摘要 :
Suppose that a destroyed network needs to be restored by a number of servers (construction crews) that are initially located at some nodes of the network (depots). Each server can restore one unit of length of the network per unit...
展开
Suppose that a destroyed network needs to be restored by a number of servers (construction crews) that are initially located at some nodes of the network (depots). Each server can restore one unit of length of the network per unit of time. When several servers are simultaneously working at the same point, their restoration speeds combine additively. The servers can travel within the already restored part of the network with infinite speed, which means that travel times are negligible with respect to construction times. It is required to minimize the time when each node becomes connected to at least one of the depots. We show that the problem is strongly NP-hard on general networks, and present fast polynomial algorithms for trees and cactus networks which are connected networks where each node and each edge belong to at most one cycle.
收起
摘要 :
Lightpath restoration is an effective approach to guaranteeing a certain degree of survivability hi WDM optical networks. Active restoration (AR) algorithm is a novel lightpath restoration scheme proposed recently [3]. In this pap...
展开
Lightpath restoration is an effective approach to guaranteeing a certain degree of survivability hi WDM optical networks. Active restoration (AR) algorithm is a novel lightpath restoration scheme proposed recently [3]. In this paper, we conduct a deeper study on AR in terms of the performance behavior and develop an analytical model on restoration probability for a optical network adopting AR. Based on the new model, the effects of wavelength channels availability, path-seeking process, wavelength selection algorithm, and the ability of wavelength converters upon restoration probability can be explored.
收起
摘要 :
The ever-increasing demand for network bandwidth makes network survivability an issue of great concern. Lightpath restoration is a valuable approach to guaranteeing an acceptable level of survivability in WDM optical networks with...
展开
The ever-increasing demand for network bandwidth makes network survivability an issue of great concern. Lightpath restoration is a valuable approach to guaranteeing an acceptable level of survivability in WDM optical networks with better resource utilization than that of its protection counterpart. Active restoration (AR) is a newly proposed lightpath restoration scheme [M. Mostafa et al. OSA Journal of Optical Networking, vol. 3, no. 4, pp. 247-260] that combines the best of protection and reactive restoration while avoiding their shortcomings. In this paper, we conduct detailed performance analysis on the restoration probability of AR-based WDM networks. In particular, analytical models of restoration probability are developed respectively for networks with full-wavelength conversion capability and for networks without wavelength conversion capability under different backup path searching schemes. Based on the new models, we investigate the effects of wavelength availability, wavelength conversion capability, path length as well as backup path seeking methods on the restoration probability.
收起
摘要 :
This paper investigates the performance of various schemes for restoration of lightpaths in an optical mesh network. We consider schemes in which backup paths for links or paths are pro-computed, but wavelength assignment is eithe...
展开
This paper investigates the performance of various schemes for restoration of lightpaths in an optical mesh network. We consider schemes in which backup paths for links or paths are pro-computed, but wavelength assignment is either pro-computed (static) or done dynamically upon failure (dynamic). In static restoration we compare the performance of link and path restoration in terms of capacity requirement and restoration time. For the dynamic restoration, we consider several dynamic wavelength reservation schemes such as backward and forward reservation with different portion of wavelength to be reserved in both directions. Their performance is evaluated in terms of restoration speed and restorability. Simulation results indicate that path protection requires less capacity than link protection for 100% restorability, and dynamic restoration with backward wavelength reservation shows better restorability than static restoration schemes, when the extra capacity is relatively small. Forward wavelength reservation shows faster restoration speed with lower restorability than the backward wavelength reservation. In general, the optimal restoration scheme depends on extra capacity available and restoration time limit. (C) 2002 Elsevier Science Inc. All rights reserved. [References: 12]
收起
摘要 :
This paper presents a collection of approximation formulas that allow a network planner to quickly estimate the size of a mesh optical network with limited inputs. In particular, it provides a set of equations that relate number o...
展开
This paper presents a collection of approximation formulas that allow a network planner to quickly estimate the size of a mesh optical network with limited inputs. In particular, it provides a set of equations that relate number of sites, average fiber connectivity, demand load and capacity for various mesh protection architectures. These results can be used to easily and quickly estimate the amount of traffic that can be carried over a given network, or, conversely, given the traffic to be supported, to assess the characteristics of the topology required (in terms of number of nodes, connectivity). Finally, this analysis can be used to estimate the restoration performance that can be expected without resorting to extensive simulation studies.
收起
摘要 :
We consider extensions of the most common mesh-restorable network capacity design formulation that enhance the dualfailure restorability of the designs. A significant finding is that while design for complete dual-failure testorab...
