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AIXLink/X.25 1.1 for AIX: Guide and Reference

Using the PAD

This section discusses starting an X.28/X.3 terminal PAD session. For information on how to start X.29 on the system, refer to "Managing the Triple-X PAD".

To start a terminal PAD session, run the xspad command. On systems where the PAD is configured this starts a terminal PAD session and provides the PAD prompt ( *, the asterisk character). Enter the PAD commands at the PAD prompt.

To start a PAD session:

  1. Ensure the PAD is configured on the system.
  2. Run xspad -l sx25a# where # is the port number.
  3. Issue the call to the remote X.25 host at the PAD prompt.
  4. Log on to the X.25 host and run the desired application.

For more information, see the xspad Command in Appendix A.


Once connected to an X.3/X.28 terminal PAD session, various commands can be issued to the PAD. Some of these commands can only be issued after a connection has been established with the remote X.25 host. Based on the PAD's profile, the commands understood by the PAD are either based on the CCITT standard or can be in a less cryptic style (advanced mode).

The start/stop DTE user may interact with the PAD using PAD commands. These commands provide:

To enter a PAD command at the terminal, the user enters the command at the PAD prompt. As long as there is not a remote host connection, the current prompt is the PAD prompt ( *, the asterisk character). To get to the prompt when connected to a remote session, press Ctrl-P.

At the prompt, the following commands can be issued:

break Sends a break character to the PAD.
call Establishes a connection to the remote X.25 host: call 34511884 , where 34511884 is the remote NUA.
clear Clears the connection with the remote X.25 host. The clear is sent from the PAD immediately. See the iclear command.
help Requests help text. See "Getting Help" for more details.
iclear Sends an "invitation to clear" to the remote X.25 DTE. This allows the remote host to send any pending data before clearing the call.
interrupt Sends an interrupt packet. The packet contents cannot be user-specified.
language Sets the language for the PAD help text to English, French, or Spanish. For example, language french.
nui This command is not implemented in the PAD.
par Reads the PAD parameters.
par? Displays all parameters.
par? 2, 3 Displays parameters 2 and 3.

In advanced mode, read or parameter can be used instead of par.

profile Displays which profiles are available, or allows you to change the profile. Enter PROFILE followed by the profile name, such as PROFILE PROFILE_51 to make changes.
read See par.
rpar/rread Reads the PAD parameters as par? does for the local PAD in implementations where a remote PAD DTE is supported.
rset/resetread Writes the PAD parameters as set? does for the local PAD in implementations where a remote PAD DTE is supported.
set Sets one or more of the PAD parameters. For example,
set 2:1, 14:2
or in advanced mode
set echo:1, lfpad:2
Note: The default profile does not allow the parameters to be changed locally as they are being controlled remotely through the TTY subsystem and the stty command. xspad does not require the use of the set command or any of the remote PAD commands (rread, rpar, rset, and rsetread).
status Indicates whether a connection to the remote X.25 host is active. Returns ENGAGED if it is active or FREE if no connection is established.

Establishing Calls

To establish a connection with a remote X.25 host, a call must be made to it. The call must be given the remote DTE's address and any call user data or facilities being requested.

X.28 Facility Codes
Facility Code Function Requested Value (text that follows the facility code)
C Charging Information  
E Called Address Extension Extended address
F Fast select with no restriction
G Closed User Group CUG number
N Network User Identification NUI string
Q Fast select with restrictions on response
R Reverse charging
D Call User Data ASCII CUD string to be added to the standard PAD call CUD. (Must be the last part of the command string.)
- Facility end marker End of facilities marker (allow CUD).

