A Survey of Survivability in Multi-Domain Optical Networks
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paper_title: LSSP: A novel local segment-shared protection for multi-domain optical mesh networks

paper_content:

This paper investigates the survivability in multi-domain optical mesh networks and presents a new model of multiple failures that is defined that there is one failed link in each single-domain and are multiple failed links in the whole multi-domains. Since the conventional Extended-Path-Shared Protection (EPSP) approach cannot provide 100% protection ability for this model, we propose a novel approach called Local Segment-Shared Protection (LSSP) to provide efficient survivability for this model. In our approach, LSPP first computes one inter-domain primary path for each connection request and follows to compute one intra-domain link-disjoint local segment-backup path for each primary-segment path in each single-domain, respectively, where the backup resources can be shared by different segment-backup paths if the corresponding primary-segment paths are link-disjoint. Compared with the conventional EPSP, although LSSP increases moderate backup resources consumption, it not only can provide 100% protection ability for multiple failures but also can perform much faster recovery time and easier survivable operation and management. The simulation results are shown to be promising.
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paper_title: Multi-layer protection in IP-over-WDM networks with and with no backup lightpath sharing

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We consider the problem of multi-layer protection in IP-over-WDM networks. In our multi-layer protection schemes, traffic is protected either at the lightpath level or at the label switched path (LSP) level based on the restoration time requirements. In lightpath-level protection, traffic on a path (LSP) is protected by routing it over primary lightpaths which are protected at the optical layer by their respective backup lightpaths. In LSP-level protection, the traffic on a primary LSP is protected at the IP-multi-protocol label switching (MPLS) layer by a backup LSP. In this case, both primary and backup LSPs traverse unprotected lightpaths. We allow two backup LSPs to share bandwidth resource on these unprotected lightpaths if their primary LSPs are link-disjoint. In lightpath-level protection, whether backup resources can be shared or not depends on the protection mechanisms used. In 1:1 dedicated protection where the backup lightpath is pre-configured at the time of setting up of the corresponding primary lightpath, sharing is not possible. However, sharing is allowed in shared protection where the backup lightpaths are configured only after failure. We consider these two schemes and refer them as multi-layer protection with no backup lightpath sharing (MLP-NLS) and multi-layer protection with backup lightpath sharing (MLP-LS). An inter-level sharing (ILS) method is proposed to improve resource utilization in MLP-NLS, by allowing dedicated backup lightpaths to be used by backup LSPs. Two integrated-routing algorithms are developed to select paths in lightpath-level protection and LSP-level protection with the objective to utilize the network resources efficiently. We verify the effectiveness of the proposed multi-layer protection schemes through simulation results on the NSFNET and Pan-European networks.
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paper_title: Dynamic establishment of differentiated survivable lightpaths in WDM mesh networks

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In the emerging next-generation transport networks, called intelligent optical transport networks, DWDM-based optical components like add-drop multiplexers and optical cross connects will have full knowledge of the wavelengths in the network, status, and traffic carrying capacity of each wavelength. With such intelligence, these intelligent optical networks could create self-connecting and self-regulating connections on-the-fly. Because these networks carry huge volume of traffic, maintaining a high level of service availability at an acceptable level of overhead is an important and critical issue. It is essential to incorporate fault-tolerance into QoS requirements. Since the delay (response time) becomes unbounded as the load approaches the link capacity, delay is usually dominated by the most heavily loaded links; therefore algorithms must attempt to minimize the delay. In this paper, we take fault-tolerance, delay, bandwidth, and availability as QoS parameters to provide varying classes of services based on the type of primary and backup lightpaths and the number of backup lightpaths for studying the problem of dynamically establishing lightpaths in WDM optical networks. The type of primary and backup lightpaths determines the QoS parameters such as response time and bandwidth. Whereas, the number of backup lightpaths determines the level of fault-tolerance and availability of the connection. Based on the service classes, any connection in the network falls into one of the seven classes, viz. single dedicated primary and single dedicated backup, single dedicated primary and multiple dedicated backups, single dedicated primary and single shared backup, single shared primary and single shared backup, single shared primary and multiple shared backup, single dedicated multi-hop primary and single dedicated multi-hop backup, and single shared multi-hop primary and single shared multi-hop backup. We conduct extensive simulation experiments to compare and evaluate the effectiveness of different classes for varying network configurations-varying number of fibers, wavelengths on physical links, and different traffic patterns.
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paper_title: Segment shared protection in mesh communications networks with bandwidth guaranteed tunnels

