This counts Signal Fail RAPS PDUs this node has transmitted out its west link, meaning this node itself detected a local signal failure condition and is announcing it to the ring. A jump in this specific counter, as opposed to the receive counter, tells an admin the fault is local to this node's own west-facing link or interface, not something happening elsewhere on the ring that's merely being relayed through. For example, if this counter increments right when this device logs a loss-of-signal alarm on its west-facing optic, that confirms this device is the originating source of the ring's protection-switch event.