Routing In Vehicular Ad Hoc Networks Research Articles

TAD-HOC Routing Protocol for Efficient VANET and Infrastructure-Oriented Communication Network

Intelligent Transportation System (ITS) is a critical factor for Vehicular Ad hoc Networks (VANET). Even though VANET belongs to the class of Mobile Ad hoc Network (MANET), none of the MANET routing protocol applies to VANET. VANET network is dynamic, due to increased vehicle speed and mobility. Vehicle mobility of VANET affects conventional routing algorithm performance, which deals with the dynamicity of the network node. The evaluation of the existing research stated that Ad hoc On-Demand Distance Vector (AODV) is an effective MANET protocol to adopt network changes for significant resource utilization and also provides effective adaptation in the network change. Due to the effective performance of the AODV protocol, it is considered as an effective routing protocol for VANET. This paper proposed an ad hoc TROPHY (TAD-HOC) routing protocol for the VANET network for increasing efficiency and effective resource utilization of the network. To improve the overall performance, ad hoc network is combined with Trustworthy VANET ROuting with grouP autHentication keYs (TROPHY) protocol. The proposed TAD-HOC protocol transmits data based on time demand in the VANET network with the desired authentication. Results of the proposed approach show the increased performance of the VANET network with packet delay, transmission range, and end-to-end delay. The comparative analysis of the proposed approach with I-AODV, AODV-R, and AODV-L shows that the proposed TAD-HOC exhibited effective performance.

Bio-inspired VANET routing optimization: an overview

This paper demonstrates a recapitulated historic evolution further to a future overview of all vehicular ad-hoc network (VANET) routing problems that concern either directly related routing tasks or targeting a set of diverse routing-related techniques with the aid of the bio-inspired approaches. In this lecture, we serialize, in a synchronous observation, the evolution and tendencies of the VANET routing problem’s solving simultaneously with the emergence of different classes of nature-based meta-heuristics, by bringing a proposed taxonomy of different major VANET routing problems seen their nature, studied range and metaheuristic types used for their optimization. Then, we follow with a visionary deduction of the other appearing routing issues of VANETs that can be approached or already began to be solved by nature-inspired optimization algorithms. Noting that each spread routing problem is illustrated with notable related works, describing initially realized conventional protocols to vulgarize different routing modules, then detailing bio-inspired protocols for VANET routing to explain the utility of nature-inspired optimization techniques. The motivation of this work came from the lack of a reference classifying the VANET-related routing problems within the notion of nature-inspired optimization. That’s further to giving and up-to-date literature on the context for opening out a visionary opinion on the tendencies of either emerging recent bio-inspired optimization approaches or the different metaheuristic-based combinations on specific VANET routing problems.

V2V Routing in VANET Based on Heuristic Q-Learning

Designing efficient routing algorithms in vehicular ad hoc networks (VANETs) plays an important role in the emerging intelligent transportation systems. In this paper, a routing algorithm based on the improved Q-learning is proposed for vehicle-to-vehicle (V2V) communications in VANETs. Firstly, a link maintenance time model is established, and the maintenance time is taken as an important parameter in the design of routing algorithm to ensure the reliability of each hop link. Aiming at the low efficiency and slow convergence of Q-learning, heuristic function and evaluation function are introduced to accelerate the update of Q-value of current optimal action, reduce unnecessary exploration, accelerate the convergence speed of Q-learning process and improve learning efficiency. The learning task is dispersed in each vehicle node in the new routing algorithm and it maintains the reliable routing path by periodically exchanging beacon information with surrounding nodes, guides the node’s forwarding action by combining the delay information between nodes to improve the efficiency of data forwarding. The performance of the algorithm is evaluated by NS2 simulator. The results show that the algorithm has a good effect on the package delivery rate and end-to-end delay.

