add t38_gateway_rx_fillin

src/mod/applications/mod_spandsp/mod_spandsp_fax.c

@@ -1160,7 +1160,6 @@ void mod_spandsp_fax_process_fax(switch_core_session_t *session, const char *dat
             break;
         }
 
-		/* Skip CNG frames (auto-generated by FreeSWITCH, usually) */
 		if (switch_test_flag(read_frame, SFF_CNG)) {
 			/* We have no real signal data for the FAX software, but we have a space in time if we have a CNG indication.
 			   Do a fill-in operation in the FAX machine, to keep things rolling along. */
@@ -1572,10 +1571,11 @@ static switch_status_t t38_gateway_on_consume_media(switch_core_session_t *sessi
 			goto end_unlock;
 		}
 
-
-		/* Skip CNG frames (auto-generated by FreeSWITCH, usually) */
-		if (!switch_test_flag(read_frame, SFF_CNG)) {
-
+        if (switch_test_flag(read_frame, SFF_CNG)) {
+			/* We have no real signal data for the FAX software, but we have a space in time if we have a CNG indication.
+			   Do a fill-in operation in the FAX machine, to keep things rolling along. */
+            t38_gateway_rx_fillin(pvt->t38_gateway_state, read_impl.samples_per_packet);
+        } else {
             if (read_fd != FAX_INVALID_SOCKET) {
                 switch_ssize_t rv;
                 do { rv = write(read_fd, read_frame->data, read_frame->datalen); } while (rv == -1 && errno == EINTR);