Shared Backup Path Protection Research Articles

Distance Adaptive Dynamic Routing and Spectrum Allocation in Elastic Optical Networks with Shared Backup Path Protection

This paper considers distance adaptive dynamic routing and spectrum assignment (RSA) for elastic optical networks with shared backup path protection (SBPP). Efficient heuristic algorithms based on spectrum window planes are proposed for implementing distance and modulation format adaptive RSA so as to maximize spare capacity sharing among multiple protection lightpaths. A differentiated sharable frequency slot cost was also defined for the first time to more efficiently share protection resource. Network performance is evaluated in terms of bandwidth blocking probability (BBP) through simulations. The proposed SBPP technique is effective in reducing BBP and improving spectral efficiency compared to conventional SBPP schemes and 1+1 path protection. The impact of transponder tunability on bandwidth blocking performance is also evaluated to show that a limited tuning range is sufficient to achieve a BBP performance close to that with full tunability.

Availability analysis of shared backup path protection under multiple-link failure scenario in WDM networks

Dedicated protection and shared protection are the main protection schemes in optical wavelength division multiplexing (WDM) networks. Shared protection techniques surpass the dedicated protection techniques by providing the same level of availability as dedicated protection with reduced spare capacity. Satisfying the service availability levels defined by the user’s service-level agreement (SLA) in a cost-effective and resource-efficient way is a major challenge for networks operators. Hence, evaluating the availability of the shared protection scheme has a great interest. We recently developed an analytical model to estimate network availability of a WDM network with shared-link connections under multiple link-failures. However, this model requires the information of all possible combinations of the unshared protection paths, which is somehow troublesome. In this paper, we propose a more practical analytical model for evaluating the availability of a WDM network with shared-link connections under multiple link-failures. The proposed model requires only an estimate of the set of shared paths of each protection path. The estimated availability of the proposed model accurately matched with that of the previous model. Finally, we compare the previous model with the proposed model to demonstrate the merits and demerits of both models illustrating the threshold at which each model performs better based on the computational complexity. The proposed model significantly contributes to the related areas by providing network operators with a practical tool to evaluate quantitatively the system-availability and, thus, the expected survivability degree of WDM optical networks with shared connections under multiple-link failures.

Optimal Design for Shared Backup Path Protected Elastic Optical Networks Under Single-Link Failure

This paper considers the network protection technique of shared backup path protection (SBPP) in comparison with 1 + 1 path protection for elastic optical networks. We develop integer linear programming (ILP) models to minimize both the required spare capacity and the maximum number of link frequency slots (FSs) used. We consider transponder tunability that corresponds to the condition of whether or not the same set of FSs is required to be used for both the working and protection lightpaths. We also apply the bandwidth squeezed restoration technique to obtain the maximum restoration levels for the affected service flows, subject to a limited FS capacity on each fiber link. Our studies show that the proposed SBPP technique requires much lower spare capacity compared to the traditional 1 + 1 path protection approach. The flexibility of allowing the working and protection lightpaths to use different sets of FSs (i.e., with full transponder tunability) has the advantage of reducing both the number of FSs needed and the spare capacity redundancy required.

Heuristic methods for single link shared backup path protection

Protecting communication networks against failures is becoming increasingly important as they have become an integrated part of our society. Cable failures are fairly common, but it is unacceptable for a single cable failure to disconnect communication for more than a few seconds--hence protection schemes are employed. In contrast to manual intervention, automatic protection schemes such as shared backup path protection (SBPP) can recover from failure quickly and efficiently. SBPP is a simple but efficient protection scheme that can be implemented in backbone networks with technology available today. In SBPP backup paths are planned in advance for every failure scenario in order to recover from failures quickly and efficiently. Planning SBPP is an NP-hard optimization problem, and previous work confirms that it is time-consuming to solve the problem in practice using exact methods. We present heuristic algorithms and lower bound methods for the SBPP planning problem. Experimental results show that the heuristic algorithms are able to find good quality solutions in minutes. A solution gap of less than $$3.5~\%$$ 3.5 % was achieved for 5 of 7 benchmark instances (and a gap of less than $$11~\%$$ 11 % for the remaining instances.)

