Some use cases like, for example, bandwidth on demand (BoD) or optical VPNs require exposure of transport network services to systems that do not use YANG, RESTCONF or other capabilities discussed in the transport network context. However, their logic will be the same: some northbound interface model and commands are translated into southbound ones. What is southbound for the upper-level systems is northbound for transport network.
The orchestrators’ market is unsettled: many solutions exist, there is no clear leader, analysts predict it to be so for some time. Amongst open solutions most noticeable are Open-O hosted by Linux Foundation and OSM (Open Source MANO) hosted by ETSI. OSM covers mainly NFV (datacenter) orchestration space, thus relatively irrelevant for the transport SDN scope. Open-O has a wider scope covering NFV and SDN services, including transport.
As there is no clear leader in orchestration, we can only make assumptions what direction to choose. The most probable technologies to be used in the beginning will be YANG to model network services, TOSCA for datacenter and cloud services, TOSCA or some new alternative for end-to-end services, non-standard RESTful interface to organize communication.