X.3 PAD Parameters A P P E N D I X F

X.3 PAD Parameters A P P E N D I X F
A P P E N D I X
F
X.3 PAD Parameters
A PAD is a packet assembler/disassembler, which is a device that collects data from a group of
terminals and periodically outputs the data in packets (data organized in a special format). A PAD
also does the reverse. That is, it can take data packets from a host and return them into a character
stream that can be transmitted to the terminals. A PAD is defined by CCITT Recommendations X.3,
X.28, and X.29.
CCITT Recommendation X.3 specifies the parameters for terminal-handling functions such as baud
rate, flow control, character echoing, and other functions, for a connection to an X.25 host. The X.3
parameters are similar in function to the Telnet options.
CCITT Recommendation X.29 specifies a protocol for setting the X.3 parameters via a network
connection. When a connection is established, the destination host can request that the PAD or
terminal change its parameters using the X.29 protocol. A PAD can refuse to do this, in which case
a terminal user can change the parameter later. A PAD cannot tell the destination host to change its
X.3 parameters, but it can communicate that its own parameters were changed.
Along with Recommendations X.3 and X.29, the CCITT also provides Recommendation X.28 to
specify the user interface for locally controlling a PAD; however, the protocol translator is not a PAD
and this recommendation is not supported.
This appendix discusses the X.3 PAD parameters. The Communication Server and Protocol
Translator Connection Guide explains how to make PAD connections and how to switch between
connections.
X.3 PAD Parameters
Following are descriptions of the X.3 parameters. Default values are noted in the descriptions. The
default value for any parameter not so noted is zero for outgoing connections or not set for incoming
PAD connections. For incoming PAD connections, the protocol translator sends an X.29 SET
PARAMETER packet to set the noted defaults.
Since the X.3 parameters describe the user’s terminal, which exists on only one side of the
connection, the PAD protocols are not always symmetric.
Some of the commands described in this section require ASCII decimal values, which are listed in
Appendix D.
X.3 PAD Parameters F-1
X.3 PAD Parameters
Parameter 1: Escape from Data Transfer (Not Supported)
Parameter 1 determines whether or not the protocol translator will be allowed to escape from data
transfer mode in order to send PAD command signals. Since the EXEC uses a two-character escape
sequence, and there is no way to set the escape character on a Telnet connection, this parameter is
refused on translation sessions as well.
Parameter 2: Local Echo Mode
Parameter 2 determines whether or not PAD is required to perform local echo of characters. This
parameter can be negotiated end-to-end on translation sessions. On incoming PAD connections,
software turns local echo off on the remote PAD to support the Cisco user interface. See Table F-1
for local echo mode values and their descriptions.
Table F-1
PAD Local Echo Mode Values
Value
Description
0
No local echo (incoming PAD connection default)
1
Local echo on (outgoing connection default)
Parameter 3: Data Forward Character
Parameter 3 sets up a packet forwarding mask; that is, it selects which character causes PAD to
forward a packet either before expiration of the Idle Timer (see parameter 4) or when in local editing
mode. See Table F-2 for data forward character values and their descriptions.
Table F-2
PAD Data Forward Character Values
Value
Description
0
None—full packet
1
Forward packet upon receipt of an alphanumeric character
2
Forward packet upon receipt of a RETURN (outgoing connection default)
4
Forward packet upon receipt of ESCAPE, BEL, ENQ, or ACK
8
Forward packet upon receipt of DEL, CAN, OR DC2
16
Forward packet upon receipt of ETX or EOT
32
Forward packet upon receipt of HT, LT, VT, or FF
64
All other characters in the ASCII chart
Because X.3 supports a wider variety of dispatch characters than Telnet does, parameter changes to
or from the default causes a translation session to negotiate in or out of line mode on the Telnet
connection.
A forwarding mask can be statically set using the terminal dispatch-character terminal parametersetting EXEC command. This command can set any character or characters as the forwarding mask,
and overrides (when logical) any values set by parameter 3.
F-2 Protocol Translator Command Reference
X.3 PAD Parameters
Parameter 4: Idle Timer
Parameter 4 controls the amount of time the software waits for new data before sending a packet in
the absence of a data forwarding character. See Table F-3 for PAD idle timer values and their
descriptions.
Table F-3
PAD Idle Timer Values
Value
Description
0
No timer
1-255
Delay value in twentieths of a second (default for both connection types is 1)
Parameter 5: Device Control (Not Supported)
Parameter 5 selects whether PAD can transmit flow control (ASCII XON/XOFF) characters during
data transfer to the terminal to control the terminal and data flow. Flow control is not directly
supported on communication servers because data must make network hops to travel to its final
destination. However, depending on the type of incoming connection, setting this parameter can
cause similar negotiations to be sent over the connection, thereby attempting to change the state of
the flow control option at the device closest to the user.
Parameter 6: PAD Service Signals (Not Supported)
Parameter 6 selects whether or not PAD is required to transmit service signals. Because the
communication server does not use Recommendation X.28 for its user interface, this parameter is
ignored.
Parameter 7: Action upon Receipt of a BREAK Signal
Parameter 7 defines the action of the PAD after receiving a BREAK signal from the terminal. See
Table F-4 for PAD BREAK signal values and their descriptions.
Table F-4
PAD BREAK Signal Values
Value
Description
0
Ignore the BREAK signal.
1
Transmit an interrupt packet to notify the remote host or another PAD that the BREAK
signal has been generated.
2
Transmit a Reset packet to reset the virtual circuit.
4
Transmit an X.29 Break indication to the remote host, or to a PAD
(outgoing connection default).
8
Escape from data transfer mode.
