Heterogeneous networks: types of layers definitions

An heterogeneous network comprises multiple layers that may represent different technologies, data plane switching granularity levels, or distinct network roles.
The different technologies refer to data flow treatment and organization. For instance it could be based on Packet Switching capable nodes, Time Division Multiplexing (eg. SDH) or Lambda Switching capable (RFC3945).
In the same control plane of switching capability the data plane granularity levels may vary according to the bandwidth capability. (eg. VC4, VC12 Virtual Containers in SDH). (RFC5212).
The distinction can also refer to client and server roles in the network, where the server is the provider of the carrier network for long distance low level connection (backbone) providing service for the transmission of many data flows of smaller bandwidth granularity.