Pub Date : 2002-07-02DOI: 10.1109/ICDCS.2002.1022304
Paulo Sérgio Almeida, Carlos Baquero, V. Fonte
Version vectors and their variants play a central role in update tracking in optimistic distributed systems. Existing mechanisms for a variable number of participants use a mapping from identities to integers, and rely on some form of global configuration or distributed naming protocol to assign unique identifiers to each participant. These approaches are incompatible with replica creation under arbitrary partitions, a typical mode of operation in mobile or poorly connected environments. We present an update tracking mechanism that overcomes this limitation; it departs from the traditional mapping and avoids the use of integer counters, while providing all the functionality of version vectors in what concerns version tracking.
{"title":"Version stamps-decentralized version vectors","authors":"Paulo Sérgio Almeida, Carlos Baquero, V. Fonte","doi":"10.1109/ICDCS.2002.1022304","DOIUrl":"https://doi.org/10.1109/ICDCS.2002.1022304","url":null,"abstract":"Version vectors and their variants play a central role in update tracking in optimistic distributed systems. Existing mechanisms for a variable number of participants use a mapping from identities to integers, and rely on some form of global configuration or distributed naming protocol to assign unique identifiers to each participant. These approaches are incompatible with replica creation under arbitrary partitions, a typical mode of operation in mobile or poorly connected environments. We present an update tracking mechanism that overcomes this limitation; it departs from the traditional mapping and avoids the use of integer counters, while providing all the functionality of version vectors in what concerns version tracking.","PeriodicalId":186210,"journal":{"name":"Proceedings 22nd International Conference on Distributed Computing Systems","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125142978","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 : 2002-07-02DOI: 10.1109/ICDCS.2002.1022244
J. Al-Muhtadi, R. Campbell, Apu Kapadia, M. D. Mickunas, Seung Yi
Ubiquitous computing is poised to revolutionize the way we compute and interact with each other. However, unless privacy concerns are taken into account early in the design process, we will end up creating a very effective distributed surveillance system, which would be a dream come true for electronic stalkers and "big brothers". We present a protocol, which preserves the privacy of users and keeps their communication anonymous. In effect, we create a "mist" that conceals users from the system and other users. Yet, users will still be able to enjoy seamless interaction with services and other entities that wander within the ubiquitous computing environment.
{"title":"Routing through the mist: privacy preserving communication in ubiquitous computing environments","authors":"J. Al-Muhtadi, R. Campbell, Apu Kapadia, M. D. Mickunas, Seung Yi","doi":"10.1109/ICDCS.2002.1022244","DOIUrl":"https://doi.org/10.1109/ICDCS.2002.1022244","url":null,"abstract":"Ubiquitous computing is poised to revolutionize the way we compute and interact with each other. However, unless privacy concerns are taken into account early in the design process, we will end up creating a very effective distributed surveillance system, which would be a dream come true for electronic stalkers and \"big brothers\". We present a protocol, which preserves the privacy of users and keeps their communication anonymous. In effect, we create a \"mist\" that conceals users from the system and other users. Yet, users will still be able to enjoy seamless interaction with services and other entities that wander within the ubiquitous computing environment.","PeriodicalId":186210,"journal":{"name":"Proceedings 22nd International Conference on Distributed Computing Systems","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114821089","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 : 2002-07-02DOI: 10.1109/ICDCS.2002.1022241
A. Messer, I. Greenberg, P. Bernadat, D. Milojicic, DeQing Chen, T. J. Giuli, Xiaohui Gu
Many visions of the future predict a world with pervasive computing, where computing services and resources permeate the environment. In these visions, people will want to execute a service on any available device without worrying about whether the service has been tailored for the device. We believe that it will be difficult to create services that can execute well on the wide variety of devices that are being developed because of problems with diversity and resource constraints. We believe that these problems can be greatly reduced by using an ad-hoc distributed platform to transparently off-load portions of a service from a resource-constrained device to a nearby server. We implemented a preliminary prototype and emulator to study this approach. Our experiments show the beneficial use of nearby resources to relieve both memory and processing constraints, when it is appropriate to do so. We believe that this approach will reduce the burden on developers by masking more device details.
