Delay Tolerant Networks Research Articles

A Simple and Energy-Efficient Flooding Scheme for Wireless Routing

In many wireless networks, such as ad hoc, sensor, and delay-tolerant networks, the destination node is determined from the source node by the flooding process. Flooding efficiency is important for nodes, because they are driven by limited batteries. In this paper, we propose a simple flooding scheme to transmit a route request (RREQ) message based on the remaining power of its own node without using control packets and complex calculations. We applied the proposed scheme to ad hoc on-demand distance vector (AODV) routing protocol as an example and carried out computer simulations (ns3). The results showed that the proposed scheme was superior to conventional schemes in static and mobile scenarios. First, we showed the limit of node density that causes the decrease of throughput in the proposed scheme and that the proposed scheme was superior in terms of energy efficiency (bits/J), including throughput and energy consumption. Next, as the number of flooding times is made uniform in the proposed scheme, all nodes will have almost the same battery replacement time. As a result, when the nodes are static, the lifetime in the proposed scheme is longer than that in the conventional scheme.

HOW CLOSELY IS PROTEIN CARBONYL (PCO) LEVEL CORRELATED WITH SEPSIS-RELATED ORGAN FUNCTION ASSESSMENT (SOFA) SCORE?

Objective: Sepsis remains an unsolved problem in hospitals since its mortality rate is not significantly reduced despite considerable therapy efforts. The most used prognostic tool is the Sepsis-related Organ Function (SOFA) score, which requires several clinical and laboratory examinations; our recent studies also showed that the protein carbonyl level (PCO) has prognostic value in predicting sepsis mortality.
 Methods: This prospective study was designed to assess the correlation between PCO values and the SOFA score following ethical approval. Adult patients aged>18 y who met the Sepsis-3 definition were included. Exclusion criteria were patients not admitted to the intensive care unit. Dropout criteria included mortality within the 1h bundle protocol. Baseline demographic data and blood collection were measured for all subjects. Subjects were treated with the 1h bundle protocol and observed for 28 d.
 Results: Fifty-nine subjects were included, with no significant differences in age, sex, diagnosis, microbiology or Charlson’s Comorbidity score between survivors and non-survivors. The SOFA score was higher in non-survivors (10.90±3.38 vs 8.11±3.07; p=0.003), as was the PCO value (24.5 [14.67-81] vs 18 [15-21.33]; p<0.001). However, the correlation between PCO and SOFA score is very weak (r=0.101; p=0.45).
 Conclusion: Both the PCO level and SOFA scores were higher in non-survivor septic patients. However, they have a very weak correlation and cannot be used interchangeably.

A new approach buffer-efficient disruption tolerant protocol in vehicular delay-tolerant network

As the percentage of Vehicles are increasing on roads, Vehicular Ad-hoc network have reached to a significant interest of the researcher in recent times. V2V network and V2I are prominent as an organized solution for attaining safety for moving vehicles on road and transmitting data for a secure journey while driving and transferring data in the form of message from one vehicle to other. VDTN is a kind of Delay Tolerant Networks (DTNs), to provide reliable and efficient communications. Various routing protocols have been used previously in VDTN to enhance the performance of the network in terms of forwarding information in the form of messages to their preferred locations. In this paper, we introduce a novel protocol called Buffer-Efficient Disruption Tolerant Routing Protocol (BEDTRP) to improve delivery delay, overhead and latency. This protocol significantly improves the communication performance such as delivery ratio and overhead in terms of increasing buffer size and bandwidth. Evaluation results show that the proposed method BEDTRP achieves high bandwidth utilization performance to provide better delivery ratio, lower delivery delay, and low overhead against buffer changes. We used ns-2 network simulator to implement Delay tolerant network protocol.

E-PRAN: Enhanced prophet routing algorithm in delay tolerant networks

Delay tolerant networks(DTN) belong to a category of SHIP (Sparse,Hybrid, Intermittent,Partitioned) networks where aim is to deliver a message with acceptable delay. In the literature of DTN, many routing protocols exist that aim to determine the optimized path from source to Destination Node(DN). One of the most commonly used algorithm is Prophet Routing Protocol (PRP). Prophet routing protocol maintains a set of delivery probabilities corresponding to every node in DTN. It exploits the opportunistic contact for message delivery. The PRP does not consider factors such as encountered node available buffer space, energy level of battery and delivery predictability of encountered node to destination node. In the proposed work, an improvised version of PRP is suggested that not only consider these factors but as a part of current research work, a new factor named as virtual credibility (VC) has been proposed. All these factors collectively results in the increase in MDR and reduced message overhead in the network.

