Patent ID: 7675936

Claim:
A passive optical network (PON) system including: a plurality of optical network units (ONUs) accommodating a user terminal, an optical line terminal (OLT) being connected to a wide area network and a passive optical network (PON) which connects between the ONUs and the OLT; the OLT transferring a downstream frame received from a communication node equipment in the wide area network to the plurality of ONUs via the PON; and the plurality of ONUs transferring the downstream frame to the user terminal, wherein the downstream frame includes a Layer 2 header and an IP packet, wherein the OLT has a frame analyzing unit that judges whether a downstream frame received from the communication node equipment is a unicast frame or a multicast frame, outputs the downstream frame received from the communication node equipment without conversion when the downstream frame received from the communication node equipment is judged as a unicast frame and removes at least a part of the Layer 2 header information from the downstream frame received from the communication node equipment and outputs the downstream frame whose length is shortened when the downstream frame received from the communication node equipment is judged as a multicast frame; and a frame generating unit that generates a PON frame by adding a PON-specific header to the downstream frame outputted from the frame analyzing unit, and wherein each of the ONUs has a downstream frame processing unit that extracts a downstream frame from the PON frame received via the PON, and adds a Layer 2 header information generated in said each GNU into the downstream frame when at least said part of the Layer 2 header information is removed.