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Quantum key distribution (QKD) can protect the exchange process of confidential information between communicating parties. By using the basic principles of quantum mechanics and combined with "one-time pad" cipher encryption, information can be unconditionally secure. The BB84 protocol first describes the method of transmitting information by photon polarization state, and it expounds the transmission process of services between trusted relays. However, due to the defects of real experimental devices, there are security vulnerabilities in QKD in a real system. The birth of measurement-device-independent quantum key distribution (MDI-QKD) protocol solves the problem, providing immunity to hacker attacks at the end of the detector. It can enable both sides of the transmission service to establish a connection and generate secret keys through an untrusted relay node to ensure information security. However, the types and properties of link nodes in quantum key distribution network (QKDN) based on partially trusted relay are more complex, which can easily result in network fault. Therefore, how to prevent the impact of failure on QKDN has become an urgent problem. In this paper, we propose a protection scheme for QKDN with partially trusted relays. The method deals with trusted and untrusted relays differently and constructs the working and protection paths of the secret key for each service. It reduces resource conflict between the protection and working paths by establishing a key protection threshold, which realizes the resource trade-off between the two factors. Simulation results show that the scheme provides effective protection to the services, and it improves the stability and reliability of QKDN based on partially trusted relay. [ABSTRACT FROM AUTHOR]

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The paper proposes a Fast ReRoute model with the realization of path and bandwidth protection scheme, which can be used in MPLS for SDN. The task of calculating the set of disjoint primary and backup paths during fast rerouting was reduced to solving the optimization problem of Integer Linear Programming. The advantage of the proposed solution is the possibility of implementing 1:1, 1:2, ..., 1:n path protection schemes without the introduction of an additional set of control (routing) variables, which contributes to reducing the dimension of the optimization problem being solved and the computational complexity of its practical implementation. The criterion of optimality of routing solutions contributes to the formation of the primary and backup disjoint paths with the highest possible bandwidth. In this case, the path with the maximum bandwidth will correspond to the primary path, while the remaining paths will be used as backup ones in decreasing order of their bandwidth. The total number of calculated disjoint paths depends on the selected redundancy scheme. The study conducted showed the efficiency and adequacy of the proposed Fast ReRoute model when using various redundancy schemes. [ABSTRACT FROM AUTHOR]

In bufferless optical burst/packet switched (OBS/OPS) networks, data (bursts or packets) may be lost due to contention or equipment failure. Diversity coding-based path protection schemes can be used to protect data from a single-trunk failure with potentially more efficient resource utilization compared to dedicated (e.g., 1 + 1) path protection schemes and help reduce the burst/packet loss ratio. This paper provides a scalable and accurate burst/packet loss ratio approximation based on the Erlang fixed-point approximation for networks that employ protection based on diversity coding and for networks that employ protection based on both diversity coding and 1 + 1 path protection. We use discrete event simulations to assess the accuracy of the approximation based on a wide range of scenarios in a 10-node circular lattice and NSFNet networks. Further, we discuss the effect of parameter settings and the effect of the choice of the wavelength selection method on the accuracy of the approximation. We consider scenarios without wavelength conversion and with full wavelength conversion and two types of users: premium and regular. The premium users, typically of mission critical services, receive protection while the regular users do not. We compare diversity coding and 1 + 1 path protection in a 10-node circular lattice network. The results show that for this example network, for the premium users and under low traffic load, the burst/packet loss ratio in OBS/OPS networks is lower for diversity coding compared to 1 + 1 path protection. However, under heavy traffic load, we observe a lower loss ratio for the case of 1 + 1 path protection. [ABSTRACT FROM AUTHOR]

A multiobjective routing model for multiprotocol label switching networks with multiple service types and path protection is presented in this article. The routing problem is formulated as a biobjective integer program, where the considered objectives are formulated according to a network-wide optimization approach,i.e.the objective functions of the route optimization problem depend explicitly on all traffic flows in the network. A disjoint path pair is considered for each traffic trunk, which guarantees protection to the associated connection. A link-path formulation is proposed for the problem, in which a set of possible pairs of paths is devised in advance for each traffic trunk. An exact method (based on the classical constraint method for solving multiobjective problems) is developed for solving the formulated problem. An extensive experimental study, with results on network performance measures in various randomly generated networks, is also presented and discussed. [ABSTRACT FROM AUTHOR]

