2-SRLG-connected partitioning in optical networks

In this paper, we study the impact of shared risk link group (SRLG) failures on shared-path protection by examining the percentage of connections that are vulnerable after SRLG failures, investigate the benefits of backup reprovisioning after SRLG failures, and evaluate different policies for backup reprovisioning. Compared with single-link failures, SRLG failures leave many more connections unprotected and vulnerable to the next failures and make the network topology much sparser. The major challenge of backup reprovisioning after SRLG failures is how to find SRLG-disjoint backup paths for those unprotected connections with a recovery ratio that is as high as possible within reasonable computational complexity. We are motivated to consider three reprovisioning policies by considering different sequences of reprovisioning according to the degree of SRLG constraints. The first policy is to reprovision backup paths for connections whose working paths traverse more SRLGs first (Policy I), and the second policy is to reprovision backup paths for connections whose working paths traverse fewer SRLGs first (Policy II). The third policy is to do backup reprovisioning randomly, i.e., we pick up an unprotected working path randomly (random reprovisioning). Extensive simulation results show that 1) SRLG failures will leave more connections unprotected compared with single-link failures, and the percentage of connections left vulnerable tends to be proportional to the SRLG size; 2) the network performance based on the first reprovisioning policy always performs best in recovery ratio; and 3) the network performance based on Policy II even underperforms the random reprovisioning. These results can be explained by the fact that connections whose working paths traverse fewer SRLGs are more flexible in finding SRLG-disjoint backup paths, and thus priority given to connections whose working paths traverse more SRLGs in Policy I can significantly improve the recovery ratio.

The 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 the common risk they share. The capability of dealing with SRLG failures is essential to network survivability. In this paper, we extend the p-cycle 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 an algorithm to generate a basic candidate p-cycle set that guarantees 100 % restorability in case of a single SRLG failure given enough spare capacities. Simulation results of optimal p-cycle design under the single SRLG failure model are presented. The spare capacity efficiency performance of the basic candidate p-cycle set is also evaluated. Finally, we give a brief overview of the SRLG failure detection problem and its impact on the restoration speed which is an important consideration of p-cycle design.

Failure recovery in IP networks is critical to high- quality service provisioning. In IP over wavelength division multiplexing (WDM) networks, a fiber carries multiple IP logical links. When a fiber fails, all the logical links it carries are disconnected simultaneously. This is called a shared risk link group (SRLG) failure. Recovery from SRLG failures using route recalculation could lead to long service disruption. In this paper, we present a scheme called multi-section shortest path first (MSSPF) that achieves ultra fast recovery from SRLG failures. MSSPF performs all the recovery related calculations in advance. On the detection of an SRLG failure, the affected IP packets are detoured to their destinations through pre-calculated paths to avoid failed links. We prove that MSSPF guarantees 100% recovery from SRLG failures and causes no permanent loops. In particular, the scheme has low complexity and can be implemented in today's networks running link-state routing protocols, e.g., open shortest path first (OSPF). The performance of our scheme is validated with a variety of practical and randomly generated topologies. Index Terms—routing, failure recovery, shared risk link group (SRLG), fast reroute.

This paper investigates the diverse routing in a wavelength division multiplexing (WDM)-based optical network under SRLG-disjoint constraints. In operational optical networks there are a lot of traffic flows within every lightpath. Any failure of one Iightpath will lead to a great loss. So we should provide path protection for the working lightpath. The concept of Shared Risk Link Groups (SRLG) is introduced in optical networks by IETF, which is defined as a group of links that share a common risk component whose failure can potentially cause the failure of all the links in the group. This concept groups all of the entities, such as wavelengths and links, etc., that are affected by a single failure. Now when path protection is employed, for any lightpath connection request, we compute two SRLG-disjoint lightpaths, one as working path and the other as protection path. There are some literatures, which propose methods for link-disjoint paths pair or node-disjoint paths pair, but few algorithms for SRLG-disjoint paths pair. The SRLG-disjoint constraints entail the general constraint-based path computation algorithms. Since this problem is an NIP-complete problem and there is no algorithm which could be used to solve this path computation in polynomial time. This paper presents a heuristic algorithm, Low-cost Pair of SRLG-Disjoint Paths Algorithm (LPSD), to solve this problem. LPSD can compute two SRLG-Disjoint paths simultaneously, and the total cost of the two paths is near optimal. Analysis and simulation are also given out.

Resiliency to link failures in optical networks is becoming increasingly important due to the increasing data rate in the fiber. Path protection schemes attempt to guarantee a backup path for a connection upon a failure in the network, thereby reducing the recovery time for a connection. In this paper, we develop a failure dependent path protection scheme that dynamically assigns a primary path and backup paths, one for each failure that would affect the primary path. A connection established on the primary path will be re-established on its backup path only if a failure in the network affects the connection. We evaluate the performance of our developed protocol and compare with an alternative approach based on sub-graph routing that achieves high network utilization and low blocking probability at the cost of re-establishing connections even if the failure in the network does not affect the primary path of the connection. We observe that up to a factor of eight reduction in the number of reconfiguration scenarios is achieved with less than 10% reduction in effective network utilization and less than 3% reduction in fairness metrics for tolerating any single link failure in NSFNET and ARPA-2 networks. The failure dependent protection approach developed in this paper is also applicable to any general failure scenarios that are modeled as shared risk link group failures.

