Wavelength-routed Networks Research Articles

Design and analysis of a conceptual wavelength-division multiplexing optical network based on self-similarity

We propose a novel multilevel wavelength-division multiplexing optical network based on the concept of self-similarity to simplify network structure and operation. Our approach lies on a simple network topology as well as an efficient wavelength management scheme being uniformly applied to all network levels. The proposed network is a compound packet-switched and wavelength-routed network with packet switching performed on the bottom level and wavelength routing on all upper levels. This network retains the efficiency of packet-switched networks and the simplicity of wavelength-routed networks. Switching operations are concentrated at some special nodes in the multilevel network, significantly simplifying the node configuration and wavelength routing. Moreover, the idea of bands is applied to unify wavelength management on all network levels. Network analysis is performed to assess the feasibility of our approach. A queueing model using the quality of service enhanced optical burst switching protocol is employed to analyze the blocking performance of the proposed network. Also, the numerical results based on the queueing model are provided.

Performance enhancement for impairment-aware SRLG failure protection in wavelength-routed optical networks

With the increase of size and number of shared risk link groups (SRLGs) in WDM networks, path protection tends to have longer working paths and backup paths due to SRLG-disjoint constraints, which makes physical impairment a major concern in working path and backup path provisioning, particularly in large-sized all optical networks. As a simple and efficient algorithm, the working path first algorithm is often used for path protection against SRLG failures, where the working path is calculated first by using the shortest-path algorithm on the graph, followed by using the SRLG-disjoint shortest path as backup path. Compared with the working path, the backup path calculated after the working path in the working path first algorithm is more vulnerable to physical impairment, since it may be much longer than the working path. As a result, if we reject those connections that cannot meet the physical impairment requirement, with SRLGs the blocking probability of path protection will be much higher. We argue that impairment must be taken into account together with capacity efficiency in a comprehensive way during SRLG-disjoint working path and backup path selection. To solve this problem, we motivate the needs to study physical impairment-aware shared-path protection by considering two policies. Policy I uses two SRLG-disjoint least impairment paths as working path and backup path, respectively, and Policy II tries to benefit from both the shortest path and the least impairment path by choosing them intelligently. Analytical and simulation results show: (1) compared with impairment-unawareness, impairment-aware SRLG failure protection performs much better in terms of blocking probability especially with strong physical impairment constraints; (2) impairment-aware SRLG failure protection can significantly reduce physical-layer blocking probability; and (3) the algorithm based on Policy II achieves a good balance between capacity efficiency and physical impairment requirement.

Comparison of 4 Multi-User Passive Network Topologies for 3 Different Quantum Key Distribution

The purpose of this paper is to compare the performance of four passive optical network topologies in implementing multi-user quantum key distribution, using 3 protocols proposed by quantum cryptography (B92, EPR, and SSP). The considered networks are the passive-star network, the optical-ring network based on the Signac interferometer, the wavelength-routed network, and the wavelength-addressed bus network. The quantum bit-error rate and sifted key rate for each of these topologies are analysed to determine their suitability for providing quantum key distribution-service to networks of various sizes. The efficiency of the three considered protocols is also determined.

Design and Evaluation of an Optical Broadcast-and-Select Network Architecture With a Centralized Multicarrier Light Source

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents the design and evaluation of our optical broadcast-and-select wavelength-routed network architecture that uses a centralized multicarrier light source (C-MCLS). The large number of optical carriers/wavelengths generated by the C-MCLS are distributed to all edge nodes (ENs), which select and modulate wavelengths to realize upstream transmission. To utilize wavelengths efficiently, we introduce a framework for wavelength allocation and selection (WAS). Both static and dynamic schemes are adopted for WAS and their implementations are shown. By using fixed or tunable band pass filters and periodic arrayed waveguide grating demultiplexers, wavelengths are selected and utilized by ENs in a static or dynamic manner. After considering the design parameters used in the implementations, wavelength allocation procedures are described. We evaluate the cost, power consumption and network performance of the proposed network. Numerical results show that it offers greatly reduced cost and power consumption compared to the conventional one when the number of required access wavelengths at EN becomes large. We delineate its applicable areas through cost comparisons. Blocking probabilities of static and dynamic schemes are analyzed to evaluate network performance. Numerical results show that by choosing appropriate design parameters, the dynamic scheme offers about 25% increase in admissible offered load under the specified blocking probability, compared to the static scheme. This indicates that the dynamic scheme makes the proposed network more robust against traffic fluctuations. </para>

