research article cooperation between trust and ... - hindawi

Research ArticleCooperation between Trust and Routing Mechanisms forRelay Node Selection in Hybrid MANET-DTN

Jan Papaj and Lubomir Dobos

Department of Electronics and Multimedia Communications, Faculty of Electrical Engineering and Informatics,Technical University of Kosice, Letna 9, 042 00 Kosice, Slovakia

Correspondence should be addressed to Jan Papaj; [email protected]

Received 4 January 2016; Revised 8 March 2016; Accepted 23 March 2016

Academic Editor: Ioannis Papapanagiotou

Copyright © 2016 J. Papaj and L. Dobos. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

Today’s mobile networks require integration of the different networks in order to transport data between mobile devices. The mainproblems of all networks occur if the communication paths are disconnected for a short time. The hybrid MANET-DTN is anevolution of the Mobile Ad Hoc Networks (MANET) and Delay/Disruption Tolerant Network (DTN) and it gives the possibilitiesof data transport between the disconnected islands of the nodes. The key problem is how to select reliable and secure nodes totransport messages between isolated islands with limited connectivity. The selection of the relay nodes is a critical factor becausethe data are transported via these devices in hostile environments. Two algorithms for a relay node selection based on trust areintroduced. These algorithms are activated if the connections are disrupted. The selected relay nodes transport data across thedisconnected environment via store-carry-forward mode. The proposed algorithms enable selecting reliable relay nodes based oncollecting routing information and contact history. We introduce the network performance analyses of these algorithms.Themainidea of the analyses is studying how the algorithms can affect the behaviour of the routing and forwarding mechanisms in thesimulator OPNET modeler.

1. Introduction

A new concept of the hybrid MANET-DTN enables aprogressive and robust communication between mobile ter-minals in the hostile and disconnected environment. Thisnetwork enables integration of the Mobile Ad Hoc Network(MANET) for situations when mobile nodes can communi-cate with each other via wireless links and Delay/DisruptionTolerant Network (DTN) in the case when the commu-nication paths never exist or the signal between mobileterminals is weak. This network integrates the benefits ofthe MANET routing algorithm for transmitting the data andDTN forwarding technique in order to obtain transportationpath between a source and destination terminals.

The Mobile Ad Hoc Network (MANET) is characterizedby multihop communication between mobile nodes by wire-less links [1]. There are also no infrastructures and routingpaths are established by routing algorithms (Figure 1). Thetraditional routing algorithms and protocols are based on

routing schemes, which can find a path for a given node pairaccording to various metrics, and data packets are transmit-ted from one intermediate relay node to the next specifiedrelay based on physical condition of wireless channels [2].The routing algorithm relies on the assumption that thenetwork graph is fully connected and fails to route messagesif there is no complete route from source to destination atthe time of sending [3]. The key mechanism is the routingprotocol that allows finding a path for a given node pair(source and destination node) according to various metrics.The routing protocols and algorithms can be classified intothree categories: reactive, proactive, and hybrid [1, 2, 4].

The Delay/Disruption Tolerant Networks (DTN) havebeen developed for intermittent communication betweenmobile terminals. The main feature of these networks ishigh propagation delays when transferring data betweendifferent terminals. DTN provides high bit error rates andthe long-term disconnections experienced in such environ-ments. DTN is proposed and designed to operate in hostile

Hindawi Publishing CorporationMobile Information SystemsVolume 2016, Article ID 7353691, 18 pageshttp://dx.doi.org/10.1155/2016/7353691

2 Mobile Information Systems

Source node

Mobile Ad Hoc Network (MANET)

Hybrid MANET-DTN

Destination node

Source node

Selected relay node(Store-carry-forward model)



Destination nodeIsolated island

Isolated island

Figure 1: Example of the MANET and hybrid MANET-DTN.

environments. DTN is characterized by very long delaypaths and frequent network partitions [5–7]. DTN consistsof human-carried mobile devices (smartphones, PDA, etc.)that communicate with each other without mobile or fixedinfrastructure. DTN forwarding algorithms allow sendingmessages via the broadcast nature and spatial diversity of thewirelessmedium. Forwarding algorithms use the store-carry-forward model and are based on stochastic approach.

Security is a key field for all types of network, notonly in MANET, DTN, or hybrid MANET-DTN [8, 9].In MANET, the security mechanisms are based on theassumption that there are connections between a sourceand target nodes (end-to-end connections) [2]. In DTN, werequire the security solutions, which provide security for allnodes, all services, and application that participate in routingand transmitting process. Based on a sporadic connectivityof nodes, it is necessary to provide secure delivery of themessages from the source node to the destination node. Thehybrid MANET-DTN integrates security issues from bothtypes of networks and provides more challenges to solvesecurity problems.

1.1. Relay Node Selection and Main Motivation in HybridMANET-DTN. In order to provide the effective communi-cation between isolated islands of mobile nodes or betweendisconnected mobile nodes, it is necessary to consider dif-ferent aspects such as disconnections, mobility, partitions,environment, and norms instead of the exceptions. Themobility in DTN is used to provide efficient communication

between unconnected groups of nodes (isolated islands).Themobile nodes forward data and also store data in the cachefor a long time. This model is called store-carry-forward [2].

