Wireless Internet has become increasingly popular due to anywhere anytime access feature. The Internet architecture was designed underlying the existing of the end-to-end path connection. The promise of wireless Internet networks is to provide roaming users connectivity anywhere anytime. However, quality of service (QoS) is still an open issue in wireless networks, which are characterized by possible intermittent connectivity and large transmission delays, due to user mobility, sparse mobile node distribution, link failures (because of hostile propagation medium), and/or other high-priority traffc. In this thesis, a credit-based user authentication scheme is proposed for delay tolerant mobile wireless networks. The proposed authentication scheme isolates the uncertain network condition in the high delay wireless backhaul with high error rate, and accelerates the overall authentication process when the mobile terminal roams in the visited network. Furthermore, an analytical study of overall network performance is presented for the authentication scheme in terms of authentication cost and delay. Simulation results demonstrate that the proposed credit-based authentication scheme reduces the overall real time transaction cost and delay for delay tolerant mobile wireless networks.

Delay- and Disruption-tolerant wireless networks (DTN), or opportunistic networks, represent a class of networks where continuous end-to-end connectivity may not be possible. DTN is a well recognized area in networking research and has attracted extensive attentions from both network designers and application developers. Applications of this emergent communication paradigm are wide ranging and include sensor networks using scheduled intermittent connectivity, vehicular DTNs for dissemination of location-dependent information (e.g., local ads, traffic reports, parking information, etc.), pocket-switched networks to allow humans to communicate without network infrastructure, and underwater acoustic networks with moderate delays and frequent interruptions due to environmental factors, etc. Security is one of the main barriers to wide-scale deployment of DTNs, but has gained little attention so far. On the one hand, similar to traditional mobile ad hoc networks, the open channel and multi-hop transmission have made DTNs vulnerable to various security threats, such as message modification/injection attack or unauthorized access and utilization of DTN resources. On the other hand, the unique security characteristics of DTNs including: long round-trip delay, frequent disconnectivity, fragmentation, opportunistic routing as well as limited computational and storage capability, make the existing security protocols designed for the conventional ad hoc networks unsuitable for DTNs. Therefore, a series of new security protocols are highly desired to meet stringent security and efficiency requirements for securing DTNs. In this research, we focus on three fundamental security issues in DTNs: efficient DTN message (or bundle) authentication, which is a critical security service for DTN security; incentive issue, which targets at stimulating selfish nodes to forward data for others; and certificate revocation issue, which is an important part of public key management and serves the foundation of any DTN security protocols. We have made the following contributions: First of all, the unique ``store-carry-and-forward'' transmission characteristic of DTNs implies that bundles from distinct/common senders may opportunistically be buffered at some common intermediate nodes. Such a ``buffering'' characteristic distinguishes DTN from any other traditional wireless networks, for which intermediate cache is not supported. To exploit such buffering opportunities, we propose an Opportunistic Batch Bundle Authentication Scheme (OBBA) to dramatically reduce the bundle authentication cost by seamlessly integrating identity-based batch signatures and Merkle tree techniques. Secondly, we propose a secure multi-layer credit based incentive scheme to stimulate bundle forwarding cooperation among DTNs nodes. The proposed scheme can be implemented in a fully distributed manner to thwart various attacks without relying on any tamper-proof hardware. In addition, we introduce several efficiency-optimization techniques to improve the overall efficiency by exploiting the unique characteristics of DTNs. Lastly, we propose a storage-efficient public key certificate validation method. Our proposed scheme exploits the opportunistic propagation to transmit Certificate Revocation List (CRL) list while taking advantage of bloom filter technique to reduce the required buffer size. We also discuss how to take advantage of cooperative checking to minimize false positive rate and storage consumption. For each research issue, detailed simulation results in terms of computational time, transmission overhead and power consumption, are given to validate the efficiency and effectiveness of the proposed security solutions.

Wireless Internet has become increasingly popular due to anywhere anytime access feature. The Internet architecture was designed underlying the existing of the end-to-end path connection. The promise of wireless Internet networks is to provide roaming users connectivity anywhere anytime. However, quality of service (QoS) is still an open issue in wireless networks, which are characterized by possible intermittent connectivity and large transmission delays, due to user mobility, sparse mobile node distribution, link failures (because of hostile propagation medium), and/or other high-priority traffc. In this thesis, a credit-based user authentication scheme is proposed for delay tolerant mobile wireless networks. The proposed authentication scheme isolates the uncertain network condition in the high delay wireless backhaul with high error rate, and accelerates the overall authentication process when the mobile terminal roams in the visited network. Furthermore, an analytical study of overall network performance is presented for the authentication scheme in terms of authentication cost and delay. Simulation results demonstrate that the proposed credit-based authentication scheme reduces the overall real time transaction cost and delay for delay tolerant mobile wireless networks.

