Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
GB/T 20851 comprises the following parts under the general title Electronic toll collection - Dedicated short range communication:
——Part 1: Physical layer;
——Part 2: Data link layer;
——Part 3: Application layer;
——Part 4: Equipment application;
——Part 5: Test methods of the main parameters in physical layer.
This is part 2 of GB/T 20851.
This part is developed in accordance with the rules given in GB/T 1.1-2009.
This part replaces GB/T 20851.2-2007 Electronic toll collection - Dedicated short range communication - Part 1: Data link layer. In addition to editorial changes, the following main technical changes have been made with respect to GB/T 20851.2-2007:
——the content of “Normative references” is modified (see clause 2 of this standard; clause 2 of Edition 2007);
——the parameter definition and value are modified for the main link layer parameter Tu, and the parameter value is modified for N1 (see clause 5 of this standard; clause 5 of Edition 2007);
——the parameters T3 and N2 are deleted in main link layer (see clause 5 of Edition 2007);
——definitions and values are added for link layer main parameters T4a, T4b, Tr1, Tr2 (see clause 5);
——the value of bit 3-0 in downlink MAC control domain is modified (see 6.3.1 of this standard; 6.3.1 of Edition 2007);
——the value of bit 4-0 in uplink MAC control domain is modified (see 6.3.2 of this standard; 6.3.2 of Edition 2007);
——requirements are added for time window management in MAC sublayer (see 8.1).
This part was proposed by and is under the jurisdiction of the National Technical Committee 268 on Intelligent Transportation Systems of Standardization Administration of China.
The previous edition replaced by this part is as follows:
——GB/T 20851.2-2007.
Electronic toll collection - Dedicated short range communication - Part 2: Data link layer
1 Scope
This part of GB/T 20851 specifies the main parameters, information frames, establishment and revocation of dedicated communication links, and requirements for MAC sublayer and LLC sublayer of the data link layer of dedicated short range communication for electronic toll collection.
This part is applicable to electronic toll collection system for highways and urban roads, and may be used as a reference for automated vehicle identification, vehicle access control, etc.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 7421-2008 Information technology - Telecommunications and information exchange between systems - High-level data link control (HDLC) procedures
GB/T 15629.2-2008 Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements - Part 2: Logical link control
GB/T 20839-2007 Intelligent transport systems - General terminology
GB/T 20851.1-2019 Electronic toll collection - Dedicated short range communication - Part 1: Physical layer
3 Terms and definitions
For the purpose of this standard, the terms and definitions given in GB/T 20839-2007 and GB/T 20851.1-2019 apply.
4 Symbols and abbreviations
4.1 Symbols
For the purposes of this document, the following symbols apply.
V(RB): receiving success or failure status variable.
V(RI): receiving sequence status variable.
V(SI): sending sequence status variable.
4.2 Abbreviations
For the purposes of this document, the following abbreviations apply.
ACK: Acknowledge
ACn: Acknowledged Command/Response
BST: Beacon Service Table
C/R: Command/Response
F: Final
FCS: Frame Check Sequence
LID: Link Identifier
LLC: Logical Link Control
LPDU: LLC Protocol Data Unit
LSDU: LLC Service Data Unit
LSB: Least Significant Bit
M: Modifier Function Bit
MAC: Medium Access Control
MSB: Most Significant Bit
OBU: On Board Unit
PDU: Protocol Data Unit
P/F: Poll/Final
RSU: Roadside Unit
UI: Unnumbered Information
VST: Vehicle Service Table
5 Main parameters of link layer
See Table 1 for the main parameters of link layer.
Table 1 Main parameters of link layer
Parameters Parameter definition Parameter value
T1 The shortest interval between the downlink frame and the subsequent adjacent uplink frame 160 μs
T2 The shortest interval between the uplink frame and the subsequent adjacent downlink frame 32 μs
Tu Common uplink window duration 3 ms
N1 Delay counter for dedicated link establishment request 0~2
T4a The maximum time before the window transfer of a dedicated uplink starts 6.84 ms
T4b The maximum time before the window transfer of a public uplink starts. 480 μs
Tr1 Time interval of frame re-transfer of public downlinks 10 ms
Tr2 Time interval of frame re-transfer of dedicated downlinks with same link identifier 10 ms
N3 Internal transfer counter
N4 Acknowledgement timer
Note: The parameter values of N3 and N4 are not specified in this part.
6 Information frames
6.1 Information frame formats
The data link layer information shall be interacted in the form of frames which include MAC address, MAC control domain, LPDU (optional), and frame check. According to the type of LPDU, it is further divided into frames containing command LPDU (see Figure 1 for its structure) and frames containing response LPDU (see Figure 2 for its structure).
Figure 1 Structure of information frame containing command LPDU
Figure 2 Structure of information frame containing response LPDU
See Figure 3 for the structure of frame not containing LPDU domain.
Figure 3 Structure of information frame structure not containing LPDU domain
6.2 Frame packaging mode
6.2.1 Frame packaging format
The information frame is transmitted synchronously, and the frame packaging format is shown in Figure 4.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Symbols and abbreviations
5 Main parameters of link layer
6 Information frames
7 Establishment and revocation of dedicated communication link
8 MAC sublayer
9 LLC sublayer
Annex A (Normative) Establishment process of dedicated point-to-point communication link
Bibliography
Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
GB/T 20851 comprises the following parts under the general title Electronic toll collection - Dedicated short range communication:
——Part 1: Physical layer;
——Part 2: Data link layer;
——Part 3: Application layer;
——Part 4: Equipment application;
——Part 5: Test methods of the main parameters in physical layer.