Fast and Efficient Network Protection Method Using Path Pre-Cross-Connected Trails

This paper investigates design methods of protection schemes in survivable WDM networks using the path protection p-trail in order to provide better capacity efficiency by eliminating the rigidness of the protection structure of the well-accepted protection scheme, the failure independent path protection (FIPP) pre-configured protection cycle (p-cycle). The flexibility in the protection structure yields lower cost in terms of spare capacity allocation while maintaining the high speed of protection switching. We develop two design approaches, the fully pre-cross-connected path protection trail (fpp-trail) and the partially pre-cross-connected path protection trail (ppp-trail), based on the degree of pre-cross-connectivity of the protection structure. In order to obtain optimally designed trails, we develop an optimization model based on a large-scale optimization technique, namely, column generation. Numerical results show that fpp-trails significantly improve the spare capacity efficiency compared to the FIPP p-cycle, and ppp-trails strike a balance between capacity redundancy and recovery delay. We observe that ppp-trails can achieve as low capacity redundancy as shared backup path protection (SBPP), while the recovery delay is kept lower than in SBPP and slightly higher than FIPP p-cycles by using selective signaling through a control plane that is aware of the location of the cross-connects that are not pre-configured in advance.

Energy-Efficient Resilience in Translucent Optical Networks With Mixed Regenerator Placement

In this paper, we investigate energy-efficient resilience designs for the translucent optical networks using mixed regenerator placement (MRP). We consider both static and dynamic traffic scenarios and aim to provide 100% restoration against single-link failures while minimizing the total energy-cost on regenerators. For static traffic scenarios, we formulate an integer linear programming (ILP) model to solve the energy-efficient p-cycle design for translucent optical networks with MRP. The ILP model optimizes the allocation of working and protection resources jointly under the quality of transmission constraint, with the objective to minimize the total energy cost. A heuristic that can sequentially optimize the p-cycle designs for connections is proposed afterward. We use simulations to evaluate the performance of the algorithms with both uniform and nonuniform traffic models. For dynamic traffic scenarios, we design an algorithm that can handle the setting-up and tearing-down of p-cycles dynamically, according to the time-variant connections. We enhance this algorithm by introducing a reoptimization procedure, which can reassemble existing p-cycles for higher energy efficiency. An ILP model is formulated and solved for the p-cycle reoptimization. We then consider two reoptimization scenarios: (1) on demand (p-cycle-oDRO) and (2) on schedule (p-cycle-oSRO). In addition to the link-based p-cycle, we also study the path-based shared backup path protection scheme.

P2-Cycles: p-Cycles with parasitic protection links

The p-cycle and its Failure Independent Path Protection (FIPP) extension are known to be efficient and agile protection strategies. The p-cycle is pre-configured such that if there is a failure, only the switches at two end nodes need to be reconfigured. In this paper, we extend the p-cycle by allowing cycles to have attached links, called Parasitic Protection Links (PPL), in order to protect paths whose source and destination nodes are not only located on the cycle but also connected by a PPL to the cycle. A p-cycle with PPL is named p2-cycle.We address the unicast service protection problem against single-link failures by using p2-cycle in mesh networks for both static and dynamic traffic scenarios. In the static case, the problem is formulated as an Integer Linear Program (ILP). We further propose two p2-cycle based heuristic algorithms, Strict Routing Protection (SRP) and Flexible Routing Protection (FRP), to address the dynamic traffic case. The numerical results show that the p2-cycle scheme provides better capacity efficiency than the FIPP p-cycle scheme in all the traffic scenarios considered and achieves only less than 1% extra total cost over the optimum in COST239, provided by Shared Backup Path Protection (SBPP) approach when the traffic load is high. We also study the failure recovery performance in terms of average number of switch reconfigurations (NOR), and show that the performance of the p2-cycle becomes much better than that of SBPP and gets close to FIPP as the traffic demand increases. In the dynamic case, both SRP and FRP outperform FIPP p-cycle schemes in terms of blocking probability in most scenarios considered. In general, the p2-cycle protection scheme outperforms the p-cycle based in terms of capacity efficiencies which being slightly slower in terms of traffic recovery speed.

