C. Michie, A. Kelly, J. Mcgeough, S. Karagiannopoulos, Ivan Andonovic
Passive optical networks (PONs) are being aggressively pursued as a means of delivering access network solutions. The cost benefits resulting from a reduction in the number of interfaces between nodes has enabled increasing deployment of a PON delivering fiber to the home and fiber to the curb. However, in many cases, the need for high split ratios or an extended-reach requires amplification to overcome additional losses. Erbium-doped amplifiers have a limited use in PONs since the operational wavelengths typically include backhaul at 1.3 mu m. Semiconductor optical amplifiers (SOAs) offer a cost-effective solution with a migration path toward integration; deployment options include its use as a preamplifier, booster, or midspan amplifier. We present a theoretical treatment that analyzes the amplified system operational requirements and justifies this analysis through the experiment. The analysis considers for the first time to our knowledge the dc offset that is introduced into the receiver as a result of the significant amplified spontaneous emission powers present in amplified PONs, where filter widths are typically 20 nm or greater.
{"title":"Optically amplified passive optical networks : a power budget analysis","authors":"C. Michie, A. Kelly, J. Mcgeough, S. Karagiannopoulos, Ivan Andonovic","doi":"10.1364/JON.8.000370","DOIUrl":"https://doi.org/10.1364/JON.8.000370","url":null,"abstract":"Passive optical networks (PONs) are being aggressively pursued as a means of delivering access network solutions. The cost benefits resulting from a reduction in the number of interfaces between nodes has enabled increasing deployment of a PON delivering fiber to the home and fiber to the curb. However, in many cases, the need for high split ratios or an extended-reach requires amplification to overcome additional losses. Erbium-doped amplifiers have a limited use in PONs since the operational wavelengths typically include backhaul at 1.3 mu m. Semiconductor optical amplifiers (SOAs) offer a cost-effective solution with a migration path toward integration; deployment options include its use as a preamplifier, booster, or midspan amplifier. We present a theoretical treatment that analyzes the amplified system operational requirements and justifies this analysis through the experiment. The analysis considers for the first time to our knowledge the dc offset that is introduced into the receiver as a result of the significant amplified spontaneous emission powers present in amplified PONs, where filter widths are typically 20 nm or greater.","PeriodicalId":49154,"journal":{"name":"Journal of Optical Networking","volume":"8 1","pages":"370-382"},"PeriodicalIF":0.0,"publicationDate":"2009-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1364/JON.8.000370","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66593232","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}
Operation of all time division multiple access passive optical networks (PONs), regardless of the layer 2 protocol in use, requires the utilization of the so-called discovery process allowing for identification and registration of newly activated optical network units (ONUs). For the duration of the discovery process, all transmissions from already registered ONUs are halted, decreasing the available upstream bandwidth. The number of discovery windows required to successfully register all contending ONUs depends on the collision probability for their registration requests. To decrease such a collision probability for registration requests, several types of collision avoidance mechanisms (CAMs) can be used in various flavors of passive optical network (xPON), as we examine in more detail. A random delay mechanism (RDM) is typically exploited in 1 Gbit/s Ethernet PON (1G-EPON) and gigabit PON (GPON), though other CAMs are also available. It is our goal therefore to examine the efficiency of all known CAMs, compare them in quantitative and qualitative manner, and recommend the best mechanism for the next generation of xPON systems, minimizing the average number of discovery cycles required to register contending ONUs (maximizing thus the registration success probability). The results indicate that RDM is indeed the best of simple, single-stage CAMs available, thus confirming the choice of both the P802.3ah Task Force (TF) and Full Service Access Network (FSAN)/ITU-T at the time when their respective 1G-EPON and GPON specifications were written.
