7. Analytical Models for QoT-Aware RWA Performance

As can be seen in Chap. 3, a large number of QoT-Aware or Impairment-Aware Routing and Wavelength assignment algorithms (IA-RWA) were designed to minimize blocking in dynamic transparent optical networks. The very vast majority of those algorithms were evaluated through extensive simulations. With time, proposed IA-RWA grew in complexity, actually making their accurate evaluation possible only using full-scale simulations. Full-scale simulations, however, tend to be lengthy for the following three reasons: (a) the growing complexity of the proposed IA-RWA techniques; (b) the increasing complexity of the networks that must be modeled (spurred for instance by the increase in the number of wavelengths that can be routed in the network—note that this could be somewhat offset by the deployment of networks with fewer, higher-capacity channels); and (c) the inclusion of more complex QoT models in the simulations—more accurate QoT models are typically more simulation intensive. In addition, establishing a new lightpath may disrupt lightpaths that are already established through the addition of cross-channel effects, such as node crosstalk or non-linear effects. Such disruption is not desirable in a transparent network, and hence in simulations of IA-RWA the QoT of any lightpath that may be disrupted by the arrival of a new demand should be evaluated. Hence, for each new demand, the QoT of many lightpaths may have to be evaluated. If a blocking rate of 10^{− 5} or less is desired, then the simulation of the arrival of (many times more than) 10⁵ lightpaths is required; if a network operator wants to test an IA-RWA in less than 10 min, then a decision must be reached for each demand in (much) less than 60 ms. This can prove difficult to achieve if QoT is to be estimated accurately.