Wavelength Path Research Articles

Impact of electrical grooming and regeneration of wavelength paths in creating hierarchical optical path networks

We assess the impact of utilizing electrical cross-connects for the intermediate grooming and 3R regeneration of wavelength paths in a hybrid hierarchical optical path network. Simulation results prove that they offer a significant cost reduction. We also investigate the dependencies of network cost on network parameters including optically-transparent reach, electrical switch port cost, and waveband capacity. It is demonstrated that it is critical to choose the waveband capacity properly in order to minimize total network cost.

Survivable Hierarchical Optical Path Network Design With Dedicated Wavelength Path Protection

In this paper, we propose a novel network design algorithm that yields the hierarchical optical path network with dedicated wavelength path protection. A hierarchical optical path network provides two granularities in implementing dedicated protection in the optical layer, namely waveband path protection and wavelength path protection. The characteristics of both protection mechanisms are investigated. We develop the concept of the source-destination Cartesian product space to aggregate closely located traffic demands, which leads to a significant reduction in network resources needed. The proposed wavelength path protection algorithm achieves lower network costs than that possible with waveband protection when traffic volume is relatively small. On the other hand, in the large traffic demand area, both schemes offer almost the same cost, which makes the waveband protection scheme attractive because of its operational simplicity. Numerical results clarify that survivable hierarchical optical path network is more cost effective than the single layer optical path network with optical layer protection, irrespective of which protection scheme is utilized.

QoT-aware lightpath set-up in GMPLS-controlled WDM networks: A survey

GMPLS-controlled Wavelength Switched Optical Networks (WSON) often undergo upgrade in bit rate or in network element switching capability. In such a scenario many wavelength paths cannot be anymore considered pre-validated from the original network design phase. Thus, it is required to verify the quality of the optical path physical signal during path computation and signaling by considering the optical network impairments (e.g., attenuation, amplified spontaneous emission, etc.). In this paper, the general problem of impairment-aware path computation is presented and then solutions based on GMPLS extensions to be used during path set-up are considered. Specifically, an overview is presented where different approaches for implementing Quality of Transmission (QoT) estimation and QoT measurements in transparent networks are outlined. In addition, techniques for exploiting sparse regeneration in translucent networks are illustrated. Numerical results show that the proposed schemes are effective in finding or designating QoT-validated paths in only few set-up attempts when a fully transparent path is available. If the transparent path becomes unfeasible, the translucent approach is adopted showing how to optimally designate intermediate regenerators to satisfy the end-to-end QoT constraints.

Hybrid-hierarchical optical path network design algorithms utilizing ILP optimization

In this paper, we present design algorithms for the hierarchical optical path networks that utilize hybrid-hierarchical optical cross-connects (hybrid-HOXCs). The hybrid-HOXCs employ a waveband cross-connect for routing waveband paths and an electrical cross-connect for grooming wavelength paths. We first develop an integer linear programming model to solve the network design problem. We then propose a 2-stage ILP-based design algorithm for hierarchical optical path networks that utilize the hybrid-HOXCs. Its effectiveness is evaluated through numerical experiments. Impact of the critical parameter, electrical/optical port cost ratios, on total network cost is also investigated.

Energy saving in optical transport networks exploiting transmission properties and wavelength path optimization

Energy consumption is becoming a fundamental topic also for telecommunication networks, where the implementation of “green” infrastructures is required. In this paper, we report a numerical investigation about energy saving in a transport network both exploiting the transmission properties that permit to reduce the number of in-line equipments (optimizing wavelength path assignment) and switching off optical links when the traffic load decreases. In particular, we investigate a European transport network based on N × 40 Gbit/s transmission and the Italian network based on the M × 10 Gbit/s transmission.

Full-Mesh Wavelength Channel Assignments Over Interconnected Star-Shaped Networks Employing Coprime-Channel-Cycle Arrayed-Waveguide Gratings

We propose and demonstrate a novel technique for interconnecting arrayed-waveguide-grating-based wavelength routing networks. Experiments reveal that this technique enables us to establish full-mesh wavelength paths between arbitrary nodes in two networks.

