Communication system and communication apparatus

A communication system which intervenes a plurality of PONS (Passive Optical Networks) between a first packet communication network and a second packet communication network, comprising:

• a first PON including a first OLT (Optical Line Terminal) connected to one or plural ONUs(Optical Network Units);
• a second PON including a second OLT connected to one or plural another ONUs;
• a first communication device of the first packet communication network;
• and
• a second communication device of the second packet communication network,
• wherein
• each of the ONUs of the first PON or the second PON transmits data toward the connected first OLT or the connected second OLT after a wait time period designated by the connected first OLT or the connected second OLT;
• the first communication device of the first packet communication network sends a first frame for measuring communication time period, to the second communication device of the second packet communication network through the first PON, and sends a second frame for measuring communication time period, to the second communication device through the second PON;
• and
• the second communication device calculates a difference of communication time period between the received first frame and the received second frame, and instructs the first OLT of the first PON or the second OLT of the second PON, for correcting a wait time period which is set to the one or plural ONUs connected to the first OLT or the second OLT, based on the difference between communication time periods.