Ref: 13930006
Title: 3Com Conversion of X.3 Parameters
date: 4/20/90

Copyright 3Com Corporation, 1991.  All rights reserved.

The CCITT protocol for 1980 defines X.3 as a set of 18 parameters that
provide basic functions for Packet Assemblers/Disassemblers (PADs) to
control an asynchronous terminal.

When a connection is established to an X.25 host, the host may modify
some of the X.3 parameters via the X.29 protocol to the GS/1-X.25.  If
total transparency is not selected, the GS/1-X.25 modifies the
parameters in the 3Com terminal server where the connection is
originally initiated.  When a connection is established from the PDN to
the GS/1-X.25, the GS/1-X.25 will set any necessary X.3 parameters via
X.29 over the PDN.

The following X.3 table is divided in four columns.  The first column
lists the eighteen X.3 parameters; the second column lists the standard
CCITT X.3 names; the third column lists the 3Com names that correspond
to the CCITT standard; and the fourth column indicates whether or not
these parameters are converted by the GS/1-X.25.


Parameter   CCITT Name          3Com Name       3Com X.25 Conversion
---------   ----------          ---------       --------------------
  1         Escape from data    ECM Character   X.3 value 1 is converted
            transfer                            to "<CNTL> P"; no
                                                conversion for other
                                                values.

  2         Echo                Echo Data       None.

  3         Data Forward        Data Forward    If parameter 15 (Local
                                                Editing) = 1, then value
                                                8 (Editing) is turned on
                                                locally and is
                                                transparent to the the
                                                host.  As a result,
                                                value 8 does not appear
                                                in the parameter list
                                                when the host performs a
                                                "read parameter."

  4         Idle Timer          Idle Timer      Since 3Com's idle timer
                                                is based on 1/60 second
                                                and X.3 is based on 1/20
                                                second, the 3Com value =
                                                X.3 value * 3, and X.3
                                                values from 85 to 255
                                                are converted to 255 in
                                                3Com values.

  5         Ancillary Device    Flow Ctl From   None.
            Control

  6         Suppression of      Inter Action    Since prompt service
            Service Signals                     signal cannot be
                                                suppressed separately
                                                from PAD service signal
                                                in 3Com environments,
                                                X.3 value 5 (4+1) is
                                                converted to 1 in
                                                3Com values.  3Com uses
                                                value 4 to indicate
                                                "command Echo/NoEcho."

  7         Break Option        Break Action    3Com does not support
                                                value 2 (RESET). Value
                                                16 is used to indicate
                                                Flush VC by 3Com.
                                                Output data will be
                                                flushed upon detection
                                                of a break signal in
                                                this case.

  8         Discard Output      Data Delivery   None.

  9         Carriage Return     Carriage Rtn    3Com allows a wider
            Padding             Padding         range than the X.3
                                                definition (0-127).
                                                None.

  10        Line Folding        Line Folding    3Com accepts this
                                                parameter but performs
                                                no action with it.

  11        DTE-C Speed         Baud Rate       This is a read-only
                                                parameter and the host
                                                should not try to set
                                                this parameter.  If a
                                                host performs a "read
                                                parameter," the 3Com
                                                values are converted to
                                                X.3 values.

  12        Flow Control of     Flow Ctl To     None.
            PAD by Terminal

  13        Line Feed after CR  Line Feed       X.3 value 3 (Line Feed
                                Insertion       Insertion after CR from
                                                DTE) is now supported by
                                                3Com.

  14        Line Feed Padding   Line Feed Pad   3Com allows a wider
                                                range than the X.3
                                                definition.  None.

  15        Editing             Local Editing   No conversion.  The 3Com
                                                parameter "command
                                                editing" is turned on
                                                when this parameter is
                                                set.

  16        Character Delete    Erase Char      None.

  17        Line Delete         Line Erase      None.

  18        Line Display        Reprint Line    None.
