# Fusion NbUP Protocol Stack

The following illustration shows the protocol stack along with the relevant standards and specifications for each layer in the stack:

The NbUP protocol (TS 29.415) is almost identical to the Iu UP protocol (TS 25.415). Because the NbUP uses the same PDU types as the Iu UP, the term IuFP is used to refer to the common framing.

The Dialogic implementation of NbUP supports the following functions:

- Transfer of user data

- Initialization

- Error event handling

- Frame quality classification

The NbUP endpoint returns a negative acknowledgement (NACK) for all other procedures with an appropriate error code.

A typical NaturalAccess application acting as a media gateway uses an NbUP endpoint along with G.711, AMR, or clear channel connected to a DS0 endpoint to transfer media between TDM and IP interfaces as shown: