4.13.5. Getting Notification of Audio-to-Fax Transition

Audio transcoding to fax 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 an audio transcoding session transitions to fax transcoding, 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 audio RTP stream is terminated. The GC_PARM_BLK does not contain any additional information.
2. IPPARM_RX_DISCONNECTED - The receive audio RTP stream is terminated. The GC_PARM_BLK does not contain any additional information.
3. IPPARM_TX_CONNECTED - Transmit fax transcoding is initiated. The datatype of the parameter is an IP_CAPABILITY structure representing the T.38 transcoder being used. See Section 4.13.1, Specifying T.38 Coder Capability for more information.
4. IPPARM_RX_CONNECTED - Receive fax transcoding is initiated. The datatype of the parameter is an IP_CAPABILITY structure representing the T.38 transcoder in use. See Section 4.13.1, Specifying T.38 Coder Capability for more information.

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