based on Kronecker products, which is used to determine the statistical errors in transmittance and reflectance of the optical structures. The analysis permits both the in-band and out-of-band statistics to be determined as functions of the statistics of random errors in optical thickness of the different layers.

WDM Systems in the C-Band Using Er 3+ -Doped Tellurite Optical Waveguide Amplifiers

A 16-channel, 2.5 Gb/s, wavelength-division multiplexing system is analyzed with its channels allocated in the 1.52-1.56 w m wavelength region in order to increase the usable amplifier bandwidth to , 45 nm. To avoid amplified spontaneous emission (ASE) noise and the nonuniform signal gain in the wavelength region, an amplifier module consisting of an Er 3+ -doped tellurite waveguide amplifier, an ASE filter, and two concatenated long-period grating filters are proposed. A tellurite-based amplifier was chosen as the amplifying element because of its broad emission bandwidth (~80 nm), its high emission cross section (6.44 2 10 -25 m 2 ), and its high rare-earth ion solubility. The amplifier model is based on propagation and populationrate equations and includes both uniform and pair-induced up-conversion mechanisms. It is solved numerically by combining finite elements and a Runge-Kutta algorithm. The analysis predicts that using the proposed amplifier module, the channels may be transmitted to a maximum distance of 1800 km, finding applications in large optical networks where either many wavelengths are required or channel spacing must be large.

Design of a cross-border optical core and access networking field trial: first outcomes of the ACTS-PELICAN project

A large advanced optical network was assembled and operated in the field, featuring access, metropolitan, and core optical networks with advanced functionality and technology in all parts of the network. It demonstrates the reliability and viability of photonic technologies, and management functions in a trial representative of a global network infrastructure. The core network is a transparent all-optical meshed network with wavelength crossconnects partly 2R-regenerating, operating at 2.5 and 10 Gb/s, and supporting various protection schemes including 1:N shared OCH protection. The metropolitan network is a ring composed of OADMs supporting OMS protection. The interconnection to the SuperPON access network is made through an ATM switch. The ATM-based SuperPON supports a dynamic medium access control (MAC) protocol. For the first time, a 10 Gb/s wavelength-converted connection was demonstrated in the field in a transparent all-optical managed network. The field trial has demonstrated many points of progress as compared to the previous state of the art: cascadability experiments in a real network with reasonable distances and low compensation, various node functions, interworking of various equipment types, new optical protection, and dynamic MAC protocol. The (transport) TMN/Q3 integrated management system played an important role to achieve the network experiments: it allowed us to provision and reconfigure the end-to-end optical paths very quickly (<3 s) from the centralized management platform. This trial is also the first one representative of an advanced global optical network infrastructure including core, metro, and access networks, supporting end-to-end multimedia services. This article reports the project results before the field deployment which took place in April 2000.

An efficient algorithm for locating soft and hard failures in WDM networks

Fault identification and location in optical networks is hampered by a multitude of factors: the redundancy and the lack of coordination (internetworking) of the managements at the different layers (WDM, SDH/SONET, ATM, IP); the large number of alarms a single failure can trigger; the difficulty in detecting some failures; and the resulting need to cope with missing or false alarms. Moreover, the problem of multiple fault location is NP-complete, so that the processing time may become an issue for large meshed optical networks. We propose an algorithm for locating multiple failures at the physical layer of a WDM network. They can be either hard failures, that is, unexpected events that suddenly interrupt the established channels; or soft failures, that is, events that progressively degrade the quality of transmission; or both, hard failures are detected at the WDM layer. Soft failures can sometimes be detected at the optical layer if proper testing equipment is deployed, but often require performance monitoring at a higher layer (SDH, ATM, or IP). Both types of failures, and both types of error monitoring, are incorporated in our algorithm, which is based on a classification and abstraction of the components of the optical layer and of the upper layer. Our algorithm does not rely on timestamps nor on failure probabilities, which are difficult to estimate and to use in practice. Moreover, our algorithm also handles missing and false alarms. The nonpolynomial computational complexity of the problem is pushed ahead into a precomputational phase, which is done off-line, when the optical channels are set up or cleared down. This results in fast on-line location of the failing components upon reception of the ringing alarms.

A practical approach for routing and wavelength assignment in large wavelength-routed optical networks

We consider large optical networks in which nodes employ wavelength-routing switches which enable the establishment of wavelength-division-multiplexed (WDM) channels, called lightpaths, between node pairs. We propose a practical approach to solve routing and wavelength assignment (RWA) of lightpaths in such networks. A large RWA problem is partitioned into several smaller subproblems, each of which may be solved independently and efficiently using well-known approximation techniques. A multicommodity flow formulation combined with randomized rounding is employed to calculate the routes for lightpaths. Wavelength assignments for lightpaths are performed based on graph-coloring techniques. Representative numerical examples indicate the accuracy of our algorithms.