Energy Efficient Inactive Node Detection Based Routing Protocol for Delay Tolerant Network

The delay tolerant network multi-copy protocols create and transmit multiple copies of each message that overload the buffer size, energy and bandwidth. The resource consumption is controlled by transmitting the messages to nodes having high encountering ability to meet their destinations. Hence, nodes loss energy only in transmitting and receiving messages and went to dead state. However, message transmission continues even though the destination is dead. This wastes the network resources because messages destining to dead node will not be able to find their destinations. The existing routing protocols focus on message transmissions and do not have any mechanism to detect inactive nodes or to stop massage replications destining to inactive nodes. In this paper we have proposed a routing protocol called as Energy Efficient Inactive Node Detecting Based Routing Protocol for Delay Tolerant Network (InD). The proposed protocol has employed the node mobility to detect inactive nodes. Moreover, an intelligent buffer management policy has been designed that detect and drop those messages which are destining to dead nodes. The real time mobility scenarios have been used to evaluate the performance of existing and proposed routing protocols under the metrics of message transmissions, message drop, and message delivery and hop count average.

Improving Small Satellite Communications and Tracking in Deep Space—A Review of the Existing Systems and Technologies With Recommendations for Improvement. Part III: The Deep Space Network

This article is the third of a three-part series in which we present the results of a study exploring concepts for improving communications and tracking capabilities of deep space SmallSats. In Part I, we discussed SmallSat direct-to-Earth links as well as SmallSat communications equipment, and provided recommendations for future work. In Part II, we focused on SmallSat navigation options, disruption tolerant networking, proximity links, and the use of the communication link for science observations. In Part III, we focus on ground support of deep space SmallSats. We present a brief overview of NASA's deep space network (DSN) along with concepts for adapting the DSN to improve support for SmallSats. We discuss approaches for increasing the DSN's efficiency in handling the anticipated increase in SmallSat communications, such as reducing setup and teardown times for a communications pass, and reducing DSN time allocated to Doppler and range measurements. A new demand access operational paradigm is proposed, which is more consistent with SmallSat communications requirements and will facilitate the DSN handling of larger numbers of spacecraft. Finally, we present the conclusion of the study as a list of recommendations to improve SmallSat communications and tracking.

Maximum flow in buffer-limited delay tolerant networks. The static approach

Delay Tolerant Networks (DTNs), such as Internet, ad hoc networks, satellite networks and sensor networks, have attracted considerable attention. The maximum flow problem has a vital importance for routing and service scheduling in networks. For delay tolerant networks there are no permanent end-to-end paths since the topology and links characteristics are time-varying. In these instances, to account properly for the evolution of the underlying system over time, we need to use dynamic network now models. When time is considered as a discrete variable, these problems can be solved by constructing an equivalent static time expanded network. This is a static approach. In this paper we study the maximum flow in a buffer-limited delay tolerant network, with static approach.

CFDP PDU Tunneling Service over DTN Between Heterogeneous Deep Space Communication Assets

In space exploration missions, the spacecraft have limited computing resources. In particular, the communications environments for these spacecraft, whether in deep space or the cislunar region, are characterized by intermittent connectivity loss, long signal-propagation delay, and high bit-error rates between spacecraft and their ground stations. Delay-Tolerant Network (DTN) has been introduced to enable automated, efficient communication among flight-mission entities in these environments. However, most flight-mission entities are not yet equipped for DTN; a mechanism is needed whereby DTN-enabled entities and non-DTN-enabled entities can easily interoperate. The CCSDS (Consultative Committee for Space Data Systems) File Delivery Protocol (CFDP) is supported in both DTN and non-DTN communication fabrics, so perhaps CFDP file transmission can serve as the common communication medium that bridges the two. When CFDP runs without a Bundle Protocol (BP), it requires a more complex CFDP implementation, and multi-hop communication is more difficult to configure. This paper presents a tunneling mechanism that relays CFDP protocol data units (PDUs) between a non-DTN-enabled CFDP entity and a DTN-enabled CFDP entity. This enables CFDP-over-link implementations to bridge into BP networks to simplify multi-hop forwarding through the BP network. A proof-of-concept implementation of the tunneling service has been developed and tested using the Interplanetary Overlay Network (ION) DTN software to evaluate this concept of CFDP PDU relay/forward functionality to enable communication between the two heterogeneous space communication fabrics. Test setup, test results, and future work on the tunneling service are also discussed.