Dynamic connection provisioning with shared protection in IP/WDM networks

SUMMARYInternet protocol (IP) traffic connections arrive dynamically at wavelength‐division multiplexing (WDM) network edges with low data rates compared with the wavelength capacity, availability, and quality‐of‐service (QoS) constraints. This paper introduces a scheme to be integrated into the control and management plane of IP/WDM networks to satisfy the availability and QoS required for IP traffic connections bundled onto a single wavelength (lightpath) in WDM networks protected by shared‐backup path protection (SBPP). This scheme consists of two main operations: (i) routing multi‐granular connections and traffic grooming policies, and (ii) providing appropriate shared protection on the basis of subscribers’ service‐level agreements in terms of data rate, availability, and blocking probability. Using the Markov chain process, a probabilistic approach is developed to conceive connection blocking probability models, which can quantify the blocking probability and service utilization of M:N and 1:N SBPP schemes. The proposed scheme and developed mathematical models have been evaluated in terms of bandwidth blocking ratio, availability satisfaction rate, network utilization, and connection blocking probability performance metrics. The obtained research results in this paper provide network operators an operational setting parameter, which controls the allocation of working and backup resources to dynamic IP traffic connections on the basis of their priority and data rate while satisfying their requirements in terms of bandwidth and availability. Copyright © 2013 John Wiley & Sons, Ltd.

Spare capacity allocation using shared backup path protection for dual link failures

This paper extends the spare capacity allocation (SCA) problem from single failures to dual link failures on mesh-like IP or WDM networks. The SCA problem pre-plans traffic flows with mutually disjoint one working and two backup paths using the shared backup path protection (SBPP) scheme. The spare provision matrix (SPM) method aggregates per-flow based information and computes the shared spare capacity for dual link failures. When compared to previous two-flow based methods, it has better scalability and flexibility. The SCA problem is formulated as a non-linear integer programming model and partitioned into two sequential linear sub-models: one finds all primary backup paths, and the other finds all secondary backup paths. We extend the terminologies in the 1+1 and 1:1 link protection for the backup path protection: using “:” to indicate backup paths with shared spare capacity; and using “+” to indicate backup paths with dedicated capacity. Numerical results from five networks show that the network redundancy of the 1+1+1 dedicated path protection is in the range of 313–400%. It drops to 96–180% in the 1:1:1 shared backup path protection without loss of dual-link resiliency, but with the trade-off of the highest complexity on spare capacity shared by all backup paths. The 1+1:1 hybrid path protection provides intermediate redundancy at 187–310% with the moderate complexity. It has dedicated primary backup paths and shared secondary backup paths. We also compare passive sharing with active sharing. They perform spare capacity sharing either after or during the backup path routing, i.e., the active sharing approach performs share spare capacity within the backup path routing, while the passive sharing does so only after all backup paths are found. The active sharing approaches always achieve lower redundancy values than the passive sharing. The reduction percentages are about 12% for 1+1:1 and 25% for 1:1:1 respectively. The extension of the Successive Survivable Routing (SSR) heuristic algorithm to the dual failure case is given and the numerical results show that SSR maintains a 4–11% gap from optimal on small or medium networks, and scales up well on large networks.

