This Recommendation defines the functional requirements of metro transport network (MTN) functionality within equipment.

This Recommendation uses the methodology defined in [ITU-T G.806], in general for transport network equipment, and is based on the architecture of MTN defined in [ITU-T G.8310] and the interfaces for metro transport networks defined in [ITU-T G.8312]. The description of the functional blocks will be generic and no particular physical partitioning of functions will be implied. The input/output information flows associated with the functional blocks serve for defining the functions of the blocks and are conceptual, not physical.

The functionality that will be defined in this Recommendation can be applied at user-to-network interfaces (UNIs) and network node interfaces (NNIs) of the metro transport network. Additionally, the overhead processing functionality necessary for operations and management of the metro transport network will also be defined.

Not every functional block defined in this Recommendation is required for every application. Different subsets of functional blocks from this Recommendation and similar Recommendations may be assembled in different ways according to the combination rules given in these Recommendations to provide a variety of different capabilities. Network operators and equipment suppliers may choose which functions must be implemented for each application.

The internal structure of the implementation of this functionality (equipment design) need not be identical to the structure of the functional model, as long as all the details of the externally observable behaviour comply with the equipment functional specification (EFS).