Ref: 99980021
Title: X.3 Parameters
Date: 1/1/88

Copyright 3Com Corporation, 1991.  All rights reserved.

The CCITT protocol defines X.3 as a set of 18 parameters that
provide basic functions for Packet Assemblers/Disassemblers (PAD0
to control an asynchronous terminal.

When a connection is established to an X.25 host, the host may
modift some of thr 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 Bridge 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 table is divided into 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 Bridge
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.

              Bridge-to-X.3 Parameter Conversions
------------------------------------------------------------------
Para-
meter
 No.   Bridge Name         CCITT Name           Conversion

 1    ECMChar           Escape to Command   X.3 value 1 converted
                        Level               to <CTRL P>;no con-
                                            version on other
                                            values.

 2    ECHOData          Echo                None

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

4     IdleTimer         Idle Timer          Since Bridge's idle
                                            timer is based on 1/
                                            60 second and X.3 is
                                            based on 1/20 second,
                                            the Bridge value -
                                            X.3 value *3; X.3
                                            values 85 through 255
                                            are converted to 255
                                            in the Bridge
                                            implementation.

5    FlowControlFrom    Ancillary           None
                        Device Control

6    InterAction        Suppression of      Since prompt service
                        Service Signals     signals cannot be
                                            suppressed separately
                                            from PAD server
                                            signals in the Bridge
                                            environment, the X.3
                                            value 5 (4+1) is
                                            converted to 1 in
                                            Bridge values; Value
                                            4 is used to indicate
                                            "command Echo/
                                            NoEcho".

 7   BReakAction        Break Options       X.3 value 2 (RESET)
                                            is not supported by
                                            the Bridge
                                            implementation;
                                            Bridge value 16
                                            (FlushVC) causes
                                            output data to be
                                            flushed when a break
                                            signal is detected.

 8   (Data Deliver)     Discard Output      None

 9   CRPad              CR Padding          None; the Bridge
                                            implementation allows
                                            a wider range than
                                            the X.3 definition.

10   None               Line Folding        The Bridge
                                            implementation
                                            accepts this
                                            parameter, but
                                            performs no action on
                                            it.


11   BAud               Binary Speed        This is a read only
                                            parameter, and the
12   FlowControlTo      Flow Control of     host should not set
                        PAD by Terminal     the baud rate
                                            parameter.  If the
                                            host performs a "read
                                            parameter", the
                                            Bridge values are
                                            converted to X.3
                                            values.

13   LFInsertion        Line Feed after CR  X.3 value 3 (LF
                                            insertion after a
                                            <CR> from DTE) is not
                                            supported in Bridge
                                            implementation;
                                            no conversion on
                                            other values.

14   LFPad              Line Feed Padding   None; the Bridge
                                            implementation allows
                                            a wider range than
                                            the X.3 definition.

15   LocalEDiting       Editing             None; Bridge
                                            parameter "command
                                            editing" is turned on
                                            when this parameter
                                            is set.

16   ERAse              Character Delete    None

17   LineERAse          Line Delete         None

18   ReprintLine        Line Display        None


.br;EXAMPLE 1

The following section describes an example in which a terminal on
the LAN is connected to an X.25 host across the GS/1-X.25.  In
this example, a connectionis made from a terminal attached to a
Communications Server on the Ethernet network, through the GS/1-
X.25, to an X.25 host.  The X.25 host is attached to the GS/1-
X.25 either directly or via a PDN>

Together, the GS/1-X.25 and the Communications Server to which
the terminal is attached appear to the X.25 host as a PAD.  When
the connectionis made, the host sends a Set Parameters PAD
packet.  The GS/1-X.25 then forwards these parameter values to
the Communications Server.  The active parameters of the server,
initially read from the default parameters, are updated according
to the values set by the host.  Note that the parameters of the
GS/1-X.25 are not involved in this configuration.

Among the parameters set by the host, two are modified by the GS/
1-X.25 before they are forwarded to the Communications Server in
the following way:

1.  Data Forwarding Condition (parameter 3):

    Data is forwarded by the Communications Server on any of the
    characters ERAse, LineERAse, ReprintLine, WordERAse, and
    VERBatim, in addition to the characters specified by the
    host.  This change made by the GS/1-X.25 is transparent to
    the host, so that is the host reads this parameter, it gets
    an indication of what is has previously set.

