An Efficient Routing Protocol Using the History of Delivery Predictability in Opportunistic Networks

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1 pplied sciences Article An Efficient Routing Protocol Using History Delivery Predictbility in Opportunistic Networks Eun Hk Lee 1, Dong Yeong Seo 2 Yun Won Chung 1, * 1 School Electronic Engineering, Soongsil University, 369 Sngdo-ro, Dongjk-gu, Seoul 06978, Kore; ttndo@ssu.c.kr 2 Deprtment Informtion Telecommuniction Engineering, Grdute School, Soongsil University, 369 Sngdo-ro, Dongjk-gu, Seoul 06978, Kore; seody@ssu.c.kr * Correspondence: ywchung@ssu.c.kr; Tel.: Received: 10 September 2018; Accepted: 2 November 2018; Published: 10 November 2018 Fetured Appliction: The proposed routing protocol cn be pplied to enble communiction in n extreme environment, where network infrstructure is not vilble. Abstrct: In opportunistic networks such s dely tolernt network, is delivered to finl destintion using opportunistic routing protocol since re is no gurnteed routing pth from sending to receiving most connections between s re temporry. In opportunistic routing, is delivered using store-crry-forwrd strtegy, where is stored in buffer, crries while moving, is forwrded to nor when contct occurs. In this pper, we propose n efficient opportunistic routing protocol using history delivery mobile s. In proposed routing protocol, if receives from nor, vlue delivery receiving to destintion for is mnged, which is defined s previous delivery. Then, when two s contct, is forwrded only if delivery or is higher thn both delivery previous delivery sending. Performnce nlysis results show tht proposed protocol performs best, in terms delivery rtio, overhed rtio, delivery ltency for vrying buffer size, genertion intervl, number s. Keywords: delivery ; routing; PRoPHET protocol; dely tolernt networks; opportunistic routing protocol 1. Introduction In opportunistic dely tolernt networks (DTN), where end-to-end routing pth is not vilble, is delivered using forwrding between s when y contct ech or [1 5]. Exmple ppliction scenrios for DTN include disster environments, where infrstructure is destroyed thus, communiction should be crried out using sprsely distributed peer s. In DTN, when genertes, it stores in its buffer crries it while moving. Then, if contcts nor opportunisticlly, it forwrds to if forwrding condition is stisfied. This kind delivery is clled store-crry-forwrd strtegy [1 5]. Figure 1 shows DTN environment, where network is frgmented connectivity between source destintion is disrupted. As shown in Figure 1, only prtil connections between neighboring s re vilble. Figure 2 shows store-crry-forwrd strtegy in DTN environments, in order to enble delivery between ny two s. When A hs to deliver, where destintion is C, it firstly stores Appl. Sci. 2018, 8, 2215; doi: /pp

2 Appl. Sci. 2018, 8, Appl. Sci. 2018, xx FOR PEER REVIEW Appl. 2018, 8, 8, FOR REVIEW in itssci. buffer. Then it PEER crries while moving forwrds it to B when A B re within communiction rnge. After tht, B stores in its buffer moves B communiction rnge. After B in buffer B re re itwithin within After tht, tht, delivered B stores stores in its its buffer while crrying until itcommuniction contcts C.rnge. The is finlly to C from B using moves while crrying it until it contcts C. The is finlly delivered to C from moves while crrying it until it contcts C. The is finlly delivered to C from opportunistic contct. B B using using opportunistic opportunistic contct. contct. Figure scenrio. An exmple exmple Dely-Tolernt-Network Figure An An exmple Dely-Tolernt-Network scenrio. The Store-Crry-Forwrd Store-Crry-Forwrd strtegy. Figure Figure The The Store-Crry-Forwrd strtegy. Mny works works relted to to DTN protocols protocols hvebeen been crriedout out [1 8].InInepidemic epidemic protocols [6], Mny Mny works relted relted to DTN DTN protocols hve hve been crried crried out [1 8]. [1 8]. In epidemic protocols protocols [6], [6], forwrds to or s whenever y re within communiction rnge. It is forwrds forwrds to to or or s s whenever whenever y y re re within within communiction communiction rnge. rnge. It It is is very simple but high overhed is ismjor drwbck due to limited buffer spce spce mobile very very simple simple but but high high overhed overhed is mjor mjor drwbck drwbck due due to to limited limited buffer buffer spce s. In spry wit protocol [7], number totl copies for ech newly generted mobile mobile s. s. In In spry spry wit wit protocol protocol [7], [7], number number totl totl copies copies for for ech ech newly newly is limited by limited L to reducel overhed. Therefore, only L-1 copies s generted generted is is limited by by L to to reduce reduce overhed. overhed. Therefore, Therefore, only only L-1 L-1 copies copies cn be disseminted to or s froms genertion in spryinphse. In wit s cn be disseminted to or from genertion spry phse. s cn be disseminted to or s from genertion in spry phse. phse, L s with hve only hve one copy delivers to destintion In In wit wit phse, phse, L L s s with with hve only only one one copy copy delivers delivers to to destintion destintion only. However, in spry phse, copies re disseminted blindly, without only. only. However, However, in in spry spry phse, phse, copies copies re re disseminted disseminted blindly, blindly, predefined criterion. criterion. In probbilistic routing protocol for intermittently connectedconnected networks without predefined In probbilistic routing protocol for intermittently without predefined criterion. In probbilistic routing protocol for intermittently connected (PRoPHET) [8], delivery between two s, which hs vlue between 0 1, networks networks (PRoPHET) (PRoPHET) [8], [8], delivery delivery between between two two s, s, which which hs hs vlue vlue between between clculted bsed on contcton history between m, m, is forwrded bsed on delivery 0is 0 1, 1, is is clculted clculted bsed bsed on contct contct history history between between m, is is forwrded forwrded bsed bsed on on. The delivery A to B, P(A,B), estimtes likelihood delivery delivery.. The The delivery delivery A A to to B, B, P(A, P(A, B), B), estimtes estimtes delivering to B. Therefore, it is highly likely tht if hs higher delivery likelihood likelihood delivering delivering to to B. B. Therefore, Therefore, it it is is highly highly likely likely tht tht if if hs hs higher higher, it is better to deliver. If two sifcontct, delivery delivery, it is better to deliver. two s contct, delivery, it is better to deliver. If two s contct, delivery delivery between mbetween increses, s defined in Eqution (1) [8]: between m m increses, increses, s s defined defined in in Eqution Eqution (1) (1) [8]: [8]: P(A, B) B)old P(A, P(A, B)old+ B)old) Pencounter, Pencounter, (1 (A, B)old) P(A, B)B)= ==P(A, P(A, B)old ++(1 (1 PP(A, P(A, B)old) Pencounter, (1) (1) (1) where re scling fctor prmeter defining n upper bound P(A,B), where P Pencounter encounter re scling fctor prmeter defining n upper bound P(A,B), respectively. respectively. As As time time psses psses on on fter fter lst lst contct, contct, delivery delivery between between A A B decreses, s defined in Eqution (2) [8]: B decreses, s defined in Eqution (2) [8]:

