This recommendation specifies the physical characteristics and call control procedures for the common interface between DTE and DCE using the start/stop transmission user service category defined in Recommendation X.1. This recommendation includes the format and procedures for selection, call progress and information provided by the DCE. It contains clauses for two-way operation. GB/T 11592-1989 Interface between data terminal equipment (DTE) and data circuit-terminating equipment (DCE) for start/stop transmission services on public data networks GB/T11592-1989 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
GB/T11592—1989
idtCCITTX.20:1984
Interface between data terminal equipment (DTE) and data circuit-terminating equipment (DCE) for start-stop transmission services on public data networksPublished on August 21, 1989
Implemented on March 1, 1990
Published by the State Administration of Technical Supervision
National Standard of the People's Republic of China
Interface between data terminal equipment (DTE) and data circuit-terminating equipment (DCE) for start-stop transmission services on public data networks This standard is equivalent to CCITT Recommendation X.20
GB/T11592—1989
CCITT-X.20—1984
This standard is used when the start/stop data terminal equipment accesses the network when my country opens the public data network. It includes the physical level interface and the signaling process on the user line.
This standard translation is based on the English version of CCITT Recommendation X.20 (1984). In the text, the word "recommendation" should be understood as standard regulations. The word "international" should be understood as international and domestic. Appendix H (reference) is an English-Chinese comparison table of nouns and terms. Approved by the State Administration of Technical Supervision on August 21, 1989 and implemented on March 1, 1990
Recommendation X.20
GB/T11592—1989
Interface between data terminal equipment (DTE) and data circuit-terminating equipment (DCE) used to start/stop transmission services on public data networks (Geneva, 1972, revised in Geneva in 1976 and 1980, revised in Malaga in 1984) CCITT takes into account:
a. Recommendations X.1 and X. 2 specifies the services and service facilities provided by public data networks; b. Recommendation X.92 specifies the hypothetical reference connection used by public synchronous data networks, c. Recommendation X.96 specifies call progress signals; d. The interface recommendations must be defined according to the architectural hierarchy, e. The interface characteristics between DTE and DCE on public data networks need to be standardized, therefore, unanimously declares that the interface between DTE and DCE on public data networks using the user service category of start-stop transmission should comply with the provisions of this recommendation. 1 Scope
1.1 This recommendation specifies the physical characteristics and call control procedures for the common interface between DTE and DCE using the user service category of start-stop transmission defined in Recommendation X.1.
1.2 This recommendation covers the formats and procedures for selection, call progress and information provided by the DCE. 1.3 Contains provisions for bidirectional operation.
2 Elements of the DTE/DCE physical interface
2.1 Interchange circuits
The interface circuits involved are listed in Table 1/X.20. Recommendation X.24 gives the definition of these interchange circuits. Table 1/X.20
Interchange circuit name
Interchange circuit
G (Note)
Signal ground or common circuit
DTE common circuit
DCE common circuit
To DCE
From DCE
Note: This conductor may be used to reduce ambient signal interference at the interface. In the case of shielded interconnecting cables, additional connection considerations are part of Recommendations X.24 and ISO4903.
2.2 Electrical characteristics
The electrical characteristics on the DCE side of the interface may be as specified in Recommendation X.26. The electrical characteristics on the DTE side of the interface may be in accordance with Recommendations X.26, X.27 (no cable termination at the load) or in accordance with the electrical characteristics defined in Recommendation V.28.
The interconnection between V.28-DTE and X.26-DCE refers to Recommendations X.26 and ISO4903. 2.3 Mechanical characteristicsbzxZ.net
For the mechanical arrangements, refer to ISO4903 (15-pin DTE/DCE interface connector and core arrangement). 2
2.4 Fault conditions on interchange circuits
GB/T11592—1989
The connection between the receiver's circuit fault detection and the specific interchange circuit, according to the type of fault detection, is given in 11 of Recommendations X.26 and 9 of Recommendations X.27.
2.4.1 Circuit R is in a fault condition
The DTE shall use fault detection type 2 and interpret the fault condition on circuit R as r=0. When using electrical characteristics in accordance with Recommendation V.28, the DTE shall interpret a generator in a de-energized condition or an open interconnecting cable as a binary zero. 2.4.2 Circuit T in a fault condition
The DTE shall interpret a fault condition on circuit T as t=0 using fault detection type 2.3 Call control characters and error checking
All characters for call control are selected from the International Character Table No. 5 as defined in Recommendation T.50. IA5 characters exchanged in call control are checked with an even number of bits in accordance with Recommendation X.4. 4 Elements of the call control phase of a circuit-switched service The state diagram given in Figure A-1/X.20 shows the relationship between the states of the "call control" phases defined below, and also indicates the transitions between these states under normal operating conditions. Figure B-1/X.20 gives an example of a graphical representation of the temporal relationship between these states and the associated timeout operations.
The "call control" phase may be terminated by either the DTE or the DCE by disconnecting the line as specified in 6 below. 4.1 Events in the call control process
(see Figure A-1/X.20)
4.1.1 Ready (state 1)
Circuits T and R present binary 0.
4.1.2 Call request (state 2)
The calling DTE indicates a call request by sending a stable binary state t-1, provided that it has previously sent "DTE ready" (t=0).
4.1.3 Proceed to select (state 3)
When the network is ready to receive the selection information, the DCE sends a stable binary state r-1. The "Select" signal should start within 6 seconds of starting to send the "Call Request".
4.1.4 Select signal sequence (state 4)
The DTE sends the "Select" signal sequence on circuit T. The format of the "Select" signal sequence is defined in 4.6.1 below. The information content and encoding of the "Select" signal sequence are contained in Appendix G and Recommendation X.121. The "Select" signal sequence should start within 6 seconds of receiving the "Select" signal and be completed within 30 seconds. The maximum allowed interval between each selection character is 6 seconds. 4.1.5 DTE Wait (state 5)
During the "DTE Wait" period, the DTE sends a stable binary state t=1. 4.1.6 Incoming call (state 8).
The DCE indicates an incoming call by sending a stable binary state r=1. 4.1.7 Call Acceptance (state 9)
The DTE shall indicate call acceptance by sending a stable binary state t=1 no later than 600 milliseconds. After 10 to 100 milliseconds, the DTE sends the call control character 0/6 (ACK). 4.1.8 Call Not Accepted (State 18)
If the DTE does not want to accept the incoming call, it shall change circuit T to a stable binary state 1 no later than 600 milliseconds. 3
GB/T11592—1989
After 10 to 100 milliseconds, the DTE sends the call control character 1/5 (NAK), followed by \DTE Disconnect Request" (State 13). 4.1.9 Call Progress Signal Sequence (State 6) When the network encounters appropriate conditions, the DCE sends a "Call Progress" signal sequence to the calling DTE on the R circuit. A "Call Progress" signal sequence consists of one or more "Call Progress" signal blocks; a "Call Progress" signal block consists of one or more "Call Progress" signals.
The format of the "Call Progress" signal sequence is defined in 4.6.2 below. The encoding of the "Call Progress" signal is provided in Appendix E. The description of the "Call Progress" signal is provided in Recommendation X.96. The DCE sends the Call Progress signal sequence within: (1) 60 seconds after the "Selection End" signal, or (2) in the case of a "Direct Call", within 60 seconds after the DTE sends the "Proceed to Select" signal. Except Except for the timeout expiration described in 4.1.4, the DCE shall not send the "Call Proceeding" signal sequence before receiving the "Selection End" signal, in which case the "Call Proceeding" signal sequence may be sent followed by the "Disconnect Indication". Note: When an error is detected in the received "Call Proceeding" signal, the DTE may choose to ignore this signal or to disconnect the line and make a new call. 4.1.10 DCE Provided Information Sequence (States 7A and 7B) The "DCE Provided Information" sequence is sent by the DCE on circuit R to the calling DTE (state 7A) or the called DTE (state 7B).
A "DCE Provided Information" sequence consists of one or more "DCE Provided Information" blocks. Each "DCE Provided Information" block has a maximum of The maximum length is 128 characters.
The format of the "Information provided by DCE" sequence is defined in 4.6.3 below. The content of "Information provided by DCE" is given in Appendix G. The "Information provided by DCE" sequence (state 7B) is sent to the DTE within 60 seconds of it starting to send the "accept call" signal. 4.1.10.1 Line Identification
"Calling" and "Called Line Identification" is an optional additional service facility. Appendix G provides the information content of "Calling" and "Called Line Identification". "Calling" and "Called Line Identification" are sent by DCE via the R circuit during state 7B or 7A respectively. When providing this service, if a "Call in Progress" signal is sent, it must be sent after all "Call in Progress" signals are sent. After that, the DCE sends the "Called Line Identification" (state 7A) to the calling DTE. When providing this service, the DCE shall send the "Calling Line Identification" (state 7B) to the called DTE after the DTE has sent the "Call Accepted".
In the case that the calling network does not provide the "Calling Line Identification" service facility, the DCE shall provide the "Simulated Line Identification" to the DTE.
4.1.10.2 Billing Information
"Billing Information" is an optional additional service facility provided during state 7B. In order to provide "Billing Information" for calls that have requested "Billing Information", the incoming call shall be established to this DTE 200 milliseconds after the DTE enters "Ready" (state 1) after completing the disconnection. Note: The 200 milliseconds here are tentative and subject to further study. The DCE sends the "Billing Information" on circuit R. The DCE shall send the "Disconnect Indication" (state 16) immediately after the last "Billing Information" block sent. When the DTE has correctly received the "Accounting Information" signal, if the DCE has not sent the above "Disconnect Indication", the DTE shall send a Disconnect Request (state 13).
The format of the "Accounting Information" is defined in 4.6.3 below. 4.1.11 Connect (state 10)
The DCE signals that the connection has been established by sending the call control character 0/6 (ACK) on circuit R. Because switching delays may occur in the network, the DTE must maintain circuit T in a stable binary state of 1 during this state. 4
4.1.12 Ready for data transfer (state 11) GB/T11592—1989
The connection established 20 milliseconds after receiving the call control character 0/6 (ACK) in state 10 can be used for data transfer between the two DTEs.
4.1.13 Events of the call control process for multipoint circuit switched service 4.1.13.1 Ready (state 1)
See 4.1.1.
4.1.13.2 Call request (state 2)
See 4.1.2.
4.1.13.3 Proceed to select (state 3)
See 4.1.3.
4.1.13.4 Select signal sequence (state 4)See 4.1.4.
The service facility request signal is used to indicate that the service category requested is point-to-multipoint. The coding used is defined in Annex F. 4.1.13.5 DTE Waiting (state 5)
See 4.1.5.
4.1.13.6 Incoming call (state 8)
See 4.1.6.
4.1.13.7 Accept incoming call (state 9)
See 4.1.7.
4.1.13.8 Do not accept incoming call (state 18)See 4.1.8.
See 4.1.9.
After sending the call progress signal associated with each called DTE, send the called line identification signal of each called DTE in the same order.
If no specific call progress signal is required for a called DTE, then, in order to maintain this order, use "00" call progress signal for this called DTE.
4.1.13.10 DCE provided information sequence (states 7A and 7B) The DCE provided information sequence is sent by the DCE on circuit R to the calling DTE (state 7A) or the called DTE (state 7B). A DCE provided information sequence consists of one or more DCE provided information blocks. The maximum length of each DCE-provided information block is 128 characters, except that the maximum length of the called line identification in a multipoint call is 512 characters. The format of the DCE-provided information sequence is defined in 4.6.3 below. The content of the DCE-provided information is given in Appendix G. The DCE-provided information sequence sent to the called DTE shall be sent within 60 seconds of it starting to send the call acceptance signal. 4.1.13.10.1 Line Identification
See 4.1.10.1.
Provide the called line identification of different called DTEs in sequence. 4.1.13.10.2 Accounting Information
See 4.1.10.2.
4.1.13.11 Connected (State 10)
See 4.1.11.
4.1.13.12 Data Ready (State 11)
See 4.1.12.
