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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 31024 consists of the following four parts under the general title Cooperative intelligent transportation systems—Dedicated short range communications: ——Part 1: General technical requirement; ——Part 2: Specification of medium access control layer and physical layer; ——Part 3: Network layer and application layer specification; ——Part 4: Equipment application specification. This part is Part 3 of GB/T 31024. This part is developed in accordance with the rules given in GB/T 1.1-2009. This part was proposed by and is under the jurisdiction of the National Technical Committee on Intelligent Transportation Systems of Standardization Administration of China (SAC/TC 268). Cooperative intelligent transportation systems— Dedicated short range communications— Part 3: Network layer and application layer specification 1 Scope This part of GB/T 31024 specifies the technical requirements of network layer and application layer for dedicated short range communication of cooperative intelligent transportation system. This part is applicable to the design and development of network layer and application layer for dedicated short range communication of cooperative intelligent transportation system. 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 5768.2 Road traffic signs and markings—Part 2: Road traffic signs GB 14886 Specifications for road traffic signal setting and installation GB/T 16262.1 Information technology—Abstract Syntax Notation One (ASN.1)—Part 1: Specification of basic notation GB/T 16262.2 Information technology—Abstract Syntax Notation One (ASN.1)—Part 2: Information object specification GB/T 16262.3 Information technology—Abstract Syntax Notation One (ASN.1)—Part 3: Constraint specification GB/T 16262.4 Information technology—Abstract Syntax Notation One (ASN.1)—Part 4: Parameterization of ASN.1 specifications GB/T 16263.2 Information technology—ASN.1 encoding rules—Part 2: Specification of Packed Encoding Rules (PER) GB 25280 Road traffic signal controller 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 dedicated short range communication wireless communication method for short range communication among traffic elements such as vehicles, infrastructures and pedestrians 3.2 dedicated short range communication management entity a universal set of dedicated short range communication management services that provides management interfaces for all data layer entities 3.3 management information base an entity used to store application configuration and status information 4 Abbreviations For the purposes of this document, the following abbreviations apply. AID Application ID DME DSRC Management Entity DSA DSRC Service Advertisement DSM DSRC Short Message DSMP DSRC Short Message Protocol DSRC Dedicated Short Range Communication GNSS Global Navigation Satellite System IP Internet Protocol LLC Logical Link Control LTE Long Term Evolution LTE-V2X LTE Vehicle to Everything MAC Media Access Control MIB Management Information Base SAP Service Access Point TCP Transmission Control Protocol UDP User Data Protocol UPER Unaligned Packet Encoding Rules 5 Technical requirements of network layer 5.1 Network layer framework The DSRC network layer framework of cooperative intelligent transportation system is shown in Figure 1. Note 1: The network layer consists of data sublayer and management sublayer. Note 2: The data sublayer mainly comprises adaptation layer, IP and TCP/UDP, as well as DSMP of cooperative intelligent transportation system. The IP protocol and the DSMP protocol are optional. The data sublayer transmits both data streams between application layers and data streams between different device management layer entities or between management layer