Path Restoration Research Articles

Research of the Network Routing Optimization Based on AODV

In the protocol of Ad Hoc network, the AODV routing protocol is the on-demand distance vector routing protocol. Because of its low cost and simple realizing, it is the hot point of wireless ad hoc network researches. This paper researches the mechanism of the AODV routing protocol, analyses its limitations and proposes a pre-judgment based on the link quality. It avoids using the local path restoration algorithm AODV-LQP in unstable area. Before the break of the low quality link, starting the link reparation will avoid the restoration in data transportation. The simulation experiment shows that the improved algorithm reduces the average time delay of end to end, and augments the packet delivery ratio.

Parameterized complexity of spare capacity allocation and the multicost Steiner subgraph problem

We study the computational complexity of the Spare Capacity Allocation problem arising in optical networks that use a shared mesh restoration scheme. In this problem we are given a network with edge capacities and point-to-point demands, and the goal is to allocate two edge-disjoint paths for each demand (a working path and a so-called restoration path, which is activated only if the working path fails) so that the capacity constraints are satisfied and the total cost of the used and reserved bandwidth is minimized. We focus on the setting where we deal with a group of demands together, and select their restoration paths simultaneously in order to minimize the total cost. We investigate how the computational complexity of this problem is affected by certain parameters, such as the number of restoration paths to be selected, or the treewidth of the network graph. To analyze the complexity of the problem, we introduce a generalization of the Steiner Forest problem that we call Multicost Steiner Subgraph. We study its parameterized complexity, and identify computationally easy and hard cases by providing hardness proofs as well as efficient (fixed-parameter tractable) algorithms.

An interpretative structural modeling based network reconfiguration strategy for power systems

The network reconfiguration is an important stage of restoring a power system after a complete blackout or a local outage. Reasonable planning of the network reconfiguration procedure is essential for rapidly restoring the power system concerned. An approach for evaluating the importance of a line is first proposed based on the line contraction concept. Then, the interpretative structural modeling (ISM) is employed to analyze the relationship among the factors having impacts on the network reconfiguration. The security and speediness of restoring generating units are considered with priority, and a method is next proposed to select the generating unit to be restored by maximizing the restoration benefit with both the generation capacity of the restored generating unit and the importance of the line in the restoration path considered. Both the start-up sequence of generating units and the related restoration paths are optimized together in the proposed method, and in this way the shortcomings of separately solving these two issues in the existing methods are avoided. Finally, the New England 10-unit 39-bus power system and the Guangdong power system in South China are employed to demonstrate the basic features of the proposed method.

Two‐stage power network reconfiguration strategy considering node importance and restored generation capacity

Network reconfiguration after complete blackout of a power system is an essential step for power system restoration. A new node importance evaluation method is presented based on the concept of regret, and maximisation of the average importance of a path is employed as the objective of finding the optimal restoration path. Then, a two-stage method is presented to optimise the network reconfiguration strategy. Specifically, the restoration sequence of generating units is first optimised so as to maximise the restored generation capacity, then the optimal restoration path is selected to restore the generating nodes concerned and the issues of selecting a serial or parallel restoration mode and the reconnecting failure of a transmission line are next considered. Both the restoration path selection and skeleton-network determination are implemented together in the proposed method, which overcomes the shortcoming of separate decision-making in the existing methods. Finally, the New England 10-unit 39-bus power system and the Guangzhou power system in South China are employed to demonstrate the basic features of the proposed method.

Experimental Assessment of Bulk Path Restoration in Multi-layer Networks Using PCE-based Global Concurrent Optimization