16
Discard output to the terminal by setting parameter 8 to a value of 1.
21
Combination of values 1, 4 and 16 (incoming connection default).
The PAD protocols allow you to send a special X.29 Indication of Break packet, send an Interrupt
packet, perform a Reset operation, act as if the Recall character had been typed, or begin discarding
output to the user. Combinations of these options are also allowed, as long as they make sense.
X.3 PAD Parameters F-3
X.3 PAD Parameters
Common options are to begin discarding output and send both an X.25 Interrupt packet and an X.29
Indication of Break packet, and these options are supported. All other options are not supported and
are silently ignored.
Parameter 8: Discard Output
Parameter 8 indicates to the PAD whether to discard received packets rather than disassemble and
transmit them. This parameter works in conjunction with parameter 7. If value 16 is chosen for
parameter 7, all output is discarded after reception of the BREAK signal. Setting parameter 8 to zero
restores normal data delivery to the terminal. See Table F-5 for PAD discard output values and their
descriptions.
Table F-5
PAD Discard Output Values
Value
Description
0
Normal data delivery to the terminal (outgoing connection default).
1
Discard all output to the terminal. Set by parameter 7; see previous description.
This parameter can also be set and unset manually using the PAD resume EXEC command.
Parameter 9: Return Padding (Not Supported)
Parameter 9 determines whether or not PAD should provide padding (insert filler characters) upon
receipt of a Return character from the terminal.
Parameter 10: Line Folding (Not Supported)
Line folding means inserting a LINE FEED at a certain point which places subsequent characters on
the next line. Parameter 10 determines selection of this function and specification of the line length.
Parameter 11: Baud Rate
Parameter 11 is a read-only value that determines the baud rate transmitted across the interface
between PAD and the terminal. See Table F-6 for PAD baud rate values and their descriptions.
F-4 Protocol Translator Command Reference
X.3 PAD Parameters
Table F-6
PAD Baud Rate Values
Value
Description (in bits per second)
10
50
5
75
9
100
0
110
1
134.5
6
150
8
200
2
300
4
600
3
1200
7
1800
11
75/1200
12
2400
13
4800
14
9600
15
19200
16
48000
17
56000
18
64000
Parameter 12: Input Flow Control (Not Supported)
Parameter 12 determines whether or not the terminal can transmit ASCII XON/XOFF (transmission
on and off) characters to PAD during the data transfer mode. Flow control is not directly supported
on protocol translators because data must make network hops to travel to its final destination.
However, depending on the type of incoming connection, setting this parameter can cause similar
negotiations to be sent over the connection, thereby attempting to change the state of the flow control
option at the device closest to the user.
Parameter 13: LINE FEED Insertion
Parameter 13 determines the procedure for inserting the LINE FEED character upon receipt of a
RETURN character. The PAD also responds to a value that results from the addition of any of the
values in Table F-7.
X.3 PAD Parameters F-5
X.3 PAD Parameters
Table F-7
PAD LINE FEED Signal Values
Value
Description
0
Do not insert the LINE FEED character (outgoing connection default).
1
Insert a LINE FEED after transmitting RETURN to the terminal.
2
Insert a LINE FEED after echoing RETURN to the terminal.
4
Insert a LINE FEED after echoing RETURN to the remote host.
Parameter 14: LINE FEED Padding (Not Supported)
Parameter 14 determines whether or not PAD should provide padding (insert filler characters) upon
receipt of a LINE FEED character from the terminal. This function is generally provided by the end
user’s operating system.
Parameter 15: Local Editing
Parameter 15 enables or disables a PAD editing function for the terminal in data transfer mode.
Enabling the editing function disables the Idle Timer (see parameter 4). The user at the terminal can
make corrections and display the line buffer containing the characters to be transmitted when the
forwarding character (see parameter 3) is received. See Table F-8 for PAD local editing function
values and their descriptions.
Table F-8
PAD Local Editing Function
Value
Description
0
Disables editing capabilities in data transfer mode. Any characters entered become part of
the data stream and are transmitted (default for both connection types).
1
Enables editing capabilities in the data transfer mode, which suspends the following PAD
operations:
• Full packet data forwarding until the edit buffer is full
• Forwarding of DATA packets upon expiration of the Idle Timer
Parameters 16, 17, and 18 provide the editing functions.
Parameter 16: Character Delete
Parameter 16 allows you to select a character that will delete characters while in PAD editing mode.
This character is valid only if parameter 15 is set to one. See Table F-9 for PAD line display editing
function values and their descriptions.
F-6 Protocol Translator Command Reference
X.3 PAD Parameters
Table F-9
PAD Line Display Editing Function
Value
Description
0-127
Select one character from the ASCII character set to represent the delete character. Default
is character 18 (CTRL-R).
Parameter 17: Line Delete
Parameter 17 allows you to select a character that will delete a line while in PAD editing mode. This
character is valid only if parameter 15 is set to one. See Table F-10 for PAD line delete editing
function values and their descriptions.
Table F-10 PAD Line Delete Editing Function
Value
Description
0-127
Select one character from the ASCII character set to represent the delete character. Default
is character 21 (CTRL-U).
Parameter 18: Line Display
Parameter 18 allows you to select a character that will display a line while in PAD editing mode.
This character is valid only if parameter 15 is set to one. See Table F-11 for PAD line display editing
function values and their descriptions.
Table F-11 PAD Line Display Editing Function
Value
Description
0-127
Select one character from the ASCII character set to represent the delete character. Default
is character 18 (CTRL-R).
X.3 PAD Parameters F-7
X.3 PAD Parameters
F-8 Protocol Translator Command Reference
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