{"title":"Comparison of collision avoidance mechanisms for the discovery process in xPON","authors":"M. Hajduczenia, H. Silva","doi":"10.1364/JON.8.000317","DOIUrl":"https://doi.org/10.1364/JON.8.000317","url":null,"abstract":"Operation of all time division multiple access passive optical networks (PONs), regardless of the layer 2 protocol in use, requires the utilization of the so-called discovery process allowing for identification and registration of newly activated optical network units (ONUs). For the duration of the discovery process, all transmissions from already registered ONUs are halted, decreasing the available upstream bandwidth. The number of discovery windows required to successfully register all contending ONUs depends on the collision probability for their registration requests. To decrease such a collision probability for registration requests, several types of collision avoidance mechanisms (CAMs) can be used in various flavors of passive optical network (xPON), as we examine in more detail. A random delay mechanism (RDM) is typically exploited in 1 Gbit/s Ethernet PON (1G-EPON) and gigabit PON (GPON), though other CAMs are also available. It is our goal therefore to examine the efficiency of all known CAMs, compare them in quantitative and qualitative manner, and recommend the best mechanism for the next generation of xPON systems, minimizing the average number of discovery cycles required to register contending ONUs (maximizing thus the registration success probability). The results indicate that RDM is indeed the best of simple, single-stage CAMs available, thus confirming the choice of both the P802.3ah Task Force (TF) and Full Service Access Network (FSAN)/ITU-T at the time when their respective 1G-EPON and GPON specifications were written.","PeriodicalId":49154,"journal":{"name":"Journal of Optical Networking","volume":"8 1","pages":"317-336"},"PeriodicalIF":0.0,"publicationDate":"2009-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1364/JON.8.000317","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66593470","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}
Presented is a fuzzy-logic-based scheduling algorithm for passive optical networks (PONs) that considers four different metrics to allocate an upstream bandwidth to optical network units (ONUs). The metrics considered are the delay of the head-of-the-line packets at the ONUs, the importance level of the packets, the relative ONU's buffer fullness, and the level of the power fluctuation from one ONU to another. One of the advantages of a fuzzy controller is the fact that, regardless of the design complexity, the controller can be implemented as a simple look-up table, which makes it ideal for high-speed operation. Further facilitation of implementation was achieved by realization of the fuzzy algorithm through a two-stage hierarchal architecture. Moreover, linear predictive filters have been used to predict the traffic arrival rate and the packet delay at the ONUs. Compared with the round-robin scheduling algorithm, the results show significant performance improvement in terms of the overall packets delay as well as jitter when the proposed algorithm in employed. Furthermore, using this algorithm would reduce the average level of power fluctuations in a PON system and will also provide high-level service differentiation between packets of different importance.
{"title":"Multiconstraints fuzzy-logic-based scheduling algorithm for passive optical networks","authors":"R. Razavi, K. Guild","doi":"10.1364/JON.8.000346","DOIUrl":"https://doi.org/10.1364/JON.8.000346","url":null,"abstract":"Presented is a fuzzy-logic-based scheduling algorithm for passive optical networks (PONs) that considers four different metrics to allocate an upstream bandwidth to optical network units (ONUs). The metrics considered are the delay of the head-of-the-line packets at the ONUs, the importance level of the packets, the relative ONU's buffer fullness, and the level of the power fluctuation from one ONU to another. One of the advantages of a fuzzy controller is the fact that, regardless of the design complexity, the controller can be implemented as a simple look-up table, which makes it ideal for high-speed operation. Further facilitation of implementation was achieved by realization of the fuzzy algorithm through a two-stage hierarchal architecture. Moreover, linear predictive filters have been used to predict the traffic arrival rate and the packet delay at the ONUs. Compared with the round-robin scheduling algorithm, the results show significant performance improvement in terms of the overall packets delay as well as jitter when the proposed algorithm in employed. Furthermore, using this algorithm would reduce the average level of power fluctuations in a PON system and will also provide high-level service differentiation between packets of different importance.","PeriodicalId":49154,"journal":{"name":"Journal of Optical Networking","volume":"8 1","pages":"346-357"},"PeriodicalIF":0.0,"publicationDate":"2009-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1364/JON.8.000346","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66593053","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}
Excess bandwidth distribution techniques have recently been proposed to improve the dynamic bandwidth allocation in Ethernet passive optical networks (EPONs). We compare existing offline excess bandwidth distribution with conventional limited interleaved polling with adaptive cycle time (IPACT-limited) in terms of packet delay performance. We identify the factors that result in packet delay reduction with excess bandwidth distribution compared to IPACT-limited and discover that existing offline excess distribution mechanisms become unstable at moderate to high loads in long-range EPONs with large round-trip propagation delays. We propose a novel online excess bandwidth distribution (OEBD) mechanism to provide stable excess bandwidth distribution even at high loads in long-range EPONs. We demonstrate how OEBD can be tuned via parameters to provide grant sizing between limited and gated service.
