1. A method for controlling transmission in an Ethernet passive optical network (EPON) which includes an Optical Line Terminal (OLT) and at least one Optical Network Unit (ONU), wherein an ONU implements a data-link layer and a physical layer, the method comprising: receiving, at the physical layer of an ONU, a word which is communicated from the data-link layer of the ONU, wherein the word may be a data word or an idle word; delaying, at the physical layer in the ONU, the word for a pre-determined amount of time before allowing the word to be transmitted by a transmitter, thereby providing time for turning the transmitter on or off; and turning the transmitter at the physical layer in the ONU on or off based on the current state of the transmitter and the content of the received words without data-link layer sending a control signal across multiple sublayers to the physical layer in the ONU.
5. The method of claim 1 , further comprising determining the amount of time for which the word is delayed based on a laser turn-on time, an automatic gain control (AGC) time, and a data and clock recovery (CDR) time.