entities and applications. Note 3: The management sublayer mainly performs functions such as system configuration and maintenance. It transmits management data streams between different devices by using the data sublayer service. The DME of cooperative intelligent transportation system is a universal set of management services, which provides management interfaces for all data sublayer entities, including DSMP protocol. Figure 1 DSRC network layer framework of cooperative intelligent transportation system 5.2 Technical requirements of data sublayer 5.2.1 General The data sublayer in the DSRC network layer of the cooperative intelligent transportation system comprises TCP/UDP, IP, DSMP and adaptation layer, wherein the IP protocol and the TCP/UDP protocol are not within the definition of this part. The IP data stream and the DSMP data stream are defined in the DSRC network layer of the cooperative intelligent transportation system. The IP data stream is shown in Figure 2, and the DSMP data stream is shown in Figure 3. Figure 2 IP data stream Figure 3 DSMP data stream 5.2.2 Adaptation layer The adaptation layer provides the transmission adaptation function between the underlying access technology and the upper layer protocol stack. The adaptation layer receives the DSMP data packet, the IP data packet, or the DME data packet sent by the upper layer, distinguishes the underlying access technology used by the data packet to be sent, and delivers the corresponding data packet to the bottom layer in line with the corresponding access technology for transmission; or receives the data packet from the bottom layer, distinguishes the upper layer protocol type to which the corresponding data packet belongs, and delivers the data packet to the specified upper layer protocol stack. The DSRC network layer services of the cooperative intelligent transportation system shall support the unacknowledged connectionless LLC operation, subnetwork access protocol and IP data transmission protocol. The adaptation layer frame format is shown in Figure 4. The adaptation layer frame contains the header and the payload. The adaptation layer payload is used to encapsulate the upper layer data packets. The bit sequence in the adaptation layer frame format is high bit first. Note: The Protocol Type is used to indicate the type of protocol used by the upper layer data packet. See Annex A for specific values. Figure 4 Adaptation layer frame format 5.2.3 DSMP 5.2.3.1 DSM data frame format The layer-by-layer packaging process of DSM is shown in Figure 5. Figure 5 Layer-by-layer packaging process of DSM The DSM data frame format is shown in Table 1. The bit sequence in the DSM data frame format is high bit first. Table 1 DSM data frame format Field 1 Field 2 Field 3 Field 4 Field 5 Field 6 Field 7 3 bits 1 bit 4 bits Var Var 2octets Var DSMP Version DSMP Option Indicator Reserved Extension AID Length Data DSMP Version DSMP Option Indicator Reserved Extension Application ID Data Length Data Note 1: DSMP Version distinguishes different DSMP version numbers (0 to 7). The DSMP Version in this part is 0. Note 2: DSMP Option Indicator indicates that the following extension appears when the value is 1 and that the following extension does not appear when the value is 0. Note 3: Reserved indicates the reserved bits, which are all zero for this version. Note 4: Extension, reserved for other information, including other information identifier, other information length and other information content, wherein other information identifier refers to Element ID, as detailed in 5.2.3.3. Information such as extension length and content will be associated with the standard version. Note 5: Application ID (AID) refers to the AID of application service provider, which is used to distinguish different applications. Note 6: Length indicates the byte length of the application layer data entity. Note 7: Data refers to the data entity hosted in application layer or management sublayer. 