{"title":"Online excess bandwidth distribution for Ethernet passive optical networks","authors":"Jason R. Ferguson, M. Reisslein, M. Mcgarry","doi":"10.1364/JON.8.000358","DOIUrl":"https://doi.org/10.1364/JON.8.000358","url":null,"abstract":"Excess bandwidth distribution techniques have recently been proposed to improve the dynamic bandwidth allocation in Ethernet passive optical networks (EPONs). We compare existing offline excess bandwidth distribution with conventional limited interleaved polling with adaptive cycle time (IPACT-limited) in terms of packet delay performance. We identify the factors that result in packet delay reduction with excess bandwidth distribution compared to IPACT-limited and discover that existing offline excess distribution mechanisms become unstable at moderate to high loads in long-range EPONs with large round-trip propagation delays. We propose a novel online excess bandwidth distribution (OEBD) mechanism to provide stable excess bandwidth distribution even at high loads in long-range EPONs. We demonstrate how OEBD can be tuned via parameters to provide grant sizing between limited and gated service.","PeriodicalId":49154,"journal":{"name":"Journal of Optical Networking","volume":"8 1","pages":"358-369"},"PeriodicalIF":0.0,"publicationDate":"2009-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1364/JON.8.000358","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66593155","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}
This paper addresses the problem of providing bandwidth and delay guarantees in passive optical networks. To resolve this problem we propose an algorithm that provides absolute bandwidth and delay bound guarantees. Simulation results show that the proposed algorithm does not breach bandwidth and delay bounds for guaranteed service traffic even under the highest loads. Additionally, we analyze the lower bound for providing delay guarantees.
{"title":"Bandwidth and delay guaranteed polling with adaptive cycle time (BDGPACT): a scheme for providing bandwidth and delay guarantees in passive optical networks","authors":"T. Berisa, A. Bazant, V. Mikac","doi":"10.1364/JON.8.000337","DOIUrl":"https://doi.org/10.1364/JON.8.000337","url":null,"abstract":"This paper addresses the problem of providing bandwidth and delay guarantees in passive optical networks. To resolve this problem we propose an algorithm that provides absolute bandwidth and delay bound guarantees. Simulation results show that the proposed algorithm does not breach bandwidth and delay bounds for guaranteed service traffic even under the highest loads. Additionally, we analyze the lower bound for providing delay guarantees.","PeriodicalId":49154,"journal":{"name":"Journal of Optical Networking","volume":"8 1","pages":"337-345"},"PeriodicalIF":0.0,"publicationDate":"2009-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1364/JON.8.000337","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66593487","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}
We propose a dynamic light-path establishment method for using wavelengths effectively. In our proposed method, a proportional, integral, derivative (PID) controller is implemented in each edge node. The edge node determines the amount of data to be transmitted with PID control so that a constant amount of data can be stored in the buffer. In addition, light paths are established and released dynamically by comparing the output signal of the PID controller with the maximum amount of data that can be transmitted with the established light paths. Because data can be stored in the buffer for a short time, it is expected that the number of established light paths decreases. We evaluate the performance of the proposed method and investigate the impact of the setting parameters. The effectiveness of the proposed method is shown through a comparison with the conventional method.
