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Characterizing content sharing properties for mobile users in open city squares
Abstract
For mobile delay-tolerant networks, different mobility models have been utilized to assess the performance of routing algorithms and applications. Substantial work has gone into understanding the contact characteristics of mobile users to allow evaluation under conditions that approximate the real world. One important finding has been recognizing that contacts humans make at a macroscopic level is derived from daily routines and social interactions so that analyzing social network structures can assist in determining, e.g., suitable peers for message forwarding. While mid- to long-term social interaction patterns assist in delivering messages at larger scales, such patterns become immaterial when considering a microscopic scale such as content sharing in a city square. At microscopic scales, we face an “open” simulation area in which nodes enter and leave rather than a closed system with a fixed set of nodes. Moreover, small scales show more dynamics (e.g., in terms of node density) and steady state analyses become insufficient. In this paper, we investigate the operation of a content sharing application, Floating Content, under such microscopic mobility conditions and characterize its behavior for city squares. For its validation, we derive a mobility model for open squares to which mobile nodes enter and from which they depart.
... Suppose that N=100, the mean sojourn time 1/ is normalized to one, and the rate of pair-wise contacts, and the time interval are free parameters. To make it simple, we use the same value of as in [26] for comparison to see if our approach is never worse than the FC model no matter what the value of is. Fig. 1 depicts solutions for the penetration p(t) as a function of time t and time interval with a initial value p(0)=1/N (the first participants get the task from the platform at the beginning). ...
... Fig. 1 depicts solutions for the penetration p(t) as a function of time t and time interval with a initial value p(0)=1/N (the first participants get the task from the platform at the beginning). In the left figure, is chosen in the same way as [26] that lim ୲→ஶ p(t) ≈ 0.8, i.e., 80% of the participants on average has the task, and the CT is about 2 minutes. In the right figure, 20% of the nodes acquire the task and the CT is about 8 minutes. ...
... The area of Xi Erqi subway station is relatively small but the density of people clustered here is relatively high. People waiting for entrance to the station often follow the direct mobility model (DMM) [26]. That means all directions equally likely. ...
The opportunity to leverage crowdsourcing-based model to
facilitate software requirements acquisition has been recognized
to maximize the advantages of the diversity of talents and
expertise available within the crowd. Identifying well-suited
participants is a common issue in crowdsourcing system.
Requirements acquisition tasks call for participants with
particular kind of domain knowledge. However, current
crowdsourcing system failed to provide such kind of
identification among participants. We observed that participants
with a particular kind of domain knowledge often have the
opportunity to cluster in particular spatiotemporal spaces. Based
on this observation, we propose a novel opportunistic participant
recruitment framework to enable organizers to recruit
participants with desired kind of domain knowledge in a more
efficient way. We analyzed the feasibility of our opportunistic
approach through both theoretic study on analytical model and
simulated experiment on real world mobility model. The results
showed the feasibility of our approach
... [4] introduces the criticality condition, a sufficient condition for the content to float indefinitely with very high probability, under various mobility models. [7] introduces an analytical model to estimate content persistence in the case of outdoor pedestrian mobility over large open spaces, such as a city square. [8], [9] characterize the mean time to information loss, on several scenarios, based on synthetic mobility and on measurement-based vehicular mobility traces. ...
... from the system until the remaining ones can be sustained in the mean field regime according to condition (7). Note that when host memory is finite, if the system is seeded with a higher number of contents than those which can be stored in host memory, the total number of floating contents decreases rapidly during the initial transient of content diffusion, until it coincides with the maximum number of contents which can be stored in host memory. ...
Floating Content (FC) is a paradigmatic example of opportunistic infrastructure-less content sharing system where information is spread upon mobile node encounters within an area which is called the replication zone. FC allows the probabilistic spatial storage of information, even in the case of unreliable communications, with no support from dedicated servers. Given the large amount of communication and storage resources typically required to guarantee content persistence despite node mobility, a major open issue for the practical viability of FC and of similar distributed storage systems is the characterization of their storage capacity, i.e., of the maximum amount of information which can be stored for a given set of system parameters. In this paper, we propose a simple yet powerful information theoretical model of the storage capacity of probabilistic distributed storage systems such as FC, based on a mean field model of opportunistic information exchange. We evaluate numerically our results, and validate the model by means of realistic simulations, showing the accuracy of our mean field approach and characterizing the properties of the FC storage capacity versus the main system parameters.
... In essence, every user becomes both a producer and a consumer of information [2]; even more, data generation and consumption are two inextricable processes as the latter also provides information about user preferences, location, interest, actions, and so forth (i.e., data generation). This people-centric sensing paradigm leads to a scenario with a diminishing presence of centralized server-based services [3]. Rather, digital services will be more and more based on crowdsensing and the ability to share the information in a distributed, decentralized way [4]. ...
... Set (ConnectedComponents) output: Set of connected components ConnectedComponents (1) Set Connected ← Bidirectional(LocalFI, ReceivedFIs); (2) Cluster ; (3) ← ∪ FirstElement(Connected); (4) ConnectedComponents ← ConnectedComponents ∪ ; (5) foreach Slot in Connected do (6) bool InsideAnyCluster ← False; (7) foreach in ConnectedComponents do (8) if IsMember (NodeId(Slot), , ReceivedFIs) then (9) ← ∪ NodeId(Slot); (10) InsideAnyCluster ← True; (11) b r e a k ; (12) end (13) end (14) if not InsideAnyCluster then (15) Cluster New; (16) New ← New ∪ NodeId(Slot); (17) ConnectedComponents ← ConnectedComponents ∪ New; (18) end (19) end Algorithm 2: Cluster set computation. ...
