GpsGate 2.0 are built up of "PlugIns" which acts as filters or endpoints. A filter can typically make a protocol conversion and an endpoint can typically read and write data to a hardware unit, a network address or a virtual port.
Most PlugIns are bi-directional. The Virtual Port is for example, But the Garmin USB PlugIn is not bi-directional. And the Garmin to NMEA plugin is not bi-directional either.