Upstream efficiency improvement method for passive optical networks

The invention relates to a method of data transmission in a network sharing a medium using a time division multiple access scheme wherein a network unit receives data packets from a subnetwork, stores the data packets in a buffer until the arrival of a time-slot and sends the data packets over the shared medium in the upstream direction during the time-slot, wherein each of the data packets includes a payload and a header, the header including a source address and a destination address. The storing the data packets in the buffer includes further steps of: determining a pair of a source address and a destination address of a received packet; determining whether a composite frame having a composite frame header including the pair of source and destination addresses already exists; if negative, creating the composite frame for the pair of source and destination addresses; and aggregating the payload of the packet to a composite frame payload of the composite frame.