3 Appl. Sci. 2018, 8, where P encounter re scling fctor prmeter defining n upper bound P(A,B), respectively. As time psses on fter lst contct, delivery between A B decreses, s defined in Eqution (2) [8]: P(A, B) = P(A, B)old γ K, (2) where γ K re ging constnt n number pssed time units fter lst contct, respectively. Additionlly, re is trnsitive property, i.e., if A B contct frequently, if B C contct frequently, it is highly probble tht A C contct frequently, s defined in Eqution (3) [8]: P(A, C) = MAX (P(A, C)old, P(A, B) P(B, C)recv β), (3) where β is scling constnt. In PRoPHET protocol, when two s contct, i.e., when y re within trnsmission rnge, y exchnge summry vectors which include ll delivery vlues ll previous contct s [8]. In this pper, PRoPHET protocol is considered s bse protocol. In PRoPHET, severl forwrding strtegies re defined. In GRTR strtegy, for exmple, to destintion to D is forwrded to B from A, if P(B,D) is lrger thn P(A,D). In GTMX strtegy, is forwrded if P(B,D) is lrger thn P(A,D) number forwrding considered is smller thn threshold vlue NFmx. In GRTR+, is forwrded to if P(B,D) is lrger thn P(A,D) P(B,D) is lrger thn Pmx, which is lrgest delivery stored by to which hs been forwrded to ever. We note tht GRTR, GTMX, GRTR+ re just mnemonics [8]. In this pper, we propose n efficient opportunistic routing protocol using delivery previously contcted, i.e., history delivery. In proposed protocol, if receives from nor, current vlue delivery receiving to destintion received is stored s previous delivery (prep) in receiving. We note tht vlue prep is defined for ech destintion individully vlue prep for is updted whenever it receives destined to. When two s contct, is forwrded to or, if delivery or is higher thn both delivery prep sending. If re is no vlue prep for considered, only current delivery vlues re compred is delivered to or if delivery or is higher. The prep cn be considered s n indictor good forwrder bsed on history delivery. Tht is, if A hs higher prep thn current delivery contct B, lthough A hs smller delivery currently thn tht contct B, it is not pproprite to disseminte to B. This is becuse too much forwrding bsed on only current delivery predictbilities result in dropping in buffer due to buffer overflow, thus, overll performnce degrdes. In PRoPHET protocol with GRTR strtegy, if with hs smll delivery, is forwrded significntly results in dropping in buffer. In order to restrict dissemintion efficiently in PRoPHET protocol, enhnced forwrding strtegies such s GTMX GRTR+ were proposed. In PRoPHET protocol with GTMX strtegy, totl number forwrding is limited by threshold vlue in ddition to bsic GRTR strtegy compring current delivery. In PRoPHET protocol with GRTR+ strtegy, dditionl condition is tht delivery receiving is lrger thn threshold probbility, which is lrgest delivery reported by to which hs been sent so fr. In PRoPHET protocol with GRTR+ strtegy, threshold probbility is non-decresing function time forwrding is too restricted s time goes on, which my result in n overll performnce degrdtion. In