The selection of forwarding relay node is the first keyissue. There are few works which deal with the selection ofthe relay nodes. The first access is based on the number oftransitions (Expected Transmission Count (ETX), ExpectedAny-Path Transmission (EAX)) which accounts for thespecific characteristics of the opportunistic paradigm [10].Other algorithms are based on a link-state algorithm for theunconstrained selection based on the Dijkstra algorithm [11].Most methods are based on generalizing the Bellman-Fordalgorithm and they prove its optimality [12, 13].

The hybrid MANET-DTN also requires the cooperationbetween mobile terminals in order to make a selection ofthe relay nodes. Relay nodes are nodes that have a higherprobability of connecting with other nodes or allowing thetransmission of the messages by wireless environment. Selec-tion of the relay nodes is made opportunistically based on anactual network environment. There is very little research onthe relay node selection for hybrid MANET-DTN due to themany additional challenges that they face in comparison withtraditional MANET or DTN.

In this paper, the novel trust based relay node selec-tion algorithms are introduced. These mechanisms enableselection of the secure mobile node used for transportationof the data across the disconnected environment. Selectedrelay nodes provide the secure mobile node selected totransport the data. If the mobile node finds a connection

Mobile Information Systems 3

the DTN forwarding mechanism is activated. The proposedmechanisms also provide wide challenges for new servicesnot only for emergency situations.

1.2. Trust in Hybrid MANET-DTN. The term trust can bereflected by reliability, utilization, availability, reputation,risk, confidence, quality of services, and other concepts[4]. Trust is targeting various scientific disciplines, such associology, economics, management, and informatics. In eachof these sectors, the trust is defined differently for a specifictype of use or focus in that area. For example, in sociologytrust is represented as a relationship in nature [14, 15], but inpsychology it is trust in ameaning of a personal attribute view.When we apply trust to MANET or even to newer hybridMANET-DTN we can classify trust into the following fourcategories [16]:

(i) Trust as a risk factor: The definition says that ifan individual node decides to send data throughambiguous path favourable and unfavourable statemay occur. This condition depends on future actionsof the recipient. The parameter trust can be used as aprediction of the future behaviour of other nodes.

(ii) Trust as a belief : Trust is understood as an individualfaith in the behaviour of nodes based on their previ-ous actions and decisions.

(iii) Trust relationship with transitivity: Trust is a weightedbinary relationship between two nodes in the net-work. As an example here we can mention hierarchi-cally constructed network, where node A, which ishigher in the hierarchy, may decide to send data tonode B, which is lower in the hierarchy, whether it istrusted or untrusted.

(iv) Confidentiality as a subjective probability: Trust is theprobability level determined on the basis of subjectivedecision-making, where a node determines the valueof the likelihood with which monitored node takescertain action at a certain time and in a specifiedcontext.

We can summarize these definitions as a trust for aparticular node in the network is a subjective assessment ofthe agent or other nodes on the reliability and accuracy ofreceived and sent information through this node in a givencontext. Trust reflects a belief or expectations for reliability,availability, integrity, and quality of service of target nodefrom the perspective of future activity and behaviour of thatnode.

We determine the metric based on various input param-eters and based on this metric we are able to determine thevalue of trust. The metric can be classified into three basiccategories [14]:

(i) Scale model: In this sense trust is computed withdiscrete confidentiality or continuous values to someextent and a predetermined threshold is used forcomparison and evaluation.

(ii) Facets model: The model is defined as certainty (con-fidence) and confidentiality to the same extent as⟨0, 1⟩ and together they represent credibility (trust-worthiness). This trustworthiness can be shown asthe shortest distance from the start to the point withcoordinates (confidentiality, integrity) in 2D space.Metrics may also be composed of several values; forexample, 𝑏 + 𝑑 + 𝑢 = 1, where 𝑏 is the belief,𝑑 is disbelief, and 𝑢 is uncertainty. Trust is thenrepresented in this space.

(iii) Fuzzy model: Some approaches use probability as ametric for determining confidentiality. Bayes statisticsare used as a parameter entering into the calculationof this probability. Another parameter can be, forexample, a number of received packets, a number offailed packets, and a number of interactions.

In general, trust is a relative term and it is possible toassign to it different values based on a specific proposal for itscomputation. For example, the trust can be assigned valuesof the interval ⟨−1, 1⟩, where −1 represents the completeuntrusted +1 opposite.

In hybridMANET-DTN, the key aspect is how these trustconcepts can be applied to modeling trust [4, 15, 17–19]. Trustfor a particular node in the network is a subjective assessmentof the agent or other nodes on the reliability and accuracy ofreceived and sent information through this node in a givencontext [15]. In this work, we are focused on direct trustcalculation (see Figure 2).

2. Novel Relay Node Selection Algorithms inHybrid MANET-DTN

The main idea of the algorithms is providing relevant andinnovative information, which will be used for selecting ofthe trusted relay nodes. These nodes will be used for trans-portation of the data messages between isolated terminals orisolated islands of the mobile terminals. Algorithms integratemonitoring of the networks for collecting of the data used fortrust computing. The main ideas for all models are displayedin Figure 3.

