This is a read-only integer, in dB ranging up to 45, reporting the current Echo Return Loss measured on this call leg, with -1 meaning the level can't be determined or level detection is disabled. An admin monitors this specifically to gauge how much echo is naturally attenuated by the line itself, before any active cancellation is applied, distinguishing it from the broader combined-loss measurement. For example, a persistently low ERL reading on a port might indicate a hybrid or impedance mismatch problem on that specific telephony line rather than an echo-canceller software issue.