2.  Interaction (parameter 6):

    Both values 1 and 5 of this parameter have the same effect on
    the Communications Server, because value 5 is converted to 1
    by the GS/1-X.25.  This change made by the GS/1-X.25 is
    transparent to the host, so that if the host reads this
    parameter, it get an indication of what it has previously
    set.

.br;EXAMPLE 2

The next example describes a configuration in which a terminal
attached to a PAD on the PDN dials in to establish a connection
to a host on the LAN.  The host coult be an X.25 host directly
attached to the GS/1-X.25 or any other host on the LAN.

The connection can be made in two patterns described below:

1.  Transparent mode server of the GS/1-X.25 is involved in this
    pattern.  THe connection is made in one steps, and it
    bypasses the GS/2-X.25 User Interface.  When the connection
    is established with the host, the GS/1-X>25 sends a
    preliminary Set Parameters packet to the PAD,  if Pad
    Initialization has been selected on that line (through
    sysgen).  X.3 parameters with reference numbers 1 through 12,
    except for parameter 11 (baud rate), are read from the
    default configuration of the port, on which the connection
    was established, and sent out to the PAD.

    If Pad Initialization was not selected on the line, the host
    decides whether to send any parameter setting it expects the
    PAD to have.

    If the host is an X.25 host, it generally sends a Set
    Parameters packet to achieve this goal.  If it is an
    asynchronous host, however, you must ensure that the PAD has
    the right settings.

2.  A connection is first made to the GS/1-X.25 User Interface.
    The GS/1-X.25 is then in Command mode.

    In the second stage, you can connect to any resource on the
    Ethernet.  The GS/1-X.25 then enters Data Transfer mode.

    More generally, the GS/1-X.25 enters Command mode every time
    the ECMChar is hit during a session.  It resumes Data
    Transfer mode when the RESume command is entered.  Either one
    of the two parameter profiles is sent out to the PAD,
    depending on whether the GS/1-X.25 is entering Command mode
    or Data Transfer mode.

.br;COMMAND MODE

    When in command mode, the GS/1-X.25 sends out a Set
    Parameters packet to the PAD with X.3 parameters having
    reference numbers from 2 to 18, except for parameter 11 (baud
    rate), parameter 9 (CR padding), and parameter 14 (LF
    padding).  The profile of parameters, shown in the
    following table, is specific to the GS/1-X.25 Command mode,
    and is sent out to the PAD every time the GS/1-X.25 enter
    Command mode.

    In the table, session parameter refers to default session
    parameter is no session has been established yet (i.e., you
    are at the User Interface and have not been connected to the
    host).  If a session has been established, session parameter
    means active session parameter, and port parameter means
    active port parameter.

    The active parameters are initially read from the default
    parameters.  They can be updated either by the host, using a
    Set Parameters packet or by using the SET command.

            Parameter Profile for Command Mode
-----------------------------------------------------------------
Para-
meter
 No.    Bridge Name                   Value
-----------------------------------------------------------------
 2      ECHOData        Depends on the LocalEditing session
                        parameter.  If LocalEditing is
                        NoCmdEditing, it depends on the
                        Interaction port parameter.  ECHOData is
                        1 (default value) if Interaction is Echo,
                        and 0 if Interaction is NoEcho.  If
                        LocalEditing is CmdEditing, ECHOData is 0
                        (disabled).

 3      DataFoward      Depends on the LocalEditing session
                        parameter.  DataForward is 2 (default
                        value) if LocalEditing is NoCmdEditing,
                        and 126 if LocalEditing is CmdEditing.

 4      IdleTimer       Depends on the LocalEditing session
                        parameter.  IdelTimer is 0 (default
                        value) if LocalEditing is NoCmdEditing,
                        and 1 if LocalEditing is CmdEditing.

