4.13.6. Getting Notification of Fax-to-Audio Transition

Fax transcoding to audio transcoding is done automatically with no intervention necessary by the application, but the application can be configured to receive notification when the transition takes place. The events for this notification must be enabled; see Section 4.14, Enabling and Disabling Unsolicited Notification Events for information on enabling streaming connection and disconnection events (EXTENSIONEVT_STREAMING_STATUS).

Once the notification events have been enabled, when a fax transcoding session transitions back to the prior audio transcoding session, four GCEV_EXTENSION events are received, each with the extID of IPEXTID_MEDIAINFO and a parameter set ID of IPSET_MEDIA_STATE.

Each GCEV_EXTENSION event contains a parameter. The parameter for each event in order of reception is as follows:

1. IPPARM_TX_DISCONNECTED - The transmit fax RTP stream is terminated. No more information is contained in the GC_PARM_BLK.
2. IPPARM_RX_DISCONNECTED - The receive fax RTP stream is terminated. No more information is contained in the GC_PARM_BLK.
3. IPPARM_TX_CONNECTED - Transmit audio transcoding is initiated. The datatype of the parameter is an IP_CAPABILITY structure representing the audio transcoder setting in use before fax transcoding was initiated. See Section 4.13.1, Specifying T.38 Coder Capability for more information.
4. IPPARM_RX_CONNECTED - Receive audio transcoding is initiated. The datatype of the parameter is an IP_CAPABILITY structure representing the audio transcoder setting in use before fax transcoding was initiated. See Section 4.13.1, Specifying T.38 Coder Capability for more information.

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