Browse Prior Art Database

Synchronous Data Communication Equipment to Data Communication Equipment Data Compression

IP.com Disclosure Number: IPCOM000114749D
Original Publication Date: 1995-Jan-01
Included in the Prior Art Database: 2005-Mar-29
Document File: 4 page(s) / 137K

Publishing Venue

IBM

Related People

Petty, JS: AUTHOR

Abstract

Described is a method which shows how data compression between synchronous Data Communication Equipments (DCEs) differs from the asynchronous DCE-to-DCE data compression such as MNP class 5 and V.42 bis that is in common use today. Notes: 1. This term, DCE, could be a modem, statistical multiplexor, time division multiplexor, or any other data communication equipment. Modems are used here for examples. 2. The term "frame" refers to a DTE-DTE protocol unit and "packet" refers to a DCE-DCE protocol unit. 3. The reader should be familiar with common DCE-DCE data compression as it is implemented in modems today.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 40% of the total text.

Synchronous Data Communication Equipment to Data Communication Equipment
Data Compression

      Described is a method which shows how data compression between
synchronous Data Communication Equipments (DCEs) differs from the
asynchronous DCE-to-DCE data compression such as MNP class 5 and V.42
bis that is in common use today.
  Notes:
  1.  This term, DCE, could be a modem, statistical multiplexor, time
       division multiplexor, or any other data communication
equipment.
       Modems are used here for examples.
  2.  The term "frame" refers to a DTE-DTE protocol unit and "packet"
       refers to a DCE-DCE protocol unit.
  3.  The reader should be familiar with common DCE-DCE data
       compression as it is implemented in modems today.

      The list below describes how data would flow from a Data
Terminal Equipment (DTE) such as a personal computer through a local
DCE such as a modem, onto a communication link, through a remote DCE
for final delivery to a remote DTE.
  1.  Synchronous data is received one frame at a time from a DTE by
a
       Universal Synchronous Receiver Transmitter (USRT) chip or
       function in the DCE.  USRTs such as the Intel 8273 or the
Zilog
       Z-8530 chip could serve or the software USRT functions in the
       IBM* 7855, 5853, and 786X modems could also be used.

    The local DCE must be programmed/configured to "understand" the
definition of a data frame as used by the local DTE.  This
configuration requirement is novel compared to asynchronous data
compression and is accomplished using standard means (such as
switch settings read by a microcontroller).  Alternatively, the
invention could be implemented to support just one synchronous
DTE-DTE protocol in which case no DCE programming would be
needed.  For example, if the local DTE uses SDLC, then the DCE
must understand that a frame is prefixed by at least one X'7E',
never contains a 7E, and is terminated by a 7E.  In addition, the DCE
must know that the last two bytes of a frame are its FCS.  Finally,
the DCE must know whether the frames will be NRZI encoded or not as
they
come from the DTE.
  2.  The protocol specific bytes are discarded by the DCE and the
       remaining bytes are stored in the DCE's transmit buffer.  For
the
       example of a DTE using the SDLC protocol, the bytes discarded
       would be the X'7E' bytes that delineate a frame and the FCS
       bytes.  In addition, for bit oriented protocols such as SDLC
and
       HDLC, extra inserted bits must be deleted from the data
stream.
  The two above steps are "business as usual" for DTEs receiving
   synchronous data across a V.24 interface.

          Additionally, the location of the end of each DTE frame in
the DCE transmit buffer must be known in the DCE to allow step 5
to be done.  This could be done using a software stack to keep
track of the addresses of...