A novel queue management policy for delay-tolerant networks

Delay-tolerant networks (DTNs) have attracted increasing attention from governments, academia and industries in recent years. They are designed to provide a communication channel that exploits the inherent mobility of trams, buses and cars. However, the resulting highly dynamic network suffers from frequent disconnections, thereby making node-to-node communications extremely challenging. Researchers have thus proposed many routing/forwarding strategies in order to achieve high delivery ratios and/or low latencies and/or low overheads. Their main idea is to have nodes store and carry information bundles until a forwarding opportunity arises. This, however, creates the following problems. Nodes may have short contacts and/or insufficient buffer space. Consequently, nodes need to determine (i) the delivery order of bundles at each forwarding opportunity and (ii) the bundles that should be dropped when their buffer is full. To this end, we propose an efficient scheduling and drop policy for use under quota-based protocols. In particular, we make use of the encounter rate of nodes and context information such as time to live, number of available replicas and maximum number of forwarded bundle replicas to derive a bundle\u27s priority. Simulation results, over a service quality metric comprising of delivery, delay and overhead, show that the proposed policy achieves up to 80 % improvement when nodes have an infinite buffer and up to 35 % when nodes have a finite buffer over six popular queuing policies: Drop Oldest (DO), Last Input First Output (LIFO), First Input First Output (FIFO), Most FOrwarded first (MOFO), LEast PRobable first (LEPR) and drop bundles with the greatest hop-count (HOP-COUNT)

Dtn and non-dtn routing protocols for inter-cubesat communications: A comprehensive survey

CubeSats, which are limited by size and mass, have limited functionality. These miniaturised satellites suffer from a low power budget, short radio range, low transmission speeds, and limited data storage capacity. Regardless of these limitations, CubeSats have been deployed to carry out many research missions, such as gravity mapping and the tracking of forest fires. One method of increasing their functionality and reducing their limitations is to form CubeSat networks, or swarms, where many CubeSats work together to carry out a mission. Nevertheless, the network might have intermittent connectivity and, accordingly, data communication becomes challenging in such a disjointed network where there is no contemporaneous path between source and destination due to satellites’ mobility pattern and given the limitations of range. In this survey, various inter-satellite routing protocols that are Delay Tolerant (DTN) and Non Delay Tolerant (Non-DTN) are considered. DTN routing protocols are considered for the scenarios where the network is disjointed with no contemporaneous path between a source and a destination. We qualitatively compare all of the above routing protocols to highlight the positive and negative points under different network constraints. We conclude that the performance of routing protocols used in aerospace communications is highly dependent on the evolving topology of the network over time. Additionally, the Non-DTN routing protocols will work efficiently if the network is dense enough to establish reliable links between CubeSats. Emphasis is also given to network capacity in terms of how buffer, energy, bandwidth, and contact duration influence the performance of DTN routing protocols, where, for example, flooding-based DTN protocols can provide superior performance in terms of maximizing delivery ratio and minimizing a delivery delay. However, such protocols are not suitable for CubeSat networks, as they harvest the limited resources of these tiny satellites and they are contrasted with forwarding-based DTN routing protocols, which are resource-friendly and produce minimum overheads on the cost of degraded delivery probability. From the literature, we found that quota-based DTN routing protocols can provide the necessary balance between delivery delay and overhead costs in many CubeSat missions

Fundamental Relation on HvBE-Algebras

In this paper, we are going to introduce a fundamental relation on $H_{v}BE$-algebra and investigate some of properties, also construct new $(H_{v})BE$-algebras via this relation. We show that quotient of any $H_{v}BE$-algebra via a regular regulation is an $H_{v}BE$-algebra and this quotient, via any strongly relation is a $BE$-algebra. Furthermore, we investigate that under what conditions some relations on $H_{v}BE$-algebra are transitive relations

A novel destination-based routing protocol (DBRP) in DTNs

In Delay Tolerant Networks (DTNs), the aim of any forwarding/routing protocols is to achieve a high delivery ratio of packets/bundles at the lowest possible bandwidth cost, buffer space and energy. Therefore, finding a protocol which uses less resource to achieve high delivery ratio and low latency is an open research question. This paper proposes a quota-based protocol which confines the number of replicas and forwards them based on the meeting history of nodes. The unique aspect of our protocol is to weight any encounter with the final destination to be much higher than any other node encounter. This aspect of the protocol is based on the idea that regardless of how small an encounter rate with the destination, given a highly correlated movement model (i.e., human behaviour) we will end up with a high delivery ratio. The results of our simulation support this hypothesis