4.2 Unsuccessful call
GB/T11592—1989
If the required connection cannot be established, the DCE shall use the "Call Progress" signal to indicate this to the calling DTE and the reason why it cannot be established. Thereafter, the DCE shall send a "DCE Disconnect Indication" (state 16). 4.3 Call Collision (state 19)
When the DCE receives a call request in response to an incoming call, a "Call Collision" is detected. At this point, the DCE can accept the call request or perform a DCE disconnection. 4.4 Direct Call
For the "Direct Call" service facility, the "Select" signal (state 4) is always bypassed. Note: The "Direct Call" service facility can only be provided on a reservation basis, not on a per-call basis. 4.5 Service Facility Registration/Deregistration Procedure
The DTE performs registration/deregistration of selectable user service facilities in accordance with the normal call establishment procedure using the "Select" sequence defined in 4.6.1 below.
The format of the "Service Facility Registration/Deregistration" signal is defined in 4.6.1.3 below. The "Service Facility Registration/Deregistration" procedure is not combined with the normal addressed call establishment procedure, but is an independent procedure. In response to the acceptance or rejection of the "Service Facility Registration/Deregistration" procedure, the network provides the appropriate "Call Proceeding Signal" followed by a "Disconnect Indication".
4.6 Format of Selection, Call Proceeding and DCE-Provided Information (see Appendix D for a description of the format syntax)
4.6.1 Format of Selection Sequence
A selection sequence consists of a "Service Facility Request" block, or an "Address" block, or a "Service Facility Request" block followed by an "Address" block, or a "Service Facility Registration/Deregistration" block.4.6.1.1 Business Facility Request Block
A "Business Facility Request" block consists of one or more "Business Facility Request" signals. Multiple "Business Facility Request" signals are separated by the character 2/12 (,\). A "Business Facility Request" signal consists of a "Supplementary Service Request" code and one or more "Business Facility" parameters that may be included. The "Business Facility Request" code, the "Business Facility" parameter and the subsequent "Business Facility" parameters are separated by the character 2/15 (". During the transition period, the 2/15 (\/\) separator is not used in some networks. The end of the supplementary service request block is indicated by character 2/13 ("一\". Appendix F provides the encoding of "Supplementary Service Request", identifiers and parameters. 4.6.1.2 Address block
An "address" block consists of one or more "address" signals. An "address" signal consists of a "full address" signal, or an "abbreviated address" signal. The beginning of an "abbreviated address" signal is indicated by the prefix character 2/14 (". "). Multiple "addresses" are separated by character 2/12 (\,"). 4.6.1.3 Service facility registration/deregistration block
A "service facility registration/deregistration" block consists of one or more "service facility registration/deregistration" signals. A "service facility registration/deregistration" signal consists of up to 4 elements, in order: "service facility request" code, "indicator", "registration" parameter, "address" signal.
If a "service facility registration/cancellation" signal contains less than 4 elements, then the unnecessary elements should be eliminated in reverse order (for example: a two-element "service facility registration/cancellation signal" should contain: "service facility request" code/"indicator" symbol). If a certain element is not required to be sent in the sequence, then the character 3/0 ("0") should be inserted in the position of each omitted element (for example: "service facility request" code/0/0/\address" signal).
Multiple "service facility registration/cancellation" signals are separated by characters 2/12 (",\). 6
GB/T11592—1989
The end of a "service facility registration/cancellation" block is indicated by characters 2/13 ("two") followed by characters 2/1 ("+"). 4.6.1.4 End of selection sequence
The end of a selection sequence is indicated by characters 2/11 ("ten"). 4.6.2 Format of Call Proceeding Sequence
A Call Proceeding block consists of one or more Call Proceeding signals. Each Call Proceeding signal need not be repeated. Multiple Call Proceeding signals are separated by characters 0/13 (\CR\) and 0/10 (\LF\). The end of a Call Proceeding block is indicated by character 2/11 ("ten"). 4.6.3 Format of DCE Supplied Information
The following format is specified for the already indicated "DCE Supplied Information" signals. "DCE Supplied Information" is preceded by IA5 characters 0/13 (\CR"), 0/11 (\LF"), and (except for "Calling Line Identification" and "Called Line Identification"), IA5 character 2/15 (\/\). In order to distinguish between different types of DCE Supplied Information, the above prefix characters are followed by one or more numeric characters, and after the numeric characters and before the actual information appears, there is character 2/15 ("/"). The character 2/11 ("ten") indicates the end of the "DCE provided information" block. The order in which the "DCE provided information" blocks transmitted to the DTE appear is variable. 4.6.3.1 Format of called and calling line identification The "calling line identification" block and the "called line identification" block start with the character 2/10 ("*\". When the "calling" or "called line identification" blocks contain a data network identification code (DNIC) or a data country code (DCC), these code blocks begin with two characters 2/10 ("**\").
