# Migrating from Fusion 3 to Fusion 4

Fusion 4 provides extended functionality and simplified programming models from earlier versions of Fusion. Fusion 4 extended features include:

Feature | Fusion 4 | Earlier Fusion releases
End-to-end gateway media channel construction and switching | Performed transparently by the MSPP service | Switching performed explicitly by application through the SWI service and the TX APIs.
Creation of connection endpoints for PSTN, host, and IP network interfaces | Performed through MSPP service | Performed through AG TRAU, HBF service, and Virtual Port APIs.
Runtime control of media channel processing (for example, fax, G.711, or G.723.1.) | Performed through MSPP service | Performed through AG TRAU, HBF service, and Virtual Port APIs.
Interfaces for both the IP network and PSTN | CG board provides both network interfaces | AG line interface board provides PSTN interface. TX board provides IP network interface
Integrated PSTN and IP call control | Performed by using a third party IP protocol stack in conjunction with Natural Access PSTN call control | Performed by using a third party IP protocol stack in conjunction with Natural Access PSTN call control

The following illustration shows a broad overview of the earlier Fusion 3 programming model:

The following illustration shows the simplified Fusion 4 programming model. Notice that all of the media processing tasks, formerly performed with several different APIs and services, are now accomplished with the MSPP service only:

In both models, application initialization, PSTN call control, and switching are controlled by Natural Access and its services (ADI, NCC, and SWI services). Call control at the IP network interface can be performed through a third party protocol stack such as the SIP or H.323.

The following table shows the operations required to create and control an end-to-end media channel from a PSTN or an IP network in a Fusion 4 and Fusion 3 application:

Gateway application media stream tasks | Fusion 4.4 application | Fusion 3.0 application
Respond to incoming PSTN calls | Natural Call Control (NCC) service | ADI service
Switch PCM data from AG or CG Series board line interfaces to AG or CG Series board ports | Set up during board configuration or performed manually (with the SWI service) | SWI service
Switch voice/fax data from PSTN ports to board DSPs | Performed transparently by the MSPP service | SWI service
Control media channel data processing | MSPP service | AG TRAU service
Transfer data to host | MSPP service | HBF service
Transfer data from board resource back to CT bus | Performed transparently by the MSPP service | SWI service
Transfer data from CT bus to IP interface | Performed transparently at board level | TPX API, Common Management API, and CPI library
Set up and control media channel endpoints at IP interface | MSPP service | Virtual Port API and RTP API
Perform IP call control | Third party protocol stack | Third party protocol stack