This article explores a recently introduced novel technique called the nested monitoring trail (m‐trail) method in all‐optical mesh networks for failure localization of any shared risk link group (SRLG) with up to undirected links. The nested m‐trail method decomposes each network topology that is at least ‐connected into virtual cycles and trails, in which sets of m‐trails that traverse through a common monitoring node (MN) can be obtained. The nested m‐trails are used in the monitoring burst (m‐burst) framework, in which the MN can localize any SRLG failure by inspecting the optical bursts traversing through it. An integer linear program (ILP) and a heuristic are proposed for the network decomposition, which are further verified by numerical experiments. We show that the proposed method significantly reduces the required fault localization latency compared with the existing methods. Finally, we demonstrate that nested m‐trails can also be used in adaptive probing to find SRLG faults in all‐optical networks. The nested m‐trail based probing method needs a significantly reduced number of sequential probes. Thus, the method overcomes one of the important hurdles to deploy adaptive probing in all‐optical networks: the large number of sequential probes needed to localize SRLG faults. © 2015 Wiley Periodicals, Inc. NETWORKS, Vol. 66(4), 347–363 2015

Ensuring network survivability is of the utmost importance in today's networks. A Shared Risk Link Group (SRLG) is the set of links in the network that share a common physical resource subject to fault(s). This concept allows an upper layer the ability to implement SRLG diverse routing. Two algorithms, the Conflicting SRLG Exclusion (CoSE) and the Iterative Modified Suurballe's Heuristic (IMSH), will be shortly reviewed. The first solves the min-min problem and the second the min-sum problem, considering SRLG-disjoint paths. It will then be described a new version of CoSE, which will be designated as CoSE-MS, for solving the min-sum problem for SRLG diverse routing. Finally CoSE-MS and IMSH performance will be compared using random networks and an optical network. Results show that CoSE-MS is a good compromise between the quality of obtained solutions and the used CPU time.

Survivable service provisioning design has been an important issue in communication networks. In this work, we study survivable service provisioning using shared path based protection under a scheduled traffic model in wavelength convertible WDM optical mesh networks with Shared Risk Link Groups (SRLGs). In the scheduled traffic model, a set of demands is given, and the setup time and teardown time of a demand are known in advance. The objective is to minimize the total network resources (e.g., the number of wavelength-links) used by working paths and protection paths of the given set of demands while 100% restorability is guaranteed against any single SRLG failure. This problem is known to be NP-hard. We therefore study a time efficient approach to approximating the optimal solution to the problem. Our proposed approach is based on an iterative survivable routing scheme that utilizes a capacity provision matrix and processes demands sequentially. Our simulation results indicate that the proposed ISR-SRLG algorithm achieves excellent performance in terms of the total network resources used.

The light-tree-based optical multicasting (LT-OM) scheme provides a spectrum- and energy-efficient method to accommodate emerging multicast services. Some studies focus on the survivability technologies for LTs against a fixed number of link failures, such as single-link failure. However, a few studies involve failure probability constraints when building LTs. It is worth noting that each link of an LT plays different important roles under failure scenarios. When calculating the failure probability of an LT, the importance of its every link should be considered. We design a link importance incorporated failure probability measuring solution (LIFPMS) for multicast LTs under independent failure model and shared risk link group failure model. Based on the LIFPMS, we put forward the minimum failure probability (MFP) problem for the LT-OM scheme. Heuristic approaches are developed to address the MFP problem in elastic optical networks. Numerical results show that the LIFPMS provides an accurate metric for calculating the failure probability of multicast LTs and enhances the reliability of the LT-OM scheme while accommodating multicast services.

Diverse routing in networks with shared risk link groups (SRLGs) is an NP-complete problem in general. In this work, we study a multi-constrained routing problem in networks with SRLGs where a path between a source and a destination is determined such that both the path cost and the weight of SRLGs to which the links of the path belong are bounded. The path cost is measured as the sum of cost of links on the path while the weight of SRLGs is calculated as the sum of the weight of individual SRLGs along the path. The solution to this problem can be used to design algorithms that find a pair of low cost SRLG-diverse paths between a source and a destination. The multi-constrained routing problem is solved in two steps. First, an algorithm is devised that finds a least cost path in the network where the path cost is defined to be the combined cost of links and SRLG weights along the path. Second, an intelligent search algorithm that integrates the algorithm of the first step is designed to solve the multi-constrained routing problem to effectively find a path with the least total link cost while the total weight of the SRLGs on the path is bounded. The performances of the proposed algorithms are evaluated via extensive simulation and are compared with the solutions obtained by integer linear programming.