5.2.3.2 AID The DSMP protocol layer is responsible for data interaction with different applications. The DSMP entity transmits the short message of interest to the application layer and receives the data packet from the application layer. In DSM, AID is used to distinguish different application layer services. In the service interaction communication process, the communication process between the application service provider (Provider) and the User is shown in Figure 6. Figure 6 Communication process between Provider and User AID is represented by variable-length byte. At present, it supports representation of up to 2 bytes, and at least 1 byte is used. See Table 2 for the representation method and Annex B for allocation suggestions. Table 2 AID representation method Highest bit of byte 0 (x indicates no concern) b7 b6 AID length (byte(s)) AID range (hex) 0 x 1 00~7F 1 0 2 80-00~BF-FF 1 1 Length ≥3 reserved Reserved Note: Each Provider can apply for an AID based on specific service requirements. 5.2.3.3 Element ID The Element ID is used to indicate the different roles of the data information and the identifier of other information in the frame structure. The specifications of Element ID are shown in Table 3. Table 3 Specifications of Element ID Element ID No. Application field Number of bytes Description — 0 Reserved — — — 1 Reserved — — — 2 Reserved — — — 3 Reserved — — Transmit power used 4 Service advertisement header 1 byte A signed number, indicating the transmit power of DSM data frame, in dBm 2D Location 5 Service advertisement header 8 bytes Location of 2D; 4 bytes for latitude and the other 4 bytes for longitude, to the nearest of 0.1 microdegrees 3D Location And Confidence 6 Service advertisement header 15 bytes Location of 3D; 4 bytes for latitude and 4 bytes for longitude, to the nearest of 0.1 microdegrees; 2 bytes for altitude, to the nearest of 0.1 m; 4 bit for position confidence; 4 bit for altitude confidence; 4 bytes for position accuracy Advertiser identifier 7 Service advertisement header 1 to 32 bytes A string, identification number of the Provider, ID string of the Provider Provider Service Context 8 Service advertisement application information 1 to 31 bytes A string, providing additional information associated with the upper layer service IPv6 address 9 Service advertisement application information 16 bytes IPv6 address Service port 10 Service advertisement application information 2 bytes Port number of the upper layer entity of the Provider host, available for services using IP address Provider MAC address 11 Service advertisement application information 6 bytes Providing the MAC address of the Provider host Channel Number 12 DSMP header 1 byte Indicating the channel number Data Rate 13 DSMP header 1 byte Indicating the data transmission rate, in 500 kbit/s Broadcast Frequency 14 Service advertisement header 1 byte Indicating the broadcast frequency of the DSA service advertisement, that is, the number of times the service advertisement is repeatedly sent within 1 s. This parameter can be used to evaluate the link quality. Area String 15 Service advertisement header 3 bytes Indicating the area to which the device belongs DSA RCPI Threshold 16 Service advertisement application information 1 byte Indicating the minimum channel power, in dBm, used by the receiving end of the DSA service advertisement message to identify whether the service is available; if below this threshold, the service can be ignored. DSA Count Threshold 17 Service advertisement application information 1 byte Indicating the minimum number of received advertisement messages used by