Pub Date : 2018-12-01DOI: 10.1109/VNC.2018.8628386
M. Sepulcre, Pedro Tercero, J. Gozálvez
Significant efforts have been devoted to date to the congestion control problem in vehicular networks. The solutions proposed so far have been designed to adapt the communication parameters to reduce and control the channel load. A totally different approach would be the compression of the data generated by each vehicle. This paper proposes and explores for the first time the use of data compression to reduce the channel load in vehicular networks. By compressing and decompressing V2X messages, the channel load generated could be reduced, thereby decreasing the interference and packet loses due to collisions. We apply this idea in this study to CAMs using existing data compression tools to have a first estimate of the compression gain that could be achieved, and the time needed to compress and decompress. The results obtained show that the CAM length could be reduced by up to around 14%, which is a non-negligible percentage given the relevance of the congestion control problem. The data compression and decompression times obtained demonstrate its potential for its integration in V2X devices. The results obtained motivate to more deeply investigate the compression of V2X messages in vehicular networks.
{"title":"Can Beacons be Compressed to Reduce the Channel Load in Vehicular Networks?","authors":"M. Sepulcre, Pedro Tercero, J. Gozálvez","doi":"10.1109/VNC.2018.8628386","DOIUrl":"https://doi.org/10.1109/VNC.2018.8628386","url":null,"abstract":"Significant efforts have been devoted to date to the congestion control problem in vehicular networks. The solutions proposed so far have been designed to adapt the communication parameters to reduce and control the channel load. A totally different approach would be the compression of the data generated by each vehicle. This paper proposes and explores for the first time the use of data compression to reduce the channel load in vehicular networks. By compressing and decompressing V2X messages, the channel load generated could be reduced, thereby decreasing the interference and packet loses due to collisions. We apply this idea in this study to CAMs using existing data compression tools to have a first estimate of the compression gain that could be achieved, and the time needed to compress and decompress. The results obtained show that the CAM length could be reduced by up to around 14%, which is a non-negligible percentage given the relevance of the congestion control problem. The data compression and decompression times obtained demonstrate its potential for its integration in V2X devices. The results obtained motivate to more deeply investigate the compression of V2X messages in vehicular networks.","PeriodicalId":335017,"journal":{"name":"2018 IEEE Vehicular Networking Conference (VNC)","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124545735","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-12-01DOI: 10.1109/VNC.2018.8628441
Wongoo Han, Sangrok Han, Hyogon Kim
TCP protocol optimized for the general Internet environment can fail to maximally realize its potential in the in-vehicular network environment such as the automotive Ethernet. In this paper, we demonstrate that a throughput pathology can develop in the TCP communication between two ECUs that are typically lower-speed machines. We find that it stems from how the processing power is divided between the TCP kernel packet processing and the sending application at the TCP sender side. Moreover, once it sets in, it persistently decreases the TCP throughput by few tens of megabits per second (Mbps) over an extended period of time. Through kernel profiling and TCP code analysis, we prescribe a remedy that solves the pathology and enables ECUs to fully materialize the maximum throughput.
{"title":"On TCP Throughput Pathology in CPU-Bound Communication over Automotive Ethernet","authors":"Wongoo Han, Sangrok Han, Hyogon Kim","doi":"10.1109/VNC.2018.8628441","DOIUrl":"https://doi.org/10.1109/VNC.2018.8628441","url":null,"abstract":"TCP protocol optimized for the general Internet environment can fail to maximally realize its potential in the in-vehicular network environment such as the automotive Ethernet. In this paper, we demonstrate that a throughput pathology can develop in the TCP communication between two ECUs that are typically lower-speed machines. We find that it stems from how the processing power is divided between the TCP kernel packet processing and the sending application at the TCP sender side. Moreover, once it sets in, it persistently decreases the TCP throughput by few tens of megabits per second (Mbps) over an extended period of time. Through kernel profiling and TCP code analysis, we prescribe a remedy that solves the pathology and enables ECUs to fully materialize the maximum throughput.","PeriodicalId":335017,"journal":{"name":"2018 IEEE Vehicular Networking Conference (VNC)","volume":"85 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125697302","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-12-01DOI: 10.1109/VNC.2018.8628399
Santos Jha, Chaitanya Yavvari, D. Wijesekera
The Security Credential Management System (SCMS) has been proposed to provide a trust framework that ensures integrity, authenticity, and unlinkability of DSRC messages by issuing pseudonyms with implicit certificates. Nevertheless, validating the integrity and authenticity of a message at an On-Board Unit (OBU) incurs processing delays of about 22ms. Given that Basic Safety Messages (BSMs) are emitted by every vehicle at a rate of 10Hz creates many messages to be validated by an ego vehicle under heavy vehicular traffic. Such traffic loads may create delays in the processing of safety critical messages. In order to avoid such delays, we propose a message processing algorithm that provides a 3 level processing priority based on the immediate neighborhood of an ego vehicle. We show that our algorithm performs well under increasing vehicular traffic loads on realistic highway scenarios measured with respect to message deadline miss ratios and accumulating unprocessed message queue lengths. Further, we propose extending SCMS with cross certification capabilities in order to facilitate seamless certificate validation across administrative boundaries with individualized SCMS trust roots.
{"title":"Pseudonym Certificate Validations under Heavy Vehicular Traffic Loads","authors":"Santos Jha, Chaitanya Yavvari, D. Wijesekera","doi":"10.1109/VNC.2018.8628399","DOIUrl":"https://doi.org/10.1109/VNC.2018.8628399","url":null,"abstract":"The Security Credential Management System (SCMS) has been proposed to provide a trust framework that ensures integrity, authenticity, and unlinkability of DSRC messages by issuing pseudonyms with implicit certificates. Nevertheless, validating the integrity and authenticity of a message at an On-Board Unit (OBU) incurs processing delays of about 22ms. Given that Basic Safety Messages (BSMs) are emitted by every vehicle at a rate of 10Hz creates many messages to be validated by an ego vehicle under heavy vehicular traffic. Such traffic loads may create delays in the processing of safety critical messages. In order to avoid such delays, we propose a message processing algorithm that provides a 3 level processing priority based on the immediate neighborhood of an ego vehicle. We show that our algorithm performs well under increasing vehicular traffic loads on realistic highway scenarios measured with respect to message deadline miss ratios and accumulating unprocessed message queue lengths. Further, we propose extending SCMS with cross certification capabilities in order to facilitate seamless certificate validation across administrative boundaries with individualized SCMS trust roots.","PeriodicalId":335017,"journal":{"name":"2018 IEEE Vehicular Networking Conference (VNC)","volume":"43 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128155644","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-12-01DOI: 10.1109/VNC.2018.8628465
Ritayan Biswas, Joonas Säe, Jukka Lempiäinen
The objective of this article is to extend the range of Ambient Backscattering Communications (ABC). The ABC technology is a key enabling technologies for Internet of Things (IoT) wireless communications. A rural open area towards Hanko, Finland is considered for the power budget calculations. FM radio waves are considered as the source of ambient RF waves as the FM radio waves have long communication range and the technology is readily available worldwide. The sensors are placed on a highway at an example distance of 30 km from the FM transmitter. There is a clear line of sight (LOS) connection between the FM transmitter and the sensors. The path loss is determined based on the sensor locations and the losses at the sensor occur due to diffraction and scattering. A power budget is calculated based on these aforementioned key system parameters. It is observed that there is around 44 dB of power margin available after the signal from the FM transmitter is backscattered (at the sensor) and the losses in the system are accounted for. This indicates that the receiver module is able to detect the signal as it is above the minimum reception level threshold for the system. Therefore, the radio waves are able to propagate further after the signal is backscattered at the sensor(s) utilizing the available power margin. Thus, the range of communication can be extended to a wider area.
