# Fusion DCE transport

DCE transport over IP transmits fax or modem traffic over a clear Fusion G.711 channel. Applications use the echo_v4.f54 echo cancellation module provided with Natural Access, along with the Fusion RFC 2833 compliant capabilities, to implement this functionality.

Fax machines and modems generate one of the ANS (2100 Hz) family of signals as part of initial negotiation. The echo_v4.f54 module detects the variations of this signal, and sends notifications to the host to initiate the transition to a G.711 clear channel.

The remote gateway is informed of the occurrence of an ANS family signal when it receives an RFC 2833 packet containing a specific ANS signal identification. When it receives this packet, the remote gateway transitions into a G.711 clear channel and configures the echo canceller appropriately.

The application transitions from Fusion voice channel to a Fusion G.711 clear channel under the following circumstances:

- Emitting side: A DS0 endpoint detects an ANS-type signal

- Receiving side: An RTP endpoint receives an ANS-type RFC 2833 packet

This topic shows the required transition steps on the emitting and receiving side of the IP network.

## Emitting side

The transition from voice data to DCE transport over IP occurs in the following way on the emitting side of the network:

Step | Action
1 | The MSPP DS0 endpoint (through its echo canceller functionality) detects an ANS-type signal from the PSTN network it and sends an ADIEVN_ECHO_CANCEL_TONE event to the application.
2 | The application configures the echo canceller for the particular connection based on the type of ANS signal detected.
3 | The application disables, disconnects, and destroys the current MSPP channel (G.723 in the illustrations).
4 | The application creates a G.711 channel configured for clear channel use, connects the channel to the existing endpoints, and enables the channel.
5 | The application sends ANS information to the remote system through an MSPCMD_ENCODE_PLAY_RFC2833 command.

For more information, refer to Transferring non-DTMF RFC 2833 events.

## Receiving side

The transition from voice data to DCE transport over IP occurs in the following way on the emitting side of the network:

Step | Action
1 | RTP endpoint detects an ANS-type RFC 2833 packet and sends MSPEVN_RFC2833_REPORT to the application.
2 | The application configures the echo canceller based on the type of ANS signal detected.
3 | The application disables, disconnects, and destroys the current MSPP channel.
4 | The application creates a G.711 channel configured for clear channel use, connects the channel to the existing endpoints, and enables the G.711 channel. DCE fax data can now be transferred through the two gateways across the IP network.