Self-healing Ring Research Articles

Demonstration of a spatial-division multiplexing self-healing ring network

This work demonstrates a spatial-division multiplexing self-healing ring protection scheme. A 3-node, 2-fiber ring with a recirculating length of 139.3 km is implemented using 4-core weakly-coupled multicore working and protection fibers and supported by core-pumped multicore amplifiers. Each node implements a spatial channel switching scheme with 8×8 traffic switches and arrays of 2×2 MEMS switches for ring protection switching with fiber bending taps to simultaneously monitor the power on all cores of the working and protection fibers. We achieve an average loss around 2 dB per network element along the protection path, which enables the use of ring protection with minimal performance impact. With this scheme, we demonstrate the protection of a line-side traffic throughput above 120 Tb/s using polarization-multiplexed 16-ary quadrature-amplitude modulation signals across the C-band.

Self-Healing Fiber Bragg Grating Sensor System Using Free-Space Optics Link and Machine Learning for Enhancing Temperature Measurement

This research investigates the integration of free-space optics (FSO) with fiber Bragg grating (FBG) sensors in self-healing ring architectures, aiming to improve reliability and signal-to-noise ratio in temperature sensing within sensor systems. The combination of FSO’s wireless connectivity and FBG sensors’ precision, known for their sensitivity and immunity to electromagnetic interference, is particularly advantageous in demanding environments such as aerospace and structural health monitoring. The self-healing architecture enhances system resilience, automatically compensating for failures to maintain consistent monitoring capabilities. This study emphasizes the use of intensity wavelength division multiplexing (IWDM) to manage the complexities of increasing the multiplexing number of FBG sensors. Challenges arise with the overlapping spectra of FBGs when multiplexing several sensors. To address this, a hybrid approach combining an unsupervised autoencoder (AE) with a convolutional neural network (CNN) is proposed, significantly enhancing the accuracy and efficiency of sensor signal detection. These advancements signify substantial progress in sensor technology, validating the effectiveness of the AE-CNN hybrid model in refining FBG sensor systems and underscoring its potential for robust and reliable applications in critical sectors.

DWDM self-healing access ring network with cost-saving, crosstalk-free and bidirectional OADM in single fiber

A cost-saving, crosstalk-free and bidirectional optical add-drop multiplexer (B-OADM) based on cascaded thin-film optical add-drop filters (TFOADFs) with optical circulators as well as the optical protection function promptly restored at the access node for a single-fiber self-healing access ring network are proposed and demonstrated. Using this B-TFOADM configuration, no crosstalk appears on the dropped and added channels, respectively. The bit-error rate performances in this B-OADM are investigated in a 2.5-Gb/s DWDM system, showing no intraband and interband crosstalk-induced power penalties. Such crosstalk-free and bidirectional architecture greatly simplifies the hub complexity as well as the low-cost components at each node are employed.

Self-Healing Ring-Based Time-Sharing Passive Optical Networks

A new ring-based time-shared passive optical network (PON), with a self-healing function to prevent the occurrence of fiber-fault, has been proposed and investigated experimentally. By using the new optical line termination and single fiber path architecture, the proposed self-healing ring topology PON can be revived promptly under single fiber failure. The system performances of the proposed access network are also measured and discussed.

A single-fiber bi-directional WDM self-healing ring network with bi-directional OADM for metro-access applications

We propose and demonstrate a single-fiber bidirectional wavelength division multiplexing self-healing ring network for metro-access applications. By incorporating a simple bi-directional optical add-drop multiplexer at each network node as well as employing our proposed alternate-path switching scheme, the bi-directional traffic can be restored promptly under single fiber failure in the ring network. All the protection switching is performed at the hub only, thus the operation, administration and management cost can be easily optimized

Characterization of pre-cross-connected trails for optical mesh network protection