{"title":"Power Budget for Wide Area Ambient Backscattering Communications","authors":"Ritayan Biswas, Joonas Säe, Jukka Lempiäinen","doi":"10.1109/VNC.2018.8628465","DOIUrl":"https://doi.org/10.1109/VNC.2018.8628465","url":null,"abstract":"The objective of this article is to extend the range of Ambient Backscattering Communications (ABC). The ABC technology is a key enabling technologies for Internet of Things (IoT) wireless communications. A rural open area towards Hanko, Finland is considered for the power budget calculations. FM radio waves are considered as the source of ambient RF waves as the FM radio waves have long communication range and the technology is readily available worldwide. The sensors are placed on a highway at an example distance of 30 km from the FM transmitter. There is a clear line of sight (LOS) connection between the FM transmitter and the sensors. The path loss is determined based on the sensor locations and the losses at the sensor occur due to diffraction and scattering. A power budget is calculated based on these aforementioned key system parameters. It is observed that there is around 44 dB of power margin available after the signal from the FM transmitter is backscattered (at the sensor) and the losses in the system are accounted for. This indicates that the receiver module is able to detect the signal as it is above the minimum reception level threshold for the system. Therefore, the radio waves are able to propagate further after the signal is backscattered at the sensor(s) utilizing the available power margin. Thus, the range of communication can be extended to a wider area.","PeriodicalId":335017,"journal":{"name":"2018 IEEE Vehicular Networking Conference (VNC)","volume":"108 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115070193","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-12-01DOI: 10.1109/VNC.2018.8628360
Mohammad Hamad, M. R. Agha, V. Prevelakis
Vehicular Ad hoc Network (VANET) is a very promising approach that aims to improve vehicle and road safety, traffic efficiency, as well as comfortability to both drivers and passengers. Different types of applications were implemented to achieve these goals. Some of these applications require the exchanging of multiple and ordered messages as well as the existence of a stable Internet connection. However, the high node mobility of VANET seems to be one of the main stumbling blocks for adopting such applications. In this paper, we have investigated through a real experiment, how the VANET mobility imposes challenges in establishing and maintaining a long-lasting connection. In addition, we have proposed a mechanism to improve the communication efficiency over VANETs. Our solution is based on the concept of intelligent proxies that can be sent from, say, one Roadside Unit to a vehicle so that the negotiation between them can be delegated to the proxy and take place locally. Using the proxy will reduce the number of exchanged network messages among vehicles and infrastructure, overcome the intermittent and short-lived connectivity challenge of the high mobility vehicular network and, consequently, increase the communication efficacy. Also, we have presented a framework that allows such proxies to operate safely and securely.
{"title":"ProSEV: Proxy-Based Secure and Efficient Vehicular Communication","authors":"Mohammad Hamad, M. R. Agha, V. Prevelakis","doi":"10.1109/VNC.2018.8628360","DOIUrl":"https://doi.org/10.1109/VNC.2018.8628360","url":null,"abstract":"Vehicular Ad hoc Network (VANET) is a very promising approach that aims to improve vehicle and road safety, traffic efficiency, as well as comfortability to both drivers and passengers. Different types of applications were implemented to achieve these goals. Some of these applications require the exchanging of multiple and ordered messages as well as the existence of a stable Internet connection. However, the high node mobility of VANET seems to be one of the main stumbling blocks for adopting such applications. In this paper, we have investigated through a real experiment, how the VANET mobility imposes challenges in establishing and maintaining a long-lasting connection. In addition, we have proposed a mechanism to improve the communication efficiency over VANETs. Our solution is based on the concept of intelligent proxies that can be sent from, say, one Roadside Unit to a vehicle so that the negotiation between them can be delegated to the proxy and take place locally. Using the proxy will reduce the number of exchanged network messages among vehicles and infrastructure, overcome the intermittent and short-lived connectivity challenge of the high mobility vehicular network and, consequently, increase the communication efficacy. Also, we have presented a framework that allows such proxies to operate safely and securely.","PeriodicalId":335017,"journal":{"name":"2018 IEEE Vehicular Networking Conference (VNC)","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114622290","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-12-01DOI: 10.1109/VNC.2018.8628364
Chang-Heng Wang, O. Altintas
The growing interest in connected and autonomous vehicles is expected to create significant traffic demands and impose serious challenge for currently allocated vehicular communication frequency bands such as 5.9 GHz band. Meanwhile, the wide bandwidth in 79 GHz band dedicated for automotive radar may greatly support such traffic demand if a joint automotive radar and communication system is deployed. In this demo, we present a preliminary proof of concept for a joint automotive radar and communication system based on commercial off-the-shelf automotive radars. In particular, the system modulates data using frequency shift keying (FSK) upon widely adopted frequency modulated continuous wave (FMCW) automotive radar.
