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DATAPAC SERVICE DESCRIPTIONS
Service - DATAPAC 3101 (ASYNC/ITI)
DATAPAC 3101 (ASYNC/ITI)
------------------------
Datapac 3101 is a network access service which enables teletypewriter
compatible devices, such as time-sharing terminals, to access the Datapac
Network.
Low speed, asynchronous devices are supported through an Interactive Terminal
Interface (ITI) in a Packet Assembler/Disassembler (PAD), which allows the
devices to access the Network over dial-up (DDD) or Dedicated Access Lines.
ITI, the end-to-end protocol for Datapac 3101, conforms to the CCITT
recommendations X.3, X.28 and X.29 and supports access to the Datapac Network
for asynchronous, start-stop character mode terminals.
X.3 specifies the operation of the PAD. It contains the specifications
for the twenty-two International parameters and their operation.
X.25 specifies the command language between the terminal and the PAD. It
also specifies the conditions which define the command mode and the data
transfer mode.
X.29 specifies the procedures to be followed by an X.25 DTE to access and
modify the parameters in the PAD as well as the data transfer procedure.
The Datapac 3101 service provides for terminal to Host (user's computer) and
terminal to terminal communication. The Host access should conform with the
X.25 protocol, using the Datapac 3000 access service, and also support the
higher level protocol conventions for ITI. Host access may also be provided
via the Datapac 3101 service for some applications. The Datapac 3101 service
also provides block mode and tape support.
INTERNATIONAL PAD PARAMETERS
----------------------------
1) Ability to Escape from Data Transfer State*
The setting of this parameter allows the user to interrupt the
communication of his or her application (data transfer mode) and interact with
the PAD (common mode). The character to do this is "Control-P". To return to
data transfer mode, press the carriage return or enter a blank command line.
If the user wants to send a "Control-P" to the Host, with this parameter set
set to one, simply hit Control-P twice and the second Control-P will go to the
Host and the user will remain in data transfer mode. This also applies to the
user data field in the call request command line.
Parameter Number: 1
Possible Values: 0 = Escape not possible.
1 = Escape is possible.
- Note: Escape from Data transfer mode may also be
possible using the break signal if parameter seven is set to eight.
2) Echo*
This parameter indicates to the PAD whether or not the terminal input
data must be echoed. This may be required if the user's terminal cannot echo
back what is being entered.
Parameter Number: 1
Possible Values: 0 = No echo.
1 = Echo.
- Note: Echo will also be affected by the setting of Parameter 20.
3) Selection of Data Forwarding Signal
This parameter indicates to the PAD the set to terminal generated
characters or conditions that will cause data to be forwarded to the
destination. For example, (CR) can be used as a data forwarding signal on
receipt of a (CR) from the local DTE Y, the PAD will forward all characters in
its buffer to the remote end, including the (CR). If P13 is set to 6.7, 22 or
23, a (LF) will be included in the packet and will delimit it. Data is also
forwarded when the buffer is full whether or not a forwarding character is
received.
Parameter Number: 3
Possible Values: 0 = No data forwarding signal.
2 = Forward on carriage return.
2 = Carriage return.
126 = All characters in columns 0 and 1
of ASCII table and the character
del of International alphabet #5.
(See Appendix 1.)
4) Selection of Idle Timer Delay
This parameter is used to determine the idle timer limit value when data
forwarding is based on timeouts. To optimize packetizing of data, no data
forwarding signal need be specified. The PAD will then packetize data based on
packet size specified (256 or 128 characters). The idle timer is used to send
any packets that are not fully filled. If idle timer is activated and the Host
requires the (CR) to input data, it still must be provided before the data send
is accepted by the Host. The idle timer does not send any empty packets.
Parameter Number: 4
Possible Values: 0 = No data forwarding on timeout is
required.
1-255 = Indicates value of the delay in
twenties of a second. (i.e., a
value of 250 makes the time wait
10 seconds)
- Note: When editing is on (P15:1), the idle timer is inactive. If this is
the only data forwarding condition, turning the editing function on could cause
a user terminal to hand or data not to be forwarded.
5) Auxiliary Device Control*
This is used for flow control of data coming from either a PC or
auxiliary device, e.g.: a paper tape machine. When set to 1 it indicates to
the PAD that the data is to be read an auxiliary I/O device connected to the
terminal. This parameter set to 2 indicates that the data is coming from an
intelligent device, i.e., a PC, and that the PAD must exert flow control
differently.
Parameter Number: 5
Possible Values: 0 = No use of X-on/X-off.
1 = Use of X-on/X-off for auxiliary
devices.
2 = Use of X-on/X-off for
intelligent terminals.
- Note: A value of 2 is recommended for PC's.
6) Suppress Network Messages
This parameter indicates to the PAD whether or not Network generated
messages are to be transmitted to the terminal.
Parameter Number: 6
Possible Values: 0 = Suppress message.
1 = Transmit message.
5 = PAD prompt (*) follows Datapac
service signals.