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This paper focuses on the problem of dynamic survivable routing for segment shared protection (SSP) in mesh communication networks provisioning bandwidth guaranteed tunnels. With SSP, a connection is settled by concatenating a series of protection domains, each of which contains a working and protection segment pair behaving as a self-healing unit for performing local restoration whenever the working segment is subject to any unexpected interruption. We first discuss the advantages of using SSP--the ability to shorten the restoration time as well as achieve a higher throughput by saving spare capacity required for 100% restorability; then the survivable routing problem is formulated into an Integer Linear Programming (ILP), where the switching/merging node pair of each protection domain along with the corresponding least-cost working and protection segment pair can be jointly determined for a dynamically arrived connection request. A novel approach of arc-reversal transformation is devised to deal with the situation that the working segments of two neighbor protection domains may overlap with each other by more than a single node. Due to a very high computation complexity induced in solving the ILP, a novel heuristic algorithm is proposed, named Cascaded Diverse Routing (CDR), to allocate protection domains for a connection request by performing diverse routing across a set of predefined candidate switching/merging node pairs. Experiments are conducted on five two-connected network topologies to verify the ILP and the CDR algorithm. We first determine the best diameter of protection domains for the CDR scheme in each network topology. Using the results of best diameters, CDR is compared with two reported schemes, namely PROMISE and OPDA. We demonstrate in the simulation results that the path-shared protection schemes are outperformed by the SSP schemes in terms of blocking probability under all possible arrangements in the experiment and that CDR yields better performance than PROMISE and OPDA due to the extra efforts in manipulating the location of working segments at the expense of longer computation time.
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paper_title: Multi-criteria p-cycle network design

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The major challenge of p-cycle network design resides in finding an optimal set of p-cycles protecting the network for a given working capacity. Existing solutions (exact and heuristic approaches), for solving the problem, find the set of p-cycles protecting the network through two steps: one step for generating candidate p-cycles and a second step for selecting the efficient ones. In this paper, we present a novel heuristic approach, which computes an efficient set of p-cycles protecting the network in one step. Our heuristic approach takes into consideration two different criteria: the redundancy and the number of p-cycles involved in the solution. Simulation study shows that our approach necessitates a lower redundancy and fewer p-cycles to protect the network compared to state-of-the-art approaches.
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paper_title: Survivability in optical networks

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Survivability, the ability of a network to withstand and recover from failures, is one of the most important requirements of networks. Its importance is magnified in fiber optic networks with throughputs on the order of gigabits and terabits per second. This article takes a look at the techniques used to achieve survivability in traditional optical networks, and how those techniques are evolving to make next-generation WDM networks survivable.
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paper_title: Path-Protection Routing and Wavelength Assignment (RWA) in WDM Mesh Networks Under Duct-Layer Constraints

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This study investigates the problem of fault management in a wavelength-division multiplexing (WDM)-based optical mesh network in which failures occur due to fiber cuts. In reality, bundles of fibers often get cut at the same time due to construction or destructive natural events, such as earthquakes. Fibers laid down in the same duct have a significant probability to fail at the same time. When path protection is employed, we require the primary path and the backup path to be duct-disjoint, so that the network is survivable under single-duct failures. Moreover, if two primary paths go through any common duct, their backup paths cannot share wavelengths on common links. This study addresses the routing and wavelength-assignment problem in a network with path protection under duct-layer constraints. Off-line algorithms for static traffic is developed to combat single-duct failures. The objective is to minimize total number of wavelengths used on all the links in the network. Both integer linear programs and a heuristic algorithm are presented and their performance is compared through numerical examples.
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paper_title: Two Approaches for Aggregation of Peer Group Topology in Hierarchical PNNI Networks

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ABSTRACTWe propose two methods for aggregation of peer group topology in hierarchical ATM networks. Both proposed aggregation methods transform a given peer group into a star graph representation. Our first approach optimally preserves, in a least square sense, the original costs of routing through the peer group. Our second approach assigns a weighted vector to the nucleus of the Logical Group Node, which quantifies the error in the compact representation. The two schemes are dual, in the sense that the first is best suited for peergroups where traffic patterns are unpredictable, and the second is suited for peergroups where traffic patterns can be characterized. Both the proposed schemes are practical: For peer groups with nodes V, links E, and n border nodes B ⊂ V, the approaches run in O(n|V|log|V| + n|E|+ poly(n)) time. The size of the final representation is small (linear in the number of border nodes) and can be computed efficiently. The scalability of the proposed algorithms makes them well-suited...
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paper_title: Minimum equivalent subspanner algorithms for topology aggregation in ATM networks

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In a hierarchical network, the process of summarizing and compressing topology information at each hierarchical level to determine the topology information to be advertised at the level above is referred to as topology aggregation. Specifically, a problem of topology aggregation is to encode a full mesh representation of a given topology with a compact auxiliary graph, such that it could be used to reconstruct the full mesh representation with little or no distortion. This paper presents some algorithms that can be used to determine, for a given topology, a minimum representation with no compromise on accuracy. The minimum representation can be used to characterize the amount of redundancy in the topology. The application of these algorithms to generate complex node representations for topology aggregation in ATM networks is discussed.
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paper_title: Topology aggregation for directed graphs

