GB/T 11591-1999 Packet Assembly and Disassembly (PAD) facilities in public data networks
Some standard content:
National Standard of the People's Republic of China
GB/T11591—1999
idtITU-TX.3:1993
Packet assembly/disassembly facility (PAD) in a public data network
Published on November 11, 1999
Implemented on June 1, 2000
Bureau of Quality and Technical Supervision of the People's Republic of China
GB/T11591—1999
This standard is equivalent to the ITU-TX.3:1993 recommendation. Introduction
This standard defines the interface between DCE/DTE of the packet assembly/disassembly facility (PAD) in the public data network of the country where the start-stop DTE enters, describes the basic functions and user optional functions of PAD, PAD parameter characteristics and a list of PAD parameters and possible values. In order to adapt to the development of domestic packet switching technology and to align with international standards, this standard has revised GB11591-1989 in accordance with the principles of perfection, applicability and practicality. The main contents of the revision are as follows: 1) The following changes have been made to the terms:
Packet assembly/disassembly facility → Packet assembly/disassembly facility
Public switched telephone network → Public switched telephone network (PSTN) release → Clear
Parity check → Parity check
Standard feature table → Standard profile
PAD transition - → PAD re-call
PAD message - PAD message
2) Seven new PAD parameters have been added to Chapter 1, and their functions have been described (1.4.19). 3) Seven new PAD parameter descriptions and lists have been added to Chapter 3 (3.23 to 3.29, Table 1). Other standards referenced in this standard are listed as follows: GB/T11590—1999 International data transmission services and optional user service facilities for public data networks (eqvITU-TX.2.1996)
GB/T11595—1999
Interface between packet-type data terminal equipment (DTE) and data circuit-terminating equipment (DCE) connected to public data networks using dedicated circuits (idtITU-TX.25:1996) GB/T11596—1999 Interface between DCE/DTE of the packet assembly and disassembly (PAD) facility for start-stop data terminals entering the national public data network (idtITU-TX.281997) GB/T11597—1999
Procedure for exchanging control information and user data between the packet assembly and disassembly (PAD) facility and a packet-type DTE or another PAD (idtITU-TX.29:1997) Appendix A of this standard is a suggestive appendix.
This standard shall replace GB/T11591—1989 from the date of implementation. This standard is proposed by the Ministry of Posts and Telecommunications of the People's Republic of China. This standard is under the jurisdiction of the Telecommunications Science Research and Planning Institute of the Ministry of Posts and Telecommunications. This standard was drafted by the Data Communication Technology Research Institute of the Ministry of Posts and Telecommunications. The main drafter of this standard is Goli.
This standard is entrusted to the Data Communication Technology Research Institute of the Ministry of Posts and Telecommunications for interpretation. I
GB/T11591—1999
ITU-T Foreword
Many countries have established public data networks that provide packet switching data transmission services, which makes it necessary to formulate some standards to promote the access of public telephone networks, circuit switching public data networks and leased circuits to packet switching public data networks. ITU-T
(a) Recommendations X.1 and X.2 specify user service categories and user facilities for public data networks, Recommendation X.96 specifies call progress signals, Recommendation X.29 specifies the communication procedures between packet assembly and disassembly (PAD) facilities and packet-type DTE or other PADs, and Recommendation X.28 specifies the DTE/DCE interface for start-stop DTE access to PAD; (b) Recommendation X.92 specifies the logical control link used for packet-switched data transmission services, especially Recommendation X.92 considers the case of PAD;
(c) It is urgently required to use the public switched telephone network, public A start-stop mode DTE used on a switched data network or leased circuit can interoperate with a packet mode DTE or another start-stop mode DTE operating in a virtual call facility employing packet switched data services; (d) a DTE operating in start-stop mode will send and receive network control information and user information in the form of characters or "break" signals; (e) a DTE operating in packet mode will send and receive network control signals and user information in the form of packets conforming to Recommendation X.25;
(f) although a packet mode DTE should not be forced to adopt the control procedures for PAD functions, some packet mode DTEs may wish to control certain specific functions of the PAD.