4 Appl. Sci. 2018, 8, proposed protocol, we lso use threshold probbility prep but it is not non-decresing function time due to ging property delivery PRoPHET protocol thus, controls dissemintions efficiently. The bsic ide using both delivery previous delivery sending proposed protocol is similr to our preliminry work presented s n extended bstrct in [9]. However, proposed work ws extended significntly from previous work from following spects: - The proposed protocol is described in more detil by completing flowchrt proposed protocol using n exmple delivery to illustrte proposed protocol. - The performnce proposed protocol is newly nlyzed thoroughly using simultion compred with four or protocols in terms delivery rtio, overhed rtio, delivery ltency. - Relted works re significntly extended in this pper. The remining prt this pper is orgnized s follows: In Section 2, we survey relted works. In Section 3, we describe lgorithm proposed protocol in detil using exmples. In Section 4, we nlyze performnce proposed protocol extensively using simultions. Finlly, we conclude this work in Section Relted Works Relted works on generl dely tolernt networks protocols hve been lredy covered by survey ppers [10 14], where uthors clssified compred relted protocols in detil. Since min focus our pper is relted to PRoPHET protocol, we review relted works on extension PRoPHET protocol for performnce enhncement. A lot works relted to PRoPHET protocol hve been crried out [15 26]. In Reference [15], number copies is limited by using socility s in order to improve performnce proposed protocol. In Reference [16], buffer is mnged by controlling delivery bsed on number copies in order to solve network performnce degrdtion problem due to excessive copies. In Reference [17], eir Epidemic or PRoPHET is selected bsed on density s. Tht is, if number simultneous contcts is smller thn threshold, Epidemic protocol is pplied. Orwise, PRoPHET protocol is pplied. By doing this, pproprite protocol, eir Epidemic or PRoPHET, is selected dynmiclly bsed on density neighboring s. In Reference [18], contct durtion, which is time durtion tht contct is mintined, contct frequency re lso considered in clcultion delivery for n efficient delivery. In Reference [19], AntPRoPHET scheme ws proposed, where nt colony optimiztion, which is one nture-inspired optimiztion technique bsed on behvior nt, ws pplied to PRoPHET protocol in order to optimize performnce PRoPHET protocol. In Reference [20], in order to reduce unnecessry forwrding, is forwrded only when delivery receiving is lrger thn sum delivery sending minimum threshold vlue, sum delivery predictbilities receiving s so fr is less thn predefined threshold vlue. In PRoPHET+ Reference [21], new metric, deliverbility, which is defined s weighted sum bttery power, loction, populrity, buffer size, delivery ws proposed. In Reference [22], hop count trversed by s well s delivery re considered to determine next hop. In Reference [23], distnce-bsed PRoPHET protocol ws proposed, where distnce between ny two s ws considered dditionlly in order to clculte delivery. In Reference [24], selects locted in smllest distnce s forwrder in order to trnsmit with highest rte. In Reference [24], uthors extended lgorithm in Reference [23] by dditionlly considering community mobility model, where rom wypoint mobility model ws considered in Reference [23]. In history encounter-bsed spry wit (HESnW) protocol [25], multiple

5 Appl. Sci. 2018, 8, probbilities from S to D re defined s multipliction delivery from S to H, which is history tht S ever contcted before, delivery from H to D. Then, is forwrded to in spry phse, eir if hs higher delivery or if s multiple probbility is higher thn delivery sending when deliver hs higher thn Appl. Sci. 2018, 8, x FOR PEER REVIEW 5 20 trnsfer threshold. In Reference [26], uthors proposed n improved PRoPHET protocol using Reference context [26], informtion uthors proposed such n improved s verge PRoPHET distnce protocol time using from context reception informtion to delivery such. s verge distnce time from reception to delivery. In In relted relted works works on on PRoPHET PRoPHET protocol protocol in in References References [15 26], [15 26], vrious vrious context context informtion informtion such such s s socility socility [15], [15], number number copies copies [16], [16], density density s s [17], [17], contct contct durtion durtion [18], [18], nt nt colony colony optimiztion optimiztion [19], [19], sum sum delivery delivery [20], weighted [20], weighted sum sum bttery power, bttery loction, power, loction, populrity, populrity, buffer size buffer delivery size delivery [21], hop count [21], [22], hop distnce count [22], [23], distnce community [23], mobility community model mobility [24], multiple model probbility [24], multiple [25], probbility verge [25], distnce verge time distnce [26] re used time to [26] decide re used to decide forwrding. forwrding. We clssify We relted clssify works relted on extended works on PRoPHET extended protocols, PRoPHET depending protocols, on depending wher delivery on wher delivery is modified using is context-dditionl modified using contextdditionl context context informtion or wher informtion dditionl or wher metrics re dditionl used for metrics forwrding re used decision for forwrding without modifying decision delivery without, modifying delivery s shown, in Figure 3. s shown in Figure Proposed Protocol Figure 3. The clssifiction relted works on extended PRoPHET protocols. In proposed protocol, if if ny receives from nor, vlue delivery receiving to destintion for is mnged s prep in in this this pper. pper. Then, Then, when when two two s s contct, contct, with with to sendto checks send ifchecks delivery if delivery or is or higher thnis both higher delivery thn both delivery previous delivery previous delivery sending, sending is forwrded., Orwise, is forwrded. isorwise, not forwrded. By doing this, not weforwrded. introduce more By doing restrictions this, we on forwrding introduce more in our restrictions proposed protocol on forwrding thn in bsic our PRoPHET proposed protocol, thn thus, bsic voidprophet excessive protocol forwrding, thus, s void efficiently. excessive Inforwrding proposed protocol, s ifefficiently. In hs not proposed been forwrded protocol, yet if from hs which not generted been forwrded yet from originlly, which generted forwrding is crried out if originlly, delivery forwrding receiving is crried out is higher if thn delivery tht sending. receiving This is becuse we is higher need to thn promote tht sending dissemintion. This when is becuse we need is just to promote generted since dissemintion prep when sending is not is just defined generted in this cse, since we need toprep forwrd sending bsed is onnot defined bsic GRTR in this strtegy cse, we need PRoPHET to forwrd protocol. bsed on bsic GRTR strtegy Figure 4 shows PRoPHET exmples protocol. forwrding in proposed protocol compred with tht PRoPHET Figure protocol 4 shows with exmples GRTR strtegy. forwrding In Figure in 4, proposed which shows protocol compred opertion with tht PRoPHET protocol PRoPHET with protocol GRTRwith strtegy, GRTR Sstrtegy. forwrds In s Figure 4, M1, which M2, shows M3 toopertion contct B, PRoPHET protocol with GRTR strtegy, S forwrds s M1, M2, M3 to contct B, B forwrds M5 to S t T = t0 bsed on comprison delivery predictbilities S B. We ssume sitution tht buffer B becomes full when it receives s M1, M2, M3. At T = t1, when B contcts C, C forwrds M6 one is dropped due to buffer overflow. Node B forwrds s M1 M3 to C. At