{"title":"Demo: A Joint Radar and Communication System Based on Commercially Available FMCW Radar","authors":"Chang-Heng Wang, O. Altintas","doi":"10.1109/VNC.2018.8628364","DOIUrl":"https://doi.org/10.1109/VNC.2018.8628364","url":null,"abstract":"The growing interest in connected and autonomous vehicles is expected to create significant traffic demands and impose serious challenge for currently allocated vehicular communication frequency bands such as 5.9 GHz band. Meanwhile, the wide bandwidth in 79 GHz band dedicated for automotive radar may greatly support such traffic demand if a joint automotive radar and communication system is deployed. In this demo, we present a preliminary proof of concept for a joint automotive radar and communication system based on commercial off-the-shelf automotive radars. In particular, the system modulates data using frequency shift keying (FSK) upon widely adopted frequency modulated continuous wave (FMCW) automotive radar.","PeriodicalId":335017,"journal":{"name":"2018 IEEE Vehicular Networking Conference (VNC)","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115988972","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-12-01DOI: 10.1109/VNC.2018.8628444
Agon Memedi, Claas Tebruegge, Julien Jahneke, F. Dressler
We investigate the impact of various headlight modules and corresponding vehicle types on the performance of Vehicular VLC (V-VLC). V-VLC is currently considered as a quite promising communication technology that is complementary to existing wireless radio-based systems. Being a line of sight communication system, V-VLC is suggested mainly for shorter range communication causing little interference to concurrently performed transmissions. Given the very promising results in the literature, we study the impact of realistic headlight modules and vehicle types. Based on photometric data and experimental validation, we show that there is a substantial impact on the communication performance. The different light distribution patterns result in a varying light density and, therefore, packet delivery ratio. We see our models as an important step towards turning V-VLC into a reliable communication technology.
{"title":"Impact of Vehicle Type and Headlight Characteristics on Vehicular VLC Performance","authors":"Agon Memedi, Claas Tebruegge, Julien Jahneke, F. Dressler","doi":"10.1109/VNC.2018.8628444","DOIUrl":"https://doi.org/10.1109/VNC.2018.8628444","url":null,"abstract":"We investigate the impact of various headlight modules and corresponding vehicle types on the performance of Vehicular VLC (V-VLC). V-VLC is currently considered as a quite promising communication technology that is complementary to existing wireless radio-based systems. Being a line of sight communication system, V-VLC is suggested mainly for shorter range communication causing little interference to concurrently performed transmissions. Given the very promising results in the literature, we study the impact of realistic headlight modules and vehicle types. Based on photometric data and experimental validation, we show that there is a substantial impact on the communication performance. The different light distribution patterns result in a varying light density and, therefore, packet delivery ratio. We see our models as an important step towards turning V-VLC into a reliable communication technology.","PeriodicalId":335017,"journal":{"name":"2018 IEEE Vehicular Networking Conference (VNC)","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122534642","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-12-01DOI: 10.1109/VNC.2018.8628443
D. Umehara, Takeyuki Shishido
Controller area network (CAN) is widely distributed as an in-vehicle communications standard. CAN with flexible data-rate (CAN FD) is defined in the ISO standards to achieve higher data rate than the legacy CAN. A number of CAN nodes are able to connect with a single transmission medium, i.e. CAN enables us to constitute cost-effective bus-topology networks. CAN puts carrier sense multiple access with collision resolution (CSMA/CR) into practice by using bit-wise arbitration based on wired logical AND in the physical layer. The prioritized message is delivered without interruption if two or more CAN nodes transmit messages at the same time thanks to the bit-wise arbitration. However, the scalability of CAN networks suffers from ringing caused by the signaling mechanism establishing the wired logical AND. We need to reduce networking materials in order to reduce the car weight, save the fuel and the cost, and develop a sustainable society by establishing more scalable CAN networks. In this paper, we show the reduced wiring technology for CAN to enhance the network scalability and the cost efficiency.
