CHAPTER 8: Packet Network Access Applications
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8.4 Special Operational Considerations
During operation of a terminal through a PDN to the host computer, some characters and commands
are echoed locally and are reflected on the terminal screen quickly. Others must be sent through the
network to the host, processed, and sent back through the network before they are observed. In general,
alphanumeric characters will echo immediately. The following functions must be processed by the host
or the LinkUp 5294 and will take one to three seconds:
• Field Advance using <TAB>, <BACKTAB>, <FIELD EXIT>, <FIELD +>, or<FIELD -> Keys
• Cursor <HOME> and <NEW LINE>
• <CLEAR>
• Reset (usually <CTRL/R>)
• <DEL>, <ERASE INPUT> and those alphanumeric characters typed while in insert mode
• <Enter>, <ROLL UP>, <ROLL DOWN>, and <DUP>
• <SYS REQ> and <ATTN>
• <CMD> key sequences
• <SCREEN REFRESH> is useful if you suspect that the screen data may have been corrupted.
Also, when using one of the generic PNA options (1 or 2), nondisplay fields such as passwords will
display due to local echo by the PAD. <SCREEN REFRESH> should be entered immediately after keying
data in a non-display field, causing the LinkUp 5294 to remove it from the display. Other fields may then
be completed as needed.
8.5 Other Special Considerations
8.5.1 S
CREEN
D
ISPLAY
E
RRORS
Because of local PAD echo, the terminal display may become garbled at times. To correct this condition,
should it occur, use the <SCREEN REFRESH> sequence for your terminal. For most terminal types, this
is accomplished by a <CTRL/W> or an <ESC W>. Refer to the Terminal User’s Handbook for the correct
key sequence for your terminal type.
If the initial LinkUp 5294 port configuration is done while connected to the network, you will encounter
locally echoed passwords and duplication of characters since the LinkUp 5294 default for PNA access is
N (None). Once the port is configured, exit to Connect Mode, complete the connect sequence, and
screen data should appear normally thereafter.
You should not observe double echo during subsequent configurations since the LinkUp 5294 will turn
off its own echoplex during reconfiguration.
8.5.2 D
ATA
F
ORWARDING TO THE
PAD
Customers using PADs at remote locations to connect terminals to the PDN should check to see if the
PAD supports escape forwarding. This capability recognizes an escape sequence from a terminal, does
not echo it, and forwards the packet to the LinkUp 5294 after a specified time period. If possible, this
method of data forwarding should be used to lessen the conflict of PAD echo and LinkUp 5294 echo of
control sequences.