Collision avoidance wavelength assignment scheme for distributed path restoration in optical networks

In wavelength-routed optical networks, the recovery ratio of interrupted connections after failures is mainly affected by adjacent-node resource reservation collisions in a distributed path restoration. This paper proposes a novel collision avoidance wavelength assignment (CA-WA) mechanism to make adjacent nodes select different wavelength assignment schemes and therefore different recovery wavelengths for the recovery routes. Simulation results show that in both single- and double-fiber failure scenarios the proposed wavelength assignment mechanism significantly reduces reservation contentions and achieves a higher recovery ratio, especially when the network load is high.

Wavelength conversion and in-band crosstalk in WDM optical networks

Wavelength-routed all-optical networks have emerged as a popular architectural solution for wide area networks and are being conceived for future broadband communications. Call connection probability in such networks depends on the number of WDM wavelengths employed and on the capability for wavelength conversion at network nodes. Equipping all the network nodes with wavelength conversion capability to reduce the blocking probability is not a cost effective solution due to the high cost of wavelength converters (WC). Hence, networks equipped with converters at only some of the nodes are more practical. However, these nodes should be identified optimally so that network blocking probability is minimized. In this paper, wavelength converters based on four wave mixing (FWM) in semiconductor optical amplifiers (SOAs) is considered. In WDM all-optical networks, in-band crosstalk is regarded as one of the major transmission impairments. In-band crosstalk usually arises when multiple signals at identical or adjacent wavelengths pass through an optical crossconnect node. In-band crosstalk leads to increased receiver BER. This paper considers in-band crosstalk arising in a network which is equipped with wavelength converters. For every dynamically arriving connection request, a route is determined using Dijikstra’s algorithm and a free wavelength is determined using the random wavelength assignment. If no common free wavelength is available, connection is tried using wavelength converters, if available, on the given route. If wavelength assignment does not succeed, the call is blocked. If wavelength assignment succeeds, the BER at the destination node is computed before establishing the lightpath. If the estimated BER exceeds 10−12, the call is blocked. Otherwise, the call is admitted. The results reveal that wavelength converters are not useful in networks that already suffer from crosstalk conditions.

Routing and wavelength assignment in wavelength-routed all-optical WDM networks

In this paper, low-complexity mathematical model has been developed which is used for the calculation of the blocking probability of network and this model does not require any simulation statistics. The implementation of the model proposed has less complexity and the computation used in this model is quite efficient. The routing algorithm has also been proposed in this paper depending upon the proposed model, which is very efficient in calculation and minimization of the blocking probability. This algorithm suggests an optimum path as a solution to routing problem. The wavelength assignment technique has also been suggested in this paper to minimize the blocking probability. The proposed model and algorithms can be implemented on different network topologies. Furthermore, the model, routing algorithm and wavelength assignment technique is also used to evaluate the blocking performance of NSFNet and EUPAN Network topology and hence used to improve its performance on the basis of the blocking probability.