Delay- and Disruption-tolerant wireless networks (DTN), or opportunistic networks, represent a class of networks where continuous end-to-end connectivity may not be possible. DTN is a well recognized area in networking research and has attracted extensive attentions from both network designers and application developers. Applications of this emergent communication paradigm are wide ranging and include sensor networks using scheduled intermittent connectivity, vehicular DTNs for dissemination of location-dependent information (e.g., local ads, traffic reports, parking information, etc.), pocket-switched networks to allow humans to communicate without network infrastructure, and underwater acoustic networks with moderate delays and frequent interruptions due to environmental factors, etc. Security is one of the main barriers to wide-scale deployment of DTNs, but has gained little attention so far. On the one hand, similar to traditional mobile ad hoc networks, the open channel and multi-hop transmission have made DTNs vulnerable to various security threats, such as message modification/injection attack or unauthorized access and utilization of DTN resources. On the other hand, the unique security characteristics of DTNs including: long round-trip delay, frequent disconnectivity, fragmentation, opportunistic routing as well as limited computational and storage capability, make the existing security protocols designed for the conventional ad hoc networks unsuitable for DTNs. Therefore, a series of new security protocols are highly desired to meet stringent security and efficiency requirements for securing DTNs. In this research, we focus on three fundamental security issues in DTNs: efficient DTN message (or bundle) authentication, which is a critical security service for DTN security; incentive issue, which targets at stimulating selfish nodes to forward data for others; and certificate revocation issue, which is an important part of public key management and serves the foundation of any DTN security protocols. We have made the following contributions: First of all, the unique ``store-carry-and-forward'' transmission characteristic of DTNs implies that bundles from distinct/common senders may opportunistically be buffered at some common intermediate nodes. Such a ``buffering'' characteristic distinguishes DTN from any other traditional wireless networks, for which intermediate cache is not supported. To exploit such buffering opportunities, we propose an Opportunistic Batch Bundle Authentication Scheme (OBBA) to dramatically reduce the bundle authentication cost by seamlessly integrating identity-based batch signatures and Merkle tree techniques. Secondly, we propose a secure multi-layer credit based incentive scheme to stimulate bundle forwarding cooperation among DTNs nodes. The proposed scheme can be implemented in a fully distributed manner to thwart various attacks without relying on any tamper-proof hardware. In addition, we introduce several efficiency-optimization techniques to improve the overall efficiency by exploiting the unique characteristics of DTNs. Lastly, we propose a storage-efficient public key certificate validation method. Our proposed scheme exploits the opportunistic propagation to transmit Certificate Revocation List (CRL) list while taking advantage of bloom filter technique to reduce the required buffer size. We also discuss how to take advantage of cooperative checking to minimize false positive rate and storage consumption. For each research issue, detailed simulation results in terms of computational time, transmission overhead and power consumption, are given to validate the efficiency and effectiveness of the proposed security solutions.