The Internet edge has evolved from a simple consumer of information and data to eager producer feeding sensed data at a societal scale. The crowdsensing paradigm is a representative example which has the potential to revolutionize the way we acquire and consume data. Indeed, especially in the era of smartphones, the geographical and temporal scopus of data is often local. For instance, users’ queries are more and more frequently about a nearby object, event, person, location, and so forth. These queries could certainly be processed and answered locally, without the need for contacting a remote server through the Internet. In this scenario, the data is alimented (sensed) by the users and, as a consequence, data lifetime is limited by human organizational factors (e.g., mobility). From this basis, data survivability in the Area of Interest (AoI) is crucial and, if not guaranteed, could undermine system deployment. Addressing this scenario, we discuss and contribute with a novel protocol named AirCache, whose aim is to guarantee data availability in the AoI while at the same time reducing the data access costs at the network edges. We assess our proposal through a simulation analysis showing that our approach effectively fulfills its design objectives.
... The IF concept was first proposed [7] with a detailed algorithm and the simulation results of the proposed method; this proposal was followed by some articles [8,9,10,11,12,13,14,15]. Since IF is realized by an information exchange between mobile nodes in the target area, the last node with information in the target area might fail to transfer that information to other nodes. ...
... Finally, we can compute E(T f ) by substituting (13) and (14) into (10), (11), and (12). ...
Information floating (IF) is an invisible infrastructure in which mobile nodes can receive information that seems to be floating in a designated area. IF is realized by successively transferring information from a mobile node to other nodes in an epidemic manner with wireless direct communication in designated areas. IF has many potential applications, such as advertisements for local communities, specific communication for disasters, alert systems for pedestrians and vehicles, and so on. To design alert systems on a road, some articles theoretically analyze the mean lifetime of the floating in a one-dimensional street. In past researches, however, identical traffic volume and velocity were assumed in all the lanes. The difference in traffic volume between lanes and the correlation between traffic volume and velocity were omitted for simplicity. In this paper, we recognize the importance of these two factors and reveal their effects on the mean lifetime of IF with a new theoretical method. In it, we consider not only the effects of the above two factors but also the complicated features of IF that were ignored in previous methods.
... targeted advertising [23]) to information (e.g. floating content [17], context-aware mobile platforms [19]), smart cities [7] or even emergency situations (e.g. crowd location, disaster management [33], etc.). ...
... Since ONs and DTNs are used to carry information opportunistically, a suitable scenario is represented by information-sharing. An example of this is floating content in open city squares [17], where mobile nodes may enter a geographically-fixed area that specifies the physical boundaries of the network (an anchor zone), spend a certain amount of time there, and then leave. While located in the anchor zone, devices (or a static access point) produce content and replicate it opportunistically to other nodes, which may use the data for themselves, or carry it in order to forward it to interested nodes. ...
This chapter discusses the challenges, state of the art, and future trends in context-aware environments (infrastructure and services) for the Internet of Things, an open and dynamic environment where new Things can join in at any time, and offer new services or improvements of old services in terms of performance and quality of service. The dynamic behavior is supported by mechanisms for Things publishing, notification, search, and/or retrieval. Self-adaptation is important in this respect. For example, when things are unable to establish direct communication, or when communication should be offloaded to cope with large throughputs, mobile collaboration can be used to facilitate communication through opportunistic networks. These types of networks, formed when mobile devices communicate only using short-range transmission protocols, usually when users are close, can help applications still exchange data. Routes are built dynamically, since each mobile device is acting according to the store-carry-and-forward paradigm. Thus, contacts are seen as opportunities to move data towards the destination. In such networks data dissemination is usually based on a publish/subscribe model.We make a critical analysis of current opportunistic approaches using the elements of a newly defined taxonomy. We review current state-of-the-art work in this area, from an IoT perspective.
... Meanwhile, in some specific cases of real human mobility, such as in disaster, military and crowd scenarios, human movement is typically modelled as a random process. For instance, the work of UrbanCount [7] used a City-Square model [9] to describe the movement of people in a city square. This movement model is actually an improvement of Random-Waypoint. ...
... [32] demonstrates the feasibility of FC (in terms of ability to sustain content persistence within the RZ for a given period of time) even in setups with sparse node distributions. [33] proposes a model for content persistence for outdoor pedestrian mobility over large open spaces, such as city squares. [34], [35] characterize the mean time to information loss in several scenarios, based on synthetic mobility and on measurement-based vehicular mobility traces. ...
Floating Content (FC) is a paradigm for localized infrastructure-less content dissemination, that aims at sharing information among nodes within a restricted geographical area by relying only on opportunistic content exchanges. FC provides the basis for the probabilistic spatial storage of shared information in a completely decentralized fashion, usually without support from dedicated infrastructure. One of the key open issues in FC is the characterization of its performance limits as functions of the system parameters, accounting for its reliance on volatile wireless exchanges and on limited user resources. This paper takes a first step towards tackling this issue, by elaborating a model for the storage capacity of FC, i.e., for the maximum amount of information that can be stored through the FC paradigm. The storage capacity of FC, and of similar probabilistic content dissemination systems, is evaluated with a powerful information theoretical approach, based on a mean field model of opportunistic information exchange. In addition, an extremely simple explicit approximate expression for storage capacity is derived. The numerical results generated by our analytical models are compared to the predictions of realistic simulations under different setups, proving the accuracy of our analytical approaches, and characterizing the properties of the FC storage capacity.
... The work in [22] applies the FC paradigm to the issue of building and delivering knowledge about traffic conditions, in order to enable drivers to optimally plan their route. In [23] authors propose another synthetic mobility model, the city square mobility model, in which nodes move within a rectangular area, and in which the number of nodes in the AZ is not constant over time. The paper derives simple conditions for content availability and persistence. ...
