Dynamic Traffic Grooming under a Differentiated Resilience Scheme for WDM Mesh Networks

Due to its huge bandwidth, optical fibre is currently widely deployed to provide a variety of telecommunications services and applications. Wavelength-division multiplexing (WDM) has emerged as the technology of choice to harness the huge bandwidth available in an optical fibre. Traffic grooming supports efficient utilization of network resources by allowing sub-wavelength granularity connections to be groomed onto a single lightpath. Fault-tolerance for WDM networks is a major architectural and design issue as a single link failure can cause loss of an enormous amount of information. However, providing 100% guaranteed resilience to all types of traffic supported by existing and future networks may be unnecessary and wasteful in terms of resource utilization and cost efficiency. This chapter investigates the problem of dynamic traffic grooming for WDM networks under a differentiated resilience scheme. We propose two differentiated resilience schemes at different grooming levels— Differentiated Resilience at Lightpath (DRAL) level scheme, and Differentiated Resilience at Connection (DRAC) level scheme. These schemes explore different ways of provisioning backup paths and tradeoff between bandwidth efficiency and the number of required grooming ports. Both schemes support three resilience classes: dedicated protection, shared protection, and restoration. Simulation is carried out to evaluate and compare the two differentiated resilience schemes. Simulation results show that the DRAL scheme is not very sensitive to the changes in the number of grooming ports, while the DRAC scheme utilizes grooming ports more aggressively as it trades grooming ports for bandwidth efficiency in routing and grooming.

Fault Management in Transparent Optical Networks

The advantages of transparent optical networks such as high capacity and low cost can be outweighed by their complex fault management and the high impact of the faults occurring within them. Indeed, transparent optical networks reduce unnecessary, complex, and expensive opto-electronic conversion, to the cost of having faults more deleterious and affecting longer distances than in opaque networks. Moreover, transparent optical networks have limited monitoring capabilities, which could hinder efficient and accurate fault detection and localization. Different approaches have been proposed in the literature to perform fault localization, targeting different fault scenarios (e.g. single/multiple faults or looking at the optical/higher layers), and considering different assumptions (e.g. ideal/existence of false or lost alarms). Furthermore, fault management depends on the placement of monitoring equipment, whose optimization has been studied and also presented in this chapter.

Optical Communication

The idea of this chapter is to give an overview on optical communication systems. The most important devices for fiber-optic transmission systems are presented, and their properties discussed. In particular, we consider such systems working with those basic components which are necessary to explain the principle of operation. Among them is the optical transmitter, consisting of a light source, typically a low speed LED or a high speed driven laser diode. Furthermore, the optical receiver has to be mentioned; it consists of a photodiode and a low noise, high bit rate, front-end amplifier. Yet, in the focus of the considerations, you will find the optical fiber as the dominant element in optical communication systems. Different fiber types are presented, and their properties explained. The joint action of these three basic components can lead to fiber-optic systems, mainly applied to data communication. The systems can operate as transmission links with bit rates up to 40 Gbit/s. But communication systems are also used for recent application areas in the MBit/s region, e.g. in aviation, automobile, and maritime industry. Therefore—besides pure glass fibers—polymer optical fibers (POF) and polymer-cladded silica (PCS) fibers have to be taken into account. Moreover, even different physical layers like optical wireless and visible light communication can be a solution.

Performance Evaluation of Survivability Approaches in Optical Networks

The chapter outlines the different survivability approaches for mesh networks under static and dynamic traffic environments. It describes the different solution options and their implementations. Also included are detailed performance analyses and evaluations for the difference survivability approaches under both traffic environments. Finally, we present a performance comparison between the different survivability approaches and end the chapter with some concluding remarks.

Protection Survivability Architectures

Survivable routing serves as one of the most important issues in optical backbone design. Due to the high data rates enabled by the wavelength division multiplexing technology, any interruption in the service results in the loss of a large amount of application data. Thus, making efforts to calculate and signal the protection resources promptly after the failure occurred would lead to an unacceptable high delay. As the main purpose of this chapter, the principles of pre-planned protection approaches in mesh optical backbone networks are discussed. The Shared Risk Link Group (SRLG) concept is introduced modeling physical and geographical dependency among seemingly unrelated link failures. Finally, methods are presented for calculating the exact end-to-end availability of a connection.