Delay Tolerant Networks (DTNs) are characterized by the lack of continuous end-to-end connections because of node mobility, constrained power sources, and limited data storage space of some or all of its nodes. Applications of DTNs include vehicular networks and sensor networks in suburban and rural areas. The intermittent connection in DTNs creates a new and challenging environment that has not been tackled before in wireless and wired networks. Traditional routing protocols fail to deliver data packets because they assume the existence of continuous end-to-end connections. To overcome the frequent disconnections, a DTN node is required to store data packets for long periods of time until it becomes in the communication range of other nodes. In addition, to increase the delivery probability, a DTN node spreads multiple copies of the same packet on the network so that one of the copies reaches the destination. Given the limited storage and energy resources of DTN nodes, there is a trade off between maximizing delivery and minimizing storage and energy consumption. DTN routing protocols can be classified as either blind routing, in which no information is provided to select the next node in the path, or guided routing, in which some network information is used to guide data packets to their destinations. In addition they differ in the amount of overhead they impose on the network and its nodes. The objective of DTN routing protocols is to deliver as many packets as possible. Acquiring network information helps in maximizing packet delivery probability and minimizing the network overhead resulting from replicating many packet copies. Network information could be node contact times and durations, node buffer capacities, packet lifetimes, and many others. The more information acquired, the higher performance could be achieved. However, the cost of acquiring the network information in terms of delay and storage could be high to the degree that render the protocol impractical. In designing a DTN routing protocol, the trade-off between the benefits of acquiring information and its costs should be considered. In this thesis, we study the routing problem in DTN with limited resources. Our objective is to design and implement routing protocols that effectively handles the intermittent connection in DTNs to achieve high packet delivery ratios with lower delivery cost. Delivery cost is represented in terms of number of transmissions per delivered packet. Decreasing the delivery cost means less network overhead and less energy consumption per node. In order to achieve that objective, we first target the optimal results that could be achieved in an ideal scenario. We formulate a mathematical model for optimal routing, assuming the presence of a global observer that can collect information about all the nodes in the network. The optimal results provide us with bounds on the performance metrics, and show the room for improvement that should be worked on. However, optimal routing with a global observer is just a theoretical model, and cannot be implemented practically. In DTNs, there is a need for a distributed routing protocol which utilizes local and easily-collectable data. Therefore, We investigate the different types of heuristic (non-optimal) distributed routing protocols, showing their strengths and weaknesses. Out of the large collection of protocols, we select four protocols that represent different routing classes and are well-known and highly referred by others working in the same area. We implement the protocols using a DTN simulator, and compare their performance under different network and node conditions. We study the impact of changing the node buffer capacities, packet lifetimes, number of nodes, and traffic load on their performance metrics, which are the delivery ratio, delivery cost, and packet average delay. Based on these comparisons, we draw conclusions and guidelines to design an efficient DTN routing protocol. Given the protocol design guidelines, we develop our first DTN routing protocol, Eco-Friendly Routing for DTN (EFR-DTN), which combines the strengths of two of the previously proposed protocols to provide better delivery ratio with low network overhead (less power consumption). The protocol utilizes node encounters to estimate the route to destination, while minimizing the number of packet copies throughout the network. All current DTN routing protocols strive to estimate the route from source to destination, which requires collecting information about node encounters. In addition to the overhead it imposes on the network to collect this information, the time to collect this information could render the data worthless to propagate through the network. Our next proposal is a routing protocol, Social Groups Based Routing (SGBR), which uses social relations among network nodes to exclude the nodes that are not expected to significantly increase the probability of delivering the packet to its destination. Using social relations among nodes, detected from node encounters, every group of nodes can form a social group. Nodes belonging to the same social group are expected to meet each other frequently, and meet nodes from other groups less frequently. Spreading packet copies inside the same social group is found to be of low-added value to the carrying node in delivering a packet to its destination. Therefore, our proposed routing protocol spreads the packet copies to other social groups, which decreases the number of copies throughout the network. We compare the new protocol with the optimal results and the existing well-known routing protocols using real-life simulations. Results show that the proposed protocol achieves higher delivery ratio and less average delay compared to other protocols with significant reduction in network overhead. Finally, we discuss the willingness of DTN nodes to cooperate in routing services. From a network perspective, all nodes are required to participate in delivering packets of each other. From a node perspective, minimizing resource consumption is a critical requirement. We investigate the degree of fair cooperation where all nodes are satisfied with their participation in the network routing services. A new credit-based system is implemented to keep track of and reward node participation in packet routing. Results show that the proposed system improves the fairness among nodes and increases their satisfaction.