Floating Content (FC) is a communication paradigm to locally share ephemeral content without direct support from infrastructure. It is based on constraining the opportunistic replication of content in a way that strikes a balance between minimizing resource usage and maximizing content availability among the intended recipients. However, existing approaches to management of FC schemes are unfit for realistic scenarios with non-uniform user distributions, resulting in heavy overdimensioning of resources allocated to FC. In this work, we propose a new version of FC, called Cellular Floating Content (CFC), which optimizes the use of bandwidth and memory by adapting the content replication and storage strategies to the spatial distribution of users, and to their mobility patterns. The main idea underlying our approach is to partition users into small “local communities”, and to optimally weight their contributions to the FC paradigm according to their specific mobility features, and to the resources required to achieve a target performance level. We characterize numerically the properties of the optimal strategies in a variety of mobility patterns and traffic conditions, showing the accuracy of our approach, and the significant savings it enables in the amount of resources necessary to run FC, which in a realistic setup can be as high as 27% with respect to traditional FC dimensioning strategies.
... On one side, many works focus on content persistence over time and propose heuristics for guaranteeing content persistence within a predefined region, which usually coincides with the AZ itself [3]. Such heuristics are often tailored to a specific context (e.g., highways or pedestrians in city squares [12]), and assume that a high likelihood of content persistence is sufficient to successfully support applications such as notifications of car accidents or traffic congestion. But they are hard to generalize for other applications that need a minimum amount of delivered contents within a given area. ...
Opportunistic communications are expected to playa crucial role in enabling context-aware vehicular services. A widely investigated opportunistic communication paradigm for storing a piece of content probabilistically in a geographica larea is Floating Content (FC). A key issue in the practical deployment of FC is how to tune content replication and caching in a way which achieves a target performance (in terms of the mean fraction of users possessing the content in a given region of space) while minimizing the use of bandwidth and host memory. Fully distributed, distance-based approaches prove highly inefficient, and may not meet the performance target,while centralized, model-based approaches do not perform well in realistic, inhomogeneous settings. In this work, we present a data-driven centralized approach to resource-efficient, QoS-aware dynamic management of FC.We propose a Deep Learning strategy, which employs a Convolutional Neural Network (CNN) to capture the relationships between patterns of users mobility, of content diffusion and replication, and FC performance in terms of resource utilization and of content availability within a given area. Numerical evaluations show the effectiveness of our approach in deriving strategies which efficiently modulate the FC operation in space and effectively adapt to mobility pattern changes over time.
... On one side, many works focus on content persistence over time and propose heuristics for guaranteeing content persistence within a predefined region, which usually coincides with the AZ itself [3]. Such heuristics are often tailored to a specific context (e.g., highways or pedestrians in city squares [12]), and assume that a high likelihood of content persistence is sufficient to successfully support applications such as notifications of car accidents or traffic congestion. But they are hard to generalize for other applications that need a minimum amount of delivered contents within a given area. ...
Opportunistic communications are expected to play a crucial role in enabling context-aware vehicular services. A widely investigated opportunistic communication paradigm for storing a piece of content probabilistically in a geographical area is Floating Content (FC). A key issue in the practical deployment of FC is how to tune content replication and caching in a way which achieves a target performance (in terms of the mean fraction of users possessing the content in a given region of space) while minimizing the use of bandwidth and host memory. Fully distributed, distance-based approaches prove highly inefficient, and may not meet the performance target, while centralized, model-based approaches do not perform well in realistic, inhomogeneous settings. In this work, we present a data-driven centralized approach to resource-efficient, QoS-aware dynamic management of FC. We propose a Deep Learning strategy, which employs a Con-volutional Neural Network (CNN) to capture the relationships between patterns of users mobility, of content diffusion and replication, and FC performance in terms of resource utilization and of content availability within a given area. Numerical evaluations show the effectiveness of our approach in deriving strategies which efficiently modulate the FC operation in space and effectively adapt to mobility pattern changes over time.
... [6] introduces the criticality condition, a sufficient condition for the content to float indefinitely with very high probability, under various mobility models. [8] introduces an analytical model to estimate content persistence in the case of outdoor pedestrian mobility over large open spaces, such as a city square. ...
Among the many proposed opportunistic content sharing schemes, Floating Content (FC) is of special interest for the vehicular environment, not only for cellular traffic offloading, but also as a natural communication paradigm for location-based context-aware vehicular applications.
Previously published results on the performance of vehicular FC have mostly focused on the conditions under which content persists over time in a given region of space, without addressing other important aspects of vehicular FC performance, such as the effectiveness with which content is replicated and made available, and the system conditions that enable good FC performance.
This work presents a first analytical model of FC performance in vehicular networks in urban settings. It is based on a new synthetic mobility model (called District Mobility Model - DMM), and it does not require a detailed knowledge of the road grid geometry.
We validate our model extensively, by comparison against numerical simulations based on real-world traces, and we prove our model accuracy under a variety of mobility patterns and traffic conditions. Our analytical and simulation results provide evidence of the effectiveness of the FC paradigm in realistic urban settings over a wide range of traffic conditions.
... This approach is a kind of best effort service, in which messages are locally generated, their availability is geographically limited, and their lifetime and diffusion depend on the mobility and resources of mobile nodes. Recently, this approach has been analytically evaluated in open city squares [25] using a custom mobility model, spatial analysis and Markov chains, and assuming that nodes may enter and leave the city square. Since the analytic model assumes too many simplifications, it is not clear if the results are realistic. ...
