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(Japanese Site)

  • Tokyo Train Chaos Caused by Failed Comm. Controller
  • February 25, 1998 (TOKYO) -- The communications network failure that brought down the Autonomous Decentralized Transport Operation Control System (ATOS) in Tokyo on Feb. 4 was caused by a LAN overload at a station on the Chuo line, the East Japan Railway Co. (JR East) said.
    The failure caused major disruption to the JR East train service in the Tokyo metropolitan region. Around 520,000 commuters were affected, with 291 trains halted and 258 delayed. JR East now says that an ATOS connection trial involving the Yamanote and Keihin Tohoku lines, to which the failure was initially ascribed, had no bearing on events.

    The failure was actually caused by starting the train control server at Saruhashi Station on the Chuo line while the station's LAN was clogged with traffic.

    Starting the train control server on a congested LAN caused the communication controller to crash at Saruhashi Station. This failure affected the communication controllers at other stations, and ultimately brought down the whole network.

    The communication controllers at the individual stations are connected in a ring configuration to the ATOS Chuo Line Network. The main feature of this architecture is that it allows cooperative interplay among a number of autonomous systems, enabling finely tuned, real-time control of train movements.

    However, if this interplay misfires, a failure at one communication controller can have repercussions throughout the network. The problem in February exposed a weakness of the ring network model.

    Measures have been put in place to prevent similar problems in future, according to JR East. These measures included replacing the failed communication controller at Saruhashi Station, revising manuals for station installations related to the communications network, instituting new emergency measures and adding network functionality that detects problems and automatically restores communications.

    At the time of the Feb. 4 failure, JR East claimed that the problem was caused by trial connection of the Yamanote and Keihin Tohoku lines into a new ATOS network.

    The company now denies that the ATOS trial caused the chaos. "There's absolutely no relationship. The cause was a local failure originating in the communication controller at Saruhashi Station," said a spokesperson.

    (Hi-Tech News Center)

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    Updated: Tue Feb 24 16:35:12 1998