To Recommendations
1) The functions and operating characteristics performed by the PAD for start-stop DTE will be described in Chapter 1 "Description of basic functions and user-selectable functions of PAD".
2) The operation of the PAD for start-stop DTE should depend on the possible values of the known PAD parameter internal variables. These PAD parameters will be described in Chapter 2 "PAD parameter characteristics". 3) The PAD parameters for start-stop DTE and the possible values of these parameters should be those listed in Chapter 3 "List of PAD parameters and possible values". 4) In the future, the extension of the PAD performance described in Chapters 1, 2 and 3 will be studied to enable it to interoperate with non-packet DTE that is not a start-stop DTE.
National Standard of the People's Republic of China
Packet assembly/disassembly facility (PAD) in a public data network
1 Description of basic functions and user-selectable functions of PAD GB/T11591—1999
idt ITU-T X.3:1993
Replaces GB/T11591—1989
1.1PAD performs many functions and has many operating characteristics. Some of these functions enable the start-stop DTE and/or packet DTE (or remote PAD) to select the configuration of the PAD so that the operation of the PAD can be adapted to the characteristics of the start-stop DTE and may be put into use. 1.2The operation of the PAD depends on the values of a set of internal variables called PAD parameters. This set of parameters is independent for each start-stop DTE. The current value of each PAD parameter specifies the operating characteristics of its associated function. 1.3 Functions of PAD
1.3.1 Basic functions include:
- Grouping characters into groups;
- Splitting the user data field of the group;
Handling the establishment, clearing, resetting and interruption procedures of virtual calls to generate service signals:
When conditions are suitable, such as when the group is full or the idle timer expires, there is a mechanism to forward the group; there is a mechanism to send data characters to the start-stop DTE, including the start, stop and parity check code elements; a mechanism to handle the "break" signal from the start-stop DTE, and edit the PAD command signal;
- A mechanism to set and read the current value of the PAD parameter. 1.3.2 Optional functions include:
Mechanism to select the standard profile;
- Automatic detection of data rate, code, parity check bit and operating characteristics, and a mechanism for the remote DTE to request a virtual call between the start-stop DTE and another DTE. 1.4 User-selectable features provided by the PAD
Many of the facilities of packet-switched data networks are available to the start-stop DTE described in user service categories 20 to 22 of Recommendation X.2, either by prior agreement or as specified for each call. In addition, the following features may be used by prior agreement: selection of the initial profile;
type of modem, rate, code and parity used by the PAD; - other operating characteristics of the DTE.
Some parameters are specified in this Recommendation to provide the following related functions: management of procedures between the start-stop DTE and the PAD, management of assembly and disassembly of a packet;
some additional functions related to the operating characteristics of the start-stop DTE; some additional functions related to videotex applications. Approved by the State Administration of Quality and Technical Supervision on November 11, 1999, and implemented on June 1, 2000
GB/T11591—1999
The control methods for these functions are specified in Recommendation X.28 for start-stop DTE and Recommendation X.29 for packet DTE or other PAD.
Table 1 lists the details of the valid values of PAD parameters standardized by ITU-T and the combinations of values. Other valid values of the relevant parameters and the combinations of values are to be determined.
1.4.1Recall PAD with a character This function enables the start-stop DTE to start leaving the data transmission state or the connecting state in order to send the PAD command signal. 1.4.2Echo
This function enables the PAD to echo the characters received from the start-stop DTE to the DTE and interpret the received characters. 1.4.3Selection of data forwarding characters
This function allows the selection of a set of specified characters (groups) received by the start-stop DTE and recognized by the PAD as an indication of the completion of the assembly and forwarding of a complete packet sequence in accordance with the provisions of Recommendation X.25. 1.4.4Selection of idle timer delay
This function allows the selection of the time interval between consecutive characters received from the start-stop DTE. When the time interval exceeds the selected value, the PAD will end the assembly of the packet and forward the packet in accordance with the provisions of the national standard Recommendation X.25. 1.4.5Auxiliary equipment control
This function is used for flow control between PAD and DTE. The PAD sends special control characters to indicate whether it is ready to receive characters from the start-stop DTE. These characters are characters used in the International Code No. 5 (IA5) to control the connection and disconnection of auxiliary transmission equipment. bzxz.net
1.4.6 Control of PAD service signals
This function enables the start-stop DTE to decide whether to send PAD service signals and in what format. 1.4.7 Selection of PAD operation when receiving a "break" signal This function allows the operation of the PAD to be selected after receiving a "break" signal from the start-stop DTE. 1.4.8 Output discard
This function enables the PAD to discard the contents of the user sequence in the packet according to the request, that is, no longer disassemble and send these contents to the start-stop DTE.
