Single Shared Risk Link Group Research Articles

A Whirling Dervish: Polynomial-Time Algorithm for the Regional SRLG-Disjoint Paths Problem

The current best practice in survivable routing is to compute link or node disjoint paths in the network topology graph. It can protect single-point failures; however, several failure events may cause the interruption of multiple network elements. The set of network elements subject to potential failure events is called Shared Risk Link Group (SRLG), identified during network planning. Unfortunately, for any given list of SRLGs, finding two paths that can survive a single SRLG failure is NP-Complete. In this paper, we provide a polynomial-time SRLG-disjoint routing algorithm for planar network topologies and a large set of SRLGs. Namely, we focus on regional failures, where the failed network elements must not be far from each other. We use a flexible definition of regional failure, where the only restrictions are that i) the topology is a planar graph, ii) each SRLG forms a set of connected edges in the dual of the planar graph, and iii) for each node <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$v$</tex-math> </inline-formula> , the links incident to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$v$</tex-math> </inline-formula> are part of an SRLG. The proposed algorithm is based on a max-min theorem. Through extensive simulations, we show that the algorithm scales well with the network size, and one of the paths returned by the algorithm is only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4$</tex-math> </inline-formula> % longer than the shortest path on average.

Optimal planning and design of SRLG-aware survivable LR-PON for wireless and FTTx networks

Protection to optical network units (ONUs) against failure of their distribution fibers (DFs) in a long-reach passive optical network (LR-PON) is highly desirable to provide uninterrupted internet services to the users. In practical network scenarios, DFs form shared-risk link groups (SRLGs). The existing SRLG-aware protection schemes depend on residual bandwidth of ONUs. Therefore, they are cost-inefficient and also fail to satisfy high reliability requirements (RRs). We for the first time propose a nonresidual bandwidth based partial protection scheme and related architecture to provide partial protection to ONUs against a single SRLG failure. Following the proposed scheme, we formulate an integer linear programming (ILP)-based optimization problem to provision backup DFs and network components for providing protection with the minimum protection cost. To meet the strict delay requirement for real-time applications, the proposed ILP model restricts the length of backup DFs to be employed to restore the traffic transmission. As the proposed ILP model becomes computationally intractable for large networks, we also propose a heuristic scheme that provides fairly close results to that of the ILP model. We assess the performance of the proposed partial protection scheme in terms of protection cost and total length of backup DFs (TLBDF). Through exhaustive simulation study we show that the proposed partial protection scheme not only satisfies high RRs but also requires much lower protection cost and TLBDF as compared to the existing SRLG-aware protection schemes.

Clustering-based multi-hop protection scheme for long-reach passive optical network against single shared-risk link group failure

The next-generation passive optical networks (NG-PONs) are expected to offer very high data rate to large number of users. Long-reach passive optical network (LR-PON) is considered to be one of the most promising solutions for NG-PONs. Since providing full protection (i.e., 100 % reliability) to each user in LR-PON is complex and cost-prohibitive, we propose in this study a novel heuristic scheme against single shared-risk link group (SRLG) failure to ensure certain degree of reliability (as determined by the network operator) to the users. In the proposed scheme (referred to as clustering-based multi-hop protection or CMHP scheme), we allocate residual capacity of backup optical network units (ONUs) among the ONUs that require protection by using bypass-based multi-hop traffic transmission strategy through backup fibers. CMHP scheme reduces the total length of backup fibers to be deployed between the ONUs (that require protection) and the respective backup ONUs through sharing of the backup fibers. In this study, we evaluate the total required length of backup fiber for a given network setting and different reliability requirements (viz. 75, 85 and 95 %). With the help of exhaustive simulations, we show that CMHP scheme significantly reduces the total length of backup fiber with reference to existing scheme to protect against single SRLG failure. We also explore a heuristic scheme referred to as clustering-based multi-hop protection with consideration of street layout (i.e., CMHP-SL) to implement CMHP scheme in practical scenario with due consideration of the street layout. CMHP-SL scheme provides protection to ONUs following a cost-efficient approach based on the existing fiber infrastructure in the distribution section.