Opportunistic Networks can provide an alternative way to support the diffusion of information in special locations within a city, particularly in crowded spaces where current wireless technologies can exhibit congestion issues. The efficiency of this diffusion relies mainly on user mobility. In fact, mobility creates the opportunities for contacts and, therefore, for data forwarding. This paper is therefore mainly focused on evaluating the dissemination of information in urban scenarios with different crowd densities and renewal rates. Through observation, we obtained real data from a local subway station and a plaza. These data were used, in combination with a pedestrian mobility simulator, to generate people mobility traces. We evaluated the diffusion of messages in these scenarios using the Direct and the Epidemic protocols. Experimental results show that content diffusion is mainly affected by two factors: degree of mobility and message size. Although it is well known that increasing the node density increases the diffusion rate, we show that, when keeping node density fixed, higher renewal rates cause the delivery ratio to drop. Moreover, we found that the relation between message size and contact duration is also a key factor, demonstrating that large messages can lead to a very low overall performance. Finally, with the aim of increasing the diffusion effectiveness of large messages, we propose an improvement over the Epidemic protocol, named EpidemicX2, based on the fragmentation of the data to be sent. The results show that the delivery ratio is increased, and the average delivery time is reduced, with no substantial increase in terms of overhead.
... Previous works showed that content items float within the AZ over time with high probability provided a criticality condition is met, which accounts for the average number of nodes in the AZ (denoted by N ), the average contact rate between any two nodes (ν), and the average node sojourn time in the AZ, expressed as in (1) [3,7]. In our case, the criticality conditions is as follows: ...
In this paper we study an opportunistic geographically constrained information sharing paradigm known under the name Floating Content (FC), considering two different mobility models that describe the behavior of pedestrians. We assume that users carrying their smartphones walk from one location to another and then stop for a while. Information transfers take place in the periods when users pause between movements. We develop analytical models to compute the performance metrics that characterize FC in this case and we validate analytical results with data collected during an experiment performed in a university campus. The comparison proves the accuracy of our analytical models. Moreover, results unveil the key relevance for FC performance of group dynamics in user movements.
... There are many real-life scenarios where opportunistic networks are being (or have already been) employed, such as disaster management [2], smart cities [3], floating content [4], mobile advertising [5], crowd management [6], context-aware platforms [7], wildlife tracking [8], Internet access in limited conditions [9], distributed social networks [10], or even data offloading and mobile cloud computing [11]. In this paper, we choose to focus on implementing a cyberinfrastructure for smart cities. ONs are extremely useful in smart cities, since they not only decrease the load on the infrastructure, but they also improve the response times. ...
... This approach is a kind of best effort service, in which messages are locally generated, their availability is geographically limited and their lifetime and diffusion depend on the mobility and resources of mobility nodes. Recently, this approach has been evaluated in open city squares in [24] using a custom mobility model, spatial analysis and Markov chains, and assuming that nodes enter and leave the city square. ...
The scarcity of bandwidth due to the explosive growth of mobile devices in 5G makes the offloading messaging workload to WiFi devices that use opportunistic connections, a very promising solution. Communications in mobile opportunistic networks take place upon the establishment of ephemeral contacts among mobile nodes using direct communication. In this paper we propose an analytical model based on population processes to evaluate data dissemination considering several parameters such as user density, contact rate, and the number of fixed nodes. From this model we obtain closed-form expressions for determining the diffusion time, the network coverage and the waiting time. Newer 5G wireless technologies like WiGig can offer multigigabit speeds, low latency, and security-protected connectivity between nearby devices. We therefore focus our work on the impact of high-speed and short-range wireless communications technologies for data dissemination in mobile opportunistic networks. Moreover, we test whether the coexistence with a fixed infrastructure can improve content dissemination, and thus justify its additional cost. Our results show that, when user density is high, the diffusion is mainly performed through the opportunistic contacts between mobile nodes, and that the diffusion coverage is close to 100%. Moreover, the diffusion is fast enough to dynamically update the information among all the participating members, so users do not need to get closer to fixed spots for receiving updated information.
... Paper [1] characterizes the critical condition, for the content to float indefinitely with very high probability, under various mobility models. [3] introduces an analytical model for content persistence for the case of outdoor pedestrian mobility in large open spaces, such as a city square. However, for any practical application, content persistence over time within the AZ is only a necessary condition for FC viability. ...
... [1] characterizes the critical condition, for the content to float indefinitely with very high probability, under various mobility models. [3] introduces an analytical model for content persistence for the case of outdoor pedestrian mobility in large open spaces, such as a city square. However, for any practical application, content persistence over time within the AZ is only a necessary condition for FC viability. ...
Among the proposed opportunistic content sharingservices, Floating Content (FC) is of special interest for thevehicular environment, not only for cellular traffic offloading but also as a natural communication paradigm for location-based context-aware vehicular applications. Existing results on theperformance of vehicular FC have focused on content persistence, without addressing the key issues of the effectiveness with which content is replicated and made available, and of what arethe conditions which enable acceptable FC performance in thevehicular environment. This work presents a first analytical model of FC performance in vehicular ad-hoc networks in urban settings. It is based on a variation of the random waypoint(RWP) mobility model, and it does not require a model of road grid geometry for its parametrization. We validate our model extensively, through numerical simulations on real-world traces, showing its accuracy on a variety of mobility patterns and traffic conditions. Through analysis and simulations, we show the feasibility of the FC paradigm in realistic urban settings over awide range of traffic conditions.