Catora: congestion avoidance through transmission ordering and resource awareness in delay tolerant networks

The proliferation of wireless mobile devices encourages research into their employment to form delay tolerant networks (DTN) for such applications as disaster response, military communications, and crowdsourcing. Within a DTN, messages are exchanged between nodes following a store-carry-forward paradigm, which is notably susceptible to congestion and can lead to a crippling in network performance. A DTN’s time-dynamic topology departs from traditional network definitions in its unpredictable and volatile nature, thus prohibiting the effective adoption of traditional network solutions to this problem. In this paper, the Catora system is proposed as a multi-copy message exchange and buffer management system designed to both aid in the delivery of prioritized messages and mitigate congestion and its degradation. Operating around the distinct ordering of messages for transfer, delivery, and deletion, Catora propagates messages so as to balance their dissemination, hasten the delivery of high priority messages, and avoid congestion through strategic buffer management. Simulations using two real-world datasets demonstrate Catora’s capability to quickly deliver more messages at reduced overhead costs when compared to benchmarks and the state-of-the-art, even when the network suffers from congestion.

Binary Galois field based asynchronous scheduling protocol for delay tolerant networks

Neighbour discovery plays a crucial role for communication in sparsely dense mobile networks, especially in delay tolerant networks, where neighbour discovery latency is generally much higher than the node contact duration. Hence, energy efficient neighbour discovery is an essential aspect of this type of network. Synchronous wake-up scheduling of the nodes can be used to decrease the neighbour discovery latency, but such scheduling cannot be applied to delay tolerant networks where the essence of the communication lies in it’s decentralization. Additionally, the synchronous process needs a global clock for node synchronization. Using a global clock is an energy hungry process. Hence, to avoid this energy hungriness, over the years, many asynchronous protocols based on wake-up scheduling have been developed in order to timely wake-up the nodes to ease the neighbour discovery process in an energy efficient manner. However, asynchronous protocols have reduced message delivery and are not fine-grained enough to support high delivery ratio. In this paper, we have used a binary Galois field based technique for designing asynchronous wake-up scheduling. A thorough analysis has been performed to demonstrate the performance of this asynchronous protocol when compared to the current state of the art in the adaptive and the non-adaptive mode. Results show that the proposed protocol in non-adaptive mode increases message delivery probability by 10% and reduces message delivery latency approximately by 7% while keeping the energy consumption constant when compared to the other existing asynchronous protocols.

Improving Small Satellite Communications and Tracking in Deep Space—A Review of the Existing Systems and Technologies With Recommendations for Improvement. Part II: Small Satellite Navigation, Proximity Links, and Communications Link Science

This article is the second of a three-part series in which we present the results of a study exploring concepts for improving communications and tracking capabilities of deep space SmallSats. In Part I, we discussed SmallSat direct-to-earth links and SmallSat communications equipment, and provided recommendations for future work. In Part II, we focus on SmallSat navigation options, Disruption Tolerant Networking (DTN), proximity links, and the use of the communication link for science observations, and we provide recommendations for future work. We have examined both radio and optical navigation options, and considered autonomous and semiautonomous navigation to reduce operational costs for planetary SmallSats. We note that communication link resilience to delay and disruption enhances spacecraft autonomy; therefore, we have provided a discussion of DTN to indicate that using DTN allows for automated data transmission and recovery, therefore, reducing manual operations. SmallSats in deep space may utilize a relay spacecraft for communications with earth or function as a relay for landed and in-orbit assets. We present a detailed examination of relay proximity links and networks where we address both proximity hardware and networking scenarios. The proximity link features that we examine include the network architecture and its relationship to DTN, proximity radios and antennas, communications link performance, and proximity navigation. The use of the communication link for science has been practiced by primary missions in deep space scenarios. (Two examples of past planetary radio science experiments can be found in the following: https://solarsystem.nasa.gov/missions/cassini/mission/spacecraft/cassini-orbiter/radio-science-subsystem/ and https://www.boulder.swri.edu/pkb/ssr/ssr-rex.pdf) Likewise, SmallSats can offer their radio links for radio science investigations. This article provides a brief introduction to radio science and presents the prerequisite features necessary for radio science observations by SmallSats. We conclude with nine recommendations based on the findings of the study. These recommendations are guidelines on the design, implementation, and operation of deep space SmallSat communication links. The adoption of some or all of the guidelines should result in an enhanced communication and tracking capability for the deep space SmallSat missions.