Survivability in Optical Networks

WDM optical networks are widely viewed as the most appropriate choice for the future Internet backbone with the potential to fulfill the ever-growing demands for bandwidth. A failure in a network such as a cable cut may result in a tremendous loss of data. Therefore, network survivability, the ability for a network to continue to provide services in the event of failures, is a very important issue in WDM optical networks. This chapter introduces the principles and state-of-the-art of survivability provisioning in optical networks, in particular, in optical networks that employ wavelength division multiplexing (WDM). Concepts of survivability provisioning in optical networks such as protection and restoration, dedicated versus shared survivability, path-based, link-based, segment-based, cycle-based survivability, and so on, are covered to provide multiple classes of quality of protection against single failure, dual-failure, multiple simultaneous failures, or shared risk link group failures, in WDM mesh networks. Recent developments in survivable service provisioning are summarized, such as survivability provisioning that takes into account the connection holding-time, survivability in WDM light-trail networks and optical burst switched networks. Finally, the chapter briefly examines future research directions.

Robust Design and Management of Optical Networks

High capacity advantage of optical networks also introduces the risk of huge data loss in case of a service interruption, even if the outage lasts a short time. Therefore, survivable and reliable design and management of optical networks is urgent. However, deployment of efficient survivability policies does not always guarantee the continuity of the service. Long failure restoration delays, multiple failures, and lack of protection resources may lead to service unavailability. Hence, connection availability arises as a design constraint, and it is defined as the probability of a connection being in the operating state at any time. Availability-constrained optical network design and availability-constrained connection provisioning are two important problems to guarantee robustness of connections in a survivable network.

Protection Architectures for WDM Passive Optical Networks

Passive Optical Networks (PON) support subscribers with bandwidth requirements more than 10 Mbps. Fiber and node failures in a PON network can lead to large amounts of data loss, while isolating the central office from the subscribers. Hence, high network availability is desired when a PON is used for business enterprises and for providing mobile backhaul services. To maximize network availability, several protection architectures have been proposed in literature. In this chapter, we critically analyze and compare novel WDM PON protection architectures amongst those proposed in the literature. The comparison is done from topology, resource utilization and power budget perspectives. We also discuss protection mechanisms that are typically used in the architectures and their impact on restoration.

Distributed Quality of Service Based Provisioning Framework for Survivable Optical Networks

This chapter provides new distributed frameworks to support Quality of Service (QoS) differentiation. These frameworks provide differentiated protection services to meet customers’ availability requirements effectively. We describe the availability-analysis for connections with different protection schemes. Through this analysis, we show how connection availability is affected by resource sharing. Based on the availability analysis, the proposed framework provisions each connection in which an appropriate level of protection is provided according to its predefined availability requirement. We consider the networks without wavelength conversion capability as well as dynamic traffic environment. In these distributed frameworks we propose several distributed schemes to provision and manage connections cost-effectively while satisfying the existing and new connections availability requirements.

Maximizing Primary Capacities in Survivable Networks

Achieving low blocking probability and connection restorability in the presence of a link failure is a major goal of network designers. Typically fault tolerant schemes try to maintain low blocking probability by maximizing the amount of primary capacity in the network. In this chapter, we assume the total capacity on each link is fixed, and then it is allocated into primary or backup capacity. The distribution of primary capacity affects blocking probability for dynamic traffic. This can be seen by simulating dynamic traffic with different ways to distribute capacities in a network. A Hamiltonian p-cycle is a capacity optimal way of allocating primary and backup capacity. However, different Hamiltonian p-cycle may deliver different blocking probability for dynamic traffic. In general, more evenly distributing the backup and primary capacity lowers the blocking probability. This chapter provides upper bounds on how much primary capacity a network can provide if it uses a link based protection strategy to guarantee survivability for one or more link failures. Using integer linear programs we show that requiring preconfiguring carries a cost in terms of capacity if the solution is structured as a set of cycles.