A survey on QoT prediction using machine learning in optical networks

• QoT prediction problem in optical networks is elaborated, including the main QoT influence factors, QoT metrics, and QoT prediction strategies. • The QoT prediction model construction is reviewed from four aspects, i.e., ML algorithm selection, dataset generation, ML frameworks, construction process of QoT prediction model. • Three kinds of QoT prediction solutions are traditional ML based QoT prediction models, transfer learning or/and active learning assisted QoT prediction models, and APLMs with ML. • Some future research directions are proposed, including digital twin based QoT prediction and transfer learning assisted light-trees QoT prediction, pre-weighted input features for QoT prediction, and improvement in adaptability of QoT prediction model. In optical networks, a connection (e.g., light-path and light-tree) is set up to carry data from its source to destination(s). When the optical signal transmits through the fiber links and optical devices, the quality of transmission (QoT) degrades due to various physical layer impairments (PLIs), including linear and nonlinear impairments. QoT is an important metric that determines the availability of a connection. Therefore, the QoT guarantee is the premise of successful connection establishment in optical networks. QoT prediction before connections establishment can provide guidance for the routing and resources allocation of connections. In order to receive the correct signal at the receiving end, during network planning design margins are introduced to compensate the inaccuracy of the QoT prediction model itself and its inputs. Improving the accuracy of prediction can make better use of network resources and reduce margins. With the help of strong computing power and data acquisition based on software defined optical network (SDON), machine learning (ML) based models are more suitable for QoT prediction than analytical models that are difficult to derive and computationally heavy. This paper provides an overview on the applications of ML technologies in QoT prediction. Firstly, we elaborate the QoT problem in optical networks, including main QoT influence factors, QoT metrics, and QoT prediction strategies. Then, suitable ML algorithms, the generation of sample data, ML frameworks and the construction of QoT prediction model, are briefly introduced. Next, three solutions of QoT prediction using various ML technologies in recent studies and their practical feasibility are reviewed and discussed in detail. Finally, based on the existing researches, we present some future research directions about the improvement of QoT prediction.