| Electronics Makers Propose Version of ADSL to ITU-Telecom
July 10, 1998 (TOKYO) -- Japanese makers proposed an ADSL technique
developed for Japan to be adopted as an international standard plan
, at an International Telecommunication Union-Telecommunication
Sector (ITU-T) specialist conference held June 27 through July 3 in
Hawaii, sources said.
|ADSL refers to asymmetric digital subscriber line.
The companies are NEC Corp., Fujitsu Ltd., Sumitomo Electric
Industries, Ltd. and others. The proposal reflects Nippon Telegraph
and Telephone Corp.'s opinion, and is assumed to be incorporated in
the ADSL Standard "G.lite" and "G.dmt" as an annex.
The ADSL Standard will be announced as an international
recommendation in October.
When a standardization organization describes two or more
specifications in one standard, the specifications are often
handled as an annex. This time, North-American specifications will
be handled as Annex A, European as Annex B and Japanese as Annex C.
The Japanese makers proposed a technique called the "dual bit map"
method. The method is effective in reducing potential interference
from NTT's integrated services digital network (ISDN) lines. NTT's
ISDN uses a higher frequency than the ISDN transmission method
utilized in other countries including the United States.
Consequently, ADSL lines are influenced more by severe noise,
When the ADSL line and ISDN line are placed closely within a cable,
the ADSL transmission speed is reduced. In the worst case, the
communications are fully disabled. NTT has pointed out this problem
, resulting from an ADSL evaluation test conducted by its laboratory
The dual bit map method is a technique to change a data transmission
speed on a time basis in consideration of characteristics of NTT's
NTT's ISDN uses the Time Compression Multiplex (TCM) method. The TCM
method is sometimes called the Ping-Pong transmission method. It is
designed to send data from an NTT station to a user home and vice
versa at the 400Hz frequency.
A simulation model showed that a cable bundling 24 ISDN lines
disables the existing ADSL when the distance exceeds 2.5km. A test
of the dual bit map method showed that transmissions can run at
about 256kbps even over a distance of 5km.
The interference appears to be relieved by the dual bit map method.
As a result, ADSL services will likely debut in Japan in the near