Elastic Optical Networks

In WDM networks using a fixed frequency grid, transmission rates can vary for different connections, leading to inefficient bandwidth utilization in optical fibers with lower-rate connections using wide frequency slots. In elastic optical networks (EONs), the frequency grid is made flexible, thereby improving the effective network capacity. A flexible frequency grid consists of smaller frequency slots, and a transmitting node can use multiple slots using suitable modulation techniques, such as optical OFDM, Nyquist-WDM and optical arbitrary waveform generation (OAWG). However, this requires bandwidth-variable transceivers (BVTs) and other devices to set up variable-rate connections. First we discuss the design challenges in EONs and describe the evolving technologies for the network elements. Then we present some offline (LP-based and heuristic) design methodologies for EONs to carry out routing and spectral allocation (RSA) for the required connections. Finally, we present some online fragmentation-aware RSA schemes for the operational EONs. (146 words)

Optical Network Control and Management

The task of network control and management is generally realized in two logical planes – control and management – which collaboratively operate to ensure smooth, secure, and survivable traffic flow in the data plane of the network. Some of the functionalities are realized in the control plane, needing real-time execution, such as recovery from network failures, and network reconfiguration due to traffic variation. Other functionalities deal with performance monitoring, configuration management, network security, accounting and billing etc., which are less time-sensitive and are addressed by the management plane. We first discuss the philosophy of multiple-layer abstraction of telecommunication networks, including control, management, and data planes, and then describe various network control and management techniques used in optical networks: operation, administration, and management (OAM) in SONET, generalized multiprotocol label switching (GMPLS), automatically switched optical network (ASON), and software-defined optical networking (SDON) in WDM networks. (141 words)

WDM Long-Haul Networks

Ever-increasing traffic in the long-haul networks called for WDM-based transmission, all the more when compared to the metro and access segments. Further, although the interconnected WDM rings served the needs of long-haul networks for some time, mesh-connected WDM networks appeared as a natural and more effective solution, with enhanced connectivity and resilience against network failures. In this chapter, we first examine the basic design challenges and the candidate node configurations for WRON-based mesh networks. Next we present various offline design methodologies for this class of networks using LP-based and heuristic schemes. Impact of wavelength conversion (WC) in mesh-configured WRONs is also examined by using analytical models, and the gain in bandwidth utilization is assessed in WRONs with full WC as compared to those without any WC. Finally, we examine some online routing and wavelength assignment schemes that can be used for operational WRONs. (143 words)