This read-only object records which protocol, by index, a historical threshold-breach entry pertains to, letting an admin reviewing past alerts identify exactly which application triggered each recorded event. It is the lookup key that turns a list of historical threshold crossings into actionable information; without it, the history table would just be a list of timestamps and rates with no indication of which traffic type caused them. Seeing repeated history entries all pointing to the same protocol index would tell an admin that one specific application is a chronic, repeat offender rather than a one-off spike.