Shared Backup Path Protection Research Articles

Link duration-aware shared backup path protection (LD-SBPP) against SRLG failure in LEO-satellite-terrestrial integrated optical networks

Large-scale disasters are very destructive to terrestrial optical networks (TONs), and most existing survivability technologies that rely solely on TONs themselves can hardly combat disasters. Satellite networks, as a promising complement to terrestrial systems, can help to improve the survivability of TONs against disasters. However, the time-varying nature of satellite networks poses new challenges to traditional survivability technologies. This paper considers the low earth orbit (LEO) satellite network-assisted shared backup path protection. Since the link-switching consumes a certain amount of time and would cause the delay jitter and the quality of transmission (QoT) fluctuation of the space lightpath, a link duration-aware shared backup path protection (LD-SBPP) scheme is proposed to search space backup lightpaths with the minimum number of link-switching. A pre-calculated snapshot continuous routing and wavelength assignment (P-SCRWA) algorithm is proposed to pre-calculate the routing and reserve spectrum resources at each continuous snapshot. Simulations show that user requests cannot be effectively protected by relying on the TON solely, while the protection can be achieved with the help of LEO satellites. The LD-SBPP scheme has high wavelength utilization efficiency, resulting in lower blocking probability. Besides, the link duration-aware strategy can greatly reduce the number of link-switching along space backup lightpaths.

Blocking aware offline survivable path provisioning of connection requests in elastic optical networks

Survivability of Elastic Optical Networks (EONs) from a link failure is an important problem. Shared Backup Path Protection (SBPP) is widely used for protection against a link failure. Backup Spectrum Reservation with Multi Path Protection (BSR-MPP) was introduced to increase backup spectrum sharing by reserving backup spectrum and employing protection with multiple backup paths. We propose a new polynomial-time strategy, Blocking Aware Survivable Path Provisioning (BASPP) that shares backup resources like SBPP and BSR-MPP but can reduce request blocking when opportunity of sharing resources does not exist. Since we address the offline problem of Survivable Routing, Modulation and Spectrum Allocation in EONs, we also propose an Integer Linear Program formulation. Results show appreciable reduction in bandwidth blocking ratio by using BASPP over existing strategies.

Planning of Survivable Wavelength-Switched Optical Networks Based on P2MP Transceivers

Nowadays, the booming of emerging network services have shifted the major traffic pattern in metro-aggregation networks from point-to-point (P2P) to hub-and-spoke (H&S). Hence, it will be promising to plan metro-aggregation networks with point-to-multipoint coherent optical transceivers (P2MP-TRXs). This work studies how to plan a survivable wavelength-switched optical network (WSON) with P2MP-TRXs and shared backup path protection (SBPP) to address single-link failures. We formulate an integer linear programming (ILP) model to place P2MP-TRXs, assign sub-carriers (SCs) to P2MP-TRXs, and calculate routing and spectrum assignment (RSA) for the working/backup lightpath between each hub-leaf P2MP-TRX pair, such that traffic demands can be satisfied with the minimum cost. A heuristic based on adaptive demand grouping (ADG) is also proposed to solve the problem time-efficiently. Extensive simulations confirmed the performance of our proposals.

Robust Design Against Network Failures of Shared Backup Path Protected SDM-EONs

The sustained growth of network traffic has aggravated transmission capacity limitation problems. Recently, elastic optical networks (EONs) based on space division multiplexing (SDM) technology have been proposed to improve spectral efficiency and overcome upper limits on capacity by expanding the spatial dimensions. Accordingly, SDM-EONs can provide higher capacity, higher spectral efficiency, and more flexible optical transmission to address future explosive data growth. However, the critical challenge for the widespread deployment of such complex networks is to ensure their survivability against various types of network failures including core failure, node failure, link failure, and shared risk link group (SRLG) failure. In this paper, we consider the robust design of an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula> -single-mode-fiber-bundle ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula> -SMFB)-based SDM-EON with shared backup path protection (SBPP). Considering the network reliability against various failures and the uncertainty in traffic volume, we focus on the routing, space, and spectrum assignment (RSSA) problems for the determination of working path and backup path. We formulate the problems as two mixed integer linear programming (MILP) models with the objective of minimizing the maximal frequency slot used (FS) index and the total number of backup FSs. In this scenario, we propose heuristic algorithms for routing decision-making and spectrum assignment. We compare spectral efficiency and execution time among the MILP models, our proposed algorithms, and an existing algorithm. Finally, we employ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Gamma$</tex-math></inline-formula> -robust optimization to handle traffic with uncertainties and compare the simulation results obtained in deterministic and nondeterministic scenarios.

