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Dialogic Corporation
4.26.5 Accepting/Rejecting a Request to Switch Between Audio
and T.38 Fax
After T.38 coder change request has been received, followed by association of T.38 Fax device with
Media device as described in Section 4.26.4, “Associating a T.38 Fax Device with a Media Device
When a Fax Request is Received”, on page 323, the application can use the gc_Extension( )
function to accept or reject the request as follows:
• To accept the request, the GC_PARM_BLK associated with the gc_Extension( ) function
includes components that indicate acceptance, specifically IPSET_SWITCH_CODEC and
IPPARM_ACCEPT. A RequestModeAck (H.323) or 200 OK (SIP) message is not sent until
the request is accepted. The following code provides an example:
/* Reject the incoming request */
INT32 acceptCodecSwitchRequest()
{
GC_PARM_BLK *parmblkp = NULL;
:
gc_util_insert_parm_val(&parmblkp, IPSET_SWITCH_CODEC, IPPARM_ACCEPT,
sizeof(int), NULL);
gc_Extension(GCTGT_GCLIB_CRN,pline->crn, IPEXTID_CHANGEMODE,
parmblkp, NULL, EV_ASYNC);
gc_util_delete_parm_blk(parmblkp);
}
• To reject the request, the GC_PARM_BLK associated with the gc_Extension( ) function
includes components that indicate rejection, specifically IPSET_SWITCH_CODEC and
IPPARM_REJECT. The reason for rejecting the request is also included in the
GC_PARM_BLK. Chapter 11, “IP-Specific Event Cause Codes” describes the supported
reject reasons that can be used in this context. For H.323, reasons prefixed by
“IPEC_Q931Cause” can be used. For SIP, reasons prefixed by “IPEC_SIPReason” can be
used. The reason parameter corresponds to a RequestModeReject cause (H.323) or a negative
response code (SIP). The following code provides an example:
/* Reject the incoming request */
INT32 rejectCodecSwitchRequest()
{
GC_PARM_BLK *parmblkp = NULL;
:
:
/* Reject with reason being busy, SIP */
gc_util_insert_parm_val(&parmblkp, IPSET_SWITCH_CODEC, IPPARM_REJECT,
sizeof(int), IPEC_SIPReasonStatus486BusyHere);
gc_Extension(GCTGT_GCLIB_CRN, pline->crn, IPEXTID_CHANGEMODE,
parmblkp, NULL, EV_ASYNC);
gc_util_delete_parm_blk(parmblkp);
}
4.26.6 Sending a T.38 Fax in a Session Without Audio Established
The Dialogic
®
Global Call API supports the transmission of fax information in a session that does
not already have an audio connection established. To send T.38 Fax in such a session, the
application must use the gc_SetConfigData( ) function to specify “Manual” mode, then associate a