1.4.9 Padding after carriage return
This function enables the PAD to automatically insert padding characters in the string sent to the start-stop DTE after the carriage return character appears, so that the printing device of the start-stop DTE can correctly complete the carriage return function. 1.4.10 Line Folding
This function enables PAD to automatically insert appropriate format control characters in the character string sent to the start-stop DTE. The maximum number of predetermined graphic characters in each line can be set. 1.4.11 Flow Control of Start-Stop DTE to PAD This function is used for flow control between the start-stop DTE and PAD. The start-stop DTE will send some special characters as an indication of whether it is ready to receive characters from the PAD. These special characters are characters used in the International Code Table No. 5 to control the connection and disconnection of auxiliary transmission equipment.
1.4.12 Insert Line Feed after Carriage Return
This function is only used in the data transmission state. It enables PAD to automatically insert a line feed character in the character string sent to or from the start-stop DTE or after each carriage return character.
1.4.13 Padding after Line Feed
This function is only used in the data transmission state. It enables the PAD to automatically insert fill characters after the line feed character appears in the character string sent to the start-stop DTE, so that the printing device of the start-stop DTE can correctly perform the line feed function. 1.4.14 Editing
This function enables the start-stop DTE to provide the editing function of word deletion, line deletion and line display in the PAD command state and data transfer state. The editing function is always available during the PAD command state. 1.4.15 Editing of PAD service signals
This function enables the start-stop DTE to have the ability to decide whether to send the edited PAD service signal and the format to be used. 1.4.16 Loopback masking
In the case where loopback can be performed (see 1.4.2), this function allows a selected set of characters (groups) received from the start-stop DTE to not be looped back to the start-stop DTE.
1.4.17 Parity Check Handling
This function enables the PAD to check the parity bits in the data stream from the start-stop DTE and/or to generate parity bits in the data stream sent to the start-stop DTE. 1.4.18 Page Wait
This function causes the PAD to pause sending characters to the start-stop DTE after sending a specified number of line feed characters. 1.4.19 Videotex Optional Functions
The following functions are defined to meet the needs of videotex applications. 1.4.19.1 Input Field Length
This function allows the maximum length of an input field to be defined to be less than or greater than the length of the data packet. When the input field is filled with characters received from the start-stop DTE, the PAD shall complete assembly and forward the complete sequence of packets in accordance with Recommendation X.25. If this function is not supported, or if the value of parameter 23 is set to 0, only the data forwarding signals defined by parameters 3 and 4 (and parameter 25 if supported) shall be used. If this function is supported and when the value of parameter 23 is not zero, the data transfer signal defined by parameters 3 and 4 (and parameter 25 if supported) shall also be used.
The input field length is defined in graphic characters (see the note to 3.23). NOTE: This function is handled by the edit buffer according to the special rules described in 3.6.1.3 of Recommendation X.28. 1.4.19.2 Frame End Signaling
This function indicates to the PAD when to start the loopback procedure. That is, immediately after receiving the frame end signal, the characters from the start-stop DTE are echoed (see 4.19.3/X.28).
