This is a read-only integer, in dB, recorded in the call history table showing the average combined echo-suppression level achieved over the duration of a now-completed call leg, with -1 meaning the level couldn't be determined or detection was disabled. An admin reviews this historical average to judge how well echo cancellation performed across an entire finished call, rather than just at a single point in time as the active-call object would show. For example, an admin investigating repeated echo complaints on a specific trunk could review this field across several completed calls to see if average echo-suppression levels consistently run low on that trunk.