RETRACTED ARTICLE: A stream position performance analysis model based on DDoS attack detection for cluster-based routing in VANET

The strength of Vehicular Ad hoc Networks (VANETs) and the rapid deployment capability, can be used in many situations where the network should be arranged in a short time and there is a need to collect sensitive information. We consider cluster-based attack detection in data compilation wherever the neighbor nodes give the important information to the cluster head. Moreover, evidence is obtainable in the cluster head may possibly be accumulated by some vehicular nodes and executes numerous responsibilities such as decision making about delivering information. The existence of malicious nodes threatens determination making through transmitting malevolent information, which is not appropriate to the VANET categorized data and might send a substantial number of packets to the vehicles or Road Side Unit (RSU). To overcome this issue, we have proposed a Stream Position Performance Analysis (SPPA) approach. This approach monitors the position of any field station in sending the information to perform a Distributed Denial of Service (DDoS) attack. The method computes various factors like Conflict field, Conflict data and Attack signature sample rate (CCA). Using all these factors, the method identifies the trustworthiness of the packet and includes it in decision making. The proposed approach increases the performance of a Distributed Denial of Service (DDoS) attack detection in a VANET environment.

Routing Protocols in Vehicle Ad-Hoc Network

Vehicular Ad-hoc Network (VANET) is associate rising autonomous dynamic topology network. It is a unique type of Mobile Ad-hoc Network during which the automobiles amendment their message with each other. VANET turns every automobile in it into a mobile node and use those nodes to make a mobile dynamic community. The aim of VANET is to produce a wi-fi connectivity and numerous programs applications like collision dodging, safety and rising the traffic ratio as designing by the Intelligent Transportation System (ITS). The transport are strained by the sensible traffic surroundings, and currently the simulations are primarily network simulations that cannot simulate the real hint of the object (vehicle). Merely as nodes in VANETS have identical excessive mobility, so there are masses of demanding situation to route the packets to there final destination which need to be addressed by means of existing/offering new solutions for the comparable. Keeping view of above, In this paper, summarize the prevailing VANET routing protocols and classify and evaluate them. Then, listing numerous classic routing algorithms and examine their characteristics and advantages and disadvantages. Eventually, by way of analyzing the reputation of vehicle-installed routing protocols, we tend to illustrate the difficulties and challenges that vehicle-mounted routing protocols can/will encounter within the future.

QoS-aware multi-path video streaming for urban VANETs using ACO algorithm

Drivers can be provided with several beneficial services associated with video streaming in a vehicular ad-hoc network (VANET). Given the dynamic topology and high mobility of VANETs, a single path cannot support the required quality of service (QoS). To maximize global QoS metrics, a two-path model is proposed based on a disjoint algorithm to forward sub-streams over diverse paths from the transmitter to the receiver vehicle. In this solution, the video information spread in separate paths is categorized based on their priority. For this purpose, the protocol for transmitting each kind of video data should be selected cautiously. The present study aims to propose an ant colony optimization-based technique to establish the primary and secondary paths and enhance the QoS of routing paths. To achieve this goal, the QoS routing issue is formulated mathematically as a problem of constrained optimization. Moreover, to achieve high-quality video streaming, inter-frames are transmitted over the user datagram protocol and intra-frames are transmitted over the transmission control protocol (TCP). TCP transmission delays are also minimized using a TCP-ETX algorithm for selecting appropriate paths. According to the simulation results, the proposed two-path solution can be used to improve the quality of video streaming and to enhance the performance in terms of end-to-end delay, packet delivery ratio, and overhead. In this way, the proposed method can outperform several prominent routing algorithms such as adaptive QoS-based routing for VANETs, geographic source routing (GSR), intersection-based geographical routing protocol, and efficient GSR.

Topology Based Routing Protocols in Vehicular Ad hoc Network

Number of routing protocols has been proposed for Vehicular Ad hoc Networks (VANETs) based on various architectures, challenges and applications. Primary aim of these protocols is to maximise throughput and to minimize packet loss. Most of the researchers facing challenges while developing efficient routing protocol. So VANET require novel type of routing protocols. Unlike wired network, router nodes are not used as dedicated and protocols have to be performed by user, which is undependable. For supporting Intelligent Traffic System efficient design of routing protocol is important in VANETs. As it must for communication, the VANET routing protocol should create an efficient route between network nodes.

