Re: 56 kbps modems

[Gary Howland <gary@systemics.com>]

Forwarded:

The reason for this, Newsbytes discovered after a chat with Bill Pechey,
technical director with Hayes' European operations, is that the 56,000
bps modem system is actually a digital variant. Instead of the modem
using an audio channel of 3,600 hertz to the exchange, the modem works
across the standard copper wiring seen on most of the world's fixed wire
phone systems.

In order to achieve the 56,000 bps transmission rate, the Rockwell
chip-powered modem will actually physically control the codec at the
telephone exchange across the copper cable. According to Pechey, if a
full 4,000 hertz were available, then an ISDN (integrated service
digital network) channel of 64,000 bps would be available.

"Since the only 3,600 hertz of the audio channel is available through
the codec, we reckon that the maximum transmission speed is around
56,000 bps. Furthermore, because of the high power levels required to
achieve this transmission speed, the back channel will only operate at
standard (analog) modem speeds," he told Newsbytes.

Pechey told Newsbytes that this back channel will support data transfers
somewhere below the 28,800 bps levels, although he noted that Rockwell
claims that 28,800 bps is achievable under ideal conditions.

"This means that the 56K system is best suited for Internet access,
where the data is being transmitted mainly in one direction. For
applications such as videoconferencing, you'd be better off looking to
ISDN for a more balanced rate," he said, noting that the main advantage
of 56k technology over ISDN is the price.

"56K modem technology is cheaper than ISDN, since you don't need an ISDN
system installed. It will work across the standard phone network using a
standard phone socket," he said.

According to Pechey, because the technology involved is closer to
conventional analog modem systems than ISDN, adding 56K transmission
technology to a standard 28,800/33,600 bps modem will not be very
expensive.

"Basically you'll have a black box that will work as a normal analog
modem at 28,800 or 33,600 bps or whatever, but when accessing the
Internet, providing the distant end of the link is a digital connection,
you'll be able to use 56K in one direction, and up to 23,800 bps in the
reverse direction," he said.


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