(Nikkei BP Group)
(No.1 High-Tech News Site in Japanese)
| [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
|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
The xDSL is a modem technology that enables data transmission over existing
copper-wire telephone lines at speeds of up to several megabits per
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
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.