lineHandoff

The lineHandoff function gives ownership of the specified call to another application. The application can be either specified directly by its filename or indirectly as the highest priority application that handles calls of the specified media mode.

LONG lineHandoff(

HCALL hCall,
LPCSTR lpszFileName,
DWORD dwMediaMode
);

Parameters

hCall

A handle to the call to be handed off. The application must be an owner of the call. The call state of hCall can be any state.

lpszFileName

A pointer to a NULL-terminated ASCII string. If this pointer parameter is non-NULL, it contains the filename of the application that is the target of the handoff. If NULL, the handoff target is the highest priority application that has opened the line for owner privilege for the specified media mode. A valid filename does not include the path of the file.

dwMediaMode

The media mode used to identify the target for the indirect handoff. The dwMediaMode parameter indirectly identifies the target application that is to receive ownership of the call. This parameter is ignored if lpszFileName is not NULL. Only a single flag may be set in the dwMediaMode parameter at any one time. This parameter uses the following LINEMEDIAMODE_ constants:

LINEMEDIAMODE_UNKNOWN

The target application is the one that handles calls of unknown media mode (unclassified calls).

LINEMEDIAMODE_INTERACTIVEVOICE

The target application is the one that handles calls with the interactive voice media mode (live conversations).

LINEMEDIAMODE_AUTOMATEDVOICE

Voice energy is present on the call and the voice is locally handled by an automated application.

LINEMEDIAMODE_DATAMODEM

The target application is the one that handles calls with the data modem media mode.

LINEMEDIAMODE_G3FAX

The target application is the one that handles calls with the group 3 fax media mode.

LINEMEDIAMODE_TDD

The target application is the one that handles calls with the TDD (Telephony Devices for the Deaf) media mode.

LINEMEDIAMODE_G4FAX

The target application is the one that handles calls with the group 4 fax media mode.

LINEMEDIAMODE_DIGITALDATA

The target application is the one that handles calls that are digital data calls.

LINEMEDIAMODE_TELETEX

The target application is the one that handles calls with the teletex media mode.

LINEMEDIAMODE_VIDEOTEX

The target application is the one that handles calls with the videotex media mode.

LINEMEDIAMODE_TELEX

The target application is the one that handles calls with the telex media mode.

LINEMEDIAMODE_MIXED

The target application is the one that handles calls with the ISDN mixed media mode.

LINEMEDIAMODE_ADSI

The target application is the one that handles calls with the ADSI (Analog Display Services Interface) media mode.

LINEMEDIAMODE_VOICEVIEW

The media mode of the call is VoiceView.

Return Values

Returns zero if the request is successful or a negative error number if an error has occurred. Possible return values are:

LINEERR_INVALCALLHANDLE, LINEERR_OPERATIONFAILED, LINEERR_INVALMEDIAMODE, LINEERR_TARGETNOTFOUND, LINEERR_INVALPOINTER, LINEERR_TARGETSELF, LINEERR_NOMEM, LINEERR_UNINITIALIZED, LINEERR_NOTOWNER.

Remarks

The lineHandoff function returns LINEERR_TARGETSELF if the calling application attempted an indirect handoff (that is, set the lpszFileName parameter to NULL) and TAPI determined that the application is itself the highest priority application for the given media mode. If LINEERR_TARGETNOTFOUND is returned, a target for the call handoff was not found. This may occur if the named application did not open the same line with the LINECALLPRIVILEGE_OWNER bit in the dwPrivileges parameter of lineOpen. Or, in the case of media-mode handoff, no application has opened the same line with the LINECALLPRIVILEGE_OWNER bit in the dwPrivileges parameter of lineOpen and with the media mode specified in the dwMediaMode parameter having been specified in the dwMediaModes parameter of lineOpen.

Call handoff allows ownership of a call to be passed among applications. There are two types of handoff. In the first type, if the application knows the filename of the target application, it can simply specify the filename of that application. If an instance of the target application has opened the line device, ownership of the call will be passed to the other application; otherwise, the handoff will fail and an error is returned. This form of handoff will succeed if the call handle is handed off to the same file name as the application requesting the handoff.

The second type of handoff is based on media mode. In this case, the application indirectly specifies the target application by means of a media mode. The highest priority application that has currently opened the line device for that media mode is the target for the handoff. If there is no such application, the handoff fails and an error is returned.

The lineHandoff function does not change the media mode of a call. To change the media mode of a call, the application should use lineSetMediaMode on the call, specifying the new media mode. This changes the call's media as stored in the call's LINECALLINFO structure.

If handoff is successful, the receiving application will receive a LINE_CALLSTATE message for the call. This message indicates that the receiving application has owner privilege to the call (dwParam3). In addition, the number of owners and/or monitors for the call may have changed. This is reported by the LINE_CALLINFO message, and the receiving application can then invoke lineGetCallStatus and lineGetCallInfo to retrieve more information about the received call.

The receiving application should first check the media mode in LINECALLINFO. If only a single media mode flag is set, the call is officially of that media mode, and the application can act accordingly. If UNKNOWN and other media mode flags are set, then the media mode of the call is officially UNKNOWN but is assumed to be of one of the media modes for which a flag is set in LINECALLINFO. The application should assume that it ought to probe for the highest priority media mode.

If the probe succeeds (either for that media mode or for another one), the application should set the media mode field in LINECALLINFO to just the single media mode that was recognized. If the media mode is for that media mode, the application can act accordingly; otherwise, if it makes a determination for another media mode, it must first hand off the call to that media mode.

If the probe fails, the application should clear the corresponding media mode flag in LINECALLINFO and hand off the call, specifying dwMediaMode as LINEMEDIAMODE_UNKNOWN. It should also deallocate its call handle (or revert back to monitoring).

If none of the media modes succeeded in making a determination, only the UNKNOWN flag will remain set in the media mode field of LINECALLINFO at the time the media application attempts to hand off the call back to UNKNOWN. The final lineHandoff will fail if the application is the only remaining owner of the call. This informs the application that it should drop the call and deallocate its handle, in which case the call is abandoned. The privileges of the invoking application to the call are unchanged by this operation, but the application can change its privileges to a call with lineSetCallPrivilege.

See Also

LINECALLINFO, lineGetCallStatus, lineOpen, lineSetCallPrivilege, lineSetMediaMode

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