Recently there has been interest in so-called pre-cross-connected protection architectures for optical networks. The main benefit of pre-cross-connected protection is that multiple cross-connection actions are not required in real time at the time of failure. This addresses the practical concern that, in a transparent optical network, one may not be able to make a series of protection path-forming cross-connections in a succession of optical spans with certainty that the resultant end-to-end connection has optical path integrity. Self-healing rings, p-cycles, and preconnected linear segment protection are examples of prior methods that employ prefailure cross-connection of protection capacity but are not end-to-end path-oriented. More recent work has proposed pre-cross-connected trails (PXTs), which are fully preconnected linear path-protecting structures. The same work also provided an online heuristic algorithm for generating PXT network designs. However, important and interesting properties such as length and cyclicity of the PXT structures remained to be characterized. We delve further into PXT network design, attempting to validate claims made previously and to understand the structural and operational properties of PXTs. This involves reimplementation of and experimentation with the above heuristic. Results show that heuristically obtained designs frequently contain PXTs of great total length and high complexity, as well as other PXTs that are equivalent to 1+1 automatic protection switching (APS) arrangements. Through diagramming and statistical analysis of PXT characteristics we give the first intuitive appreciation of the structure and function of PXTs.

A scalable and decentralized fast-rerouting scheme with efficient bandwidth sharing

This paper focuses on the protection of virtual circuits (Label Switched Paths, LSPs) in a (G)MPLS (Generalised Multi-Protocol Label Switching) network. The proposed algorithm is designed to protect traffic with strong delay requirements such as EF (Expedited Forwarding) ordered aggregates in a DiffServ domain. Indeed, for this type of application, we need fast restoration in case of failure. The duplication of all the packets in a 1 + 1 end-to-end restoration scheme consumes a large amount of bandwidth. Furthermore, end-to-end recovery with bandwidth sharing schemes are usually considered to be far too slow. Local fast-rerouting is a solution which can compete with restoration times and bandwidth consumption offered by SONET self-healing rings. Our scheme includes a sophisticated resource mechanism based on the concepts of backup-backup aggregation and backup-primary aggregation. The path selection algorithm is also designed to efficiently reduce the resource usage. Moreover, when considering LSPs at different preemption levels, our algorithm is able to correctly calculate the amount of bandwidth that can be preempted despite the sharing of resource. We show that our approach, though local, can compete with the state-of-the-art end-to-end recovery schemes in terms of resource consumption. The major contribution of our scheme, the backup-primary aggregation, was then also used in the context of end-to-end recovery and improved its performance substantially. To be able to save a maximum amount of bandwidth in a decentralised implementation, the nodes that compute backup LSPs need to obtain a certain amount of link-state information. We propose a solution where the nodes learn almost all the information they need with RSVP messages. This drastically reduces the information that needs to be flooded in the whole network and is the first scalable decentralised solution capable of sharing a large amount of bandwidth.

Amplifier Placement Methods for Metropolitan WDM Ring Networks

This paper presents two new amplifier placement methods to minimize the number of amplifiers in metropolitan wavelength-division-multiplexing (WDM) rings based on integer programming techniques. The first method describes the amplifier placement problem exactly and uses a nonlinear programming solver to obtain a solution. The second method approximates some requirements in the problem and employs a linear programming solver to derive the amplifier placement solution. A new amplifier placement method for self-healing WDM rings is also reported in this paper. The new method is based on iteratively solving an amplifier placement problem for a ring network under different link failure scenarios. The solution provides a minimum number of amplifiers required to operate the self-healing ring under a normal or any single-link or single-node failure conditions.

Closed-form solution for reliability of SCI-based multiprocessor systems using Weibull distribution and self-healing rings

This paper introduces a new closed-form solution for the reliability of large-scale multiprocessor systems. The systems are based on SCI rings interconnected in hierarchical structures. Reliability expressions using enumeration technique are derived assuming Weibull failure process. The reliability function derived in this paper is general and valid for any hierarchical ring-based system with arbitrary number of levels. The hierarchical interconnections are constructed from self-healing rings and basic rings. The analysis shows the improvement achieved in reliability when self-healing rings are used. Although we used hierarchical systems based on SCI rings, the technique followed in this work is applied for any type of rings such as slotted or token rings.

Closed-form solution for reliability of SCI-based multiprocessor systems using Weibull distribution and self-healing rings

This paper introduces a new closed-form solution for the reliability of large-scale multiprocessor systems . The systems are based on SCI rings interconnected in hierarchical structures. Reliability expressions using enumeration technique are derived assuming Weibull failure process. The reliability function derived in this paper is general and valid for any hierarchical ring-based system with arbitrary number of levels. The hierarchical interconnections are constructed from self-healing rings and basic rings. The analysis shows the improvement achieved in reliability when self-healing rings are used. Although we used hierarchical systems based on SCI rings, the technique followed in this work is applied for any type of rings such as slotted or token rings .

