CHAPTER 8: Packet Network Access Applications
77
They are generally handled by the LinkUp 5294, without requiring any information to go to the host.
•
Host PAD —
The PAD located at the host end of the network. In an X.25 network with
minicomputers and asynchronous terminals, this is the PAD located at the minicomputer end of the
network. In the LinkUp 5294 implementation where IBM hosts are used, this is the PAD located at
the LinkUp 5294.
•
PAD —
Packet Assembler-Disassembler. This is a physical interface node with an asynchronous (RS-
232C) port on one side and an X.25 protocol interface on the other side. A PAD is similar to an
asynchronous modem in that both provide an interface to specialized communications lines.
•
PNA —
Packet Network Access. The LinkUp 5294 feature which allows connection of asynchronous
terminals through an X.25 network.
•
PDN —
Packet Data Network. A network of private or public communications lines which use X.25
protocol.
•
Packet —
A collection of asynchronous data of varying length addressed for a specific destination.
•
Terminal PAD —
The PAD located at the asynchronous terminal end of the X.25 network.
8.2 Using the LinkUp 5294 with PDNs
In order to explain the way the LinkUp 5294 handles keystroke echo and cursor positioning with PDNs,
it is necessary to explain how the LinkUp 5294 handles these with a directly connected terminal.
Figure 8-2 shows the flow of information between the keyboard, display, and the LinkUp 5294 when
alphanumeric or cursor movement keys are pressed.
A =
Press the Up Arrow key. Up Arrow keycode goes to the LinkUp 5294.
B =
The LinkUp 5294 echoes the Up Arrow to the display (or in some cases sends a cursor address)
and the cursor is repositioned.
Figure 8-2. Cursor Movement Echo.
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
DataLynx
B
A
Host
Terminal
LinkUp 5294
