Switching from voice to fax

Fusion gateways configured for voice/fax switchover initially treat all calls as voice transmissions. The following table shows how Fusion gateways switch from voice to fax processing mode in the presence of fax data:

Step

Fax station 1

(calling machine)

Emitting gateway

 

Receiving gateway

 

Fax station 2

(called machine)

1

Sends CNG tone

Transfers CNG tone over a voice connection.

Transfers CNG tone over a voice connection.

Receives the CNG tone

Sends a CED tone

2

Receives CED tone

Receives the T.38 packet:

  • T38UDP endpoint detects the first valid T.38 packet and sends an event to the application.

  • Application disables the voice channel and enables the fax channel.

  • Application sends a command to DS0 endpoint, switching it from voice to fax transmission mode.

  • Fax channel transfers fax data to PSTN.

 

Receives the CED tone:

  • DS0 endpoint detects the CED tone and sends an event to the application.

  • Application disables the voice channel and enables the fax channel.

  • Application sends a command to DS0 endpoint, switching it from voice to fax transmission mode.

  • Fax channel starts sending T.38 packets.

 

 

3

Fax transmission

Fax transmission

Fax transmission

Fax transmission

4

Disconnects

Ends fax transmission (or disconnects) and switches DS0 endpoint back to voice mode.

Disconnects and switches DS0 endpoint back to voice mode.

Disconnects

After the fax connection is disabled, you can reuse the connection after disabling and then re-enabling the T38UDP endpoint.

For information about MSPP service functions and information about MSPP service T.38 filters and filter commands, refer to the Dialogic® NaturalAccess™ Media Stream Protocol Processing API Developer's Manual.