A Hybrid Routing Algorithm for Delay Tolerant Networks

Transcription

1 Sensors & Transucers 2013 by IFSA A Hybri Routing Algorithm for Delay Tolerant Networs Jianbo LI, Jixing XU, Lei YOU, Chenqu DAI, Jieheng WU Information Engineering College of Qingao University, Ningxia Roa 308, Qingao , China Tel.: (+86) lijianboqu@gmail.com Receive: 19 December 2013 /Accepte: 29 December 2013 /Publishe: 30 December 2013 Abstract: The unavailability of an en-to-en path poses great challenges in routing algorithms for elay tolerant networs (DTNs). Meanwhile, routing protocols for the traitional A-hoc or Mobile A hoc NETwors (MANETs) cannot wor well ue to the failure of assumption that networ connections are available in most of time. In this article, we put forwar a hybri routing algorithm to combine the classical Spray&Wait an PRoPHETalgorithms. The propose protocol essentially bases on an unsymmetrical Spray&Wait at the first stage, an then aaptively allocates the message copy count on eman by using the elivery probability use in PRoPHETalgorithm for the purpose of maing forwaring ecision more sensible. Finally, each noe taes the real time inter-contact interval an average inter-contact interval with the message estination into consieration in orer to ynamically ajust its message copy count, thus maing timely an rational routing ecision base on the real time networ conition. Extensive simulations have been conucte to verify the effectiveness an efficiency of our algorithm an the results emonstrate that our algorithm achieves a higher elivery probability an lower average message latency uner Ranom Wal an Ranom Waypoint mobility moels, as compare to Spray&Wait, PRoPHET, Epiemic an FirstContact. Copyright 2013 IFSA. Keywors: Delay tolerant networs, SPRAY&Wait, PRoPHET, Hybri routing, Aaptive routing. 1. Introuction In recent years, elay tolerant networ as a emerging networ has receive extensive attentions. It is originally applie in military battlefiel networs an emergency rescue networs. Now the concept of DTN has been applie in various fiels, such as internet access service networs [1], Vehicular A Hoc Networs [2-4], Habitat Monitoring Networs [5], an unerwater sensor networs [6], etc. These special application networs eploye in challenging environments are characterize by intermittent connectivity [7-9], frequent partitions, high noe mobility an low noe ensity, etc. So there may never be a complete en to en path between the sener an the receiver. In this case, the existing routing protocols base traitional TCP/IP are ifficult to get satisfying routing performance. Consequently, the successful message transmissions in such networs face great challenges. Now, the routing esign for elay tolerant networs has become the focus of wireless networ research fiels. Delay Tolerant Networ first originate from Interplanetary Networs (IPN [10]), which was use to solve the communication problems between planets. In 2003, Kevin Fall propose the concept of DTN. Soon afterwars, the DTN Research Group (DTNRG) put forwar the DTN networ architecture, which introuce a bunle layer to cope with heterogeneous networs. An with the help of the bunle layer, DTN routing aopts the store-carry an forwar strategy to relay messages hop by hop for 510 Article number P_RP_0036