Link utility aware geographic routing for urban VANETs using two-hop neighbor information

Routing in Vehicular Ad Hoc Networks (VANETs) is a challenging problem. While geographic routing protocols are preferred for VANETs due to their scalability, they are focused on finding next-hop nodes closer to the destination without considering their current load or network traffic. In addition, routing decisions based on only one-hop neighbors information might be less optimal since they do not consider the availability of further suitable nodes for forwarding. Thus, such selected next-hop nodes may become overloaded with too much traffic that exceeds their available bandwidth, and may even result in significant packet losses if no other node suitable for forwarding can be found. In this paper, we propose a novel geographic routing protocol named Geo-LU. The proposed protocol improves the routing performance by extending the local view of the network topology at the current forwarder to include two-hop neighbor information. Moreover, it utilizes our proposed link utility (LU) measure. LU considers the utility of a two-hop neighbor link by considering the minimum residual bandwidth on that link and its packet loss rate. By incorporating two-hop neighbor information and our proposed LU measure, the proposed protocol, Geo-LU, can react appropriately to the increased network traffic and to the frequent topology dis-connectivity in VANETs as confirmed by our simulation results.

Performance Evaluation of Routing Protocols in Vehicular Ad-Hoc Networks (VANETs): A Comparative Study

VANET is a novel way for fast-moving autos to connect. VANET provided traffic engineering, management, emergency information to avoid accidents, and other user applications. VANETs are similar to Mobile Ad hoc Networks (MANETs), but they have fast speeds, mobility, adequate storage and processing power, unexpected node density, difficult communication environments with limited connection lifespans, etc. Hence, VANET protocol testing needs realism. Vehicular Ad hoc Network (VANET) is a new communication paradigm that allows road network V2V and V2I communication (V2I). It supports traffic engineering, emergency information transfer, and other user applications. Vehicular networks distribute data about road traffic conditions to keep vehicles safe and efficient. VANET Applications' characteristics—different network density, fast vehicle movement—make data dissemination difficult. Performance requirements determine these protocols' vehicle area network applicability. Vehicles talking with each other and roadside units constitute Vehicular Ad-Hoc Networks (VANETs), a specific type of MANET (RSUs). VANETs allow safety, traffic management, and infotainment. Due to vehicle mobility and frequent network topology changes, VANETs have routing difficulties. This paper compares VANET routing protocols. . Simulations reveal that mobility pattern, network density, and traffic load affect protocol performance.

Inter-vehicle distance-based location aware multi-hop routing in vehicular ad-hoc network

The vehicular ad-hoc network (VANET) is a self-organized wireless ad-hoc network created by movable vehicles of the limited transmission range R to transmit traffic-related information to nearby vehicles on demand. It is worthy to mention that in VANET the vehicles are the source of transmission of data packets so that it works as a node. Vehicles restricted transmission range causes the route to participate in data transmission from the source S to destination D may vanish seldom. Therefore, a stable route from source to destination needs to deliver data packets at the intended destination. This paper presented an inter-vehicle distance-based location-aware multi-hop routing (LAMHR) in the vehicular ad-hoc network to enhance the vehicle's connectivity. LAMR predicts the future location of the nodes to select an optimal next forwarder towards the destination to establish a stable route from source to destination. In this paper, to obtain the inter-vehicle distance, a geometry-based localization technique has developed that impact on the vehicle's connectivity. Performance of the LAMHR has evaluated in terms of the path vanish, node broadcasting time, packet delivery ratio and throughput. Through the simulated results, it has shown that the proposed LAMHR model gives high performance comparatively the existing fuzzy logic-based directional location routing (FLDLR), directional-location aided routing (D-LAR) and location aided routing (LAR) protocols.

V2VR: Reliable Hybrid-Network-Oriented V2V Data Transmission and Routing Considering RSUs and Connectivity Probability

Vehicular ad hoc networks (VANETs) have been widely used in intelligent transportation systems (ITSs) for purposes such as the control of unmanned aerial vehicles (UAVs) and trajectory prediction. However, an efficient and reliable data routing decision scheme is critical for VANETs due to the feature of self-organizing wireless multi-hop communication. Compared with wireless networks, which are unstable and have limited bandwidth, wired networks normally provide longer transmission distances, higher network speeds and greater reliability. To address this problem, this paper proposes a reliable VANET routing decision scheme based on the Manhattan mobility model, which considers the integration of roadside units (RSUs) into wireless and wired modes for data transmission and routing optimization. First, the problems of frequently moving vehicles and network connectivity are analyzed based on road networks and the motion information of vehicle nodes. Second, an improved greedy algorithm for vehicle wireless communication is used for network optimization, and a wired RSU network is also applied. In addition, routing decision analysis is carried out in accordance with the probabilistic model for various transmission ranges by checking the connectivity among vehicles and RSUs. Finally, comprehensive experiments show that our proposed method can support real-time planning and improve network transmission performance compared with other baseline protocol approaches in terms of several metrics, including package delivery ratio, time delay and wireless hops.