Joint wireless and optical resources allocation for availability-guaranteed service in survivable fiber-wireless access network

The fiber-wireless (FIWi) access network not only leverages the technical merits of wireless and optical access networks, but also provides a potential opportunity for the design of survivable access networks. Previous works have studied the survivability of FiWi access network against network component failure by means of backup fiber deployment and wireless rerouting. However, most of these works put less attention on the connection availability and ignore the joint allocation of wireless and optical resources, which plays an important role in improving the global network performance gain. In this paper, we consider a notable failure scenario in FiWi access network but less mentioned in previous works, i.e., single shared-risk link group failure. We first propose a model for FiWi network to estimate the connection availability of service demand. Then, a novel resource allocation approach is proposed to provide the availability-guaranteed service. Under the requirements of bandwidth and connection availability, we deal with the optimal allocation of joint wireless and optical resources with the objective of minimum resource consumption. Numerical results demonstrate that the proposed scheme can reduce the resource consumption significantly compared to the resource allocation without considering connection availability.

Two Heuristics for Calculating a Shared Risk Link Group Disjoint Set of Paths of Min-Sum Cost

A shared risk link group (SRLG) is a set of links which share a common risk of failure. Routing protocols in Generalized MultiProtocol Label Switching, using distributed SRLG information, can calculate paths avoiding certain SRLGs. For single SRLG failure an end-to-end SRLG-disjoint path pair can be calculated, but to ensure connection in the event of multiple SRLG failures a set with more than two end-to-end SRLG-disjoint paths should be used. Two heuristic, the Conflicting SRLG-Exclusion Min Sum (CoSE-MS) and the Iterative Modified Suurballes's Heuristic (IMSH), for calculating node and SRLG-disjoint path pairs, which use the Modified Suurballes's Heuristic, are reviewed and new versions (CoSE-MScd and IMSHd) are proposed, which may improve the number of obtained optimal solutions. Moreover two new heuristics are proposed: kCoSE-MScd and kIMSHd, to calculate a set of $$k$$k node and SRLG-disjoint paths, seeking to minimize its total cost. To the best of our knowledge these heuristics are a first proposal for seeking a set of $$k\, (k>2)$$k(k>2) node and SRLG-disjoint paths of minimal additive cost. The performance of the proposed heuristics is evaluated using a real network structure, where SRLGs were randomly defined. The number of solutions found, the percentage of optimal solutions and the relative error of the sub-optimal solutions are presented. Also the CPU time for solving the problem in a path computation element is reported.

Protection Approach against SRLG Failure for Survivable Long-Reach Passive Optical Network in Smart Grid

Long-Reach Passive Optical Network (LR-PON) is widely acknowledged as a promising solution for communication system in smart grid. Survivability is one of the key issues in the planning of LR-PON because massive high-rate traffic flows may be interrupted in case of network component failure. However, the survivability issue of LR-PON is addressed in few works. Most of previous works focus on single distribution fiber failure and remain untouched the simultaneous failure of multiple distribution fibers. In this paper, we focus on the survivability of LR-PON against single Shared-Risk Link Group (SRLG) failure. A reliability model is proposed to represent the probability of reliable connection for each Optical Network Unit (ONU). Based on this reliability model, we propose a novel Backup Fibers Protection (BFP) approach, aiming at the optimization of joint allocating backup capacity and deploying backup fibers. Through extensive simulation, we investigate the performance of BFP and demonstrate its effectiveness in different scenarios.