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This paper addresses the problem of aggregating the topology of a sub-network in a compact way with minimum distortion. The problem arises from networks that have a hierarchical structure, where each sub-network must advertise the cost of routing between each pair of its border nodes. The straight-forward solution of advertising the exact cost for each pair has a quadratic cost which is not practical. We look at the realistic scenario of networks where all links are bidirectional, but their cost (or distance) in the opposite directions might differ significantly. The paper presents a solution with distortion that is bounded by the logarithm of the number of border nodes and the square-root of the asymmetry in the cost of a link. This is the first time that a theoretical bound is given to an undirected graph. We show how to apply our solution to PNNI, and suggest some other heuristics that are tested to perform better than the provenly bounded solution.
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paper_title: Reliability In Single Domain Vs. Multi Domain Optical Mesh Networks

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Network reliability is an important element of a service level agreement and is typically evaluated based on the number of unavailable minutes per year. The widespread belief is that networks with faster restoration times are more reliable, created by the assumption that fast restoration from a failure leads to smaller down time. This is not necessarily the case since it has been shown that reliability may have little to do with the restoration speed when the restoration time is small compared to the mean time to repair of the failed elements. In this paper, we compare the reliability of optical mesh networks with multi domain restoration and single domain restoration using both dedicated mesh protection and shared mesh restoration, and show that splitting a network into multiple domains increases the overall reliability.
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paper_title: Subpath protection for scalability and fast recovery in optical WDM mesh networks

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This paper investigates survivable lightpath provisioning and fast protection switching for generic mesh-based optical networks employing wavelength-division multiplexing (WDM). We propose subpath protection, which is a generalization of shared-path protection. The main ideas of subpath protection are: 1) to partition a large optical network into smaller domains and 2) to apply shared-path protection to the optical network such that an intradomain lightpath does not use resources of other domains and the primary/backup paths of an interdomain lightpath exit a domain (and enter another domain) through a common domain-border node. We mathematically formulate the routing and wavelength-assignment (RWA) problem under subpath protection for a given set of lightpath requests, prove that the problem is NP-complete, and develop a heuristic to find efficient solutions. Comparisons between subpath protection and shared-path protection on a nationwide network with dozens of wavelengths per fiber show that, for a modest sacrifice in resource utilization, subpath protection achieves improved survivability, much higher scalability, and significantly reduced fault-recovery time.
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paper_title: Dynamic routing for shared path protection in multidomain optical mesh networks

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The routing problem for shared path protection in multidomain optical mesh ::: networks is more difficult than that in single-domain mesh networks due to the lack of ::: complete and global knowledge of the network topology and bandwidth allocation. To ::: overcome this difficulty, we propose an aggregated network modeling by underestimation ::: with a two-step routing strategy. In the first step, a rough routing solution is ::: sketched in a virtual network that is the topology aggregation of the multidomain ::: network. A complete routing is then determined by solving routing problems within the ::: original single-domain networks. The first step can be solved by either using an exact ::: mathematical program or a heuristic, whereas the second step is always solved by ::: heuristics. Computational results show the relevance of the aggregated network modeling. ::: They also prove the scalability of the proposed routing for multidomain networks and its ::: efficiency in comparison with the optimal solution obtained by use of the complete ::: information scenario. In addition, we believe that short working paths lead to a higher ::: possibility of sharing backup resources between backup paths. Our mathematical program ::: model minimizes the total requested resources and at the same time provides a short ::: working path, resulting in a further overall saving of resources.
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paper_title: Survivability in optical networks

paper_content:

Survivability, the ability of a network to withstand and recover from failures, is one of the most important requirements of networks. Its importance is magnified in fiber optic networks with throughputs on the order of gigabits and terabits per second. This article takes a look at the techniques used to achieve survivability in traditional optical networks, and how those techniques are evolving to make next-generation WDM networks survivable.
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paper_title: LSSP: A novel local segment-shared protection for multi-domain optical mesh networks

paper_content:

This paper investigates the survivability in multi-domain optical mesh networks and presents a new model of multiple failures that is defined that there is one failed link in each single-domain and are multiple failed links in the whole multi-domains. Since the conventional Extended-Path-Shared Protection (EPSP) approach cannot provide 100% protection ability for this model, we propose a novel approach called Local Segment-Shared Protection (LSSP) to provide efficient survivability for this model. In our approach, LSPP first computes one inter-domain primary path for each connection request and follows to compute one intra-domain link-disjoint local segment-backup path for each primary-segment path in each single-domain, respectively, where the backup resources can be shared by different segment-backup paths if the corresponding primary-segment paths are link-disjoint. Compared with the conventional EPSP, although LSSP increases moderate backup resources consumption, it not only can provide 100% protection ability for multiple failures but also can perform much faster recovery time and easier survivable operation and management. The simulation results are shown to be promising.
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paper_title: On segment-shared protection for dynamic connections in multi-domain optical mesh networks

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Abstract We propose a novel protection algorithm called Enhanced Local Segment-Shared Protection (ELSSP) for dynamic connections in multi-domain optical mesh networks. ELSSP assigns rational link-cost on the virtual topology when calculating the primary path, and provides segment-shared protection in the passing domains of the primary path. Simulation results show the good network performance of ELSSP.
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paper_title: A novel domain-by-domain survivable mechanism in multi-domain wavelength-division-multiplexing optical networks☆

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Abstract In multi-domain wavelength-division-multiplexing (WDM) optical networks, the inter-domain routing is a challenge since each single-domain cannot view the full network topology. At the same time, survivability is also an important issue in optical networks since the failures of fiber links or network nodes may lead to a lot of traffic being blocked. In this paper, we study the survivability in multi-domain WDM optical networks, and propose a new survivable mechanism called load balanced domain-by-domain routing (LBDDR). In LBDDR, in order to obtain the efficient inter-domain survivable routes, we present the domain-by-domain routing (DDR) method which can find the intra-domain sub-working path and sub-backup path in each single-domain to form the inter-domain working path and backup path for each demand. In order to reduce the blocking probability, we present the load balanced routing method which can encourage the traffic to be uniformly distributed on the links with more free wavelengths. Simulation results show that, compared with conventional mechanism, LBDDR can obtain better performances.
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paper_title: A shared sub-path protection strategy in multi-domain optical networks

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In this paper, a shared sub-path protection mechanism for multi-domain optical networks is proposed. It divides the computed working path into several working sub-paths which span two domains. For each working sub-path, two intra-domain and an inter-domain backup sub-paths are computed to protect intra-domain and inter-domain failures. Simulation results show it has shorter failure recovery time and is resource efficient.
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paper_title: On The Bandwidth Efficiency of Pre-Crossconnected Trails

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Recently, the use of pre-crossconnected trails (PXTs) has been proposed for fault tolerant WDM optical networks. Arranging protection bandwidth into PXTs eliminates the need for switch reconfiguration after a failure which leads to faster recovery times. The researchers who introduced PXTs gave experimental results showing that PXT protection performs not much worse and sometimes better than conventional algorithms in terms of bandwidth efficiency. Their experiments compared a greedy PXT algorithm with a simple non-greedy conventional algorithm, so there remained some question about the effect of the PXT constraint itself on bandwidth efficiency. In this paper, we explore this topic further. We use experimental results to compare simple and greedy heuristics both with and without the PXT constraint. Our results show that the PXT variations require significantly more bandwidth overhead than their conventional counterparts especially in larger networks.
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Title: A Survey of Survivability in Multi-Domain Optical Networks

Section 1: Introduction
Description 1: Introduce the basic concepts of Wavelength Division Multiplexing (WDM) technologies, the importance of network survivability, challenges in multi-domain networks, and the scope of the survey.

Section 2: Survivability in WDM Optical Networks
Description 2: Discuss various component failures in networks, explain restoration and protection methods, and compare the efficiency of different survivability mechanisms at the WDM layer.

Section 3: Network Model
Description 3: Provide details of the multi-domain optical network model, including the graphical representation, types of nodes, and assumptions used in the study for simpler calculations.

Section 4: Topology Aggregation Models
Description 4: Explain different topology aggregation models used to reduce topology information size while maintaining routing performance, and introduce the Single Node, Full Mesh, and Star models.

Section 5: State-of-the-Art
Description 5: Review various solutions proposed for survivability in multi-domain optical networks, analyzing each solution's advantages, disadvantages, and specific assumptions made.

Section 6: Simulation model
Description 6: Present a qualitative and quantitative evaluation model to compare the performance of the described solutions, using network topologies and traffic models.

Section 7: Performance metrics
Description 7: Detail the metrics used to measure capacity efficiency and recovery time, such as Resource Utilization, Ratio of Rejected Connections, and Recovery Time, and present the corresponding simulation results.

Section 8: Analysis
Description 8: Provide a comparative analysis of different survivability schemes, highlighting which solutions offer better resource utilization, recovery times, and overall performance.

Section 9: Conclusion
Description 9: Summarize the survey findings, noting the key challenges in multi-domain optical network survivability and suggesting potential areas for future research.