Generalized multi-protocol label switching-based multi-layer networks (MLN) combining packet and optical switching lead to jointly leverage intrinsic per-layer benefits such as statistical multiplexing and huge transport capacity. By doing so, efficient network resource utilization is attained through MLN traffic engineering (TE) strategies, i.e. grooming. In this context, an optical link failure may cause the disruption of multiple groomed packet label switched paths (LSPs). Thereby, efficient recovery schemes such as restoration are required. In dynamic restoration, the centralized path computation element (PCE) sequentially computes backup paths for the set of failed packet LSPs using the TE database (TED). Since the TED is not updated until an LSP is actually set up, it is very likely that the PCE assigns the same network resources to different backup paths. This does increase resource contention and not fully exploits the potential grooming opportunities among the backup LSPs; consequently, the restorability metric performs poorly. To improve this, a designed PCE global concurrent optimization (GCO) architecture is implemented favoring grooming and lowering resource contention. The addressed problem, referred to as bulk path restoration in multi-layer optical networks (BAREMO), is formally modeled and stated using a mixed integer linear programming formulation. Then, a heuristic algorithm solving the BAREMO problem is devised. The experimental performance evaluation is conducted within the ADRENALINE testbed. Besides validating the PCE GCO architecture, its performance is compared with a sequential PCE for several traffic loads and failure rates. The results show that the PCE GCO improves remarkably restorability compared to the sequential PCE at the expenses, however, of increasing the restoration time.

Quantitative classification and environmental interpretation of secondary forests 18 years after the invasion of pine forests by Bursaphelenchus xylophilus (Nematoda: Aphelenchoididae) in China.

With growing concerns over the serious ecological problems in pine forests ( Pinus massoniana , P. thunbergii ) caused by the invasion of Bursaphelenchus xylophilus (the pine wood nematode), a particular challenge is to determine the succession and restoration of damaged pine forests in Asia. We used two-way indicator species analysis and canonical correlation analysis for the hierarchical classification of existing secondary forests that have been restored since the invasion of B. xylophilus 18 years ago. Biserial correlation analysis was used to relate the spatial distribution of species to environmental factors. After 18 years of natural recovery, the original pine forest had evolved into seven types of secondary forest. Seven environmental factors, namely soil depth, humus depth, soil pH, aspect, slope position, bare rock ratio, and distance to the sea, were significantly correlated with species distribution. Furthermore, we proposed specific reform measures and suggestions for the different types of secondary forest formed after the damage and identified the factors driving the various forms of restoration. These results suggest that it is possible to predict the restoration paths of damaged pine forests, which would reduce the negative impact of B. xylophilus invasions.

Survivable routing and wavelength assignment performance improvement using primary-backup multiplexing with 100% fault recovery guarantee

In this paper, we address the problem of designing survivable optical networks. Path Protection (PP) and Link Protection (LP) schemes are the main means of protecting Wavelength-Division Multiplexed (WDM) networks from the losses caused by a component failure. We here propose to use a new generalization of the PP scheme called Partial Path Protection (PPP). PPP designates a different restoration path for every link failure of every primary path. Based on the PPP scheme, an Integer Linear Programming (ILP) model and a heuristic algorithm are presented to tackle the problem of establishing a set of static connections, referred to as Dependable connections (D-connections), with fault-tolerant requirements under Shared Risk Link Group (SRLG) constraints. Both approaches aim at maximizing the overall network throughput by minimizing the total bandwidth consumption using two resource sharing techniques, namely Primary-Backup Multiplexing (PBM) and Backup-Backup Multiplexing (BBM). To the best of our knowledge, this is the first attempt to combine these two techniques when routing static D-connections and performed in such a way that 100% fault-recovery is still guaranteed for all established connections. Multiple simulation studies have been carried out on different network topologies to evaluate the performance of the proposed solutions. These performance results are also compared to those of previously proposed approaches in the literature, to outline the improvements brought by our approaches.

Hybrid Survivability Schemes Achieving High Connection Availability With a Reduced Amount of Backup Resources [Invited

