A Joint Replication-Migration-based Routing in Delay Tolerant Networks

Abstract—Delay tolerant networks (DTNs) use mobility-assisted routing, where nodes carry, store, and forward data to each other in order to overcome the intermittent connectivity and limited network capacity of this type of network. In this paper, we propose a routing protocol that includes two mechanisms: message replication and message migration. Each mechanism has two steps: message selection and node selection. In message repli-cation, we choose the smallest hop-count message to replicate. The hop-count threshold is used to control the replication speed. We propose a metric called 2-hop activity level to measure the relay node’s transmission capacity, which is used in node selection. Our protocol includes a novel message migration policy that is used to overcome the limited buffer space and bandwidth of DTN nodes. We validate our protocol via extensive simulation experiments; we use a combination of synthetic and real mobility traces. Index Terms—Buffer management, delay tolerant networks (DTNs), message migration, message replication, routing. I

Forward correction and fountain codes in delay tolerant networks

Abstract—Delay tolerant Ad-hoc Networks make use of mobility of relay nodes to compensate for lack of permanent connectivity and thus enable communication between nodes that are out of range of each other. To decrease delivery delay, the information that needs to be delivered is replicated in the network. Our objective in this paper is to study replication mechanisms that include coding in order to improve the probability of successful delivery within a given time limit. We propose an analytical approach that allows to quantify tradeoffs between resources and performance measures (energy and delay). We study the effect of coding on the performance of the network while optimizing parameters that govern routing. Our results, based on fluid approximations, are compared to simulations which validate the model 1. Index Terms—Forward correction, fountain codes, delay tolerant networks I

SOCIAL AND LOCATION BASED ROUTING IN DELAY TOLERANT NETWORKS

Delay tolerant networks (DTNs) are a special type of wireless mobile networks which may lack continuous network connectivity. Routing in DTNs is very challenging as it must handle network partitions, long delays, and dynamic topology in such networks. Recently, the consideration of social characteristics of mobile nodes provides a new angle of view in the design of DTNs routing protocols. In many DTNs, a multitude of mobile devices are used and carried by people (e.g. pocket switched networks and vehicular networks), whose behaviors are better described by social models. This opens the new possibilities of social-based routing, in which the knowledge of social characteristics is used for making better forwarding decision. However, the social relations do not necessarily reflect the true device communication opportunities in a dynamic DTN. On the other hand, the increasing availability of location technologies (GPS, GSM networks, etc.) enables mobile devices to obtain their locations easily. Consider that an individual’s location history in the real world implies his/her social interests and behaviors to some extent, in this dissertation, we study new social based DTN routing protocols, which utilize location and/or social features to achieve efficient and stable routing for delay tolerant networks. We first incorporate the location features into the social-based DTN routing methods to improve their performance by treating location similarity among nodes as possible social relationship. Then, we dis- cuss the possibility and methods to further improve routing performance by adding limited amount of throw-boxes into the networks to aid the DTN relay. Several throw-boxes based routing protocols and location selection methods for throw-boxes are proposed. All pro- posed routing methods are evaluated via extensive simulations with real life trace data (such as MIT reality, Nokia MDC, and Orange D4D)