展开
We consider extensions of the most common mesh-restorable network capacity design formulation that enhance the dualfailure restorability of the designs. A significant finding is that while design for complete dual-failure testorability can require up to triple the spare capacity, dual failure restorability can be provided for a fairly large set of priority paths with little or no more spare capacity than required for single-failure restorability. As a reference case we first study the capacity needs under complete dual-failure restorability. This shows extremely high spare capacity penalties. A second design model allows a user to specify a total capacity (or budget) limit and obtain the highest average dual-failure restorability possible for that investment limit. This formulation, and a relationship between dual-failure restorability and availability, can be used to trace-out the capacity-versus-availability trade-off curve for a mesh network. A third design strategy supports multiple-restorability service class definitions ranging from best-efforts-only to an assurance of complete single and dual-failure restorability on a per-demand basis. This lets a network operator tailor the investment in protection capacity to provide ultra-high availability on a service-selective basis, while avoiding the very high investment that would be required to support complete dual-failure restorability of the network as a whole.
收起
摘要 :
Cascading failures are one of the most severe threats to cyber-physical power systems. Most studies explore the cascading failure problem from the attacker's perspective while recovering the system from cascading failures is still...
展开
Cascading failures are one of the most severe threats to cyber-physical power systems. Most studies explore the cascading failure problem from the attacker's perspective while recovering the system from cascading failures is still lacking. This paper proposes a sequential recovery analysis process built within the framework of the cascading failure model, which considers the coupling mechanism of cyber-physical power systems and cascading failures. Then the improved Q-learning based on candidate room and dynamic factor idea of simulated annealing is employed to achieve faster and more efficient identification of optimal recovery sequence for failed lines under resource-limited conditions. Finally, the load recovery performance of four recovery strategies in the single-layer and double-layer systems are compared. The simulation results prove the effectiveness of the proposed sequential recovery process and the recovery strategy based on improved Q-learning.(c) 2022 The Franklin Institute. Published by Elsevier Ltd. All rights reserved.
收起
摘要 :
This study focuses on environmental governance in Rwanda through a social network lens, with the aim to understand actors? connections, their priorities and their values within the restoration landscape at the national, district a...
展开
This study focuses on environmental governance in Rwanda through a social network lens, with the aim to understand actors? connections, their priorities and their values within the restoration landscape at the national, district and community scales in Gatsibo. Diverse, reliable, and resilient networks of information, finance, and seedlings are essential for the restoration movement to be sustainable. The study identifies that key resource flows are not directly accessible to the farmers, who are the key implementers of restoration in Rwanda. The study identifies the need to first understand and then strengthen these networks by mapping actors? resource flows, priorities and values, and then developing a strategy for change. By considering actor networks, restoration interventions can be more efficient regarding resources, collaboration and outreach. Moreover, conflicts and bottlenecks can be more easily anticipated.
收起
摘要 :
Network and load recovery (NLR) during power system restoration is a multi-step mixed-integer nonlinear programming (MINP) problem. The NLR is difficult to be solved as it is NP-hard. Thus, NLR is commonly solved step by step, whi...
展开
Network and load recovery (NLR) during power system restoration is a multi-step mixed-integer nonlinear programming (MINP) problem. The NLR is difficult to be solved as it is NP-hard. Thus, NLR is commonly solved step by step, which is short-sighted and will result in longer restoration time. To obtain a far-sighted NLR plan, this paper proposes an improved two-stage optimization method for NLR. The first stage adopts a mixed-integer linear programming (MILP) model to obtain optimal solutions of integer variables in NIB, namely the load pick-up schedules and transmission line charging schedules. Then in the second stage, a continuous non-linear optimization method based on AC power flow with frequency constraints and load model is established to minimize the restoration duration of the plan generated in the first stage step by step. Case studies are undertaken on a 10 machine 39-bus system and Southeast Hubei Provincial power system of China. Simulation results indicate that the restoration plan obtained from the improved two-stage optimization method is highly effective, while the computational efficient meets the intensive need for restoration scheduling after blackouts.
收起
摘要 :
The span-restorable meta-mesh model was previously designed as a cutting-edge technique that enhanced the spare capacity efficiency in low average nodal degree networks. In this technique, lightpaths that fully traverse chains of ...
展开
The span-restorable meta-mesh model was previously designed as a cutting-edge technique that enhanced the spare capacity efficiency in low average nodal degree networks. In this technique, lightpaths that fully traverse chains of degree-2 nodes are provided with a logical express bypass span allowing a distinction between the internal and external working flow capacity that transit the chain. In the event of span failure, lightpaths which would normally traverse the chain in its entirety are allowed to fail back to its anchor nodes such that only the intrachain flow requires allocation of spare capacity. Previous work on the meta-mesh design considered only single failure restorability. The work herein analyzes dual span failure situations by developing two new integer linear programming models. The first model provides the minimum total cost of designing a meta-mesh network capable of withstanding dual span failure scenarios. The second model offers a maximization of the dual failure restorability by minimizing the number of nonrestored working capacities with a given limit of total spare capacity investment. Experiments are performed on six master test-case networks of various topologies and scales.
收起
原文获取