Thanks! "OLT" was also new to me. In case others find it helpful:

OLT = Optical Line Terminal.

In ISP fiber (typically GPON/EPON) infrastructure, it’s the provider-side device at the central office/headend that terminates and controls the passive optical network: it connects upstream into the ISP’s aggregation/core network and downstream via fiber (through splitters) to many customers’ ONTs/ONUs, handling PON line control, provisioning, QoS, and traffic aggregation.