Challenges for GMPLS lightpath provisioning in transparent optical networks: Wavelength constraints in routing and signaling

GMPLS has introduced several enhancements to the MPLS-TE routing and signaling control plane protocols to handle dynamic lightpath provisioning in wavelength-routed networks. Specifically, the GMPLS signaling protocol has been enhanced to support two new provisioning functionalities, namely, the minimization of the setup delay, and the setup of bidirectional connection requests. In both cases, the source node must perform a wavelength allocation for either minimizing the setup delay (i.e., the suggested label) or requesting a bidirectional connection (i.e., the upstream label). However, these GMPLS provisioning functionalities present important deficiencies when applied to wavelength-routed networks with the wavelength continuity constraint, degrading the network performance considerably. The reason is that the standard GMPLS routing protocols flood link attributes only at bandwidth granularity, that is, no per-wavelength channel granularity is disseminated. Therefore, the source node is unable to perform an optimal wavelength assignment that fulfils the wavelength continuity constraint along the complete route toward the destination. In this article we present and experimentally evaluate an enhanced routing-based solution in the ADRENALINE testbed to handle the wavelength continuity constraint.

Lightpath- and Light-Tree-Based Groupcast Routing and Wavelength Assignment in Mesh Optical Networks

With wide deployment of optical transport networks and the emergence of bandwidth-intensive applications, the idea of multicasts and groupcasts in optical networks stems from the ability to set up optical point-to-multipoint (multicast) and multipoint-to-multipoint (groupcast) sessions in wavelength-routed networks. As the technology for intelligent optical networks grows, optical groupcast applications (such as grid computing, distributed interactive simulations, multimedia-rich interactive services, virtual private network services, personal–customized content authoring services, and Ethernet LAN services) will become widely popular. In this paper we introduce the concept of groupcast routing and wavelength assignment (GC-RWA) and evaluate the performance of GC-RWA for light-forests corresponding to the groupcast sessions, when these light-forests are composed of lightpaths and light-trees.

Efficient Wavelength Assignment Methods for Distributed Lightpath Restorations in Wavelength-Routed Networks

In distributed lightpath restoration in wavelength-routed networks, different restoration operations may compete for the same wavelength on the same link and get blocked though there are still plenty of idle capacities on the link. In this paper, we propose two different wavelength assignment methods within the same framework for lowering such type of blocking. Simulation results show that the proposed methods significantly outperform the existing ones. Theoretical analysis confirms the optimality of the proposed methods for a special case; while for a few most important more general cases, it is shown that the optimal performance cannot be guaranteed by any distributed wavelength assignment method with a predefined wavelength searching sequence. For different cases where the original lightpath establishment has adopted random and first-fit wavelength assignments respectively, we discuss the different concerns in developing efficient distributed restoration schemes.

Joint optimization of delay and congestion in wavelength-routed optical networks using genetic algorithms

A new multipurpose genetic algorithm, based on Pareto optimality, is proposed to design logical topologies for wavelength-routed optical networks with the aim of minimizing both the congestion and the end-to-end delay. Simulation results show its efficiency when compared with other previously proposed algorithms, achieving in most cases optimal or near-optimal solutions, and in less time than other methods. Moreover, since the algorithm relies on Pareto optimality, not only does it obtain a single logical topology but a set of them, so that the network designer can easily select the most appropriate one according to the current network requirements.

Label Preference Schemes for Lightpath Provisioning and Restoration in Distributed GMPLS Networks

In wavelength-routed networks based on a GMPLS control plane, the resource reservation protocol with traffic engineering extensions (RSVP-TE) allows to establish end-to-end lightpaths. The resource reservation can be blocked due to lack of available resources (forward blocking) or due to resource contentions (backward blocking). In wavelength-routed networks, the backward blocking is the predominant blocking contribution, when traffic load is low or highly-dynamic and when lightpath restoration takes place. To reduce the backward blocking, the paper proposes two label preference (LP) schemes compliant with RSVP-TE message exchanges. LP schemes provide the destination node with a label identifying the preferred wavelength to reserve. The preferred label is computed in a distributed way during the forward signaling phase, with the objective of assigning disjoint wavelengths to reservation attempts that may contend the resources. Simulation results demonstrate that, compared to other schemes, LP schemes are effective in reducing the backward blocking during both lightpath provisioning and restoration, without negatively impacting the forward blocking.