When this function is not supported or when the value of parameter 24 is set to zero, the loopback procedure shall be carried out according to the interleaving rules in 4.19/X.28, 4.19.1/X.28 and 4.19.2/X.28. 1.4.19.3 Extended Data Transfer Signaling Selection This function allows the selection of a specified character (group) or character sequence received by the start-stop DTE that is recognized by the PAD as an indication of the completion of the assembly and forwarding of a complete packet sequence in accordance with Recommendation X.25. If this function is not supported, or when the value of parameter 25 is set to 0, data transfer signaling shall be performed in accordance with 4.4/X.28. 1.4.19.4 Display Interrupt
This function allows the selection of a character from the characters received by the start-stop DTE as an indication to the PAD that it should discard the contents of the user sequence received from the X.25 DTE, rather than disassembling and sending them to the start-stop DTE. In addition, characters previously received from the start-stop DTE but not yet sent to the X.25 DTE are also discarded. 1.4.19.5 Display Interrupt Acknowledgement
This function allows the selection of a character by the PAD to be sent to the start-stop DTE after the display interrupt described by parameter 26 has been performed. 1.4.19.6 Distinct Character Editing
This function allows the X.25 DTE to instruct the PAD on how to handle identifiable characters, particularly when performing character deletion, line deletion, or length of an input field. This function enables the PAD to know the type of encoding used for identifiable characters so that editing functions can be performed correctly. When this function is not supported or if the value of parameter 28 is set to 0, the basic character set is assumed. When this function is supported and when the value of parameter 28 is not 0, the parameter value indicates the encoding of the identifiable characters used. 1.4.19.7 Extended Echo Mask
GB/T11591—1999
In the case where echo is enabled (i.e. parameter 2 is not equal to 0), this function allows a selected set of characters (groups) received from a start-stop DTE to not be sent, or to be sent to a start-stop DTE. 2 Characteristics of PAD Parameters
2.1 Parameters are identified in this standard by decimal reference numbers. 2.2 Possible values of parameters are represented in this standard by decimal numbers. 2.3 Specific procedures described in Recommendations X.28 and X.29 may be used to initialize, read and modify PAD parameter values. 2.4 Determination of PAD parameter values
2.4.1 Initial values of PAD parameters
At initialization, the initial value of each PAD parameter is set according to a predetermined set of values called the initial standard profile. Table 1/X.28 gives details of the initial values of each parameter for the transparent and simple standard profiles that have been agreed upon by ITU-T. Networks may also provide additional standard profiles to provide different sets of predetermined values for PAD parameters. 2.4.2 Current values of PAD parameters
The current values of PAD parameters are values that may have been modified by the PAD, the origin-end DTE and/or the packet DTE (or the remote PAD). 3 List of PAD parameters and their possible values
3.1 Recall PAD with a character Parameter number 1
This parameter has the following optional values:
Not possible
Possible, using character 1/0 (DLE)
Possible, using a graphic character specified by the user represented by decimal 0,
represented by decimal 1,
-represented by decimal 32 to 126.
The graphic character specified by the user to leave the data transfer state and recall the PAD is a decimal value represented by binary according to Recommendation T.50.
3.2 Echo
Parameter Number 2
This parameter has the following possible values:
Do not echo
Echo (see Note 1)
Echo all characters except the data forwarding sequence specified by parameter 25 (see Note 3)
Scrambled echo character (see Note 2)
is represented by decimal 0;
is represented by decimal 1,
one is represented by decimal 2, and
is represented by decimal 32 to 126.
1 If parameter 20 is implemented, the echo character and selection depends on the value of parameter 20. 2 This decimal value represents the character to be sent back to the start-stop DTE. 3 If parameter 29 is implemented, the selection of the echo character depends on the value of parameter 29. 3.3 Selection of data forwarding characters
Parameter number 3
This parameter is represented by the encoding of the following basic functions. Each basic function has a decimal value as follows: No data forwarding character
Alphanumeric characters (AZ, az, 0-9) character CR
Characters ESC, BEL, ENQ, ACK
-represented by decimal 0;
-represented by decimal 1;
-represented by decimal 2,
-represented by decimal 4,
Characters DEL, CAN, DC2
Characters EXT, EOT
Characters HT, LF, VT, FF
All other characters not included in the above in columns 0 and 1 of IA5
GB/T 11591—1999
is represented by decimal 8,
is represented by decimal 16;
is represented by decimal 32,
is represented by decimal 64.