6 Appl. Sci. 2018, 8, x FOR PEER REVIEW 6 20 Appl. Sci. 2018, 8, In Figure 4b, S forwrds s M2 M3 does not forwrd M1, contrry to cse in Figure 4 since prep M1 S is higher thn delivery B forwrds M5 to S t T = t 0 bsed on comprison delivery predictbilities B t T = t0. Node B does not forwrd M5 to S. At T = t1, B S B. We ssume sitution tht buffer B becomes full when it receives forwrds M3 to C receives M7 from C by compring delivery s M1, M2, M3. At T = t 1, when B contcts C, C forwrds M6 prep vlues. Node C forwrds s M6 M7 to E receives one is dropped due to buffer overflow. Node B forwrds s M1 M3 to M9 from E t T = t2. We note tht dissemintion is efficiently restricted in C. At T = t 2, C contcts E forwrds s M1, M6, M7 to E receives proposed protocol no drop occurs in considered forwrding scenrio, contrry to s M8 M9. At this time, buffer C overflows one is dropped. PRoPHET protocol with GRTR strtegy, this results in n overll performnce Additionlly, buffer B becomes full. enhncement. () (b) Figure Exmples forwrding scenrio. () PRoPHET with GRTR, (b) (b) Proposed protocol. In Figure 5 shows 4b, Sflowchrt forwrds s proposed M2 protocol. M3 When does not two forwrd s A B contct, M1, contrry y tirstly cse exchnge in Figure summry 4 since vectors prepwhich include M1informtion S is higher thn s delivery y hve in ir buffer B t ll T = tdelivery 0. Node B does not forwrd vlues ech M5to toll or S. previously At T = t 1, contcted B forwrds s. We note M3 tht to vlues C receives prep re not exchnged M7 fromduring Ccontct. by compring Then A delivery chooses which does prepnot vlues. exist Node in C forwrds B. If destintion s M6 M7 to in E A receives is B, it is delivered M9 from to E tb. T Orwise, = t 2. We note thta compres dissemintion delivery is efficiently restricted itself inwith tht proposed protocol B. If P(A,D) no is lrger drop thn occurs P(B,D), in considered is not forwrding forwrded scenrio, to contrry B. If P(A,D) to is PRoPHET not lrger protocol thn with P(B,D), GRTRA strtegy, checks if prep(a,d) this results exists. in nwe overll note performnce tht if enhncement. is generted in A

7 Appl. Sci. 2018, 8, Figure 5 shows flowchrt proposed protocol. When two s A B contct, y firstly exchnge summry vectors which include informtion s y hve in ir buffer ll delivery vlues ech to ll or previously contcted s. We note tht vlues prep re not exchnged during contct. Then A chooses which does not exist in B. If destintion in A is B, it is delivered to B. Orwise, A compres delivery itself with tht B. If P(A,D) Appl. Sci. 2018, 8, x FOR PEER REVIEW 7 20 is lrger thn P(B,D), is not forwrded to B. If P(A,D) is not lrger thn P(B,D), originlly A checks if prep(a,d) hs not been exists. forwrded We note tht to nor if before, is generted tht is, in prep(a,d) A originlly does not exist. hs If prep(a,d) not been forwrded does not exist, to nor before, is forwrded tht is, to prep(a,d) B since doesp(a,d) not exist. not If prep(a,d) lrger thn does P(B,D). not If exist, prep(a,d) exists, is forwrded vlue P(B,D) to is Bcompred since P(A,D) with is tht not lrger prep(a,d). thn P(B,D). If P(B,D) If prep(a,d) is lrger exists, thn prep(a,d), vlue P(B,D) is compred is forwrded with tht to prep(a,d). B, IfpreP(B,D) is lrger is set thn s P(B,D). prep(a,d), Orwise, is forwrded is not torwrded. B, If prep(b,d) considered is set s P(B,D). Orwise, not lst, is not sme forwrded. procedure If pplies considered to remining is not s. lst, sme procedure pplies to remining s. Figure5. 5. A flowchrt proposed protocol. Figure Figure 6 shows shows n n exmple exmple delivery delivery proposed proposed protocol. protocol. Node Node A B B hve hve tble tble for for list list s s well well s s delivery delivery prep prep or or s. s. For For exmple, exmple, in in Figure Figure 6, 6, A hs hs s s M1, M1, M2, M2, M3, M3, M4. M4. Delivery Delivery for for s s B, B, C, C, D, D, E, E, F re re stored stored but but prep prep is is stored stored only only for for s s C, C, D, D, E, E, since since we we ssume ssume tht tht A A hs hs not not exchnged exchnged with with B B F yet. F Additionlly, yet. Additionlly, B hs s B hs s M5, M6, M5, M6, M7. M7. Delivery for s A, C, D, E, F re stored but prep informtion is stored only for C, D, E, F. As shown in Figure 6b, fter contct, M1 is not forwrded to B since delivery B is not higher thn A. Messge M2 is forwrded to B since current delivery prep for D, which is destintion M2, re higher thn those A. M3 is delivered to B since destintion

8 Appl. Sci. 2018, 8, Delivery for s A, C, D, E, F re stored but prep informtion is stored only for C, D, E, F. As shown in Figure 6b, fter contct, M1 is not forwrded to B since delivery B is not higher thn A. Messge M2 is forwrded to B since current delivery prep for D, which is destintion M2, re higher thn those A. M3 is delivered to B since destintion M3 is B informtion prep delivery for B A re updted. Messge M4 is forwrded to B with rtionle similr to M2. Only M7 B is forwrded to A since A hs higher delivery prep. Appl. Sci. 2018, 8, x FOR PEER REVIEW 8 20 () (b) Figure 6. An exmple delivery: () before contct, (b) fter contct. 4. Performnce Anlysis In this section, we nlyze performnce proposed protocol using n opportunistic network environment (ONE) simultor developed by Helsinki University [27,28]. Then, we compre performnce proposed protocol with PRoPHET protocol with GRTR strtegy,

