This Recommendation specifies common elements and signal structures used by various types of flexible optical transport network (FlexO) interfaces, both for single vendor applications and multi-vendor interoperable applications. Such definitions include FlexO frame, FlexO instance interleaving, mapping procedures to FlexO-n(e) and FlexO overhead. FlexO interfaces support bonding (i.e., grouping) of multiple interfaces such that one or more client signals (e.g., OTUCn or Ethernet) can be transferred via one or more optical tributary signals (OTSi) over one or more physical interfaces. Interoperable short-reach and long-reach interfaces are defined in other Recommendations such as [ITU-T G.709.3], [ITU-T G.709.5] and [ITU-T G.709.6].

In addition, some introduction material for the various short and long-reach applications is included.