1-Fiber WDM Self-Healing Ring With Bidirectional Optical Add/Drop Multiplexers

We propose a 1-fiber bidirectional WDM self-healing ring that has bidirectional optical add/drop multiplexers. A simple fault detection method is proposed, and no signal degradation due to in-band crosstalk is demonstrated in the failure state. The power penalty of the ring transmission was less than 1 dB at a BER 10/sup -12/ in the normal and failure state.

A tabu search algorithm for self-healing ring network design

We consider the problem of designing self-healing rings in order to protect the transmission of telecommunication demands in a zonal network. This problem stems from a real application with operational constraints such as dual homing and hop limit per ring. A modeling approach taking into account ring interactions is proposed as well as a tabu search heuristic for solving it. Computational results for a comprehensive set of real and randomly generated instances are presented.

Bidirectional WDM self-healing ring network for hub/remote nodes

We demonstrate a bidirectional wavelength-division-multiplexing self-healing ring network for hub/remote nodes with a single strand of fiber. In this network, self-healing can be achieved within 8 ms. The transmission capacity can be doubled in the operating state. We observed the improvement of power penalty due to the spectral filtering in the realized network with 2.5-Gb/s directly modulated signals.

Optimal design of survivable mesh networks based on line switched WDM self-healing rings

Network survivability provided at the optical layer is a desirable feature in modern high-speed networks. For example, the wavelength division multiplexed (WDM) self-healing ring (or SHR/WDM) provides a simple and fast optically transparent protection mechanism against any single fault in the ring. Multiple self-healing rings may be deployed to design a survivable optical mesh network by superposing a set of rings on the arbitrary topology. However, the optimum design of such a network requires the joint solution of three subproblems: the ring cover of the arbitrary topology (the RC subproblem); the routing of the working lightpaths between end node pairs to carry the offered traffic demands (the WL subproblem); and the provisioning of the SHR/WDM spare wavelengths to protect every line that carries working lightpaths (the SW subproblem). The complexity of the problem is exacerbated when software and hardware requirements pose additional design constraints on the optimization process. The paper presents an approach to optimizing the design of a network with arbitrary topology protected by multiple SHRs/WDM. Three design constraints are taken into account, namely, the maximum number of rings acceptable on the same line, the maximum number of rings acceptable at the same node, and the maximum ring size. The first objective is to minimize the total wavelength mileage (working and protection) required in the given topology to carry a set of traffic demands. The exact definition of the problem is given based on an integer linear programming (ILP) formulation that takes into account the design subproblems and constraints and assumes ubiquitous wavelength conversion availability. To circumvent the computational complexity of the exact problem formulation, a suboptimal solution is proposed based on an efficient pruning of the solution space. By jointly solving the three design subproblems, it is numerically demonstrated that the proposed optimization technique yields up to 12% reduction of the total wavelength mileage when compared to solutions obtained by sequentially and independently solving the subproblems. The second objective is to reduce the number of wavelength converters required in the solution produced by the ILP formulation. Two approaches are proposed in this case that trade the required wavelength mileage for the number of wavelength converters.

A novel fiber-laser-based sensor network with self-healing function

We present a novel fiber-laser-based sensor network with self-healing function and demonstrate its effectiveness. The network survivability and capacity for a multipoint sensor system are enhanced by adding switches in a self-healing ring architecture. The fiber laser adopted in this system is a linear-cavity fiber Bragg grating (FBG) laser leading to the signal-to-noise ratio over 52 dB for the sensor network. The network survivability of a ten-point FBG sensor is experimentally examined. The experimental results show that the proposed system can facilitate reliable sensing networks for a large-scale and multipoint smart structure.

Wavelength Assignment to Minimize the Number of SONET ADMs in WDM Rings

Optical wavelength division multiplexing (WDM) rings are being deployed to support SONET/SDH self-healing rings. In such systems, multiple SONET/SDH self-healing rings are realized over a single physical optical ring through wavelength division multiplexing. The cost of such a system is dominated by the SONET add/drop multiplexers (ADMs). To minimize the system cost, algorithms must be developed to assign wavelengths to lightpaths in the system so that the number of ADMs required is minimized. This problem of optimal wavelength assignment to minimize the number of SONET ADMs is known to be NP-hard. Existing heuristic algorithms for this problem include the assign first heuristic, the iterative matching heuristic and the iterative merging heuristic. In this paper, we develop an integer linear programming (ILP) formulation for this problem, propose a new wavelength assignment heuristic, and evaluate the existing and the newly proposed heuristic using the ILP formulation. We conclude that the performance of the newly proposed heuristic is very close to optimal.