This is part 2 of GB/T 20851.
This part is developed in accordance with the rules given in GB/T 1.1-2009.
This part replaces GB/T 20851.2-2007 Electronic toll collection - Dedicated short range communication - Part 1: Data link layer. In addition to editorial changes, the following main technical changes have been made with respect to GB/T 20851.2-2007:
——the content of “Normative references” is modified (see clause 2 of this standard; clause 2 of Edition 2007);
——the parameter definition and value are modified for the main link layer parameter Tu, and the parameter value is modified for N1 (see clause 5 of this standard; clause 5 of Edition 2007);
——the parameters T3 and N2 are deleted in main link layer (see clause 5 of Edition 2007);
——definitions and values are added for link layer main parameters T4a, T4b, Tr1, Tr2 (see clause 5);
——the value of bit 3-0 in downlink MAC control domain is modified (see 6.3.1 of this standard; 6.3.1 of Edition 2007);
——the value of bit 4-0 in uplink MAC control domain is modified (see 6.3.2 of this standard; 6.3.2 of Edition 2007);
——requirements are added for time window management in MAC sublayer (see 8.1).
This part was proposed by and is under the jurisdiction of the National Technical Committee 268 on Intelligent Transportation Systems of Standardization Administration of China.
The previous edition replaced by this part is as follows:
——GB/T 20851.2-2007.
Electronic toll collection - Dedicated short range communication - Part 2: Data link layer
1 Scope
This part of GB/T 20851 specifies the main parameters, information frames, establishment and revocation of dedicated communication links, and requirements for MAC sublayer and LLC sublayer of the data link layer of dedicated short range communication for electronic toll collection.
This part is applicable to electronic toll collection system for highways and urban roads, and may be used as a reference for automated vehicle identification, vehicle access control, etc.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 7421-2008 Information technology - Telecommunications and information exchange between systems - High-level data link control (HDLC) procedures
GB/T 15629.2-2008 Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements - Part 2: Logical link control
GB/T 20839-2007 Intelligent transport systems - General terminology
GB/T 20851.1-2019 Electronic toll collection - Dedicated short range communication - Part 1: Physical layer
3 Terms and definitions
For the purpose of this standard, the terms and definitions given in GB/T 20839-2007 and GB/T 20851.1-2019 apply.
4 Symbols and abbreviations
4.1 Symbols
For the purposes of this document, the following symbols apply.
V(RB): receiving success or failure status variable.
V(RI): receiving sequence status variable.
V(SI): sending sequence status variable.
4.2 Abbreviations
For the purposes of this document, the following abbreviations apply.
ACK: Acknowledge
ACn: Acknowledged Command/Response
BST: Beacon Service Table
C/R: Command/Response
F: Final
FCS: Frame Check Sequence
LID: Link Identifier
LLC: Logical Link Control
LPDU: LLC Protocol Data Unit
LSDU: LLC Service Data Unit
LSB: Least Significant Bit
M: Modifier Function Bit
MAC: Medium Access Control
MSB: Most Significant Bit
OBU: On Board Unit
PDU: Protocol Data Unit
P/F: Poll/Final
RSU: Roadside Unit
UI: Unnumbered Information
VST: Vehicle Service Table
5 Main parameters of link layer
See Table 1 for the main parameters of link layer.
Table 1 Main parameters of link layer
Parameters Parameter definition Parameter value
T1 The shortest interval between the downlink frame and the subsequent adjacent uplink frame 160 μs
T2 The shortest interval between the uplink frame and the subsequent adjacent downlink frame 32 μs
Tu Common uplink window duration 3 ms
N1 Delay counter for dedicated link establishment request 0~2
T4a The maximum time before the window transfer of a dedicated uplink starts 6.84 ms
T4b The maximum time before the window transfer of a public uplink starts. 480 μs
Tr1 Time interval of frame re-transfer of public downlinks 10 ms
Tr2 Time interval of frame re-transfer of dedicated downlinks with same link identifier 10 ms
N3 Internal transfer counter
N4 Acknowledgement timer
Note: The parameter values of N3 and N4 are not specified in this part.
6 Information frames
6.1 Information frame formats
The data link layer information shall be interacted in the form of frames which include MAC address, MAC control domain, LPDU (optional), and frame check. According to the type of LPDU, it is further divided into frames containing command LPDU (see Figure 1 for its structure) and frames containing response LPDU (see Figure 2 for its structure).
Figure 1 Structure of information frame containing command LPDU
Figure 2 Structure of information frame containing response LPDU
See Figure 3 for the structure of frame not containing LPDU domain.
Figure 3 Structure of information frame structure not containing LPDU domain
6.2 Frame packaging mode
6.2.1 Frame packaging format
The information frame is transmitted synchronously, and the frame packaging format is shown in Figure 4.
Contents of GB/T 20851.2-2019
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Symbols and abbreviations
5 Main parameters of link layer
6 Information frames
7 Establishment and revocation of dedicated communication link
8 MAC sublayer
9 LLC sublayer
Annex A (Normative) Establishment process of dedicated point-to-point communication link
Bibliography