Enhancement of failure independent path protection preconfigured cycles for electric power communication networks

For the purpose of improving the resources utilization efficiency and decrease network redundancy of electric power communication network (EPCN), the paper explores using failure independent path protection preconfigured cycle (FIPP p-Cycle) to provide backup paths for electric communication service and presents a protection algorithm of enhanced FIPP p-Cycle with traffic grooming (EFIPP-TG). Firstly, the multiplexing conditions of FIPP p-Cycle are analyzed specifically, and we propose a FIPP p-Cycle multiplexing algorithm to improve the utilization efficiency of backup resources. Then segment protection algorithm for working path is designed to decrease service blocking ratio as much as possible. In addition, by taking advantage of traffic grooming strategy, the routing paths of services are optimized, yielding effective decrease of network blocking probability. Simulation results from different topologies demonstrate that compared with traditional FIPP p-Cycle scheme, other p-Cycle based protection algorithms and shared backup path protection algorithm, the proposed EFIPP-TG algorithm can significantly reduce the redundancy and blocking probability of networks, shorten the length of backup path and hence improve the reliability of service and performance of network survivability.

Robust RMSA design for shared backup path protection based EON against nonlinear impairments

We focus on quality of transmission (QoT) guaranteed routing, modulation, and spectrum allocation (RMSA) in shared backup path protection (SBPP) based elastic optical networks (EONs) in the presence of nonlinear impairments. Allocating a suitable modulation format (MF) to ensure end-to-end QoT (E2E QoT) in a survivable EON offers critical challenges because each single link failure results in the failure of different network connections. As a consequence, different working and backup path allocations exist in the network for different failures, which lead to different nonlinear interference (NLI) power on any frequency slots (FSs). This demands a robust RMSA design to decide the suitable MF for each FS to ensure the E2E QoT under two scenarios: any single link failure and no failure. For this purpose, we propose a robust SBPP-NLI aware (SBPP-NLIA) algorithm to ensure E2E QoT with a multi-objective function that enables the joint sharing of backup FSs as well as transceivers and minimizes the overall network fragmentation. In the process, we introduce robust bitloading in our SBPP-NLIA to allocate different MFs for different FSs where we also perform optimal MF allocation for each FS of every connection. Next, we ensure the QoT of existing connections while establishing each new connection without reserving any margin. To achieve this with less complexity, we propose a recursive method to calculate the NLI for existing connections. Simulation results demonstrate that our proposed SBPP-NLIA performs 10.01% and 14.19% better in terms of, respectively, the bandwidth blocking probability and fragmentation compared to a full-load assumption scheme with an 85 Tb/s traffic load.

Protection against failure of machine-learning-based QoT prediction

Machine learning (ML)-based methods are being widely explored to predict the quality of transmission (QoT) of a lightpath. They are expected to reduce the signal-to-noise ratio margin reserved for the lightpath, thus improving the spectrum efficiency of an optical network. However, many studies on this prediction are often based on synthetic datasets or datasets obtained from laboratories. As such, these datasets may not accurately represent the entire state space of a practical optical network, which is exposed in harsh environments. There are risks of failure when using these ML-based QoT prediction models. Thus, it is necessary to develop a mechanism that can guarantee the reliability of lightpath service even if the prediction model fails. For this scenario, we propose to employ the conventional network protection techniques that are usually implemented to protect against network node/link failures to also protect against the failure of QoT prediction. Based on the two representative protection techniques, i.e., 1 + 1 dedicated path protection and shared backup path protection (SBPP), the performance of the proposed protection mechanism is evaluated by reserving different margins for the working and protection lightpaths. For 1 + 1 path protection, we find that the proposed mechanism can achieve a zero design margin (D-margin) for a working lightpath, thereby significantly improving network spectrum efficiency, while not sacrificing the availability of lightpath services. For SBPP, we find that an optimal D-margin should be identified to balance the spectrum efficiency and service availability; the proposed mechanism can save up to 0.5-dB D-margin for a working lightpath, while guaranteeing service availability.