Proposed models are based on the direct model for thetrust computation. Models are also based on the assumptionthat each node in the network receives information aboutother nodes. The collected data are stored in each node andlater used in the calculation of the preliminary and finalvalues of trust, which are used for selection of the relay nodes.The proposed algorithm is working on the network layer ofthe MANET layer model and is designed for collecting ofthe routing and data node information throughout the entireoperations specified for the routing.

2.1. Designed Relay Node Selection Algorithms in HybridMANET-DTN. As we mentioned before, the first algorithmenablesmonitoring of the routing process in theMANET andDTNenvironment. Figure 4 shows themain idea and the flowdiagram of the proposed algorithm for calculation of trust


(1) Recommendation from a neighboring node U3(1) Direct interaction between mobile nodes

(1) Recommendation from a neighboring node U3(2) Direct interaction between nodes

Direct trust establishment Undirect trust establishment

Hybrid trust establishment

U1 U2(2)

(1)U1 U2

(2)

(1)

U3

U1 U2

(1)

U3

(3)

(2)

(3) Trust calculation based on therecommendations and collected parameters

(2) Trust calculation based onthe monitored parameters

(2) Trust calculation based onthe recommendation from node U3

Figure 2: Three basic models for trust computation used for hybrid MANET-DTN.

and selection of the relay nodes.The algorithm can be dividedinto two main phases [4]:

(i) Phase of obtaining and storing information.(ii) Phase of trust computing.

These phases are carried out whenever the packet isreceived by the node. It is for this reason that the finalvalue of the trust is always up to date and it makes changesdynamically, as well as changing the network topology, whichis related to the mobility of nodes. The final value of the trustreflects the current state of the parameters obtained from thenetwork [4].

2.1.1. Phase of Obtaining and Storing Information. The algo-rithm for the trust calculation is triggered whenever achange occurs in the obtained parameters.The routing packetcoming from the lower layer (physical and data link layer) isencapsulated and the network layer is an IP packet containingdifferent information [4].

The one such important piece of information is collectedfrom the routing packets (DSR reactive routing protocol).This information tells what kind of packet goes. In theproposed algorithm, the incoming packets are used as param-eters which enter into the final calculation of trust and thefollowing parameters are used for calculation: a total numberof route request packets received at node, a total numberof route reply packets received at node, a total number ofroute error packets received at node, a total number ofroute acknowledgement packets received at the node, a totalnumber of data packets received at node, a number of routerequests received from each node, a number of route repliesreceived from each node, a number of path errors received

from each node, number of route replies received from eachnode, and number of data packets received from each node.

The data from this phase are stored in the data structurein memory on each node separately. Each node storesinformation about nodes with whom it came in contact. Thealgorithms also exchange routing information or data trafficbetween each other. Each node in the network is independentand has the possibility of calculating the final value of trustto the other node. Information is stored in a format whichhas the form of a table and is available during the timewhen the node is part of the network. After this time, thevalues will be set up to the minimum that means they willbe marked as untrusted. This structure is dynamic and itssize can vary based on the number of nodes with which nodecommunicates [4].

Figure 5 illustrates the phase of obtaining and savingparameters and we can see four communicating nodes ID 1,ID 2, ID 3, and ID 4. In this scenario, node ID 1 sends apacket type route request to node ID 4 and node ID 2 sendsa route error packet to node ID 3. From a node ID 4 point ofview, node updates the parameter table and stores new valuesinto the structure. That structure is dynamic in size becauseit is not known in advance how many nodes in the networkcan be located and how many nodes can communicate withthis node [4].

2.1.2. Phase of Trust Parameter Computing Trust. After re-trieving and updating the parameters in the table of parame-ters for each node, it is necessary to calculate and update thevalue of trust. At this stage, the value of the trust is calculatedfrom the obtained parameters. Computing of trust is based onthe direct model for the calculation of trust. This means thatthe resulting value was not sent further to other nodes as arecommendation and it serves locally on that node and helps


Start

DTN forwardingmechanism(PRoPHET)

MANETrouting processes

Yes

Process of trust computing

No

Relay nodeselection based on trust

Destination nodes?

No

End

Yes

Monitoringof communicationin network

Existingconnections?

Figure 3: The main idea of the new algorithms for the relay nodesselection in hybrid MANET-DTN.

the node to decide during relay node selection. In our case,the calculated value of thrust will be used as a one parameterfor the selection of the relay node or nodes in a situationwhere there is a disconnection in the network and the nodewill not have a backuppath to the destinationnode (Figure 6).The actual calculation of trust can be divided into two parts[4]:

(i) Trust calculation from routing information 𝑇𝑠: it gives

information about how the trust will be affected bythe routing activities on the given node.

(ii) Trust calculation from data packets 𝑇𝑑: it gives infor-

mation about how the data transmission (withoutrouting packets) can affect the trust on the given node.

