Hitachi, Ltd.

Hitachi Communication Technologies, Ltd.

Masaki Nara

Tetsuro Yoshimoto

Naoko Nagasaki

Takahito Yuda

When an IPv4/v6 dual stack terminal communicating via TCP on IPv6 fails to promptly switch over to IPv4 after the ICMPv6 fails due to a soft error, the problem should be resolved at the prior stage server rather than on the complicated terminal. The server at a stage prior to the terminal receives TCP packets from the terminal to find the TCP connection status on the terminal. When the terminal connection status is SYN-SENT or SYN-RECEIVED, and the server receives an unaddressed soft error such as ICMPv6 'Destination Unreachable: no route to destination (ICMP type=1: code 0)' for that terminal, the server rewrites the ICMPv6 contents as a hard error such as 'Destination Unreachable: communication with destination administratively prohibited (ICMP type=1: code 1)' and sends it the terminal.

ICMP translator

A transmission system comprising a relaying apparatus and concentrated subscriber line transmission apparatuses, the relaying apparatus including a first buffer memory for buffering a control request to be transmitted to one of the concentrated subscriber line transmission apparatuses, a second buffer memory for buffering data to be downloaded to specific one of the concentrated subscriber line transmission apparatuses, and a control unit for generating maintenance frames each including a control request, and download frames each including download data, and transmitting these frames to one of the concentrated subscriber line transmission apparatuses, selectively. The control unit controls the transmission of download frames, depending on status of traffic of frames being relayed from the communication network toward one of the concentrated subscriber line transmission apparatuses and on whether a control request awaiting transmission is buffered.

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Yokohama, Japan

Masaki Nara