Complete OLT buying guide covering GPON/EPON/XGS-PON standards, port density calculation, brand comparison (Huawei, ZTE, FiberHome, VSOL), and deployment tips for ISPs and network operators. What is an OLT and Why Does It Matter? An Optical Line Terminal (OLT) is the core device in a Passive. Selecting the right Optical Line Terminal (OLT) is one of the most important decisions Internet Service Providers (ISPs) face when designing or expanding their networks. It acts as the gateway between the service provider's core network and the fiber access network connected to subscribers.