# Call control and message functions

Use the following functions to monitor calls and send messages to the remote terminal:

Function | Description
h324_h223SkewIndication | Sends an H.223 skew indication to the terminal.
h324FormatEvent | Formats an H.324M event into a string for print diagnostics.
h324ModifyOutVideoChannelParam | Closes an existing video logical channel and then re-opens the channel with user-supplied logical channel parameters.
h324PassthruDTMFMode | Sets the DTMF mode and payload IF for RFC 2833 DTMF events sent on a pass-through channel.
h324PassthruPlayRFC2833 | Plays an application-provided RFC 2833 DTMF event onto the IP network in RTP encapsulation.
h324RoundTripDelay | Sends a round trip delay message to the remote terminal.
h324SubmitEvent | Submits Natural Access events from the event queue to the H.324M Middleware.
h324UserIndication | Sends a user indication (UII H.245) message to the terminal.
h324VendorIDIndication | Sends a vendor ID indication to the remote terminal.
h324VideoFastUpdate | Sends a video fast update message to the remote terminal.
h324VideoTemporalSpatialTradeoff | Sends a VideoTemporalSpatialTradeoff message to the remote terminal.