7) Procedure on Break
This parameter is used to indicate how the PAD should process a break
signal that is received from the terminal while the terminal is in data
transfer state.
Parameter Number: 7
Possible Values: 0 = Nothing. (remain in data transfer
mode)
1 = Interrupt. (remain in data
transfer mode)
2 = Reset. (remain in data transfer
mode)
4 = Send an "indication of break"
message to the packet mode DTE.
(remain in data transfer mode)
8 = Escape from, data transfer ,mode
(i.e., enter command mode)
16 = Discard output to terminal
activate Parameter 8 (P8:1)
(remain in data transfer mode)
21 = A combination of 1, 4 and 16.
- Note: The break signal is ignored if the virtual circuit is not established
while in command state. The break signal will delete the current line.
The valid values for P7 are 0, 1, 2, 8 and 21.
8) Discard Output
This parameter is used in conjunction with Parameter 7. Depending upon
the break procedure selected, this parameter may be set by the PAD when the
terminal user requests that terminal data be discarded. This parameter must
then be reset by the destination computer to allow normal delivery. The PAD
will discard all packets destined for the terminal from the time the PAD sets
this parameter (i.e., it receives a break signal when Parameter 7 is set to 21)
to the time the parameter is reset by the destination. It can only be reset by
the destination.
Parameter Number: 8
Possible Values: 0 = Normal delivery of output to
terminal.
1 = Discard output to terminal.
9) Padding after Carriage Return
This parameter is used to specify the number of padding characters to be
inserted by the PAD following a CR R transmitted to the terminal. Padding
allows time for the carriage to return on mechanical printing devices.
Parameter Number: 9
Possible Values: 0 = 2 padding characters will be
inserted at 110 bps and 4
padding characters will be
inserted at higher speeds, in
command mode only. (no padding
is done in data transfer mode)
1-255 = The number of padding characters
to be inserted in both data
transfer and command mode.
10) Line Folding
This parameter indicates the maximum number of printable characters that
can be displayed on the terminal before the PAD must send a format effector
(i.e.., <CR><LF>). This permits more data to be transmitted in one packet
while still letting the user print out more than one line, i.e., printing out
forms.
11) Transmission Speed (Read only)
This parameter is set by the PAD as a result of transmission speed
detection if the terminal accesses an autobaud port. When a private port with
fixed speed is used, this parameter is set based on the pre-stored information
selected at subscription time.
Parameter Number: 11
Possible Values: 0 = 110 bps
2 = 300 bps
3 = 1200 bps
4 = 2400 bps
12 FLOW CONTROL
This parameter allows the terminal user to signal the PAD that the
terminal cannot receive any more data, i.e., to flow control data coming from
the network. When it is set to 1, the terminal user can request that the PAD
stop sending data by transmitting a "Control S". the PAD then suspends
transmission of the data until a "control Q" is received.
Parameter Number: 12
Possible Values: 0 = No use of X-on/X-off for flow
control.
1 = Use X-on/X-off for flow control.
13) Linefeed Insertion
(Similar to National Parameter 126
This parameter specifies when the PAD should insert linefeeds <LF>
receipt of a carriage return <CR> from the terminal, PAD or the destination
Host.
Parameter Number: 13
Show Possible Values: 0 = Insert no <LF>.
1 = Insert <LF> to terminal upon
receipt of a <CR> from Host.
4 = Insert < > to terminal after a
<CR> from terminal or on PAD
generated <CR>.
5 = Insert <LF> to terminal on <CR>
from PAD terminal or Host.
6 = Insert <LF> to terminal on <CR>
from terminal and insert <LF> in
data Host on <CR> from terminal.
7 = Insert <LF> to terminal on <CR>
from PAD, terminal or Host and
insert <LF> in data to Host on
<CR> from terminal..
16 = Insert <LF> to terminal after
a PAD generated<CR>.
17 = Insert <LF> to terminal after
a PAD generated<CR> or Host
generated <CR>.
20 = Insert <LF> to terminal on <CR>
from terminal.
21 = Insert <LF> to terminal on <CR>
from terminal to host
22 = Insert <LF> to terminal on <CR>
from terminal. Insert <LF> in
data to Host <CR> from terminal.
23 = Insert <LF> to terminal on <CR>
from terminal or Host. Insert
<LF> in data to Host on <CR>
from terminal
14) Padding Characters after Linefeed
To allow for mechanical paper feed, this parameter is used to specify the
number of padding characters to be inserted by the PAD following <LF>
transmitted to the terminal in data transfer mode only.
Parameter Number: 14
Possible Values: 0-255 = Number of padding character
(NUI) sent to the terminal
after transmission of a <LF>
to the terminal.
15) Control of Editing Functions*
This parameter specifies whether or not editing is allowed in data
transfer mode. It is always available in command mode. This controls
parameters 16, 17 and 18.
ParameterNumber: 15
Possible Values: 0 = Editing only in command mode.
1 = Editing in command and data
transfer mode.
- Note: Setting Parameter 15 to 1 will cause the operation of the idle timer
(Parameter 4) to become disabled.