the receiving end of the DSA service advertisement message to identify whether the service is available; if the number of received messages at a DSA Count Threshold Interval is less than this value, the receiving end may ignore this service. DSA Count Threshold Interval 18 Service advertisement application information 1 byte Indicating the corresponding time interval for counting the number of DSA received, in 100 ms, valid between 1 and 255. If not specified, it is 1 s by default. — 19~255 Reserved — 5.3 Technical requirements of management sublayer 5.3.1 Application registration Before using management sublayer services, the application needs to be registered with the DME first. An application running on a DSRC device needs to be registered as a user application, so that the DME can send the received DSM to the corresponding application. 5.3.2 Service management Service management belongs to the internal operation of the device, and the corresponding functions are optional. When an application issues a service usage request to the DME, the DME will initialize the requested service. An example of the service management process is shown in Figure 7. Figure 7 Example of service request information flow The main forms of service requests include Provider Service Request, User Service Request, Short Message Service Request, and Timing Notification Service Request. These four forms of service request are described as follows: a) For DME, the Provider Service Request indicates that the upper layer wants it to send the DSA. After accepting the Provider Service Request, the DME will generate a corresponding provider service request entry in the MIB and consider the service request when deciding the channel access allocation. b) For DME, the User Service Request indicates that the upper layer entity is interested in the available services that meet the specified standards. The request indicates the action to be taken when the DME identifies such available services. After accepting the User Service Request, the DME will generate a corresponding user service request entry in the MIB and consider the service request when deciding the channel access allocation. c) For DME, the Short Message Service Request indicates that the upper layer entity wants to receive a DSM with the specified AID. After accepting the Short Message Service Request, the DME will generate a corresponding short message service request entry in the MIB and deliver any received DSM with the matching AID to the requested upper layer entity. d) For DME, the Timing Notification Service Request indicates that another management entity wants it to send a timing notification frame on its behalf. After accepting the Timing Notification Service Request, the DME will consider the service request when deciding the channel access allocation, and generate a timing notification to the access layer management entity. When the DME receives a service request of a different action type, it will take different countermeasures, as follows: a) When receiving a service request whose action type is "Add", corresponding service information should be added in the MIB; b) When receiving a service request whose action type is "Update", corresponding service information should be updated in the MIB; c) When receiving a service request whose action type is "Delete", corresponding service information should be deleted in the MIB. 5.3.3 MIB maintenance The MIB operation process is shown in Figure 8. The MIB is responsible for management and maintenance of the application configuration and status information of the DSRC modules of the cooperative intelligent transportation system. The DME sets and queries the MIB information through specified signaling. After receiving a service request message, the DME establishes a MIB information table corresponding to the service in the MIB. The information table item includes application configuration and status information, and the transmission environment configuration of the service data is based on the status information. Figure 8 MIB operation process See Annex C for a list of MIB messages. 