A "called line identification" block consists of one or more "called line identification" signals. Multiple "called line identification" signals are separated by characters 0/13 ("CR") and 0/10 ("LF"). The character 2/11 ("+") indicates the end of the "calling line identification" signal and the "called line identification" block. The "analog line identification" block is represented by characters 2/10 (\*\) followed by characters 2/11 (\+\). 4.6.3.2 Format of billing information
The "billing information" block consists of characters 0/13 ( The "charging information" block is indicated by character 2/11 ("ten") followed by an auxiliary IA5 numeric character (1 or 2 or 3) and 0/10 (\LF\), and 2/15 (\/\) followed by character 2/15 (/"), and character 2/11 ("ten") indicates the end of the "charging information" block. 5 Data Transfer Phase
5.1 Data Transfer (State 12), Point-to-Point Circuit Switched Service The events during "data transfer" are the responsibility of the DTE. 5.2 Data Transfer, Leased Circuit Service
5.2.1 Ready
Binary 1 is present on circuits T and R.
5.2.2 Send Data (State 12S)
The data sent by the DTE on circuit T is delivered to the far-end DTE on circuit R. 5.2.3 Receive data (state 12R)
Receive data sent by the other DTE on circuit R. 5.2.4 Data transmission (state 12)
Transmit data on circuits T and R.
5.2.5 End of data transmission
The end of data transmission is the responsibility of DTE.
5.3 Data transmission (state 12), the events during data transmission of centralized multipoint circuit switching service are the responsibility of DTF. 6 Disconnection phase
In centralized multipoint call:
GB/T11592—1989
Disconnection by the central DTE means disconnection of this call. Disconnection of a remote DTE only disconnects the call to this DTE, but not to others. The call established by the far-end DTF is not affected; the disconnection of this call is caused by the disconnection of the last far-end DTE still in the call state. 6.1 Disconnection by DTE (states 13, 14, 15) The DTE indicates disconnection by sending a stable binary state t=0. The "DTE disconnect request" (state 13) must be greater than 210 milliseconds. The DCE shall reply to the "DCE disconnect confirmation" (state 14) within 6 seconds by sending a stable binary state r=0 for more than 210 milliseconds, and shall not invert the circuit R to binary 1 before the DTE is ready (state 1). Within 210490 milliseconds after the start of the "DCE disconnect confirmation", the DTE shall be ready to accept the "incoming call", that is, it is in state 15, "DTE ready".
6.2 Disconnection by DCE (states 16, 17, 15) The DCE indicates disconnection to the DTE by sending a stable binary state r=0, and the "DCE disconnect indication" state 16) must be greater than 210 milliseconds.
Within 210 to 490 milliseconds after the start of the "DCE disconnect indication", the DTE indicates the DCE disconnect confirmation (state 17) by sending a stable binary state t=0 for a time greater than 210 milliseconds. Within 490 milliseconds after the start of the "DTE disconnect confirmation", the DTE is ready to accept incoming calls. That is, it is in state 15, "DTE ready".
6.3 DCE ready (state 1)
490 milliseconds after the start of the "DCE or DTE disconnect confirmation", the DCE is ready to accept new "call requests" 6.4 Disconnect collision
If the "DTE disconnect request" and the "DCE disconnect indication" occur at the same time or within the 210 millisecond overlap time, then the DTE continues its disconnect process.
7 Test loop
Establishing a test loop is provided in X.150 Definition and principles for using these test loops for maintenance testing. 7.1 DTE test loop - Class 1 loop
This loop is used for basic testing of DTE operation. For verification, the signal sent by the DTE is looped back inside it. The loop should be set up inside the DTE, as close as possible to the DTE/DCE interface. The DTE is under test condition with circuit T connected to circuit R. Loop 1 can be established from the "data transfer" state or the "ready" state. In some networks, for short routine tests during the "data transfer" state, the DTE should keep the state of the interchange circuit in the same state as before this test.