Intersection Fog-Based Distributed Routing for V2V Communication in Urban Vehicular Ad Hoc Networks

Due to the characteristics of urban vehicular ad hoc networks (VANETs), many difficulties exist when designing routing protocols. In this paper, we focus on designing an efficient routing strategy for vehicle-to-vehicle (V2V) communication in urban VANETs. Because, the characteristics of urban VANET routing performance are affected mainly by intersections, traffic lights, and traffic conditions, we propose an intersection-based distributed routing (IDR) strategy. In view of the fact that traffic lights are used to cause vehicles to stop at intersections, we propose an intersection vehicle fog (IVF) model, in which waiting vehicles dynamically form a collection or fog of vehicles at an intersection. Acting as infrastructure components, the IVFs proactively establish multihop links with adjacent intersections and analyze the traffic conditions on adjacent road segments using fuzzy logic. This approach offloads a large part of the routing work. During routing, the IVFs adjust the routing direction based on the real-time position of the destination, thus avoiding rerouting. Each time an IVF makes a distributed routing decision, the IDR model employs the ant colony optimization (ACO) algorithm to identify an optimal routing path whose connectivity is based on the traffic conditions existing in the multihop links between intersections. Because of the high connectivity of the routing path, the model requires only packet forwarding and not carrying when transmitting along the routing path, which reduces the transmission delay and increases the transmission ratio. The presented mathematical analyses and simulation results demonstrate that our proposed routing strategy is feasible and that it achieves relatively high performance.

Location‐based data delivery between vehicles and infrastructure

Multi-hop routing in vehicular ad-hoc networks (VANETs) and wireless sensor networks has attracted significant interest of researchers in the wireless ad-hoc networks community. Most multi-hop routing protocols in VANET are based around the idea of choosing the next destination, which will provide the shortest-delay to reach a destination. To ensure better monitoring and reporting of road condition information, this study proposes location-based data forwarding through roadside sensors using k-shortest path routing combined with Q-learning. Q-learning is used for exploration of the sensing field to determine those sensors which have a higher queuing delay during peak hours as well as those which have comparatively lower delays. The use of Q-learning for exploration (sans routing) enables faster convergence for the sensors as compared to those techniques which utilise naive Q-learning for shortest path routing. Secondly, multi-hop routing is being combined with source coding (Huffman and Arithmetic coding) to compress the data payload of packets. This has shown some promising results for the VANETs employing dedicated short-range communication.

Middle-Order Vehicle-Based Clustering Model for Reducing Packet Loss in Vehicular Ad-hoc Networks

Vehicular Ad-hoc NETworks (VANETs) are typically termed as a wireless ad-hoc network that contains extreme node mobility and also the network carries a great significance in various traffic-oriented commercial applications and safety services. Due to its high mobility, routing in VANET has been a challenging work and also proving a higher rate of packet delivery ratio with reduced packet loss has been more important to be considered in route formations. With that note, this paper contributes to developing a clustering model called Middle-Order Vehicle-based Clustering (MOVC) model for managing the frequent topological change and high vehicle mobility, and efficiently handling the typical road traffic scenario. Moreover, the algorithm is intended to maintain the cluster to be constant for managing the vehicles in effective ways and also to provide uninterrupted communication between the vehicles. An algorithm for Effective Cluster Head Election (ECHE) is also derived in this paper for proficiently handling the frequency variation on the highways. Further, the model is simulated and evaluated on the basis of various metrics of VANET routing, specifically packet loss, packet delivery ratio, network lifetime and throughput. The results show that the proposed mechanism outperforms the results of existing models.

