Review otu-type identities

[italobusi]

The identities are not yet used by any other model

• Check if they are needed when other models (e.g., for tunnel models) mature

The following OTU types are defined but the references are missing, since not defined by ITU-T G.709:

• OTU1e

• OTU1f

• OTU2e

• OTU2f

• OTU3e1

• Check if they are needed and where they are defined (some, but not all, are defined in G.Sup43)

[italobusi]

Agreed to define identities only for the standard OTU types defined in G.709