5.3.4 Service advertisement The DSRC Service Advertisement (DSA) of the cooperative intelligent transportation system shall be encapsulated in the data part of the DSM, and the AID in the DSM shall be set to the value of the AID corresponding to the DSA. The DSA information flow is shown in Figure 9. Note: The interaction between the application layer and the DME has no chronological requirements at the sending and receiving ends. Figure 9 DSA information flow The DSA message frame format is shown in Table 4, and the bit sequence in the DSA frame format is high bit first. Table 4 DSA message frame format Variable Variable Header Application Info Frame header Application information The DSA Header extension format is shown in Table 5. Table 5 DSA Header extension format Field 1 Field 2 Field 3 Field 4 Field 5 Field 6 4 bits 1 bit 3 bits 4 bits 4 bits Var DSA Version DSA Header Option Indicator Reserved DSA Identifier Content Count Header Extension DSA Version DSA Header Option Indicator Reserved DSA ID Content Count Header Extension Note 1: DSA Version distinguishes different DSA version numbers (0 to 15). The DSA Version in this part is 0. Note 2: DSA Header Option Indicator indicates that the Header Extension appears when the value is 1 and that the Header Extension does not appear when the value is 0. Note 3: Reserved, for extension. Note 4: DSA ID is used to identify the uniqueness of the DSA. Note 5: Content Count is used to identify whether it is a repetition of the previous DSA when the DSA ID is the same. Note 6: Header Extension, reserved for other information. The Application Info extension is shown in Table 6. It can be repeated multiple times except for the first field. Table 6 Application Info field format 1 byte Variable Variable Application Info Count AID Application Extension Application Info Count Application ID Application Extension Note 1: The Application Info Count indicates the total number of Application Info. Note 2: The AID format is shown in 5.2.3.2. Note 3: The Application Extension indicates the application-related information. 5.4 Access point and service primitive 5.4.1 Service Access Point (SAP) The SAP of the DSRC network layer is shown in Figure 10. Figure 10 SAP of DSRC network layer of the cooperative intelligent transportation system 5.4.2 Access layer service primitive 5.4.2.1 ACCESS-LAYER.request ACCESS-LAYER.request is used to send the access data requested by the upper layer. Service primitive parameters: The ACCESS-LAYER.request service primitive parameters are shown in Table 7. Table 7 ACCESS-LAYER.request service primitive parameters Name Type Effective range Description Source_address MAC address — Source MAC address Destination_address MAC address — Destination MAC address Data Byte string N/A Data sent by the upper layer to the access layer Priority Integer 1~8 8 priority descriptions PDCP SDU type Enumeration {IP, Non-IP} When the upper layer data packet is an IP data packet, the value is set to IP; when the upper layer data packet is a DSMP data packet or a DME data packet, the value is set to Non-IP. Extension Bit string Not defined For extension Note 1: See the underlying standard for the MAC address. Note 2: The supporting device randomly generates the source MAC address and the AID-based destination MAC address. The mapping relation between the AID and the destination MAC address is given in the underlying standard. 