{"title":"Light-path establishment with PID control for effective wavelength utilization in all-optical wavelength-division multiplexing networks","authors":"T. Tachibana, Kenji Sugimoto","doi":"10.1364/JON.8.000383","DOIUrl":"https://doi.org/10.1364/JON.8.000383","url":null,"abstract":"We propose a dynamic light-path establishment method for using wavelengths effectively. In our proposed method, a proportional, integral, derivative (PID) controller is implemented in each edge node. The edge node determines the amount of data to be transmitted with PID control so that a constant amount of data can be stored in the buffer. In addition, light paths are established and released dynamically by comparing the output signal of the PID controller with the maximum amount of data that can be transmitted with the established light paths. Because data can be stored in the buffer for a short time, it is expected that the number of established light paths decreases. We evaluate the performance of the proposed method and investigate the impact of the setting parameters. The effectiveness of the proposed method is shown through a comparison with the conventional method.","PeriodicalId":49154,"journal":{"name":"Journal of Optical Networking","volume":"8 1","pages":"383-392"},"PeriodicalIF":0.0,"publicationDate":"2009-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1364/JON.8.000383","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66593347","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}
We indicate that the frequency drift of WDM light sources for uplink transmission in carrier-distributed WDM-based access networks severely impacts the loss budget. To prevent this, we propose a multifrequency monitoring-stabilization technique that simplifies the configuration of WDM light sources. To achieve more precise frequency stabilization the bias current used to drive each laser diode is dithered. The key techniques are adding an offset bias to the detected error signal and offsetting the center frequency of the array waveguide grating port against the ITU-T grid frequency to achieve effective frequency stabilization. Experiments show that the relative frequency deviation of +/-25 GHz can be suppressed to better than +/-2.5 GHz.
{"title":"Frequency stabilization by dithering bias current of laser diodes for carrier-distributed WDM-based access networks","authors":"M. Fujiwara, H. Suzuki, H. Kimura, K. Kumozaki","doi":"10.1364/JON.8.000295","DOIUrl":"https://doi.org/10.1364/JON.8.000295","url":null,"abstract":"We indicate that the frequency drift of WDM light sources for uplink transmission in carrier-distributed WDM-based access networks severely impacts the loss budget. To prevent this, we propose a multifrequency monitoring-stabilization technique that simplifies the configuration of WDM light sources. To achieve more precise frequency stabilization the bias current used to drive each laser diode is dithered. The key techniques are adding an offset bias to the detected error signal and offsetting the center frequency of the array waveguide grating port against the ITU-T grid frequency to achieve effective frequency stabilization. Experiments show that the relative frequency deviation of +/-25 GHz can be suppressed to better than +/-2.5 GHz.","PeriodicalId":49154,"journal":{"name":"Journal of Optical Networking","volume":"8 1","pages":"295-305"},"PeriodicalIF":0.0,"publicationDate":"2009-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1364/JON.8.000295","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66592971","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}
We demonstrate what we believe to be a novel WDM-PON architecture compatible with radio-over-fiber systems to provide both wired and wireless services. A frequency-quadrupled modulation scheme is employed to generate optical millimeter waves and realize centralized lightwaves in radio-over-fiber systems.
{"title":"Low-cost optical line terminal for a WDM-PON compatible with radio-over-fiber systems","authors":"Z. Dong, J. Lu, Z. Cao, L. Chen","doi":"10.1364/JON.8.000244","DOIUrl":"https://doi.org/10.1364/JON.8.000244","url":null,"abstract":"We demonstrate what we believe to be a novel WDM-PON architecture compatible with radio-over-fiber systems to provide both wired and wireless services. A frequency-quadrupled modulation scheme is employed to generate optical millimeter waves and realize centralized lightwaves in radio-over-fiber systems.","PeriodicalId":49154,"journal":{"name":"Journal of Optical Networking","volume":"8 1","pages":"244-248"},"PeriodicalIF":0.0,"publicationDate":"2009-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1364/JON.8.000244","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66592925","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}
M. Milosavljevic, Y. Shachaf, P. Kourtessis, J. Senior
The interoperability of standard WiMAX and gigabit passive optical networks (GPONs) is shown to overcome the wireless spectrum congestion and provide resilience for GPON through the use of overlapping radio cells. The application of centralized control in the optical line terminal and time division multiplexing for upstream transmission enables efficient dynamic bandwidth allocation for wireless users on a single wavelength as well as minimized optical beat interference at the optical receiver. The viability of bidirectional transmission of multiple uncoded IEEE 802.16d channels by means of a single radio-frequency subcarrier at transmission rates of 50 and 15 Mbits/s downstream and upstream, respectively, for distances of up to 21 km of integrated GPON and WiMAX microcell links is demonstrated.