Note: The decimal representation of each value of this parameter can be coded to represent a certain function or a combination of several functions, see Table 1. 3.4 Selection of Idle Timer Delay
Parameter Number 4
This parameter has the following optional values:
Any number from 0 to 255
is represented by the corresponding decimal number.
The number 0 indicates that no data forwarding is required on timeout: The value between 1 and 255 represents the delay value in units of one twentieth of a second. Note
1 Some PAD implementations may not provide all possible values of the idle timer delay within the optional range. In this case, if the selected value is not available, the PAD will select the next larger available value in the range. 2 The effect of idle timer delay on data forwarding may be subject to flow control constraints. 3.5 Auxiliary equipment control
Parameter number 5
This parameter has the following optional values:
Do not use X-ON (DC1) and X-OFF (DC3) Use X-ON and X-OFF (data transmission)
Use X-ON and X-OFF (data transmission and command) 3.6 Control parameter number 6 of PAD service signal and PAD command signal
Represented by decimal 0;
Represented by decimal 1,
Represented by decimal 2.
Each basic function has a decimal value as follows: This parameter is represented by the encoding of the following basic functions. No service signals are sent to the start-stop DTE per
Service signals other than the prompt PAD service signal are sent in standard format. Service signals other than the prompt PAD service signal are sent only in the format specified by parameter 19. Edit PAD service signals are sent in standard format. Prompt PAD service signals are sent in a network-dependent format. PAD service signals and PAD command signals in extended conversational format are sent. Extended conversational processing, PAD service signals in English, PAD service signals in French, PAD service signals in Spanish. Note
is represented by decimal 0;
is represented by decimal 1;
is represented by decimal 2;
is represented by decimal 4, and
is represented by decimal 8 to 15.
is represented by decimal 16;
is represented by decimal 32;
is represented by decimal 48.
1 The decimal representation of the values of this parameter may be encoded to represent a function or combination of functions, see Table 1. The transmission of service signals is controlled by values 0, 1, 2, 4, and 5. In addition, the actual text of the service signals is controlled by values 16 and above. 2 Values 64 to 240 that are multiples of 16 represent other languages provided on a network-dependent basis. 3 Values 16 to 240 that are multiples of 16 may be combined with values 8 to 15 to provide a network-dependent extended dialog type (e.g., value 41 is equivalent to 32 plus 9, which is network-dependent French). 4 In the extended dialog type, in order to determine whether service signals are used, values 16 to 240 that are multiples of 16 may be combined with the following values: 0 for no service signals, 1 for service signals for non-prompt services, 2 for only editing service signals, and 5 (4 plus 1) for both service signals and prompt service signals. 3.7 The selection parameter number of the PAD operation upon receiving the "break" signal from the start-stop DTE is 7
This parameter is represented by the coding of the following basic functions. Each basic function has a decimal value, as shown below: 5
No operation
GB/T11591—1999
Send an interrupt packet to the packet DTE or other PAD Reset
Send a "break" indication to the packet DTE or other PAD The PAD message leaves the data transmission state
Discard the output to the start-stop DTE
Represented by decimal 0;
Represented by decimal 1;
Represented by decimal 2;
Represented by decimal 4;
-Represented by decimal 8;
Represented by decimal 16.
Note: The decimal representation of the values of this parameter may be coded to represent a function or a combination of functions, see Table 1. 3.8 Output Discard
Parameter Number 8
This parameter has the following possible values:
Normal data transmission to start-stop DTE
Discard output to start-stop DTE
3.9 Padding after carriage return
Parameter Number 9
This parameter has the following possible values:
Any number from 0 to 255
- is represented by decimal 0;
is represented by decimal 1.
is represented by the corresponding decimal number.
A value between 0 and 255 indicates the number of padding characters generated by the PAD after a carriage return character is sent to the start-stop DTE. When parameter 9 is 0, there is no padding except for some padding characters included by the PAD service signal according to the data rate of the start-stop DTE.