5.4.2.2 ACCESS-LAYER.indication ACCESS-LAYER.indication is used to indicate that the upper layer has received the access data. Service primitive parameters: The ACCESS-LAYER.indication service primitive parameters are shown in Table 8. Table 8 ACCESS-LAYER.indication service primitive parameters Name Type Effective range Description Source_address MAC address — Source MAC address Destination_address MAC address — Destination MAC address Priority Integer 1~8 8 priority descriptions Data Byte string N/A Data sent by the access layer to the upper layer Note: See the underlying standard for the MAC address. 5.4.3 Adaptation layer service primitive 5.4.3.1 ADAPTATION-LAYER.request ADAPTATION-LAYER.request is used to send the adaptation layer data requested by the upper layer. Service primitive parameters: The ADAPTATION-LAYER.request service primitive parameters are shown in Table 9. Table 9 ADAPTATION-LAYER.request service primitive parameters Name Type Effective range Description ApplicationIdentifier String — Provider AID ProtocolType Integer See Annex A See Annex A Source_address Adaptation layer address Any effective unicast adaptation layer address From its own device, see Annex D Destination_address Adaptation layer address Any effective adaptation layer address From DSM.request, see Annex D Data String All DSM data Priority Integer 1~8 From DSM.request Extension Bit string Not defined For extension 5.4.3.2 ADAPTATION-LAYER.indication ADAPTATION-LAYER.indication is used to indicate that the upper layer has received the adaptation layer data. Service primitive parameters: The ADAPTATION-LAYER.indication service primitive parameters are shown in Table 10. Table 10 ADAPTATION-LAYER.indication service primitive parameters Name Type Effective range Description ProtocolType Integer See Annex A See Annex A Source_address Adaptation layer address Any effective unicast adaptation layer address See Annex D Destination_address Adaptation layer address Any effective adaptation layer address See Annex D Data String All — Priority Integer 1~8 From ACCESS-LAYER.indication 5.4.4 DSM service primitive 5.4.4.1 DSM.request DSM.request is used by the upper layer to request to send the DSM data. Service primitive parameters: The DSM.request service primitive parameters are shown in Table 11. Table 11 DSM.request service primitive parameters Name Type Effective range Description ApplicationIdentifier String — Provider AID ProtocolType Integer See Annex A See Annex A Priority Integer 1~8 Inserted into ADAPTATION-LAYER.request Length Integer 1~65 535 Byte length of the DSM data entity Data String Not defined DSM data entity Peer MAC address MAC address Any effective unicast, multicast or broadcast MAC address Optional, if any, inserted into ADAPTATION-LAYER.request DsmpHeaderExtensions Bit string Not defined Specified frame header extension 5.4.4.2 DSM.indication DSM.indication is used to indicate that the upper layer or the entity in the DSM service request table in the MIB has received the DSM data. For example, if the AID in the DSM indicates that the message is a DSA, the DSMP will send DSM.indication to the DME. Service primitive parameters: The DSM.indication service primitive parameters are shown in Table 12. Table 12 DSM.indication service primitive parameters Name Type Effective range Description DSMP Version Integer 0~7 Obtained from DSMP header ApplicationIdentifier String — Provider AID, obtained from DSMP header Length Integer 1~65 535 Obtained from DSMP header Data String Not defined Obtained from DSMP header Peer MAC address MAC address Any effective unicast MAC address Obtained from ADAPTATION-LAYER.indication Priority Integer 1~8 Obtained from the bottom layer 5.4.5 DME service primitive 5.4.5.1 DME-ProviderService.request DME-ProviderService.request indicates that the upper layer entity of the Provider requests to transmit a DSA, which