From Network Design to Dynamic Provisioning and Restoration in Optical Cross - Connect Mesh Networks : An Architectural and Algorithmic Overview

o accommodate the exponential growth of the Internet, transport networks based on wavelength-division multi-plexing (WDM) technology [1] are increasingly being deployed in carrier networks. WDM technology harnesses the enormous bandwidth of the fiber (potentially tens of terabits per second) by multiplexing hundreds of optical channels, each of which operates at speeds of several gigabits per second. Point-to-point WDM links that multiplex several tens of optical channels are currently being deployed in the carrier networks. Figure 1 illustrates the architecture of an optical network where multiple optical cross-connects/switches (OXCs) are interconnected via WDM links in a general topology (referred to as an optical mesh network [1]). An optical mesh network allows for flexible use of wavelength channels, enabling capacity efficient provisioning and restoration. An OXC has multiple ports and is capable of switching an optical wavelength channel (e.g., at OC-48, OC-192 rates) from an input port to an output port. In general, optical switches can be purely optical, electronic , or a combination of optical and electronic, depending on the degree to which signals remain in the optical or electronic domains within the switch. In this article we assume that the optical network allows for full wavelength conversion (i.e., any wavelength channel on an input port can be switched to any wavelength channels on output ports). These switches typically have an electronic switch fabric and perform opto-electronic conversion of the incoming light signal for intelligent processing. They are referred to as optical-electronic-optical (O-E-O) switches. Wavelength conversion is enabled by the O-E-O switch and/or transponders at the WDM system. An optical network allows dynamic provisioning of optical layer connections, called lightpaths, between clients connected to the network. The provisioning activity consists of establishing suitable cross-connects in each OXC in the connection path such that end-to-end connectivity is realized. Lightpaths can be protected against failure of network components such as lasers, fiber links, and nodes. The interaction between OXCs in a network is over a well-defined signaling and routing interface. This interface includes both IP and multiproto-col label switching (MPLS)-based protocols for provisioning of optical layer connections as well as proprietary protocols for restoration of such connections after failures. A consensus is emerging in the industry on utilizing an IP-centric control plane within optical networks to support dynamic provisioning and restoration of optical layer connections. Figure 1 also depicts the interfaces to client networks (the user–network interface, UNI [2]) and to other external …