A game equilibrated rapid dynamic restoration strategy in ASON

A dynamic equilibrated heuristic algorithm based on the D* principle and mixed-strategy game theory is proposed to resolve the restoration problem at the wavelength level in an automatically switched optical network (ASON). The cost of each edge and the wavelength occupancy was taken into account comprehensively. Nash equilibration between wavelength occupancy and path cost is solved and the evaluation function of the D* algorithm is constructed dynamically using game theory with a mixed strategy. Then, the system restores broken connections rapidly through dynamic route and wavelength assignment (RWA) and ensures a more balanced distribution of network resources in the process of dynamic channel restoration. Simulation results show that the blocking probability is reduced and the restoration probability is promoted effectively by this algorithm. In addition, the rapid and intelligent performance behavior of this algorithm can meet the requirements of restoration time.

Hierarchical Optical Path Network Design Algorithm Considering Waveband Protection

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper proposes a hierarchical optical path network design algorithm employing dedicated protection in the waveband layer. The proposed algorithm reduces network costs by joint optimization of grooming wavelength paths and placing waveband paths as well as ensures network survivability. It realizes node and link disjoint protection based on the observation that a pair of primary and backup waveband paths forms a loop. The algorithm attains high waveband utilization rates by employing the newly developed concept of a concatenated loop chain, which consists of a series of waveband paths. Analyses demonstrate that the proposed algorithm is superior to not only the simple End-to-End method but also the single layer optical path networks that employ wavelength path protection. The results also show that reliable hierarchical optical path networks offering waveband protection can be realized with marginal cost increase from unprotected single layer optical path networks. </para>

Wavelength Path Reconfigurable AWG-STAR Employing Coprime-Channel-Cycle Arrayed-Waveguide Gratings

We propose a novel reconfigurable AWG-STAR (physical star topology network with arrayed-waveguide grating router) that employs two kinds of cyclic-frequency arrayed-waveguide gratings whose repetition channel numbers are coprime. We demonstrate that all the wavelength paths can be assigned independently with excellent transmission characteristics.

Common path two-wavelength homodyne counting interferometer development

The linearity of displacement measurement is an important parameter in nanometrology. The development of the common path two-wavelength (633 nm and 532 nm) homodyne counting interferometer within the Nanotrace project is described. These two differential interferometers are also designed for the elimination of optical path drifts and fluctuations. Their short-term instability is projected to be in the order of tens of pm in the single wavelength path difference and below 10 pm in the difference of these two wavelength path differences. This solution enables better real-time validation of interferometer fringe interpolation. The whole system could be transportable and measure displacements up to 100 µm under ambient air conditions under cover. Refractive index compensation will also be included.

Automated adaptive on-line Multi-Layer Traffic Engineering through “tailoring” wavelength-paths in the Fragment Graph

In Multi-Layer networks, where more than one layer is switched, i.e., connections are set up using not only the upper, e.g., IP layer but the underlying wavelength layer as well leads often to suboptimal performance due to long wavelength paths, that do not allow routing the traffic along the shortest path. The role of MLTE (Multi-Layer Traffic Engineering) is to cut (fragment) these long wavelength-paths into parts (fragments) that allow better routing at the upper layer, or to concatenate (defragment) two or more fragments into longer paths when the network load is low and therefore fewer hops are preferred. In this paper we present a new model, the Fragment Graph (FG) and an algorithm for this model that supports Fragmentation and De-Fragmentation of wavelength paths making the network always instantly adapt to changing traffic conditions. We introduce the notion of shadow links to model “ λ -path tailoring”. We implicitly assume that the wavelength paths carry such, e.g., IP traffic that can be interrupted for a few milliseconds and that even allows minor packet reordering. To show the superior performance of our approach in various network and traffic conditions we have carried out an intensive simulation study where we compare blocking ratios and path lengths and we analyze the dynamic behavior and fairness of the proposed and of reference methods.

Low crosstalk and variable wavelength conversion using multiple QPM LiNbO 3 waveguide module

A multiple quasi-phase matched LiNbO3 device in a four-port fibre-pigtail module for variable difference frequency generation (DFG) is described. The module structure realises DFG pumped by second-harmonic light that results in wavelength conversion with low crosstalk. The module is also used to demonstrate polarisation-insensitive conversion. This device technology will be useful for future photonic networks that employ a grouped wavelength path.