9 Appl. Sci. 2018, 8, Performnce Anlysis In this section, we nlyze performnce proposed protocol using n opportunistic network environment (ONE) simultor developed by Helsinki University [27,28]. Then, we compre performnce proposed protocol with PRoPHET protocol with GRTR strtegy, PRoPHET protocol with GRTR+ strtegy, PRoPHET protocol with GTMX strtegy, modified HESnW [25] protocol, with confidence intervl 95%. The modified HESnW is selected s compring protocol since it is one ltest protocols using contct history informtion mobile. In modified HESnW protocol, which is clled HEPRoPHET herefter, we pplied concept multiple probbility HESnW to forwrding decision PRoPHET protocol. In HEPRoPHET, is forwrded to nor eir if hs higher delivery or if s multiple probbility is higher thn delivery sending when deliver hs higher thn trnsfer threshold. The performnce proposed protocol is compred with PRoPHET protocol with GRTR, PRoPHET with GRTR+, PRoPHET with GTMX, HEPRoPHET in terms delivery rtio, overhed rtio, delivery ltency, defined s follows: delivery rtio = number delivered s number creted s (4) overhed rtio = number relyed s number delivered s number delivered s delivery ltency = sum delivered s dely number delivered s We ssume prmeter vlues for simultion s listed in Tble 1, where U[x, y] denotes uniform distribution between x y. We lso note tht we romly generte source destintion for out totl 126 s. Figures 7 9 show delivery rtio, overhed rtio, overhed rtio, delivery ltency for vrying buffer size pedestrin cr from 10 Mbytes to 90 Mbytes, where buffer size trms is 10 times tht vrying buffer size pedestrin cr. In Figure 7, delivery rtios ll compred protocols increse s vlue buffer size increses, becuse more s cn be ccommodted in buffer thus dropped s decrese. Therefore, more s cn be delivered to destintion successfully without being dropped during delivery due to overflow buffer. The proposed protocol hs highest delivery rtio for ll considered buffer sizes since proposed protocol efficiently restricts forwrding by considering prep, thus, delivery rtio is highest. Figure 8 shows overhed rtio for different buffer sizes. Overhed rtios ll protocols decrese s vlue buffer size increses since delivery rtio increses s buffer size increses for ll protocols, thus, overhed rtio decreses s cn be seen in Eqution (5). We note tht effect incresed relyed s is minor since number generted s is fixed. The overhed rtio proposed protocol is smllest out ll considered protocols since proposed protocol restricts forwrded s efficiently hs smller number forwrded s. It lso hs higher delivery rtio. (5) (6)

10 Appl. Sci. 2018, 8, Prmeter Tble 1. The simultion prmeter vlues. Vlue Are size (m 2 ) [25,29] Number rngseeds 5 Router PRoPHET Router P encounter 0.75 [30] γ 0.98 [30] 0 β 0.25 [30] NFmx 5 Pmx (initil vlue) 0 Movement model Speed (m/s) Number totl s Number pedestrin Number crs Number trms pedestrin, cr: Shortest Pth Mp Bsed Movement [25] trm: Mp Route Movement [25] pedestrin: U[0.5, 1.5] [25] cr: U[2.7, 13.9] trm: U[7, 10] 126 (defult) 80 (defult) 40 (defult) 6 (defult) Simultion time (s) 216,000 Trnsmission rnge (m) pedestrin, cr: 10 (interfce1) (defult) [19] trm: 10 (interfce1), 1000 (interfce2) (defult) [19] Pcket trnsmission speed 250 Kbyte/s [19] Appl. Sci. 2018, 8, x FOR PEER REVIEW pedestrin, cr: 50 (defult) Buffer size (MBytes) trm: 500 (defult) delivery due to overflow buffer. The proposed protocol hs highest delivery rtio for Messge intervl (s) U[25 s, 35 s] ll considered buffer sizes since proposed protocol efficiently restricts forwrding Messge size (Bytes) U[500 k~1 M] [30] by considering prep, thus, delivery rtio is highest. Figure 7. The delivery rtio for different buffer sizes. Figure 8 shows overhed rtio for different buffer sizes. Overhed rtios ll protocols decrese s vlue buffer size increses since delivery rtio increses s buffer size increses for ll protocols, thus, overhed rtio decreses s cn be seen in Eqution (5). We note tht effect incresed relyed s is minor since number generted

11 decrese s vlue buffer size increses since delivery rtio increses s buffer size increses for ll protocols, thus, overhed rtio decreses s cn be seen in Eqution (5). We note tht effect incresed relyed s is minor since number generted s is fixed. The overhed rtio proposed protocol is smllest out ll considered Appl. protocols Sci. 2018, since 8, 2215 proposed protocol restricts forwrded s efficiently hs smller number forwrded s. It lso hs higher delivery rtio. Appl. Sci. 2018, 8, x FOR PEER REVIEW Figure 8. The overhed rtio for different buffer sizes Figure 9 shows delivery ltency for fordifferent buffer buffer sizes. sizes. The The delivery delivery ltencies ltencies ll ll considered considered protocols protocols increse increse s vlue vlue buffer size sizeincreses since more s re ccommodted in buffer s,, thus, thus, longer ltencies re re required required to deliver to deliver s s to to finl finl destintion destintion s, s, given given limited limited contct contct durtion durtion between between s. s. The The proposed proposed protocol protocol hs hs smllest smllest delivery delivery ltency ltency since since proposed proposed protocol protocol restricts restricts forwrded forwrded s efficiently s efficiently, thus, hs, thus, smller hs number smller number s ins buffer, in which buffer, results which in results fster in fster delivery to delivery finl destintion to finl destintion s. s. Figure 9. The delivery ltency for different buffer sizes. Figures show delivery rtio, overhed rtio, delivery ltency for vrying genertion intervls vrying from U[5 s, 15 s] to U[45 s, 55 s], when buffer sizes pedestrin cr re 50 Mbytes buffer size trm is 500 Mbytes. In Figure 10, delivery rtios ll compred protocols increse s vlue genertion intervl increses becuse fewer s re generted when genertion intervl increses more s cn be delivered to destintion successfully without being dropped during delivery due to overflow buffer. The proposed protocol hs highest delivery rtio for

12 Appl. Sci. 2018, 8, pedestrin cr re 50 Mbytes buffer size trm is 500 Mbytes. In Figure 10, delivery rtios Appl. Sci. 2018, 8, x FOR PEER REVIEW ll compred protocols increse s vlue genertion intervl increses becuse fewer s re generted when genertion intervl increses more s increse s number trms increses since trms crry more s with lrge enough buffer cn be delivered to destintion successfully without being dropped during delivery due to size, thus, more s cn be delivered successfully for lrger number trms. We note overflow buffer. The proposed protocol hs highest delivery rtio for ll considered tht proposed protocol hs highest delivery rtio for ll considered buffer sizes since buffer sizes since proposed protocol efficiently restricts forwrding by considering prep proposed protocol efficiently restricts forwrding by considering prep, thus,, thus, delivery rtio is highest. delivery rtio is highest. Figure 10. The delivery rtio for different genertion intervls. Figure The overhed rtio for different intervls. intervls. Figure 14 shows overhed rtio. Overhed rtios ll protocols increse s number trms increses since more s re relyed due to more forwrders. The overhed rtio proposed protocol is smllest out ll considered protocols, since proposed protocol restricts forwrded s efficiently hs smller number forwrded s lso hs lower overhed rtio.

13 Figure 15 shows delivery ltency. Delivery ltencies ll protocols decrese s number s increses since s cn be forwrded quickly with help more forwrders, delivered to destintion s more quickly. The proposed protocol hs smllest delivery ltency since proposed protocol restricts forwrded s efficiently, thus, Appl. hs Sci. smller 2018, 8, 2215 number s in buffer, which results in fster delivery to 13finl 20 destintion s. Figure 12. The delivery ltency for different intervls. Figure 11 shows overhed rtio. Overhed rtios ll protocols increse s genertion intervl increses. This is becuse effect decresed delivered s when genertion intervl is high in Eqution (5) is more dominnt thn tht decresed relyed s. The overhed rtio proposed protocol is smllest out ll considered protocols since proposed protocol restricts forwrded s efficiently, hs smller number forwrded s, lso hs higher delivery rtio. Figure 12 shows delivery ltency. The delivery ltencies ll protocols decrese s genertion intervl increses since higher genertion intervl results in fewer s in buffer thus chnce forwrding during short contct durtion is lrger for fixed buffer size. The proposed protocol hs smllest delivery ltency since proposed protocol restricts forwrded s efficiently, thus, hs smller number s in buffer, which results in fster delivery to finl destintion s. Figures show delivery rtio, overhed rtio, delivery ltency, for vrying number trms from 3 to 27, where number pedestrins is 80 number crs is 40, which re defult vlues in ONE simultor. In Figure 13, delivery rtios ll protocols increse s number trms increses since trms crry more s with lrge enough buffer size, thus, more s cn be delivered successfully for lrger number trms. We note tht proposed protocol hs highest delivery rtio for ll considered buffer sizes since proposed protocol efficiently restricts forwrding by considering prep, thus, delivery rtio is highest. Figure 13. The delivery rtio for different numbers trms. Figure 14 shows overhed rtio. Overhed rtios ll protocols increse s number trms increses since more s re relyed due to more forwrders. The overhed rtio proposed protocol is smllest out ll considered protocols, since proposed protocol restricts forwrded s efficiently hs smller number forwrded s lso hs lower overhed rtio.

14 Appl. Sci. 2018, 8, Figure 12. The delivery ltency for different intervls. Appl. Sci. 2018, 8, x FOR PEER Figure REVIEW 13. The delivery rtio for different numbers trms Figure 13. The delivery rtio for different numbers trms. Figure 14. The overhed rtio for different numbers trms. Figure 14. The overhed rtio for different numbers trms. Figure 15 shows delivery ltency. Delivery ltencies ll protocols decrese s number s increses since s cn be forwrded quickly with help more forwrders, delivered to destintion s more quickly. The proposed protocol hs smllest delivery ltency since proposed protocol restricts forwrded s efficiently, thus, hs smller number s in buffer, which results in fster delivery to finl destintion s.

