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For this technology to operate, several things are required:

  1. The modems on both ends of the link must implement this new
     technology. During startup, the modems "identify" themselves and their
     capabilities to each other. Only if both modems have this capability
     do they try to establish a 56 Kbps connection.
  2. The central site modem pool must have a digital connection to the
     network, such as with a T1 or E1 line (which may or may not be ISDN).
  3. There must be no conversions of the digital signal within the network.
     Any conversions will prevent the modem DSP in the central site from
     generating the proper voltage levels on the analog line which will
     prevent this technique from operating. Examples of digital conversions
     are: (1) mu-law to A-law or vice versa (this means users will not be
     able to use this technology for communications between the US and
     Europe), (2) conversion to ADPCM, such as occurs in transatlantic
     submarine cables, (3) conversion to analog and back to digital
     somewhere along the link, or (4) other signal conversions such as
     AT&T's TrueVoice™ [9] .

To check if a fully digital path exists, with no conversions, the modems
send a "probing" signal between themselves. If conversions are detected,
the connection is established at V.34 rates.

These limitations are not serious, especially for Internet access which
generally involves a local telephone call.

Summary

The 56 Kbps technique announced by Rockwell Semiconductor Systems is
achieved by viewing the public switched telephone network as a digital
network instead of an analog network. Overcoming the limitations of the
analog loop at the customer site is not easy but can be accomplished
through the use of standard modem techniques.

It is easier to overcome these limitations in the "downstream" direction,
resulting in an asymmetrical modem technology with higher data rates from
the service provider to the user than in the return direction.

The theoretical Shannon's limit for this technique is close to 64 Kbps,
depending upon the local loop.

Rockwell will work with partners to submit this specification to the
appropriate standards bodies so that an interoperability specification can
be ratified and published.

This new communication technology announced by Rockwell Semiconductor
Systems promises to provide a new era in dial up communications
capabilities, especially for bit starved Internet power users, and another
life extension for the "analog" modem.

     Rockwell Semiconductor Systems is the fastest growing business
     segment of Rockwell. Based in Newport Beach, Calif., it comprises
     the Multimedia Communications Division and the Wireless
     Communications Division. The Multimedia Communications Division
     is the world leader in facsimile and PC modem devices for
     personal communications electronics. The Wireless Communications
     Division offers total system solutions for advanced cordless
     telephony and global positioning system (GPS) receiver engines
     and is developing products and technologies to address the
     Personal Communications Services (PCS) and wireless packet data
     markets.

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Footnotes

1. Central site modems are those installed at a service provider, such as
an Internet service provider, or at a corporation to allow many
simultaneous connections for Remote LAN access. They are generally
manufactured as cards containing many modems which plug into the device
which provides the appropriate access.

2. A T1 line is a digital service provided by the telephone company to
provision the equivalent of 24 individual voice lines. It operates at 1.544
Mbps. An E1 line is the European equivalent and provisions the equivalent
of 30 individual voice lines. It operates at 2.048 Mbps.

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