From these two subcalculations we get the final value oftrust 𝑇, which is registered and stored in each node data

structure. Analyses of individual fragment values are givenin

𝑇𝑠= 𝑊RREQ ∗ (

𝑅REQ

𝑅REQT) +𝑊RREP ∗ (

𝑅REP𝑅REPT)

+𝑊RERR ∗ (𝑅RERR𝑅RERRT) +𝑊RACK

∗ (𝑅RACK𝑅RACKT) ,

𝑇𝑑= 𝑊𝑑∗ (𝐷

𝐷𝑡

) ,

(1)

where 𝑇𝑠and 𝑇

𝑑are mentioned partial trust values computed

from routing and data traffic on given node.The values𝑇𝑠,𝑇𝑑,

and 𝑇 will be updated after the packets will be received. If anew mobile node will be in a network, the algorithm assignsthe node as a node with the minimum value of trust and,from this time, the values of the trust will be computed andupdated.

Furthermore𝑊RREQ,𝑊RREP,𝑊RERR,𝑊RACK, and𝑊𝑑 areconstants, which define a weight of trust value, and thatresulting value will be in the selected range. Constants can bechanged based on the types of attacks and on the basis of whatwe want to balance with the individual parameters enteringinto the calculation of trust. The values in the numerator ofthe equation represent the number of packets of each typefrom specific nodes in the network. Values 𝑅RREQT, 𝑅RREPT,𝑅RERRT,𝑅RACKT, and𝐷𝑡 represent the total number of packetsfrom all nodes received on the given node and 𝑅RREQ, 𝑅RREP,𝑅RERR, 𝑅RACK, and 𝐷 are the values of the specific packetsreceived from a given node.The value representing final valueof trust 𝑇 is shown in

𝑇 = 𝑇𝑠+ 𝑇𝑑, (2)

where 𝑇𝑠and 𝑇

𝑑values are partial trust mentioned above.

The nodes with higher value of these parameters are selectedas a secure relay node for transportation messages betweenisolated islands (see Figure 1).

2.2. Enhancement of the Algorithm for Selection of the RelayNode in Hybrid MANET-DTN. The main idea of this algo-rithm is also displayed in Figures 3 and 7. It is an extensionof the previous model (see Section 2.1). The values of trustcomputed from formula (2) are stored in memory and theyare available for selection of the trusted nodes for the casethat newly computed values of trust are inadequate.

The extension and enhancement are based on using ofthe parameter trust that is obtained from the history ofcontacts. Specifically, the parameters number of transmissionsand length of transmission are used for selecting of therelay node. Values of these parameters will be obtainedduring direct communication with other mobile nodes. Thenumber of transfers will be evaluated from incoming andoutgoing routing packets. The length of the transmission willbe evaluated only from the received packet and it will beavailable during a time when a node is part of the network.


Start

MANETrouting process(sent packet)

Yes

No

No

No

No

Yes

Yes

Yes

No

Yes

End

Selection of therelay nodes basedon the highervalue of T

Computationof the trust value T

Computationof the trust valueTs

Computationof the trust valueTd

Number of datapacket actualizationinstances (D)

Send datato selectedrelay node

Is itdata packet?

Is itRREQ?

Is itRREP?

Is itACK?

Is itRERR?

Number of route request (RREQ)packet actualizationinstances

Number of routereply (RREP)packet actualizationinstances

Number of routeacknowledgement(RACK) packetactualizationinstances

Number of routeerror (RERR)packet actualization instances

Are pathsdisconnected?

Figure 4: The flowchart of the algorithm for hybrid MANET-DTN.

In this enhancement of the algorithm, the direct trustcomputation is applied, too. It means that the trust iscalculated based on the parameters which itself acquired andwhich relate to the neighbor nodes. The advantage of thisapproach lies in the fact that the trust reflects the views

only for the actual node and it cannot be distorted bymalicious nodes. The disadvantage is the loss of a numberof values about the trust of the node, resulting in the loss ofobjectivity in evaluating the trust. The modification relies onthe following steps:


RREQ

RACK

RREQ RREP RERR RACKNodeID Received Total Received Total Received Total Received TotalID_1

ID_2

234 87 12 25 82

475 24 88 13 265

RREQ

RERR

ID_1

ID_2

ID_4 ID_3

DATA

TrustReceived Sent1228

0,426

DATA

DATA

−0,816

4325 + 12674 + 1

2467 + 1

124 + 129 + 1268 + 1

548 + 1147 + 1128 + 1

· · ·

Figure 5: Collecting of the routing data for trust computing in hybrid MANET-DTN.

Node ID_1 trusts ID_4

Node ID_4 sends informationabout node ID_2 to ID_1

ID_4

ID_1

X

ID_2

Node ID_4 trusts ID_2

Node ID_2 sends informationabout node ID_X to ID_4

Node ID_2 trusts ID_X

Figure 6: Promotion calculated value of the trust between nodes during computing of the trust in hybrid MANET-DTN.

(i) Phase of initialization and obtaining the values ofnumber of transmissions and length of transmissionfor trust computing in hybrid MANET-DTN.

(ii) Phase of trust computing for a relay node selection.

2.2.1. Phases of Initialization and Obtaining the Values ofNumber of Transmissions and Length of Transmission for TrustComputing in Hybrid MANET-DTN. Initialization phasedeals with establishing of the parameter table, where themeeting records of nodes togetherwith the values ofmonitor-ing parameters as the value of the trust will be recorded.There

will be also the variables which will hold the value of eachparameter involved in the calculation of the trust, namely,

(i) the identifier of the current node (AU),

(ii) the identifier of the previous node (PU),

(iii) the time of creation of the packet (CV),

(iv) the time of receipt of the packet (CP),

(v) the length of the current transmission DP (differencebetween CP and CV),


Start

Detection of the routing activities

Is itreceived packet?