The Impact of Rogue Nodes on the Dependability of Opportunistic Networks

Opportunistic Networks (OppNets) are an extension to the classical Mobile Ad hoc Networks (MANETs) where the network is not dependent on any infrastructure (e.g. Access Points or centralized administrative nodes). OppNets can be more flexible than MANETs because an end to end path does not exist and much longer delays can be expected. Whereas a Rogue Access Point is typically immobile in the legacy infrastructure based networks and can have considerable impact on the overall connectivity, the research question in this project evaluates how the pattern and mobility of a rogue nodes impact the dependability and overall "Average Latency" in an Opportunistic Network Environment. We have simulated a subset of the mathematical modeling performed in a previous publication in this regard. Ad hoc networks are very challenging to model due to their mobility and intricate routing schemes. We strategically started our research by exploring the evolution of Opportunistic networks, and then implemented the rogue behavior by utilizing The ONE (Opportunistic Network Environment, by Nokia Research Centre) simulator to carry out our research over rogue behavior. The ONE simulator is an open source simulator developed in Java, simulating the layer 3 of the OSI model. The Rogue behavior is implemented in the simulator to observe the effect of rogue nodes. Finally we extracted the desired dataset to measure the latency by carefully simulating the intended behavior, keeping rest of the parameters (e.g. Node Movement Models, Signal Range and Strength, Point of Interest (POI) etc) unchanged. Our results are encouraging, and coincide with the average latency deterioration patterns as modeled by the previous researchers, with a few exceptions. The practical implementation of plug-in in ONE simulator has shown that only a very high degree of rogue nodes impact the latency, making OppNets more resilient and less vulnerable to malicious attacks

Performance evaluation of cooperation strategies for m-health services and applications

Health telematics are becoming a major improvement for patients’ lives, especially for disabled, elderly, and chronically ill people. Information and communication technologies have rapidly grown along with the mobile Internet concept of anywhere and anytime connection. In this context, Mobile Health (m-Health) proposes healthcare services delivering, overcoming geographical, temporal and even organizational barriers. Pervasive and m-Health services aim to respond several emerging problems in health services, including the increasing number of chronic diseases related to lifestyle, high costs in existing national health services, the need to empower patients and families to self-care and manage their own healthcare, and the need to provide direct access to health services, regardless the time and place. Mobile Health (m- Health) systems include the use of mobile devices and applications that interact with patients and caretakers. However, mobile devices have several constraints (such as, processor, energy, and storage resource limitations), affecting the quality of service and user experience. Architectures based on mobile devices and wireless communications presents several challenged issues and constraints, such as, battery and storage capacity, broadcast constraints, interferences, disconnections, noises, limited bandwidths, and network delays. In this sense, cooperation-based approaches are presented as a solution to solve such limitations, focusing on increasing network connectivity, communication rates, and reliability. Cooperation is an important research topic that has been growing in recent years. With the advent of wireless networks, several recent studies present cooperation mechanisms and algorithms as a solution to improve wireless networks performance. In the absence of a stable network infrastructure, mobile nodes cooperate with each other performing all networking functionalities. For example, it can support intermediate nodes forwarding packets between two distant nodes. This Thesis proposes a novel cooperation strategy for m-Health services and applications. This reputation-based scheme uses a Web-service to handle all the nodes reputation and networking permissions. Its main goal is to provide Internet services to mobile devices without network connectivity through cooperation with neighbor devices. Therefore resolving the above mentioned network problems and resulting in a major improvement for m-Health network architectures performances. A performance evaluation of this proposal through a real network scenario demonstrating and validating this cooperative scheme using a real m-Health application is presented. A cryptography solution for m-Health applications under cooperative environments, called DE4MHA, is also proposed and evaluated using the same real network scenario and the same m-Health application. Finally, this work proposes, a generalized cooperative application framework, called MobiCoop, that extends the incentive-based cooperative scheme for m-Health applications for all mobile applications. Its performance evaluation is also presented through a real network scenario demonstrating and validating MobiCoop using different mobile applications