Performance of Delay Tolerant Network Protocol in Smart City Scenario

The smart city is being developed in many big cities to support local governments for resources and infrastructure optimization in terms of enhancing services for the citizen. Large investment costs are required to implement a communication network for the smart city infrastructure (i.e. Internet of Things (IoT) devices) using 4G or Wi-Fi networks. This study aims to implement Delay Tolerant Network (DTN) as a low-cost alternative network for the smart city. We use Surabaya smart city plan scenario in which smart mobility services are provided in city transportation and infrastructure. The IoT devices are installed in numerous locations and continuously transmit messages to the monitoring server located in the city hall, bus and car employed as a DTN node. In this paper, as a preliminary research, we investigate the performance of well-known DTN routing protocols (Epidemic, Maxprop, and ProphetV2) with our proposed protocol called Spray and Hop Distance (SNHD). The evaluation is performed using the ONE simulator in terms of the number of delivered messages, the average latency, and the overhead ratio. The results show the performance of SNHD is better than the well-known DTN protocols in various conditions when the total size of delivered messages is large. Unfortunately, none of those routing protocols has a good performance in all of the scenario conditions. In the future, we desire to implement this system in real smart city system in Surabaya and do simulation with more realistic scenario such as real traffic-trace.

A shortest-path tree approach for routing in space networks

A new space era is bringing deployments of thousands of networked assets in near-Earth and deep-space. Delay-Tolerant Networking (DTN) protocols and algorithms such as Contact Graph Routing (CGR) are state-of-the-art technologies certainly capable of achieving this ambitious objective. Nevertheless, in this paper, we highlight and analyze the roots of current scalability limits of CGR, to then propose more efficient alternatives. In particular, we leverage a different graph modeling approach that enables optimizations such as priority queues and spanning-tree searches in the core route determination process. While such abstract data types are difficult to adapt to CGR, we incorporate them into a novel Shortest-Path Tree Approach for Routing in Space Networks (SPSN), which is presented as a compute-efficient alternative. This paper thoroughly describes the SPSN approach including route object modeling, capacity-oriented search, and potential route management techniques. Prototype evaluations analyzed in this paper present significant evidence that SPSN outperforms legacy CGR in more than an order of magnitude in contact plans comprising thousands of contacts.

A Utility Driven Post Disaster Emergency Resource Allocation System Using DTN

Two of the most dominant challenges in post disaster emergency resource allocation are: 1) understanding the exact utility, i.e., exigency, of emergency resources and 2) collecting and transmitting the need for these resources to the control station from where resources are allocated. Measuring the utility of resources with precision becomes tricky in a dynamic post disaster scenario, where demands are constantly evolving and supplies trickle in at an uncertain rate. Moreover, collection and transmission of resource needs of far-flung areas are easier said than done owing to the post disaster disruption of communication infrastructure. These result in the ad-hoc allocation of emergency resources to the shelters. In this paper, we first derive a utility function for dynamically enumerating the shelter specific utility of each emergency resource. Subsequently, we propose an opportunistic knowledge sharing scheme for gathering and disseminating resource needs to the control station using a smartphone-based delay tolerant network. Finally, based on these opportunistically transmitted needs, we formulate a utility driven optimal resource allocation model which minimizes overall resource deficit and total resource deployment time. The proposed system optimally assigns constrained emergency resources to different shelters, so that high-utility resources are deployed fast. The effectiveness of the proposed system is evaluated using ONE simulator and LINGO optimization modeling tool. Exhaustive simulation is done to evaluate the comparative performance of our system with a number of competing schemes. Results show that our system outperforms all these schemes in a fully connected scenario. It is also observed that even in an intermittently connected environment, the performance of our system is almost at par with the competing schemes.