Robust QoT Assured Resource Allocation in Shared Backup Path Protection Based EONs

Survivability is mission-critical for elastic optical networks (EONs) as they are expected to carry an enormous amount of data. In this paper, we consider the problem of designing shared backup path protection (SBPP) based EON that facilitates the minimum quality-of-transmission (QoT) assured allocation against physical layer impairments (PLIs) under any single link/shared risk link group (SRLG) failure for static and dynamic traffic scenarios. In general, the effect of PLIs on lightpath varies based on the location of failure of a link as it introduces different active working and backup paths. To address these issues in the design of SBPP EON, we formulate a mixed integer linear programming (MILP) based robust optimization framework for static traffic with the objective of minimizing overall fragmentation. In this process, we use the efficient robust bitloading technique for spectrum allocation where each frequency slot of a request is assigned with different modulation format. In addition, we propose novel SBPP-impairment aware (SBPP-IA) algorithm considering the limitations of MILP for larger networks. For this purpose, we introduce a novel sorting technique named most congested working-least congested backup first (MCW-LCBF) to sort the given set of requests. Next, we employ our SBPP-IA algorithm for dynamic traffic scenario and compare it with existing algorithms in terms of different QoT parameters. Further, we guarantee the QoT of existing requests while allocating each new request without reserving any margin. We demonstrated through simulations that our study provides 33.94-41.02% more QoT guaranteed requests compared to existing ones at 70 Tbps traffic load.

A deep neural network with a fuzzy multi-objective optimization model for fault analysis in an elastic optical network

The elastic optical network (EON) is the most attractive architecture for the next generation of optical networks. Dealing with high bit-rate traffic, EON faces the challenge of ensuring survivability to operate with stringent Service Level Agreements. This article proposes a Deep Neural Network model with a multi-objective Fuzzy Inference System (FIS) to solve the Routing and Spectrum Assignment problem with Shared Backup Path Protection. The algorithm aims to optimize the trade-off between blocking probability (BP) and fault restoration ratio (FRR). It uses a new spectrum-fragmentation metric to improve the FRR of affected connections. The FIS adds features of load balancing and alignment of allocation path solutions. We use figures of merit as BP of connection requests, FRR, spectrum utilization ratio, and connection downtime to evaluate the algorithm performance. The proposed algorithm organizes traffic in a less fragmented way, efficiently uses routing and protection resources, and performs well compared to similar algorithms related in the literature.

Crosstalk-Aware Shared Backup Path Protection in Multi-Core Fiber Elastic Optical Networks

Elastic optical networks employing multi-core fibers (MCF-EON) have the potential to expand significantly the transmission capacity of optical transport. However, wide deployment of such networks depends on addressing effectively two critical challenges: inter-core crosstalk, which may cause serious signal performance degradation in an MCF link, and survivability against network failures that may cause enormous data loss. In this article, we consider the design of MCF-EONs with shared-backup path protection (SBPP), one of the most efficient techniques for protecting network traffic. Specifically, we tackle the crosstalk-aware routing, core, and spectrum assignment (CA-RCSA) problem with the objective of jointly minimizing the network spectrum resources used and the total inter-core crosstalk. We formulate the problem as an integer linear programming (ILP) model subject to strict inter-core crosstalk limits for each provisioned lightpath, and we also propose an auxiliary graph (AG) based heuristic algorithm for lightpath provisioning. Simulation studies show that our algorithm is effective in terms of the objectives, and it is efficient to perform close to the ILP model in small networks, for which solving the ILP is feasible.

Spectrum Expansion/Contraction and Survivable Routing and Spectrum Assignment problems on EONs with time-varying traffic

For serving time-varying traffic on an Elastic Optical Networks (EONs), the spectrum allocated previously for the connection request should be expanded or contracted to meet the traffic requirement. For the survivable connection, both the primary and the backup lightpaths of the connection request should be expanded/contracted at the same time. In this paper, the Survivable Routing and Spectrum Allocation (SRSA) problem and the Spectrum Expansion Contraction (SEC) problem for SRSA on EONs with time-varying traffic are studied. In this article, two protecting schemes, Dedicated Path Protection (DPP) and Shared Backup Path Protection (SBPP) are considered. For each protecting scheme, two dynamic survivable routing algorithms and the respective SEC operations are developed to solve it. In the proposed algorithms, both the weighted hop distance and spectrum fragmentation are considered jointly. These algorithms are examined through simulations to find the best parameter for each algorithm. The results show that the blocked ratio (BR) of requests can be reduced by about 3%, if the spectrum fragmentation is considered. And, using SEC operation in time-varying traffic can reduce the BR of request about 1% and speed up the computation compared to the normal release and add operation.