Yes

Yes

No

Is it sent packet?

No No

Yes

No

End

Start

Yes

IP address of the source node

Actual node AU =IP address of the destination node

Actual node AU =

Actualization

for actual nodePPi and MPP

Previous nodePU = AU

Previous nodePU = AU

AU = PU? AU = PU?

(a)

Start

Is itreceived packet?

Find addresses of the source node

No

Find CV and CP

Yes

End

Actualization DPi and MDP

Length of transmissionDP = CP − CV

(b)

Figure 7: Flowchart for collecting parameters: (a) number of transmissions and (b) length of the transmission in hybrid MANET-DTN.

(vi) parameter number of transmissions between the 𝑖-nodes (PP

𝑖),

(vii) length of transmission between 𝑖th nodes (DP𝑖),

(viii) maximum number of transmissions with nodes(MPP),

(ix) maximum transmission distance among all nodes(MDP),

(x) the length of the current transmission DP (differencebetween CP and CV),

(xi) parameter number of transmissions between the 𝑖-nodes (PP

𝑖),

(xii) normalized number of transfers with the 𝑖-node(NPP𝑖),


(xiii) standardized transmission distance of the 𝑖-node(NDP

𝑖),

(xiv) weight for standardized number of transmissions(𝑊𝑝),

(xv) weight for standard length (𝑊𝑑),

(xvi) transfers and the value of confidentiality for the 𝑖-node (𝑇

𝑖).

The number of transmissions is obtained from incomingand outgoing routing packets and it represents the numberand frequency of the meetings with other mobile nodes (seeFigure 7(a)). It is the most fundamental parameter history ofmeetings and gives an approximate view of the relationshipbetween nodes. The value of this parameter depends on thenumber of packets sent and received between two nodes.Theproposed algorithm enables determining routing activity inthe network; it means that node received or sent packets.If there is no activity, the phase of initialization is activatedand algorithm waits for the routing transmission. If thereare detected routing activities, node identifier in the form ofan IP address is stored in the variable AU into the currentnode; then the algorithm compares the current identifierto distinguish whether it is a new transmission or only thetransmission of multiple packets to one goal. If this is a newtransfer, it updates the value of the number of transmissionsfor the 𝑖-node based on the IP address. It also updates thevalue of the total number of transmissions and the totalnumber of times of all nodes. Finally, the IP address as anidentifier of the previous node is inserted into the variablefor the previous node PU and the algorithm is terminated,respectively, and enters the initial state.

At the same time, the length of the transmission isactivated (see Figure 7(b)). This parameter is an extension ofthe parameter number of transmissions and gives a betterview of the history of contacts. The combination of theseparameters allows defining precisely the relationship betweentwo nodes and also the trust. If a packet is received, it is foundwhich node was the sender of the packet; then the variablevalue CV puts the time when the packet was created. Thevariable time of receipt CP is inserting time data when apacket has been received. From the last two parameters DPcan be calculated as the difference between the received timeand time of creation of the packet.This value should be addedto a specific DP

𝑖value in the table of parameters. All DP

𝑖

values are compared in the nodes and a maximum value oftransmission MDP will be used as the highest value. Finally,the algorithm will go into the initial state again or stop andwill wait for incoming packet transfer. After obtaining theseparameter values, an algorithm calculates the value of trust.This value will reflect the view of one node to another, andtrust will be used to select a trusted relay node.

2.2.2. Phase of Trust Computing for a Relay Node Selection.Based on collected values mentioned in Section 2.2.1, thealgorithm for trust computing is activated.The values of theseparameters are updated whenever the packets are received,or sent (Figure 8); in this way, the trust value updates theactual state of the network. Each mobile node has stored

information about number and length of transmissions.These values are computed as

MPP = max𝑛

∑PP𝑖,

MDP = max𝑛

∑DP𝑖,

(3)

where 𝑖 is order of the node and 𝑛 is number of the nodes. Allthese values are normalized by the following formulas:

MPP𝑖=

PP𝑖

MPP,

MDP𝑖=

DP𝑖

MDP.

(4)

After normalization, the values will be in the rangebetween 0 and 1. At the same time, each value of describinga relationship or proportion of the total, respectively, ismaximum value. This ensures the relevance of each valuefor each parameter will reflect the relationship between theactual state history meetings. After this step, the process ofweighting is applied.Theweights are given information aboutthe importance of this parameter and it is in the range ⟨0, 1⟩and the total sum of values is equal to 1. The total valuesof the trust for each mobile node are then computed by thefollowing formula:

𝑇𝑖= 𝑊𝑝∗NPP

𝑖+𝑊𝑑∗NDP

𝑖, (5)

where

𝑊𝑝+𝑊𝑑= 1. (6)

As we mentioned the given algorithm is an extension ofthe algorithm described in Section 2.1. After computing ofthe value trust, the values of 𝑇

𝑖will be compared with stored

values 𝑇 collected during the first stage (Section 2.1) andthe trusted relay node is selected as a node with a maximalnumber of trust values.