Example Calls

The following are typical calls that might be made from the PAD command prompt:

call 3536647 Establish a call to NUA 3536647
call 3536647 F,R- Request fast select and reverse charge
call 3536647 R- D user1 Have ASCII based CUD "user1"
call 3536647,9093388 Make the call with the local (calling) address of 9093388 included

Connected Sessions

After a call has been placed to the remote X.25 host, it can be rejected by the network, or the remote host, or accepted by the remote host. If rejected, a clear packet is received and results in a message similar to those described in "Ending Calls". Once connected, the terminal is under the control of the TTY system of the remote host. Typically a login screen is presented. After the user has logged in, it can be used the same as other attached TTYs.

Once a session is established, the TERM type and stty settings should be verified. The TERM type should be set to the type of terminal you are using, for example, TERM=aixterm . The stty settings can be verified with stty -a . The row and column attributes need to be updated if using X-Windows and the size of the window is not equal to 80x25 (default setting). The echo, echoe, and echok attributes might also need to be turned


To change an stty attribute, enter one of the following commands:

stty echo (turns echo on)
stty -echo (turns echo off)
stty 50 rows (updates the row setting to 50)

Ending Calls

Once a connection is established, there are a number of ways in which it can be terminated. Termination of the login shell used to log in to the remote X.25 host closes the connection and results in a message such as the following:

CLEAR DTE 0 241 - Call cleared, by remote device, data may be lost

As the session was terminated above the PAD layer, the PAD code did not expect it and so could not tell if it was user-initiated or not. If it was user-initiated, then no data was lost.

An alternative is to press Ctrl-P to get to the PAD command prompt, and then enter iclear. The iclear command causes the local terminal PAD to send a request to the host PAD to clear the connection. The host PAD software then issues the clear, but without regard for any applications that might be running on the remote host under this login. As the remote PAD software issues the command to clear the connection, the diagnostic software is likely to reflect this as being an expected clear.

CLEAR PAD 0 0 - Call cleared, remote request

The additional text is given when advanced mode is enabled through the profile; otherwise the base clearing reason is given.

Exiting xspad

From the PAD command prompt that is reached by ending the call as described above, enter ^k (Ctrl-K) to terminate the xspad program. The xspad application must not have a call established when attempting to terminate xspad.

Automatic Termination and Identification for AIXLink/X.25 1.1.3 (and later)

The PAD application is automatically exited upon termination of the X.25 Host connection. This optional feature is enabled using the -x flag with the xspad command (for example, xspad -x -l sx25a0 ).

The PAD default is to enter ^k (Ctrl-K) before exiting. If an X.25 Host connection terminates and the user does not exit, the user can initiate another X.25 connection using the same X.28 STREAMs connection.

Note: This feature applies only to xspad (the user space PAD application).

Getting Help

Help is provided through the help command. To list the help topics, enter help list . Each of the PAD commands has help text associated with it (for example, help call) . Also each PAD parameter and profile has help text. The language in which the text is displayed can be changed using the language command.

Clearing Codes

When the call is cleared, the information passed in the X.25 clear packet is displayed. When advanced mode has been selected through use of the appropriate profile, a more detailed text explanation of the clear is given. Otherwise, the base cause is displayed as follows:

OCC Remote DTE busy
NC Network congestion
INV Invalid facility
NA Access barred
ERR Local procedure error
RPE Remote procedure error
NP Number not assigned
DER DTE out of order
PAD DTE clearing
DTE DTE device clearing
RNA Reverse charging rejected
ID Incompatible destination
SA Ship cannot be contacted
FNA Fast select rejected
ROO Cannot route as requested

PAD Parameters

The operation of the PAD depends on the value of a set of internal variables called PAD parameters. An independent set of parameters exists for each start/stop mode DTE. The current value of each PAD parameter defines the operational characteristic of the related function.

Initially, the values of the parameters are chosen by selecting one of the available profiles. Subsequent changes for a given terminal session are done under control of the session's TTY subsystem on the host PAD. When the application being run requires a change to the terminal characteristics, it modifies the session's stty structure which in turn causes the X.29 protocol to issue a change to the session's X.3 parameters held in the terminal PAD.