If this loop is established in the "data transfer" state, the DCE can continue to pass data to this DTE during the test as if the DTE was in normal operation. The recovery of any errors that may occur when the test loop is activated is the responsibility of the DTE. 7.2 Local Test Loops - Type 3 Loops The local test loop (Type 3 loop) is used to test the operation of part or all of the DTE, interconnecting cables, and local DCE. Loop 3 can be established in any state.
For tests on leased circuits and short-term tests on circuit-switched connections, the DCE on the outside line should continue to assume the state that existed before the test (for example, the "data transfer" state or the "ready" state). If this is not feasible (for example, in some cases for loop 3a) or is undesirable (for example, long-term tests in circuit-switched applications), the DCE should terminate the existing call. Manual control should be provided on the DCE for activating this test loop. Consideration of automatic control is a subject for further study. The specific implementation of the test loop in the DCE is determined by each country, but at least one of the following local loops must be implemented. 7.2.1 Loop 3d
GB/T11592—1989
This loop is used to test the operation of the DTE, including the operation of the interconnecting cable, and to return the transmitted signal to the DTE for verification. This loop is set up inside the local DCE, but does not include the interchange circuit generator and load. When the DCE is in the test state, circuit T is connected to circuit R inside it. Note: When test loop 3d is operated, the effective length of the interface cable is doubled. Therefore, in order to ensure the correct operation of loop 3d, the maximum cable length of the DTE/DCE interface should be half of the length when normally transmitting data signal rate. 7.2.2 Loop 3c
This loop is used to test the operation of the DTE, including the interconnecting cable, DCE interchange circuit generator and load. The structure of loop 3c is the same as that of loop 3d given in 7.2.1, except that the interchange circuit generator and load are included when looping circuit T back to circuit R. However, the comments on the limitation of interface cable length do not apply. 7.2.3 Loop 3b
This loop is used to test the operation of the DTE and the line coding, control logic and all circuits of the DCE except line signal conditioning circuits (such as impedance matching transformers, amplifiers, equalizers, etc.). The structure of loop 3b is the same as that of loop 3c given in 7.2.2, except for the location of the loopback point. NOTE: In some networks, the activation of loop 3b will cause the disconnection of existing connections. 7.2.4 Loop 3a
This loop is used to test the operation of the DTE and DCE. The loop should include as much of the DCE's operating circuitry as possible, especially the line signal conditioning circuits. In some cases, the loop may also include devices such as attenuators, equalizers or test loop switches. During the test state of loop 3a, the subscriber line is terminated appropriately. The structure of loop 3a is the same as that of loop 3b given in 7.2.3, except for the location of the loopback point. NOTE: In some networks, the activation of loop 3a will cause the disconnection of existing connections. 7.3 Network Test Loops Type 2 Loops
The network test loop (Type 2 loop) is used by the Administration's test centre to test the operation of leased or subscriber lines, and some or all of the circuits of the DCE. These are discussed below. 7.3.1 Overview
The loop can be controlled manually by the DCE, or automatically by the network. The implementation of this loop and the method used to implement automatic control are nationally defined.
In the event of a collision between a call request and activation of this loop, the loop activation command has priority. While this loop is being tested, the DCE sends T=07.3.2 Implementation of Type 2 Loops
The specific implementation of this loop in the DCE is nationally defined, but at least one of the following network test loops should be implemented. 7.3.2.1 Loop 2b
This loop is used by the Administration's test centre and/or the selected DTE to test the operation of subscriber lines and all circuits of the DCE, excluding interchange circuit generators and loads.
When the DCE is in the loop 2b test state, it connects circuit R to circuit T internally. At its interface, the DCE sends r = 0.
7.3.2.2 Loop 2a
This loop is used by the test center of the competent authority or by the remote DTE to test the operation of the subscriber line and the entire DCE. Except for the location of the loopback point, the structure of loop 2a is the same as that of loop 2b given in 7.3.2.1. 9
Definition of symbols used in the state diagram
DTE DCE
Position search
Situation
DTE DCE
's skin separation
GB/T11592—1989
Appendix A
(to Recommendation X.20)
Interface signaling state diagram
(supplement)
State number
Signals on circuit T
Signals on circuit R
Sending interchange circuit
Receiving interchange circuit
DTE and DCE data signals
Stable binary State
Any value
Characters in the international 5-number table (recommendations V.3 and X.4)IA5 character 0/6
IA5 character 1/5
Transfer, and indicate the DTE or DCE responsible for this transferEFIE
YI1, etc.