Compliance of ventilator associated pneumonia care bundle by staff nurses in critical care units

INTRODUCTION: Ventilator-associated pneumonia (VAP) is a type of hospital-acquired pneumonia that occurs in patients who are mechanically ventilated for more than 48 hours. VAP is the leading cause of nosocomial infections in patients in intensive care units (ICUs). The pathogenesis of VAP originates from microbial pathogens that are aspirated through the tracheal tube cuff and into the lower respiratory tract. Subsequent colonization and overwhelming of the host's mechanical, body fluids, and cellular defense mechanisms leads to the development of VAP. Objectives:1. To assess the compliance on VAP care Bundle by staff nurses in critical care units.2. To identify the reason for the non-compliance on VAP care bundle.3.To associate the level of compliance on VAP care bundle with demographic variables. Material and Methods: A Descriptive study conducted in critical care units at a tertiary teaching hospital at Puducherry. Institutional review board permission was obtained. The data collection period was one month in the year 2018. The population was nurses who are taking care of mechanical ventilator patients. Samples were selected by census method. The sample size was 50. After getting group consent (verbal consent) from each staff nurses, they were observed by using observational checklist to assess the compliance of VAP care bundle in critical care units. After continuous 3 observations, the participant information sheet was provided and written consent was obtained from each staff nurses. After that the data related to demographic variables and self administered questionnaires on compliance of VAP care bundle was administered over a period of 20 minutes for every participant. Results: In the present study majority 76% (38) staff nurses had average level of compliance to VAP care bundle, 72% (36) of the staff nurses belongs to the age group of 22-25 years,86% (43) of them were females ,96% (48) had completed BSc Nursing,46% (23) of them had 13-36 months of working experience and 58%(29) had not attended CNE regarding VAP care bundle. Conclusion: The present study assessed the level of compliance of VAP care bundle by staff nurses in critical care units. The practices were observed by using observational checklist and the reasons for non compliance to VAP care bundle given by staff nurses were expensive equipment, lack of awareness and dependence on doctor’s order. The study concludes that the level of compliance among majority of staff nurses were average, so there is need for improvement in nurses performance in implementing VAP care bundle protocol in critical care units.

Efficient photo crowdsourcing with evolving POIs under delay-tolerant network environment

In a disaster or battlefield zone, rescue workers, soldiers, and other survivors (referred to as nodes) may need to survey damages and send images to the command and control center (the server) in a hop-by-hop fashion in the absence of any communication infrastructure. The server considers some area/landmark as the point of interest (POI) and distributes a request to the nodes to collect more information about them. Nodes take photos of POIs and share them with each other using the store and forward paradigm, also called Delay-tolerant Networks (DTNs), to send the photos to the server. Due to the highly intermittent contact characteristics of nodes in a DTN network and bandwidth and storage limitations, redundant photos need to be removed in this forwarding technique, whereas photos that cover different angles and views of the POIs need to be shared. Another challenge is that, over time, some server-listed POIs may not be of importance anymore, whereas some new POIs might be of more interest. In this work, we propose a scheme that is able to dynamically update the list of POIs based on the current photo metadata, with reduced consumption of the bandwidth, energy, and storage at DTN nodes by sending only important photos of POIs. In the performance evaluation, we show the scalability of our approach, and also show that it provides the same level of photo coverage but consumes much less energy and bandwidth than other related schemes.

A Diverse Band-Aware Dynamic Spectrum Access Network Architecture for Delay-Tolerant Smart City Applications