The following is a list of the X.3 PAD parameters:

par 1
PAD Recall
This parameter specifies the character that you can type at the terminal to interrupt data flow with the X.25 host (in order to enter commands addressed to the PAD). Possible values are:
0 Data flow can not be interrupted. The user can not enter PAD commands.
1 The escape character sequence is Ctrl-P.
32-126 Value of the PAD recall character in decimal.
Note: If you set this parameter to 0, you will not be able to change the PAD parameters any further.
par 2
This parameter specifies whether the characters received from the terminal are to be transmitted back to the terminal as well as being interpreted by the PAD. Possible values are:
0 No echo by the PAD.
1 Local echo by the PAD.
Note: When working in line mode, this parameter should be set to 1 to get an echo from the PAD, and the echo provided by the host should be disabled with the command stty -echo.
This parameter specifies the conditions under which a string of input characters from a terminal is converted to a data packet and forwarded to the X.25 Network. Possible values are:
0 Data forwarding not controlled by a character.
1 Data forwarding on alphanumeric characters.
2 Data forwarding on receipt of carriage return (ENTER).
4 Data forwarding on receipt of ESC, BEL, ENQ, or ACK.
8 Data forwarding on receipt of DEL, CAN, or DC2.
16 Data forwarding on receipt of EXT, or EOT.
32 Data forwarding on receipt of HT, LF, VT, or FF.
64 Data forwarding on receipt of any character from column 0 and 1 of the ASCII code page.

If this parameter is set to 0, every character typed at the terminal is sent by the PAD in an individual packet. For the other values, the PAD acts as a buffer and sends a packet only when the specified character is entered. If you are working on your terminal in line mode, entering UNIX commands for example, you may set this parameter to 18 and packets will be sent to the host only when you press Enter, Ctrl-C, or Ctrl-D.

par 4
This parameter specifies a timeout period for the reception of characters from the terminal. After this timeout expires, characters already received by the PAD are formatted into a data packet and sent to the X.25 network. Possible values are:
0 No timeout period is used.
1-255 Timeout period expressed in units of 0.05 seconds.

This parameter, when set to a non-zero value, improves the data transfer rate from the terminal to the host. In this case, the time delay between the PAD receiving two consecutive characters is lower than the timeout period, so the PAD accumulates and sends data only when it has a full packet, or when the file transfer application has stopped sending characters. When using line mode, the value of this parameter should be 0.

par 5
Controls the ancillary device. Possible values are:
0 No use of X-ON and X-OFF.
1 Use of X-ON and X-OFF during data transfer.
2 Use of X-ON and X-OFF during commands and data transfer.
par 6
Controls the service signals and dialog mode for the terminal. Possible values are:
0 No service signals are sent to the terminal.
1 Service signals other than prompt PAD service are transmitted in standard format.
4 Service signal prompt PAD service is transmitted in standard format.
8-15 PAD service signals are transmitted in a network-dependent format.
16 English extended dialog mode.
32 French extended dialog mode.
48 Spanish extended dialog mode.
par 7
Specifies the action of the PAD on receipt of a break signal from the terminal. Possible values are:
0 Not applicable.
1 Interrupt.
2 Reset.
4 Send to DTE an indication of break PAD message.
8 Escape from data transfer state.
16 Discard output to terminal.
par 8
Selects whether the data output should be sent to the terminal or discarded. Possible values are:
0 Normal data delivery.
1 Discard output to terminal.
par 9
CR Padding
Specifies the number of padding characters sent to the terminal after a CR character (Enter). Range 0 to 255.
par 10 - Line
Specifies the number of characters sent to the terminal without inserting an appropriate formatting character. Possible values are:
0 No line folding.
1-255 Number of characters.
par 11
Specifies the line speed of the terminal attached to the PAD. This parameter can only be read, not changed.
Line Speed Parameter Values
Speed (bps) value Speed (bps) value
50 10 1800 7
75 5 75/1200 11
100 9 2400 12
110 0 4800 13
134.5 1 9600 14
150 6 19200 15
200 8 48000 16
300 2 56000 17
600 4 64000 18
1200 3

