TSPI_lineAddToConference function (tspi.h)

The TSPI_lineAddToConference function adds the call specified by hdConsultCall to the conference call specified by hdConfCall.


LONG TSPIAPI TSPI_lineAddToConference(
  HDRVCALL      hdConfCall,
  HDRVCALL      hdConsultCall



The identifier of the asynchronous request.


The handle to the conference call. The call state of hdConfCall can be onHoldPendingConference or onHold.


The handle to the call to be added to the conference call. This call cannot be either a parent of another conference or a participant in any conference. Depending on the device capabilities indicated in LINEADDRESSCAPS, the hdConsultCall parameter may not necessarily have been established using TSPI_lineSetupConference or TSPI_linePrepareAddToConference. The call state of hdConsultCall can be connected, onHold, proceeding, or ringback.

Return value

Returns dwRequestID or an error number if an error occurs. The lResult actual parameter of the corresponding ASYNC_COMPLETION is zero if the function succeeds or an error number if an error occurs. Possible return values are as follows:



The service provider returns LINEERR_INVALCALLHANDLE if hdConsultCall is a parent of another conference or already a participant in a conference, or hdConsultCall cannot be added for other reasons, such as it must have been established using TSPI_lineSetupConference or TSPI_linePrepareAddToConference.

Note  The call handle of the added party remains valid after adding the call to a conference; typically, its state changes to conferenced while the state of the conference call becomes connected. The handle to an individual participating call can be used later to remove that party from the conference call using TSPI_lineRemoveFromConference.
The call states of the calls participating in a conference are not independent. For example, when dropping a conference call, all participating calls can automatically become idle. TAPI can consult the line's device capabilities to determine what form of conference removal is available. TAPI or its client applications should track the LINE_CALLSTATE messages to determine what happened to the calls involved.

The conference call is established either through TSPI_lineSetupConference or TSPI_lineCompleteTransfer. Typically, the call added to a conference is established using TSPI_lineSetupConference or TSPI_linePrepareAddToConference. Some switches may allow adding of an arbitrary call to conference, and such a call may have been set up using TSPI_lineMakeCall and be on (hard) hold. All calls that are part of a conference must exist on the same open line.

Any monitoring (media, tones, digits) on a conference call applies only to the hdConfCall parameter, not to the individual participating calls.

This function has no restrictions based on privilege as in the corresponding function at the TAPI level. There is no explicit requirement for the service provider to track the relationships between the "parent" conference call and its participants, because there is no TSPI correspondence to the TAPI function. Many service providers may find it necessary to track these relationships internally to implement the other conference call management functions.


Target Platform Windows
Header tspi.h

See also