Delay Tolerant Networks (DTNs) are characterized by the lack of continuous end-to-end connections because of node mobility, constrained power sources, and limited data storage space of some or all of its nodes. Applications of DTNs include vehicular networks and sensor networks in suburban and rural areas. The intermittent connection in DTNs creates a new and challenging environment that has not been tackled before in wireless and wired networks. Traditional routing protocols fail to deliver data packets because they assume the existence of continuous end-to-end connections. To overcome the frequent disconnections, a DTN node is required to store data packets for long periods of time until it becomes in the communication range of other nodes. In addition, to increase the delivery probability, a DTN node spreads multiple copies of the same packet on the network so that one of the copies reaches the destination. Given the limited storage and energy resources of DTN nodes, there is a trade off between maximizing delivery and minimizing storage and energy consumption. DTN routing protocols can be classified as either blind routing, in which no information is provided to select the next node in the path, or guided routing, in which some network information is used to guide data packets to their destinations. In addition they differ in the amount of overhead they impose on the network and its nodes. The objective of DTN routing protocols is to deliver as many packets as possible. Acquiring network information helps in maximizing packet delivery probability and minimizing the network overhead resulting from replicating many packet copies. Network information could be node contact times and durations, node buffer capacities, packet lifetimes, and many others. The more information acquired, the higher performance could be achieved. However, the cost of acquiring the network information in terms of delay and storage could be high to the degree that render the protocol impractical. In designing a DTN routing protocol, the trade-off between the benefits of acquiring information and its costs should be considered. In this thesis, we study the routing problem in DTN with limited resources. Our objective is to design and implement routing protocols that effectively handles the intermittent connection in DTNs to achieve high packet delivery ratios with lower delivery cost. Delivery cost is represented in terms of number of transmissions per delivered packet. Decreasing the delivery cost means less network overhead and less energy consumption per node. In order to achieve that objective, we first target the optimal results that could be achieved in an ideal scenario. We formulate a mathematical model for optimal routing, assuming the presence of a global observer that can collect information about all the nodes in the network. The optimal results provide us with bounds on the performance metrics, and show the room for improvement that should be worked on. However, optimal routing with a global observer is just a theoretical model, and cannot be implemented practically. In DTNs, there is a need for a distributed routing protocol which utilizes local and easily-collectable data. Therefore, We investigate the different types of heuristic (non-optimal) distributed routing protocols, showing their strengths and weaknesses. Out of the large collection of protocols, we select four protocols that represent different routing classes and are well-known and highly referred by others working in the same area. We implement the protocols using a DTN simulator, and compare their performance under different network and node conditions. We study the impact of changing the node buffer capacities, packet lifetimes, number of nodes, and traffic load on their performance metrics, which are the delivery ratio, delivery cost, and packet average delay. Based on these comparisons, we draw conclusions and guidelines to design an efficient DTN routing protocol. Given the protocol design guidelines, we develop our first DTN routing protocol, Eco-Friendly Routing for DTN (EFR-DTN), which combines the strengths of two of the previously proposed protocols to provide better delivery ratio with low network overhead (less power consumption). The protocol utilizes node encounters to estimate the route to destination, while minimizing the number of packet copies throughout the network. All current DTN routing protocols strive to estimate the route from source to destination, which requires collecting information about node encounters. In addition to the overhead it imposes on the network to collect this information, the time to collect this information could render the data worthless to propagate through the network. Our next proposal is a routing protocol, Social Groups Based Routing (SGBR), which uses social relations among network nodes to exclude the nodes that are not expected to significantly increase the probability of delivering the packet to its destination. Using social relations among nodes, detected from node encounters, every group of nodes can form a social group. Nodes belonging to the same social group are expected to meet each other frequently, and meet nodes from other groups less frequently. Spreading packet copies inside the same social group is found to be of low-added value to the carrying node in delivering a packet to its destination. Therefore, our proposed routing protocol spreads the packet copies to other social groups, which decreases the number of copies throughout the network. We compare the new protocol with the optimal results and the existing well-known routing protocols using real-life simulations. Results show that the proposed protocol achieves higher delivery ratio and less average delay compared to other protocols with significant reduction in network overhead. Finally, we discuss the willingness of DTN nodes to cooperate in routing services. From a network perspective, all nodes are required to participate in delivering packets of each other. From a node perspective, minimizing resource consumption is a critical requirement. We investigate the degree of fair cooperation where all nodes are satisfied with their participation in the network routing services. A new credit-based system is implemented to keep track of and reward node participation in packet routing. Results show that the proposed system improves the fairness among nodes and increases their satisfaction.