3. Simulations and Results

The main objective of simulations is to analyse how theproposed algorithms can affect the behaviour of the networkin the sense of the network performance. As a simulation tool,theOPNETmodeler simulator [20]was used for testing of theproposed mechanisms. OPNET provides a lot of useful toolsfor analysing of the mobile networks and enables simulatingMANET with different routing protocol as well [1]. TheDynamic Source Routing protocol was used for testing andthe collected values represent a reference value for analysingof the behaviour of the MANET [1].

Moreover, we have implemented the PRoPHET forward-ing mechanism based on the history of past encounters(Figure 9) [20].This algorithmenables simulation of theDTNin OPNET modeler. The implementation allows simulatingcases based on the bundle concept as epidemic forwardingand the routing algorithm based on the history of pastencounters. PRoPHET is specifically intended to provide


Start

Yes

Monitoring of therouting traffic(Section 2.1)

No

YesNo

Transport data(PRoPHET)

Existingconnection(s) to node(s)?

YesNo

Computing Ti

Computing NDPi

Computing NPPi

Is thereactualization ofDP and PPi?

Comparison of values T and Ti,Ti > T?

Sent data to selected relay node with trust value T

Sent data to selected relay node with trust value Ti

Figure 8: Process of the trust computing in hybrid MANET-DTN.


Table 1: Simulation setup for OPNET modeler.

Parameters ValuesSimulation area 2000m × 2000mSimulation time 1000 sTransmission range 250mTransmitted power 1mWType of service CBRNumber of nodes 20, 40, 60, 80, 100Speed of nodes 0–6m/sMobility model Mobility model Default RandomWaypointNodes location RandomPause time 10 sSimulation runs 100Number of values per simulation 1000Reference values of trust 𝑊RREQ = 0.2,𝑊RREP = 0.5,𝑊RERR = 0.2,𝑊RACK = 0.2,𝑊𝑑 = 0.3,𝑊𝑝 = 0.7

Figure 9: PRoPHET forwarding model for DTN in OPNET mod-eler.

routing services in a bundle network environment. It ismentioned that the PRoPHET is defined to run over reliableTCP, the submessages are provided with sequence numbers,and this, together with a capability for positive, would allowPRoPHET to operate over an unreliable protocol such asUDPor directly over IP [21, 22].

In order to check the functionality of the proposedalgorithms, the following simulation scenarios were used toanalyse the network performance of the proposed mecha-nisms:

(i) MANET model (DSR): MANET used standard DSRprotocol without the possibility of finding commu-nication paths between mobile nodes if there aredisconnections.

(ii) MANET model with TRUST (DSR TRUST1): it isMANETwithDSRprotocol.The possibility of finding

a secure relay node based on trust is implemented (seeSection 2.1).

(iii) MANET model with TRUST (DSR TRUST2): itis enhanced version of model DSR TRUST1 (seeSection 2.2).

(iv) DTN model (DTN): it is extension of model DSRTRUST2 with the PRoPHET protocol. This modelenables finding a communication path via store-carry-forwardmodel if the communication links are discon-nected during the transportation of the packets.

The simulation setup and parameters for the OPNETmodeler are summarized in Table 1. During simulations, theaverage delay, average number of hops parameters, averagerouting traffic sent, average routing traffic received, totaltraffic load, average number of salvaged packets, averagenumber of route request (RREQ) packets, average number ofroute reply (RREP) packets, average time for path discovery,and average number of retransmissions are used for analysinghow the proposed algorithm can affect network behaviour.The final values in graphs and tables are average values col-lected from 100 simulation runs. Figure 10 shows simulationscenario for 20 mobile nodes in OPNET modeler.

The average delay provides the average amount of thetime that is necessary for useful transmission of the packetbetween source and destination nodes. The average numberof hops represents a number of transmissions necessary to findthe end-to-end connection between a source and destinationmobile node. The average amounts of routing traffic sent andreceived provide information about how many pieces of datathe routing protocol needs to send to the network untilthe communication paths are found. The total traffic loadindicates how the network will be loaded with the routingtraffic if mobile nodes start sending data packet. Parametersaverage amounts of route request (RREQ) and reply (RREP)packets show the number of routing packets sent by routingprotocol DSR to neighbors mobile nodes during a processof establishment of the communication paths. Time for pathdiscovery is the average time necessary for path selection.


Figure 10: Example of the simulation scenario with randomlyplaced mobile nodes in OPNET modeler.

The average amounts of the salvaged packets give us infor-mation about how many packets were salvaged by routingprotocol during routing or forwarding. The average amountsof retransmissions show how many times are necessary forresending the routing packet if the communication paths aredisconnected. The average amounts of the salvaged packetsgive us information about how many packets were salvagedby routing protocol during routing or forwarding.