Routing, Spectrum and Modulation Level Assignment, and Scheduling in Survivable Elastic Optical Networks Supporting Multi-Class Traffic

As elastic optical networks (EONs) are expected to convey high bitrate connections, a failure in these networks causes vast data losses. Thus, addressing the problem of survivability in EONs is of great importance. In this paper, survivability of an EON with multiclass traffic is investigated, where each traffic type needs specific protection mechanism and scheduling strategy. In particular, a connection request may demand for dedicated path protection, shared backup path protection, or restoration mechanism. Besides, it can tolerate a pre-determined delay and be scheduled at future time slots, referred to as advance reservation, or must be served immediately without any delay, referred to as immediate reservation. Accordingly, we formulate an integer linear programming (ILP) to solve the routing, spectrum and modulation level assignment, and scheduling problems in both static and dynamic operation scenarios. In addition, to reduce the complexity of the ILP formulation in large scale networks, we propose a number of heuristic algorithms, in which two and three methods are considered for path selection and resource allocation, respectively. We evaluate the proposed heuristic algorithms in a small scale network by comparing their performance with the ILP formulation, then we apply them in a realistic large scale network. We compare all algorithms in terms of blocking probability, initial delay, and spectrum efficiency. Our results reveal that by using load-aware path selection and first-fit frequency-slice and time-slot assignment strategies the best compromise between blocking probability and initial delay is obtained.

On the Efficiency of Survivable Flex-Grid SDM Networks

In this paper, we focus on the performance of a survivable flex-grid network with space division multiplexing (SDM). To provide network survivability, we use dedicated path protection and shared backup path protection. For both schemes, we also consider squeezed protection that allocates backup resources only for a part of the primary flow. The squeezed protection is considered for the protection level changing from 0% (no flows are protected) up to 100% (full network protection) with a step of 10%. Moreover, we consider two SDM switching policies—independent ( SDM-indsw ) and joint ( SDM-jsw ). In this paper, we define all considered problem versions using integer linear programming technique as well as propose a dedicated heuristic algorithm. Then, we perform extensive simulations focused on the performance of a survivable SDM network in terms of the spectrum usage. The results show that the path protection in an SDM network brings additional spectrum consumption; however, the amount of additional resources depends on various factors such as required protection level, applied protection method, switching policy, and traffic pattern. Moreover, the results also reveal that SDM-indsw is much more spectrum-efficient than SDM-jsw considering all protection methods and levels. It uses, on average, half of the spectrum required for SDM-jsw . Additionally, the investigation shows that SDM-jsw is especially spectrum-inefficient when realizing variable-size demands (sets including both small and large demands).

Optimized design and availability analysis of large-scale shared backup path protected networks

Traditional integer linear programming model for shared backup path networks allows only one working route and one backup route per demand and does not scale well. By introducing multiple working routes and backup routes, the traditional multi-flow model solves in a faster manner. This paper seeks improvements on the traditional multi-flow model and develops an algorithm to assess availability for multi-flow shared backup path protection models. Experiments on 165 networks testify that the newly proposed model is 51% faster on average with similar total cost and overall network availability, compared with the traditional multi-flow model. All the networks in this paper are designed to be 100% single-failure restorable, and major findings regarding these networks include: (1) total cost of assigning backup capacity to each span dwindles away with increasing network average nodal degree; (2) network availability first rises then falls as network average nodal degree increases; and (3) when network scale increases, network availability decreases with fluctuations. The results found are explained with two case studies in this paper.

Adaptive Modulation and Regeneration-Aware Routing and Spectrum Assignment in SBPP-Based Elastic Optical Networks

We focus on the Regenerator sharing, adaptive Modulation, Routing, and Spectrum assignment (RMRS) problem in a shared backup path protection based elastic optical network. Three regenerator placement strategies and the mechanisms of how to efficiently use/share the placed regenerators are proposed. An efficient heuristic algorithm is also developed for the RMRS problem to maximize regenerator and spectrum sharing among protection lightpaths with the joint consideration of modulation format and spectrum conversion capabilities of each traversed regenerator along a lightpath. Based on the performance study in terms of bandwidth blocking probability (BBP), we find that the proposed strategies and heuristic algorithm are efficient in signal regenerator utilization to significantly reduce BBP. It is also found that in addition to signal regeneration, the capabilities of modulation format conversion and spectrum conversion provided by each regenerator are helpful in reducing BBP, and as expected, the capability of spectrum conversion plays a more important role than the modulation format conversion for performance improvement. Finally, it is also interesting to find that there exists a saturation trend between the improvement of BBP performance and the increase in the number of regenerators. A limited number of signal regenerators sparsely placed in a network is sufficient to achieve a good BBP performance.

