# Loopback connections

Loopback connections enable applications to monitor the status and quality of voice data transmission within the Fusion gateway. An MSPP loopback receives voice data from a network source, processes the data through a voice channel, and then returns the data to its point of origin (that is, the endpoint from which it was received).

Fusion provides two methods for looping back voice data depending on the type of network (IP or PSTN) from which the data originates:

Loopback | Description
DS0 (PSTN-side) | The gateway receives voice data from an IP network through an RTP endpoint, processes the data through a voice channel, loops the data back at the DS0 endpoint (using the Switching service), and sends the data back to the RTP endpoint that originally received the data.
RTP (IP-side) | The gateway receives voice data from a PSTN through a DS0 endpoint, processes the data through a voice channel, loops the data back at the IP layer (by appropriately configuring the endpoint's local and remote IP address), and sends the data back through the receive side of the IP stack.

In both loopback scenarios, the voice data goes through the full set of voice channel processing. That is, the data is encoded and then decoded, or vice versa.