Fast Efficient Design of Shared Backup Path Protected Networks Using a Multi-Flow Optimization Model

Core communication networks have seen significant traffic increases in recent years, and availability requirements also continue to increase. This fact has led to a wide array of network design improvements, particularly in the area of network survivability. The various survivability mechanisms and accompanying design models that have been developed use diverse strategies to provision spare capacity throughout a network to restore traffic in case of a failure. The break of a fiber line continues to be the most common type of network failure, and this paper addresses at a common protection mechanism called shared backup path protection (SBPP), which is quite efficient at dealing with this type of failure. SBPP is a popular survivability mechanism, and there has been a significant amount of work done with it in recent years. However, the SBPP integer linear program (ILP) design model has proven difficult to solve using reasonable computing and time resources. While many algorithms and heuristics have been developed to design SBPP-based networks, it has been difficult to know how well these designs perform compared to ILP optimized networks. This paper presents a new SBPP-type protection mechanism and accompanying ILP model that solves in a couple orders of magnitude less time than the benchmark approach by allowing multiple working and backup routes (we compare to one representative version of the traditional approach as our benchmark). This new mechanism and accompanying model will allow better benchmarking of SBPP-like network designs, and enhance further study into the performance of SBPP relative to other network survivability approaches.

Overlay Protection Against Link Failures Using Network Coding

This paper introduces a network coding-based protection scheme against single- and multiple-link failures. The proposed strategy ensures that in a connection, each node receives two copies of the same data unit: one copy on the working circuit and a second copy that can be extracted from linear combinations of data units transmitted on a shared protection path. This guarantees instantaneous recovery of data units upon the failure of a working circuit. The strategy can be implemented at an overlay layer, which makes its deployment simple and scalable. While the proposed strategy is similar in spirit to the work of Kamal in 2007 2010, there are significant differences. In particular, it provides protection against multiple-link failures. The new scheme is simpler, less expensive, and does not require the synchronization required by the original scheme. The sharing of the protection circuit by a number of connections is the key to the reduction of the cost of protection. This paper also conducts a comparison of the cost of the proposed scheme to the 1 + 1 and shared backup path protection (SBPP) strategies and establishes the benefits of our strategy.

Performance Evaluation of Impairment-Aware Routing Under Single- and Double-Link Failures

This work evaluates the performance of an impairment-aware routing (IAR) scheme in the presence of single- and dual-link failures. Network resilience is provided through a shared backup path protection scheme, enhanced with a reinforced sharing mechanism. The results indicate that the IAR scheme provides significantly lower connection blocking compared with traditional minimum-hop routing because physical impairments have a significant contribution to the overall network blocking probability. Dual-link failures are also considered, and the performance of a network designed to be resilient to single-link failures is evaluated. Simulation results show low connection loss rates due to dual failures that can be further improved using a restoration mechanism activated on the occurrence of dual failures.

Spare capacity reprovisioning for high availability shared backup path protection connections

Shared backup path protection (SBPP) has been widely studied in the Generalized MPLS (GMPLS) networks due to its efficient spare capacity sharing as well as simplicity and flexibility in service provisioning. This paper presents a novel availability evaluation strategy for the end-to-end (E2E) availability of an SBPP connection by considering up to two simultaneous failures, where the sequence of failures in a failure pattern is considered. To minimize the redundancy while meeting the E2E availability requirement, partial restoration is defined and embedded in the developed model, by which a novel parameter, called a protection level, is manipulated. Based on the proposed availability model, two Linear Program (LP) formulations are introduced, which aim to perform spare capacity reprovisioning along each link for dynamic allocation of SBPP connections under either failure-dependent or failure-independent policies. Extensive simulations are conducted to validate the proposed availability model and demonstrate the effectiveness of the spare capacity reprovisioning architecture. The proposed availability-aware spare capacity reprovisioning approaches are then implemented on top of a well known survivable routing scheme – Successive Survivable Routing (SSR), where the spare capacity saving ratio is taken as the performance measure. We will show that the proposed spare capacity reprovisioning framework is an effective approach for achieving the GMPLS-based recovery in packet-switched networks.

