LINKUP 5294 WITH DL5294 FIRMWARE
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8. Packet Network Access Applications
Packet Network Access support allows the LinkUp 5294 to be used in X.25 and other network
environments facilitating transmission of asynchronous data. The LinkUp 5294 is located between the
IBM host computer and the host PAD (Packet Assembler-Disassembler), as shown in Figure 8-1. The host
PAD provides the interface between the LinkUp 5294 and the X.25 network. The terminal is connected
to the Packet Data Network (PDN) through the terminal PAD. The terminal can be directly cabled to the
PAD, or can dial into a public PAD port.
Figure 8-1. A Packet Data Network Environment.
The LinkUp 5294 will convert the host’s synchronous data into an asynchronous data stream. The host
PAD will bundle the asynchronous data into a packet and transmit it over the X.25 network to the
terminal PAD. The terminal PAD will unbundle the asynchronous packet and send the data stream to
the terminal. Conversely, the terminal’s asynchronous data stream will be assembled into a packet and
transmitted by the terminal PAD. The host PAD will receive the packet, unbundle it, and pass the
asynchronous data stream to the LinkUp 5294. The LinkUp 5294 will now convert the asynchronous
data into a synchronous data stream and send it to the host.
8.1 Terminology
The following abbreviations are used throughout this section
•
AID Keys —
Attention Identifiers. These are keys that require host processing. They are: <CLEAR>,
<Enter>, Command keys, Roll keys, <HELP> and <PRINT>. When these keys are pressed, the LinkUp
5294 will normally lock the terminal’s keyboard and send the information to the host. The host will
generally return data for the display and signal the LinkUp 5294 to unlock the keyboard.
•
Auto Exit Field —
This is a type of field which is defined by the input field attributes of the IBM host
application. After the operator has entered the last character of the field, the cursor will be
positioned to the next input field automatically, without requiring the operator to press <TAB> or
<FIELD EXIT>.
•
Character Echo —
This causes a character to appear on a terminal’s display after a key on the
keyboard has been pressed.
• Cursor Movement Keys —
These are the Up Arrow, Down Arrow, Left Arrow, and Right Arrow keys.
ON
SYS OK DCE
DTE
TXD
RXD
RTS
CTS
DTR
DSR
CD
RI/SYN
TXC
RXC
I/O FLT
CHANNEL ERROR
CH SEL
RESET
DataLynx /5294
TM
X.25
PDN
Terminal
PAD
Host
PAD
Terminal
DataLynx/5294
Host
LinkUp 5294