Pluggable control and the role of Transport API [Invited Tutorial]

This tutorial presents an overview of the recent developments of Transport API (TAPI, versions 2.5–2.6) as an open and standard north-bound interface for optical networks and its evolution and challenges to address the control of (coherent) pluggable devices as, for example, per TIP MANTRA reference architectures, along with an in-depth overview of the technologies, abstractions, and control-plane mechanisms required to operate such networks. We first review the softwarization of networks thanks to SDN, the adoption of model-driven development, the transition from discrete transponders to coherent pluggables, and the role of standardized interfaces such as OpenConfig or CMIS. Next, we elaborate on the foundations of TAPI, including its multi-layer information model, recent developments such as impairment extensions, and the representation of transceiver operational modes through TAPI profiles. The key challenge addressed is the control of coherent pluggables within packet–optical devices, where single/dual south-bound interfaces, Open-XR architectures, and MANTRA-inspired IPoWDM control models introduce coordination and synchronization requirements. We consider the role of TAPI in such control models along with the role of streaming telemetry for aspects such as distributed state synchronization and the use of PCE/digital twins for enabling closed-loop and autonomous operation.