Resilient Optical Transport Networks

Introduction

Nowadays client networks such as Internet Protocol (IP) networks, asynchronous transfer mode (ATM), synchronous optical networking (SONET) and synchronous digital hierarchy (SDH) networks, and so on, employ DWDM optical transport networks to carry data, voice and videos (Murthy and Gurusamy, 2004). The modern optical transport networks are able to provide a huge amount of bandwidth at multiple tetra bits per second (Tb/s) transmission rate by employing fiber optic cables, nodal devices like optical cross-connect switches (OXCs) and optical add-drop multiplexers (OADMs), and the DWDM technology (Kartalopoulos, 2000; Mukherjee, 2000).

The DWDM optical transport networks are being increasingly deployed in the next generation telecommunication networks through the integration of IP over DWDM networks. This may reduce the protocol overhead, the implementation complexity and cost (Rajagolapan, et al., 2000; Ghani, Dixit, & Wang, 2003). Therefore the provisioning of acceptable services in the presence of failures and attacks is a major issue, particularly for future IP services with enhanced quality of service (QoS).

The DWDM optical networks are prone to failures such as link and node failures at the optical layer. These failures can potentially lead to a catastrophic loss of data and revenues, producing an unacceptable deterioration in the delivered quality of service (QoS). Therefore, one of the most important optical network design issues is survivability (Zhou, & Subramaniam, 2000), which is the ability of a network to provide continuous services at an acceptable level in the presence of different failure scenarios (Gerstel & Ramasawami, 2000; Zhang, & Mukherjee, 2004). Reasons of designing fault tolerant optical transport networks are summarized as follows:

• 1.

  Increasingly, end-users of client networks demand reliable communications and services with assured quality (M´edard & Lumetta, 2002).

• 2.

  The unexpected failures of network components such as link and node failures at the optical layer may result in multiple failures at client layers.

• 3.

  The aggregated bandwidth on the order of several Tb/s per fiber causes enormous data and revenue loss in the event of network’s failures.

• 4.

  Fault tolerance and traffic restoration at the optical transport layer have several advantages, such as shorter restoration time, efficient resource utilization, and protocol transparency, over those at the client layers.

• 5.

  The failures at the optical layer and data loss would affect the delivered QoS by client networks to end-users.

While survivability in optical networks is highly desirable, redundant resources are necessarily employed to cover the failures, which increases the network cost.

This chapter reviews some major issues of designing fault tolerant Dense-Wavelength-Division-Multiplexing (DWDM) optical transport networks for service provisioning with quality of service assurance in the presence of failures for the next generation high-speed telecommunication networks. We summarize the main reasons of developing survivable DWDM optical transport networks and the failures scenarios of network components and links. The survivability schemes based on protection and restoration architectures and the traffic demand models are surveyed. The routing and wavelength assignment (RWA) problems which lie at the heart of designing the wavelength-routed DWDM optical transport networks are reviewed. Solution approaches such as integer linear programming (ILP), heuristics, and intelligent genetic algorithm based approaches, are reviewed. The K-shortest path procedure which is needed to design reliable communication networks is presented. The main problems of accommodating future demand uncertainties for designing the robust networks are discussed. Finally the quality of service (QoS) issues that arise in the deployment of resilient DWDM backbones are summarized.