Elastic optical networks (EONs) have been pointed out as a promising candidate for transporting data with high transmission rates in adaptive optical networks. Consequently, the occurrence of a failure in a simple element may cause the interruption of various services. Survival mechanisms have been crucial to try to overcome the problems created by possible failures. In this paper, we propose a new dedicated path protection mechanism for link-failure survivability in EONs, referred to as Spectrum Continuity and Contiguity based Dedicated Protection (SCCDP). SCCDP tries to avoid the trap topology problem in search for a link-disjoint route pair. In addition, the calculation of the link-disjoint routes is based on modified version of the Dijkstra's algorithm, referred to as Spectrum Continuity and Contiguity based Shortest Path (SCCSP), which chooses the pair of routes according to the end-to-end spectrum continuity and contiguity. The performance of the proposed algorithm is compared to other well-known algorithms in the Literature. Two different network topologies are used in our simulations for comparison purposes. Our proposal achieved better results concerning blocking probability. [ABSTRACT FROM AUTHOR]

As people become more and more connected to each other through Internet services, the needs to ensure reliability in Internet connection become unavoidable. To serve data traffic with varying degree of importance when maintaining the lowest operational expense is one of challenges faced by network engineers. Critical data traffic must be protected from termination caused by unwanted failures that could happen along the data path, but at the same time, the operational expense spent on the path protection must be kept as minimal as possible. It ensures that the Internet provider can still gain reasonable profits from its services. In this study, the operational expense of the path protection system with partial bandwidth based on the toggling dual cost (TDC) algorithm aims to be optimized. The algorithm is modeled by a Petri net, a powerful tool for modeling asynchronous and concurrent systems. The model is analyzed based on the Petri net properties, namely, boundedness and liveness. Based on boundedness and liveness, the proposed model can have no overflow or deadlock problem in its implementation. The network engineers can optimize the TDC algorithm to maximum efficiency, in order to gain reasonable profits without sacrificing the network reliability. [ABSTRACT FROM AUTHOR]

In this paper, we focus on the survivability of elastic optical networks (EONs) that jointly support two types of traffic demands: unicast and anycast. To provide network survivability, we apply multipath routing; i.e., we allow the splitting of a demand into a number of routing paths if the paths' combination guarantees the realization of a specific demand volume in the case of a single link failure. We formulate the corresponding optimization problem as an integer linear program (ILP) and propose a survivable multipath allocation (SMA) algorithm to solve the problem in a reasonable amount of time. Next, we perform numerical experiments to compare the efficiency (ability to provide a good-quality solution in a reasonable amount of time) of the ILP model and SMA as well as to evaluate the impact of survivable multipath routing on the objective defined as a maximum spectrum usage in EONs. Our results show that the SMA method finds good-quality solutions in a reasonable amount of time and that survivable multipath routing in EONs requires additional spectrum resources, up to 45%. However, the amount of additional resources depends on the required protection level, amount of anycast traffic, the maximum number of paths used for demand realization, and the considered network topology. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

Copyright of Research & Exploration in Laboratory is the property of Research & Exploration in Laboratory and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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:?) 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. [ABSTRACT FROM PUBLISHER]

The path computation element (PCE) enables optimal path computation in single-domain (G)MPLS networks. To overcome the lack of traffic engineering (TE) information in multi-domain networks and to preserve both computation optimality and domain confidentiality, the backward-recursive PCE-based computation (BRPC) procedure has been standardized. BRPC procedure is based on PCE protocol (PCEP) and enables synchronized computation of TE label-switched paths with the requested level of reliability and quality of service requirements (i.e., guaranteed bandwidth). In this paper, the problem of computing $$K$$ -survivable optimal multi-domain paths by resorting to BRPC procedure is analyzed. Extensions to PCEP protocol are discussed to achieve path optimality when domain information is kept confidential. The optimality is theoretically proved, and the computational complexity is shown to be more efficient than existing approaches. The discussed extensions are experimentally validated in an MPLS network test bed based on commercial equipments and are shown to have performance comparable to standard PCEP approach. [ABSTRACT FROM AUTHOR]

Application opportunities associated with video, voice, and data triple-play result in a dramatic demand increase in metro transport networks, with traffic patterns becoming increasingly dynamic and difficult to predict. This is driving the need of core networks with a high degree of flexibility and multigranularities to carry traffic. We propose to investigate the question of what this means in terms of dynamic protection provisioning. In other words, we want to study how stable are the protection structures under dynamic traffic, i.e., how much and how often they need to be updated in a dynamic survivable WDM network. While most studies on the stability of protection structures have been conducted on p-cycles and link shared protection, we propose to investigate here the stability of failure-independent path-protecting (FIPP) p-cycles under dynamic traffic. For doing so, we design and develop an original scalable mathematical model that we solve using large-scale optimization tools. Numerical results show that FIPP p-cycles are remarkably stable under the evaluation of the number of required optical bypass reconfigurations under dynamic traffic. [ABSTRACT FROM AUTHOR]