Dynamic RWA with FWM-induced crosstalk awareness and modulation format conversion in wavelength-routed optical networks

The constraint of signal transmission quality and network resources utilization in transparent optical networks are herein addressed through a representative cost function based upon an impairment-constraint-base routing (ICBR) approach, taking into account link capacity utilization and the nonlinear physical effect, in the primary instance due to Four-Wave Mixing (FWM)-induced crosstalk. The FWM effect is considered one of the most severe physical impairments for the future photonic networks since the accumulation of FWM crosstalk may cause a fatal degradation in the teletraffic network performance. This paper presents an added functionality to the network model design based on all-optical modulation format conversion from conventional on-off keying (OOK) to quadrature phase-shift keying (QPSK) sending more data within the same bandwidth while minimizing the blocking probability. The joint effect of physical impairment (i.e., FWM-induced crosstalk) awareness and two different modulation formats is considered through numerical simulations. The proposed scheme is expected to realize an all-optical transparent interconnection between networks that employ diverse modulation formats. Results show that the proposed FWM-aware Routing and Wavelength Assignment (RWA) algorithm leads to a more realistic system performance while giving a significant improvement on the network performance.

Wavelength pre-assignment collision schedule for wavelength-routed optical networks

A novel wavelength assignment scheme called the wavelength pre-assignment collision schedule (WPCS) is proposed for wavelength-routed networks. The WPCS pre-assigns the wavelength at the forward detection phase, and schedules the potential collision by priority. The potential collision is scheduled at the forward detection phase and the blocking of the wavelength assignment is reduced. Simulation is conducted with several other existing schemes. The numerical results show that WPCS performs better than other schemes in blocking probability under various traffic conditions.

Optimal RWA for Static Traffic in Transmission-Impaired Wavelength-Routed Networks

Physical-layer degradations can severely limit the capacity of all-optical wavelength-routed networks, and powerful routing and wavelength assignment (RWA) algorithms are needed to minimize their effect. An optimal RWA technique is presented that minimizes the number of wavelengths needed to serve a set of static call provisioning requests. The optimal solution is compared to classical suboptimal algorithms and results show that route selection is more critical than wavelength assignment if multiple paths are available. Physical impairments become less significant in mesh networks than in tandem networks.

Design algorithms for path-level grooming of traffic in WDM metro optical networks

Recent research in new architecture design for wavelength-routed networks is focused on grooming (aggregation) of traffic at the optical layer. Typically, this is achieved in three steps: (1) configure the circuit in the form of a path or a tree; (2) use optical devices such as couplers or splitters to allow multiple users to share a circuit through point to point (P2P), point to multipoint (P2MP), multipoint to point (MP2P), or multipoint to multipoint (MP2MP); and (3) provide an arbitration mechanism to avoid contention among end users. We compare the performance of architectures that aggregate traffic at the path level. Based on extensive simulations, we conclude that, for the studied topology and traffic, (1) MP2MP outperforms other architectures by multiple orders of magnitude in single-hop scenarios, (2) P2P performs the best in multihop transceiver-constrained scenarios, and (3) P2MP performs the best in multihop wavelength-constrained scenarios.

