Transfer Reliability and Congestion Control Strategies in Opportunistic Networks: A Survey
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paper_title: TCP-BuS: Improving TCP performance in wireless Ad Hoc networks

paper_content:

Reliable data transmission over a wireless multi-hop network, called the ad hoc network, has proven to be non-trivial. The TCP (transmission control protocol), a widely used end-to-end reliable transport protocol in a wired network, is not entirely suitable when applied to a wireless ad hoc network due to TCP's congestion control schemes. In particular, the TCP at the source considers the network as congested when detecting packet losses or timeouts. However, in a wireless ad hoc network when a route disconnection occurs because of node movement, the network mistakes this as a congestion. Therefore, the conventional TCP congestion control mechanism cannot be applied, because a route disconnection must be handled differently from a network congestion. We propose a new mechanism that improves the TCP performance in a wireless ad hoc network where each node can buffer packets during a route disconnection and reestablishment. Additionally, we incorporate new measures to deal with the reliable transmission of important control messages. Our simulation results further confirmed these advantages.
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paper_title: Ad-hoc on-demand distance vector routing

paper_content:

An ad-hoc network is the cooperative engagement of a collection of mobile nodes without the required intervention of any centralized access point or existing infrastructure. We present Ad-hoc On Demand Distance Vector Routing (AODV), a novel algorithm for the operation of such ad-hoc networks. Each mobile host operates as a specialized router, and routes are obtained as needed (i.e., on-demand) with little or no reliance on periodic advertisements. Our new routing algorithm is quite suitable for a dynamic self starting network, as required by users wishing to utilize ad-hoc networks. AODV provides loop-free routes even while repairing broken links. Because the protocol does not require global periodic routing advertisements, the demand on the overall bandwidth available to the mobile nodes is substantially less than in those protocols that do necessitate such advertisements. Nevertheless we can still maintain most of the advantages of basic distance vector routing mechanisms. We show that our algorithm scales to large populations of mobile nodes wishing to form ad-hoc networks. We also include an evaluation methodology and simulation results to verify the operation of our algorithm.
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paper_title: Rate-control snoop : a reliable transport protocol for heterogeneous networks with wired and wireless links

paper_content:

In this paper, a new reliable transport protocol called rate-control snoop is proposed for improving TCP performance over error-prone wireless links. It is implemented at a base station where it performs rate-based transmission control based on characteristics of a data path. The proposed protocol monitors every packet that passes through the path and asks the sender to reduce the transmission rate when packet losses are detected only at a wired link. The performance of the proposed protocol is evaluated by simulations and it shows better throughput than TCP Reno, TCP-Snoop, and end-to-end rate control TCP.
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paper_title: Analysis of TCP performance over mobile ad hoc networks

paper_content:

Mobile ad hoc networks have attracted attention lately as a means of providing continuous network connectivity to mobile computing devices regardless of physical location. Recent research has focused primarily on the routing protocols needed in such an environment. In this paper, we investigate the effects that link breakage due to mobility has on TCP performance. Through simulation, we show that TCP throughput drops significantly when nodes move, due to TCP's inability to recognize the difference between link failure and congestion. We also analyze specific examples, such as a situation where throughput is zero for a particular connection. We introduce a new metric, expected throughput, for the comparison of throughput in multi-hop networks, and then use this metric to show how the use of explicit link failure notification (ELFN) techniques can significantly improve TCP performance.
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paper_title: Optimized link state routing protocol for ad hoc networks

paper_content:

In this paper we propose and discuss an optimized link state routing protocol, named OLSR, for mobile wireless networks. The protocol is based on the link state algorithm and it is proactive (or table-driven) in nature. It employs periodic exchange of messages to maintain topology information of the network at each node. OLSR is an optimization over a pure link state protocol as it compacts the size of information sent in the messages, and furthermore, reduces the number of retransmissions to flood these messages in an entire network. For this purpose, the protocol uses the multipoint relaying technique to efficiently and economically flood its control messages. It provides optimal routes in terms of number of hops, which are immediately available when needed. The proposed protocol is best suitable for large and dense ad hoc networks.
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paper_title: TOM: Topology oriented maintenance in sparse Wireless Sensor Networks

paper_content:

The physical number of sensor nodes constitutes a major cost factor for Wireless Sensor Networks (WSN) deployments. Hence, a natural goal is to minimize the number of sensor nodes to be deployed, while still maintaining the desired properties of the WSN. However, sparse networks even while connected, usually suffer from topology irregularities that negatively impact the network lifetime and responsiveness, i.e., sensor data delivery reliability and latency. In addition, sensor node failures easily complicate/enforce/aggravate these irregularities. Valuable efforts have been conducted to discover topology specific anomalies such as coverage holes or critical/bottleneck nodes. Unfortunately, these efforts suffer from at least one of the following drawbacks: (a) They are centralized and consequently inefficient in large-scale networks, (b) they are tailored to one class of anomalies, or (c) do not propose how to remedy the identified anomaly. In this paper, we focus on sparse WSN which usually show varied topology irregularities and propose an in-network and localized strategy that efficiently (i) discovers generic topology irregularities, and (ii) identifies locations for minimal number of new augmented sensor deployments to remedy topology irregularities and sustain the desired operational requirements. We show the effectiveness and efficiency of the solution through a set of extensive simulations.
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paper_title: PETRA: performance enhancing transport architecture for Satellite communications

paper_content:

This paper presents a performance enhancing transport architecture for the satellite environment. This solution improves the network transport performance by overcoming the limits imposed by a transmission control protocol/Internet protocol (TCP/IP)-based stack suite, while maintaining the interfaces offered by it. This is an important issue since TCP/IP is widely used and most of the applications are based on it. The work starts from the state-of-the-art about the transport layer over satellite by distinguishing two alternative frameworks: the black box (BB) and the complete knowledge (CK) approaches. In the former, the network is considered as a "black box" and only modifications in the terminal tools are permitted. In the latter, the complete control of any network element is allowed so as a performance optimization procedure is possible. The proposed architecture [called Performance Enhancing Transport Architecture (PETRA)] is designed in all details using the second approach. PETRA uses network elements, called relay entities, to isolate the satellite portions in case of heterogeneous networks, while a transport layer protocol stack is used to optimize the transport of information over satellite links. A special satellite transport protocol, that is part of the transport layer protocol stack, is used over such links to perform error recovery. Simulation results show that the proposed framework significantly enhances throughput performance.
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paper_title: Social Pocket Switched Networks

paper_content:

Pocket Switched Network (PSN) communications paradigm builds on opportunistic contacts between mobile devices and human mobility to disseminate content without relying on any infrastructure. We propose MobiClique, a mobile social software that builds and maintains an ad hoc social network overlay over a Pocket Switched Network and allows users to exchange messages between each other and groups of users sharing similar interests. We describe MobiClique implementation and initial experimental results.
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paper_title: Satellite-based Internet: a tutorial

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In a satellite-based Internet system, satellites are used to interconnect heterogeneous network segments and to provide ubiquitous direct Internet access to homes and businesses. This article presents satellite-based Internet architectures and discusses multiple access control, routing, satellite transport, and integrating satellite networks into the global Internet.
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paper_title: Energy-efficient computing for wildlife tracking: design tradeoffs and early experiences with ZebraNet

paper_content:

Over the past decade, mobile computing and wireless communication have become increasingly important drivers of many new computing applications. The field of wireless sensor networks particularly focuses on applications involving autonomous use of compute, sensing, and wireless communication devices for both scientific and commercial purposes. This paper examines the research decisions and design tradeoffs that arise when applying wireless peer-to-peer networking techniques in a mobile sensor network designed to support wildlife tracking for biology research.The ZebraNet system includes custom tracking collars (nodes) carried by animals under study across a large, wild area; the collars operate as a peer-to-peer network to deliver logged data back to researchers. The collars include global positioning system (GPS), Flash memory, wireless transceivers, and a small CPU; essentially each node is a small, wireless computing device. Since there is no cellular service or broadcast communication covering the region where animals are studied, ad hoc, peer-to-peer routing is needed. Although numerous ad hoc protocols exist, additional challenges arise because the researchers themselves are mobile and thus there is no fixed base station towards which to aim data. Overall, our goal is to use the least energy, storage, and other resources necessary to maintain a reliable system with a very high `data homing' success rate. We plan to deploy a 30-node ZebraNet system at the Mpala Research Centre in central Kenya. More broadly, we believe that the domain-centric protocols and energy tradeoffs presented here for ZebraNet will have general applicability in other wireless and sensor applications.
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paper_title: Routing in a delay tolerant network

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We formulate the delay-tolerant networking routing problem, where messages are to be moved end-to-end across a connectivity graph that is time-varying but whose dynamics may be known in advance. The problem has the added constraints of finite buffers at each node and the general property that no contemporaneous end-to-end path may ever exist. This situation limits the applicability of traditional routing approaches that tend to treat outages as failures and seek to find an existing end-to-end path. We propose a framework for evaluating routing algorithms in such environments. We then develop several algorithms and use simulations to compare their performance with respect to the amount of knowledge they require about network topology. We find that, as expected, the algorithms using the least knowledge tend to perform poorly. We also find that with limited additional knowledge, far less than complete global knowledge, efficient algorithms can be constructed for routing in such environments. To the best of our knowledge this is the first such investigation of routing issues in DTNs.
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paper_title: Epidemic Routing for Partially-Connected Ad Hoc Networks