Path protection ensures continuity of network services against link failure by assigning a link-disjoint secondary path to protect the primary path. Existing path protection schemes are classified into dedicated- and shared-path protections. However, these schemes either require high redundancy or substantial response time to resolve link failure. The end-to-end partial bandwidth protection scheme, denoted as α+1 protection, offers an alternative where only critical real-time information of the primary path is duplicated over the secondary path. The parameter α is defined as the ratio of the protection bandwidth (of secondary path) to the full bandwidth (of primary path). The challenge of α+1 protection is to identify a pair of primary-secondary paths with lowest total cost comprising the optimal solution. This paper derives the properties inherent in the optimal solution and subsequently presents two optimum paths-finding algorithms. The performance of the proposed algorithms over existing approaches is then compared through simulation. [ABSTRACT FROM AUTHOR]

Recently, the need for energy-efficient and sustainable capacity growth has become stringent for telecommunication networks and great efforts have been produced to reduce their power consumption. Optical technologies based on Wavelength Division Multiplexing are well-recognized as a promising solution for greening the future Internet. One relevant approach to achieve such power savings consists in aggregating traffic flows in few network links, so that power can be saved by switching-off some unused network devices. However, the need to ensure network resiliency against link and/or node failures imposes that still the resources reserved to protect connections become available immediately after a failure occurs. Therefore, a possible solution is to set some devices into low-power sleep-mode, so that they can be rapidly re-activated and provide fast connection recovery. In this paper we focus on the power-efficiency of protected IP-over-WDM networks and provide a comprehensive comparison of four different protection strategies, namely Shared-Link, Shared-Path, Dedicated-Link and Dedicated-Path Protection (SLP, SPP, DLP and DPP respectively) in a sleep-mode scenario. In the proposed design strategies we assume that low-power sleep-mode is enabled for devices used for protection. Mathematical models for a power-aware design with sleep-mode is proposed for the four protection strategies. We show that relevant power savings (up to about 60%) can be obtained for all the protection strategies by setting protection devices into sleep-mode. [ABSTRACT FROM AUTHOR]

As optical networks are evolving from traditional opaque networks toward future transparent networks, physical impairments from transmission and switching have become the significant transparent reach limitation for signals. To overcome physical impairments, sparsely deploying optical-electrical-optical regenerators in transparent networks is currently the most economic and reliable solution, namely translucent networks. We study the impairment aware protection issues and propose an impairment aware sharing constraint relaxed path protection (ISRPP) scheme for single-link failures in translucent optical networks. By relaxing the traditional sharing constraint in a limited degree, ISRPP effectively enhances the resource utilization on both wavelengths and regenerators, which contributes to improve the performance of connection blocking probability. Simulation results show that ISRPP can obtain notable resource efficiency and achieve satisfactory tradeoff between blocking probability and vulnerability ratio with respect to its counterpart. [ABSTRACT FROM AUTHOR]

We develop diverse routing schemes for dealing with multiple, possibly correlated, failures. While disjoint path protection can effectively deal with isolated single link failures, recovering from multiple failures is not guaranteed. In particular, events such as natural disasters or intentional attacks can lead to multiple correlated failures, for which recovery mechanisms are not well understood. We take a probabilistic view of network failures where multiple failure events can occur simultaneously, and develop algorithms for finding diverse routes with minimum joint failure probability. Moreover, we develop a novel Probabilistic Shared Risk Link Group (PSRLG) framework for modeling correlated failures. In this context, we formulate the problem of finding two paths with minimum joint failure probability as an integer nonlinear program (INLP) and develop approximations and linear relaxations that can find nearly optimal solutions in most cases. [ABSTRACT FROM PUBLISHER]