3.10 Line Folding
Parameter Number 10
This parameter has the following optional values:
No folding
Any number between 1 and 255
is represented by decimal 0 and
is represented by the corresponding decimal number.
A value between 1 and 255 indicates the number of graphic characters per line sent by the PAD, excluding the corresponding format control characters inserted.
3.11 Bit Rate
This is a read-only parameter that cannot be changed by either DTE at either end. It enables the packet DTE to access the characteristics of the start-stop DTE known to the PAD.
Parameter number 11
This parameter has the following values:
50bit/s
75bit/s
100bit/s
110bit/s
134.5bit/s
150bit/s
200bit/s
300bit/s
600bit/s
1200bit/s
1800bit/s
75/1200bit/s
is represented by decimal 10,
is represented by decimal 5,
is represented by decimal 9,
is represented by decimal 0,
is represented by decimal 1;
is represented by decimal 6;
is represented by decimal 8 ;
- is represented by decimal 2,
- is represented by decimal 4,
- is represented by decimal 3;
is represented by decimal 7,
- is represented by decimal 11;
2400bit/s
4800bit/s
9600bit/s
19200bit/s
48000bit/s
56000bit/s
64000bit/s
14400bit/s
GB/T 11591—1999
- is represented by decimal 12;
- is represented by decimal 13;
- is represented by decimal 14;
- is represented by decimal 15;
- is represented by decimal 16,
- is represented by decimal 17,
- is represented by decimal 18,
is represented by decimal 19.
Note: The values that can be achieved by each PAD depend on the range of DTE data transmission rates supported. All known rates are assigned a decimal value in order to avoid future modifications to this standard. 3.12 Start-stop DTE to PAD flow control parameter number 12
This parameter has the following optional values:
Cannot use X-ON (DC1) and X-OFF (DC3) for flow controlUse X-ON and X-OFF for flow control
3.13 Insert newline after carriage return
Parameter number 13
This parameter is represented by the following basic function encoding. Every time a newline character is not inserted, it is represented by decimal 0;
is represented by decimal 1.
A decimal value, as shown below:
Basic functions are all
Represented by decimal 0;
Insert a line feed after each carriage return in the data stream sent to the start-stop DTE Insert a line feed after each carriage return in the data stream received from the start-stop DTE Insert a line feed after each carriage return in the return stream sent to the start-stop DTE Note
Represented by decimal 1;
Represented by decimal 2;
Represented by decimal 4.
1 The decimal representation of each value of this parameter can be encoded to represent a certain function or a combination of several functions, see Table 1. 2This function can only be used in data transmission status. 3.14 Line Feed Padding
Parameter Number 14
This parameter has the following optional values:
Any number from 0 to 255
A value between 0 and 255 indicates the number of padding characters that should be generated by the PAD after a line feed character is sent to the start-stop DTE during the data transfer state.
3.15 Edit
Parameter Number 15
This parameter has the following optional values:
Not used in data transfer state Edit
Used in data transfer state Edit
The use of a value of 1 will suspend the following operations of the PAD: - is represented by decimal 0;
- is represented by decimal 1.
a) Transfer data with a full packet before the edit buffer is filled #b) Transfer data when the idle timer period expires. NOTE: The value of parameter 4 remains unchanged.
3.16 Character deletion
Parameter number 16
This parameter has the following optional values:
A character in the International Code Table No. 5
GB/T11591—1999
-represented in decimal from 0 to 127.
A user-defined character for character deletion, which is a decimal value of the binary representation in accordance with Recommendation T.50. Character 1/34/7 sequence
Character 1/31/3 sequence
Character 2/102/10 sequence
3.17 Line Delete
Parameter Number 17
This parameter has the following possible values:
A character from International Code Table No. 5
—represented by decimal 128;
—represented by decimal 129;
—represented by decimal 130.
Represented by decimal 0 to 127.
The user-specified character for line delete, which is the decimal value of the binary representation in accordance with Recommendation T.50. 3.18 Line display
Parameter number 18
This parameter has the following possible values:
A character from the International Code Table No. 5
- represented by decimal 0 to 127.