15 Appl. Sci. 2018, 8, Figure 14. The overhed rtio for different numbers trms. Figure 15. The delivery ltency for different numbers trms. Figures show delivery rtio, rtio, overhed overhed rtio, rtio, delivery delivery ltency ltency for vrying for vrying number number pedestrins pedestrins from 40 to from 360, 40 where to 360, where number number trms is 6trms is 6 number number crs is 40, crs which is re 40, which defult re vlues defult in vlues ONEin simultor. ONE simultor. In Figure In 16, Figure delivery 16, rtio delivery rtio proposed proposed protocol protocol increses increses number s number s increses s increses from 40 to from 80 since 40 to more 80 since pedestrins more pedestrins cn ct scn ct s forwrders forwrders more s more s cn be delivered cn be delivered successfully. successfully. However, However, delivery delivery rtio rtio proposed proposed protocol protocol slightly slightly decreses decreses when when number number s s is higher is higher thn 80 thn since 80 since effect effect more more forwrding forwrding resulting resulting drop drop due due to buffer to buffer overflow overflow restricts restricts successful delivery delivery since since buffer buffer size size pedestrin pedestrin is notis sufficient. not sufficient. The delivery The delivery rtios rtios or protocols or protocols decrese decrese significntly significntly due to due moreto more dropping dropping buffer. in We buffer. notewe tht note proposed tht proposed protocol protocol hs highest hs delivery highest rtio delivery for ll rtio for considered ll considered buffer sizes buffer sincesizes proposed since protocol efficiently restricts forwrding by considering prep, thus, delivery rtio is highest. Figure 17 shows overhed rtio. Overhed rtios ll protocols increse s number s increses since more s re relyed due to more forwrders rte increse is more significnt s number pedestrins is higher becuse number delivered s decreses for high number pedestrins. The overhed rtio proposed protocol hs smllest out ll considered protocols since proposed protocol restricts forwrded s efficiently hs smller number forwrded s, lso hs higher delivery rtio. Figure 18 shows delivery ltency. Delivery ltencies ll protocols decrese s number pedestrins increses since s cn be forwrded quickly with help more forwrders delivered to destintion s more quickly. The proposed protocol hs smllest delivery ltency since proposed protocol restricts forwrded s efficiently, thus, hs smller number s in buffer, which results in fster delivery to finl destintion s.

16 Appl. Sci. 2018, 8, x FOR PEER REVIEW Appl. proposed Sci. 2018, protocol 8, 2215 efficiently restricts forwrding by considering prep, thus, delivery rtio is highest. Appl. Sci. 2018, 8, x FOR PEER Figure REVIEW 16. The delivery rtio for different numbers pedestrins Figure 17 shows overhed rtio. Overhed rtios ll protocols increse s number s increses since more s re relyed due to more forwrders rte increse is more significnt s number pedestrins is higher becuse number delivered s decreses for high number pedestrins. The overhed rtio proposed protocol hs smllest out ll considered protocols since proposed protocol restricts forwrded s efficiently hs smller number forwrded s, lso hs higher delivery rtio. Figure 18 shows delivery ltency. Delivery ltencies ll protocols decrese s number pedestrins increses since s cn be forwrded quickly with help more forwrders delivered to destintion s more quickly. The proposed protocol hs smllest delivery ltency since proposed protocol restricts forwrded s efficiently, thus, hs smller number s in buffer, which results in fster delivery to finl destintion s. Figures show delivery rtio, overhed rtio, delivery ltency for vrying number crs from 40 to 360, where number trms is 6 number pedestrins is 80, which is defult setting in ONE simultor. In Figure 19, delivery rtio proposed protocol increses s number s increses from 40 to 120 since more crs cn ct s forwrders more s cn be delivered successfully. However, delivery rtio proposed protocol slightly decreses when number s is higher thn 120 since effect Figure 17. The overhed rtio for different numbers pedestrins. more forwrding resulting drop due to buffer overflow restricts successful Figures delivery 19 21since show buffer delivery size rtio, cr overhed is not sufficient. rtio, The delivery ltency rtios for or vrying protocols number decrese significntly crs from 40due to 360, to more wheres number dropping trms in is 6 buffer. number We note tht pedestrins proposed is 80, which protocol is hs defult highest setting delivery in rtio ONE for simultor. ll considered In Figurebuffer 19, sizes delivery since rtio proposed proposed protocol protocol efficiently increses restricts s number forwrding s increses by considering from 40preP to 120, since thus, more crs delivery cn ctrtio s is forwrders highest. The shpe more delivery s rtios cn bell delivered protocols successfully. is similr However, to tht Figure delivery 16, insted rtio tht proposed Figure 14, protocol since slightly buffer decreses size when cr is number sme s tht s is higher pedestrin, thn 120 which since is significntly effect more smller thn tht forwrding trm. resulting drop due to buffer overflow restricts successful delivery since buffer size cr is not sufficient. The delivery rtios or protocols decrese significntly due to more s dropping in buffer. We note tht proposed protocol hs highest delivery rtio for ll considered buffer sizes since proposed protocol efficiently

17 Appl. Sci. 2018, 8, restricts forwrding by considering prep, thus, delivery rtio is highest. The shpe delivery rtios ll protocols is similr to tht Figure 16, insted tht Figure 14, since buffer size cr is sme s tht pedestrin, which is significntly smller thn tht trm. Figure 17. The overhed rtio for different numbers pedestrins. Figure 18. The delivery ltency for different numbers pedestrins. Appl. Sci. 2018, 8, x FOR PEER REVIEW Figure 20 shows overhed rtio. Overhed rtios ll protocols increse s number s increses since more s re relyed due to more forwrders rte increse is more significnt s number crs is higher becuse number delivered s decreses for high number crs. The overhed rtio proposed protocol hs smllest out ll considered protocols since proposed protocol restricts forwrded s efficiently hs smller number forwrded s lso hs higher delivery rtio. Figure 19. The delivery rtio for different numbers crs. Figure 19. The delivery rtio for different numbers crs.