... Floating content: PSNs are also applicable in sharing geographical area-based content in public areas (such as city squares, shopping malls, airport terminals, tourist sites and university campuses) where many people gather. Users enter, spend some amount of time and leave these areas, which are also known as anchor zones [114] in literature. Data relevant to the anchor zone is created and allowed to float within its geographical boundaries, such that, a device within the anchor zone may copy data required by the user or transport it for the sake of other users that may be interested in the content, while those exiting the anchor zone delete it. ...
A pocket switched network (PSN) is dynamically formed by people who carry portable handheld devices. Interest in PSNs is driven by the increasing number of handheld devices, the several wireless interfaces they possess, as well as their ability to store, carry and forward data. The lack of fixed network topology distinguishes PSNs from traditional networks, and unlike other types of mobile networks, nodes in PSNs closely follow human movement patterns. As a result, PSNs are faced with new challenges especially in the aspect of routing. Although various routing protocols have been proposed, most of them focus on optimizing the performance of networking primitives for traditional networks such as unicast, broadcast and multicast. However, these primitives themselves appear to be insufficient due to new application opportunities presented by PSNs. This paper adopts a user scenario based approach to determine the current state of PSN routing protocols. Specifically, four modes of data transfer are established from six generalized PSN user scenarios. Due to the wide range of existing routing proposals, a new taxonomy is proposed to facilitate analysis of their compatibility with the established modes of data transfer. The analysis provides new insights into application based routing approaches for realizing next-generation PSN routing protocols.
... Through this geographically constrained opportunistic replication mechanism, a given content item is stored probabilistically in a spatial region, typically without the support of fixed infrastructure, and it is made available to users traversing the AZ through opportunistic exchanges with nodes in the AZ. Specifically, the theory shows that, within the AZ, content items float over time with high probability, based on a criticality condition, which accounts for the average number of nodes in the AZ, the average node contact rate, and the average node sojourn time in the AZ [5,7]. When the criticality condition is satisfied, the expected lifetime of a content item is infinite under the fluid limit approximation of [5]. ...
This work presents the first experimental evaluation of the Floating Content (FC) communication paradigm in a campus/large office setting. By logging information transfer events we have characterized mobility patterns, and we have assessed the performance of services implemented using the FC paradigm. Our results unveil the key relevance of group dynamics in user movements for the FC performance. Surprisingly, in such an environment, our results show that a relatively low user density is enough to guarantee content persistence over time, contrarily to predictions from available models. Based on these experimental findings, we develop a novel simple analytical model that accounts for the peculiarities of the mobility patterns in such a setting, and that can accurately predict the effectiveness of FC for the implementation of services in a campus/large office setting.
... Another potential practical use of DTNs is in regard to floating content in areas such as open city squares [26], where mobile nodes enter a geographical zone (called an anchor zone), spend some time in it and then leave. While in the anchor zone (which gives the physical boundaries of the network), the mobile devices produce content and opportunistically replicate it to other nodes. ...
Evolutionary algorithms are metaheuristic algorithms that provide quasioptimal solutions in a reasonable time. They have been applied to many optimization problems in a high number of scientific areas. In this survey paper, we focus on the application of evolutionary algorithms to solve optimization problems related to a type of complex network like mobile multihop ad hoc networks. Since its origin, mobile multihop ad hoc network has evolved causing new types of multihop networks to appear such as vehicular ad hoc networks and delay tolerant networks, leading to the solution of new issues and optimization problems. In this survey, we review the main work presented for each type of mobile multihop ad hoc network and we also present some innovative ideas and open challenges to guide further research in this topic.
... Another potential practical use of opportunistic networks is in regard to floating content in areas such as open city squares [7], where mobile nodes enter a geographical zone (called an anchor zone), spend some time in it and then leave. While in the anchor zone (which gives the physical boundaries of the network), the mobile devices produce content and opportunistically replicate it to other nodes. ...
When mobile devices are unable to establish direct communication, or when communication should be offloaded to cope with large throughputs, mobile collaboration can be used to facilitate communication through opportunistic networks. These types of networks, formed when mobile devices communicate only using short-range transmission protocols, usually when users are close, can help applications still exchange data. Routes are built dynamically, since each mobile device is acting according to the store-carry-and-forward paradigm. Thus, contacts are seen as opportunities to move data towards the destination. In such networks data dissemination is usually based on a publish/subscribe model. Opportunistic data dissemination also raises questions concerning user privacy and incentives. In this the authors present a motivation of using opportunistic networks in various real life use cases, and then analyze existing relevant work in the area of data dissemination. The authors present the categories of a proposed taxonomy that captures the capabilities of data dissemination techniques used in opportunistic networks. Moreover, the authors survey relevant techniques and analyze them using the proposed taxonomy.
The combination of Mobile Crowdsensing (MCS) with Opportunistic Networking (OppNet) allows mobile users to share sensed data easily and conveniently without the use of fixed infrastructure. OppNet is based on intermittent connectivity among wireless mobile devices, in which mobile nodes may store, carry and forward messages (sensing information) by taking advantage of wireless ad-hoc communication opportunities. A common approach for the diffusion of this sensing data in OppNet is the epidemic protocol, which carries out a fast data diffusion at the expense of increasing the usage of local buffers on mobile nodes and also the number of transmissions, thereby limiting scalability.
A way to reduce this consumption of local resources is to set a message expiration time that forces the removal of old messages from local buffers. Since dropping messages too early may reduce the speed of information diffusion, we propose a dynamic expiration time setting to limit this effect. Moreover, we introduce an epidemic diffusion model for evaluating the impact of the expiration time. This model allows us to obtain optimal expiration times that achieve performances similar to those other approaches where no expiration is considered, with a significant reduction of local buffer and network usage. Furthermore, in our proposed model, the buffer utilisation remains steady with the number of nodes, whereas in other approaches it increases sharply. Finally, our approach is evaluated and validated in a mobile crowdsensing scenario, where students collect and broadcast information regarding a university campus, showing a significant reduction on buffer usage and nodes message transmissions, and therefore, decreasing battery consumption.