Delay-tolerant networks (DTNs) are dynamic networks in which senders and receivers are often completely disconnected from each other, often for long periods of time. DTNs are enjoying a burgeoning interest from the research community largely due to the vast potential for meaningful applications, e.g., to enable access to the Internet in remote rural areas, monitor animal behavioral patterns, connect participants in mobile search and rescue applications, provide connectivity in urban environments, and support space communications. Existing work in DTNs generally focuses either on solutions for very specific applications or domains, or on general-purpose protocol-level solutions intended to work across multiple domains. In this proposal, we take a more systems-oriented approach to DTNs. Since applications operating in these dynamic environments would like their connections to be supported by the network technology best suited to the combination of the communication session's requirements and instantaneous network context, we develop a middleware architecture that enables seamless migrations from one communication style to another in response to changing network conditions. We also enable context-awareness in DTNs, using this awareness to adapt communications to more efficiently use network resources. Finally, we explore the systems issues inherent to such a middleware and provide an implementation of it that we test on a mobile computing testbed made up of autonomous robots. / text

In recent years, significant advances have been achieved in communication networks and electric power systems. Communication networks are developed to provide services within not only well-connected network environments such as wireless local area networks, but also challenged network environments where continuous end-to-end connections can hardly be established between information sources and destinations. Delay tolerant network (DTN) is proposed to achieve this objective by utilizing a store-carry-and-forward routing scheme. However, as the network connections in DTNs are intermittent in nature, the management of network resources such as communication bandwidth and buffer storage becomes a challenging issue. On the other hand, the smart grid is to explore information and communication technologies in electric power grids to achieve electricity delivery in a more efficient and reliable way. A high penetration level of electric vehicles and renewable power generation is expected in the future smart grid. However, the randomness of electric vehicle mobility and the intermittency of renewable power generation bring new challenges to the resources management in the smart grid, such as electric power, energy storage, and communication bandwidth management. This thesis consists of two parts. In part I, we focus on the resource management in DTNs. Specifically, we investigate data dissemination and on-demand data delivery which are two of the major data services in DTNs. Two kinds of mobile nodes are considered for the two types of services which correspond to the pedestrians and high-speed train passengers, respectively. For pedestrian nodes, the roadside wireless local area networks are used as an auxiliary communication infrastructure for data service delivery. We consider a cooperative data dissemination approach with a packet pre-downloading mechanism and propose a double-loop receiver-initiated medium access control scheme to resolve the channel contention among multiple direct/relay links and exploit the predictable traffic characteristics as a result of packet pre-downloading. For high-speed train nodes, we investigate on-demand data service delivery via a cellular/infostation integrated network. The optimal resource allocation problem is formulated by taking account of the intermittent network connectivity and multi-service demands. In order to achieve efficient resource allocation with low computational complexity, the original problem is transformed into a single-machine preemptive scheduling problem and an online resource allocation algorithm is proposed. If the link from the backbone network to an infostation is a bottleneck, a service pre-downloading algorithm is also proposed to facilitate the resource allocation. In part II, we focus on resource management in the smart grid. We first investigate the optimal energy delivery for plug-in hybrid electric vehicles via vehicle-to-grid systems. A dynamic programming formulation is established by considering the bidirectional energy flow, non-stationary energy demand, battery characteristics, and time-of-use electricity price. We prove the optimality of a state-dependent double-threshold policy based on the stochastic inventory theory. A modified backward iteration algorithm is devised for practical applications, where an exponentially weighted moving average algorithm is used to estimate the statistics of vehicle mobility and energy demand. Then, we propose a decentralized economic dispatch approach for microgrids such that the optimal decision on power generation is made by each distributed generation unit locally via multiagent coordination. To avoid a slow convergence speed of multiagent coordination, we propose a heterogeneous wireless network architecture for microgrids. Two multiagent coordination schemes are proposed for the single-stage and hierarchical operation modes, respectively. The optimal number of activated cellular communication devices is obtained based on the tradeoff between communication and generation costs.