Spare Capacity Reprovisioning for Shared Backup Path Protection in Dynamic Generalized Multi-Protocol Label Switched Networks

Spare capacity allocation serves as one of the most critical tasks in dynamic GMPLS networks to meet the stringent network availability constraint stipulated in the SLA of each connection. In this paper, an availability-aware spare capacity reconfiguration scheme based on shared backup path protection (SBPP) is proposed, aiming to guarantee the E2E availability of each LSP. We first provide an E2E availability model for a SBPP connection that is composed of a working and a SRG-disjoint shared backup LSP pair in the presence of all possible single, and dual simultaneous failures. Partial restoration is identified to further improve the capacity efficiency, and achieve finer service differentiation. For this purpose, restoration attempt is defined as a parameter for each connection that can be manipulated at the source node when the spare capacity of each link is scheduled. Based on the developed model, a linear program (LP) is formulated to perform inter-arrival spare capacity reconfiguration along each pre-determined shared backup LSP to meet the availability constraint of each connection. Simulation is conducted to verify the derived formulation, and to demonstrate the benefits gained in terms of the spare capacity saving ratio, where the conventional SBPP scheme that achieves 100% restorability for any single failure is taken as a benchmark. We will show that the simulation results validate the proposed E2E availability model, where a significant reduction on the required redundancy can be achieved in the effort of meeting a specific availability constraint for each SBPP connection.

TROP: A Novel Approximate Link-State Dissemination Framework For Dynamic Survivable Routing in MPLS Networks

In this paper, a novel approximate link-state dissemination framework, called TROP, is proposed for shared backup path protection (SBPP) in multiprotocol label switching (MPLS) networks. While performing dynamic explicit survivable routing in a distributed environment, link-state dissemination may cause a nontrivial signaling overhead in the process of exploring spare resource sharing among individual backup label switched paths (LSPs). Several previously reported studies have tackled this problem by initiating a compromise between the amount of dissemination and the achievable extent of resource sharing. The paper first summarizes the previously reported schemes into a compact and general link-state dissemination framework by way of singular value decomposition (SVD). To improve the accuracy of the matrix reconstruction and to eliminate the overestimation of the sharable spare capacity along each link, a novel SVD approach based on the min-plus algebra (also called tropical semirings) is introduced. Simulation results show that the proposed schemes can achieve a lower blocking probability than that by all the other counterpart schemes while taking the same complexity of link-state dissemination. This great advantage is gained at the expense of a longer computation time for solving a linear program (LP) in each dissemination cycle at the core nodes. We also consider the stale link-state phenomena that may cause imprecision in the routing information at the ingress nodes due to the delay in the periodic/event-driven link-state update message advertisement.

Toward jointly optimized design of failure-independent path-protecting p-cycle networks

Failure-independent path-protecting (FIPP) p-cycles are an extension of the basic concept of p-cycles to provide an end-to-end path-protecting mechanism. Initial work showed that FIPP p-cycle networks are comparable in capacity efficiency to existing methods of shared-backup path protection but employ fully pre-cross-connected protection paths. This makes FIPP p-cycles as fast as conventional span protecting p-cycles, and much faster than shared-backup path protection where spare channels must be assembled into protection paths in real time following a failure. The property of full pre-cross-connection of the protection structures is also an attractive advantage in transparent optical networking, where on-the-fly transparent concatenation of wavelength channels to form protection paths may not provide an adequate a priori assurance of optical path integrity. Thus, there are several motivations for interest in this new concept. Prior work on this topic has, however, considered only the design of FIPP p-cycle networks where the working demands are routed before decisions are made about the protection structures. Here we consider the problem of jointly optimized FIPP p-cycle network design and provide some insights, guidelines, and a semiheuristic procedure for coordinated routing of working demands and the generation of the protection structures.

Spare Capacity Allocation in Two-Layer Networks

In this paper we consider the problem of provisioning spare capacity in two-layer backbone networks using shared backup path protection. First, two spare capacity allocation (SCA) optimization problems are formulated as integer linear programming (ILP) models for the cases of protection at the top layer against failures at the bottom layer. The first model captures failure propagation using overlay information between two layers for backup paths to meet diversity requirements. The second model improves bandwidth efficiency by moving spare capacity sharing from the top layer to the bottom layer. This exposes a tradeoff between bandwidth efficiency and extra cross-layer operation. Next, the SCA model for common pool protection is developed to allow spare capacity sharing between two layers. Our previous SCA heuristic technique, successive survivable routing (SSR) is extended for these optimization problems. Numerical results for a variety of networks indicate that the common pool protection is attractive to enhance bandwidth efficiency without loss of survivability and that the SSR heuristic quickly results in near optimal solutions