The character specified by the user for line display, in accordance with Recommendation T.50, is the binary representation of a decimal value. 3.19 Edit PAD service signal
Parameter number 19
This parameter has the following possible values:
Do not edit PAD service signal
Edit PAD service signal for printing terminals
Edit PAD service signal for display terminals
Use a character from the International Code Table No. 5 as the edit PAD service signal
Note: If the value of parameter 6 is set to 0, this parameter is not used. 3.20 Echo Mask
Parameter number 20
is represented by decimal 0,
is represented by decimal 1,
is represented by decimal 2;
is represented by decimal 8 and 32 to 126.
This parameter is represented by the encoding of the following basic functions. Each basic function has a decimal value as follows: No echo mask (all characters are echoed) Do not echo the character CR
Do not echo the character LF
Do not echo the characters VT, HT, FF
Do not echo the characters BEL, BS
Do not echo the characters ESC, ENQ
is represented by decimal 0,
is represented by decimal 1;
is represented by decimal 2;
is represented by decimal 4;
= decimal 8;
- decimal 16,
- decimal 32;
characters ACK, NAK, STX, SOH, EOT, ETB, ETX are not returned
editing characters specified by parameters 16, 17 and 18 are not returned. All other characters in columns 0 and 1 of International Code Table No. 5 that are not listed above and the character DEL are not returned.
- decimal 64,
- decimal 128.
1 The decimal representation of the values of this parameter may be coded to represent a function or combination of functions, see Table 1. 2 If parameters 5, 12 and 22 are set to non-zero values, X-ON and X-OFF are not returned. 3 The PAD recall character specified by the value of parameter 1 is not returned. 4 If a character is not to be echoed, simply specify the character with a single value of parameter 20. 8
5 This parameter is used only when parameter 2 is set to 1. GB/T11591—1999
6 If the edit function cannot be used, the value 64 (combined value) of parameter 20 is not applicable. 3.21 Parity check processing
Parameter number 21
This parameter has the following optional values:
No parity check or generation
Parity check
Parity generation
No parity check transparent transmission bit 8
is represented by decimal 0,
is represented by decimal 1;
is represented by decimal 2;
is represented by decimal 4.
1 The decimal representation of each value of this parameter may be encoded to represent a function or combination of functions, see Table 1. 2 Unless other means are used to determine parity, when parameter 21 is set to zero, each character generated by the PAD itself (such as the PAD service signal) must be even parity.
3.22 Page Wait
Parameter number 22
This parameter has the following optional values:
Page Wait cannot be used
The page wait status after n line feed characters is sent by the PAD to the start-stop DTE
3.23 Input field length
Parameter number 23
This parameter has the following optional values:
No input field length
The length of the input field (in graphic characters) is represented by decimal 0;
is represented by decimal 1 to 255.
is represented by decimal 0;
is represented by decimal 1 to 255.
Note: The implementer should take into account the fact that a graphic character can be encoded using several bytes. The definition of graphic characters is given in Annexes A/T.101, B/T.101 and C/T.101.
3.24 Frame end
Parameter number 24
This parameter has the following optional values:
No frame end signal
The frame end condition is satisfied when this character is receivedThe frame end condition is satisfied when a complete packet sequence is receivedThe frame end condition is satisfied when the timer endsThe frame end condition is satisfied when the timer endsThe decimal 0 is represented,
is represented by decimal 1 to 31,
is represented by decimal 32;
is represented by decimal 64. The value of the
timer is service-dependent and should be within the range of 15s, with a typical value of 3s. The value of this timer cannot be changed by either the X.25 DTE or the start-stop DTE. Note: The decimal representation of each value can be coded to represent a function or a combination of functions (see Table 1). The PAD shall consider the received X.25 reset packet, X.25 clear indication packet or any X.29\PAD message as a "frame end" signal.
3.25 Selection parameter number of extended data forwarding signal 25
This parameter is represented by the encoding of the following basic functions. Each basic function has a decimal value as follows: No extended data forwarding condition
Starting with a two-character sequence of 1/3
is represented by decimal 0;
is represented by decimal 1,
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