is generated by the upper layer entity as needed. After received, the DME generates a DME-ProviderService.confirm, indicating whether the request is accepted. Foreword i 1 Scope 2 Normative references 3 Terms and definitions 4 Abbreviations 5 Technical requirements of network layer 6 Interactive data set of application layer Annex A (Informative) Classification and value of Protocal Type Annex B (Informative) Preferred AID port number allocation Annex C (Informative) MIB message Annex D (Informative) Example of source/destination address design for adaptation layer Bibliography 合作式智能运输系统 专用短程通信 第3部分：网络层和应用层规范 1 范围 GB/T 31024的本部分规定了合作式智能运输系统专用短程通信网络层技术要求和应用层技术要求。 本部分适用于合作式智能运输系统专用短程通信网络层及应用层的设计与开发。 2规范性引用文件 下列文件对于本文件的应用是必不可少的。凡是注日期的引用文件，仅注日期的版本适用于本文件。凡是不注日期的引用文件，其最新版本(包括所有的修改单)适用于本文件。 GB 5768.2 道路交通标志和标线 第2部分：道路交通标志 GB 14886 道路交通信号灯设置与安装规范 GB/T 16262.1 信息技术 抽象语法记法一(ASN.1)第1部分：基本记法规范 GB/T 16262.2 信息技术 抽象语法记法一(ASN.1)第2部分：信息客体规范 GB/T 16262.3 信息技术 抽象语法记法一(ASN.1)第3部分：约束规范 GB/T 16262.4 信息技术 抽象语法记法一(ASN.1)第4部分：ASN.1规范的参数化 GB/T 16263.2信息技术 ASN.1编码规则 第2部分：紧缩编码规则(PER)规范 GB 25280道路交通信号控制机 3术语和定义 下列术语和定义适用于本文件。 3.1 专用短程通信dedicated short range communication 用于车辆、基础设施、行人等交通要素之间进行短程通信的无线通信方式。 3.2 专用短程通信管理实体dedicated short range communication management entity 专用短程通信管理业务的通用集合，为所有的数据层实体提供管理接口。 3.3 管理信息库management information base 用于存储应用配置及状态信息的实体。 4 缩略语 下列缩略语适用于本文件。 AID：应用标识(Application ID) DME：专用短程通信管理实体(DSRC Management Entity) DSA：专用短程通信业务公告(DSRC Service Advertisement) DSM：专用短程通信短消息(DSRC Short Message) DSMP：专用短程通信短消息协议(DSRC Short Message Protocol) DSRC：专用短程通信(Dedicated Short Range Communication) GNSS：全球导航卫星系统(Global Navigation Satellite System) IP：因特网互连协议(Internet Protocol) LLC：逻辑链路控制(Logical Link Control) LTE：长期演进技术(Long Term Evolution) LTE-V2X：基于LTE的车用无线通信技术(LTE Vehicle to Everything) MAC：介质访问控制(Media Access Control) MIB：管理信息库(Management Information Base) SAP：服务接入点(Service Access Point) TCP：传输控制协议(Transmission Control Protocol) UDP：用户数据报协议(User Data Protocol) UPER：非对齐压缩编码规则(Unaligned Packet Encoding Rules) 5网络层技术要求 5.1 网络层框架 合作式智能运输系统专用短程通信的网络层框架见图1。 应用层 管理子层 专用短程通信管理实体 DME 专用短程通信短消息协议 DSMP 适配层(Adaption Layer) 数据子层 网络层 接入层 注1：网络层由数据子层和管理子层两部分构成。 注2：数据子层主要包括适配层(Adaptation Layer)、IP和TCP/UDP以及合作式智能运输系统DSMP。其中IP协议和DSMP协议都是可选。数据子层既传输应用层间的数据流，也传输不同设备管理层实体间或管理层实体与应用间的数据流。 注3：管理子层主要完成系统配置及维护等功能。管理子层通过使用数据子层服务在不同设备间传递管理数据流。其中，合作式智能运输系统DME是管理业务的通用集合。DME为所有的数据子层实体提供管理接口，包括DSMP协议。 图1 合作式智能运输系统专用短程通信网络层框架 5.2数据子层技术要求 5.2.1 概述 合作式智能运输系统专用短程通信网络层中的数据子层包括TCP/UDP、IP、DSMP和适配层，其中IP协议和TCP/UDP协议不在本部分定义范围内。 合作式智能运输系统专用短程通信网络层中规定了IP数据流和DSMP数据流，IP数据流见图2，DSMP数据流见图3。 应用层 适配层 接入层 服务请求过程 数据 数据 接入层 适配层 应用层 服务请求过程 数据 图2 IP数据流 应用层 适配层 接入层 接入层 适配层 应用层 图3 DSMP数据流 5.2.2 适配层 适配层提供底层接入技术与上层协议栈之间的传输适配功能。其中，适配层接收上层发送的DSMP数据包、IP数据包或DME数据包，区分待发送数据包所使用的底层接入技术，并将相应数据包递交到符合对应接入技术的底层进行传输；或接收来自底层的数据包，区分相应数据包所属的上层协议类型，并将数据包递交给指定的上层协议栈。 合作式智能运输系统专用短程通信网络层业务需支持无连接无确认的LLC操作、子网接入协议和IP数据报传输协议。 适配层帧格式见图4，适配层帧包含适配层帧头以及适配层有效载荷两部分。适配层有效载荷用于封装上层数据包。适配层帧格式中的比特顺序为高位在前。 1字节 协议类型Protocol Type 数据Data 适配层帧头 适配层有效载荷 注：协议类型(Protocol Type)，用于指示上层数据包所使用的协议类型。具体取值参见附录A。 图4适配层帧格式 5.2.3 专用短程通信短消息协议 5.2.3.1 DSM数据帧格式 DSM逐层打包流程见图5。 应用层/管理子层 适配层 适配层 接入层 适配层 接入层 接入技术相关 图5 DSM逐层打包流程 DSM的数据帧格式见表1。DSM数据帧格式中的比特顺序为高位在前。 表1 DSM数据帧格式 字段一 字段二 字段三 字段四 字段五 字段六 字段七 3 bits 1 bit 4 bits Var Var 2octets Var DSMP Version DSMP Option Indicator Reserved Extension AID Length Data DSMP版本 DSMP可选域指示 预留 扩展域 应用标识 数据长度 数据 注1：DSMP版本(Version)，区分不同的DSMP版本号(0～7)。本部分中DSMP版本取值为0。 注2：DSMP可选域指示(DSMP Option Indicator)，取值为1表示后面的扩展域出现，取值为0表示后面的扩展域不出现。 注3：预留域(Reserved)，预留比特，此版本全部取0。 注4：扩展域(Extension)，预留可用于其他信息，包含其他信息标识、其他信息长度和其他信息内容三部分，其他信息标识就是Element ID，具体见5.2.3.3。扩展域长度、内容等信息将与标准版本相关联。 注5：应用标识(Application ID，AID)，应用服务商的应用标识，区分不同的应用。 注6：数据长度(Length)，表示应用层数据实体的字节长度。 注7：数据(Data)，是承载的应用层或管理子层数据实体。 5.2.3.2 应用标识 DSMP协议层负责与不同应用的数据交互。DSMP实体将应用层感兴趣的短消息传输到应用层，并接收来自应用层的数据包。