{"title":"Ringing Mitigation Schemes for Controller Area Network","authors":"D. Umehara, Takeyuki Shishido","doi":"10.1109/VNC.2018.8628443","DOIUrl":"https://doi.org/10.1109/VNC.2018.8628443","url":null,"abstract":"Controller area network (CAN) is widely distributed as an in-vehicle communications standard. CAN with flexible data-rate (CAN FD) is defined in the ISO standards to achieve higher data rate than the legacy CAN. A number of CAN nodes are able to connect with a single transmission medium, i.e. CAN enables us to constitute cost-effective bus-topology networks. CAN puts carrier sense multiple access with collision resolution (CSMA/CR) into practice by using bit-wise arbitration based on wired logical AND in the physical layer. The prioritized message is delivered without interruption if two or more CAN nodes transmit messages at the same time thanks to the bit-wise arbitration. However, the scalability of CAN networks suffers from ringing caused by the signaling mechanism establishing the wired logical AND. We need to reduce networking materials in order to reduce the car weight, save the fuel and the cost, and develop a sustainable society by establishing more scalable CAN networks. In this paper, we show the reduced wiring technology for CAN to enhance the network scalability and the cost efficiency.","PeriodicalId":335017,"journal":{"name":"2018 IEEE Vehicular Networking Conference (VNC)","volume":"86 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123304692","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-12-01DOI: 10.1109/VNC.2018.8628345
Wen-Ping Lai, Kuan-Chun Chiu
Network functions virtualization (NFV) based service chaining is one of the key enablers to speed up innovations of 5G networks for differential service needs in terms of network slicing. In this demonstration, we showcase automatic deployment of a service chain or slice (i.e., a load-balanced web-database system with memory cache), consisting of 4 different virtual network functions (VNFs) connected with proper mutual relations, on a x86-PC bare metal server running with Linux. Dynamic scaling-up of such a service chain without service interruption is also demonstrated by adding one more web server, during the run time, based on the fact that its relations with the others can be automatically copied and established. Our stress tests show the load*duration responses with the stress level before and after the scaling-up, and their difference becomes dramatically amplified as the stress level gets high.
{"title":"Demo: Automatic Deployment and Dynamic Scaling of NFV Service Chaining on Bare Metal (SCBM)","authors":"Wen-Ping Lai, Kuan-Chun Chiu","doi":"10.1109/VNC.2018.8628345","DOIUrl":"https://doi.org/10.1109/VNC.2018.8628345","url":null,"abstract":"Network functions virtualization (NFV) based service chaining is one of the key enablers to speed up innovations of 5G networks for differential service needs in terms of network slicing. In this demonstration, we showcase automatic deployment of a service chain or slice (i.e., a load-balanced web-database system with memory cache), consisting of 4 different virtual network functions (VNFs) connected with proper mutual relations, on a x86-PC bare metal server running with Linux. Dynamic scaling-up of such a service chain without service interruption is also demonstrated by adding one more web server, during the run time, based on the fact that its relations with the others can be automatically copied and established. Our stress tests show the load*duration responses with the stress level before and after the scaling-up, and their difference becomes dramatically amplified as the stress level gets high.","PeriodicalId":335017,"journal":{"name":"2018 IEEE Vehicular Networking Conference (VNC)","volume":"75 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129314079","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：