With the increase of size and number of shared risk link groups (SRLGs) in WDM networks, path protection tends to have longer working paths and backup paths due to SRLG-disjoint constraints, which makes physical impairment a major concern in working path and backup path provisioning, particularly in large-sized all optical networks. As a simple and efficient algorithm, the working path first algorithm is often used for path protection against SRLG failures, where the working path is calculated first by using the shortest-path algorithm on the graph, followed by using the SRLG-disjoint shortest path as backup path. Compared with the working path, the backup path calculated after the working path in the working path first algorithm is more vulnerable to physical impairment, since it may be much longer than the working path. As a result, if we reject those connections that cannot meet the physical impairment requirement, with SRLGs the blocking probability of path protection will be much higher. We argue that impairment must be taken into account together with capacity efficiency in a comprehensive way during SRLG-disjoint working path and backup path selection. To solve this problem, we motivate the needs to study physical impairment-aware shared-path protection by considering two policies. Policy I uses two SRLG-disjoint least impairment paths as working path and backup path, respectively, and Policy II tries to benefit from both the shortest path and the least impairment path by choosing them intelligently. Analytical and simulation results show: (1) compared with impairment-unawareness, impairment-aware SRLG failure protection performs much better in terms of blocking probability especially with strong physical impairment constraints; (2) impairment-aware SRLG failure protection can significantly reduce physical-layer blocking probability; and (3) the algorithm based on Policy II achieves a good balance between capacity efficiency and physical impairment requirement. [ABSTRACT FROM AUTHOR]

In wavelength division multiplexing (WDM) networks, failures may imply severe loss of data due to the high transmission rates, leading to the need for employment of protective mechanisms. Transparency and switching in all-optical networks cause physical impairment, which can significantly degrade signal quality. If the signal quality along a path is below acceptable values, this path cannot be used for incoming requests in the establishment of lightpaths. Therefore, quality must be checked by the routing and wavelength assignment algorithm. The present article introduces two novel algorithms for shared path protection in WDM networks that take into consideration the Polarization Mode Dispersion, Amplifier Spontaneous Emission, and homowavelength cross-talk physical impairments during path selection. The efficiency of these algorithms is compared to that of their impairment-unaware counterparts. [ABSTRACT FROM AUTHOR]

Failure-Independent Path-Protecting (FIPP) p-cycle is an extension of the span-protecting p-cycle, and an alternative approach for providing fully pre-connected protection paths with end-to-end failure-independent path protection (Kodian and Gorver, J. of Lightwave Technol., vol. 23, no. 10, pp. 324 1-3259). We study the unavailability of end-to-end traffic in FIPP-based mesh networks, which are designed to protect against single failures, and present an availability-aware network design method. Our design method allocates FIPP p-cycles such that the end-to-end unavailability of the protected demands is bounded by an upper limit which we can control. Our study will also focus on determining whether FIPP p-cycles will maintain their resource efficiency advantages over span p-cycles when the network design is based on limiting the unavailability. Our results first show that the length of the FIPP p-cycle plays a vital role in determining the avail- ability of the working path(s). Similar to span-protecting p-cycles, higher service working path(s) availability is obtained when the FLPP p-cycle(s) contains fewer hops. Results also indicate the important role of the number of demands protected by the same FIPP p-cycle. We notice that the higher the desired availability is, the less efficient the FIPP method becomes. This relationship is due to the fact that, to achieve higher service availability, the design will limit the number of demands sharing the same FIPP cycle. Accordingly, we affirm that, when the network design limits the service unavailability, FIPP tends to be less efficient, and its redundancy is 8-13% higher than span-protecting p-cycles. Additionally, we observe that, when we do not limit the unavailability, the average availability for span-protecting p-cycles tends to be more than the FIPP p-cycle method. We present our findings. [ABSTRACT FROM AUTHOR]

This paper develops a framework to support multiple protection strategies in optical networks, which is in general applicable to any connection-oriented network. The capacity available on a link for routing primary and backup connections are computed depending on the protection strategy. The paper also develops a model for computing service outage and failure recovery times for a connection where notifications of failure location are broadcast in the network. The effectiveness of employing multiple protection strategies is established by studying the performance of three networks for traffic with four types of protection requirement. [ABSTRACT FROM AUTHOR]

The article introduces two new and efficient integer linear program formulations for dynamic wavelength allocation in survivable multifiber wavelength-division multiplexing (WDM) networks, using dedicated and shared protection. Single-fiber networks, both with and without wavelength conversion, can be treated as a special case of these formulations. It tests the formulations on several WDM networks.