Connection Availability Analysis of Shared Backup Path-Protected Mesh Networks

Dual-span failures dominate the system unavailability in a mesh-restorable network with full restorability to single-span failures. Traditional availability analysis based on reliability block diagrams is not suitable for survivable networks with shared spare capacity. Therefore, a new concept is proposed to facilitate the calculations of connection availability. A U.S. network consisting of 19 nodes and 28 spans yielding 171 bidirectional connections is investigated. We find that networks with shared backup path protection can have average connection unavailabilities of the same order of magnitude as those with dedicated automatic protection switching, however, with a much better capacity efficiency. The proposed method can exactly calculate the unavailability of a specific connection with known restoration details or the average connection performance without any restoration details by presuming the dual-span failures to be the only failure mode and an arbitrary allocation rule of spare capacity

Failure-independent path-protecting p-cycles: efficient and simple fully preconnected optical-path protection

We propose a new technique for optical-network protection called failure-independent path-protecting (FIPP) p-cycles. The method is based on an extension of p-cycle concepts to retain the property of full preconnection of protection paths, while adding the property of end-to-end failure-independent path-protection switching against either span or node failures. An issue with applying the popular method of shared-backup path protection (SBPP) to an optical network is that spare channels for the backup path must be cross connected on the fly upon failure. It takes time and signaling to make the required cross connections, but more importantly, until all connections are made, it is not actually known if the backup optical path will have adequate transmission integrity. Thus, speed and optical-path integrity are important reasons to try to have backup paths fully preconnected before failure. With fully preconnected protection, not only can very fast restoration be attained, but the optical-path engineering can also be assured prior to failure. Regular p-cycles are fully preconnected, but are not end-to-end path-protecting structures. SBPP is capacity efficient and failure independent-failures only need to be detected at the end nodes and the end nodes activate and switch over to one predefined backup route for each working path-but the backup paths are not preconnected. FIPP p-cycles support the same failure-independent end-node-activated switching of SBPP, but with the fully preconnected protection-path property of p-cycles. As a fully preconnected and path-oriented scheme, FIPP p-cycles are, therefore, potentially more attractive for optical networks than SBPP. Results confirm that FIPP p-cycle network designs will exhibit capacity efficiency that is characteristic of path-oriented schemes and may be as capacity efficient as SBPP, but more conclusive comparisons on larger scale networks await further study.

On the resource efficiency of virtual concatenation in SDH/SONET mesh transport networks bearing protected scheduled connections

Virtual concatenation (VCAT) is a Synchronous Digital Hierarchy (SDH)/Synchronous Optical Network (SONET) network functionality recently standardized by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T). VCAT provides the flexibility required to efficiently allocate network resources to Ethernet, Fiber Channel (FC), Enterprise System Connection (ESCON), and other important data traffic signals. In this article, we assess the resources' gain provided by VCAT with respect to contiguous concatenation (CCAT) in SDH/SONET mesh transport networks bearing protected scheduled connection demands (SCDs). As explained later, an SCD is a connection demand for which the set-up and tear-down dates are known in advance. We define mathematical models to quantify the add/drop and transmission resources required to instantiate a set of protected SCDs in VCAT- and CCAT-capable networks. Quantification of transmission resources requires a routing and slot assignment (RSA) problem to be solved. We formulate the RSA problem in VCAT- and CCAT-capable networks as two different combinatorial optimization problems: RSA in VCAT-capable networks (RSAv) and RSA in CCAT-capable networks (RSAc), respectively. Protection of the SCDs is considered in the formulations using a shared backup path protection (SBPP) technique. We propose a simulated annealing (SA)-based meta-heuristic algorithm to compute approximate solutions to these problems (i.e., solutions whose cost approximates the cost of the optimal ones). The gain in transmission resources and the cost structure of add/drop resources making VCAT-capable networks more economical are analyzed for different traffic scenarios.