16) Character Deletion
(Similar to National Parameter 118)
This parameter specifies the ASCII character to be used as a "character
delete" character for local editing by the PAD. The default value is set to
127 (the delete or del key).
Parameter Number: 16
Possible Values: 0 = Turn off the character
editing (command and data
transfer mode).
1-127 = Character delete character
(Appendix K).
17) Line Deletion
(Similar to National Parameter 119)
This parameter specifies the ASCII character to be used as a "line
delete" character for local editing by the PAD. The default value is set to 24
(Control X). On some older terminal the Control X key will clear the screen as
well as delete the line.
Parameter Number: 17
Possible Values: 0 = No key will delete a character
1-127 = ASCII code for the "line
delete" character.
18) Line Display
(Similar to National Parameter 120)
This parameter specifies the ASCII character to be used as a "line
display" character for local editing by the PAD. The default value is set to
18 (Control R).
Parameter Number: 18
Possible Values: 0 = No key will delete a character
1-127 = ASCII code for the "line
display" character.
19) Editing Service Signals*
This parameter defines the format of the service signal sent to terminal
upon execution of the editing functions (P16 or P17).
Parameter Number: 19
Possible Values: 0 = No service on editing
1 = Backslash is displayed for
each character deleted,
"***" is displayed for each
line deleted.
2 = <BS> <SP> <BS> is displayed
for each character deleted,
<BS> <SP> <BS> is repeated
"***" is repeated for each
character on the line deleted.
32-126 = The specified character is
displayed for each character
deleted, "***" is displayed
for each line deleted.
- Note: Value 1 is recommended for printing terminals and Value 2 when PAD
echo is off (P2 = 0) and the character "delete" character is defined as <BS>
(P16 = 8). The PAD does not send an editing service signal to the terminal
upon execution to the character delete editing function; however, the character
will still be deleted from the PAD buffer.
For video display terminal product a <BS>, but the character will
still be deleted from the PAD.
20) Echo Mask*
This parameter specifies a set of characters not to be echoed to the
terminal.
Parameter Number: 20
Possible Values: 0 = All characters echoed (except)
X-on/X-off which depend on the
setting of P5, P12 and P22).
1 = No echo of <CR>
2 = No echo of <LF>
4 = No echo of <VT>, <HT>, <FF>
8 = No echo of <BEL>, <BS>
16 = No echo of <ESC>, <ENQ>
32 = No echo of <ACK>, <NAK>,
<STX>,<SOH>, <EDT><ETB>, <ETX>
128 = No echoing of all other
characters in Column 0 and 1
of ASCII table in Appendix 1
Plus <DEL>
- Note: This parameter is only active when echo in on (P2 - 1).
21) Parity Detected or Checked
(Similar to National Parameter 123)
This parameter specifies whether or not the PAD should detect, check and
generate parity. This parameter is set to 0 when the user wishes to transmit
8-bit data.
Parameter Number: 21
Possible Values: 0 = No detected or checked.
3 = Parity checked and detected.
22) Page Wait
This parameter controls the ability to set a terminal page size which,
when reached, causes the PAD to stop all further output to the terminal.
Parameter Number: 22
Possible Values: 0 = No page wait.
1-255 = Page wait size.
The PAD will resume normal transmission when any of the following occurs:
- on receipt of the page wait cancellation (X-on); or
- on resetting Parameter 22 to zero.
NATIONAL PARAMETERS
The following parameters are specific to the Datapac interactive terminal
interface (Datapac 3101 Service).
P118 Character Deletion
P119 Line Deletion
P120 Line Display
P12, 122 Additional Data Forwarding Signals
These parameters 121 and 122 allow the definition of one or two additional
data forwarding signals. These signals are in addition to any that are
specified by Parameter 3 and 4.
Parameter Number: 121, 122
Possible Values: 0 = None.
1-127 = ASCII code of additional data
forwarding signal.
P123 Parity Treatment
This parameter specifies whether or not the PAD should detect and check parity
and performs the same function as International Parameter 2.
Parameter Number: 123
Possible Values: 0 = No detected or checked.
1 = Parity checked and detected.
125) Output Pending Timer
This parameter specifies the length of time, if any, that terminal output will
be blocked by terminal input.
Parameter Number: 125
Possible Values: 0 = Output.
1-255 = Value of delay in seconds..
126) Linefeed Insertion
Parameter Number: 126 See International Parameter 13
GENERAL NOTES ABOUT PARAMETERS
The setting of any of parameters 16 (118), 17 (119), or 18 (120) to a non-zero
value will also set Parameter 15 to 1 when Parameter 4 is zero. In the 1984
software level, setting both editing (P15) is off. This operation is according
to CCITT 1984 standards.
If the character chosen for a certain parameter has already been selected to
be used with another parameter, then the function with the highest priority is
selected upon receipt of the character. This priority scheme is as follows:
1) escape from command state;
2) flow control;
3) line display;
4) line delete;
5) character delete;
6) packet forwarding.
All of the above parameters are changeable by the user. However, it should be
noted that the Host computer can also change these parameters.