Maximizing connection availability in wavelength division multiplexing (WDM) networks is critical because even small disruptions can cause huge data losses. However, there is a trade-off between the level of network survivability and the cost related to the backup resources to be provided. One-hundred percent survivability can be achieved by dedicated path protection (DPP) with multiple prereserved protection paths for each provisioned connection, i.e., DPP (1:N). Unfortunately, the blocking probability performance of DPP (1:N) is negatively affected by the large number of prereserved backup wavelengths standing by unutilized. On the other hand, path restoration (PR)-based solutions ensure good blocking performance at the expense of lower connection availability. The work in this paper aims at finding hybrid network survivability strategies that combine the benefits of both techniques (i.e., high availability with low blocking rate). More specifically, the paper focuses on a double link failure scenario and proposes two strategies. The first one couples DPP (1:1) with path restoration (referred to as DPP + PR) to minimize the number of dropped connections. The second scheme adds the concept of backup reprovisioning (BR), referred to as DPP + BR + PR, in order to further increase the connection availability achieved by DPP + PR. Integer linear programming models for the implementation of the proposed schemes are formulated. Extensive performance evaluation conducted in a path-computation-element-based WDM network scenario shows that DPP + BR + PR and DPP + PR can significantly lower the blocking probability value compared to DPP (1:2) without compromising too much in terms of connection availability.

Optimization of Restoration Paths of Power System after Blackout

Optimization of restoration paths of power system after blackout is a multi-stage, multi-target, multi-variable combinatorial problem in the power system restoration. This paper presents a reasonable model and effectually method. The proposed model is considered as a typical partial minimum spanning tree problem from the mathematical point of view which considering all kinds of constraints. Improved data envelopment analysis (DEA) was used to get the weight which considering line charging reactive power, weather conditions, operation time and betweenness of transmission lines. The improved genetic algorithm method is employed to solve this problem. Finally, an example is given which proves the strategy of the line restoration can effectively handle the uncertainty of the system recovery process, to guarantee the system successfully restored after the catastrophic accidents.

Adaptive Spectrum Control and Management in Elastic Optical Networks

Elastic optical networking (EON) has emerged in recent years as a promising solution for implementing flexible bandwidth channels (flexpaths) that efficiently match the allocated bandwidth with the traffic demand using agile granularities of spectrum allocation. However, the additional flexibility in such networks raises challenges in terms of efficient control and management of spectrum resources. Among them, three important issues are (1) mitigation of spectral fragmentation, (2) implementation of impairment awareness and enhancement of robustness against impairments for potentially large-bandwidth flexpaths, and (3) design of an efficient restoration scheme to combat network failures. This paper presents an adaptive spectrum control and management scheme, which includes: dynamic on-demand spectral defragmentation, adaptive combinational quality of transmission (QoT) restoration (ACQR) and supervisory channel-assisted active restoration, to account for the three issues above. We present scalable networking algorithms and experimental demonstrations that address these issues in an EON testbed. Simulation results show that the defragmentation technique is capable of reducing the provisioning blocking probability by half with only one defragmentation module on each link. Then, we also show that the ACQR can efficiently restore many degraded flexpaths on the same impaired link while reducing the restoration blocking probability by a factor of 10 compared with the conventional rerouting method. At last, we show via simulation the advantages of using supervisory channels to determine restoration path quality and selection in EON restorations. This paper also presents experimental demonstrations to corroborate the effectiveness and feasibility of implementing these capabilities in next generation optical networks.

OSNR-based Restoration Algorithm for Optical Network Resilience to Node Failures

In this paper we propose a novel algorithm to restore calls upon a single node failure in all-optical networks. Our proposal aims to restore the maximum number of disrupted lightpaths by each node failure. The algorithm performs a path restoration searching for the route that presents the higher optical signal-to-noise ratio (OSNR). We compared our proposal to three other well-known approaches found in the literature, in two different network topologies. We observed that our proposal obtained lower failure rates in the restoration process for six different analyzed scenarios, considering several physical layer impairments.

Intercycle switching (ICS)-based dynamic reconfiguration of p-cycle for dual-failure survivability of WDM networks

Today, the most promising technique used for the survivability of optical transport networks is p-cycle. However, it provides longer restoration path at failure state of the network. The intercycle switching (ICS) is one of the recent approaches that is based on idle p-cycles and is used for shortening the length of restoration path in single-fault model. Utilization of idle p-cycles degrades the inherent dual-failure restorability of single-failure design model of p-cycle, whereas ICS releases the maximum portion of conventional restoration path by utilizing a small segment of the idle p-cycle. Here, the authors proposed a new approach to reconfiguring the released portion of restoration path and unused segment of corresponding idle p-cycle as new cycle(s). In respect of idle p-cycles, the new reconfigured cycle(s) provides more dual-failure restorability in single-failure design of p-cycle. Therefore, the proposed approach mitigates the above-said drawback of ICS and minimizes additional spare capacity requirement for dual-failure survivability.