The recent years have seen an enormous advance in wireless communication technology and co-existence of various types of wireless networks, which requires effective inter-networking among the heterogeneous wireless networks in order to support user roaming over the networks while maintaining the connectivity. One of main challenges to achieve the connectivity over heterogeneous wireless networks is potential intermittent connections caused by user roaming. The issue is how to maintain the connection as the user roams and how to ensure service quality in the presence of a long disconnection period. In this dissertation, we apply the delay tolerant network (DTN) framework to heterogeneous terrestrial wireless networks, and propose a system architecture to achieve the connectivity in the presence of excessive long delays and intermittent paths. We study several possible approaches, discuss the applicability of each of the approaches and propose the super node architecture. To demonstrate the effectiveness of the proposed super node architecture, we give a simulation study that compares the system performance under the super node architecture and under the epidemic based architecture. Within the proposed architecture that employs the idea of super nodes, we further study how to effectively route a message over access networks. We present a new routing technique for mobile ad-hoc networks (MANETs) based on the DTN system architecture. We introduce the concept of virtual network topology and redefine the dominating-set based routing for the challenged network environment under consideration. In addition, we propose a time based methodology to predict the probability of future contacts between node pairs to construct the virtual network topology. We present a simulation study that demonstrates the effectiveness of the proposed routing approach as compared with the epidemic routing, and that the time based technique for predicting the future contacts gives better performance compared with that using the number of previous contacts. We further extend the dominating set routing technique through analyzing the underlying node mobility model. We shed some light on how using node mobility model can improve contact probability estimation. Based on our findings we propose a new algorithm that improves the routing performance by minimizing the selected dominating set size. Information security challenges in the super node architecture are introduced. We further address two main security challenges: The first is how to prevent unauthorized nodes from using the network resources, and the second is how to achieve end-to-end secure message exchange over the network. Our proposed solutions are based on asymmetric key cryptography techniques. Moreover, we introduce a new idea of separating the problem of source authentication from the problem of message authorization. We propose a new technique that employs the one-way key chain to use symmetric key cryptographic techniques to address the problems under consideration.

Delay-tolerant networking (DTN) has recently received considerable attention from the research community. This type of networks is characterized by frequent disconnections due to propagation phenomena, node mobility, and power outages. Thus, the complete path between the source and the destination may never have existed. This context requires the design of new communication paradigms and techniques that will make communication possible in these environments. To achieve message delivery, researchers have proposed the use of store-carry-and-forward protocols, whereby a node may store the message and carry it until an appropriate forwarding opportunity arises. Many flooding-routing schemes have been proposed for DTNs in order to increase the probability of message delivery. However, these schemes suffer from excessive energy consumption, severe contention that significantly degrades their performance, especially if we account for the fact that each node could be a hand-held and battery-powered device with stringent buffer size limitation. With such buffer limitations at the DTN nodes, message drop/loss could happen due to buffer overflow. In order to address the problem and improve the performance of DTNs, this thesis focuses on two main design objectives; first, the design and evaluation of new multi-copy routing schemes; second, the design and evaluation of new scheduling and dropping policies to reduce message drop/loss due to buffer overflow. To fulfill the first objective, a protocol called Self Adaptive Routing Protocol (SARP) is introduced. It is a multi-copy scheme designed to suit resource-sufficient DTNs. Based on SARP, two multi-copy routing schemes are further developed to suit resource-limited DTNs, in which compensating the traffic demand become a challenge: i) the Self Adaptive Utility-based Routing Protocol (SAURP), ii) and the Adaptive Reinforcement based Routing Protocol (ARBRP). The introduced protocols form a new framework of DTNs aiming to significantly reduce the resource requirements of flooding-based routing schemes. Each introduced scheme has its own way of exploring the possibility of taking mobile nodes as message carriers in order to increase the delivery ratio of the messages. In SAURP, the best carrier for a message characterized by jointly considering the inter-contact time that is obtained using a novel contact model and the network status, such as including wireless link condition and nodal buffer availability. In ARBRP, the routing problem is solved by manipulating a collaborative reinforcement learning technique, where a group of nodes can cooperate with each other to make a forwarding decision for the stored messages based on a cost function at each contact with another node. ARBRP is characterized by not only considering the contact time statistics, but also looks into the feedback on user behavior and network conditions, such as congestion and buffer occupancy sampled during each previous contact with any other node. The thesis argues and proves that the nodal movement and the predicted collocation with the message recipient can serve as meaningful information to achieve an intelligent message forwarding decision at each node. Therefore, the introduced protocols can achieve high efficiency via an adaptive and intelligent routing mechanism according to network conditions. To fulfill the second objective, we further enhanced the performance of DTN routing by introducing message scheduling and dropping policies such that the delivery ratio is increased and/or the delivery delay is reduced. This thesis investigates new buffer management and scheduling policies to improve the performance of flooding and utility-based forwarding routing in DTNs, such that the forwarding/dropping decision can be made at a node during each contact for either optimal message delivery ratio or message delivery delay. To examine their effectiveness, the introduced protocols and the buffer management and scheduling policies have been implemented and compared to a number of existing counterpart approaches. A near-realistic mobility model is used for testing. A number of scenarios are used to evaluate the performance of the introduced techniques in terms of delivery delay, ratio, and the number of transmissions performed.