Many-to-Many (M2M) communication, which allows a group of nodes to communicate with each other simultaneously, has been shown to help battle contention for scarce resources in Delay Tolerant Networks (DTNs), and hence improve their performance. In this paper, we address for the first time the problem of joint message scheduling and drop in a DTN which employs M2M communication. We develop a generic framework, assuming the routing algorithm provides us with a utility function (derived in order to optimize some desired metric) which helps us compute utilities associated with each message. The goal of our joint message scheduling and drop framework is to maximize the increase in total utility. We formulate the problem of joint message scheduling and drop in DTNs that employ M2M communication as an integer optimization problem and show how to reduce it into a number of many-to-one problems. In order to solve the many-to-one integer optimization problems obtained, we develop an efficient but 1/2 -approximate greedy algorithm (Almost-Greedy), and use it to develop an optimal solution (DynOpt). Finally, we use DynOpt to develop an (1 - ε)- approximate Fully Polynomial Time Approximation Scheme (eOpt) that lets us choose a tradeoffs between complexity and accuracy. The problem of joint message scheduling and drop in DTNs employing the traditional one-to-one communication is a special case of our problem where the communicating group size is limited to 2 and hence our contribution provides a theoretical formulation and theoretically proven solutions for that problem too. We compare our algorithms against adaptations of the state of the art one-to-one scheduling and drop policies to the M2M communication case using simulations and find that our algorithms significantly improve the performance of the network.

With the advent of wireless technologies such as Wi-Fi Direct and Near Field Communication (NFC), infrastructure-less Peer-to-Peer (P2P) content sharing among mobile devices is set to become more ubiquitous. Delay-Tolerant Networks (DTNs), with their opportunistic message forwarding strategy, can be leveraged to provide seamless connectivity in such scenarios. To the best of our knowledge, little has been done to understand the performance of DTNs under realistic settings involving the interplay of diverse factors such as bundle fragmentation, scheduling, and buffer spacing. In this paper, we look at Queueing Petri Nets (QPNs) as a modeling framework to study the performance of DTN routing. We develop QPN models for DTNs of increasing complexity in an incremental fashion, starting from a network that employs the rudimentary direct transmission routing protocol to a network that employs a family of multi-hop and replication-based routing protocols (namely (p, q) -epidemic routing). The complete QPN model considers a number of realistic factors that impact performance such as finite buffer space, finite link bandwidth, bundles with different priorities and intra-scheduling delays arising due to different levels of the memory hierarchy at the nodes. We come up with a three-fold validation scheme to assert the veracity of our proposed models, via comparison of results obtained from simulations of the QPN vis-a-vis those obtained from direct simulation of the underlying DTN and experimental results obtained from a testbed of Android based devices that employ a mobility emulation scheme. We also show a case to exemplify the analytical capability of the QPN, by deriving the underlying reachability graph and constructing an equivalent stochastic jump process. We identify the stochastic process to be a Semi-Markov Process (SMP) and hence arrive at a closed form expression for the end-to-end delivery latency by computing the hitting time of the SMP. We find that the model accurately captures the behavior of a DTN in numerous realistic scenarios, showing the efficacy of QPNs as a suitable modeling framework for evaluating the DTN routing protocols.

With the advent of wireless technologies such as Wi-Fi Direct and Near Field Communication (NFC), Peer-to-Peer (P2P) content sharing among mobile devices is set to become more ubiquitous. Delay-Tolerant Networks (DTNs)-with their rudimentary direct delivery routing protocol-can be leveraged to provide seamless connectivity in such scenarios. To the best of our knowledge, little has been done to understand the performance of DTNs under realistic settings involving the interplay of diverse factors such as bundle fragmentation, scheduling, and buffer spacing. In this paper, we present a Queueing Petri Net (QPN) abstraction of DTNs that enables us to evaluate the underlying network's performance. Our model is novel in its ability to capture bundle fragmentation, scheduling, and buffer spacing put together. We proceed to evaluate the veracity of the model by involving QPN evaluation using the SimQPN tool and simulation of the underlying DTN using the ONE simulator. We find that the model successfully predicts the performance of the underlying network to a high degree of accuracy.

Unlike traditional mobile networks, the store, carry, and forward paradigm of DTN architecture, enables a resource hungry DTN node (such as mobile phone) to carry the messages until it physically meets the destination node or a potential relay node. The storage and communication of the node are precious resources that play a vital role in the DTN routing. The state-of-the-art DTN research, models the node as a monolithic storage structure with the single communication antenna for data transfer. However, the practical bi-level hierarchical storage structure and the latest wireless technologies such as MIMO in the mobile phones, exemplify the oversimplified nature of the existing node abstraction. To this end, my PhD research focuses on the DTN performance modeling with a pragmatic node abstraction.