Understanding Urban Human Mobility for Network Applications

Understanding urban human mobility is crucial for various mobile and network applications. This thesis addresses two key challenges presented by mobile applications, namely urban mobility modeling and its applications in Delay Tolerant Networks (DTNs). First, we model urban human mobility with transportation mode information. Our research is based on two real-life GPS datasets containing approximately 20 and 10 million GPS samples. Previous research has suggested that the trajectories in human mobility have statistically similar features as Lévy Walks. We attempt to explain the Lévy Walks behavior by decomposing them into different classes according to the different transportation modes, such as Walk/Run, Bike, Train/ Subway or Car/Taxi/Bus. We show that human mobility can be modelled as a mixture of different transportation modes, and that these single movement patterns can be approximated by a lognormal distribution rather than a power-law distribution. Then, we demonstrate that the mixture of the decomposed lognormal flight distributions associated with each modality is a power-law distribution, providing an explanation for the emergence of Lévy Walks patterns that characterize human mobility patterns. Second, we find that urban human mobility exhibits strong spatial and temporal patterns. We leverage such human mobility patterns to derive an optimal routing algorithm that minimizes the hop count while maximizing the number of needed nodes in DTNs. We propose a solution framework, called Ameba, for timely data delivery in DTNs. Simulation results with experimental traces indicate that Ameba achieves a comparable delivery ratio to a Flooding-based algorithm, but with much lower overhead. Third, we infer the functions of the sub-areas in three cities by analyzing urban mobility patterns. The analysis is based on three large taxi GPS datasets in Rome, San Francisco and Beijing containing 21, 11 and 17 million GPS points, respectively. We categorize the city regions into four categories, workplaces, entertainment places, residential places and other places. We show that the identification of these functional sub-areas can be utilized to increase the efficiency of urban DTN applications. The three topics pertaining to urban mobility examined in the thesis support the design and implementation of network applications for urban environments.Ihmisen liikkumisen ymmärtäminen on erittäin tärkeää monille mobiiliverkkojen sovelluksille. Tämä väitöskirja käsittelee mobiilikäyttäjien liikkuvuuden mallintamista ja sen soveltamista viiveitä sietävään tiedonvälitykseen urbaanissa ympäristössä. Aloitamme mallintamalla mobiilikäyttäjien liikkuvuutta ottaen huomioon kulkumuodon. Tutkimuksemme perustuu kahteen laajaan GPS-data-aineistoon. Käytetyissä data-aineisto koostuu 10 ja 20 miljoonan havaintopisteen kulkuvälineet sisältävistä GPS-tiedoista. Aikaisemmat tutkimukset ovat ehdottaneet, että liikkuvuusmalleilla on samankaltaisia tilastollisia ominaisuuksia kuin Lévy-kävelyillä. Tutkimuksemme selittää Lévy-kävelyiden käyttäytymisen jakamalla ne erilaisiin kulkumuotoihin, kuten kävely/juoksu, polkupyöräily, juna/metro tai auto/taksi/bussi. Näytämme, että ihmisten liikkuvuus voidaan mallintaa eri kulkumuotojen yhdistelminä ja että yksittäiset liikkuvuusmallit voidaan arvioida logaritmisella normaalijakaumalla paremmin kuin potenssilakia noudattavalla jakaumalla. Lisäksi osoitamme, että yhdistelmä kävelyjen lavennetusta logaritmisesta normaalijakaumasta eri kulkumuotojen kanssa on potenssilakia noudattava jakauma, joka selittää ihmisten liikkuvuusmalleja luonnehtivien Lévy-kävelymallien esiintymisen. Toiseksi osoitamme, että urbaanin ihmisen liikkuvuuteen kuuluu vahvoja aikaan ja paikkaan liittyviä malleja. Johdamme näistä ihmisten liikkuvuusmalleista optimaalisen reititysalgoritmin, joka minimoi tarvittavien hyppyjen määrän ja maksimoi tarvittavien solmujen määrän viiveitä sietävissä verkoissa. Esitämme ratkaisuksi arkkitehtuurikehyksen nimeltä Ameba, joka takaa oikea-aikaisen viestien välityksen viiveitä sietävissä verkoissa. Simulointitulosten perusteella Ameba saavuttaa tulvitukseen perustuvien algoritmien kanssa vertailukelpoisen viestien kuljetussuhteen, mutta pienemmällä resurssikustannuksella. Kolmanneksi päättelemme maantieteellisten osa-alueiden funktiot analysoimalla kolmen kaupungin urbaaneja liikkumismalleja. Analyysi perustuu kolmeen laajaan taksien GPS-paikkatiedosta. GPS-data on kerätty Roomassa, San Franciscossa, ja Pekingissä ja koostuu 21, 11, ja 17 miljoonasta havaintopisteestä. Luokittelemme kaupunkien alueet neljään luokkaan: työpaikat, viihde-, asuin-, ja muut paikat. Näytämme, että näiden luokkien tunnistamista voidaan käyttää parantamaan viiveitä sietävien verkkojen sovellusten tehokkuutta. Kaikki tässä väitöskirjassa käsitellyt mobiilikäyttäjien liikkuvuuden mallintamisen aihepiirit edesauttavat urbaanien ympäristöjen verkkojen sovellusten suunnittelua ja toteutusta

