ITU-T Recommendation G.806 "Characteristics of transport equipment - Description methodology and generic functionality" specifies a methodology to describe equipment for transport networks based on the transport processing functions and architectural entities defined in ITU-T Recommendation G.805.
It defines the set of generic atomic and compound functions and the set of rules how to combine them.
The detailed characteristic of equipment functional blocks of specific transport networks (e.g., SDH, OTN) is defined in follow-up Recommendations based on this methodology, i.e. G.783 resp. G.798.
Equipment can then be described by an Equipment Functional Specification (EFS) which lists the atomic functions and their interconnection.
In addition generic functionality, processes and overall performance objectives for transport networks are defined in this Recommendation.