Backup Paths Research Articles

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.

Cost-Effective Survivable Virtual Optical Network Mapping in Flexible Bandwidth Optical Networks

This paper addresses the minimum network cost problem for survivable virtual optical network mapping in flexible bandwidth optical networks. For each virtual link, we provide dedicated-path protection, i.e., primary path and backup path, to guarantee high survivability on the physical network. To simplify the virtual links mapping, an extended auxiliary graph is constructed by coordinating the virtual optical network and the physical network. We develop an integer linear program (ILP) model, the LBSD (the largest bandwidth requirement (LB) of virtual links versus the shortest distance (SD)) mapping approach, the LCSD (the largest computing (LC) resources requirement versus the shortest distance) mapping approach to minimize the network cost for a given set of VONs. For comparison, we also introduce one baseline mapping approach, named LCLC (the largest computing resources requirement versus the largest computing resources (LC) provisioning), and the lower bound. Simulation results show that, comparing to the LCLC mapping approach, the ILP model, the LBSD and LCSD mapping approaches not only solve the problem of minimizing the total network cost but also guarantee that the spectrum usage and the number of regenerators are minimum. The ILP model and the LBSD mapping approach are greatly close to a lower bound of network cost and perform the same results as a lower bound of spectrum usage in both the 6-node network and the 14-node network. As a result, our proposed LBSD mapping approach can efficiently reduce the network cost, spectrum usage, and the number of regenerators, which is near the optimal solutions of the ILP model.

Power-aware virtual optical network provisioning in flexible bandwidth optical networks [Invited

Considering the virtual network infrastructure as a service, optical network virtualization can facilitate the physical infrastructure sharing among different clients and applications that require optical network resources. Obviously, mapping multiple virtual network infrastructures onto the same physical network infrastructure is one of the greatest challenges related to optical network virtualization in flexible bandwidth optical networks. In order to efficiently address the virtual optical network (VON) provisioning problem, we can first obtain the virtual links' order and the virtual nodes' order based on their characteristics, such as the bandwidth requirement on virtual links and computing resources on virtual nodes. We then preconfigure the primary and backup paths for all node-pairs in the physical optical network, and the auxiliary graph is constructed by preconfiguring primary and backup paths. Two VON mapping approaches that include the power-aware virtual-links mapping (PVLM) approach and the power-aware virtual-nodes mapping (PVNM) approach are developed to reduce power consumption for a given set of VONs in flexible bandwidth optical networks with the distributed data centers. Simulation results show that our proposed PVLM approach can greatly reduce power consumption and save spectrum resources compared to the PVNM approach for the single-line rate and the mixed-line rate in flexible bandwidth optical networks with the distributed data centers.

A Dynamic Backup Path Management Method for TDMA Based WiMAX Client WMNs

This paper proposes a backup path management method for time division multiple access (TDMA) based client wireless mesh networks (WMNs). In a TDMA based client WMN, as links/nodes fail or as nodes perform handover and as flows enter and leave the network, the paths between various nodes change as well as the bandwidth available along these paths. In these networks, to support the quality of service requirements of flows, backup paths with the required bandwidth need to be established dynamically. Some methods are proposed in the literature to establish backup paths which handle link/node failures and node handover in ad hoc networks, but none of these methods can provide backup paths with the required bandwidth dynamically. To address that issue, the present paper proposes a backup path management method which is adaptive to both topological changes and traffic changes in a network. Each node along the current path between a source and a destination finds backup paths with the required bandwidth in order to handle failure of the link to its downstream node and its own failure or handover. Nodes use two-hop neighborhood information and slots status information of two-hop neighbors to establish backup paths. We prove that the number of backup paths available when a node N searches for backup paths to handle its own failure are more than the number of backup paths available when some other node searches for the backup paths for the failure of node N. Performance of the proposed method is compared with the performance of a naive path management (NPM) method in which always the source establishes backup paths whenever a link/node fails or a node performs handover, and also with the performance of a backup path management method proposed in the literature. The proposed method significantly outperforms the NPM method and the method selected from the literature. For example, when the speed of the mobile nodes is 50 m/s, the packet delivery ratio with the proposed method is 63 % more than the NPM method and 35 % more than the method selected from the literature.

