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This is an
excript from an article in Network Magazine that explains the
whole story about 56K modems, the whos,
whys and wheres of the whole thing. Hope
this is informative to you all.
THE 56K
MODEM BATTLE
In
February 1997, the International
Telecommunications Union (ITU)finally
approved a 56K standard for modems, which
it is calling V.90. By doing so, the
organization opened the door for vendors
to develop 56Kbit/sec modems with the
assurance that products will interoperate
and deliver 56Kbit/sec service.
When modem
technology first hit the 33.6Kbit/sec
mark, it was initially thought that
modems had reached their performance
ceiling. The main technical obstacle lay
in the fact that data traveling from a
modem to its destination had to undergo
two conversions: an analog-to-digital
conversion and digital-to-analog
conversion.
To
illustrate, when a signal is sent from a
modem, it travels over a telephone line
in analog form until it hits the
telephone company’s system. At that
point, the signal is converted into
digital form by the telephone system.
Then, after the digital signal passes
through the telephone system, it is
converted back to analog form in order to
travel over standard telephone lines to
its
destination.
The
problem is that during the
analog-to-digital conversion, the signal
suffers some loss due to quantization
noise, which limits the signal to about
33.6Kbits/sec under the best of
conditions.
Vendors
found a way around this limit by creating
a different approach to modems. For the
new model to work, one end of the
connection (the service provider’s,
whether it be an ISP or the user’s
corporate network) would have to have a
direct digital connection to the public
telephone system. This “server”
side connection transmits data in digital
form over its connection and through the
telephone system. When the signal reaches
the user’s analog connection, it is
converted from digital to analog.
In this
case, the signal never undergoes the
limiting analog-to-digital conversion
process. Under the best of conditions,
this model allows for 56Kbit/sec
performance. Data from the user must
still be converted from analog to digital
when it reaches the public telephone
system, and thus is limited to
33.6Kbit/sec performance. However, when
accessing the Web, download speed usually
is much more important than upload speed.
The
problem with the new model was that two
different 56K technologies appeared:
56KFlex, developed by Lucent Technologies
and Rockwell; and x2, developed by U.S.
Robotics. To fuel the problem, the two
approaches were not compatible. So, if
users wanted 56Kbit/sec performance, they
had to make sure their 56K modem used the
same technology as their service
provider’s.
Realizing
the problems inherent in the situation,
the ITU has been working on a solution.
In February 1998, the organization nailed
down the technical specifications for 56K
modems, and has started the formal
approval process. According to the ITU,
the new V.90 standard will be up for
formal approval in September 1998.
With the
emergence of the V.90 standard, vendors
are already beginning to offer upgrades
to current x2 and 56KFlex-based modems
that will enable them to be
V.90-compliant.
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