Algorithms to Find Two-Hop Routing Policies in Multiclass Delay Tolerant Networks

Most of the literature on delay tolerant networks (DTNs) focuses on optimal routing policies exploiting a priori knowledge about nodes mobility traces. For the case in which no a priori knowledge is available (very common in practice), apart from basic epidemic routing, the main approaches focus on controlling two-hop routing policies. However, these latter results commonly employ fluid approximation techniques, which, in principle, do not provide any theoretical bound over the approximation ratio. In our work, we focus on the case without a priori mobility knowledge and we provide approximation algorithms with theoretical guarantees that can be applied to cases where the number of hops allowed in the routing process is arbitrary. Our approach is rather flexible allowing us to address heterogeneous mobility patterns and transmission technologies, to consider explicitly the signaling and transmission costs, and to include also nodes discarding packets after a local timeout. We then provide a comprehensive performance evaluation of our algorithms, showing that two-hop routing provides the best tradeoff between delay and energy and that, in this case, they find solutions very close to the optimal ones with a low overhead. Finally, we compare our methods against some state-of-the-art approaches by means of a DTN simulation environment in realistic settings

Application Platforms, Routing Algorithms and Mobility Behavior in Mobile Disruption-Tolerant Networks

Mobile disruption-tolerant networks (DTNs), experience frequent and long duration partitions due to the low density of mobile nodes. In these networks, traditional networking models relying on end-to-end communication cease to work. The topological characteristics of mobile DTNs impose unique challenges for the design and validation of routing protocols and applications. We investigate challenges of mobile DTNs from three different viewpoints: the application layer, a routing perspective, and by studying mobility patterns. In the application layer, we have built 7DS (7th Degree of Separation) as a modular platform to develop mobile disruption-tolerant applications. 7DS offers a class of disruption-tolerant applications to exchange data with other mobile users in the mobile DTN or with the global Internet. In the routing layer, we have designed and implemented PEEP as an interest-aware and energy efficient routing protocol which automatically extracts individual interests of mobile users and estimates the global popularity of data items throughout the network. PEEP considers mobile users' interests and global popularity of data items in its routing decisions to route data toward the community of mobile users who are interested in that data content. Mobility of mobile users impacts the conditions in which routing protocols for mobile DTNs must operate and types of applications that could be provided for mobile networks in general. The current synthetic mobility models do not reflect real-world mobile users' behavior. Trace-based mobility models, also, are based on traces that either represent a specific population of mobile users or do not have enough granularities in representing mobility of mobile users for example cell tower traces. We use Sense Networks' GPS traces that are being collected by monitoring a broad spectrum of mobile users. Using these traces, we employ a Markovian approach to extract inherent patterns in human mobility. We design and implement a new routing algorithm for mobile DTNs based on our Markovian analysis of the human mobility. We explore how the knowledge of the mobility improves the performance of our Markov based routing algorithm. We show that that our Markov based routing algorithm increases the rate of data delivery to popular destinations with consuming less energy than legacy algorithms

A Message Transfer Framework for Enhanced Reliability in Delay-and Disruption-Tolerant Networks