Energy-Efficient Survivable Grooming in Software-Defined Elastic Optical Networks

Survivability in the OpenFlow-based software-defined elastic optical networks (SD-EONs) are more challenging than that in the conventional optical networks because failures can affect control plane operations. Meanwhile, traffic grooming is enabled by sliceable transponders can reduce power consumption and obtain higher spectrum efficiency. In this paper, we study the survivable grooming routing and spectrum allocation in SD-EON. First, provide an integer linear programming formulation to minimize both the required transponders and the maximum number of occupied frequency slots. Then, we develop a heuristic algorithm called shared backup path grooming protection (SBPGP) to get enough protection and less resources consumption. Extensive simulations are performed to study the power consumption of optical elements in data plane. Numerical results show that the proposed SBPGP scheme achieves better performances than the traditional shared backup path protection without grooming.

Survivable Network Capacity Allocation and Topology Design Using Multi-period Network Augmentation

This paper examines the effect of incorporating multi-period network augmentation into the survivable network design process. The framework presented can handle variable restorability requirements, potential economies of scale, and technology shifts. By utilizing a multi-period planning model, shifts and uncertainties in demand and policy can be accounted for. This study examined the design of survivable networks using both demand-wise shared protection and shared backup path protection (representing opposite ends of the mesh network efficiency spectrum) with topology augmentation over multiple time horizons.

Protection lightpath-based hitless spectrum defragmentation for distance adaptive elastic optical networks.

Spectrum defragmentation can improve spectrum utilization for an elastic optical network (EON). However, most of the existing studies have focused on defragmentation for working lightpaths, which may affect upper-layer network services. This paper considers protection lightpath-based hitless spectrum defragmentation for distance adaptive elastic optical networks. Without affecting working lightpaths, but defragmenting spectra for protection lightpaths, we expect to achieve truly hitless spectrum defragmentation for an EON. Shared backup path protection (SBPP) technique is employed as a representative network protection technique to evaluate the benefit of the proposed defragmentation scheme. To smooth the network spectra for future arriving lightpath requests so as to reduce bandwidth blocking probability (BBP), we propose two defragmentation triggering mechanisms, namely, defragmentation upon blocking (BTD) and batch defragmentation (BD). For each of them, we also propose two spectrum defragmentation algorithms, namely, defragmentation with sequentially releasing and re-establishing protection lightpaths (SR-D) and defragmentation with jointly releasing and re-establishing protection lightpaths (JR-D). The performances of these proposed algorithms are evaluated from perspectives of BBP and average number of reconfigurations per successfully established lightpath service (ANR). Simulation results show that compared to the case without defragmentation, the proposed scheme is effective to reduce BBP, which trades off with ANR.

Explore Maximal Potential Capacity of WDM Optical Networks Using Time Domain Hybrid Modulation Technique

The recent emerging time domain hybrid modulation (TDHM) technique is considered promising because it can realize continuous adaptation between spectral efficiency and transparent reach through appropriately allocating the time slot occupancy ratios of different modulation formats in a time-division multiplexing (TDM) frame. This technique is expected to achieve more efficient spectrum utilization or higher transmission capacity than the traditional transmission technique based on discrete modulation formats. For the point-to-point transmission system, the benefit of the TDHM technique has been experimentally verified. However, its benefit from the whole network perspective has not been explored yet. In this paper, we apply the TDHM technique to the optical network to maximize its transmission capacity. To evaluate the benefit of this technique, we consider the routing and wavelength assignment problem for the TDHM-based WDM network, for which we develop an integer linear programming model and a waveplane-based heuristic algorithm to maximize the total network transmission capacity for the cases with and without network protection. For the protection case, the shared backup path protection technique is employed owing to its efficiency of spare capacity sharing and simplicity in network operation. The simulation study shows that compared to the design with discrete modulation formats, the TDHM-based approach can significantly increase the network transmission capacity.

Benefit of adaptive FEC in shared backup path protected elastic optical network.

We apply an adaptive forward error correction (FEC) allocation strategy to an Elastic Optical Network (EON) operated with shared backup path protection (SBPP). To maximize the protected network capacity that can be carried, an Integer Linear Programing (ILP) model and a spectrum window plane (SWP)-based heuristic algorithm are developed. Simulation results show that the FEC coding overhead required by the adaptive FEC scheme is significantly lower than that needed by a fixed FEC allocation strategy resulting in higher network capacity for the adaptive strategy. The adaptive FEC allocation strategy can also significantly outperform the fixed FEC allocation strategy both in terms of the spare capacity redundancy and the average FEC coding overhead needed per optical channel. The proposed heuristic algorithm is efficient and not only performs closer to the ILP model but also does much better than the shortest-path algorithm.