In a wireless ad hoc network, nodes cooperate to forward packets for each other over possibly multi-hop paths, to allow nodes not within direct wireless transmission range to communicate. Many routing protocols have been proposed for the ad hoc network environment, several of which operate on-demand and utilize a route cache listing links that this node has learned. In such protocols, aggressive caching of overheard routes can significantly improve performance; in particular, overhead can be reduced by leverag-ing information received in packets overheard or forwarded from other nodes, including other routing packets and the source routes on other data packets. Unfortunately, such information sharing can substantially increase the risk of cache cross-pollution, since stale routing information in one node's cache, representing a link that no longer exists, can easily be added into the caches of other nodes. Even when a node has actually learned that a link no longer exists, it is still possible for that node to again hear the stale information. In this paper, we present a new mechanism which we call epoch numbers, to reduce this problem of cache staleness, by preventing the re-learning of stale knowledge of a link after having earlier heard that the link has broken. Our scheme does not rely on ad hoc mechanisms such as short-lived negative caching; rather, we allow a node having heard both of a broken link and a discovery of the same link to sequence the two events in order to determine whether the link break or the link discovery occurred before the other.
{"title":"Ensuring cache freshness in on-demand ad hoc network routing protocols","authors":"Yih-Chun Hu, David B. Johnson","doi":"10.1145/584490.584496","DOIUrl":"https://doi.org/10.1145/584490.584496","url":null,"abstract":"In a wireless ad hoc network, nodes cooperate to forward packets for each other over possibly multi-hop paths, to allow nodes not within direct wireless transmission range to communicate. Many routing protocols have been proposed for the ad hoc network environment, several of which operate on-demand and utilize a route cache listing links that this node has learned. In such protocols, aggressive caching of overheard routes can significantly improve performance; in particular, overhead can be reduced by leverag-ing information received in packets overheard or forwarded from other nodes, including other routing packets and the source routes on other data packets. Unfortunately, such information sharing can substantially increase the risk of cache cross-pollution, since stale routing information in one node's cache, representing a link that no longer exists, can easily be added into the caches of other nodes. Even when a node has actually learned that a link no longer exists, it is still possible for that node to again hear the stale information. In this paper, we present a new mechanism which we call epoch numbers, to reduce this problem of cache staleness, by preventing the re-learning of stale knowledge of a link after having earlier heard that the link has broken. Our scheme does not rely on ad hoc mechanisms such as short-lived negative caching; rather, we allow a node having heard both of a broken link and a discovery of the same link to sequence the two events in order to determine whether the link break or the link discovery occurred before the other.","PeriodicalId":344182,"journal":{"name":"Principles of Mobile Computing","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117150688","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}
In this paper we analyze the node spatial distribution generated by nodes moving according to the random waypoint model, which is widely used in the simulation of mobile ad hoc networks. We extend an existing analysis for the case in which nodes are continuously moving (i.e., the pause time is 0) to the more general case in which nodes have arbitrary pause times between movements. We also generalize the mobility model, allowing the nodes to remain stationary for the entire simulation time with a given probabilit . Our analysis shows that the structure of the resulting as asymptotic spatial density is composed by three distinct components: the initial, the pause and the mobilit component. The relative values of these components depend on the mobilit parameters. We derive an explicit formula of the one-dimensional node spatial density, and an approximated formula for the two-dimensional case.The quality of this approximation is verified through experimentation, which shows that the accuracy heavily depends on the choice of the mobilit parameters.
{"title":"An analysis of the node spatial distribution of the random waypoint mobility model for ad hoc networks","authors":"G. Resta, P. Santi","doi":"10.1145/584490.584500","DOIUrl":"https://doi.org/10.1145/584490.584500","url":null,"abstract":"In this paper we analyze the node spatial distribution generated by nodes moving according to the random waypoint model, which is widely used in the simulation of mobile ad hoc networks. We extend an existing analysis for the case in which nodes are continuously moving (i.e., the pause time is 0) to the more general case in which nodes have arbitrary pause times between movements. We also generalize the mobility model, allowing the nodes to remain stationary for the entire simulation time with a given probabilit . Our analysis shows that the structure of the resulting as asymptotic spatial density is composed by three distinct components: the initial, the pause and the mobilit component. The relative values of these components depend on the mobilit parameters. We derive an explicit formula of the one-dimensional node spatial density, and an approximated formula for the two-dimensional case.The quality of this approximation is verified through experimentation, which shows that the accuracy heavily depends on the choice of the mobilit parameters.","PeriodicalId":344182,"journal":{"name":"Principles of Mobile Computing","volume":"206 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133927717","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 proposes to define a caching service for Web Services in mobile wireless ad-hoc networks. The paper discusses many of the issues that need to be tackled in order to realize such a service, and proposes some solutions, some of which are based on previous experience with distributed object caching.
{"title":"Caching web services in mobile ad-hoc networks: opportunities and challenges","authors":"R. Friedman","doi":"10.1145/584490.584508","DOIUrl":"https://doi.org/10.1145/584490.584508","url":null,"abstract":"This paper proposes to define a caching service for Web Services in mobile wireless ad-hoc networks. The paper discusses many of the issues that need to be tackled in order to realize such a service, and proposes some solutions, some of which are based on previous experience with distributed object caching.","PeriodicalId":344182,"journal":{"name":"Principles of Mobile Computing","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133563398","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}
Seamless handover is a fundamental concern in any system with mobility. It is the attempt to provide a given QoS also during the process of migration from one domain (e.g. served by an access point) to another. Its major goal is to hide from the application (or user) any difference between the normal service offered within a domain and during a migration.In this paper we characterize the notion of "seamless handover" in a general framework, identify the fundamental problems, discuss different aspects of this notion, and give a taxonomy of possible approaches to achieve it. We also review concrete examples in mobile computing and mobile computation, map these approaches to our classification and propose a unified architectural framework for implementing seamless handover.
{"title":"General approaches for implementing seamless handover","authors":"M. Endler, Vera Nagamuta","doi":"10.1145/584490.584494","DOIUrl":"https://doi.org/10.1145/584490.584494","url":null,"abstract":"Seamless handover is a fundamental concern in any system with mobility. It is the attempt to provide a given QoS also during the process of migration from one domain (e.g. served by an access point) to another. Its major goal is to hide from the application (or user) any difference between the normal service offered within a domain and during a migration.In this paper we characterize the notion of \"seamless handover\" in a general framework, identify the fundamental problems, discuss different aspects of this notion, and give a taxonomy of possible approaches to achieve it. We also review concrete examples in mobile computing and mobile computation, map these approaches to our classification and propose a unified architectural framework for implementing seamless handover.","PeriodicalId":344182,"journal":{"name":"Principles of Mobile Computing","volume":"86 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121401981","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}
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