The Hacker's Encyclopedia 1998

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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.