Information floating (IF) permits mobile nodes to transmit information to other nodes by direct wireless communication only in transmittable areas (TAs), thus avoiding unneeded and inefficient information distribution to irrelevant areas, which is a problem with the so-called epidemic communication used in delay tolerant networks. In this paper, we propose applying IF to sensor networking to find and share available routes in disaster situations. In this proposal, IF gathers and shares information without any assistance from gateways, which is normally required for conventional wireless sensor networks. A performance evaluation based on computer simulation results is presented. Furthermore, we demonstrate that the proposed method is effective by highlighting its advantageous properties and directly comparing it with a method based on epidemic communication. Our findings suggest that the proposed method is a promising step toward more effective countermeasures against restricted access in disaster zones.
Multihop wireless networks are mobile communication systems that do not require infrastructure, unlike cellular systems. In the multihop wireless networks, information is sent to a destination node via a connected multihop wireless path between the source and destination nodes. Epidemic communication and information floating are more flexible networking technologies than multihop wireless networks. Epidemic communication delivers information by spatially spreading information through direct wireless communication and the movement of mobile nodes having information. Information floating delivers information to unspecified nodes in a specific area, without the disordered spread of information, by permitting direct wireless communication only in a designated area. These methods of information delivery utilizing direct information exchange between mobile nodes and the movement of mobile nodes carrying information have gathered attention. In this paper, we explain epidemic communication, information floating, and their applications to safety and security focusing on the relationship with the characteristic mobility of mobile nodes in applications to safety/security. We also explain research on information floating from a new viewpoint, considering new factors such as that information floating causes changes in the behavior of mobile nodes, and this change in behavior affects information floating.
Opportunistic networks are the next step in the evolution of mobile networks, especially, since the number of human-carried mobile devices such as smartphones and tablets has greatly increased in the past few years. They assume unselfish communication between devices based on a store-carry-and-forward paradigm, where mobile nodes carry each other’s data through the network, which is exchanged opportunistically. In this chapter, we present opportunistic networks in detail and show various real-life scenarios where such networks have been successfully deployed or are about to be, such as disaster management, smart cities, wildlife tracking, context-aware platforms, etc. We highlight the challenges in designing successful data routing and dissemination algorithms for opportunistic networks, and present some of the most important techniques and algorithms that have been proposed in the past few years. We show the most important issues for each of them, and attempt to propose solutions for improving opportunistic routing and dissemination. Finally, we present what the future trends in this area of research might be, from information-centric networks to the Internet of Things.
Over the last decades, modeling of user mobility has become increasingly important in mobile networking research and development. This has led to the adoption of modeling techniques from other disciplines such as kinetic theory or urban planning. Yet these techniques generate movement behavior that is often perceived as not “realistic” for humans or provides only a macroscopic view on mobility. More recent approaches infer mobility models from real traces provided by positioning technologies or by the marks the mobile users leave in the wireless network. However, there is no common framework for assessing and comparing mobility models.
In an attempt to provide a solid foundation for realistic mobility modeling in mobile networking research, we take an engineering approach and thoroughly discuss the required steps of model creation and validation. In this context, we survey how and to what extent existing mobility modeling approaches implement the proposed steps. This also summarizes helpful information for readers who do not want to develop a new model, but rather intend to choose among existing ones.
In opportunistic networking, characterizing contact patterns between mobile users is essential for assessing feasibility and performance of opportunistic applications. There has been significant efforts in deriving this characterization, based on observations and trace analyses; however, most of the findings arise from studying contact opportunities at large spatial and temporal scales. Moreover, the user population is considered to be constant: no users can join or leave the system. Yet, there are many examples of scenarios which do not fully adhere to the previous assumption and cannot be accurately described at large scales. Urban environments, such as smaller city districts, are characterized by highly dynamic user populations. We believe that scenarios with varying population requires further investigation. In this paper, we present a novel modeling approach to study operation of opportunistic applications in scenarios where the population size is subjected to frequent changes, that is, it exhibits churn. We also propose an application for estimating the size of a mobile crowd, which we then use to validate our model in four scenarios: a city area, subway station, a conference and a scenario with a synthetic mobility model. We show that the model provides good representations of the investigated scenarios.
The growing ubiquity and pervasiveness of sensors and smart devices, with the consequent availability of a large amount of "local" and contextualized information, are giving rise to a wealth of "context-aware" applications and services. In this work we consider an opportunistic communication scheme called Floating Content (FC), which was specifically designed for serverless distributed context-aware applications. So far, the performance analysis of FC, and in particular of content lifetime and availability, was based on simplified system models and fluid system analysis. The resulting performance estimates did not account for the effects of propagation characteristics, mobility patterns, and communication protocols, all factors known to significantly affect the performance of opportunistic communication schemes. This article studies the main issues related to the performance of FC service in a realistic office setting through a first experimental evaluation of a mobile app for Android devices. Our experimental results confirm the feasibility of FC service for supporting practical context-aware mobile applications in office settings.
The Opportunistic Networking Environment (ONE) Simulator is an extensible tool for evaluating protocols and mobility models for delay-tolerant networking. ONE allows easily plugging in mobility models, contact traces, routing modules, applications, and report modules. In this paper, we describe how to instrument the ONE simulator for two content sharing applications: spreading content in waves across mostly stationary nodes and geo-based content sharing between mobile nodes using Floating Content. Both are included in the ONE simulator version 1.5.1.
