Paradoxically, with an ever-increasing traffic demand, today transport-network operators experience a progressive erosion of their margins. The alarms of change are set, and Software Define Networking (SDN) is coming to the rescue with the promise of reducing Capital expenditures (CapEx) and Operational expenses (OpEx). Driven by economic needs and network innovation facilities, today transport SDN (T-SDN) is a reality. It gained big momentum in the last years, however in the networking industry, the transport network will be perhaps the last segment to embrace SDN, mainly due to the heterogeneous nature and complexity of the optical equipment composing it. This survey guides the reader through a fascinating technological adventure that provides an organic analysis of the T-SDN development and evolution considering contributions from: academic research, standardization bodies, industrial development, open source projects and alliances among them. After creating a comprehensive picture of T-SDN, we provide an analysis of many open issues that are expected to need significant future work, and give our vision in this path towards a fully programmable and dynamic transport network.

Use of disaggregated equipment in optical transport networks is emerging as an attractive solution to bring flexibility and break vendor lock-in dependencies. The disaggregation process requires standard protocols and interfaces between the control plane and network equipment. NETCONF has been selected as the standard protocol and multiple initiatives are currently working on the definition of standard models for each type of data plane devices. Different levels of disaggregation of the data plane are under evaluation, and it is still not clear up to which level it will be useful to disaggregate the data plane. The disaggregation of optical networks yielded the development of several SDN-based controllers providing an environment for creating and deploying networking application on optical networks. Among them, the ONOS controller features the most active community with the recent establishment of the ODTN working group, specifically focused on the introduction of required functionality to control and monitor disaggregated transport networks. This paper reports on the state-of-art, potentials and limitations of the ONOS controller applied to disaggregated optical networks with specific focus on the ongoing activities within the ODTN working group. Then, the paper describes a set of experiments performed on a setup including both emulated and real optical devices controlled with ONOS. The performed experiments consider both the establishment of a connectivity service and the recovery of the connectivity in case of failure on the data plane.

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state-of-art, potentials and limitations of the ONOS controller applied to disaggregated optical networks are reported. Focus is on the on-going ODTN project. Results of experimental demonstrations are reported to prove the feasibility of proposed approach.