This read-write object sets the ECN (Explicit Congestion Notification) threshold for the logical port; once the combined queue depth of all connections mapped to the port exceeds it, the appropriate FECN or BECN bit gets set on traffic in the relevant direction. An administrator tunes this threshold to control how aggressively the port signals congestion to connected devices before actually dropping traffic. For example, lowering this threshold would cause the port to start marking frames with FECN/BECN sooner, giving endpoints more advance warning of building congestion.