The random waypoint model is a commonly used mobility model for simulations of wireless communication networks. In this paper, we present analytical derivations of some fundamental stochastic properties of this model with respect to: (a) the length and duration of a movement epoch, (b) the chosen direction angle at the beginning of a movement epoch, and (c) the cell change rate of the random waypoint mobility model when used within the context of cellular networks. Our results and methods can be used to compare the random waypoint model with other mobility models. The results on the movement epoch duration as well as on the cell change rate enable us to make a statement about the 'degree of mobility' of a certain simulation scenario. The direction distribution explains in an analytical manner the effect that nodes tend to move back to the middle of the system area.
The random waypoint model is a commonly used mobility model for simulations of wireless communication networks. By giving a formal description of this model in terms of a discrete-time stochastic process, we investigate some of its fundamental stochastic properties with respect to: (a) the transition length and time of a mobile node between two waypoints, (b) the spatial distribution of nodes, (c) the direction angle at the beginning of a movement transition, and (d) the cell change rate if the model is used in a cellular-structured system area.The results of this paper are of practical value for performance analysis of mobile networks and give a deeper understanding of the behavior of this mobility model. Such understanding is necessary to avoid misinterpretation of simulation results. The movement duration and the cell change rate enable us to make a statement about the “degree of mobility” of a certain simulation scenario. Knowledge of the spatial node distribution is essential for all investigations in which the relative location of the mobile nodes is important. Finally, the direction distribution explains in an analytical manner the effect that nodes tend to move back to the middle of the system area.
Opportunistic communication between mobile nodes allows for asynchronous content sharing within groups. Limiting the spread of information to a geographic area creates an infrastructure-less variant of digital graffiti, a social network with coupling in space and limited decoupling in time. Due to its nature, this kind of a communication network lends itself readily to name-oriented abstractions. In this paper, we extend our previous work on floating content, extract its fundamental characteristics, and define a system model and a simple API with a set of basic programming elements to support applications in leveraging opportunistic content sharing as a generic communication facility. We validate our API through application examples and show how their communication needs are mapped to our model. In addition, we also implement our API in our simulator and demonstrate the feasibility of these kinds of applications.
Embedded sensors in mobile devices such as cars and smart phones present new opportunities to collect location-specific data about an environment. This data can be used to enable new real-time location-based applications. A major chal-lenge is efficiently collecting, storing and sharing the data. This paper proposes Locus, a location-based data overlay for DTNs. Locus keeps objects at specific physical locations in the network using whatever devices currently are nearby. Nodes copy objects between themselves to maintain the lo-cality of data. Location utility functions prioritize objects for replication and enable location-based forwarding of data look-ups. As a first-of-its-kind application, Locus is com-pared against other possible replication policies and shown to achieve query success rates nearly 4 times higher than other approaches.
We consider an opportunistic content sharing system designed to store and distribute local spatio-temporal “floating” information in uncoordinated P2P fashion relying solely on the mobile nodes passing through the area of interest, referred to as the anchor zone. Nodes within the anchor zone exchange the information in opportunistic manner, i.e., whenever two nodes come within each others' transmission range. Outside the anchor zone, the nodes are free to delete the information, since it is deemed relevant only for the nodes residing inside the anchor zone. Due to the random nature of the operation, there are no guarantees, e.g., for the information availability. By means of analytical models, we show that such a system, without any supporting infrastructure, can be a viable and surprisingly reliable option for content sharing as long as a certain criterion, referred to as the criticality condition, is met. The important quantity is the average number of encounters a randomly chosen node experiences during its sojourn time in the anchor zone, which again depends on the communication range and the mobility pattern. The theoretical studies are complemented with simulation experiments with various mobility models showing good agreement with the analytical results.
Content sharing via the Internet is a widespread means for people to foster their relationships irrespective of physical distance. While network-based social applications are essential to overcome distances and connect people around the world, relying on infrastructure services for location-aware services may often not be desirable. In this paper, we propose and analyze a fully distributed variant of an ephemeral content sharing service, solely dependent on the mobile devices in the vicinity using principles of opportunistic networking. The net result is a best effort service for floating content in which: 1) information dissemination is geographically limited; 2) the lifetime and spreading of information depends on interested nodes being available; 3) traffic can only be created and caused locally; and 4) content can only be added, but not deleted. We present the general model for floating content and results from our on-going evaluation. Our results show that floating content systems are feasible in scenarios which correspond to typical urban settings, in terms of number of nodes and their density, node mobility, and device capabilities.
In this work we present a middleware architecture for a mobile peer-to-peer content distribution system. Our architecture allows wireless content dissemination between mobile nodes without relying on infrastructure support. Contents are exchanged opportunistically when nodes are within communication range. Applications access the service of our platform through a publish/subscribe interface and therefore do not have to deal with low-level opportunistic networking issues or matching and soliciting of contents. Our architecture consists of three key components. A content structure that facilitates dividing contents into logical topics and allows for efficient matching of content lookups and downloading under sporadic node connectivity. A solicitation protocol that allows nodes to solicit content meta-information in order to discover contents available at a neighboring node and to download content entries disjointedly from different nodes. An API that allows applications to access the system services through a publish/subscribe interface. In this work we describe the design and implementation of our architecture. We also discuss potential applications and present evaluation results from profiling of our system.
