Embodiments of the present invention provide a downstream data frame transmitting method. The method includes: generating, by an OLT, a downstream data frame, where the downstream data frame includes a frame header and a payload, the frame header includes a physical synchronization sequence (Psync) field, and the Psync field is used to identify the downstream data frame, where when a value of the Psync field is a first value, the Psync field is further used to indicate that payload data is protected by forward error correction (FEC); or when a value of the Psync field is a second value, the Psync field is further used to indicate that payload data is not protected by FEC; and sending, by the OLT, the downstream data frame. The embodiments of the present invention can reduce a bit error rate of a FEC indication status and improve reliability of the FEC indication status.
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