There is an opinion of some experts that BGP LS and PCEP will be gradually forgotten with wider adoption of YANG and segment routing as they provide enough means to model and manage topology and paths. However, according to the major vendors’ presentations it is not the case for at least 2-3 years.
Other experts argue that YANG is not well suited for representation and modeling complex services with workflows, relationships, dependencies, thus it might be less useful on the higher levels of network management hierarchy (end-to-end service orchestrators, for example). They propose to use TOSCA for service modeling.
OpenFlow-based solutions and intent-based approach to network management are adding complexity to the unclear future.
It is not clear now what approach will win in the end and in what niche. Thus, the choices for the transport network architecture should be based on the following assumptions:
- It is highly unlikely that traditional routers will be completely replaced (by white-boxes, for example) in transport network core in short and medium term - traditional vendors’ architectures will still be important
- Different use cases might require different management approaches – architecture should be flexible enough to leverage advancing developments
BGP LS, PCEP, YANG and OpenFlow will coexist at least on the southbound interfaces of SDN controllers, YANG and TOSCA will coexist in the northbound ones, some unmentioned newcomers will get traction as well. At first sight it might be considered as unnecessary variability, but in fact in specific use cases the choice will be limited to 1-2 options.
Transport SDN architecture flexibility must be achieved through the integration capabilities of hierarchical SDN controllers and relevant mid/upper-level management applications:
- Hierarchical controller is to abstract complexity and changes of the below levels (southbound interfaces) through integrated service view (northbound interfaces)
Orchestrators and optimization applications are to manage end-to-end services and manipulate their parameters. Some of the applications might be integrated with the SDN controllers and some will be standalone ones.