Emergency path restoration problems

We consider the problem of optimally scheduling the restoration of edges of a transportation network destroyed/damaged by a disaster. The restoration is performed by service units (servers) which have fixed restoration speeds. If several servers work simultaneously at the same point of the network, their collective restoration speed is the sum of their individual restoration speeds. The servers are initially located at some nodes. Each server can travel within the already restored part of the network with infinite speed, that is, at any time can immediately relocate to another point of the same connected component of the already restored part of the network. It is required to minimize a scheduling objective that can be expressed as the maximum or the sum of nondecreasing functions of the recovery times of the nodes, where the recovery time of a node is the time when the node is reached for the first time by a server. We present polynomial-time algorithms on path networks for problems with fixed initial locations of the servers. For problems with flexible locations that should also be optimized, we present polynomial-time algorithms for the case of equal restoration speeds of the servers, and prove that the problems are strongly NP-hard if the restoration speeds of the servers can be different.

OCC: Ordered congestion control with cross layer support in Manet routing

In the recent times many accessible congestion control procedures have no capability to differentiate involving two major problems like packet loss by link crash and packet loss by congestion. Consequently these resolutions effect in form of wastage of possessions because they target only on the packet drop by link crash that has a needless importance. Consumption of energy and possessions in order to make the basis node attentive regarding the congestion occurring in routing path is the supplementary drawback in most of the accessible procedures. This way of concentrating mainly on standardizing the outlet load at the basis node stage is the boundary to the present accessible procedures. It is already known that as a reason of link crash and congestion packet loss in the network routing largely occurs. In this article a new cross layer and path restoration procedure has been put forward. We also put forwarded two algorithms namely Path discovery Algorithm and congestion handling algorithm. In this approach of cross layer it comprises of 3 kinds of layers called network, MAC and transport layers. In this introduced approach the MAC and network layers have dynamic functionalities in identifying the congestion and standardization where the functionalities of network and transport layers are distinguished in bearing the congestion i.e. congestion endurance. The produced tentative results illustrate an enhanced management of congestion and its endurance by this approach.

End-to-End Restorable Oblivious Routing of Hose Model Traffic

Two-phase routing, where traffic is first distributed to intermediate nodes before being routed to the final destination, has been recently proposed for handling widely fluctuating traffic without the need to adapt network routing to changing traffic. Preconfiguring the network in a traffic-independent manner using two-phase routing simplifies network operation considerably. In this paper, we extend this routing scheme by providing resiliency against link failures through end-to-end shared backup path restoration. We view this as important progress toward adding carrier-class reliability to the robustness of the scheme so as to facilitate its future deployment in Internet service provider (ISP) networks. In shared backup path restoration, each connection consists of a link-disjoint primary and backup path pair; two backup paths can share bandwidth on their common links if their primary paths are link-disjoint. We show that the optimization problem for maximum throughput two-phase routing with shared backup path restoration is NP-hard. Assuming an approximation oracle for a certain disjoint paths problem (called SBPR-DISJOINT-PATHS, which is also NP-hard) involving the dual variables of a path indexed linear programming formulation for the problem, we design a combinatorial algorithm with provable guarantees. We also provide heuristics for finding approximating solutions to the SBPR-DISJOINT-PATHS problem. We evaluate the throughput performance and number of intermediate nodes in two-phase routing for the above and other restoration mechanisms for two-phase routing on actual ISP topologies collected for the Rocketfuel project and three research network topologies.