Optimised Tail-based Routing for VANETs using Multi-Objective Particle Swarm Optimisation with Angle Searching

Routing protocols for vehicular ad hoc networks (VANETs) are highly important, as they are essential for operating the concept of intelligent transportation system and several other applications. VANET Routing entails awareness about the nature of the road and various other parameters that affect the performance of the protocol. Optimising the VANET routing guarantees optimal metrics, such as low E2E delay, high packet delivery ratio (PDR) and low overhead. Since its performance is of multi-objective nature, it needs multi-objective optimisation as well. Most researchers have focused on a single objective or weighted average for multi-objective optimisation. Only a few of the studies have tackled the actual multi-objective optimisation of VANET routing. In this article, we propose a novel reactive routing protocol named tail-based routing, based on the concept of location-aided routing (LAR). We first re-defined the request zone to reduce the lateral width with respect to the lateral distance between the source and destination and named it tail. Next, we incorporated angle searching with crowding distance inside the multi-objective optimisation MO-PSO and called it MO-PSO-angle. Then, we conducted optimisation of tail-based routing using MO-PSO-angle and compared it with optimised LAR, which exhibited the superiority of the latter. The best improvement was at the optimisation point with a 96% improvement of PDR and a 313% improvement in E2E delay.

New Discrete Cuckoo Search Optimization Algorithms for Effective Route Discovery in IoT-Based Vehicular Ad-Hoc Networks

Recently, the Internet of Things (IoT) is widely considered in vehicular ad-hoc networks (VANETs) for use in intelligent transportation systems. In particular, the pervasive deployment of different sensors in modern vehicles has unlocked interesting possibilities for improving routing performance in VANETs. Nevertheless, the discovery of short single loop-free routes for effective and efficient information dissemination in VANETs remains a challenge. This challenge proves more difficult to solve since it reduces to the case of finding the shortest Hamiltonian path for effective routing in VANETs. Consequently, in this paper, we propose two discretized variants of the cuckoo search optimization (CSO) algorithm, namely, the Levy flight-based discrete CSO (LF-DCSO) and the random walk-based discrete CSO (RW-DCSO) for effective route discovery in VANETs. In addition, we investigated the inverse mutation operator gleaned from genetic algorithm (GA) in order to improve the exploration properties of our DCSO variants. We describe a new objective function that effectively models the reliability of individual links between nodes that comprise a single route. A detailed report of the routing protocol that controls the routing process is presented. Our proposed methods were compared against the roulette wheel-based GA and the improved k-means-based GA termed IGAROT. Specifically, our findings reveal that there was no significant difference in the performance of the different methods in the low vehicle density scenario, however, in the medium vehicle density scenario, the RW-DCSO algorithm achieved 2.56%, 100%, and 128.57% percentage increment in its route reliability score over the LF-DCSO, RW-GA, and IGAROT algorithms, respectively. Whereas in the high vehicle density scenario, the LF-DCSO algorithm achieved a percentage increment of 42.85%, 525%, and 733.33% in the route reliability score obtained over the RW-DCSO, IGAROT, and RW-GA algorithms, respectively. Such results suggest that our methods are able to guarantee effective routing in VANETs.

Hybridization of Monarch Butterfly and Grey Wolf Optimization for Optimal Routing in VANET

The routing process in Vehicular Ad hoc Networks (VANET) remains a more demanding task in city backgrounds. Identifying an optimal end-to-end path that satisfies reduced overhead and delay control is still facing a lot of difficulties and limitations in recent days. These limitations are owing to the increased movement of vehicles, the repeated failures of a path, and the varied obstacles that might have an effect on the consistency of the data routing and transmission. Hence, this paper intends to present an enhanced VANET routing model by considering the network quality metrics including congestion, travel, collision and QoS awareness cost. Accordingly, in the proposed work, a cost model is modeled as the solution for the vehicle routing problem by taking into account the above-mentioned constraints. For determining the optimal route, this research work establishes a new hybrid algorithm known as Grey Updated Butterfly Operator (GU-BO) that links both the concepts of Monarch Butterfly Optimization (MBO) Algorithm and Grey Wolf Optimization (GWO). Finally, the performance of the implemented approach is compared over other conventional approaches with respect to congestion and cost analysis, and proves its superiority of proposed work over others.

