This carries the pseudowire's signaling-layer PW ID (the value exchanged via LDP) within the notification, and per its description, for a static PW this simply reflects whatever value was locally configured by the operator since static PWs don't rely on dynamic signaling for ID assignment. This is useful alongside the table index because the PW ID is what would actually appear in packet captures or LDP debug output, letting an admin correlate a trap directly to low-level protocol traces. A trap showing PW ID 5001 gives the exact value to search for when reviewing LDP session logs around the time of the alert.