Design methodology for WDM backbone networks using FWM-aware heuristic algorithm

The problem of lightpath topology design (LTD) and traffic routing over the lightpaths for wavelength-routed optical backbone networks has been investigated extensively in the past using heuristic as well as linear-programming based approaches. Sensitivity of such long-haul backbones to physical-layer impairments is required to be adequately addressed during LTD phase to improve overall performance. For optical communication using wavelength-division multiplexing (WDM) over a long-haul fiber backbone, four-wave mixing (FWM) may become one of the significant transmission impairments. Intrinsically, for a WDM-based wavelength-routed network with wavelengths assigned using equally-spaced channels, the generated FWM components are found to remain more crowded at the center of the fiber transmission window. Using this observation, we propose an LTD scheme employing a unique wavelength assignment (WA) technique, wherein long lightpaths (traversing through a larger number of fiber links) are allocated wavelengths at the either edges of the fiber transmission window whereas short lightpaths (consisting of fewer fiber links) are placed in the middle of the transmission window, thereby reducing the FWM crosstalk for long lightpaths. Since long lightpaths comprise of large numbers of fiber links and intermediate nodes, they experience large amplified spontaneous emission (ASE) noise and switch crosstalk. Therefore, by using the proposed WA technique, long lightpaths while suffering from more ASE noise and switch crosstalk get subjected to lesser FWM crosstalk leading to a more uniform distribution of overall optical signal-to-noise ratio for all the lightpaths across the network. Analysis of our results indicates that the proposed FWM-aware LTD scheme with the novel WA technique can achieve similar congestion levels (of lightpaths) and bandwidth utilization efficiency without any need of additional network resources as compared with the existing FWM-unaware LTD schemes.

Impact of routing and wavelength selection strategies on GMPLS-controlled distributed restoration

The restorability problem in wavelength-routed networks without wavelength converters is investigated. A distributed control plane based on the generalized multiprotocol label switching (GMPLS) suite is considered for disseminating link-state information and reserving network resources. Different routing and wavelength selection strategies are proposed and a detailed performance analysis is carried out during restoration. Simulation results evaluate the blocking probability due to both lack of available resources (i.e., forward blocking) and resource contentions (i.e., backward blocking). Performance comparison provides some insightful suggestions to be applied to GMPLS-controlled wavelength-routed networks without wavelength converters. First, it is recommended to perform routing and wavelength selection separately at the lightpath source and destination, respectively. Second, routing can be computed on link-state information advertised during provisioning, without the need of flooding link-state information during restoration. In fact, during restoration, the resource contention among concurrent signaling instances is the dominant cause of blocking (i.e., backward blocking overcomes forward blocking). For this reason, intelligent routing and wavelength selection strategies aiming at avoiding or limiting resource contentions can help to improve restorability. In particular, among those strategies, the proposed wavelength selection has a better ability to reduce resource contentions than the routing strategies.

Survivability in waveband switching optical networks: Challenges and new ideas

With the developmental trend of ultra-high speed and ultra-large capacity required in optical networks, the number of wavelengths in each fiber greatly keeps increasing and the consequence is that the size (i.e., number of switching ports) and cost of conventional Optical Cross-Connects (OXCs) are excessively enhanced. Therefore, the technique called Waveband Switching (WBS) has been proposed to reduce the number of switching ports for saving the costs. At the same time, the survivability for optical networks is a very important issue since each wavelength channel has the transmission rate over several gigabits per second and the failures may lead to a lot of traffic blocked. Combining the WBS technique and survivability in optical networks, in this paper we comprehensively review the existing survivable schemes in WBS optical networks which are quite different from conventional survivable schemes in Wavelength-Routed (WR) optical networks. Then, we analyze the shortages of the current researches and prospect the challenges for survivability in WBS optical networks. Finally, we propose new ideas for designing survivable schemes to well guide the future work of researchers in WBS optical networks.

Relation of OSNR and PLR for nonintrusive fault detection in all-optical IP-Ethernet-WDM networks

I present an analytical expression for the relation of the packet loss rate (PLR) with respect to the channel optical signal-to-noise ratio measured nonintrusively in an all-optical, wavelength-routed network. This closed-form expression is aimed for rapid, nonintrusive fault detection of lambda services. This relation will help achieve reliable all-optical networks with no extra optoelectrical cost due to monitoring, and yet have digital parameters such as the PLR in the service level agreements. Analytical results considering performance thresholds for triple-play services, gigabit Ethernet framing, and forward error correction are discussed.