Quality of Recovery Evaluation of the Protection Schemes for Fiber-Wireless Access Networks

AbstractWith the rapid development of fiber-wireless (FiWi) access network, the protection schemes have got more and more attention due to the risk of huge data loss when failures occur. However, there are few studies on the performance evaluation of the FiWi protection schemes by the unified evaluation criterion. In this paper, quality of recovery (QoR) method was adopted to evaluate the performance of three typical protection schemes (MPMC scheme, OBOF scheme and RPMF scheme) against the segment-level failure in FiWi access network. The QoR models of the three schemes were derived in terms of availability, quality of backup path, recovery time and redundancy. To compare the performance of the three protection schemes comprehensively, five different classes of network services such as emergency service, prioritized elastic service, conversational service, etc. were utilized by means of assigning different QoR weights. Simulation results showed that, for the most service cases, RPMF scheme was proved to be the best solution to enhance the survivability when planning the FiWi access network.

Bulk Restoration for SDN-Based Transport Network

We propose a bulk restoration scheme for software defined networking- (SDN-) based transport network. To enhance the network survivability and improve the throughput, we allow disrupted flows to be recovered synchronously in dynamic order. In addition backup paths are scheduled globally by applying the principles of load balance. We model the bulk restoration problem using a mixed integer linear programming (MILP) formulation. Then, a heuristic algorithm is devised. The proposed algorithm is verified by simulation and the results are analyzed comparing with sequential restoration schemes.

Attack-Aware Dedicated Path Protection in Optical Networks

Due to the high data rates in optical networks, physical-layer attacks targeting service degradation, such as power jamming, can potentially lead to large data and revenue losses. Conventional network survivability approaches which establish link-disjoint working and backup paths to protect from component faults may not provide adequate protection for such attacks. Namely, the working and the backup paths, although link-disjoint, might both be affected by a single attack scenario due to specific attack propagation characteristics. To enhance the existing survivability approaches, we utilize the concept of an attack group (AG) which incorporates these characteristics to identify connections which can simultaneously be affected by a single attack. We apply this concept to dedicated path protection (DPP) and develop attack-aware DPP (AA-DPP) approaches which aim to establish AG-disjoint primary and backup paths in a cost-effective manner. We provide a two-step ILP formulation for the routing and wavelength assignment of the working and backup paths, as well as a heuristic for larger problem instances. Numerical results indicate that the proposed approaches provide dedicated path protection schemes with enhanced attack protection without using more resources (i.e., wavelengths, average path lengths) than standard DPP methods.

Fault Tolerant Tree Management for Node Failures in Wireless Sensor Network

Today, Wireless Sensor Network (WSN) is a vital technology required in every phase of development. During data aggregation in Wireless Sensor Network (WSN), there may be possibility of various types of failures. Apart from hardware failures, failures may occur due to bad channel conditions and energy drain. Hence a routing tree should be built towards each sink which is fault tolerant. In this study, we propose to develop a fault tolerant tree management technique in which every node selects a path towards the sink effectively and also maintains a backup path simultaneously. This can be achieved by mutual communication between the neighboring nodes in the network. The backup path is selected based on the link quality, residual energy and load metrics. Simulation results show that the proposed technique reduces the delay and overhead and improves packet delivery ratio.

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.

