Set Of P-cycles Research Articles

Link-protection and FIPP p-cycle designs in translucent elastic optical networks

Elastic optical networks (EONs) are able to provide high spectrum utilization efficiency due to flexibility in resource assignment. In translucent EONs, by employing regenerators and using advanced modulation formats for transmission, spectrum efficiency can be further improved. Survivability is regarded as an important aspect of EONs, and p-cycle protection is considered to be an attractive scheme due to its fast restoration and high protection efficiency. In this paper, we propose methods for evaluating and selecting p-cycles for both link protection (LP) and failure-independent path protection (FIPP) to survive single-link failures. After considering the various factors that affect the performance of a p-cycle, we propose two evaluation metrics for LP and FIPP, namely, individual p-cycle cost and set of cycles cost. Based on these metrics, we propose two algorithms for selecting a set of p-cycles in translucent EONs: Traffic Independent P-cycle Selection (TIPS), which selects a set of cycles without knowledge of the traffic, and Traffic-Oriented P-cycle Selection (TOPS), which takes given traffic information into account. A routing and spectrum assignment algorithm is designed for translucent EONs, and our p-cycle design algorithms are evaluated using both static and dynamic traffic models. Simulation results show that the proposed algorithms have better performance than commonly used baseline algorithms. We also compare the performance of LP p-cycles and FIPP p-cycles.

P-Cycle-based protection of multicast connections in metropolitan area optical networks with physical layer impairments constraints

This paper investigates the problem of protecting multicast sessions in optical networks utilizing a novel cycle-based heuristic algorithm called Q-based p-Cycles Heuristic (QBPCH), that is used for the decomposition of the graph network into a set of p-cycles, while taking into account the physical layer impairments (PLIs) via a Q-budgeting approach. In this technique the length of these cycles is constrained in order to limit the effect of the impairments on the protection paths. The proposed scheme exhibits improved performance in terms of blocking probability, when compared to another proposed heuristic, namely p-Cycles Heuristic (PCH), that aims at decomposing the graph network into a set of p-cycles that maximizes the number of straddling links in the network. Both proposed schemes are also compared to a traditional ring cover heuristic (RC) and to a Hamiltonian cycle (HC) approach and it is shown that QBPCH performs the best in terms of blocking probability when the PLIs are considered.

Hybrid FRR/p-cycle design for link and node protection in MPLS networks

Survivable MPLS technologies are crucial in ensuring reliable communication services. The fast reroute (FRR) mechanism has been standardized to achieve fast local repair of label switched paths (LSPs) in the event of link or node failures. We present a suite of hybrid protection schemes for MPLS networks that combine the well-known p-cycle method with FRR technology. Whereas with pure FRR backup paths are planned by each node individually, the hybrid schemes employ a set of p-cycles that may be selected using techniques that take a holistic view of the network so as to share protection bandwidth effectively. The hybrid FRR/p-cycle methods are fully RFC 4090-compliant, yet allow network operators to leverage a large existing body of p-cycle design techniques. Numerical results on realistic network topologies indicate that the hybrid approach is successful in combining the advantages of p-cycle design and FRR.

Optimal Selection of p-cycles on WDM Optical Networks with Shared Risk Link Group Independent Restorability using Genetic Algorithm

The techniques for protection against failures in optical networks have been discussed in many scientific papers. In the case of Wavelength Division Multiplexing (WDM) optical networks, the p-cycles strategy of protection is a promising approach that combines the speed of ring protection and efficiency of resource utilization in mesh protection. In real networks, several optical links may fail at the same time when nodes or ducts failures happen. These sets of links with simultaneous fails can be determined a priori, and they are called Shared Risk Link Groups (SRLG). This paper proposes an approach based on Genetic Algorithm to find the best set of p-cycles that protects the network traffic against SRLG. Independent SRLG restoration is also achieved for better and faster network recovery in case of failures. This makes recovery faster and more efficiently. In addition we present a new algorithm for selecting candidates cycles, specific to this problem. The experimental results show viability of the proposed approach by achieving good performance in comparison to an exact algorithm of the state of the art.

A Simple Generalized Approach to Node Failure Recovery with Span-Protecting p-Cycles

This paper shows that, viewed in a generalized “two-hop” framework for node failure recovery, p-cycles actually have a very high inherent ability to restore paths transiting through a failed node. We also showed that with relatively little, if any, extra spare capacity, the principle is also amenable to explicit design of networks for 100% node and span failure protection with a single efficient set of p-cycles that support both functions. This is very different than the often-prevailing assumption that “ordinary” p-cycles offer no node protection, or only the same node-protection as a BLSR ring embodies. Indeed, the two-hop paradigm for recovery of affected paths transiting failed nodes could provide an attractive option for future network operators in that “ordinary” p-cycles are more localized, fast acting, and simple to plan and operate than any other option such as NEPCs, flow-protecting p-cycles or FIPPs.

Self-fault isolation in transparent p-cycle networks: p-cycles as their own m-cycles

Span protection has advantages in speed, locality of action and simplicity but requires that the failed span be located in real time. Recent work proposed a novel type of rapid fault-localization via monitoring cycles (m-cycles). Span-protecting structures (e.g. p-cycles) are designed and operated separately from the monitoring cycles in this architecture. We investigate whether it is feasible to design a p-cycle network such that the set of p-cycles used for protection could also serve as a set of fault localizing m-cycles. The main contribution is to show that this can be achieved with the same localization effectiveness as separately designed w-cycle solutions at little or no extra cost.

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.

Hamiltonian p-cycles for fiber-level protection in homogeneous and semi-homogeneous optical networks

Recently there has been interest in DWDM-based optical networks that are assumed to employ exactly two working fibers uniformly on every span (or "link"). At the fiber level such networks are referred to as homogeneous networks. An interesting and highly efficient strategy for protection of such networks is to use a single dark-fiber p-cycle formed on a Hamiltonian cycle (if it exists). We show that in a homogeneous Hamiltonian network, a Hamiltonian p-cycle is the most efficient overall solution, although interestingly it does not always correspond to the individually most efficient p-cycle that can be formed. We also consider p-cycle planning in non-Hamiltonian but homogeneous networks and introduce the concept of a semi-homogenous network, specifically linked to the p-cycle concept. The proposed semi-homogeneous class of network actually realizes the theoretical lower bound on span-restorable networks in terms of network redundancy. Such networks also provide a strategy to accommodate certain patterns of capacity growth beyond a homogenous network without any increase in protection capacity. The work also demonstrates and explains why a single Hamiltonian p-cycle is not as efficient as a specifically optimized set of individual p-cycles in a "capacitated" (non-homogeneous) network where the working capacity on each span varies in a general way. These discussions provide new options for DWDM network architecture and also clarify some possible confusions about the applicability of Hamiltonian p-cycles and generalized sets of p-cycles.