{"title":"Towards a distributed platform for resource-constrained devices","authors":"A. Messer, I. Greenberg, P. Bernadat, D. Milojicic, DeQing Chen, T. J. Giuli, Xiaohui Gu","doi":"10.1109/ICDCS.2002.1022241","DOIUrl":"https://doi.org/10.1109/ICDCS.2002.1022241","url":null,"abstract":"Many visions of the future predict a world with pervasive computing, where computing services and resources permeate the environment. In these visions, people will want to execute a service on any available device without worrying about whether the service has been tailored for the device. We believe that it will be difficult to create services that can execute well on the wide variety of devices that are being developed because of problems with diversity and resource constraints. We believe that these problems can be greatly reduced by using an ad-hoc distributed platform to transparently off-load portions of a service from a resource-constrained device to a nearby server. We implemented a preliminary prototype and emulator to study this approach. Our experiments show the beneficial use of nearby resources to relieve both memory and processing constraints, when it is appropriate to do so. We believe that this approach will reduce the burden on developers by masking more device details.","PeriodicalId":186210,"journal":{"name":"Proceedings 22nd International Conference on Distributed Computing Systems","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123873556","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 : 2002-07-02DOI: 10.1109/ICDCS.2002.1022250
A. Riabov, Zhen Liu, J. Wolf, Philip S. Yu, Li Zhang
We consider efficient communication schemes based on both network-supported and application-level multicast techniques for content-based publication-subscription systems. We show that the communication costs depend heavily on the network configurations, distribution of publications and subscriptions. We devise new algorithms and adapt existing partitional data clustering algorithms. These algorithms can be used to determine multicast groups with as much commonality as possible, based on the totality of subscribers' interests. They perform well in the context of highly heterogeneous subscriptions, and they also scale well. An efficiency of 60% to 80% with respect to the ideal solution can be achieved with a small number of multicast groups (less than 100 in our experiments). Some of these same concepts can be applied to match publications to subscribers in real-time, and also to determine dynamically whether to unicast, multicast or broadcast information about the events over the network to the matched subscribers. We demonstrate the quality of our algorithms via simulation experiments.
{"title":"Clustering algorithms for content-based publication-subscription systems","authors":"A. Riabov, Zhen Liu, J. Wolf, Philip S. Yu, Li Zhang","doi":"10.1109/ICDCS.2002.1022250","DOIUrl":"https://doi.org/10.1109/ICDCS.2002.1022250","url":null,"abstract":"We consider efficient communication schemes based on both network-supported and application-level multicast techniques for content-based publication-subscription systems. We show that the communication costs depend heavily on the network configurations, distribution of publications and subscriptions. We devise new algorithms and adapt existing partitional data clustering algorithms. These algorithms can be used to determine multicast groups with as much commonality as possible, based on the totality of subscribers' interests. They perform well in the context of highly heterogeneous subscriptions, and they also scale well. An efficiency of 60% to 80% with respect to the ideal solution can be achieved with a small number of multicast groups (less than 100 in our experiments). Some of these same concepts can be applied to match publications to subscribers in real-time, and also to determine dynamically whether to unicast, multicast or broadcast information about the events over the network to the matched subscribers. We demonstrate the quality of our algorithms via simulation experiments.","PeriodicalId":186210,"journal":{"name":"Proceedings 22nd International Conference on Distributed Computing Systems","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125414064","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 : 2002-07-02DOI: 10.1109/ICDCS.2002.1022273
Sébastien Baehni, P. Eugster, R. Guerraoui
Just as the remote procedure call (RPC) turned out to be a very effective OS abstraction in building client-server applications over LANs, type-based publish-subscribe (TPS) can be viewed as a high-level candidate abstraction for building peer-to-peer (P2P) applications over WANs. This paper relates our preliminary, though positive, experience of implementing and using TPS over JXTA, which can be viewed as the P2P counterpart to sockets. We show that, at least for P2P applications with the Java type model, TPS provides a high-level programming support that ensures type safety and encapsulation, without hampering the decoupled nature of these applications. Furthermore, the loss of flexibility (inherent to the use of any high level abstraction) and the performance overhead, are negligible with respect to the simplicity gained by using TPS.
{"title":"OS support for P2P programming: a case for TPS","authors":"Sébastien Baehni, P. Eugster, R. Guerraoui","doi":"10.1109/ICDCS.2002.1022273","DOIUrl":"https://doi.org/10.1109/ICDCS.2002.1022273","url":null,"abstract":"Just as the remote procedure call (RPC) turned out to be a very effective OS abstraction in building client-server applications over LANs, type-based publish-subscribe (TPS) can be viewed as a high-level candidate abstraction for building peer-to-peer (P2P) applications over WANs. This paper relates our preliminary, though positive, experience of implementing and using TPS over JXTA, which can be viewed as the P2P counterpart to sockets. We show that, at least for P2P applications with the Java type model, TPS provides a high-level programming support that ensures type safety and encapsulation, without hampering the decoupled nature of these applications. Furthermore, the loss of flexibility (inherent to the use of any high level abstraction) and the performance overhead, are negligible with respect to the simplicity gained by using TPS.","PeriodicalId":186210,"journal":{"name":"Proceedings 22nd International Conference on Distributed Computing Systems","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129515879","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 : 2002-07-02DOI: 10.1109/ICDCS.2002.1022277
A. Tripathi, Tanvir Ahmed, Richa Kumar, Shremattie Jaman
We present the execution model of policy-driven middleware for building secure distributed collaboration systems from their high level specifications. Our specification model supports nested collaboration activities, and uses role-based security policies and event count based coordination specification. From the specifications of a collaboration environment, appropriate policy modules are derived for enforcing security and coordination requirements. Policy-driven distributed middleware provides services to users to join roles in an activity, perform role specific operations, or create new activities. We describe the design challenges for middleware and present the run-time structures and protocols supported by it for creating activities, roles, and objects.