According to the Smart City Council, an adequate telecommunications infrastructure is vital for the success of businesses, industries as well as residents of Smart cities. However, currently available standard and cellular technologies, such as 3/4G, GSM (Global System for Mobile Communications) and LTE (Long-Term Evolution), are rapidly reaching their limit mainly due to increased traffic demand. Such limitations are only going to worsen in the next years, due to the advent of Internet of Things technologies that are expected to interconnect billions of devices to the Internet. In this paper, we propose a novel network architecture that supports several delay-tolerant (non-real-time) Smart city applications and services (e.g., gathering air pollution information), and therefore, a promising approach to address the burdening of increased traffic demand to Smart city’s legacy standard and cellular communication infrastructure. The proposed architecture is based on an innovative diverse band-aware Dynamic Spectrum Access ( d-DSA ) paradigm, that allows a certain wireless device to opportunistically access idle channels in multiple licensed/unlicensed spectrum bands. d-DSA radio devices are mounted on Smart city’s urban vehicles (e.g., taxis) that act as mobile routers to gather, carry, and forward various types of data traffic. This results in a time-varying and unpredictable delay-tolerant network (DTN) where each node can access whitespace channels and transmit in multiple spectrum bands. Given lack of research in efficient routing schemes for such d-DSA DTN networks, we propose a distributed and lightweight d-DSA aware Geographical Routing (dDSA-GR) protocol, that utilizes a weighted linear metric for selecting a suitable spectrum band, and classic georouting principle for choosing next hop node in the path route between any node pair in d-DSA DTNs. Results on realistic traces based on the map of Lexington, KY, USA, show that our dDSA-GR routing protocol outperforms baseline approaches in terms of network delay, message delivery ratio, and energy efficiency, under all considered scenarios.

Selfishness in Vehicular Delay-Tolerant Networks: A Review.

Various operational communication models are using Delay-Tolerant Network as a communication tool in recent times. In such a communication paradigm, sometimes there are disconnections and interferences as well as high delays like vehicle Ad hoc networks (VANETs). A new research mechanism, namely, the vehicle Delay-tolerant network (VDTN), is introduced due to several similar characteristics. The store-carry-forward mechanism in VDTNs is beneficial in forwarding the messages to the destination without end-to-end connectivity. To accomplish this task, the cooperation of nodes is needed to forward messages to the destination. However, we cannot be sure that all the nodes in the network will cooperate and contribute their computing resources for message forwarding without any reward. Furthermore, there are some selfish nodes in the network which may not cooperate to forward the messages, and are inclined to increase their own resources. This is one of the major challenges in VDTNs and incentive mechanisms are used as a major solution. This paper presents a detailed study of the recently proposed incentive schemes for VDTNs. This paper also gives some open challenges and future directions for interested researchers in the future.

An Efficient Delay Tolerant Networks Routing Protocol for Information-Centric Networking

Delay tolerant networks (DTN) is a good candidate for delivering information-centric networking (ICN) messages in fragmented networks due to disaster. In order to efficiently deliver ICN messages in DTN, the characteristics of multiple requester nodes for the same content and multiple provider nodes for the same request should be used efficiently. In this paper, we propose an efficient DTN routing protocol for ICN. In the proposed protocol, requester information for request packet, which is called an Interest in ICN, is shared by exchanging status table with requested Data ID, requester ID, and satisfaction flag, where satisfaction flag is defined to show the delivery status of Data, so that unnecessary forwarding of Data is avoided. Data is forwarded to a more probable node by comparing average delivery predictability to a set of requesters. Performance of the proposed protocol was evaluated using simulation from the aspect of Data delivery probability and Data overhead, for varying buffer sizes, number of relay nodes, and time-to-live (TTL) of Data. The results show that the proposed protocol has better Data delivery probability, compared to content distribution and retrieval framework in disaster networks for public protection (CIDOR) and opportunistic forwarding (OF) protocols, although there is a tradeoff from the aspect of Data overhead for varying buffer sizes and number of relay nodes.

Modeling on Body Delay Tolerant Network Sink Locality of Wireless Body Area Networks for Different Body Postures

Due to the recent advancements in the field of wireless communication and Wireless Sensor Networks, the Wireless Body Area Networks (WBANs) have become an area of concern for researchers. In military operations, patient monitoring, sports field, among other wireless body area networks is used for real time monitoring and smart sensing for eHealth operations.In these WBAN, disconnections between the body sensors occur quite often and sometimes of significant duration due to the postural mobility nature of the human. These consequently affects the efficiency of the entire network hence the need for Delay Tolerant Network (DTN). The DTN minimizes delays and adapts itself to cope with long delays if they occur. One of the vital mechanisms that can be employed to enhance the efficiency of the network is to determine the optimal postural locality of the sink node.