Optical Node Architectures

Abstract

This chapter provides an overview of prominent optical network node architectures beginning with basic nonwavelength channel reconfigurable nodes through to the most advanced reconfigurable node configurations. The generic functionality of an optical network node is summarized as it pertains to network performance (Sect. 8.1), functionality and network topology, including characteristics such as colorless, directionless and contentionless switching and flexible spectrum channel definition. A variety of node architectures are then described in detail (Sect. 8.2), highlighting the capabilities and flexibilities these architectures provide and what the key devices necessary to construct each node architecture are and their attributes. A general overview of how the performance of the overall network depends upon the various node architectures and the implementing devices (Sect. 8.3), including the addition of optical noise, optical filtering and optical channel crosstalk is provided, followed by a description of general approaches to optically monitoring and validating the optical signals traversing the node. Finally, a summary of general forward-looking trends for reconfigurable optical network nodes is provided. Optical communication in essence involves the transportation of optical, data-carrying signals between two desired locations separated by a physical distance, generally over optical fiber, in order to provide communication of that data between those two locations. Optical communication networking, however, refers to an optical transportation infrastructure that provides optical communication between multitudes of separate locations using a common infrastructure over which those optical data-carrying signals propagate. In practice, this common infrastructure generally consists of a network of optical nodes located at traffic communication end-points and interconnected by optical fibers. Leveraging such a common infrastructure provides economic advantages as a large number of communication links can be supported between diverse locations by that infrastructure. In addition, an operational advantage is generally further achieved as additional communication links can be introduced onto that network over time as the demand arises, providing the network operator the ability to grow the overall traffic-carrying capability of their network in alignment with their needs. As traffic capacity growth patterns are generally difficult to accurately predict, network operators are generally interested in an optical network infrastructure that provides them the ability to flexibly and efficiently support the introduction of new communication links generally between any pairs of nodes within the network as the need arises and with minimal restrictions from already deployed traffic. This maximizes the growth lifetime of the network and consequently the utility of the network infrastructure investment they have already made.