Lexicographical minimization of routing hops in hop-constrained node survivable networks

In this paper, we address a hop-constrained node survivable traffic engineering problem in the context of packet switched networks with source based routing. Consider a telecommunications network with given link capacities that was dimensioned for a set of commodities, with estimated demand values, such that each commodity demand is routed through a set of node disjoint service and backup paths, all with at most H hops. When the network is put in operation, the real demand values might be different from the initial estimated ones. So, we aim to determine a set of hop-constrained service and backup paths for each commodity, with known demand values, such that the whole set of paths does not violate the link capacities. The traffic engineering goal is related with the hop minimization of only the service paths. We aim to minimize the number of routing hops in a lexicographical sense, i.e., minimize the number of service paths with the worst number of hops; then, among all such solutions, minimize the number of service paths with the second worst number of hops; and so on. We address two traffic engineering variants: in the first variant, all service paths of each commodity are accounted for in the objective function while in the second variant only the worst service path of each commodity is accounted for in the objective function. We first present and discuss three classes of Integer Linear Programming hop-indexed models--disaggregated, mixed and aggregated--for both variants. Then, we prove that, although the three classes are not equivalent, they provide the same Linear Programming relaxation bounds for each variant. Finally, we present computational results showing that, as a consequence, the more compact aggregated models are more efficient in obtaining the optimal integer solutions.

A Robust Optimization Approach to Backup Network Design With Random Failures

This paper presents a scheme in which a dedicated backup network is designed to provide protection from random link failures. Upon a link failure in the primary network, traffic is rerouted through a preplanned path in the backup network. We introduce a novel approach for dealing with random link failures, in which probabilistic survivability guarantees are provided to limit capacity overprovisioning. We show that the optimal backup routing strategy in this respect depends on the reliability of the primary network. Specifically, as primary links become less likely to fail, the optimal backup networks employ more resource sharing among backup paths. We apply results from the field of robust optimization to formulate an ILP for the design and capacity provisioning of these backup networks. We then propose a simulated annealing heuristic to solve this problem for large-scale networks and present simulation results that verify our analysis and approach.

MANET환경에서 Interrupt Message와 Backup path 기법에 기반한 AODV의 성능개선

MANET 환경에서 빈번한 경로 단절은 반복된 경로 탐색으로 인해 제어 패킷 오버헤드와 패킷 손실을 증가시킨다. AODV-I는 event driven방식을 이용하여 주기적인 Hello 메시지를 제거함으로써 AODV의 성능을 개선하였다. Hello 메시지와 달리 각 이벤트마다 전송되는 인터럽트 메시지는 이웃노드의 상태를 알 수 있어 링크 단절을 탐지 및 예측도 할 수 있다. 따라서 AODV-I의 성능은 각 인터럽트 메시지 종류에 따라 처리 절차를 추가함으로써 더욱 개선될 수 있고, 또한 AODV의 단일경로로 인한 문제를 백업 경로기법을 추가하여 개선하는 것도 가능하다. 본 연구에서는 경로 탐색 수와 전송 지연을 줄이기 위해 개선된 백업 경로방식과 인터럽트 메시지 방식을 결합한 AODV-IB를 제안한다. AODV-IB는 각 인터럽트 메시지마다 링크 단절 예측과 탐지에 대한 처리 절차를 추가하여 AODV-I를 개선한다. 또한 추가적인 제어 패킷 없이 지연을 최소화하도록 개선한 백업 경로 방식도 구현한다. QualNet 5.0을 사용하여 구현한 시뮬레이션 결과는 AODV-I에 비해 제안하는 AODV-IB가 더 좋은 성능을 나타낸다. In MANET, frequent route breaks lead to repeated route discovery process and this increases control packet overhead and packet drop. AODV-I improves performance of AODV by using the event driven approach which removes periodic Hello message. Unlike the Hello message, Interrupt message which is sent for each event can detect and predict the link failure because it allows node to know the status of the neighbor node. From this characteristics of Interrupt message, performance of AODV-I can be further improved by adding a processing procedures for each type of Interrupt message and it is also possible to improve AODV-I by adding the Backup path scheme because it originally has problems due to a single path of AODV. In this paper, we propose AODV-IB that combines improved Backup path scheme and Interrupt message approach of AODV-I in order to reduce transmission delay and the number of route discoveries. AODV-IB improves AODV-I by adding proper processing procedures for the link failure prediction and detection for each Interrupt message. We also implement improved Backup path strategy in AODV-IB by minimizing delay without additional Control packet. Simulation results, using the simulator QualNet 5.0, indicate that proposed AODV-IB performs better than AODV-I.