Data management in delay tolerant networks

Delay Tolerant Networks (DTNs) are characterized by the lack of contemporaneous paths between any source and destination node. In these networks, nodes act as relays, whereby they cooperatively help forward data bundles from a source to a destination node. As a basic forwarding strategy, nodes may flood bundles to every encountered node. However, flooding results in congestion and unnecessarily consume precious resources such as buffer space and bandwidth. To this end, many routing protocols select a next hop node based on metrics such as delivery probability and encounter rates. Another strategy is one adopted by quota based protocols in order to reduce resource usage. Namely, for each bundle, only a limited number of copies or replicas are disseminated throughout the network. However, they suffer from low delivery ratios as their dissemination rate is low. Hence, bundles need to be efficiently managed in order to achieve high delivery ratios, low delays and low overheads. Another key challenge is considering both routing and buffer management simultaneously when network resources such as bandwidth and buffer are limited and the number of replicas for each bundle is finite. Under such conditions, sender nodes need to select a next hop node that results in a high delivery ratio. In addition, as nodes may need to send a large number of bundles in each contact, their communication bandwidth may not be sufficient to transmit all buffered bundles. In addition, due to limited buffer size, when replicas are dropped by nodes when their buffer overflows, the delivery probability of the corresponding bundles reduces. This is because no provisions are provided to replace a dropped replica in order to maintain a high delivery ratio. This thesis proposes a quota-based protocol that is based on weighting nodes that have encountered the final destination higher than any other nodes. This fact is based on the idea that regardless of how small an encounter rate with the destination is, given a highly correlated movement model, e.g., human, we will end up with a high delivery ratio. This idea is then studied analytically using a time homogeneous semi- Markov process (THSMP). Analysis shows that a targeted forwarding strategy based on contact history with a destination improves bundle delivery when there are finite replicas. A destination-based routing protocol (DBRP) is then proposed to specifically target nodes that have a history with a bundle\u27s destination. Simulation studies over three scenarios show that in terms of a composite metric comprising of delivery, delay and overhead, DBRP achieves up to 57% improvement over three well-known routing protocols, namely PROPHET, EBR and Spray and Wait. Moreover, DBRP results in nodes experiencing at least 28% lower buffer consumption. The second proposed method investigated in this thesis is an efficient scheduling and drop policy called QM-EBRP for use under quota based protocols. In particular, QM-EBRP makes use of the encounter rate of vehicles and context information such as time to live, number of available replicas and maximum number of forwarded bundle replicas to derive a bundle\u27s priority. Simulation results, over a service quality metric comprising of delivery, delay and overhead, show that the proposed policy achieves up to 80% improvement when vehicles have infinite buffer space and up to 35% when vehicles have finite buffer space over six popular queuing policies: Drop Oldest (DO), Last Input First Output (LIFO), First Input First Output (FIFO), Most FOrwarded first (MOFO), LEast PRobable first (LEPR), and drop bundles with greatest hop count (HOP-COUNT). Lastly, this thesis considers a Mobility-Based Routing Protocol (MBRP) that constructs a space-time graph at every node by recording the mobility pattern of nodes upon each contact. In particular, nodes do not have full knowledge of the network topology. Also, the space-time graph is dynamic, meaning the trajectory of nodes may only be valid for a given period of time. As the space-time graph may be incomplete, MBRP presents a heuristic that evaluates encountered nodes based on their recorded mobility patterns in order to disseminate a finite number of replicas. MBRP has been evaluated over a realistic environment comprising of vehicles with both periodic and dynamic mobility patterns. The simulation results, over a service quality metric comprising of delivery, delay and overhead, show that MBRP achieves up to 105% improvement as compared to four well-known routing protocols namely, EBR, EPIDEMIC, MAXPROP, and PROPHET. Finally, MBRP is capable of achieving 50% of the performance attained by the optimal algorithm, whereby all nodes are preloaded with the space-time graph

A novel data forwarding strategy for a drone delay tolerant network with range extension

Amazon, Uber Eats, and United Parcel Service (UPS) are planning to launch drone delivery services in the near future. Indeed, recently, Google has received Federal Aviation Administration (FAA) approval for its Wings delivery platform. Amazon claims that a drone logistics network is more cost-efficient and quicker than a motor vehicle delivery network. In this paper, we propose a data delivery service by the drone network in addition to parcel delivery. We propose Heuristic Flight Path Planning (HFPP) that plans a drone\u27s flight path based on parcel delivery destination as well as data delivery destinations (waypoints). We further extend the solution to include drone charging stations for range extension. Our simulation studies show that our proposed method has delivered the data and consignments such that HFPP delivers up to 33% more data packets compared with Encounter-Based Routing (EBR), Epidemic, and a similar path planning method. Also, HFPP reduces the data delivery delays by up to 72% while the overhead ratio is low

A novel mobility-based routing protocol for semi-predictable disruption tolerant networks

This letter considers routing in delay tolerant networks whereby nodes have semi-predictable mobility patterns within a time period. We propose a mobility-based routing protocol (MBRP) where nodes construct a space-time graph dynamically. As the space-time graph may be incomplete, MBRP presents a heuristic that evaluates encountered nodes based on their recorded mobility patterns in order to disseminate a finite number of bundle replicas. Simulation results, over a service quality metric comprising of delivery, delay and overhead, show that MBRP achieves up to 105 % improvement as compared to four well-known routing protocols. Finally, MBRP is capable of achieving 50 % of the performance attained by the optimal algorithm, whereby all nodes are preloaded with a space-time graph