3.1. Comparison of the MANET and DTN in DisconnectedEnvironment. In this section, we present the numericalresults, depicting the relation between DSR (MANET) andDTN in a disconnected environment. We analyse howthe disconnection of the communication paths affects thebehaviour of the network. The simulations are focused onthe situations when communication paths are disconnectedfor a short time interval while routing protocol cannotestablish an end-to-end connection. The results also showwhy MANET cannot be used for delivering of the messagesin this environment. In these simulations, we simulate thedisconnection of the communication paths. The discon-nection of the communication paths was simulated withshort transmission ranges on nodes and by using randommobility model. The mobile nodes were moved randomlyacross the network with randomly selected speed and theDSR routing protocol cannot establish communication pathsbetween mobile terminals. For this reason, an average delayand an average number of hops have been analysed. Collectedresults show why integration between DSR (MANET) andDTN routing mechanisms is necessary.

Figure 11 shows the average delay for DSR (MANET)and DTN models with respect to the different numberand moving speed of mobile nodes. If the communicationpaths were disconnected, the values were higher for DSR(MANET) than for DTN. Based on the idea of DSR, therouting mechanism sends the routing packets in order to

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find communication paths and, on the other side in DTN,the PRoPHET protocol unicast only the packet for the nodeswhich are directly connected to the selected mobile node.Wecan also see that delay for 60, 80, and 100 nodes is increasedfor DTN.This situation is explained by the fact that the DTNforward messages directly to selected relay node or nodesthat are randomly across the simulation area until they finda suitable node to transport message. The node may not be anode that is looking for the shortest path between the sourceand the destination node.The values of average delay for DSR(MANET) are almost 2 times higher than values for DTN.

The second analysed parameter is the average numberof hops. Model DSR provides the routing mechanisms ifthe communication paths are disconnected that is resultingin a significant number of hops for networks with thehighest number of the mobile nodes (Figure 12). In DTN, thePRoPHETprotocol enables finding destination nodewith thelower number of hops based on the idea of the forwardingmechanism. If the communication paths are disconnected fora short time theDTN shows better results in comparisonwithMANET (Figures 11 and 12).


Table 2: Values of the average routing traffic send [kbit/s] fordifferent number and speed of nodes.

Numberof nodes Model Speed of nodes

2m/s 4m/s 6m/s

20DSR 0.708 0.753 0.651DSR TRUST1 0.701 0.826 0.948DSR TRUST2 0.712 0.823 0.922





3.2. Network Analysis of the Hybrid MANET-DTN in Dis-connected Environment. In these simulations, we analysethe network performance analysis of three models DSR,DSR TRUST1, and DSR TRUST2 from the routing perspec-tive. The main idea is to study how the implementation ofalgorithms can affect the routing mechanisms and also howthe implementation of the designed mechanisms can affectthe total network performance. This simulation is focusedon the situation when the communication paths will bedisconnected during transmission of the data. In this case,the routing paths will be broken and trust algorithm will beactivated in order to find the relay node.This selected trustedrelay node then will transport messages until the connectionto another node is established.

During simulation, the average amount of routing trafficsent, an average amount of routing traffic received, total trafficload, an average number of route request (RREQ) packets, anaverage number of route reply (RREP) packets, an averagenumber of retransmissions, and an average time for pathdiscovery are analysed. Parameters give us an analysis of howthe implementation of the proposed algorithms will affect therouting processes for different speed and the number of themobile nodes.

Tables 2 and 3 show how the average routing data sentand received is impacted by the disconnection of the commu-nication paths. In the case of disconnected communicationpaths, the results increase with higher speed and numberof the mobile nodes. Model DSR TRUST1 has generally thehighest average routing traffic sent and received as comparedto DSR. We obtained better results for model DSR TRUST2due to the existence of an enhanced trust algorithm, which isimplemented directly in the mobile nodes. The routing dataare resent only if the mobile node is trusted. Enhancementalso enables using the contact history, which gives better

Table 3: Values of the average routing traffic received [kbit/s] fordifferent number and speed of nodes.


2m/s 4m/s 6m/s


40DSR 2.067 3.086 2.,185DSR TRUST1 6.847 2.851 2.478DSR TRUST2 6.732 2.586 2.317




Table 4: Values of the total traffic load [kbit/s] for different numberand speed of nodes.


2m/s 4m/s 6m/s






possibilities of finding a trusted relay node for transportationof the data in the situation when the communication pathsare disconnected.

Table 4 shows the network performance analysis of thesemodels in terms of the total traffic load for the situation thatcommunication paths are disconnected. In this situation, theDSR routing protocol limited transport to only the routingpackets in order to find communication paths. As can beviewed, the network performance of theDSR TRUST2 is bet-ter in all situations and for networks with the lower number


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Figure 13: Average number of salvaged packets for different speed of mobile nodes: (a) 2m/s, (b) 4m/s, and (c) 6m/s.

of mobile nodes. The models (DSR TRUST1, DSR TRUST2)obtain better results in comparison with DSR, but thesemodels enable transportation routing and data packet viaa trusted relay node in the situation when communicationpaths are disconnected or if there are no available mobilenodes for communication. In this situation, the PRoPHETforwarding mechanism has been activated.