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.

A Novel Protection Guaranteed, Quality of Transmission Aware Routing and Wavelength Assignment Algorithm for All-optical Networks

Transparent All Optical Networks carry huge traffic and any link failure can cause the loss of gigabits of data; hence protection and its guarantee becomes necessary at the time of failure. Many protection schemes were presented in the literature, but none of them speaks about protection guarantee. Also, in all optical networks, due to absence of regeneration capabilities, the physical layer impairments(PLI) accumulates along the lightpaths (LP) which causes sharp degradation of the Quality of Transmission (QoT), as measured by signal bit error rates (BER). The problem of protection with QoT issues was rarely studied in the literature. In this work, a novel protection backup path ensured, QoT aware Routing and Wavelength Assignment (RWA) algorithm called “Virtual Lit –Exhaustive Highest Q factor” (V-Lit EHQ) is presented which exhibits desirable qualities for reliable network operation. The results of the proposed work are compared with the standard QoT aware versions of the Shortest Path-First Fit schemes for both lit and dark protection. The blocking probability (BP) and BER are taken as the performance matrices and the proposed algorithm found to be outperforming as shown through simulations.

Bandwidth-adaptability protection with content connectivity against disaster in elastic optical datacenter networks

Due to disasters in communication networks, the risk of large-scale failure is on the rise. Hence, how to recover failed requests caused by disaster with minimum spectrum resources is an important issue for network operators. In the past years, elastic optical networks provide a new way to reduce the spectrum consumption in optical networks. Based on the technology, bandwidth-adaptability protection with content connectivity (BCP) is proposed in this study. We first introduce the concept of BCP, which includes path calculation and spectrum allocation. For path calculation, working path and backup path employ links in different shared risk link groups to avoid disaster failure in optical networks. For spectrum allocation, modulation format of backup path is adjusted according to the requirement of point-to-content requests to reduce the spectrum consumption. Then, an integer linear program and two heuristic algorithms (BCP_KSP, BCP_MSP) are proposed for static and dynamic traffic scenarios, respectively. Simulation results show that, compared to traditional method without bandwidth adaptability, BCP has better performance in terms of spectrum resource utilization and blocking probability.

OPTIMIZATION OF DISJOINTS FOR MINIMIZATION OF FAILURE IN WDM OPTICAL NETWORK

In an optical network, the fiber optic cable is used for communication between the nodes in a network by passing lights. The main problem in optical network is finding the link disjoints as well as optimal solution for the disjoints. To tolerate a single link failure in the network, the enhanced active path first algorithm is used which computes the re-routed back-up path. The multiple link failure in a network called fibre span disjoint path problem is solved using integer linear programming algorithm. The loop back recovery is used to provide pre-planned recovery of link or node failures in a network which allows dynamic choice of routes over pre-planned directions. Considering reliability in a mesh networks, the reliability algorithm helps to achieve the maximum reliability in two-path protection. It addresses the multiple disjoint failures that arise in a network and discusses the best solution between paths shared nodes or links. The unified algorithm is used to generate the optimal results with minimum cost for multiple link failures. The heuristic algorithm namely maximum arbitrary double-link protection algorithm helps to pre-compute the back-up path for double-link failures. In all the above approaches the shortest optimized path must be improved. To find the best shortest path, link-disjoint lightpath algorithm is designed to compute the disjoint occurred in a network and it also satisfies the wavelength continuity constraint in wavelength division multiplexing. A polynomial time algorithm Wavelength Division Multiplexing – Passive Optical Networking is used to compute the disjoint happen in the network. The overall time efficiency is analyzed and performance is evaluated through simulations.