{"title":"Design of a policy-driven middleware for secure distributed collaboration","authors":"A. Tripathi, Tanvir Ahmed, Richa Kumar, Shremattie Jaman","doi":"10.1109/ICDCS.2002.1022277","DOIUrl":"https://doi.org/10.1109/ICDCS.2002.1022277","url":null,"abstract":"We present the execution model of policy-driven middleware for building secure distributed collaboration systems from their high level specifications. Our specification model supports nested collaboration activities, and uses role-based security policies and event count based coordination specification. From the specifications of a collaboration environment, appropriate policy modules are derived for enforcing security and coordination requirements. Policy-driven distributed middleware provides services to users to join roles in an activity, perform role specific operations, or create new activities. We describe the design challenges for middleware and present the run-time structures and protocols supported by it for creating activities, roles, and objects.","PeriodicalId":186210,"journal":{"name":"Proceedings 22nd International Conference on Distributed Computing Systems","volume":"238 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121306347","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 : 2002-07-02DOI: 10.1109/ICDCS.2002.1022305
V. Garg, Chakarat Skawratananond
We present a method of timestamping messages and events in synchronous computations that capture the order relationship with vectors of size less than or equal to the size of the vertex cover of the communication topology of the system. Our method is fundamentally different from the techniques of Fidge (1989) and Mattern (1989). The timestamps in our method do not use one component per process but still guarantee that the order relationship is captured accurately. Our algorithm is online and only requires piggybacking of timestamps on program messages. It is applicable to all programs that either use programming languages based on synchronous communication such as CSP or use synchronous remote procedure calls.
{"title":"Timestamping messages in synchronous computations","authors":"V. Garg, Chakarat Skawratananond","doi":"10.1109/ICDCS.2002.1022305","DOIUrl":"https://doi.org/10.1109/ICDCS.2002.1022305","url":null,"abstract":"We present a method of timestamping messages and events in synchronous computations that capture the order relationship with vectors of size less than or equal to the size of the vertex cover of the communication topology of the system. Our method is fundamentally different from the techniques of Fidge (1989) and Mattern (1989). The timestamps in our method do not use one component per process but still guarantee that the order relationship is captured accurately. Our algorithm is online and only requires piggybacking of timestamps on program messages. It is applicable to all programs that either use programming languages based on synchronous communication such as CSP or use synchronous remote procedure calls.","PeriodicalId":186210,"journal":{"name":"Proceedings 22nd International Conference on Distributed Computing Systems","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116474263","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 : 2002-07-02DOI: 10.1109/ICDCS.2002.1022281
H. Khurana, V. Gligor, J. Linn
We argue that joint administration of access policies for a dynamic coalition formed by autonomous domains requires that these domains set up a coalition authority that distributes attribute certificates authorizing access to policy objects (e.g., ACLs). Control over the issuance of such certificates is retained by member domains separately holding shares of the joint coalition authority's private key with which they sign the attribute certificates. Hence, any (proper) subset of the member domains need not be trusted to protect the private key. However, application servers that implement joint administration of access policies based on attribute certificates must trust all the signers of those certificates, namely all member domains of the coalition. To capture these trust relations we extend existing access control logics and show that the extensions are sound. To reason about joint administration of access policies, we illustrate an authorization protocol in our logic for accessing policy objects using threshold attribute certificates.
