This carries, within a notification concerning a protected pseudowire pair, the PW ID of the primary (working) pseudowire in that pair, letting the trap recipient understand the broader protection context of whatever event triggered the notification. This is useful specifically when the notification concerns a secondary/backup PW event, since it tells the admin which primary PW this backup is protecting without a separate lookup. If a trap reports an event on a backup PW alongside a primary PW ID, the admin knows exactly which working service is the one actually being protected by whatever changed.