在DSM中，AID用来区分不同的应用层业务。 业务交互通信过程中，应用服务提供者(Provider)和用户(User)的通信流程的示意见图6。 图6 Provider和User的通信流程示意 AID采用变长字节表示形式，目前最多支持2个字节的表示，最少采用1个字节表示，方式见表2，分配建议参见附录B。 表2 AID表示方法 字节0的最高位(x表示不关心)b7 b6 AID长度(字节) AID范围(十六进制) 0 x 1 00～7F 1 0 2 80-00～BF-FF 1 1 长度≥3保留 保留 注：各应用提供方可根据具体的业务需求申请AID。 5.2.3.3 元素标识 Element ID(元素标识)用于表示数据信息的不同作用，用于在帧结构中指示其他信息的标识。El-ement ID规定见表3。 表3 Element ID规定 Element ID 编号 应用域 字节数 描述 — 0 保留 — — — 1 保留 — — — 2 保留 — — — 3 保留 — — 传输功率 (Transmit power used) 4 业务公告帧头 1字节 表示传输DSM数据帧的发送功率。单位为dBm。有符号数 2D地址 (2D Location) 5 业务公告帧头 8字节 2D位置。4个字节表示纬度，4个字节表示经度。精确至0.1微度 3D地址 (3DLocationAndConfidence) 6 业务公告帧头 15字节 3D位置，4个字节表示纬度，4个字节表示经度。经纬度精确至0.1微度。2个字节表示海拔，精确至0.1 m。4 bit表示位置置信度。4 bit表示海拔置信度。4字节表示位置精确度 应用服务者公告识别号 (Advertiser identifier) 7 业务公告帧头 1～32字节 字符串，应用提供者的识别号，应用服务者标识字符串 应用提供者服务上下文 (Provider Service Context) 8 业务公告应用信息 1～31字节 字符串，提供与上层服务关联的补充信息 IPv6地址 (IPv6 address) 9 业务公告应用信息 16字节 IPv6地址 服务端口 (Service port) 10 业务公告应用信息 2字节 为应用服务提供者主机的上层实体的端口号，服务采用IP地址时适用 应用提供者MAC地址 (Provider MAC address) 11 业务公告应用信息 6字节 提供应用服务提供者主机的MAC地址 信道号 (Channel Number) 12 DSMP帧头 1字节 表示信道号 数据速率 (DataRate) 13 DSMP帧头 1字节 表示数据发射速率，单位为500 kbit/s DSA公告发送频率 (Broadcast Frequency) 14 业务公告帧头 1字节 表示DSA服务公告的广播频率，即在1 s内服务公告重复发送的次数。此参数可以用来评估链路质量 区域信息 (Area String) 15 业务公告帧头 3字节 表示设备归属区域 表3(续) Element ID 编号 应用域 字节数 描述 DSA接收信道功率阈值 (DSA RCPI Threshold) 16 业务公告应用信息 1字节 表示DSA服务公告消息的接收端用于识别服务是否可用的最小信道功率值，低于此阈值以下时可以忽略此服务。单位dBm DSA接收个数阈值 (DSA Count Threshold) 17 业务公告应用信息 1字节 表示DSA服务公告消息的接收端用于识别服务是否可用的公告消息最小接收个数的阈值，当在一个统计周期(DSA Count Threshold Interval)内接收到的消息数目低于此值时，接收端可忽略此服务 DSA接收个数统计周期(DSA Count Threshold Interval) 18 业务公告应用信息 1字节 表示统计DSA接收个数时对应的时间间隔，单位100 ms，有效取值1～255。如果不指定时，默认取值1 s — 19～255 保留 — 5.3管理子层技术要求 5.3.1 应用注册 在使用管理子层业务前，应用需先在DME处注册。专用短程通信设备上运行的应用需先注册为一个用户应用，使得DME可将接收到的DSM发送到对应的应用。 5.3.2 服务管理 服务管理属于设备内部操作，相应的功能可选。当某个应用向DME发出使用服务请求，DME便会初始化被请求的服务。服务管理过程示例见图7。 应用层 图7服务请求信息流示例 服务请求的主要形式包括提供者服务请求、用户服务请求、短消息服务请求、定时通知服务请求，这四种形式的服务请求具体描述如下： a)对于DME来说，提供者服务请求表示上层希望它发送DSA。DME接受提供者服务请求之后会产生MIB中对应的提供者服务请求表条目，并在决定信道接入分配时考虑该服务请求。b)对于DME来说，用户服务请求表示上层实体对满足指定标准的可用服务感兴趣。请求表明当DME识别这种可用服务时要采取的行动。DME接受用户服务请求会产生MIB中对应的用户服务请求表条目，并在决定信道接入分配时考虑该服务请求。 c)对于DME来说，短消息服务请求表示上层实体想要接收到一个指定AID的DSM。DME接受短消息服务请求产生MIB中对应的短消息服务请求表条目，并将任何接收到的带有匹配AID的DSM投递到所请求的上层实体。 d)对于DME来说，定时通知服务请求表明另一个管理实体希望它代为发送定时通知帧。DME接受定时通知服务请求会在决定信道接入分配时考虑服务请求，并对接入层管理实体产生定时通知。 当DME接收到不同动作类型的服务请求时，会采取不同的应对方式，具体如下： a)当接收到动作类型为“增加”的服务请求时，在MIB中增加对应的服务信息； b)当接收到动作类型为“更新”的服务请求时，更新MIB中对应的服务信息； c)当接收到动作类型为“删除”的服务请求时，删除MIB中对应的服务信息。 5.3.3 MIB维护 MIB操作流程见图8，MIB负责管理维护合作式智能运输系统专用短程通信模块的应用配置及状态信息。DME通过指定的信令设置、查询MIB信息。DME接收到一个业务请求消息后会在MIB中建立一个对应该业务的MIB信息表，该信息表项包含应用配置及状态信息，业务数据的传输环境配置基于该状态信息。 应用层 图8 MIB操作流程 MIB消息列表参见附录C。 5.3.4 业务公告 合作式智能运输系统专用短程通信业务公告(DSRC Service Advertisement，DSA)应封装在DSM的data部分，并将DSM中的AID设置为DSA对应的AID取值。DSA的信息流见图9。 应用层 注：应用层与DME的交互在收发两端没有时间先后顺序的要求。 图9 DSA信息流 DSA的消息帧格式见表4，DSA帧格式中的比特顺序为高位在前。 表4 DSA消息帧格式 变量 变量 Header Application Info 帧头 应用信息 其中DSA Header域展开格式见表5。 表5 DSA Header域展开格式 字段一 字段二 字段三 字段四 字段五 字段六 4 bits 1 bit 3 bits 4 bits 4 bits Var DSA Version DSA Header Option Indicator Reserved DSA Identifier Content Count Header Extension DSA版本 DSA Header可选域指示 预留 DSA ID 内容计数 Header扩展域 注1：DSA版本(DSA Version)，区分不同的DSA版本号(0～15)。本部分中DSA版本取值为0。 注2：DSA Header可选域指示(DSA Header Option Indicator)，取值为1表示出现Header扩展域，取值为0表示不出现Header扩展域。 注3：预留(Reserved)，用于扩展。 注4：DSA ID(DSA Identifier)，用于识别DSA的唯一性。 注5：内容计数(Content Count)，用于在DSA ID相同时，识别是否是上一个DSA的重复。 注6：Header扩展域(Header Extension)，预留可用于其他信息。 Application Info域展开见表6，除第一个域外可多次重复。 表6 Application Info域格式 1字节 变量 变量 Application Info Count AID Application Extension Application Info计数 应用标识 应用扩展域 注1：Application Info计数(Application Info Count)，表示后面总共有几个Application Info。 注2：应用标识(AID)，格式见5.2.3.2。 注3：应用扩展域(Application Extension)，指示应用相关的信息。 5.4接入点及服务原语 5.4.1 服务接入点(SAP) 专用短程通信网络层服务接入点见图10。 |
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