Field Trial of 640-Gbit/s-Throughput, Granularity-Flexible Optical Network Using Packet-Selective ROADM Prototype

Reconfigurable optical add/drop multiplexers (ROADMs) are able to provide flexible wavelength path provisioning in wavelength division multiplexing (WDM) networks. However, the capability of conventional ROADMs is limited to handling wavelength paths, and it does not support fine granularity in add/drop multiplexing of packets. Recently, we have proposed and demonstrated a packet-selective ROADM that combines an acoustooptic wavelength-tunable filter (AOTF) and an optical packet ADM (PADM) using optical code label processing. It provides more efficient utilization of wavelengths than conventional ROADMs. However, the bit rate of the demonstration was limited up to 10 Gbit/s. In this paper, we newly develop a label-selectivity-enhanced optical en/decoder, which allows the optical label recognition with 40-Gbit/s nonreturn-to-zero (NRZ) data packets, and a wide pass-band AOTF for 40-Gbit/s signals. Furthermore, we develop 640-Gbit/s throughput, packet-selective ROADM prototype, and demonstrate a field trial of granularity-flexible 3-node optical network over 173 km. error-free packet ADMs (error rate of under 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> ) for all 16-wavelength channels at all nodes are obtained.

Optical Cross-Connect Switch Architectures for Hierarchical Optical Path Networks

SUMMARY This paper proposes new switch architectures for hierarchical optical path cross-connect (HOXC) systems. The architectures allow incremental expansion of system scale in terms of the number of input/output fiber ports, wavebands, and optical paths per waveband. These features assure the cost-effective introduction of HOXCs even at the outset when traffic volume is not so large. Furthermore the effectiveness of the proposed switch architectures is demonstrated in a comparison with singlelayer OXCs (conventional OXCs). The results provide useful criteria for the introduction of HOXCs in terms of hardware scale. Broadband access including ADSL and FTTH is being rapidly adopted throughout the world and, as a result, traffic is continually increasing. The maximum number of WDM wavelengths per fiber now exceeds one hundred, and wavelength routing using ROADMs (Reconfigurable OADMs) is being widely adopted to develop cost-effective networks [1]. GMPLS controlled OXCs have also been used to create nation-wide testbeds [2]. Further traffic expansion is expected in the near future with the introduction of new broadband services including IP TV and high definition TV. This will result in a significant increase in the number of wavelength paths that are to be cross-connected at nodes, and hence optical node throughput needs to be greatly enhanced. To resolve this problem, the hierarchical optical path crossconnect (HOXC) [3]–[5] is being investigated; it can handle hierarchical bandwidth optical paths, wavelength paths and wavebands (WBs) which consist of multiple wavelength paths. Indeed, several studies have targeted the development of hierarchical optical path network design algorithms [6]– [9], these algorithms were shown to greatly lower network cost compared to conventional single-layer optical path networks for a wide range of traffic demand. Most of the works evaluated the effectiveness in terms of the total number of OXC and HOXC ports compared to those of single-layer OXCs. Another study [10] showed that an HOXC with nonuniform WB size can not only improve node throughput but also reduce cross-connect node cost. The key components needed to develop HOXCs are waveband multi/demultiplexers (WB MUX/DEMUX),

An efficient hierarchical optical path network design algorithm based on a traffic demand expression in a cartesian product space

We propose a hierarchical optical path network design algorithm. In order to efficiently accommodate wavelength paths in each waveband path, we define a source-destination Cartesian product space that allows the 'closeness' among wavelength paths to be assessed. By grouping 'close' wavelength paths, found by searching for clusters in the space, we iteratively create waveband paths that efficiently accommodate the wavelength paths. Numerical experiments demonstrate that the proposed algorithm offers lower total network cost than the conventional algorithms. The results also show that the hierarchical optical path network is effective even when traffic demand is relatively small.

Hybrid Link/Path-Based Design for Translucent Photonic Network Dimensioning

The advancement of ultralong-haul transmission technology has dramatically enhanced the all-optical reaches. However, the actual situations of installed fiber and sites for terrestrial network often prevent implementing a purely transparent network, and thus, opaque reshaping retiming regenerating (3R) regeneration is required to guarantee optical signal reachability. Since 3R regenerators based on optical/electrical/optical conversion tend to dominate the total network costs, an efficient network design method that allocates a minimum number of 3R regenerators to optimum locations is essential to build a cost-effective photonic network. In this paper, we propose such a network-dimensioning method by combining the advantages of link-based and path-based design approaches. It first guarantees optical signal reachability for any possible traffic demand in each segmented linear link. After combining all the links, excessive regenerators are eliminated based on the optical signal quality check with -factor calculation for each wavelength path. A trial design of a large-scale mesh network demonstrated a significant cost savings of more than 30% in comparison with a conventional link-based design. In the trial, the impact of fiber loss coefficient over the total network cost was investigated quantitatively, addressing the importance of such quantitative modeling and analysis.