{"title":"Interoperability of GPON and WiMAX for network capacity enhancement and resilience","authors":"M. Milosavljevic, Y. Shachaf, P. Kourtessis, J. Senior","doi":"10.1364/JON.8.000285","DOIUrl":"https://doi.org/10.1364/JON.8.000285","url":null,"abstract":"The interoperability of standard WiMAX and gigabit passive optical networks (GPONs) is shown to overcome the wireless spectrum congestion and provide resilience for GPON through the use of overlapping radio cells. The application of centralized control in the optical line terminal and time division multiplexing for upstream transmission enables efficient dynamic bandwidth allocation for wireless users on a single wavelength as well as minimized optical beat interference at the optical receiver. The viability of bidirectional transmission of multiple uncoded IEEE 802.16d channels by means of a single radio-frequency subcarrier at transmission rates of 50 and 15 Mbits/s downstream and upstream, respectively, for distances of up to 21 km of integrated GPON and WiMAX microcell links is demonstrated.","PeriodicalId":49154,"journal":{"name":"Journal of Optical Networking","volume":"8 1","pages":"285-294"},"PeriodicalIF":0.0,"publicationDate":"2009-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1364/JON.8.000285","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66592968","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}
Spectral and waveform reshaping schemes can enhance the transmission distance of fiber links that use directly modulated lasers as transmitters. We prove the feasibility of using a simple Fabry-Perot (FP) etalon as the spectral reshaper for applications in wavelength division multiplexing (WDM) access networks. The transient chirp and adiabatic chirp of a directly modulated laser are analyzed in detail by using the time-resolved chirp measurement. The effects of the original extinction ratio and the adiabatic chirp on the spectral reshaping are clarified to obtain the optimal operation conditions. It is shown that placing a single-cavity FP etalon filter after multiple 10 Gbits/s directly modulated lasers can extend their transmission distances from 50 km in the 1.55 μm wavelength window. Due to the limited filtering capability of the etalon, the choice of the original extinction ratio and finesse of the etalon is discussed in detail from the experiments and simulation.
{"title":"Spectral filtering of multiple directly modulated channels for WDM access networks by using an FP etalon","authors":"Shu-Chuan Lin, San-Liang Lee, Chun-Liang Yang","doi":"10.1364/JON.8.000306","DOIUrl":"https://doi.org/10.1364/JON.8.000306","url":null,"abstract":"Spectral and waveform reshaping schemes can enhance the transmission distance of fiber links that use directly modulated lasers as transmitters. We prove the feasibility of using a simple Fabry-Perot (FP) etalon as the spectral reshaper for applications in wavelength division multiplexing (WDM) access networks. The transient chirp and adiabatic chirp of a directly modulated laser are analyzed in detail by using the time-resolved chirp measurement. The effects of the original extinction ratio and the adiabatic chirp on the spectral reshaping are clarified to obtain the optimal operation conditions. It is shown that placing a single-cavity FP etalon filter after multiple 10 Gbits/s directly modulated lasers can extend their transmission distances from 50 km in the 1.55 μm wavelength window. Due to the limited filtering capability of the etalon, the choice of the original extinction ratio and finesse of the etalon is discussed in detail from the experiments and simulation.","PeriodicalId":49154,"journal":{"name":"Journal of Optical Networking","volume":"8 1","pages":"306-316"},"PeriodicalIF":0.0,"publicationDate":"2009-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1364/JON.8.000306","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66593462","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：