Tables 5 and 6 summarize the average number of RREQand RREP packets sent to the network while communicationpaths are discovered and established. Results show thatmodel DSR TRUST2 provides better results in all cases.If the communication paths will be disconnected, modelDSR resends a lot of routing packets and in this way thenetwork will be loaded only by routing packets. On theother side, model DSR TRUST1 enables selecting relay nodeonly based on the routing parameters (see Section 2.1) andrelay node selection will be impacted in a negative senseby this situation. The proposed extension (DSR TRUST2)eliminates this situation and it enables selecting trusted relaynode with respect to contact history. It also provides theability to decrease the number of routing packets sent tothe network. It means that DSR TRUST2 enables decreasingthe number of sent RREQ packets on the network and also

Table 5: Average number of route request (RREQ) packets [pack-ets/s] for different number and speed of nodes in hybrid MANET-DTN.


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Figure 14: Comparison of the average number of retransmissions for different speed of mobile nodes: (a) 2m/s, (b) 4m/s, and (c) 6m/s indisconnected environment.

enables increasing the average number of RREP used for theestablishment of the communication paths. These results arein a strong correlation with results from Section 3.1.

The average number of salvaged packets is discussed too.Figure 13 shows how many packets are salvaged during thesending of routing packets in disconnected environments.The graphical result shows that implementation of modelsDSR TRUST1 and DSR TRUST2 to secure the selection ofrelay node enables salvaging a lot of packets in comparisonwith DSR model. It stems from the fact that the algorithmsallow selecting only trusted nodes for transmission of mes-sages between the mobile environments. We can see, fromthe results, that implementation of the DSR TRUST1 andDSR TRUST2 provides higher values of the salvage packetsin all situations. On the other side, if the speed of mobilenodes is increased, the number of salvaged packets begins todramatically fall down for model DSR in comparison withmodels DSR TRUST1 and DSR TRUST2. We can concludethat the selection of the relay nodes gives the opportunitiesto transport messages between mobile nodes and save more

packets from dropping. The proposed algorithms allow sav-ing a lot of packets for networks with the lower number ofmobile nodes that are moving with lower speed across thenetwork.

Figure 14 gives information about how many retransmis-sions are necessary to be resent from nodes to the networkwhile the communication path between nodes is established.Results show that models DSR TRUST1 and DSR TRUST2decrease the number of retransmissions in comparison withDSR in disconnected environments.The trust algorithm for arelay node selection enables selection of the nodes that havea higher possibility of establishing the trusted routing pathsbetween nodes in disconnected environments. We can alsosee that using history of contact is a simple and useful tool,implemented in DSR TRUST2, such that it allows reducingthis value to the minimum.

Next studied parameter is the average time for pathdiscovery. The parameter gives information about time thatis required for the establishment of the communicationpath between mobile nodes. Based on the results showed


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Figure 15: Comparison of the average time for path discovery for different speed of mobile nodes: (a) 2m/s, (b) 4m/s, and (c) 6m/s indisconnected environment.

Table 6: Average number of route reply (RREP) packets [packets/s]for different number and speed of nodes in hybrid MANET-DTN.


2m/s 4m/s 6m/s






in Figure 15 we can conclude that model DSR TRUST2needs less time in comparison with model DSR TRUST1.On the other side, model DSR requires more time to estab-lish the communication paths. We can also see that thoseimplemented algorithms in DSR TRUST1 and DSR TRUST2models provide the possibility of finding a path if there aredisconnected ones and also the possibility of shortening thetime for path establishment if routing protocol DSR cannotfind communication paths.

4. Conclusion

Hybrid MANET-DTN is an evolution of mobile networksthat integrate MANET and DTN into one complex network.Hybrid MANET-DTN enables transportation of the databetween different mobile terminals in the situation whenthe communication paths are disconnected or never exist.The communication does not rely on end-to-end connection,but it is based on the store-carry-forward model integratedfrom DTN. Hybrid MANET-DTN give new challenges fora new application and services. The main idea of hybridMANET-DTN provides the ability to use the network not


only for personal use but also for emerging applications andservices. The main problem of the hybrid MANET-DTN issecurity and relay node selection. In the paper, we introducetwo models for the secure selection of the relay nodes basedon the trust.

In the paper, the network performance analysis of theproposed algorithms is presented. The goal of the analysisdemonstrates that those proposed algorithms to relay nodeselection do not affect the network performance. The fourmodels DSR, DSR TRUST1, DSR TRUST2, and DTN havebeen tested in OPNET modeler. Based on collecting resultswe can conclude that trust algorithm for selection of the relaynode provides the useful tool to a selection of the optimaltrusted path in the case of disconnected environment andalso this algorithm allows enhancing the performance ofthe hybrid MANET-DTN from the routing point of view.We show that model DSR TRUST2 gives better results incomparison with model DSR TRUST1. Selecting relay nodesbased on contact history also enables reducing the risk of theusing of the malicious mobile node.

Themain problem of these algorithms is how to optimizea selection of the relay node if there is more than one nodewith the same values of the trust. For this reason, wewill focuson the design of the method of the relay node selection basedon game theory with respect to trust algorithm. The mainidea of this algorithm will combine routing properties of theMANET and DTN in order to increase the performance ofthe hybridMANET-DTN and also provides the secure trans-portation of the data across the disconnected environment.

Competing Interests

The authors declare that they have no competing interests.

Acknowledgments

This work has been performed in the framework of theMinistry of Education of Slovak Republic under researchVEGA 1/0075/15 (100%).

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