A new approach for routing and wavelength assignment for permanent and reliable wavelength paths in wide all-optical WDM networks

This article proposes a new approach for routing and wavelength assignment (RWA) for permanent and reliable wavelength paths (WP) in wide all-optical WDM networks with wavelength continuity constraint. Given a number of available wavelengths on each optical fiber, for each simple link failure of the network, we seek to maximize the number of satisfied requests for connections. This is known as RWAP problem. In our algorithm, called RWA with Minimum Loaded Link for Permanent and Reliable wavelength paths (MLL-PR), routing is based on the search for the optimal path while trying to minimize the maximum load on the links of the network in order to minimize the maximum link capacity and then minimize the number of dropped lightpaths after any link failure. The wavelength assignment is based on a graph coloring method using tabu-search. A series of experiments using two well-known networks (ARPANET and NSFNET) have been carried out in order to evaluate the performance of our approach, in terms of the number of blocked demands, for different failure scenarios. Generally, our results are better than those provided by the current solving approaches taken as reference.

Fast Restoration Based on Alternative Wavelength Paths in a Wide Area Optical IP Network

In this article we describe an experimental investigation of IP network restoration based on wavelength recovery. We propose a procedure for metro and wide area gigabit Ethernet networks that allows us to route the wavelength in case of link failure to another existing link by exploiting wavelength division multiplexing in the fiber. Such a procedure is obtained by means of an optical switch that is managed by a loss-of-light signal that is generated by a router in case of link failure. Such a method has been tested in an IP network consisting of three core routers with optical gigabit Ethernet interfaces connected by means of 50-km-long single-mode fibers between Rome and Pomezia. Compared with other conventional restoration techniques, such as OSPF and MPLS, our method -in very fast (20 ms) and is compatible with real-time TV services and low-cost chips.

All-optical wavelength-path service with quality assurance by multilayer integration system

In the future all-optical network controlled by generalized multiprotocol label switching (GMPLS), the wavelength path between end nodes will change dynamically. This inevitably means that the fiber parameters along the wavelength path will also vary. This variation in fiber parameters influences the signal quality of high-speed-transmission system (bit rates over 40 Gb/s). Therefore, at a path setup, the fiber-parameter effect should be adequately compensated. Moreover, the path setup must be completed fast enough to meet the network-application demands. To realize the rapid setup of adequate paths, a multilayer integration system for all-optical wavelength-path quality assurance is proposed. This multilayer integration system is evaluated in a field trial. In the trial, the GMPLS control plane, measurement plane, and data plane coordinated to maintain the quality of a 40-Gb/s wavelength path that would otherwise be degraded by the influence of chromatic dispersion. It is also demonstrated that the multilayer integration system can assure the signal quality in the face of not only chromatic dispersion but also degradation in the optical signal-to-noise ratio by the use of a 2R regeneration system. Our experiments confirm that the proposed multilayer integration system is an essential part of future all-optical networks.

A packet-switched hybrid optical network with service guarantees

We show that our proposed optical packet switched (OPS) hybrid network model supports both high throughput efficiency and guaranteed service transport (GST) with no packet loss and constant delay. The network comprises a wavelength routed optical network (WRON) enabling GST, and a statistically multiplexed (SM) network enabling high throughput. In the WRON, packets follow a fixed wavelength path and forwarding is based on the packets wavelength, while in the SM network, packets are switched according to header information. High reliability of GST packet forwarding is possible, because the forwarding does not depend on the operation of the packet switch. A novel node design supporting three Quality of Service (QoS) classes is proposed and described in detail. It facilitates full sharing of the link bandwidth by segregating GST packets and SM packets using polarization time division multiplexing (PTDM). SM packets are differentiated into two specified sub-QoS classes employing a novel buffer reservation technique and asynchronous buffer scheduling algorithm AIP3Q. We present a detailed analysis of the node throughput performance, demonstrating that buffering resource requirements are reduced in the optical packet switch, because processing and buffering of GST packets is avoided. The SM packet QoS differentiation permits a further reduction of buffer resources