This read-only value reports whether the switch port's transmit packet buffer has crossed into a congested state, meaning the buffered-packet count rose above the configured rising threshold and has not yet fallen back below the falling threshold. An administrator watches this to catch a port that is backing up outbound traffic before packets start dropping. For example, an uplink port feeding a saturated downstream link would flip into this congested state while its transmit queue fills faster than it can drain.