This object supplies the unique index, ranging up to 65535, that identifies one specific fan within its tray inside SNMP trap definitions for fan events. An admin uses it to pinpoint exactly which fan inside a tray (which may hold several fans) is the source of an incoming fan alarm, since the tray-level index alone would not distinguish individual fans. For example, a trap reporting fan notif index 12 within tray notif index 2 tells the admin to look at fan 12 specifically inside tray 2.