This chapter contains the following sections:
The SX.25 pad program fully supports the packet assembler/disassembler (pad) functionality defined in the X.3/X.28/X.29 recommendations.
The X.3 recommendation defines a set of parameters that the pad program uses to identify and control the terminal; for example, echo or data forwarding. The parameter values can be preset, set by the terminal user, and/or set by the remote host. A complete set of parameter values is called a profile.
The X.28 recommendation defines control procedures, user commands, and the service signals sent by the pad program to your terminal.
The X.29 recommendation defines the control messages sent between the pad program and the remote host. These messages are carried as X.25 qualified data packets.
When you use the pad program in SX.25, you use either command mode or call mode. In command mode, the pad program expects one of the commands described in Chapter 2, “SX.25 Pad Program Commands.” In call mode, all the characters you enter are treated as data to be sent to the host you have called. The exception to this is the BREAKIN sequence <Ctrl-P a>, which returns you to command mode.
The user interface of the pad program provides the commands defined by the X.28 recommendation, plus a set of more user-friendly commands. Refer to Chapter 2, “SX.25 Pad Program Commands.”
The concepts of message, native, and transparent modes are recognized. Use these commands to select a combination of X.3 parameter values. Refer to “Selecting an Operating Mode” later in this chapter.
Commands are recognized as complete words or as fixed abbreviations. The abbreviated form has exactly the same effect as the full command.
You can enter commands to the pad program in either uppercase or lowercase.
After typing the command
pad |
you enter command mode and the prompt is:
PAD: |
If you make a mistake when typing a command, but notice this before pressing the Return key, you can correct the line as you go along. The pad program lets you delete the previous character in the command line using the Backspace key. Commands are not processed until you press the Return key.
There are two steps in logging on to a host using SX.25 across either the remote or the local network.
Run the pad program. At the system prompt enter:
pad |
The pad program prompt is displayed:
PAD: |
Call a host.
Alternatively, you can supply a hostname as a parameter to the pad command. Enter:
pad hostname |
The pad program acts according to the terminal type setting defined by the profile being used. You can select the profile by means of the profile command. This lets you choose one of the standard profiles. Your network administrator will know which profile is best for you. If you are using a display terminal, you can set the current terminal type by typing:
PAD: vdu |
For details, see Chapter 2, “SX.25 Pad Program Commands.”
When you are making a call, you are connected from a terminal to a remote host and characters typed on the keyboard appear on your video screen. How do the characters get there?
This is known as “echoing” and depends on the type of host machine you are connected to and, in some cases, on the application program you are running. Some types of terminal output echo characters to the screen, which restricts the number of ways they can be used. Most terminals rely on the machine they are attached to for the “echo.” There are a number of ways this can be achieved:
If you are using a screen editor or similar application, the host application program must carry out all the screen formatting functions, so the pad program transfers the data directly, without interpreting it at all.
With less critical applications, or simple command line entry, the pad program itself can provide the echo and format the data, relieving the host computer of these tasks and reducing the load on the network.
For this reason, the pad program in SX.25 supports three kinds of call modes:
Message mode is the default mode of operation. It involves line-at-a-time exchange between the terminal and the host. In other words, everything you type on one line is sent to the host after you press Return. The pad program is responsible for the detailed control of the terminal, including echoing typed input, input editing, and output formatting.
Transparent output mode of operation may be needed in some cases where the host application controls all output formatting and no characters are intercepted or generated by the pad program.
Native mode of operation means that the characters you type are forwarded to the host immediately. The host has total control of the terminal, including echoing user input, input editing, and output formatting.
From any of these modes, you can return to command mode by issuing the BREAKIN sequence:
<Ctrl p> a
That is, press <Ctrl> and p together, then a.
In normal operation, you should not need to change the mode yourself. However, the application that you are running (on the currently connected host) may change the mode of operation. For example, a screen editor as described above can select native mode. On exit, the application should reset the mode to its previous value.
The MESSAGE, TRANSPARENT, and NATIVE commands let you set the mode of operation explicitly, as required. These commands are described in Chapter 2, “SX.25 Pad Program Commands.”
Setting the mode type affects the values of the following X.3 parameters:
Echo | (parameter number 2) |
Data Forwarding Timeout | (parameter number 4) |
Line Folding Width | (parameter number 10) |
Local Editing | (parameter number 15) |
The effects of the mode changes on these parameters are shown in Table 1-1.
Table 1-1. Effects of Mode Changes on X.3 Parameters
| Parameter |
|
|
|
|---|---|---|---|---|
| 2 | 4 | 10 | 15 |
Native | 0 | 1 | 0 | 0 |
Transparent | 1 | 0 | 0 | 1 |
Message | 1 | 0 | 80 | 1 |
Various escape code sequences are effective if you are currently in message or transparent mode.
An escape code sequence consists of pressing the current BREAKIN character (the default is <Ctrl p>), followed by one of the following characters:
a | |
b | send a break signal to the currently connected host |
e | reverse the current echo state (until <Return> typed) |
r | reset the current call (if any) |
t | forward the current buffered line |
char | put the character into the buffer; used mainly for control characters DLE, DC2, and CAN. |
First, are you already connected to a host? If not, refer to “Starting a Session” earlier in this chapter. If you have just started a session as previously described, you are not yet connected to a host. If you have not started a session and there is no connection, check the options available by typing:
hosts |
This lists all the available hosts to which you can connect, giving both their names and aliases. The list looks something like this:
HOSTS AVAILABLE ~~~~~~~~~~~~~~~ Name : Thirdfloor-mini-room4 Alias: mini34 Name : Thirdfloor-mini-room3 Alias: mini33 Name : Secondfloor-mini-room6 Alias: mini26 |
You can scroll through the list of hosts using pg, or another pager, if you have used the PAGER environment variable to specify one. For details, refer to the pg (1) manual page. Press Return to see the rest of the display.
For example, to make a new connection to the host mini33, enter:
PAD: call mini33
The pad program responds with:
Connecting ..
If the connection is successful, the following message appears:
Connected
If this message does not appear, turn to Chapter 3, “Troubleshooting.” Otherwise, the login prompt of the host appears.
You are now free to use your terminal as you would normally.
To provide sophisticated screen management, a number of host computers need to know what type (make) of terminal you are using. Describe your terminal to the host computer you plan to use. When you access other computers, or access a computer from a different type of terminal, you need to describe your terminal again.
For example, on IRIX systems the terminal can be described by specifying “TERM” at run time. Alternatively, if you always use the same type of terminal, it can be permanently set up in your user environment file .login or .profile.
To return to command mode from call mode and regain access to the user commands, use the BREAKIN sequence <Ctrl-p a >.
The BREAKIN sequence defaults to <Ctrl-p a> but can be altered to any other key sequence by using the BREAKIN command. Refer to the description of this command in Chapter 2, “SX.25 Pad Program Commands.”
An important point about closing a connection is that you may not need to, depending on the setup of the host to which you are connected. Most hosts close the connection automatically when you log off. Thus the most important thing about closing a connection is:
REMEMBER TO LOG OFF FROM THE HOST
If you do not log off, the network resources on the host may get used up. Eventually you cannot reconnect to the host unless your system administrator sorts things out.
An alternative way of closing the connection is to press the BREAKIN sequence to bring up the pad program prompt and enter:
clear <return> |
This closes the connection. Now you can either enter
quit |
to exit from the pad program or
CALL |
to access another host.
Alternatively, you can close the connection and quit the pad program in one step by returning to the pad program prompt and entering:
quit |