Green IP over WDM mesh networks with connection availability guarantee

Energy efficiency has been well recognized as an important objective in IP over WDM mesh networks. In this paper, we study the problem of green IP over WDM mesh networks with connection availability guarantee under static traffic demands. We first present a virtual link power model for the two-layer networks, which is built on the power consumption value of the commercial network devices. Based on the energy-aware two-layer auxiliary graph, we propose a new heuristic algorithm named Availability-Guaranteed Energy-Efficient Design for Two-Layer Optical Networks (AGED_TON). The AGED_TON algorithm first constructs initial energy-efficient virtual topology on which connection requests are carried, and then routes working path and backup path of lightpaths on physical topology. In the procedure of AGED_TON algorithm, connection availability is considered for path calculating to achieve a good tradeoff between connection availability and energy efficiency. Compared with previous green networking algorithms, our proposed AGED_TON algorithm reduces energy consumption significantly and guarantees connection availability at the satisfactory level.

Mitigation fault of node mobility for the MANET networks by constructing a backup path with loop free: enhance the recovery mechanism for pro-active MANET protocol

The performance implications of link or node failures in Mobile Ad-hoc Network (MANET) networks are studied in details. Several recovery mechanisms are proposed to reduce the impact of failure and guarantee a loop-free in the network. These mechanisms seek to reduce recovery time, which remains undesirably long in the current routing protocols in wired and wireless networks. Hence, we evaluate the efficiency of the Optimized Link State Routing Protocol with and without recovery paths under varying environment with different node densities. In addition, the mobility of nodes is changing the speed movements when they start to move from area to another one. This paper assists in ascertaining the effect of varying node densities on the connectivity's life between mobile nodes in the network. Hence, it showed the effect of a local recovery mechanism resulted in achieving a significant improvement in network performance by seeking a long life backup path between source and destination for different nodes density. Real time applications are required to be supported by mobile ad hoc networks by finding an efficient recovery mechanism. This is because the MANET networks allow the nodes to move from one area to another without any notification. The real time applications traffics are considered as a sensitive application, and it is the most affected by failure through the occurrence of delay and loss of packets. It is, therefore, not suitable for use by players. In mobile ad hoc networks, routing protocol functions are based on many factors, such as, node mobility and density and broken paths. According to these factors, the paper was further extended to develop a recovery mechanism in MANET based on the mobility and density of nodes to alleviate the impact of the frequent loss of connection due to the flexibility of free nodes, which move from one area to another without pre-notification. The aim behind recovery mechanism is to reduce current recovery time to enhance the Quality of Service in the MANET.

Independent Transient Plane Design for Protection in OpenFlow-Based Networks

Network protection against link failure is required to allow packets to reach the destination with minimal packet loss when a failure occurs. When a link fails, traffic that attempts to use the failed link is interrupted. Typically, routers in the network discover the failure and find a new route to bypass the failed link. Alternatively, well-known segment protection schemes can also be used to speed up the link recovery time by rerouting packets locally through precalculated protection paths. However, several backup paths have to be prepared for each primary path, making path configuration rather complex and poorly scalable. This paper proposes a design for fast rerouting in an OpenFlow-based network. This new design reduces the number of flow entries and the number of configuration messages needed for network rerouting, which in turn reduces the memory size needed in each switch and the CPU load at the controller. We show empirically and using simulations that our design can reduce the number of flow entries and configuration messages needed by about 60% and 75%, respectively, when compared with an existing OpenFlow-based segment protection design. Furthermore, we implement the proposed design on a pan-European network and show that our design can recover from a link failure in as little as 25 ms.

Mitigation Fault for High and Low Density Nodes over Ad-hoc Networks by using Alternative Backup Paths

Mitigation Fault for High and Low Density Nodes over Ad-hoc Networks by using Alternative Backup Paths