Many infrastructure-less networks require quick, ad hoc deployment and the ability to deliver messages even if no instantaneous end-to-end path can be found. Such networks include large-scale disaster recovery networks, mobile sensor networks for ecological monitoring, ocean sensor networks, people networks, vehicular networks and projects for connectivity in developing regions such as TIER (Technology and Infrastructure for Emerging Regions). These types of networks can be realized with delay-and disruption-tolerant network (DTN) technology. Generally, messages in DTNs are transferred hop-by-hop toward the destination in an overlay above the transport layer called the ''bundle layer''. Unlike mobile ad hoc networks (MANETs), DTNs can tolerate disruption on end-to-end paths by taking advantage of temporal links emerging between nodes as nodes move in the network. Intermediate nodes store messages before forwarding opportunities become available. A series of encounters (i.e., coming within mutual transmission range) among different nodes will eventually deliver the message to the desired destination. The message delivery performance (such as delivery ratio and delay) in a DTN highly depends on time elapsed between encounters (inter-contact time) and the time two nodes remain in each others communication range once a contact is established (contact-duration). As messages are forwarded opportunistically among nodes, it is important to have sufficient contact opportunities in the network for faster, more reliable delivery of messages. In this thesis, we propose a simple yet efficient method for increasing DTN performance by increasing the contact duration of encountered nodes (i.e., mobile devices). Our proposed sticky transfer framework and protocol enable nodes in DTNs to collect neighbors' information, evaluate their movement patterns and amounts of data to transfer in order to make decisions of whether to ''stick'' with a neighbor to complete the necessary data transfers. Nodes intelligently negotiate sticky transfer parameters such as stick duration, mobility speed and movement directions based on user preferences and collected information. The sticky transfer framework can be combined with any DTN routing protocol to improve its performance. Our simulation results show that the proposed framework can improve the message delivery ratio by up to 38% and the end-to-end message transfer delay by up to 36%

Efficient Routing Protocol in Delay Tolerant Networks (DTNs)

Modern Internet protocols demonstrate inefficient performance in those networks where the connectivity between end nodes has intermittent property due to dynamic topology or resource constraints. Network environments where the nodes are characterized by opportunistic connectivity are referred to as Delay Tolerant Networks (DTNs). Highly usable in numerous practical applications such as low-density mobile ad hoc networks, command/response military networks and wireless sensor networks, DTNs have been one of the growing topics of interest characterized by significant amount of research efforts invested in this area over the past decade. Routing is one of the major components significantly affecting the overall performance of DTN networks in terms of resource consumption, data delivery and latency. Over the past few years a number of routing protocols have been proposed. The focus of this thesis is on description, classification and comparison of these protocols. We discuss the state-of-the-art routing schemes and methods in opportunistic networks and classify them into two main deterministic and stochastic routing categories. The classification is based on forwarding decisions in routing methods adopted with or without the knowledge about the network topology and nodes trajectories. The protocols in each class have their own advantages and shortcomings. In the stochastic routing protocols category, simple flooding-based protocols are feasible approaches in those networks where there is a little or no information about the network topology and there is no resource restriction. Epidemic routing is a flooding- based protocol relying upon the distribution of messages through the networks to deliver information to their destinations. To demonstrate the performance of the epidemic routing protocol for information delivery in networks with intermittent connectivities, we provide several simulation experiments and show that this protocol with reasonable aggregate resource consumption, ensures eventual message delivery in networks, using minimal assumptions regarding nodes trajectories, network topology and connectivity of underlying networks and only based on sufficient number of random pair-wise exchanges of messages among mobile nodes. In the following, we introduce the recently proposed network coding concept and discuss coding-based information delivery advantages in wireless networks. Network coding is a recently introduced paradigm to efficiently disseminate data in wireless networks in which data flows coming from multiple sources are combined to increase throughput, reduce delay, and enhance robustness against node failures. Finally, we present some simulation experiments to show the superiority of network coding for information delivery in wireless networks, compared to pure flooding-based mechanisms. /Kir1