18 Appl. Sci. 2018, 8, Figure 19. The delivery rtio for different numbers crs. Appl. Sci. 2018, 8, x FOR PEER Figure REVIEW 20. The overhed rtio for different numbers crs Figure 21 shows delivery ltency. Delivery ltencies ll protocols decrese s number crs increses since s cn be forwrded quickly with help more forwrders delivered to destintion s more quickly. The proposed protocol hs smllest delivery ltency since proposed protocol restricts forwrded s efficiently, thus, hs smller number s in buffer, which results in fster delivery to finl destintion s. Figure 21. The delivery ltency for different numbers crs. 5. Conclusions Figure 20 shows overhed rtio. Overhed rtios ll protocols increse s number s increses since more s re relyed due to more forwrders rte In this pper, we proposed n efficient opportunistic routing protocol using delivery increse is more significnt s number crs is higher becuse number delivered s prep. We nlyzed performnce proposed protocol using ONE decreses for high number crs. The overhed rtio proposed protocol hs smllest out simultor compred with tht or compring protocols for vrying environments. ll considered protocols since proposed protocol restricts forwrded s efficiently Performnce nlyses showed tht proposed protocol performs better thn PRoPHET hs smller number forwrded s lso hs higher delivery rtio. protocol with GRTR strtegy, PRoPHET protocol with GRTR+ strtegy, PRoPHET protocol with Figure 21 shows delivery ltency. Delivery ltencies ll protocols decrese s GTMX strtegy, HEPRoPHET, in terms delivery rtio, overhed rtio, delivery ltency number crs increses since s cn be forwrded quickly with help more for vrying buffer sizes, genertion intervls, number s by efficiently restricting forwrders delivered to destintion s more quickly. The proposed protocol hs smllest forwrded s. Author Contributions: E.H.L., D.Y.S. Y.W.C. conceived designed proposed scheme. E.H.L. D.Y.S. conceived designed simultions; E.H.L. D.Y.S. performed simultions; D.Y.S. Y.W.C. nlyzed dt; Y.W.C. wrote pper. Authors hve red pproved finl mnuscript.

19 Appl. Sci. 2018, 8, delivery ltency since proposed protocol restricts forwrded s efficiently, thus, hs smller number s in buffer, which results in fster delivery to finl destintion s. 5. Conclusions In this pper, we proposed n efficient opportunistic routing protocol using delivery prep. We nlyzed performnce proposed protocol using ONE simultor compred with tht or compring protocols for vrying environments. Performnce nlyses showed tht proposed protocol performs better thn PRoPHET protocol with GRTR strtegy, PRoPHET protocol with GRTR+ strtegy, PRoPHET protocol with GTMX strtegy, HEPRoPHET, in terms delivery rtio, overhed rtio, delivery ltency for vrying buffer sizes, genertion intervls, number s by efficiently restricting forwrded s. Author Contributions: E.H.L., D.Y.S. Y.W.C. conceived designed proposed scheme. E.H.L. D.Y.S. conceived designed simultions; E.H.L. D.Y.S. performed simultions; D.Y.S. Y.W.C. nlyzed dt; Y.W.C. wrote pper. Authors hve red pproved finl mnuscript. Funding: This reserch Dong Yeong Seo Yun Won Chung ws supported by Bsic Science Reserch Progrm through Ntionl Reserch Foundtion Kore (NRF) funded by Ministry Science, ICT & Future Plnning (NRF-2016R1D1A1B ). Conflicts Interest: The uthor(s) declred no potentil conflicts interest with respect to reserch, uthorship, /or publiction this rticle. References 1. Fll, K. A dely-tolernt network rchitecture for chllenged internets. In Proceedings 2003 Conference on Applictions, Technologies, Architectures, Protocols for Computer Communictions (SIGCOMM 03), Krlsruhe, Germny, August Burleigh, S.; Hooke, A.; Torgerson, L.; Fll, K.; Cerf, V.; Durst, B.; Scott, K. Dely-tolernt networking: An pproch to interplnetry internet. IEEE Commun. Mg. 2003, 41, [CrossRef] 3. Dely Tolernt Networking Reserch Group. Avilble online: (ccessed on 15 Februry 2018). 4. Zhng, Z. Routing in intermittently connected mobile d hoc networks dely tolernt networks: Overview chllenges. IEEE Commun. Surv. Tutor. 2006, 8, [CrossRef] 5. Mrtin-Cmpillo, A.; Crowcrt, J.; Yoneki, E.; Mrti, R. Evluting opportunistic networks in disster scenrios. J. Netw. Comput. Appl. 2013, 36, [CrossRef] 6. Zhng, X.; Negli, G.; Kurose, J.; Towsley, D. Performnce modeling epidemic routing. Comput. Netw. 2007, 51, [CrossRef] 7. Spyropoulos, T.; Psounis, K.; Rghvendr, C.S. Spry wit: An efficient routing scheme for intermittently connected mobile networks. In Proceedings ACM SIGCOMM Workshop on Dely-tolernt Networking, Phildelphi, PA, USA, 26 August Lindgren, A.; Dori, A.; Dvies, E.; Grsic, S. Probbilistic routing protocol for intermittently connected networks. ACM SIGMOBILE Mob. Comput. Commun. Rev. 2003, 7, [CrossRef] 9. Lee, E.H.; Seo, D.Y.; Chung, Y.W. An improved forwrding strtegy in opportunistic network. In Proceedings Future Genertion Communiction Networking, Jeju, Kore, November Khbbz, M.; Assi, C.M.; Fwz, W.F. Disruption-Tolernt Networking: A Comprehensive Survey on Recent Developments Persisting Chllenges. IEEE Commun. Surv. Tutor. 2012, 14, [CrossRef] 11. Co, Y.; Sun, Z. Routing in Dely/Disruption Tolernt Networks: A Txonomy, Survey Chllenges. IEEE Commun. Surv. Tutor. 2013, 15, [CrossRef] 12. Zhu, Y.; Xu, B.; Shi, X.; Wng, Y. A Survey Socil-Bsed Routing in Dely Tolernt Networks: Positive Negtive Socil Effects. IEEE Commun. Surv. Tutor. 2013, 15, [CrossRef] 13. Wei, K.; King, X.; Xu, K. A Survey Socil-Awre Routing Protocols in Dely Tolernt Networks: Applictions, Txonomy Design-Relted Issues. IEEE Commun. Surv. Tutor. 2014, 16,

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