 5      FlowCtlFrom     Read from the FlowCtlFrom session
                        parameter.  Default value: 1.

 6      InterAction     1

 7      BReakAction     1

 8      Data Delivery   0

10      Line Folding    0

12      FlowCtlTo       Read from the FlowCtlTo session
                        parameter.  Default value: 1.

13      LFInsertion     5

16      ERAse           Read from the ERAse session parameter.
                        Default value: 8(for ^U).

17      LineERAse       Read from the LineERAse session
                        parameter.  Default value: 21 (for ^U).

18      ReprintLine     Read from the ReprintLine session
                        parameter.  Default value: 18 (for ^R).


The LocalEditing parameter has two components: one is used in
Command mode (CmdEditing/NoCmdEditing), and the other in Data
Transfer mode (DataEditing/NoDataEditing).  You are allowed a
choice where editing is done when the GS/1-X.25 is in Command
mode.

If editing is to be done locally on the PAD, the session
parameter LocalEditing must be NoCmdEditing regardless of whether
DataEditing is On of Off.  In this case, the parameter profile
sent to the PAD has DataForward set to CR, IdleTimer disabled,
EchoData depending on whether Interaction is Echo or NoEcho, and
LocalEditing enabled.

If editing is to be done by the GS/1-X.25, the session parameter
LocalEditing must be CmdEditing regardless of whether DataEditing
is On or Off.  In this case, the parameter profile that is sent
to the PAD has DataForward set to CR as well as any control
character in columns 0 and 1 of the ASCII table, IdleTimer equal
to 0.05 second, and LocalEditing disabled.

Two parameters are treated differently from others, when they are
set by the host.  When the host sets parameter 1 (PAD recall
character), it does not affect the GS/1-X.25's ECMChar.  The
change will affect the PAD only.  This ensures that you can get
to the PAD as well as the GS/1-X.25 User Interface, using two
different characters.  THe GS/1-X.25 ECMChar can be changed using
the SET command.

When the host sets parameter 15 (local editing), only the
DataEditing part of the LocalEditing session parameter is
affected.  This is consistent with the fact that CmdEditing or
NoCmdEditing is in effect only when the GS/1-X.25 is in Command
mode, and should not be changed by the host.

.br;Data Transfer Mode

When the GS/1-X.25 enters Data Transfew mode, it sends a
parameter profile, with all the parameters read from the active
session parameters.  Those in turn are initially read from the
default session parameters.  They can be changed by the host, bu
means of a Set Parameter packet, or by using the SET command.

The following table displays the parameter profile sent to the
PAD every time the GS/1-X.25 enters Data Transfer mode.  The
value of each parameter is read from the session parameter.

            Parameter Profile
         for Data Transfer Mode
 ---------------------------------------
Para-
meter                            Default
 No.         Bridge Name          Value
----------------------------------------
  2         ECHOData                0
  3         DataForward             0
  4         IdleTimer               1
  5         FlowCtlFrom             1
  7         BReakAction            21
  8         Data Delivery           0
 10         Line Folding            0
 12         FlowCtlTo               1
 13         LFInsertion             0
 15         LocalEditing            0
 16         ERAse                   8
 17         LineERAse              21
 18         ReprintLine            18

When you set a parameter on the GS/1-X.25 using the SET command,
the Pad will not be updated on that change until the GS/1-X.25
enters Data Transfer mode or resumes Command mode.  The PAD will
be updates immediately only if the parameter being set is
LocalEditing.

You can change the value of LocalEditing using the following
syntax:

SET LocalEditing = CmdEditing

After you have entered the command, a Set Parameters packets is
sent out immediately to the PAD, which contains the four
parameters listed below:

      SET Parameters for CMDEditing
-------------------------------------------
Para-
meter                               Default
No.          Bridge Name             Value
-------------------------------------------
  2         ECHOData                    0
  3         DataForward                126
  4         IdleTimer                   1
 15         LocalEditing                0


If you set LocalEditing to NoCmdEditing, the Set Parameters
packet that is sent to the PAD immediately contains the four
parameters listed below:

      SET Parameters for NoCmdEditing
-----------------------------------------------
Para-
meter                             Default
 No.      Bridge Name              Value
-----------------------------------------------
 2        ECHOData         1 or 0 depending on
                           the Interaction port
 3        DataForward      parameter

 4        IdleTimer        0

15        LocalEditing     1