A 3-stage fuzzy-decision tree model for traffic signal optimization in urban city via a SDN based VANET architecture

One of the main challenges for developed cities is vehicle traffic and its management. Because of physical structures and cross roads of urban intersections, traffic flows may cause time delay, congestion, traffic accidents and more fuel/time consumption. For these reasons, there are many studies on traffic management systems which are a part of smart city applications in both literature and practice. In recent years, it seems that VANET (Vehicular Ad Hoc Networks) architecture has been preferred in these studies, which enables vehicles to easily communicate with each other or devices on the edge of the road and also to transfer the related traffic data to the center. On the other hand, there are many studies on a new network paradigm called SDN (Software Defined Networks) that solves problems such as performance, programmability, scalability, security and management difficulties in today’s traditional networks. Depending on all this, in this study, we will present an architectural proposal about how to use SDN and VANET network paradigms together in traffic management systems in order to use both existing intersection management system modules more adaptively and future traffic based services to be added in desired service quality without changing the communication infrastructure. Also in this study, a 3-stage fuzzy-decision tree model was proposed for traffic signaling which is the most important problems of urban traffic by focusing environmental factors (accident situation, priority vehicle transition etc.) and activity information (road construction, meeting, train and bus schedule etc. ) not only vehicle density unlike other signaling studies in literature. The proposed model also generates/sends a dynamic flow input to SDN agent vehicles and SDN agent RSU (Road Side Unit) in intersection for making VANET routing protocols (AODV-ad hoc on-demand distance vector, DSDV-destination-sequenced distance vector) selection automatically according to traffic incident and density. In order to measure the functionality of the SDN based VANET architecture and 3 stage fuzzy-decision tree model on it for the transmission infrastructure of the traffic management, performance tests were performed on different traffic and network scenarios on Adapazarı City Centre Model. SDN based VANET architecture was compared with traditional systems according to transmission infrastructure and also proposed 3-stage fuzzy-decision model was compared with signaling techiques in literature such as fixed-time signaling, Webster equation, ant colony algorithm and particle swarm optimization under same traffic and network scenarios. The results obtained from performance tests shows that the proposed 3-stage fuzzy-decision model has %15-17 better performance than fixed-time signaling and webster equation and also %9-11 better performance that particle swarm and ant colony optimizations in low density traffic scenarios. In high density and dynamic traffic scenarios these rates reach %20-22 compared to fixed-time signaling and webster equation and %14-15 compared to particle swarm and ant colony optimizations. In addition in this study, proposed SDN based VANET architecture was compared to traditional VANET ITS architectures within the same traffic and network scenarios. According to obtained results, it is shown that the proposed SDN based VANET has %30-40 better performance than traditional systems in end-end delay, throughput and packet loss rate criteria.

Highly Anonymous Mobility-Tolerant Location-Based Onion Routing for VANETs

Vehicular ad hoc networks (VANETs) have received considerable attention in recent years. Like any other network, privacy and anonymity are a requirement in VANETs. Classic anonymous routing protocols such as onion routing algorithm are fragile in mobile networks due to frequent link breaks. In this article, we propose a novel onion-based anonymous routing protocol for highly mobile vehicular networks. It introduces the concept of location-based dynamic relay groups. In this concept, vehicles dynamically form groups around specific locations to act as cryptographic onion relays. The proposed protocol satisfies source anonymity, destination anonymity, and route anonymity features and is very scalable. Employment of pseudo-IDs further helps in keeping the real identity of vehicles anonymous. The proposed protocol can modify the chain structure on the fly and make it longer to maintain source/destination location anonymity or cut it short to maintain performance. The extensive simulations conducted based on the SUMO traffic simulator showed that the proposed protocol significantly outperforms the naive onion routing protocol in terms of delivery ratio, delay and number of retransmissions.

Survey on Routing Protocols for Vehicular Ad Hoc Networks Based on Multimetrics

In the last few years, many routing protocols have been proposed for vehicular ad hoc networks (VANETs) because of their specific characteristics. Protocols that use several metrics have been shown to be the most adequate to VANETs due to their effectiveness in dealing with dynamic environment changes due to vehicle mobility. Metrics such as distance, density, link stability, speed, and position were selected by the authors for the best proposal. Several surveys of routing proposals have been generated to categorize contributions and their application scenarios, but none of them focused on multimetric approaches. In this paper, we present a review of the routing protocols based on more than one metric to select the best route in a VANET. The main objective of this research was to present the contemporary most frequently used metrics in the different proposals and their application scenarios. This review helps in the selection protocols or the creation of metrics when a new protocol is designed.This survey of multimetric VANET routing protocols employed systematic literature-review (SLR) methodology in four well-knownown databases that allowed to analyze current state-of-the-art proposals. In addition, this paper provides a description of these multimetric routing protocols. Our findings indicate that distance and speed are the most popular and versatile metrics. Finally, we define some possible directions for future research related to the use of this class of protocols.