Solstice X.25 9.2 PAD User's Guide

Packet Assembler Disassembler (PAD)

A Packet Assembler Disassembler (PAD) forms part of the Solstice X.25 software. It allows you to make standard terminal connections to remote machines that support any standard implementation of X.25.

Figure 1-1 PAD Summary

Figure 1-1 shows some of the ways you can use Solstice X.25 to make connections with remote devices:

PAD calls from Sun workstations running Solstice X.25 to Sun workstations and servers running Solstice X.25 and to remote systems running other implementations of X.25.
PAD calls from one X.25 device to another, from where the user can rlogin to a non-X.25 IP host.

Note -

All of the connections shown in the diagram are made across the X.25 Packet Switched Data Network.

A PAD program allows a terminal to communicate with an X.25 PSDN. It does this by assembling characters generated by an asynchronous terminal into packets for forwarding across the PSDN, and by disassembling packets received from a PSDN into a character stream that can be read by a terminal.

Figure 1-2 Outgoing and Incoming PAD call

The PAD program that forms part of Solstice X.25 lets you make PAD calls using a terminal session on a workstation, or using a physical terminal attached to a server. Workstations and servers can receive PAD calls from Sun and non-Sun machines, as long as they use a standard implementation of X.25 and the PAD protocols.

The PAD Protocols

The way a PAD operates is defined by a set of protocols, described in three ITU-T recommendations:

X.3 defines the way the PAD program itself works.
X.28 defines the way that interaction between the PAD and the terminal is handled.
X.29 defines the way that interaction between the PAD and the PSDN is handled.

These three standards are often referred to together as triple X. This is sometimes written XXX.

Command Mode and Call Mode

The pad program operates in two modes:

In command mode, you communicate with the pad program. Use command mode to enter commands specifying the way you want the pad program to work, for example to change the way echoing is handled.
In call mode, you communicate with the remote host.

The PAD Hosts Database

The PAD hosts database is a list of remote hosts with associated parameters created by the System Administrator using the Solstice X.25 configuration tool x25tool. You can make PAD calls to remote hosts that are in the PAD hosts database simply by referring to them by name. You can also make PAD calls to remote hosts that are not in the PAD hosts database, but in this case you must specify parameters before connecting to the remote host.

By default, when you issue the pad command, the pad program will check the PAD Hosts Database to see if the specifed host matches one of the alias defined in the database. If there is a match, the pad program will use the parameters defined in the database to establish a connection.

If you use the -noaddrparse option with the pad program, the PAD program will not search the PAD Hosts Database.

Echoing

Echoing refers to the mechanism used to display characters typed on the keyboard on the terminal screen. The Solstice X.25 pad program supports the following echo modes:

message mode: This is the default. The PAD echoes the characters you type and handles line-editing. The pad program stores all of the characters in a line, until you either press Return or type the 81st character. Then the PAD sends the line to the remote host. This is the most appropriate type of echoing to use when you are using the operating system functions of the remote host. Using the PAD to handle echoing and line-editing minimizes the burden placed on the network and the remote host.
native mode: The remote host echoes the characters you type and handles line-editing. This is the appropriate mode to use for many screen-oriented applications. Using native mode places a high burden on both the network and remote host.
transparent mode: The PAD echoes the characters you type, but does not format them. Transparent mode is not often used.

Your System Administrator should have configured the most appropriate echo mode for your system. If you need to, you can over-ride this setting on a per-call basis.

Terminal Type

Hosts running the Solaris operating environment require you to specify the type of terminal you are using when you log in using a PAD call. This is because the X.29 protocol does not require the transfer of this information. If you are logging into non-Sun machines, check with the System Administrator to find out if you need to specify the terminal type.

PAD Parameters

Your System Administrator should have configured the appropriate PAD parameters for your local system. If you need to change or override them, refer to Solstice X.25 9.2 Administration Guide.