PAD

Packet Assembly/Disassembly (PAD) is an X.25-specific concept. Traditionally, only X.25 terminals could connect to an X.25 network. These terminals must be packet terminals that support X.25 procedures in terms of hardware and software. However, many terminals in common use are non-X.25 terminals. They either have no intelligence available with packet terminals or have intelligence but do not support X.25 procedures. Examples of such terminals are keyboards, monitors, and printers. To allow these devices to communicate on X.25 networks, X.25 PAD was developed.

X.25 PAD provides a mechanism to connect non-X.25 terminals to an X.25 network. As shown in Figure 130, a PAD facility is placed between non-X.25 terminals and an X.25 network, allowing them to communicate with other terminals across the X.25 network.

X.25 PAD provides the following functions:

• X.25 procedures support for connectivity and communication with X.25 networks.

• Non-X.25 procedures support for connectivity with non-X.25 terminals.

• Capabilities allowing non-X.25 terminals to set up calls, transmit data, and clear calls.

• Capabilities allowing non-X.25 terminals to observe and modify interface parameters to accommodate to different terminals.

X.25 PAD facilities are regarded as procedure translators or network servers, helping different terminals access X.25 networks.

The system implements X.29 and X.3 protocols in the X.25 PAD protocol suite. In addition, it implements X.29-based Telnet. This allows you to Telnet to a remote router through X.25 PAD when IP-based Telnet is not preferred for security sake, as shown in Figure 131.