Real-time traffic will be a predominant traffic type in the next generation networks, and networks with 100% reliability and availability will be required by real-time premium traffic. It is believed that QoS guarantees could be better provided by connection oriented networks such as Multi Protocol Label Switching (MPLS). These connection oriented networks are more vulnerable to network failure. Conventional path protection methods perform re-routing to cope with this. However, re-routing always causes packet losses and results in service outage. These losses are bursty in nature and highly degrade the QoS of the real-time premium traffic. Thus, 100% availability cannot be achieved by conventional methods. The novel path protection proposed in this paper recovers the bursty packet losses due to re-routing by using forward error correction (FEC) path. Therefore, it can provide network architecture with no service outage for such traffic. The numerical results show that the proposed method can achieve a very high availability for real-time premium traffic in future IP/MPLS networks. [ABSTRACT FROM AUTHOR]

Previous research on survivability with differentiated reliability in wavelength-division-multiplexing (WDM) optical mesh networks mostly considered the failure probability of a fiber link with the link length that may not be a good solution for consideration of shared-risk link groups (SRLGs). In this paper, we propose a new model of failure probability with the SRLG constraints in WDM optical mesh networks. Based on this model, we present the backup resources assignment and the routing selection method with the differentiated reliable requirements of users. To evaluate the performances of this model, we propose a novel survivable routing algorithm called partial SRLG-disjoint protection (PSDP) to tolerate the single-SRLG failure. Compared with the previous algorithm, PSDP can obtain a better resource utilization ratio and lower blocking probability. Simulation results are shown to be promising. [ABSTRACT FROM PUBLISHER]

In this paper we investigate traffic engineering for fault restoration techniques in Multiprotocol Label Switching networks carrying QoS and best effort traffic. We consider off-line computation of the working and backup paths for the QoS traffic as well as the paths for the best effort traffic. Two cases of 1+1 and 1:1 path protection are considered. Our algorithms allow for control on the size of the label space for each router in the network and ensures that the created routes are loop free. In addition, explicit routes can be accommodated supporting both node and link affinity. [ABSTRACT FROM AUTHOR]

Extant (optical) networks normally offer two degrees of service reliability: full protection in the presence of a single fault in the network, and no protection at all. This situation reflects the historical duality that has its roots in the once divided telephone and data environment. The telephone circuit oriented service requires protection, i.e., provisioning of readily available spare resources to replace working resources in case of a fault. The datagram oriented service relies upon restoration, i.e., dynamic search for and reallocation of affected resources via actions such as routing table updates. The current trend in networking, however, is gradually driving the design of networks toward a unified solution that will jointly support traditional voice and data services, as well as a variety of novel multimedia applications. The growing importance of concepts, such as quality of service (QoS) and differentiated services—which provide multiple levels of service performance in the same network—evidences this trend. Consistently with this evolution, the concept of differentiated reliability (DiR) is formally introduced in the paper and applied to provide multiple reliability degrees (or classes) at the same network layer using a common protection mechanism, i.e., path switching. According to the DiR concept, each connection is guaranteed a minimum reliability degree, or equivalently a maximum downtime ratio, that is chosen by the client. The reliability degree chosen for a given connection is thus determined by the application requirements, and not by the actual network topology, design constraints, robustness of the network components, and span of the connection. An efficient algorithm is proposed to sub-optimally design the wavelength division multiplexing (WDM) layer of a ring and illustrate the advantages of the DiR concept. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

Survivable traffic grooming (STG) is a promising approach to provide reliable and resource-efficient multigranularity connection services in wavelength-division-multiplexing (WDM) optical networks. In this paper, we study the STG problem in WDM mesh optical networks employing path protection at the connection level. Both dedicated-protection and shared-protection schemes are considered. Given network resources, the objective of the STG problem is to maximize network throughput. To enable survivability under various kinds of single failures, such as fiber cut and duct cut, we consider the general shared-risk-link-group (SRLG) diverse routing constraints. We first resort to the integer-linear-programming (ILP) approach to obtain optimal solutions. To address its high computational complexity, we then propose three efficient heuristics, namely separated survivable grooming algorithm (SSGA), integrated survivable grooming algorithm (ISGA), and tabu-search survivable grooming algorithm (TSGA). While SSGA and ISGA correspond to an overlay network model and a peer network model, respectively, TSGA further improves the grooming results from SSGA and ISGA by incorporating the effective tabu-search (TS) method. Numerical results show that the heuristics achieve comparable solutions to the ILP approach, which uses significantly longer running times than the heuristics. [ABSTRACT FROM PUBLISHER]