Optimal Design of WDM Ring Networks to Minimize SDH ADMs

In this paper, we study the routing and wavelength assignment in WDM ring network supporting multiple high-level SONET/SDH self-healing rings. The optimal design of ring networks was formulated by using integer linear programming (ILP) and solved numerically. The objective of our optimization is to minimize the number of ADMs (Add-Drop Multiplexer) used in high-level SDH layer, the cost of which is dominant in WDM ring networks supporting SDH services as pointed out recently. For the first time, the impact of route selection and traffic patterns was demonstrated in this paper. Through the extensive numerical simulations, these results of two typical ring network architectures, bi-directional and unidirectional rings, were compared under different traffic patterns. Our simulation results show that proper route selection can result in significant ADMs saving in bi-directional ring network.

Fiber‐ring laser‐based fiber grating sensor system using self‐healing ring architecture

AbstractThis paper presents a self‐healing fiber grating sensor system and demonstrates its effectiveness. The self‐healing function is constructed by using a primary ring architecture incorporated with several ring sub‐networks. To enhance the sensing signal when a breakpoint suddenly occurs in the network, we employ a fiber‐ring laser‐based sensor system. The network survivability of an 11‐point FBG sensor is experimentally examined. The proposed fiber grating sensor system can increase the reliability of a sensing network. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 441–444, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10633

Future WAN architecture driven by services, traffic volume, and technology trends

Wide area networks (WANs) today involve protocol and topological hierarchies. Protocol hierarchy involves Internet protocol (IP), asynchronous transfer mode (ATM), synchronous optical network (SONET), and dense wavelength division multiplexing (DWDM). Self-healing SONET rings provide very fast restoration, and DWDM allows the creation of multiple wavelengths (“virtual fibers”) from a single optical fiber, providing ever-increasing capacity to the SONET layer. Topological hierarchy involves edge nodes and core nodes for IP, ATM, and SONET. It provides traffic aggregation and statistical multiplexing, takes advantage of transport bandwidth and economy of size of packet/cell switches, and allows easier operations. A confluence of factors, however, is driving changes in this network architecture. Explosive growth in traffic volume and emergence of true multiwavelength, multiservice optical networks will make flatter (more heavily meshed) service networks supported by an optical core network more economical in the future. In this paper, we discuss the factors driving this shift in the network architecture, quantify its cost advantage, describe its impact on the requirements for network elements comprising the optical transport network (OTN) and the service network, and discuss new management/control paradigms as well as opportunities for new revenue-generating services resulting from the new architecture.

A comparison of next-generation IP-centric transport architectures

The popularity of the Internet and Internet protocol (IP)-based intranets is promising enormous growth in data traffic originating from IP endpoints, prompting network operators to reconsider network architectures so that they can most effectively absorb the projected growth. At the same time, new technologies are being introduced at a phenomenal pace, providing network operators with numerous and complex choices involving dense wavelength division multiplexing (DWDM), synchronous optical networks (SONETs), packet over SONET (POS), packet over wavelength (POW), and asynchronous transfer mode (ATM). In this paper, we evaluate alternative transport architectures for carrying IP-based traffic using the projected traffic data, nodal configuration, and optical fiber connectivity of a realistic, national-scale IP backbone. We compare the option of carrying IP directly versus IP over ATM for three types of transport architecture: SONET bidirectional line-switched rings (BLSRs); mesh networks of optical (or electrical) cross connects; and DWDMs without underlying optical cross connects (OXCs) - that is, with one or more wavelength links between each pair of IP switches. These options also include restoration choices. SONET BLSRs provide fast restoration based on self-healing ring technology. OXCs provide fast restoration for underlying mesh at the wavelength level. For point-to-point wavelength links, we consider service-level (IP and ATM) restoration. We compare these options in terms of many network characteristics - port counts, circuit miles, wavelength miles, fiber miles, and overall cost - and consider all the critical constraints and flexibilities for each choice.