Hitachi, Ltd.

Makoto Hasegawa

Atsushi Otani

Tohru Kazawa

Kazuyori Umematsu

Hisa Tsuzuki

In a communication system using a PON, time synchronization of a slave device such as a base station is realized with respect to a master device such as an L2SW or the base station. Time information acquired by a GPS satellite is corrected by ranging information of a discovery function of an OLT so as to be reflected on time information of each ONU. A propagation delay from the L2SW to the OLT is obtained with the use of a delay estimation mechanism, a propagation delay from the OLT to the ONU which is obtained by ranging is added to obtain a propagation delay from the L2SW to the ONU. The obtained propagation delay from the L2SW to the ONU is added to the transmitted time stamp value whereby a time stamp value received at a base station or femtocell side becomes a time into which the propagation delay to the ONU is incorporated, and absolute values of clock timers can be synchronized with each other. The addition process can be realized by rewriting the time stamp value of the packet within the OLT or the ONU.

Communication system and time synchronization method

In a premises gateway device that performs encryption or decryption under the IPsec, the throughput of a processor is varied depending on a type of data to be treated in order to realize reduction in power consumption. In the premises gateway device to which a telephone, PCs, and a home appliance that are pieces of home network equipment are connected and which transmits or receives data using an ISP and an IPsec tunnel via an ONU, an OLT, and a carrier network, relevant home network equipment and a data rate are decided based on the data to be treated. The frequency of a clock to be fed to the processor is varied depending on the information.

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Samukawa, Japan

Makoto Hasegawa