On Path Restoration for Censored Outcomes

Dimension reduction, model and variable selection are ubiquitous concepts in modern statistical science and deriving new methods beyond the scope of current methodology is noteworthy. This article briefly reviews existing regularization methods for penalized least squares and likelihood for survival data and their extension to a certain class of penalized estimating function. We show that if one's goal is to estimate the entire regularized coefficient path using the observed survival data, then all current strategies fail for the Buckley-James estimating function. We propose a novel two-stage method to estimate and restore the entire Dantzig-regularized coefficient path for censored outcomes in a least-squares framework. We apply our methods to a microarray study of lung andenocarcinoma with sample size n = 200 and p = 1036 gene predictors and find 10 genes that are consistently selected across different criteria and an additional 14 genes that merit further investigation. In simulation studies, we found that the proposed path restoration and variable selection technique has the potential to perform as well as existing methods that begin with a proper convex loss function at the outset.

Star-Block Design in Two-Level Survivable Optical Networks

An efficient fault restoration framework is proposed for accomplishing loopback recovery in optical networks. The pro posed p-cycle-based framework achieves both a minimal spare capacity requirement and a rapid restoration time. In the proposed approach, an algorithm designated as Star-Block is used to simplify the original topology to a 2-connected graph and to partition the graph into multiple blocks, where each block contains a center node and the minimum number of neighboring nodes that collectively form a complete cycle. The simplified graph is then restored to the original topology using conventional graph rules. The Block Selection algorithm is then used to assign the edges be longing to multiple blocks to an appropriate block for fault recovery purposes. Within each block, the working flows are restored in real-time via local p-cycles on the on-cycle and spoke fibers. The performance of the proposed protection framework is evaluated numerically in terms of the spare capacity to working capacity ratio and the length of the restoration path. The framework has a better spare capacity efficiency than existing loopback recovery schemes or the conventional p-cycles approach. In addition, the Star-Block decomposition algorithm shortens the average length of the restoration path and therefore reduces the restoration time. Finally, the protection scheme not only provides a differentiated recovery service for traffic with different QoS requirements in the event of single-link failures within a single block, but also supports multiple-fault restoration for the case in which multiple single-link failures occur simultaneously.

Path Restoration Schemes for MPLS Networks

The authors have presented an overview and simulation of several path restoration schemes for MPLS networks. Each scheme has its own advantages and disadvantages that make them appropriate for different applications. These characteristics include recovery time in case of failure, packet loss, packet reordering, and recovery delay. The decision of implementing some of these schemes in a real network depends on how much resources are available and the requirements of the network user's. Furthermore, simulation results based on OMNET+ + show that the simple dynamic scheme has the lowest arrival time when compared to the other reported path restoration schemes. Future work will be focused on investigating further comparisons and enhancements of these schemes.

Fast Simulation of Service Availability in Mesh Networks With Dynamic Path Restoration

A fast simulation technique based on importance sampling is developed for the analysis of path service availability in mesh networks with dynamic path restoration. The method combines the simulation of the path rerouting algorithm with a “dynamic path failure importance sampling” (DPFS) scheme to estimate path availabilities efficiently. In DPFS, the failure rates of network elements are biased at increased rates until path failures are observed under rerouting. The simulated model uses “failure equivalence groups,” with finite/infinite sources of failure events and finite/infinite pools of repair personnel, to facilitate the modeling of bidirectional link failures, multiple in-series link cuts, optical amplifier failures along links, node failures, and more general geographically distributed failure scenarios. The analysis of a large mesh network example demonstrates the practicality of the technique.

PTDF-Based Automatic Restoration Path Selection

After a power system blackout, system restoration is a critical task for the dispatchers. With the stringent requirements for faster and more efficient system restoration, an objective transmission restoration path selection procedure, including the option to check constraints, may be more responsive in handling unexpected system changes and in providing directed guidance to the dispatchers to identify the optimal transmission path and to deliver power to other power plants or to pick up load as needed. This paper presents a power transfer distribution factor (PTDF)-based path selection approach for large-scale power systems. Two types of restoration performance indices are utilized considering all possible restoration paths, which are then ranked according to their expected performance characteristics as reflected by the restoration performance index. PTDFs and weighting factors are used to determine the ordered list of restoration paths, which can enable the load to be picked up by lightly loaded lines or relieve stress on heavily loaded lines. Test results which are primarily concerned with load restoration in the outaged system are provided based on a realistic restoration exercise for the Western region of the Entergy transmission system.