Planning of survivable long-reach passive optical network (LR-PON) against single shared-risk link group (SRLG) failure

Long-Reach Passive Optical Network (LR-PON) is known as a promising and economical solution for Next-Generation PON (NG-PON). Survivability is one of the key issues in the planning of LR-PON because massive high-rate traffic flows may be interrupted in case of network component failure. However, the survivability issue for LR-PON is addressed in little works. More importantly, most of the previous works focus on single distribution fiber failure and remain untouched the simultaneous failure of multiple distribution fibers, which is a possible failure scenario in LR-PON. In this paper, we focus on the survivability of LR-PON against single Shared-Risk Link Group (SRLG) failure. A reliability model is proposed to represent the disconnection probability of the ONUs. Based on this reliability model, we propose a novel Backup Fibers Protection (BFP) scheme. In the BFP scheme, we deal with the optimization problem of allocating backup capacity and deploying backup fibers. Under the constraint of reliability requirement, our objective is to fully protect all traffic demand in the network with the minimum deployment cost of backup fibers. Both ILP-based approach and heuristic approach are proposed to solve the optimization problem in the BFP scheme. To the best of our knowledge, this paper is the first work regarding the survivability of LR-PON against single SRLG failure. Through extensive simulation, we investigate the performance of BFP and demonstrate its effectiveness in different scenarios.

On Shared Risk Link Group Optimization [Invited

Shared risk link groups (SRLGs) have been defined and implemented in many network planning tools and routing protocols. A single SRLG represents one potential failure, and a large service provider&#x2019;s network could easily contain tens of thousands of potential failures. The greater the number of SRLGs, the more difficult it is to attain good performance from planning tools (like routers) whose computations are dependent on the number of SRLGs. For many routing protocols using SRLG information, the situation becomes even worse, because a routing protocol may have space constraints to hold a limited number of SRLGs. These issues create a challenge to optimize the SRLG calculations such that the SRLG-related functions are not impacted or the impacts on the SRLG-related functions are limited. This paper takes a closer look at the SRLG optimization issue and identifies the facts/observations of SRLGs. Then we propose algorithms for how to reduce the number of SRLGs for different applications based on our observations.

Adjacent Link Failure Localization With Monitoring Trails in All-Optical Mesh Networks

Being reported as the most general monitoring structure for out-of-band failure localization approach, the monitoring trail (m-trail) framework has been witnessed with great efficiency and promises to serve in the future Internet backbone with all-optical mesh wavelength division multiplex (WDM) networks. Motivated by its potential and significance, this paper investigates failure localization in all-optical mesh networks using m-trails. By considering shared risk link groups (SRLGs) with up to all adjacent links of any node in the network, a novel algorithm of m-trail allocation for achieving unambiguous failure localization (UFL) of any single SRLG failure is developed. The proposed algorithm aims to minimize the number of required m-trails and can achieve superb performance with respect to the computation efficiency. We claim that among all the previously reported counterparts, this paper has considered one of the most applicable scenarios to the design of network backbone, and the proposed method can be easily extended to the case of node failure localization. Extensive simulation is conducted to verify the proposed algorithm in comparison to its existing counterparts.

P-Cycle Design in Survivable WDM Networks with Shared Risk Link Groups (SRLGs)

p-Cycle survivable network design under the single link failure assumption has been studied extensively. Shared risk link group (SRLG) is a concept that better reflects the nature of network failures. An SRLG is a set of links that may fail simultaneously because of a common risk they share. The capability of dealing with SRLG failures is essential to network survivability. In this paper, we extend the p-cycle survivable network design from the single link failure model to the single SRLG failure model. An integer linear programming (ILP) formulation that minimizes spare capacity requirement is provided. To avoid enumerating all cycles of a network, we also provide a polynomial-time algorithm to generate a basic candidate p-cycle set that guarantees 100% restorability in case of any single SRLG failure given enough spare capacities. Moreover, we present the SRLG failure detection problem that prevents fast restoration upon an SRLG failure. To solve this problem, we introduce the concept of SRLG-independent restorability, which enables the restoration of each link in a failed SRLG to start immediately without knowing which SRLG has failed. We present an approach to optimal p-cycle design with SRLG-independent restorability and show that it is NP-hard to generate a candidate p-cycle set such that each link can be SRLG-independently restored by at least one cycle in the set.