GB/T11592—1989
Digital transmission
Transmission
Accepted!
Note: To simplify the state diagram, state 6 (call progress signal) and state 7 (information provided by DCE) are combined. Figure A-1/X.20
Call control phases for circuit switching services1 Overview
The loop may be controlled manually by the DCE or automatically by the network. The control of this loop and the method used to achieve automatic control are determined by each country.
In the event of a collision between a call request and the activation of this loop, the loop activation command has priority. While testing this loop, the DCE sends T=07.3.2 Implementation of type 2 loop
The specific implementation of this loop in the DCE is determined by each country, but at least one of the following network test loops should be implemented. 7.3.2.1 Loop 2b
This loop is used by the test center of the competent authority and/or the selected DTE to test the operation of all circuits of the subscriber line and the DCE except the interchange circuit generator and the load.
When the DCE is in the loop 2b test state, it connects circuit R to circuit T internally. At its interface, the DCE sends r=0.
7.3.2.2 Loop 2a
This loop is used by the test center of the administration or by the remote DTE to test the operation of the subscriber line and all DCEs. The structure of loop 2a is the same as that of loop 2b given in 7.3.2.1, except for the location of the loopback point. 9
Definition of symbols used in the state diagram
DTE DCE
Position search
Situation
DTE DCE
's skin separation
GB/T11592—1989
Appendix A
(to Recommendation X.20)
Interface signaling state diagram
(supplement)
State number
Signals on circuit T
Signals on circuit R
Sending interchange circuit
Receiving interchange circuit
DTE and DCE data signals
Stable binary State
Any value
Characters in the international 5-number table (recommendations V.3 and X.4)IA5 character 0/6
IA5 character 1/5
Transfer, and indicate the DTE or DCE responsible for this transferEFIE
YI1, etc.
GB/T11592—1989
Digital transmission
Transmission
Accepted!
Note: To simplify the state diagram, state 6 (call progress signal) and state 7 (information provided by DCE) are combined. Figure A-1/X.20
Call control phases for circuit switching services1 Overview
The loop may be controlled manually by the DCE or automatically by the network. The control of this loop and the method used to achieve automatic control are determined by each country.
In the event of a collision between a call request and the activation of this loop, the loop activation command has priority. While testing this loop, the DCE sends T=07.3.2 Implementation of type 2 loop
The specific implementation of this loop in the DCE is determined by each country, but at least one of the following network test loops should be implemented. 7.3.2.1 Loop 2b
This loop is used by the test center of the competent authority and/or the selected DTE to test the operation of all circuits of the subscriber line and the DCE except the interchange circuit generator and the load.
When the DCE is in the loop 2b test state, it connects circuit R to circuit T internally. At its interface, the DCE sends r=0.
7.3.2.2 Loop 2a
This loop is used by the test center of the administration or by the remote DTE to test the operation of the subscriber line and all DCEs. The structure of loop 2a is the same as that of loop 2b given in 7.3.2.1, except for the location of the loopback point. 9
Definition of symbols used in the state diagram
DTE DCE
Position search
Situation
DTE DCE
's skin separation
GB/T11592—1989
Appendix A
(to Recommendation X.20)
Interface signaling state diagram
(supplement)
State number
Signals on circuit T
Signals on circuit R
Sending interchange circuit
Receiving interchange circuit
DTE and DCE data signals
Stable binary State
Any value
Characters in the international 5-number table (recommendations V.3 and X.4)IA5 character 0/6
IA5 character 1/5
Transfer, and indicate the DTE or DCE responsible for this transferEFIE
YI1, etc.
GB/T11592—1989
Digital transmission
Transmission
Accepted!
Note: To simplify the state diagram, state 6 (call progress signal) and state 7 (information provided by DCE) are combined. Figure A-1/X.20
Call control phases for circuit switching services
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