par 12
Terminal Flow Control
Controls the flow between the PAD and the terminal. Possible values are:
0 No use of X-ON and X-OFF.
1 Use of X-ON and X-OFF.
par 13
Specifies whether a Line Feed character is inserted after a Carriage Return. Possible values are:
0 No linefeed insertion.
1 Send linefeed to the terminal after sending a carriage return.
2 Add a linefeed after each carriage return to the data being sent from the terminal.
4 Echo a linefeed after each carriage return
par 14
LF Padding
Specifies the number of padding characters sent to the terminal after an LF character. Range 0 to 255.
par 15
Controls use of local editing to the terminal and PAD. The PAD allows the terminal to edit the PAD command signals sent to the PAD before they are processed. Parameters 15 through 19 control this function. Possible values are:
0 No use of editing in data transfer mode.
1 No linefeed insertion.
par 16
Char Delete
Specifies the character from International Alphabet 5 (IA5) that is to request character deletion for the PAD editing buffer.
0 - 127 Valid range. 127 is character 7/15 (DEL).
par 17
Line Delete
Specifies the character from IA5 that causes the PAD to delete the contents of its edit buffer.
0 - 127 Valid range. 24 is character 1/8 (CAN).
par 18
Line Display
Specifies the character from IA5 that causes the PAD to display the contents of its edit buffer.
0 - 127 Valid range. 18 is character 1/2 (DC2).
par 19
Editing Signals
Controls the editing of PAD service signals. Possible values are:
0 No editing allowed.
1 Editing allowed for printing terminals.
2 Editing allowed for display terminals.
8, 32-126 Character from IA5.
par 20
Selects what characters are echoed when local echo is enabled (parameter 2). Possible values are:
0 All characters are echoed.
1 CR character is not echoed.
2 LF character is not echoed.
4 VT, HT, FF characters are not echoed.
8 BEL and BS characters are not echoed.
16 ESC and ENQ characters are not echoed.
32 ACK, NAK, STX, SOH, EOT, ETB, and ETX characters are not echoed.
64 Characters designated by PAR 16-18 are not echoed.
128 No echo of characters in columns 0 and 1, not mentioned above, or the DEL character.
Note: If parameters 5, 12, or 22 is set to a non-zero value, the characters XON and XOFF are NOT echoed.
par 21
Specifies the parity used when sending data to and from the terminal. Possible values are:
0 No parity generated or checked.
1 Parity checking.
2 Parity generating.
par 22
Page Wait
Controls screen scrolling if page wait is to be used. Possible values are:
0 Page wait disabled.
1-255 Number of line feed characters before page wait.

PAD Profiles

Within the terminal PAD, there are four available profiles. Which profile is loaded for a particular session is controlled by the PROF command. The command to list what profiles are available is help prof. By default, the PROFILE_51 profile is used.

The following profiles are implemented:

50 Standard profile with minimum textual information.
51 Standard profile with extended textual information.
90 CCITT simple profile.
91 CCITT transparent profile.

The settings of the X.3 parameters for each of the profiles are:

X.3 Parameter Settings for Each Profile

50 51 90 91
1 1 1 1 0
2 1 1 1 0
3 2 2 126 0
4 0 0 0 20
5 0 0 1 0
6 5 16 1 0
7 21 21 2 2
8 0 0 0 0
9 0 0 0 0
10 0 0 0 0
11 14 14 14 14
12 1 1 1 0
13 5 5 0 0
14 0 0 0 0
15 1 1 0 0
16 8 8 127 127
17 3 3 24 24
18 18 18 18 18
19 2 2 1 1
20 64 64 0 0
21 0 0 0 0
22 0 0 0 0

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