In a POL, the PON transmits GEM data frames, and Ethernet frames are transmitted upstream by an OLT and downstream by an ONU

The statement contains a critical error regarding the direction of data transmission. In any PON system, including POL, the Optical Line Terminal (OLT) is the central office equipment, and the Optical Network Unit (ONU) is the user-side equipment. Therefore, the OLT transmits data downstream to the ONUs, and the ONUs transmit data upstream to the OLT. The statement incorrectly reverses these roles. While it is correct that PON uses GPON Encapsulation Method (GEM) frames to transport data, the description of the data flow is fundamentally wrong.

The statement is factually incorrect because it reverses the universally defined directions of upstream and downstream traffic in a PON architecture. The OLT is always the source of downstream traffic, and the ONU is the source of upstream traffic.

1. Huawei Enterprise. (2020). GPON Technical White Paper. Section 1.2, "GPON System Composition." This section defines the roles: "An OLT is an aggregation device located at the central office (CO) for terminating the PON protocol." and "An ONU is user-side equipment... It communicates with the OLT." This establishes the OLT as central and the ONU as peripheral, defining the downstream (OLT to ONU) and upstream (ONU to OLT) directions.

2. Huawei Enterprise. (2020). GPON Technical White Paper. Section 2.2, "GPON Downstream Transmission." This section explicitly states: "In the downstream direction, data is broadcast from the OLT to all ONUs." This confirms the OLT's role in downstream transmission.