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  • [WORLD PC EXPO 98] NTT Releases First Results of xDSL Field Trials
  • October 6, 1998 (TOKYO) -- Nippon Telegraph and Telephone Corp. released the first results of its ongoing digital subscriber line (xDSL) field trials.
    Transmission speeds of 512kbps were achieved over line distances of up to 2.5km, according to NTT's findings announced at WORLD PC FORUM 98, held Sept. 30-Oct. 3 at Makuhari Messe in Chiba prefecture near Tokyo.

    The xDSL is a modem technology that enables data transmission over existing copper-wire telephone lines at speeds of up to several megabits per second.

    The technology is attracting interest because it has the potential to transform existing phone lines into high-speed access lines to the Internet and other types of networks.

    So far, the NTT field trials have shown that maximum transmission speed declines as distance increases. Using the ADSL test lines already in operation, NTT believes that it can achieve maximum bit rates of 6Mbps over 500 meters, 1.5Mbps over 1.5km and 512kbps over 2.5km, according to Fumihiro Ashiya, senior manager of the Metallic Transmission Systems Project being conducted by NTT's Access Network Systems Laboratories.

    In the future, it may be possible to extend the ADSL transmission distance by utilizing dual bitmap (DBM) technology. NTT is currently giving serious consideration to DBM as a means of reducing adverse effects from ISDN lines.

    DBM works in synchronization with ISDN, reducing data traffic when noise levels are high and transmitting more data when noise is low.

    One difficulty, however, is that xDSL communications may be impossible in some situations, even when using a DBM system.

    This is because, apart from the problems with ISDN lines, the thinness and age of copper wires also have adverse effects on xDSL.

    The result, then, is that some subscribers may enjoy fast access, even though they live far from the telephone exchange. But inevitably there will be other subscribers who cannot use xDSL services, although they live quite near the exchange.

    "The xDSL services can probably be offered quite widely, if people accept that xDSL may not be available in some cases," Ashiya said.

    (Nikkei Communications)

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    Updated: Mon Oct 5 13:28:40 1998 PDT