Content sharing using personal web pages, blogs, or online social networks is a common means for people to maintain contact with their friends, colleagues, and acquaintances. While such means are essential to overcome distances, using infrastructure services for location-based services may not be desirable. In this paper, we analyze a fully distributed variant of an ephemeral content sharing service, solely dependent on the mobile devices in the vicinity using principles of opportunistic networking. The net result is a best effort service for floating content in which: 1) information dissemination is geographically limited; 2) the lifetime and spreading of information depends on interested nodes being available; 3) content can only be created and distributed locally; and 4) content can only be added, but not explicitly deleted. First we present our system design and summarize its analytical modeling. Then we perform extensive evaluation for a map-based mobility model in downtown Helsinki to assess the operational range for floating content, which, at the same time also validate the analytical results obtained for a more abstract model of the system.
Podcasting has become a very popular and successful Internet service in a short time. This success illustrates the interest for participatory broadcasting, in its actual form however, podcasting is only available with fixed infrastructure support to retrieve publicized episodes. We aim at releasing this limitation and present herein our podcasting system architecture together with a prototype implementation based on opportunistic wireless networking that allows us to extend podcasting to ad hoc domains.
In this paper we study the so-called random,waypoint (RWP) mobility model in the context of cellular networks. In the RWP model the nodes, i.e., mobile users, move along a zigzag path consisting of straight legs from one waypoint to the next. Each waypoint is assumed,to be drawn from the uniform distribution over the given convex domain. In this paper we characterise the key performance measures, mean handover rate and mean sojourn time from the point of view of an arbitrary cell, as well as the mean handover rate in the network. To this end, we present an exact analytical formula for the mean arrival rate across an arbitrary curve. This result together with the pdf of the node location, allows us to compute all other interesting measures. The results are illustrated by several numerical examples. For instance, as a straightforward application of these results one can easily adjust the model parameters in a simulation so that the scenario matches well with, e.g., the measured sojourn times in a cell. Keywords: random waypoint model, mobility modelling, cellular networks, handovers
A piece of Hovering Information is a geo-localized information residing in a highly dynamic environment such as a mobile ad hoc network. This information is attached to a geographical point, called the anchor location, and to its vicinity area, called anchor area. A piece of hovering information is responsible for keeping itself alive, available and accessible to other devices within its anchor area. Hovering information uses mechanisms such as active hopping, replication and dissemination among mobile nodes to satisfy the above requirements. It does not rely on any central server. This paper presents the hovering information concept and discusses results of simulations performed for two algorithms aiming to ensure the availability of a piece of hovering information at its anchor area.
Podcasting has become popular for dissemination of streaming contents over the Internet. It is based on software clients that query servers for updates of subscribed content feeds. Podcasting may be used for any media content, but it is most commonly associated with audio streams. It provides a simple, no-frills broadcasting system for delay tolerant contents. A main limitation with this system is the inflexible separation of downloading to a docked media player and expending of the data when on the move. We herein present how podcast could be supported by our previously proposed delay-tolerant broadcasting system in order to reduce the expected times between updates and to provide a new ad hoc podcasting mode among mobile nodes. Our system substitutes the client-server paradigm inherent in present podcasting by a peer-to-peer paradigm where mobile nodes provide each other with contents. We present the protocol for this, and an evaluation of solicitation and caching strategies that greatly affect the application-level throughput. Our design is aiming at simplicity in order to enable implementation in mobile phones with media players and other devices that communicate over short ranges by means of Bluetooth or wireless LAN.
The random waypoint model (RWP) is one of the most widely used mobility models in performance analysis of ad hoc networks. We analyze the stationary spatial distribution of a node moving according to the RWP model in a given convex area. For this, we give an explicit expression, which is in the form of a one-dimensional integral giving the density up to a normalization constant. This result is also generalized to the case where the waypoints have a nonuniform distribution. As a special case, we study a modified RWP model, where the waypoints are on the perimeter. The analytical results are illustrated through numerical examples. Moreover, the analytical results are applied to study certain performance aspects of ad hoc networks, namely, connectivity and traffic load distribution.
In "Stationary distributions for the random waypoint mobility model" (TMC, Vol. 3, No, 1), Navidi and Camp find the stationary distribution of the random waypoint model, with or without pause on a rectangular area. In this short note, we show that, under the stationary regime, speed and location are independent.
Delay-tolerant Networking (DTN) enables communication in sparse mobile ad-hoc networks and other challenged environments where traditional networking fails and new routing and application protocols are required. Past experience with DTN routing and application protocols has shown that their performance is highly dependent on the underlying mobility and node characteristics. Evaluating DTN protocols across many scenarios requires suitable simulation tools. This paper presents the Opportunistic Networking Environment (ONE) simulator specifically designed for evaluating DTN routing and application protocols. It allows users to create scenarios based upon different synthetic movement models and real-world traces and offers a framework for implementing routing and application protocols (already including six well-known routing protocols). Interactive visualization and post-processing tools support evaluating experiments and an emulation mode allows the ONE simulator to become part of a real-world DTN testbed. We show sample simulations to demonstrate the simulator's flexible support for DTN protocol evaluation.
In simulations of mobile ad hoc networks, the probability distribution governing the movement of the nodes typically varies over time and converges to a "steady-state" distribution, known in the probability literature as the stationary distribution. Some published simulation results ignore this initialization discrepancy. For those results that attempt to account for this discrepancy, the practice is to discard an initial sequence of observations from a simulation in the hope that the remaining values will closely represent the stationary distribution. This approach is inefficient and not always reliable. However, if the initial locations and speeds of the nodes are chosen from the stationary distribution, convergence is immediate and no data need be discarded. We derive the stationary distributions for location, speed, and pause time for the random waypoint mobility model. We then show how to implement the random waypoint mobility model in order to construct more efficient and reliable simulations for mobile ad hoc networks. Simulation results, which verify the correctness of our method, are included. In addition, implementation of our method for the NS-2 simulator is available.