{"title":"Reasoning about joint administration of access policies for coalition resources","authors":"H. Khurana, V. Gligor, J. Linn","doi":"10.1109/ICDCS.2002.1022281","DOIUrl":"https://doi.org/10.1109/ICDCS.2002.1022281","url":null,"abstract":"We argue that joint administration of access policies for a dynamic coalition formed by autonomous domains requires that these domains set up a coalition authority that distributes attribute certificates authorizing access to policy objects (e.g., ACLs). Control over the issuance of such certificates is retained by member domains separately holding shares of the joint coalition authority's private key with which they sign the attribute certificates. Hence, any (proper) subset of the member domains need not be trusted to protect the private key. However, application servers that implement joint administration of access policies based on attribute certificates must trust all the signers of those certificates, namely all member domains of the coalition. To capture these trust relations we extend existing access control logics and show that the extensions are sound. To reason about joint administration of access policies, we illustrate an authorization protocol in our logic for accessing policy objects using threshold attribute certificates.","PeriodicalId":186210,"journal":{"name":"Proceedings 22nd International Conference on Distributed Computing Systems","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125119035","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 : 2002-07-02DOI: 10.1109/ICDCS.2002.1022252
Shudong Jin, Azer Bestavros, A. Iyengar
Internet streaming applications are affected by adverse network conditions such as high packet loss rates and long delays. This paper aims at mitigating such effects by leveraging the availability of client-side caching proxies. We present a novel caching architecture and associated cache management algorithms that turn edge caches into accelerators of streaming media delivery. A salient feature of our caching algorithms is that they allow partial caching of streaming media objects and joint delivery of content from caches and origin servers. The caching algorithms we propose are both network-aware and stream-aware; they take into account the popularity of streaming media objects, their bit-rate requirements, and the available bandwidth between clients and servers. Using realistic models of Internet bandwidth derived from proxy cache logs and measured over real Internet paths, we have conducted simulations to evaluate the performance of various cache management alternatives. Our experiments demonstrate that network-aware caching algorithms can significantly reduce service delay and improve overall stream quality. Our experiments also show that partial caching is particularly effective when bandwidth variability is not very high.
{"title":"Accelerating Internet streaming media delivery using network-aware partial caching","authors":"Shudong Jin, Azer Bestavros, A. Iyengar","doi":"10.1109/ICDCS.2002.1022252","DOIUrl":"https://doi.org/10.1109/ICDCS.2002.1022252","url":null,"abstract":"Internet streaming applications are affected by adverse network conditions such as high packet loss rates and long delays. This paper aims at mitigating such effects by leveraging the availability of client-side caching proxies. We present a novel caching architecture and associated cache management algorithms that turn edge caches into accelerators of streaming media delivery. A salient feature of our caching algorithms is that they allow partial caching of streaming media objects and joint delivery of content from caches and origin servers. The caching algorithms we propose are both network-aware and stream-aware; they take into account the popularity of streaming media objects, their bit-rate requirements, and the available bandwidth between clients and servers. Using realistic models of Internet bandwidth derived from proxy cache logs and measured over real Internet paths, we have conducted simulations to evaluate the performance of various cache management alternatives. Our experiments demonstrate that network-aware caching algorithms can significantly reduce service delay and improve overall stream quality. Our experiments also show that partial caching is particularly effective when bandwidth variability is not very high.","PeriodicalId":186210,"journal":{"name":"Proceedings 22nd International Conference on Distributed Computing Systems","volume":"142 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131901168","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 : 2002-07-02DOI: 10.1109/ICDCS.2002.1022266
Wenbing Zhao, L. Moser, P. Melliar-Smith
In this paper we describe a software infrastructure that unifies replication and transaction processing in three-tier architectures and, thus, provides high availability and fault tolerance for enterprise applications. The infrastructure is based on the Fault Tolerant CORBA and CORBA Object Transaction Service standards, and works with commercial-off-the-shelf application servers and database systems. The infrastructure replicates the application servers to protect the business logic processing. In addition, it replicates the transaction coordinator which renders the two-phase commit protocol non-blocking and, thus, avoids potentially long service disruptions caused by coordinator failure. The infrastructure handles the interactions between the application servers and the database servers through replicated gateways that prevent duplicate requests from reaching the database servers. The infrastructure implements client-side automatic failover mechanisms, which guarantees that clients know the outcome of the requests that they have made. The infrastructure starts the transactions at the application servers, and retries aborted transactions, caused by process or communication failures, automatically on the behalf of the clients.
{"title":"Unification of replication and transaction processing in three-tier architectures","authors":"Wenbing Zhao, L. Moser, P. Melliar-Smith","doi":"10.1109/ICDCS.2002.1022266","DOIUrl":"https://doi.org/10.1109/ICDCS.2002.1022266","url":null,"abstract":"In this paper we describe a software infrastructure that unifies replication and transaction processing in three-tier architectures and, thus, provides high availability and fault tolerance for enterprise applications. The infrastructure is based on the Fault Tolerant CORBA and CORBA Object Transaction Service standards, and works with commercial-off-the-shelf application servers and database systems. The infrastructure replicates the application servers to protect the business logic processing. In addition, it replicates the transaction coordinator which renders the two-phase commit protocol non-blocking and, thus, avoids potentially long service disruptions caused by coordinator failure. The infrastructure handles the interactions between the application servers and the database servers through replicated gateways that prevent duplicate requests from reaching the database servers. The infrastructure implements client-side automatic failover mechanisms, which guarantees that clients know the outcome of the requests that they have made. The infrastructure starts the transactions at the application servers, and retries aborted transactions, caused by process or communication failures, automatically on the behalf of the clients.","PeriodicalId":186210,"journal":{"name":"Proceedings 22nd International Conference on Distributed Computing Systems","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134402983","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：