This study presents a wavelength-routing scheme with spare reconfiguration (SR) to construct dependable all-optical wavelength-division-multiplexing (WDM) networks. Path protection using shared spare lightpaths is a general wavelength-routing method for reducing blocking probability while minimizing demand for spare resources. However, in a dynamic traffic environment, this method may still yield a poor performance because a wavelength on a link is very likely to be continuously held by a spare lightpath and to be unable to be assigned to the working lightpath of a new connection. This study develops a spare reconfiguration mechanism with wavelength reassignment (SR_WR) and path reassignment (SR_PR) to make the spare dynamic and thus further reduce the blocking probability. The proposed wavelength routing with SR proceeds in three stages and has polynomial time complexity. Extensive simulation experiments were conducted on the NSFNET and the K5 fully connected network to investigate the performance of the proposed wavelength routing with SR. Results of this study show that the proposed wavelength routing with SR can reduce the blocking probability compared with the general wavelength routing with just shared spare lightpaths by choosing a positive tuning cost. In addition, the improvement of the blocking performance is maximized when using SR_WR followed by SR_PR. [ABSTRACT FROM PUBLISHER]

The exponential growth of data traffic has led to substantial deployment of wavelength-division multiplexing networks. Reliability becomes increasingly important as the number of critical applications that depend on proper operation of these networks grows. Protection against failures of links or nodes can be achieved using a wide variety of approaches, which offer tradeoffs in terms of speed of recovery, cost of equipment, protection capacity, and management overhead. Optically transparent networks provide several advantages over optically opaque networks for supporting the growing communication demands, but suffer from several drawbacks that make direct application of the most capacity-efficient protection schemes difficult. In this paper, we introduce a flooding-based recovery scheme for optically transparent networks that provides 100% recovery from all single link and node failures in a capacity-efficient manner. In essence, this scheme applies the notion of active flooding of backup traffic introduced by generalized loopback to the problem of path protection. Our recovery scheme can achieve fast restoration (comparable to rings) with little data loss by using backup traffic flooding without the overhead of signaling and setup of intermediate cross-connects along the recovery path. We present simulation results for online provisioning of lightpaths with uniformly distributed traffic demands over optically transparent networks using our restoration scheme. The results show that the scheme offers an interesting tradeoff between capacity cost and recovery speed for all-optical networks. For five representative networks, the approach limits data loss to about 20 ms while using 14% less capacity relative to dedicated (1:1) mesh protection. Shared mesh protection (path protection) with a wavelength continuity constraint uses 19% less capacity with roughly 90 ms of data loss. [ABSTRACT FROM PUBLISHER]

We analyse and compare a protection mechanism based on load distribution with a typical protection mechanism in an multiprotocol label switching (MPLS) network. The protection mechanism based on load distribution is modelled as a fully shared mechanism (FSM) and the typical protection mechanism is a partially shared mechanism (PSM). By comparing the FSM and the PSM, we numerically analyse the effect of load distribution in path protection of MPLS. The comparison is based on numerical equations representing the relationship between service reliability and resource utilization. From the equations, we show that both the FSM and the PSM have a tradeoff between service reliability and resource utilization. In addition, we provide solutions for the FSM and the PSM to determine the amount of bandwidth occupied according to the requested service reliability. The comparison of the FSM and the PSM shows that the PSM cannot provide greater service reliability than the FSM under the same utilization. In addition, the PSM is not capable of accommodating greater resource utilization than the FSM for the same level of service reliability. However, an appropriate choice of the number of protection paths allows the PSM to provide the same level of service reliability as the FSM. The choice is the maximum among the possible numbers of protection paths of the PSM. In short, the typical protection mechanism is as good as the FSM in terms of service reliability and resource utilization even though the FSM is an attractive alternative to the typical protection mechanism. Copyright © 2003 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Very high-speed optical ring networks were recently developed for metropolitan area network (MAN). In such high-speed networks, survivability is a very important issue since a single failure leads to a disastrous service interruption. In this paper, we propose a design method for the reliable ring network based on optical compression TDM. We assume a single failure; at most a single link fails at a time. We then propose methods to establish paths accommodating all traffic demands among nodes. As protection/restoration methods, we consider a dedicated path protection, a shared path protection, and a path restoration method. For these networks, we first derive theoretical lower bounds on the numbers of slots and frames in order to accommodate all paths among nodes. We next propose path accommodation algorithms which allocate paths to slots in order to achieve the theoretical lower bound as closely as possible. Our proposed path accommodation methods are evaluated through several numerical examples. Three protection/restoration methods are also compared by applying our algorithms in order to investigate which method is suitable for optical compression TDM. The numerical results show that the shared path protection and path restoration methods can achieve better performance than the dedicated path protection method. Copyright © 2002 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]