For 100% shared risk link group (SRLG) failure protection, conventional full path protection has to satisfy SRLG-disjoint constraints, i.e., its working path and backup path cannot go though the same SRLG. With the increase of size and number of SRLGs, capacity efficiency of conventional shared full path protection becomes poorer due to SRLG-disjoint constraints and the blocking probability becomes much higher due to severe traps. To solve these problems, we present a partial path protection scheme where SRLG-disjoint backup paths may only cover part of the working path. Full path protection becomes a special case of partial path protection, in which the backup path covers the full working path. By choosing the most survivable partial backup path as backup path, we can make the impact of SRLG failures as low as possible and accept as many as possible connection requests. Assuming every SRLG has the same probability to fail, we present a heuristic algorithm to find the most survivable partial backup path by choosing full path protection first, iteratively computing partial backup paths and choosing the most survivable one. The benefit of this heuristic algorithm is that it can find the optimal results within less iteration. Analytical and simulation results show that, compared to conventional full path protection, our proposed scheme can significantly reduce blocking probability with little sacrifice on survivability. The proposed scheme is very useful particularly when the network contains a lot of SRLGs and the blocking probability of conventional full path protection becomes too high.

The logical ring topology is a simple protection scheme in WDM networks. The failure of a single physical fiber link may cause the failure of multiple lightpaths. The service becomes unprotected if the failure propagates to the logical ring topology. In this paper, we focus on the elimination of failure propagation from the physical WDM network to the logical topology. We propose a method to make the augmented logical ring topology survivable. The augmented survivable edges (ASE) is based on the connectivity problem of the logical topology. Our method makes the modification of logical ring topology cost-effective, i.e., with the minimal number of the additional edges to the original logical ring topology. Finally, we show the results on various network cases

We consider the problem of designing logical optical network topology for a given physical topology (or fiber layout) and a given traffic demand matrix between the end-users. Traffic between the end-users is carried in a packet-switched form and the objective of our logical topology design is to minimize the maximum congestion on the logical links in the logical topology. The logical links are realized by wavelength continuous paths or lightpaths between end-users and they are routed via wavelength-selective routers. Note that a topology with lower maximum link congestion will allow its traffic demand matrix to be scaled up by a larger factor. In the logical topology each node is equipped with a limited number of optical transceivers, hence logical connections cannot be set-up between every pair of nodes. We present an improved bound for maximum congestion on any link in logical topology and present an algorithm for constructing a logical topology that reduces the maximum congestion on any logical link.

Wavelength Division Multiplexed (WDM) networks that route optical connections using intelligent optical cross-connects (OXCs) is firmly established as the core constituent of next generation networks. Rapid failure recovery is fundamental to building reliable transport networks. Mesh restoration promises cost effective failure recovery compared with legacy ring networks, and is now seeing large-scale deployment. Many carriers are migrating away from SONET ring restoration for their core transport networks and replacing it with mesh restoration through “intelligent” O-E-O cross-connects (XC). The mesh restoration is typically provided via two fiber-disjoint paths: a service path and a restoration path. this scheme can restore any single link failure or node failure. And by used shared mesh restoration, although every service route is assigned a restoration route, no dedicated capacity needs to be reserved for the restoration route, resulting in capacity savings. The restoration approach we propose is Centralized Pre-computing, Local Distributed Optimization, and Shared Disjoint-backup Path. This approach combines the merits of centralized and distributed solutions. It avoids the scalability issues of centralized solutions by using a distributed control plane for disjoint service path computation and restoration path provisioning. Moreover, if the service routes of two demands are disjoint, no single failure will affect both demands simultaneously. This means that the restoration routes of these two demands can share link capacities, because these two routes will not be activated at the same time. So we can say, this restoration capacity sharing approach achieves low restoration capacity and fast restoration speed, while requiring few control plane changes.

Recently, there is a growing interest in the applications of wireless sensor networks (WSNs). A set of sensor nodes is deployed in order to collectively survey an area of interest and/or perform specific surveillance tasks in some of the applications, such as battlefield reconnaissance. Due to the harsh deployment environments and limited energy supply, nodes may fail, which impacts the connectivity of the whole network. Since a single node failure (cut-vertex) will destroy the connectivity and divide the network into disjoint blocks, most of the existing studies focus on the problem of single node failure. However, the failure of multiple nodes would be a disaster to the whole network and must be repaired effectively. Only few studies are proposed to handle the problem of multiple cut-vertex failures, which is a special case of multiple node failures. Therefore, this paper proposes a comprehensive solution to address the problems of node failure (single and multiple). Collaborative Single Node Failure Restoration algorithm (CSFR) is presented to solve the problem of single node failure only with cooperative communication, but CSFR-M, which is the extension of CSFR, handles the single node failure problem more effectively with node motion. Moreover, Collaborative Connectivity Restoration Algorithm (CCRA) is proposed on the basis of cooperative communication and node maneuverability to restore network connectivity after multiple nodes fail. CSFR-M and CCRA are reactive methods that initiate the connectivity restoration after detecting the node failure(s). In order to further minimize the energy dissipation, CCRA opts to simplify the recovery process by gridding. Moreover, the distance that an individual node needs to travel during recovery is reduced by choosing the nearest suitable candidates. Finally, extensive simulations validate the performance of CSFR, CSFR-M and CCRA.