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Mobile ad hoc routing protocols allow nodes with wireless adaptors to communicate with one another without any pre-existing network infrastructure. Existing ad hoc routing protocols, while robust to rapidly changing network topology, assume the presence of a connected path from source to destination. Given power limitations, the advent of short-range wireless networks, and the wide physical conditions over which ad hoc networks must be deployed, in some scenarios it is likely that this assumption is invalid. In this work, we develop techniques to deliver messages in the case where there is never a connected path from source to destination or when a network partition exists at the time a message is originated. To this end, we introduce Epidemic Routing, where random pair-wise exchanges of messages among mobile hosts ensure eventual message delivery. The goals of Epidemic Routing are to: i) maximize message delivery rate, ii) minimize message latency, and iii) minimize the total resources consumed in message delivery. Through an implementation in the Monarch simulator, we show that Epidemic Routing achieves eventual delivery of 100% of messages with reasonable aggregate resource consumption in a number of interesting scenarios.
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paper_title: Social network analysis for routing in disconnected delay-tolerant MANETs

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Message delivery in sparse Mobile Ad hoc Networks (MANETs) is difficult due to the fact that the network graph is rarely (if ever) connected. A key challenge is to find a route that can provide good delivery performance and low end-to-end delay in a disconnected network graph where nodes may move freely. This paper presents a multidisciplinary solution based on the consideration of the so-called small world dynamics which have been proposed for economy and social studies and have recently revealed to be a successful approach to be exploited for characterising information propagation in wireless networks. To this purpose, some bridge nodes are identified based on their centrality characteristics, i.e., on their capability to broker information exchange among otherwise disconnected nodes. Due to the complexity of the centrality metrics in populated networks the concept of ego networks is exploited where nodes are not required to exchange information about the entire network topology, but only locally available information is considered. Then SimBet Routing is proposed which exploits the exchange of pre-estimated "betweenness' centrality metrics and locally determined social "similarity' to the destination node. We present simulations using real trace data to demonstrate that SimBet Routing results in delivery performance close to Epidemic Routing but with significantly reduced overhead. Additionally, we show that SimBet Routing outperforms PRoPHET Routing, particularly when the sending and receiving nodes have low connectivity.
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paper_title: Probabilistic routing in intermittently connected networks

paper_content:

We consider the problem of routing in intermittently connected networks. In such networks there is no guarantee that a fully connected path between source and destination exist at any time, rendering traditional routing protocols unable to deliver messages between hosts. We propose a probabilistic routing protocol for such networks.
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paper_title: Accommodating Transient Connectivity in Ad Hoc and Mobile Settings

paper_content:

Much of the work on networking and communications is based on the premise that components interact in one of two ways: either they are connected via a stable wired or wireless network, or they make use of persistent storage repositories accessible to the communicating parties. A new generation of networks raises serious questions about the validity of these fundamental assumptions. In mobile ad hoc wireless networks connections are transient and availability of persistent storage is rare. This paper is concerned with achieving communication among mobile devices that may never find themselves in direct or indirect contact with each other at any point in time. A unique feature of our contribution is the idea of exploiting information associated with the motion and availability profiles of the devices making up the ad hoc network. This is the starting point for an investigation into a range of possible solutions whose essential features are controlled by the manner in which motion profiles are acquired and the extent to which such knowledge is available across an ad hoc network.
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paper_title: BUBBLE Rap: Social-Based Forwarding in Delay-Tolerant Networks

paper_content:

The increasing penetration of smart devices with networking capability form novel networks. Such networks, also referred as pocket switched networks (PSNs), are intermittently connected and represent a paradigm shift of forwarding data in an ad hoc manner. The social structure and interaction of users of such devices dictate the performance of routing protocols in PSNs. To that end, social information is an essential metric for designing forwarding algorithms for such types of networks. Previous methods relied on building and updating routing tables to cope with dynamic network conditions. On the downside, it has been shown that such approaches end up being cost ineffective due to the partial capture of the transient network behavior. A more promising approach would be to capture the intrinsic characteristics of such networks and utilize them in the design of routing algorithms. In this paper, we exploit two social and structural metrics, namely centrality and community, using real human mobility traces. The contributions of this paper are two-fold. First, we design and evaluate BUBBLE, a novel social-based forwarding algorithm, that utilizes the aforementioned metrics to enhance delivery performance. Second, we empirically show that BUBBLE can substantially improve forwarding performance compared to a number of previously proposed algorithms including the benchmarking history-based PROPHET algorithm, and social-based forwarding SimBet algorithm.
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paper_title: MaxProp: Routing for Vehicle-Based Disruption-Tolerant Networks

paper_content:

Disruption-tolerant networks (DTNs) attempt to route network messages via intermittently connected nodes. Routing in such environments is difficult because peers have little information about the state of the partitioned network and transfer opportunities between peers are of limited duration. In this paper, we propose MaxProp, a protocol for effective routing of DTN messages. MaxProp is based on prioritizing both the schedule of packets transmitted to other peers and the schedule of packets to be dropped. These priorities are based on the path likelihoods to peers according to historical data and also on several complementary mechanisms, including acknowledgments, a head-start for new packets, and lists of previous intermediaries. Our evaluations show that MaxProp performs better than protocols that have access to an oracle that knows the schedule of meetings between peers. Our evaluations are based on 60 days of traces from a real DTN network we have deployed on 30 buses. Our network, called UMassDieselNet, serves a large geographic area between five colleges. We also evaluate MaxProp on simulated topologies and show it performs well in a wide variety of DTN environments.
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paper_title: Routing in Delay/Disruption Tolerant Networks: A Taxonomy, Survey and Challenges

paper_content:

The introduction of intelligent devices with short range wireless communication techniques has motivated the development of Mobile Ad hoc NETworks (MANETs) during the last few years. However, traditional end-to-end based routing algorithms designed for MANETs are not much robust in the challenged networks suffering from frequent disruption, sparse network density and limited device capability. Such challenged networks, also known as Intermittently Connected Networks (ICNs) adopt the Store-Carry-Forward (SCF) behavior arising from the mobility of mobile nodes for message relaying. In this article, we consider the term ICNs as Delay/Disruption Tolerant Networks (DTNs) for the purpose of generalization, since DTNs have been envisioned for different applications with a large number of proposed routing algorithms. Motivated by the great interest from the research community, we firstly review the existing unicasting issue of DTNs because of its extensive research stage. Then, we also address multicasting and anycasting issues in DTNs considering their perspectives. A detail survey based on our taxonomy over the period from 2006 to 2010 is not only provided but also a comparison is given. We further identify the remaining challenges and open issues followed by an evaluation framework proposed for routing in DTNs. Finally, we summarize our contribution with three future research topics highlighted.
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paper_title: Data MULEs: modeling a three-tier architecture for sparse sensor networks

paper_content:

This paper presents and analyzes an architecture to collect sensor data in sparse sensor networks. Our approach exploits the presence of mobile entities (called MULEs) present in the environment. MULEs pick up data from the sensors when in close range, buffer it, and drop off the data to wired access points. This can lead to substantial power savings at the sensors as they only have to transmit over a short range. This paper focuses on a simple analytical model for understanding performance as system parameters are scaled. Our model assumes two-dimensional random walk for mobility and incorporates key system variables such as number of MULEs, sensors and access points. The performance metrics observed are the data success rate (the fraction of generated data that reaches the access points) and the required buffer capacities on the sensors and the MULEs. The modeling along with simulation results can be used for further analysis and provide certain guidelines for deployment of such systems.
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paper_title: Performance of TCP protocols in deep space communication networks

paper_content:

The communication requirements for space missions necessitate to address the problems due to deep space communication networks. In this letter, the effects of slow start algorithm, propagation delay and the link errors on the throughput performance of transport layer protocols are investigated in deep space communication networks. The objective of this letter is to demonstrate through experimental results that existing TCP protocols are far from satisfying the deep space communication requirements and point out the urgent need for new TCP solutions.
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paper_title: Requirements for Internet Hosts -- Communication Layers

paper_content:

This RFC is an official specification for the Internet community. It ::: incorporates by reference, amends, corrects, and supplements the ::: primary protocol standards documents relating to hosts. [STANDARDS- ::: TRACK]
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paper_title: Rate-control snoop : a reliable transport protocol for heterogeneous networks with wired and wireless links

paper_content:

In this paper, a new reliable transport protocol called rate-control snoop is proposed for improving TCP performance over error-prone wireless links. It is implemented at a base station where it performs rate-based transmission control based on characteristics of a data path. The proposed protocol monitors every packet that passes through the path and asks the sender to reduce the transmission rate when packet losses are detected only at a wired link. The performance of the proposed protocol is evaluated by simulations and it shows better throughput than TCP Reno, TCP-Snoop, and end-to-end rate control TCP.
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paper_title: Analysis of TCP performance over mobile ad hoc networks

paper_content:

Mobile ad hoc networks have attracted attention lately as a means of providing continuous network connectivity to mobile computing devices regardless of physical location. Recent research has focused primarily on the routing protocols needed in such an environment. In this paper, we investigate the effects that link breakage due to mobility has on TCP performance. Through simulation, we show that TCP throughput drops significantly when nodes move, due to TCP's inability to recognize the difference between link failure and congestion. We also analyze specific examples, such as a situation where throughput is zero for a particular connection. We introduce a new metric, expected throughput, for the comparison of throughput in multi-hop networks, and then use this metric to show how the use of explicit link failure notification (ELFN) techniques can significantly improve TCP performance.
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paper_title: Protocols for reliable data transport in space internet

paper_content:

A variety of protocols have been proposed for reliable data transport in space Internet and similar network environments. It is necessary to conduct a survey on these protocols to investigate and compare among them. In this article, we present a survey on the protocols proposed for reliable data transport in space Internet, with a focus on the latest developments. The survey includes the following contents: (1) classification of these protocols into different approaches; (2) discussions and comments on the design and operation methods of the protocols; and (3) comparisons and comments on the main techniques and performance of the protocols.
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paper_title: TP-planet: a reliable transport protocol for interplanetary Internet

paper_content:

Space exploration missions are crucial for acquisition of information about space and the Universe. The entire success of a mission is directly related to the satisfaction of its communications needs. For this goal, the challenges posed by the InterPlaNetary (IPN) Internet need to be addressed. Current transmission control protocols (TCPs) have very poor performance in the IPN Internet, which is characterized by extremely high propagation delays, link errors, asymmetrical bandwidth, and blackouts. The window-based congestion control, which injects a new packet into the network upon an ACK reception, is responsible for such performance degradation due to high propagation delay. Slow start algorithms of the existing TCPs further contribute to the performance degradation by wasting long time periods to reach the actual data rate. Moreover, wireless link errors amplify the problem by misleading the TCP source to unnecessarily throttle the congestion window. The recovery from erroneous window decrease takes a certain amount of time, which is proportional to the round-trip time (RTT) and further decreases the network performance. In this paper, a reliable transport protocol (TP-Planet) is presented for data traffic in the IPN Internet. It is intended to address the challenges and to achieve high throughput performance and reliable data transmission on deep-space links of the IPN Backbone Network. TP-Planet deploys a rate-based additive-increase multiplicative-decrease (AIMD) congestion control, whose AIMD parameters are tuned to help avoid throughput degradation. TP-Planet replaces the inefficient slow start algorithm with a novel Initial State algorithm, which allows the capture of link resources in a very fast and controlled manner. A new congestion detection and control mechanism is developed, which decouples congestion decisions from single packet losses in order to avoid the erroneous congestion decisions due to high link errors. In order to reduce the effects of blackout conditions on the throughput performance, TP-Planet incorporates the blackout state procedure into the protocol operation. The bandwidth asymmetry problem is addressed by the adoption of delayed selective acknowledgment (SACK). Simulation experiments show that the TP-Planet significantly improves the throughput performance and addresses the challenges posed by the IPN Backbone Network.
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paper_title: Mobility increases the capacity of ad-hoc wireless networks

paper_content:

The capacity of ad hoc wireless networks is constrained by the mutual interference of concurrent transmissions between nodes. We study a model of an ad hoc network where n nodes communicate in random source-destination pairs. These nodes are assumed to be mobile. We examine the per-session throughput for applications with loose delay constraints, such that the topology changes over the time-scale of packet delivery. Under this assumption, the per-user throughput can increase dramatically when nodes are mobile rather than fixed. This improvement can be achieved by exploiting a form of multiuser diversity via packet relaying.
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paper_title: Transport Layer Issues in Delay Tolerant Mobile Networks

paper_content:

The tremendous increase in wireless devices and user mobility have ultimately resulted in a new set of networking challenges that previously did not exist. Some of these challenges include large delays, intermittent connectivity and most importantly, the absence of an end-to-end path from sources to destinations. Networks characterized by one or more of these challenges are called Delay Tolerant Networks (DTNs). Researchers have studied DTNs with a major focus on routing issues in such extreme environments. As a result, in this paper, we shift this focus towards addressing and studying transport layer issues in extreme networking environments. We particularly concentrate on investigating and comparing several reliability approaches in a specific category of DTNs known as Delay Tolerant Mobile Networks (DTMNs). We present four different reliability approaches in DTMNs. We also evaluate these approaches under various network conditions via simulation. Our goals from this study are to examine the impact of these reliability approaches, understand the tradeoffs between them, and open the way for further work in transport layer issues in delay tolerant networks.
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paper_title: Game Theory: Analysis of Conflict

paper_content:

Preface 1. Decision-Theoretic Foundations 1.1 Game Theory, Rationality, and Intelligence 1.2 Basic Concepts of Decision Theory 1.3 Axioms 1.4 The Expected-Utility Maximization Theorem 1.5 Equivalent Representations 1.6 Bayesian Conditional-Probability Systems 1.7 Limitations of the Bayesian Model 1.8 Domination 1.9 Proofs of the Domination Theorems Exercises 2. Basic Models 2.1 Games in Extensive Form 2.2 Strategic Form and the Normal Representation 2.3 Equivalence of Strategic-Form Games 2.4 Reduced Normal Representations 2.5 Elimination of Dominated Strategies 2.6 Multiagent Representations 2.7 Common Knowledge 2.8 Bayesian Games 2.9 Modeling Games with Incomplete Information Exercises 3. Equilibria of Strategic-Form Games 3.1 Domination and Ratonalizability 3.2 Nash Equilibrium 3.3 Computing Nash Equilibria 3.4 Significance of Nash Equilibria 3.5 The Focal-Point Effect 3.6 The Decision-Analytic Approach to Games 3.7 Evolution. Resistance. and Risk Dominance 3.8 Two-Person Zero-Sum Games 3.9 Bayesian Equilibria 3.10 Purification of Randomized Strategies in Equilibria 3.11 Auctions 3.12 Proof of Existence of Equilibrium 3.13 Infinite Strategy Sets Exercises 4. Sequential Equilibria of Extensive-Form Games 4.1 Mixed Strategies and Behavioral Strategies 4.2 Equilibria in Behavioral Strategies 4.3 Sequential Rationality at Information States with Positive Probability 4.4 Consistent Beliefs and Sequential Rationality at All Information States 4.5 Computing Sequential Equilibria 4.6 Subgame-Perfect Equilibria 4.7 Games with Perfect Information 4.8 Adding Chance Events with Small Probability 4.9 Forward Induction 4.10 Voting and Binary Agendas 4.11 Technical Proofs Exercises 5. Refinements of Equilibrium in Strategic Form 5.1 Introduction 5.2 Perfect Equilibria 5.3 Existence of Perfect and Sequential Equilibria 5.4 Proper Equilibria 5.5 Persistent Equilibria 5.6 Stable Sets 01 Equilibria 5.7 Generic Properties 5.8 Conclusions Exercises 6. Games with Communication 6.1 Contracts and Correlated Strategies 6.2 Correlated Equilibria 6.3 Bayesian Games with Communication 6.4 Bayesian Collective-Choice Problems and Bayesian Bargaining Problems 6.5 Trading Problems with Linear Utility 6.6 General Participation Constraints for Bayesian Games with Contracts 6.7 Sender-Receiver Games 6.8 Acceptable and Predominant Correlated Equilibria 6.9 Communication in Extensive-Form and Multistage Games Exercises Bibliographic Note 7. Repeated Games 7.1 The Repeated Prisoners Dilemma 7.2 A General Model of Repeated Garnet 7.3 Stationary Equilibria of Repeated Games with Complete State Information and Discounting 7.4 Repeated Games with Standard Information: Examples 7.5 General Feasibility Theorems for Standard Repeated Games 7.6 Finitely Repeated Games and the Role of Initial Doubt 7.7 Imperfect Observability of Moves 7.8 Repeated Wines in Large Decentralized Groups 7.9 Repeated Games with Incomplete Information 7.10 Continuous Time 7.11 Evolutionary Simulation of Repeated Games Exercises 8. Bargaining and Cooperation in Two-Person Games 8.1 Noncooperative Foundations of Cooperative Game Theory 8.2 Two-Person Bargaining Problems and the Nash Bargaining Solution 8.3 Interpersonal Comparisons of Weighted Utility 8.4 Transferable Utility 8.5 Rational Threats 8.6 Other Bargaining Solutions 8.7 An Alternating-Offer Bargaining Game 8.8 An Alternating-Offer Game with Incomplete Information 8.9 A Discrete Alternating-Offer Game 8.10 Renegotiation Exercises 9. Coalitions in Cooperative Games 9.1 Introduction to Coalitional Analysis 9.2 Characteristic Functions with Transferable Utility 9.3 The Core 9.4 The Shapkey Value 9.5 Values with Cooperation Structures 9.6 Other Solution Concepts 9.7 Colational Games with Nontransferable Utility 9.8 Cores without Transferable Utility 9.9 Values without Transferable Utility Exercises Bibliographic Note 10. Cooperation under Uncertainty 10.1 Introduction 10.2 Concepts of Efficiency 10.3 An Example 10.4 Ex Post Inefficiency and Subsequent Oilers 10.5 Computing Incentive-Efficient Mechanisms 10.6 Inscrutability and Durability 10.7 Mechanism Selection by an Informed Principal 10.8 Neutral Bargaining Solutions 10.9 Dynamic Matching Processes with Incomplete Information Exercises Bibliography Index
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paper_title: Autonomous Congestion Control in Delay-Tolerant Networks

paper_content:

Congestion control is an important feature that directly affects network performance. Network congestion may cause loss of data or long delays. Although this problem has been studied extensively in the Internet, the solutions for Internet congestion control do not apply readily to challenged network environments such as Delay Tolerant Networks (DTN) where end-to-end connectivity may not exist continuously and latency can be high. In DTN, end-to-end rate control is not feasible. This calls for congestion control mechanisms where the decisions can be made autonomously with local information only. We use an economic pricing model and propose a rule-based congestion control mechanism where each router can autonomously decide on whether to accept a bundle (data) based on local information such as available storage and the value and risk of accepting the bundle (derived from historical statistics).
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paper_title: Congestion management in delay tolerant networks

paper_content:

In delay tolerant networks, custody transfer can provide certain degree of reliability as a custodian node cannot discard a message unless its life time expires or the custody is transferred to another node after a commitment. This creates a challenging decision making problem at a node in determining whether to accept a custody transfer: on one hand, it is beneficial to accept a large number of messages as it can potentially advance the messages toward their ultimate destinations and network utilization can be maximized; on the other hand, if the receiving node over-commits itself by accepting too many messages, it may find itself setting aside an excessive amount of storage and thereby preventing itself from receiving further potentially important, high yield (in terms of network utilization) messages. To solve this problem, in this paper, we apply the concept of revenue management, and employ dynamic programming to develop a congestion management strategy for delay tolerant networks. For a class of network utility functions, we show that the optimal solution is completely distributed in nature where only the local information such as available storage space of a node is required. This is particularly important given the nature of delay tolerant networks where global information is often not available and the network is inherently dynamic. Our simulation results show that the proposed congestion management scheme is effective in avoiding congestion and balancing network load among the nodes.
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paper_title: Fair Routing in Delay Tolerant Networks

paper_content:

The typical state-of-the-art routing algorithms for delay tolerant networks are based on best next hop hill-climbing heuristics in order to achieve throughput and efficiency. The combination of these heuristics and the social network structure leads the routing to direct most of the traffic through a small subset of good users. For instance, in the SimBet algorithm, the top 10% of users carry out 54% of all the forwards and 85% of all the handovers. This unfair load distribution is not sustainable as it can quickly deplete constraint resources in heavily utilized mobile devices (e.g. storage, battery, budget, etc.). Moreover, because a small number of users carry a significant amount of the traffic, the system is not robust to random failures and attacks. To overcome these inefficiencies, this paper introduces Fair-Route, a routing algorithm for delay tolerant networks inspired by the social processes of perceived interaction strength, where messages are preferably forwarded to users that have a stronger social relation with the target of the message; and assortativity, that limits the exchange of messages to those users with similar "social status". We compare the performance of FairRoute to the state-of-the-art algorithms by extensive simulations on the MIT reality mining dataset. The results show that our algorithm outperforms existing algorithms in the de facto benchmark of throughput vs. forwards. Furthermore, it distributes better the load; the top 10% carry out 26% of the forwards and 28% of the handovers without any loss in performance.
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paper_title: A sociability-based routing scheme for delay-tolerant networks

paper_content:

The problem of choosing the best forwarders in Delay-Tolerant Networks (DTNs) is crucial for minimizing the delay in packet delivery and for keeping the amount of generated traffic under control. In this paper, we introduce sociable routing, a novel routing strategy that selects a subset of optimal forwarders among all the nodes and relies on them for an efficient delivery. The key idea is that of assigning to each network node a time-varying scalar parameter which captures its social behavior in terms of frequency and types of encounters. This sociability concept is widely discussed and mathematically formalized. Simulation results of a DTN of vehicles in urban environment, driven by real mobility traces, and employing sociable routing, is presented. Encouraging results show that sociable routing, compared to other known protocols, achieves a good compromise in terms of delay performance and amount of generated traffic.
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paper_title: Opportunistic content distribution in an urban setting

paper_content:

This paper investigates the feasibility of a city-wide content distribution architecture composed of short range wireless access points. We look at how a target group of intermittently and partially connected mobile nodes can improve the diffusion of information within the group by leveraging fixed and mobile nodes that are exterior to the group. The fixed nodes are data sources, and the external mobile nodes are data relays, and we examine the trade off between the use of each in order to obtain high satisfaction within the target group, which consists of data sinks. We conducted an experiment in Cambridge, UK, to gather mobility traces that we used for the study of this content distribution architecture. In this scenario, the simple fact that members of the target group collaborate leads to a delivery ratio of 90%. In addition, the use of external mobile nodes to relay the information slightly increases the delivery ratio while significantly decreasing the delay.
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paper_title: An enhanced congestion aware adaptive routing protocol for opportunistic networks

paper_content:

The adaptive routing protocol recently proposed by researchers for opportunistic networks often makes an assumption that when each node makes an intelligent decision of choosing a best forwarder node to route its messages, the chosen forwarder will often have a large buffer storage and will always altruistically devote its resources for forwarding those messages towards their destination nodes. However, copies of messages fill up buffers on receiving intermediate nodes very quickly when few nodes become more central than the other nodes and when the connectivity becomes more and more intermittent. This paper investigates about a more realistic behavior of mobile opportunistic nodes where the storage buffer in nodes gets full very quickly, especially at the more centric nodes, when such nodes store, carry and forward messages for other nodes. Because of these practical issues, messages passed to most popular nodes just get dropped when the buffers get filled up which ultimately results in the performance degradation of the network. We investigate the cases of buffer overflow and analyze how the performance of a considered opportunistic networking environment can get degraded when buffers get overflowed. We then propose an algorithmic approach where nodes choose the potential nodes based not only on potential nodes' predicted connectivity to other nodes but also based on the other factors such as available buffer space in the potential intermediate nodes and the intermediate nodes' willingness to store, carry and forward messages for other nodes. Our initial simulation based experiment results are encouraging and indicate that a congestion aware adaptive routing protocol performs well and the overall network performance increases by means of the number of messages delivered when the message forwarding is constrained by the buffer size.
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paper_title: Towards designing a routing protocol for opportunistic networks

paper_content:

Intermittently connected opportunistic networks experience frequent disconnections and shorter contact durations. Therefore routing of messages towards their destinations needs to be handled from various points of view. Predictability and connectedness are two information which can be determined by participating mobile nodes of an opportunistic content distribution network using their past contacts. Epidemic or probabilistic routing protocols do not fully utilize these information to route messages towards their destinations. In this paper we describe the routing algorithm, implementation details, experiment design and the performance validation of a new, adaptive routing protocol which utilizes the predictability and connectedness information to route messages efficiently. Simulation based comparative studies show that the proposed routing protocol outperforms existing Epidemic and probabilistic routing protocols in delivering messages.
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paper_title: A complex network analysis of human mobility

paper_content:

Opportunistic networks use human mobility and consequent wireless contacts between mobile devices, to disseminate data in a peer-to-peer manner. To grasp the potential and limitations of such networks, as well as to design appropriate algorithms and protocols, it is key to understand the statistics of contacts. To date, contact analysis has mainly focused on statistics such as inter-contact and contact distributions. While these pair-wise properties are important, we argue that structural properties of contacts need more thorough analysis. For example, communities of tightly connected nodes, have a great impact on the performance of opportunistic networks and the design of algorithms and protocols.
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paper_title: Pocket switched networks and human mobility in conference environments

paper_content:

Pocket Switched Networks (PSN) make use of both human mobility and local/global connectivity in order to transfer data between mobile users' devices. This falls under the Delay Tolerant Networking (DTN) space, focusing on the use of opportunistic networking. One key problem in PSN is in designing forwarding algorithms which cope with human mobility patterns. We present an experiment measuring forty-one humans' mobility at the Infocom 2005 conference. The results of this experiment are similar to our previous experiments in corporate and academic working environments, in exhibiting a power-law distrbution for the time between node contacts. We then discuss the implications of these results on the design of forwarding algorithms for PSN.
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paper_title: Social network analysis for routing in disconnected delay-tolerant MANETs

paper_content:

Message delivery in sparse Mobile Ad hoc Networks (MANETs) is difficult due to the fact that the network graph is rarely (if ever) connected. A key challenge is to find a route that can provide good delivery performance and low end-to-end delay in a disconnected network graph where nodes may move freely. This paper presents a multidisciplinary solution based on the consideration of the so-called small world dynamics which have been proposed for economy and social studies and have recently revealed to be a successful approach to be exploited for characterising information propagation in wireless networks. To this purpose, some bridge nodes are identified based on their centrality characteristics, i.e., on their capability to broker information exchange among otherwise disconnected nodes. Due to the complexity of the centrality metrics in populated networks the concept of ego networks is exploited where nodes are not required to exchange information about the entire network topology, but only locally available information is considered. Then SimBet Routing is proposed which exploits the exchange of pre-estimated "betweenness' centrality metrics and locally determined social "similarity' to the destination node. We present simulations using real trace data to demonstrate that SimBet Routing results in delivery performance close to Epidemic Routing but with significantly reduced overhead. Additionally, we show that SimBet Routing outperforms PRoPHET Routing, particularly when the sending and receiving nodes have low connectivity.
---
paper_title: Traffic distribution and network capacity analysis in social opportunistic networks

paper_content:

Social opportunistic networks are intermittently connected mobile ad hoc networks (ICNs) that exploit human mobility to physically carry messages between disconnected parts of the network. Human mobility thus plays an essential role in the performance of forwarding protocols in the networks, and people's movements are in turn affected by their social interactions with each other. In this paper we present an analysis of the traffic distribution among the nodes of social opportunistic networks and its impact on network capacity. For our analysis, we use a human contact graph that represents a social network of individuals. We characterize the graph as a scale-free network and apply forwarding strategies based on the information required by a node to select relays for its messages, categorising this information either as isolated or complete network or local network knowledge. We use a social network property, centrality, for the forwarding strategies, additionally considering tie strength in the forwarding metric and investigate their impact on traffic distribution. We show that all the strategies result in unfair traffic distribution due to a strong non-random structure of the networks, where hub nodes process much more relay traffic than non-hub nodes. Finally, we present a mathematical model of network capacity as an upper-bound of network delivery performance where hub nodes' resources become the limiting factors, and show that including tie strength in the forwarding metric improves the network capacity.
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paper_title: BUBBLE Rap: Social-Based Forwarding in Delay-Tolerant Networks

paper_content:

The increasing penetration of smart devices with networking capability form novel networks. Such networks, also referred as pocket switched networks (PSNs), are intermittently connected and represent a paradigm shift of forwarding data in an ad hoc manner. The social structure and interaction of users of such devices dictate the performance of routing protocols in PSNs. To that end, social information is an essential metric for designing forwarding algorithms for such types of networks. Previous methods relied on building and updating routing tables to cope with dynamic network conditions. On the downside, it has been shown that such approaches end up being cost ineffective due to the partial capture of the transient network behavior. A more promising approach would be to capture the intrinsic characteristics of such networks and utilize them in the design of routing algorithms. In this paper, we exploit two social and structural metrics, namely centrality and community, using real human mobility traces. The contributions of this paper are two-fold. First, we design and evaluate BUBBLE, a novel social-based forwarding algorithm, that utilizes the aforementioned metrics to enhance delivery performance. Second, we empirically show that BUBBLE can substantially improve forwarding performance compared to a number of previously proposed algorithms including the benchmarking history-based PROPHET algorithm, and social-based forwarding SimBet algorithm.
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paper_title: Congestion aware forwarding in delay tolerant and social opportunistic networks

paper_content:

We propose an approach for opportunistic forwarding that supports optimization of multipoint high volume data flow transfer while maintaining high buffer availability and low delays. This paper explores a number of social, buffer and delay heuristics to offload the traffic from congested parts of the network and spread it over less congested parts of the network in order to keep low delays, high success ratios and high availability of nodes. We conduct an extensive set of experiments for assessing the performance of four newly proposed heuristics and compare them with Epidemic, Prophet, Spay and Wait and Spay and Focus protocols over real connectivity driven traces (RollerNet) and with a realistic publish subscribe filecasting application. We look into success ratio of answered queries, download times (delays) and availability of buffer across eight protocols for varying congestion levels in the face of increasing number of publishers and topic popularity. We show that all of our combined metrics perform better than Epidemic protocol, Prophet, Spray and Wait, Spray and Focus and our previous prototype across all the assessed criteria.
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paper_title: Disruption-Tolerant Networking: A Comprehensive Survey on Recent Developments and Persisting Challenges

paper_content:

Nowadays, wireless networks are witnessing several deployments in various extreme environments where they suffer from different levels of link disruptions depending on the severity of the operating conditions. In all cases, their operation requirements are differently altered and their performance is negatively affected rendering them heterogeneous by nature. In the open literature, these networks are known as Intermittently Connected Networks (ICNs). The existing Internet protocols fail to operate properly in the context of ICNs, thus raising a variety of new challenging problems that are attracting the attention of the networking research community. Delay-/Disruption-Tolerant Networking emerged as a highly active area of research where networking experts compete in addressing the various ICN problems. Over time, unicast routing, one of the architectural key components common to all ICNs, became an almost independent field of research in which significant efforts continue to be invested. In contrast, network architectural designs, scheduling and forwarding issues dating from the early days of Inter-Planetary Networks (IPNs) have received relatively little attention and accumulate numerous pending challenges. Moreover, the gap caused by the lack of accurate ICN mathematical models is still large irrespective of some of the appreciated seminal works in this direction. This paper sheds the light over the latest advancements in each of the above-mentioned research sectors and highlight pending open issues in each of them.
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paper_title: A DTN congestion avoidance strategy based on path avoidance

paper_content:

The traditional congestion control mechanisms are established upon the assumption that there is a contemporaneous end-to-end path in the network and these methods can't be used in DTN. This paper has proposed a new congestion avoidance mechanism based on path avoidance for DTN. This mechanism optimizes the management of node storage and divides the node state into normal state, congestion adjacent state, congestion state. Based on the different node states correspondingly separate strategies is employed to avoiding congestion. Simulation is performed through OPNET and the results demonstrate that new avoidance mechanism can effectively decrease the average delivery delay.
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paper_title: Token Based Congestion Control for DTNs

paper_content:

Delay tolerant networks (DTN) are characterized by intermittent connectivity, long delays and often constrained bandwidth. We consider mobile networks where node mobility and covert operation cause frequent disconnections. Nodes will see each other frequently but due to their movement, end-to-end paths do not remain stable long enough to complete a data transfer or even a simple data exchange, much less allow current congestion control protocols to react to these highly dynamic environments. To address the challenge of congestion control in DTNs we have implemented a novel congestion control mechanism based on the use of tokens. Network nodes must possess a token in order to inject messages into the network. Tokens are initially uniformly distributed but thereafter move randomly throughout the network. Using a discrete event simulator we show Token Based Congestion Control (TBCC) results in a reduction in the amount of dropped messages due to network congestion. In cases where drops are not allowed we add a constraint to the forwarding algorithm and show that network transit times are reduced by as much as 40% and total transit times, defined as the time from message generation until delivery to the destination, are reduced by 20%. We also show 36% reduction in the amount of intermediate network storage required. These results are significant since they show a reduction in both space (network storage) and time.
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paper_title: Forwarding and Replication Strategies for DTN with Resource Constraints

paper_content:

Disruption tolerant network (DTN) refers to the type of sparse mobile ad hoc network where the nodes are connected intermittently. A common strategy to cope with intermittent network connectivity is to use multiple-copy routing for message delivery. However, the resultant replicates of messages incur significant burden on the bandwidth and storage requirements of each node. In this paper, we investigate the effect of excessive message-replications in multiple-copy routing in DTNs under communication bandwidth and buffer constraints. By modeling the message delivery process as a Markov chain, we first analytically derive the delivery latency as a function of message-replication limit for the single-message-delivery case. The performance of the multiple-message-multiple-flow case is then evaluated via extensive simulations. For the latter, we observe that there is an optimal value for the message-replication limit of each message beyond which network performance will degrade. Finally, we propose an alternative forwarding and message-dropping strategy to address the problem of unfairness found in the basic FIFO-with-blocking strategy. Our results show that the average message delivery delay can be reduced by as much as 25% with the proposed scheme.
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paper_title: Probabilistic routing in intermittently connected networks

paper_content:

We consider the problem of routing in intermittently connected networks. In such networks there is no guarantee that a fully connected path between source and destination exist at any time, rendering traditional routing protocols unable to deliver messages between hosts. We propose a probabilistic routing protocol for such networks.
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paper_title: Framework for utility driven congestion control in delay tolerant opportunistic networks

paper_content:

Detecting and dealing with congestion in delay tolerant opportunistic networks is an important and challenging problem. In this paper we describe CAFREP, a unified congestion control framework for routing in such networks that adapts both data sending rates and data forwarding policies through a novel reactive fully distributed approach. CAFREP enables congestion control by detecting and reacting to congested nodes and congested parts of the network by using implicit hybrid contact and resources congestion heuristic. CAFREP exploits localized relative utility based approach to offload the traffic from more to less congested parts of the network, and replicate at adaptively lower rate in parts of the network with higher congestion. We extensively evaluate CAFREP against a number of state of the art adaptive and non-adaptive DTN routing protocols across a number of different metrics over three real trace driven experiments with different mobility and connectivity patterns such as Infocom 2006, Rollernet and Dieselnet CRAWDAD data sets. We show that CAFREP performs well in three different connectivity datasets and continuously outperforms four other protocols in terms of maintaining higher node availability and success ratio while keeping lower delays, lower packet loss rates and lower number of forwarded packets for increasing congestion levels.
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paper_title: Encounter-Based Routing in DTNs

paper_content:

Current work in routing protocols for delay and disruption tolerant networks leverage epidemic-style algorithms that trade off injecting many copies of messages into the network for increased probability of message delivery. However, such techniques can cause a large amount of contention in the network, increase overall delays, and drain each mobile node's limited battery supply. We present a new DTN routing algorithm, called Encounter-Based Routing (EBR), which maximizes delivery ratios while minimizing overhead and delay. Furthermore, we present a means of securing EBR against black hole denial- of-service attacks. EBR achieves up to a 40% improvement in message delivery over the current state-of-the-art, as well as achieving up to a 145% increase in goodput. Also, we further show how EBR outperforms other protocols by introduce three new composite metrics that better characterize DTN routing performance.
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paper_title: MaxProp: Routing for Vehicle-Based Disruption-Tolerant Networks

paper_content:

Disruption-tolerant networks (DTNs) attempt to route network messages via intermittently connected nodes. Routing in such environments is difficult because peers have little information about the state of the partitioned network and transfer opportunities between peers are of limited duration. In this paper, we propose MaxProp, a protocol for effective routing of DTN messages. MaxProp is based on prioritizing both the schedule of packets transmitted to other peers and the schedule of packets to be dropped. These priorities are based on the path likelihoods to peers according to historical data and also on several complementary mechanisms, including acknowledgments, a head-start for new packets, and lists of previous intermediaries. Our evaluations show that MaxProp performs better than protocols that have access to an oracle that knows the schedule of meetings between peers. Our evaluations are based on 60 days of traces from a real DTN network we have deployed on 30 buses. Our network, called UMassDieselNet, serves a large geographic area between five colleges. We also evaluate MaxProp on simulated topologies and show it performs well in a wide variety of DTN environments.
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paper_title: Congestion aware forwarding in delay tolerant and social opportunistic networks

paper_content:

We propose an approach for opportunistic forwarding that supports optimization of multipoint high volume data flow transfer while maintaining high buffer availability and low delays. This paper explores a number of social, buffer and delay heuristics to offload the traffic from congested parts of the network and spread it over less congested parts of the network in order to keep low delays, high success ratios and high availability of nodes. We conduct an extensive set of experiments for assessing the performance of four newly proposed heuristics and compare them with Epidemic, Prophet, Spay and Wait and Spay and Focus protocols over real connectivity driven traces (RollerNet) and with a realistic publish subscribe filecasting application. We look into success ratio of answered queries, download times (delays) and availability of buffer across eight protocols for varying congestion levels in the face of increasing number of publishers and topic popularity. We show that all of our combined metrics perform better than Epidemic protocol, Prophet, Spray and Wait, Spray and Focus and our previous prototype across all the assessed criteria.
---
paper_title: Retiring Replicants: Congestion Control for Intermittently-Connected Networks

paper_content:

The widespread availability of mobile wireless devices offers growing opportunities for the formation of temporary networks with only intermittent connectivity. These intermittently-connected networks (ICNs) typically lack stable end-to-end paths. In order to improve the delivery rates of the networks, new store-carry-and-forward protocols have been proposed which often use message replication as a forwarding mechanism. Message replication is effective at improving delivery, but given the limited resources of ICN nodes, such as buffer space, bandwidth and energy, as well as the highly dynamic nature of these networks, replication can easily overwhelm node resources. In this work we propose a novel node-based replication management algorithm which addresses buffer congestion by dynamically limiting the replication a node performs during each encounter. The insight for our algorithm comes from a stochastic model of message delivery in ICNs with constrained buffer space. We show through simulation that our algorithm is effective, nearly tripling delivery rates in some scenarios, and imposes little overhead.
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paper_title: A Novel Congestion Control Strategy in Delay Tolerant Networks

paper_content:

Delay-Tolerant Networks(DTN) are wireless networks where disconnections may occur frequently due to node mobility, power outages and propagation phenomena. In order to achieve data delivery, store-and-forward protocols are used in DTN and routing protocols based on epidemic message dissemination has been proposed, such as Epidemic routing. Under Epidemic routing, packets can be completely delivered between any two nodes if each node buffer is big enough and the communication time is long enough after one node contacts another one. But congestion will occur easily at one node if the buffer of this node is limited under epidemic routing in DTN. In order to solve this problem, a novel congestion control strategy called average forwarding number based on epidemic routing(AFNER) has been proposed based on epidemic routing protocols. Using simulations based on a random waypoint model, the results show the improvement of AFNER congestion control strategy.
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paper_title: Forwarding in opportunistic networks with resource constraints

paper_content:

Effective forwarding in mobile opportunistic networks is a challenge, given the unpredictable mobility of nodes, short contact durations between nodes, wireless interference and limited buffer sizes. Most forwarding algorithms aim at decreasing costs (relative to flooding the network) by forwarding only to nodes which are likely to be good relays. While it is non-trivial to decide if an encountered node is a good relay or not at the moment of encounter, it is harder still to prioritize which messages to transmit under the presence of short contact durations and which messages to drop when buffers become full. The main objective of this paper is to study different message prioritization schemes using real measurements. Such schemes can be broadly divided into two categories - schemes which do not use any network information, and schemes which do. Examples of the former set of schemes include FIFO/LIFO etc. For the latter set of schemes, there is a key design choice: On one hand, we have the following scheme: when a forwarding opportunity presents itself, assign high priorities to messages which are relatively close to their intended destination. On the other hand, we can assign high priorities to messages which are farther away from their destination than closer messages. In order to decide if messages are close to their destination or not, we have to rely on a forwarding algorithm. For this, we use delegation forwarding schemes which have been shown to be efficient in terms of cost incurred in the network. We develop a new set of prioritization schemes based on delegation schemes. We consider these schemes in our empirical study.
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paper_title: An optimal joint scheduling and drop policy for Delay Tolerant Networks

paper_content:

Delay tolerant networks (DTN) are wireless networks where disconnections may occur frequently. In order to achieve data delivery in DTNs, researchers have proposed the use of store-carry-and-forward protocols: there, a node may store a message in its buffer and carry it along for long periods of time, until an appropriate forwarding opportunity arises. Multiple message replicas are often propagated to increase delivery probability. This combination of long-term storage and replication imposes a high storage and bandwidth overhead. Thus, efficient scheduling and drop policies are necessary to: (i) decide on the order by which messages should be replicated when contact durations are limited, and (ii) which messages should be discarded when nodespsila buffers operate close to their capacity. In this paper, we propose an efficient joint scheduling and drop policy that can optimize different performance metrics, like average delay and delivery probability. Using the theory of encounter-based message dissemination, we first propose an optimal policy based on global knowledge about the network. Then, we introduce a distributed algorithm that can approximate the performance of the optimal algorithm, in practice. Using simulations based on a synthetic mobility model and a real mobility trace, we show that our optimal policy and its distributed variant outperform existing resource allocation schemes for DTNs, such as the RAPID protocol [4], both in terms of average delivery ratio and delivery delay.
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paper_title: Evaluation of Queueing Policies and Forwarding Strategies for Routing in Intermittently Connected Networks

paper_content:

Delay tolerant networking (DTN) and more specifically the subset known as intermittently connected networking, is emerging as a solution for supporting asynchronous data transfers in challenging environments where a fully connected end-to-end path between a source and destination may never exist. Message delivery in such networks is enabled via scheduled or opportunistic communication based on transitive local connectivity among nodes influenced by factors such as node mobility. Given the inherently store-and-forward and opportunistic nature of the DTN architecture, the choice of buffer management policies and message forwarding strategies can have a major impact on system performance. In this paper, we propose and evaluate different combinations of queueing policies and forwarding strategies for intermittently connected networks. We show that a probabilistic routing approach along with the correct choice of buffer management policy and forwarding strategy can result in much performance improvements in terms of message delivery, overhead and end-to-end delay.
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paper_title: Congestion avoidance in a data-centric opportunistic network

paper_content:

In order to achieve data delivery in an opportunistic network, data is replicated when it is transmitted to nodes within communication reach and that are likely to be able to forward it closer to the destination. This replication and the unpredictable contact times due to mobility necessitate buffer management strategies to avoid buffer overflow on nodes. In this paper, we investigate buffer management strategies based on local forwarding statistics and relevance of the data for other nodes. The results obtained on our emulation platform for opportunistic networks show that strategies with a high data refresh rate achieve the most efficient delivery and generate the smallest overhead on our community and mobility scenarios.
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paper_title: Fair Routing in Delay Tolerant Networks

paper_content:

The typical state-of-the-art routing algorithms for delay tolerant networks are based on best next hop hill-climbing heuristics in order to achieve throughput and efficiency. The combination of these heuristics and the social network structure leads the routing to direct most of the traffic through a small subset of good users. For instance, in the SimBet algorithm, the top 10% of users carry out 54% of all the forwards and 85% of all the handovers. This unfair load distribution is not sustainable as it can quickly deplete constraint resources in heavily utilized mobile devices (e.g. storage, battery, budget, etc.). Moreover, because a small number of users carry a significant amount of the traffic, the system is not robust to random failures and attacks. To overcome these inefficiencies, this paper introduces Fair-Route, a routing algorithm for delay tolerant networks inspired by the social processes of perceived interaction strength, where messages are preferably forwarded to users that have a stronger social relation with the target of the message; and assortativity, that limits the exchange of messages to those users with similar "social status". We compare the performance of FairRoute to the state-of-the-art algorithms by extensive simulations on the MIT reality mining dataset. The results show that our algorithm outperforms existing algorithms in the de facto benchmark of throughput vs. forwards. Furthermore, it distributes better the load; the top 10% carry out 26% of the forwards and 28% of the handovers without any loss in performance.
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paper_title: Forwarding and Replication Strategies for DTN with Resource Constraints

paper_content:

Disruption tolerant network (DTN) refers to the type of sparse mobile ad hoc network where the nodes are connected intermittently. A common strategy to cope with intermittent network connectivity is to use multiple-copy routing for message delivery. However, the resultant replicates of messages incur significant burden on the bandwidth and storage requirements of each node. In this paper, we investigate the effect of excessive message-replications in multiple-copy routing in DTNs under communication bandwidth and buffer constraints. By modeling the message delivery process as a Markov chain, we first analytically derive the delivery latency as a function of message-replication limit for the single-message-delivery case. The performance of the multiple-message-multiple-flow case is then evaluated via extensive simulations. For the latter, we observe that there is an optimal value for the message-replication limit of each message beyond which network performance will degrade. Finally, we propose an alternative forwarding and message-dropping strategy to address the problem of unfairness found in the basic FIFO-with-blocking strategy. Our results show that the average message delivery delay can be reduced by as much as 25% with the proposed scheme.
---
paper_title: Delay-/Disruption-Tolerant Networking: State of the Art and Future Challenges

paper_content:

Networking for challenged environments, or Delay- and Disruption-Tolerant Networking as it is now most commonly referred to, has attracted great attention in the past few years by the networking research community. Connectivity disruptions, limited network capacity, energy and storage constraints of the participating, mobile devices and the arbitrary movement of nodes are only a few of the challenges that the protocol stack has to deal with. Clearly, current Internet protocols (i.e., the TCP/IP protocol stack) suer and can fail under such conditions. In this paper, we initially give the DTN Problem Statement; we contend that not all applications have the same requirements from the system and hence, equal (blind) treatment of all data packets will result in reduced network eciency. Based on that we propose a Design Position for DTN protocols, which states that protocol design has to be done proactively, on the basis of the application’s requirements. We then survey the most recent contributions on the whole spectrum of Delay- and Disruption-Tolerant Networking, from the architectural and the application point of view down to the transport- and the network-layer of the emerging DTN protocol stack. We nd that although not explicitly mentioned
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paper_title: Cisco IP Routing: Packet Forwarding and Intra-Domain Routing Protocols

paper_content:

Preface. 1. Overview of Cisco Routers. Description of a Cisco Router. Interfacing With Routers. Router Configuration. Monitoring and Troubleshooting Tools. The Test Lab. References. 2. Review of IP Addressing. IP Addressing. Subnetting. Special Addressing Rules. Classful and Classless Addressing. Variable Length Subnet Masks. IP Addressing Details In Cisco Routers. Frequently Asked Questions. References. 3. Routing and Forwarding Processes. Packet-Switched Technologies. Router Operation Overview. Routing Information Sources. Static Routing. Dynamic Routing. Default Routing. Basic Forwarding Algorithm. Classful Routing Operations. Classless Routing Operations. 4. Routing Table Maintenance. Routing Information Sources. Routing Table Maintenance. Summary. Frequently Asked Questions. 5. Packet Forwarding. Overview of IP Forwarding. Packet Input. Forwarding Engine. Packet Delivery. Forwarding Methods in Cisco IOS. Load Sharing in Cisco IOS. Summary. Frequently Asked Questions. References. 6. Static Routes. Static Routes in Cisco Routers. Backup Static Routes. Using Static Routes in NBMA and Dialup Environments. Default Routes. Routing Loops and Discard Routes. Implementation Scenarios. Frequently Asked Questions. 7. Dynamic Routing Protocols in Cisco IOS. Common Functionality of Dynamic Routing Protocols. Routing Protocol Configuration. Routing Protocol Data Structures. Route Redistribution. Events Processed by Routing Protocols. Summary. Frequently Asked Questions. References. 8. Distance-Vector Routing Protocols. Distance-Vector Principles. Routing Information Protocol. Interior Gateway Routing Protocol. References. 9. Link-State Routing Protocols. Introduction to Link-State Routing. Open Shortest Path First (OSPF). References. 10. Enhanced IGRP. Basic Description and History. Theoretical Basis. Subsystems and Data Structures. Message Format. Input Processing. Internal Event Processing. Sending EIGRP Packets. Shortest Path Calculation. Default Route Support. Route Aggregation. EIGRP Stub Router Extension. EIGRP Configuration. Configuration Examples. Bibliography. Index. 0201604736T10152001
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paper_title: Centrality and Network Flow

paper_content:

Centrality measures, or at least popular interpretations of these measures, make implicit assumptions about the manner in which traffic flows through a network. For example, some measures count only geodesic paths, apparently assuming that whatever flows through the network only moves along the shortest possible paths. This paper lays out a typology of network flows based on two dimensions of variation, namely the kinds of trajectories that traffic may follow (geodesics, paths, trails, or walks) and the method of spread (broadcast, serial replication, or transfer). Measures of centrality are then matched to the kinds of flows that they are appropriate for. Simulations are used to examine the relationship between type of flow and the differential importance of nodes with respect to key measurements such as speed of reception of traffic and frequency of receiving traffic. It is shown that the off-the-shelf formulas for centrality measures are fully applicable only for the specific flow processes they are designed for, and that when they are applied to other flow processes they get the “wrong” answer. It is noted that the most commonly used centrality measures are not appropriate for most of the flows we are routinely interested in. A key claim made in this paper is that centrality measures can be regarded as generating expected values for certain kinds of node outcomes (such as speed and frequency of reception) given implicit models of how traffic flows, and that this provides a new and useful way of thinking about centrality. © 2004 Elsevier B.V. All rights reserved.
---
paper_title: Social network analysis for routing in disconnected delay-tolerant MANETs

paper_content:

Message delivery in sparse Mobile Ad hoc Networks (MANETs) is difficult due to the fact that the network graph is rarely (if ever) connected. A key challenge is to find a route that can provide good delivery performance and low end-to-end delay in a disconnected network graph where nodes may move freely. This paper presents a multidisciplinary solution based on the consideration of the so-called small world dynamics which have been proposed for economy and social studies and have recently revealed to be a successful approach to be exploited for characterising information propagation in wireless networks. To this purpose, some bridge nodes are identified based on their centrality characteristics, i.e., on their capability to broker information exchange among otherwise disconnected nodes. Due to the complexity of the centrality metrics in populated networks the concept of ego networks is exploited where nodes are not required to exchange information about the entire network topology, but only locally available information is considered. Then SimBet Routing is proposed which exploits the exchange of pre-estimated "betweenness' centrality metrics and locally determined social "similarity' to the destination node. We present simulations using real trace data to demonstrate that SimBet Routing results in delivery performance close to Epidemic Routing but with significantly reduced overhead. Additionally, we show that SimBet Routing outperforms PRoPHET Routing, particularly when the sending and receiving nodes have low connectivity.
---
paper_title: Traffic distribution and network capacity analysis in social opportunistic networks

paper_content:

Social opportunistic networks are intermittently connected mobile ad hoc networks (ICNs) that exploit human mobility to physically carry messages between disconnected parts of the network. Human mobility thus plays an essential role in the performance of forwarding protocols in the networks, and people's movements are in turn affected by their social interactions with each other. In this paper we present an analysis of the traffic distribution among the nodes of social opportunistic networks and its impact on network capacity. For our analysis, we use a human contact graph that represents a social network of individuals. We characterize the graph as a scale-free network and apply forwarding strategies based on the information required by a node to select relays for its messages, categorising this information either as isolated or complete network or local network knowledge. We use a social network property, centrality, for the forwarding strategies, additionally considering tie strength in the forwarding metric and investigate their impact on traffic distribution. We show that all the strategies result in unfair traffic distribution due to a strong non-random structure of the networks, where hub nodes process much more relay traffic than non-hub nodes. Finally, we present a mathematical model of network capacity as an upper-bound of network delivery performance where hub nodes' resources become the limiting factors, and show that including tie strength in the forwarding metric improves the network capacity.
---
paper_title: Autonomous Congestion Control in Delay-Tolerant Networks

paper_content:

Congestion control is an important feature that directly affects network performance. Network congestion may cause loss of data or long delays. Although this problem has been studied extensively in the Internet, the solutions for Internet congestion control do not apply readily to challenged network environments such as Delay Tolerant Networks (DTN) where end-to-end connectivity may not exist continuously and latency can be high. In DTN, end-to-end rate control is not feasible. This calls for congestion control mechanisms where the decisions can be made autonomously with local information only. We use an economic pricing model and propose a rule-based congestion control mechanism where each router can autonomously decide on whether to accept a bundle (data) based on local information such as available storage and the value and risk of accepting the bundle (derived from historical statistics).
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paper_title: Social network analysis concepts in the design of wireless Ad Hoc network protocols

paper_content:

This article presents a survey of ad hoc networking protocols that have used concepts such as centrality metrics and community formation from the area of social network analysis, which is seen as a network measurement task that deals with structural properties of the network graph. We recognize the synergy among social network analysis and ad hoc networking as a fertile research area that can provide significant advances for the design of network protocols, especially in environments where the communication is opportunistic in nature and therefore cannot be easily or efficiently described as an optimization problem, and other systematic approaches like cross-layer optimization are more difficult to apply.
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paper_title: Routing in Delay/Disruption Tolerant Networks: A Taxonomy, Survey and Challenges

paper_content:

The introduction of intelligent devices with short range wireless communication techniques has motivated the development of Mobile Ad hoc NETworks (MANETs) during the last few years. However, traditional end-to-end based routing algorithms designed for MANETs are not much robust in the challenged networks suffering from frequent disruption, sparse network density and limited device capability. Such challenged networks, also known as Intermittently Connected Networks (ICNs) adopt the Store-Carry-Forward (SCF) behavior arising from the mobility of mobile nodes for message relaying. In this article, we consider the term ICNs as Delay/Disruption Tolerant Networks (DTNs) for the purpose of generalization, since DTNs have been envisioned for different applications with a large number of proposed routing algorithms. Motivated by the great interest from the research community, we firstly review the existing unicasting issue of DTNs because of its extensive research stage. Then, we also address multicasting and anycasting issues in DTNs considering their perspectives. A detail survey based on our taxonomy over the period from 2006 to 2010 is not only provided but also a comparison is given. We further identify the remaining challenges and open issues followed by an evaluation framework proposed for routing in DTNs. Finally, we summarize our contribution with three future research topics highlighted.
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paper_title: Congestion aware forwarding in delay tolerant and social opportunistic networks

paper_content:

We propose an approach for opportunistic forwarding that supports optimization of multipoint high volume data flow transfer while maintaining high buffer availability and low delays. This paper explores a number of social, buffer and delay heuristics to offload the traffic from congested parts of the network and spread it over less congested parts of the network in order to keep low delays, high success ratios and high availability of nodes. We conduct an extensive set of experiments for assessing the performance of four newly proposed heuristics and compare them with Epidemic, Prophet, Spay and Wait and Spay and Focus protocols over real connectivity driven traces (RollerNet) and with a realistic publish subscribe filecasting application. We look into success ratio of answered queries, download times (delays) and availability of buffer across eight protocols for varying congestion levels in the face of increasing number of publishers and topic popularity. We show that all of our combined metrics perform better than Epidemic protocol, Prophet, Spray and Wait, Spray and Focus and our previous prototype across all the assessed criteria.
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paper_title: Token Based Congestion Control for DTNs

paper_content:

Delay tolerant networks (DTN) are characterized by intermittent connectivity, long delays and often constrained bandwidth. We consider mobile networks where node mobility and covert operation cause frequent disconnections. Nodes will see each other frequently but due to their movement, end-to-end paths do not remain stable long enough to complete a data transfer or even a simple data exchange, much less allow current congestion control protocols to react to these highly dynamic environments. To address the challenge of congestion control in DTNs we have implemented a novel congestion control mechanism based on the use of tokens. Network nodes must possess a token in order to inject messages into the network. Tokens are initially uniformly distributed but thereafter move randomly throughout the network. Using a discrete event simulator we show Token Based Congestion Control (TBCC) results in a reduction in the amount of dropped messages due to network congestion. In cases where drops are not allowed we add a constraint to the forwarding algorithm and show that network transit times are reduced by as much as 40% and total transit times, defined as the time from message generation until delivery to the destination, are reduced by 20%. We also show 36% reduction in the amount of intermediate network storage required. These results are significant since they show a reduction in both space (network storage) and time.
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paper_title: Retiring Replicants: Congestion Control for Intermittently-Connected Networks

paper_content:

The widespread availability of mobile wireless devices offers growing opportunities for the formation of temporary networks with only intermittent connectivity. These intermittently-connected networks (ICNs) typically lack stable end-to-end paths. In order to improve the delivery rates of the networks, new store-carry-and-forward protocols have been proposed which often use message replication as a forwarding mechanism. Message replication is effective at improving delivery, but given the limited resources of ICN nodes, such as buffer space, bandwidth and energy, as well as the highly dynamic nature of these networks, replication can easily overwhelm node resources. In this work we propose a novel node-based replication management algorithm which addresses buffer congestion by dynamically limiting the replication a node performs during each encounter. The insight for our algorithm comes from a stochastic model of message delivery in ICNs with constrained buffer space. We show through simulation that our algorithm is effective, nearly tripling delivery rates in some scenarios, and imposes little overhead.
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paper_title: SMS-Based Medical Diagnostic Telemetry Data Transmission Protocol for Medical Sensors

paper_content:

People with special medical monitoring needs can, these days, be sent home and remotely monitored through the use of data logging medical sensors and a transmission base-station. While this can improve quality of life by allowing the patient to spend most of their time at home, most current technologies rely on hardwired landline technology or expensive mobile data transmissions to transmit data to a medical facility. The aim of this paper is to investigate and develop an approach to increase the freedom of a monitored patient and decrease costs by utilising mobile technologies and SMS messaging to transmit data from patient to medico. To this end, we evaluated the capabilities of SMS and propose a generic communications protocol which can work within the constraints of the SMS format, but provide the necessary redundancy and robustness to be used for the transmission of non-critical medical telemetry from data logging medical sensors.
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paper_title: A Novel Congestion Control Strategy in Delay Tolerant Networks

paper_content:

Delay-Tolerant Networks(DTN) are wireless networks where disconnections may occur frequently due to node mobility, power outages and propagation phenomena. In order to achieve data delivery, store-and-forward protocols are used in DTN and routing protocols based on epidemic message dissemination has been proposed, such as Epidemic routing. Under Epidemic routing, packets can be completely delivered between any two nodes if each node buffer is big enough and the communication time is long enough after one node contacts another one. But congestion will occur easily at one node if the buffer of this node is limited under epidemic routing in DTN. In order to solve this problem, a novel congestion control strategy called average forwarding number based on epidemic routing(AFNER) has been proposed based on epidemic routing protocols. Using simulations based on a random waypoint model, the results show the improvement of AFNER congestion control strategy.
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paper_title: An optimal joint scheduling and drop policy for Delay Tolerant Networks

paper_content:

Delay tolerant networks (DTN) are wireless networks where disconnections may occur frequently. In order to achieve data delivery in DTNs, researchers have proposed the use of store-carry-and-forward protocols: there, a node may store a message in its buffer and carry it along for long periods of time, until an appropriate forwarding opportunity arises. Multiple message replicas are often propagated to increase delivery probability. This combination of long-term storage and replication imposes a high storage and bandwidth overhead. Thus, efficient scheduling and drop policies are necessary to: (i) decide on the order by which messages should be replicated when contact durations are limited, and (ii) which messages should be discarded when nodespsila buffers operate close to their capacity. In this paper, we propose an efficient joint scheduling and drop policy that can optimize different performance metrics, like average delay and delivery probability. Using the theory of encounter-based message dissemination, we first propose an optimal policy based on global knowledge about the network. Then, we introduce a distributed algorithm that can approximate the performance of the optimal algorithm, in practice. Using simulations based on a synthetic mobility model and a real mobility trace, we show that our optimal policy and its distributed variant outperform existing resource allocation schemes for DTNs, such as the RAPID protocol [4], both in terms of average delivery ratio and delivery delay.
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paper_title: Forwarding and Replication Strategies for DTN with Resource Constraints

paper_content:

Disruption tolerant network (DTN) refers to the type of sparse mobile ad hoc network where the nodes are connected intermittently. A common strategy to cope with intermittent network connectivity is to use multiple-copy routing for message delivery. However, the resultant replicates of messages incur significant burden on the bandwidth and storage requirements of each node. In this paper, we investigate the effect of excessive message-replications in multiple-copy routing in DTNs under communication bandwidth and buffer constraints. By modeling the message delivery process as a Markov chain, we first analytically derive the delivery latency as a function of message-replication limit for the single-message-delivery case. The performance of the multiple-message-multiple-flow case is then evaluated via extensive simulations. For the latter, we observe that there is an optimal value for the message-replication limit of each message beyond which network performance will degrade. Finally, we propose an alternative forwarding and message-dropping strategy to address the problem of unfairness found in the basic FIFO-with-blocking strategy. Our results show that the average message delivery delay can be reduced by as much as 25% with the proposed scheme.
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paper_title: Token Based Congestion Control for DTNs

paper_content:

Delay tolerant networks (DTN) are characterized by intermittent connectivity, long delays and often constrained bandwidth. We consider mobile networks where node mobility and covert operation cause frequent disconnections. Nodes will see each other frequently but due to their movement, end-to-end paths do not remain stable long enough to complete a data transfer or even a simple data exchange, much less allow current congestion control protocols to react to these highly dynamic environments. To address the challenge of congestion control in DTNs we have implemented a novel congestion control mechanism based on the use of tokens. Network nodes must possess a token in order to inject messages into the network. Tokens are initially uniformly distributed but thereafter move randomly throughout the network. Using a discrete event simulator we show Token Based Congestion Control (TBCC) results in a reduction in the amount of dropped messages due to network congestion. In cases where drops are not allowed we add a constraint to the forwarding algorithm and show that network transit times are reduced by as much as 40% and total transit times, defined as the time from message generation until delivery to the destination, are reduced by 20%. We also show 36% reduction in the amount of intermediate network storage required. These results are significant since they show a reduction in both space (network storage) and time.
---
paper_title: Retiring Replicants: Congestion Control for Intermittently-Connected Networks

paper_content:

The widespread availability of mobile wireless devices offers growing opportunities for the formation of temporary networks with only intermittent connectivity. These intermittently-connected networks (ICNs) typically lack stable end-to-end paths. In order to improve the delivery rates of the networks, new store-carry-and-forward protocols have been proposed which often use message replication as a forwarding mechanism. Message replication is effective at improving delivery, but given the limited resources of ICN nodes, such as buffer space, bandwidth and energy, as well as the highly dynamic nature of these networks, replication can easily overwhelm node resources. In this work we propose a novel node-based replication management algorithm which addresses buffer congestion by dynamically limiting the replication a node performs during each encounter. The insight for our algorithm comes from a stochastic model of message delivery in ICNs with constrained buffer space. We show through simulation that our algorithm is effective, nearly tripling delivery rates in some scenarios, and imposes little overhead.
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Title: Transfer Reliability and Congestion Control Strategies in Opportunistic Networks: A Survey

Section 1: ICN Overview
Description 1: This section provides an overview of intermittently connected networks (ICNs) and their characteristics, including examples and challenges.

Section 2: Delay-Tolerant Networking (DTN) Architecture
Description 2: This section describes the architecture of delay-tolerant networking (DTN), including its layers and mechanisms for managing data transfer in intermittently connected networks.

Section 3: ICN Routing Strategies
Description 3: This section reviews the routing strategies used in ICNs, discussing their complexity and categorizing them based on node contact regularity.

Section 4: Poor Performance of TCP in ICNs
Description 4: This section outlines the limitations of TCP in ICNs and discusses why TCP-based protocols fail in these networks due to long delays and frequent disconnections.

Section 5: Transfer Reliability and Congestion Control in Opportunistic Networks
Description 5: This section identifies the specific requirements and challenges of transfer reliability and congestion control in opportunistic networks, distinct from other ICNs.

Section 6: Reliable Message Transfer
Description 6: This section discusses various strategies for ensuring reliable message transfer in opportunistic networks, including custody transfer and return receipt mechanisms.

Section 7: Congestion Control (Single-Copy Case)
Description 7: This section reviews storage congestion management and avoidance strategies for single-copy forwarding in opportunistic networks.

Section 8: Congestion Control (Multiple-Copy Case)
Description 8: This section discusses message replication management and drop policies for handling storage congestion in multiple-copy forwarding scenarios in opportunistic networks.

Section 9: Discussion and Future Research Issues
Description 9: This section identifies open research issues and areas for future research in transfer reliability and congestion control for opportunistic networks.

Section 10: Conclusion
Description 10: This section summarizes the main contributions of the survey and emphasizes the importance of transfer reliability and congestion control in opportunistic networks.