This accessible-for-notify Unsigned32 identifies the interconnect port number within a chassis that a related trap is reporting on. It's carried as an object in interconnect-related notifications like tmnxSfmIcPortDown, letting an admin's trap receiver know exactly which port triggered the alarm without polling the table separately. For example, a trap payload containing tmnxNotifyIcPortNum 6 tells the admin the alarm concerns interconnect port 6.