2 the, thus it can be able to cope with frequent networ topology partitions to some extent. But in most DTN application scenarios, it may be very ifficult to capture the global networ topology nowlege. In this case, DTN routing is still ifficult to mae the right routing selection for the purpose of getting a satisfying routing performance. A simple an irect approach is to increase the number of message copies, which can increase the chance of encountering the final estination noe, but also inevitably consume a large number of networ resource. But in most DTN application scenarios, the buffer resource is extremely limite. So the esirable way is to get a goo balance between the higher elivery rate an less consumption of resources. In this paper, we first propose to limit the number of message copies for the purpose of getting a balance between higher message elivery ratio an less resource consumption. An then we tae full use of the elivery probability between two noes to istribute message copies reasonably. Besies, we also propose to ynamically ajust the number of message copies base on the real time networ conition. Finally, a hybri routing algorithm for elay tolerant networs is propose to improve routing performance. The rest of this paper is organize as follows. We iscuss some relate wors in Section 2. In section 3, we give a etaile escription of the propose algorithm. The performance evaluations an comparisons among the propose algorithm, First Contact, Spray&Wait, Epiemic an PRoPHET are presente in Section 4. Finally, section 5 summarizes this paper an gives future research irections. 2. Relate Wor After the DTN architecture was presente, a lot of researches have propose many typical DTN routing algorithms. The early DTN routing algorithms are base on single copy strategy. For example, Direct Delivery [11] an First Contact [12].They only eliver one single copy of the message in the entire networ. The big avantages of this in of routing algorithms are that they only nee to consume little resource an can lower the networ overhea ratio. But ue to the frequent networ topology partitions, they are ifficult to get satisfying message elivery ratios. In orer to improve message elivery ratio, many multi-copy base routing algorithms have been propose. Epiemic [13] is the typical algorithm, which tries to replicate all carrie message to all encountere noes without evaluating these noes. It can lower the message elivery latency to some extent, but it also leas to a high networ overhea ratio. Besies, it will create a lot of reunant message copies, so it is still ifficult to get a satisfying routing performance when the buffer resource is insufficient. Base on this conition, Spraty&Wait [14] an Spray&Focus [15] mae improvements by limiting the number of message copies. Only in spray perio can they replicate L message copies to L ifferent intermeiate relay noes. In wait perio or focus perio, they o not replicate message copies any more. By limiting the number of message copies, they can control the networ overhea ratio an reuce the consumption of networ resource. But they also o not evaluate the encountere noes when istributing the message copies. So their message istribution strategies are not sensible enough. PROPHET [16] a typical routing algorithm base on history utility, which taes full use of the regular mobility patterns of noes an uses the capture encounter history information an transitive property to preict an upate the elivery probability between two noes. An then it taes into account the elivery probability when selecting next hop relay noes. By evaluating every encountere noe, it only selects the neighbor with a bigger elivery probability as the next hop relay noe. So in this case, its routing selection is more accurate than that of Epiemic, thus improving the message elivery ratio. In [17], several nowlege oracle base routing protocols are propose. By abstracting a weighte graph from the capture global networ topology information, they apply ifferent moifie Dijstra algorithms on the graph to see the shortest path. However the potential epenence on the pre-nown nowlege oracle highly constraine the practicality of these protocols. [18-19] propose some typical routing protocols base fixe infrastructures. An [20-22] put forwar to some mobile infrastructures assistant routing schemes. These routing schemes can improve networ routing performance by introucing the extra infrastructures. Besies, [23-25] present some coing base routing schemes, which can compensate the egrae routing performance to some extent. Most DTN routing protocols more or less rely on extra assistant information or some assumption of the networ topology so as to enhance the routing performance, while sacrificing the practicality an simplicity. 3. Routing Framewor Inmost DTN application scenarios, the buffer resource is extremely limite. So in this case, controlling the number of message copies is a esirable scheme to improve routing performance. But the classical Spray&Waitis not sensible enough when istributing message copies. So in this article, by taing full use of the elivery probability use in PRoPHET, we reasonably allocate message copies an finally put forwar a hybri routing algorithm to implement unsymmetrical spray routing. Besies, in orer to mae timely an rational routing ecision base on the real time networ conition, we also ynamically ajust message copy count on relay 511

3 noes by taing the real time inter-contact interval an average inter-contact interval with the message estination into consieration Delivery Preictability Calculation In orer to istribute message copies more sensible, we propose to allocate message copies accoring to elivery preictability. Here, we use the three propose equations in PROPHET [16] to preict an upate the probability of encountering a certain noe. When two noes a an b encounter, the equation (1) is use to preict the elivery preictability that noe a has for noe b, where P [0,1] is an initialization constant. init P P( ( 1 P( ) Pinit (1) When two noes o not encounter each other for a perio of time, the elivery preictability shoul be reuce in the process. The equation(2) is the aging function, where is the aging constant, an is the number of time units that have elapse since the last time the preictability was age. P P( (2) The elivery preictability between two noes also has the transitive property. So if noe a encounters noe b very frequently, an noe b also encounters noe c very frequently, then noe a may also be a goo forwarer to relay messages estine for noe c. P P 1 P P P (3) c) c) ( c) ) ( b, c) noe, La ( m ) is the number of message copies that noe a is carrying, an La ( m ) is the number of message copies that we re-allocate to noe a. L a L ( m ) P P ) ) P ( b, ) ( L a ( m ) L b ( m )) (4) m ) ( L ( m ) L ( m ) L ( m )) (5) b ( a b a 3.3. Inter-Contact Interval In orer to timely an rationally ajust the number of message copies base on the real time networ conition, every noe nees to recor the two time interval an m, where represents the time that have elapse since the last time they encountere, an m enotes the average encounter time interval which is upate accoring to the equation (6). Their etaile upate processes are shown in Fig. 1. Algorithm 1. Upate an m value Require: When connection between a an b is up Ensure: 1. = currenttime - lastupatetime; 2. lastupatetime currenttime; 3. m am (1 ) m (, ) a b Fig. 1. Upate an m value. m( ( 1 ) (6) 3.2. Message Copies Distribution In most DTN application scenarios, noes o not move aroun completely ranomly. On the contrary, the two noes which encountere each other very frequently in the past are more liely to encounter each other again in the near future. So in this case, we tae into account the elivery probability when istributing message copies. The intermeiate relay noe with a bigger elivery probability is more liely to finish message transmission successfully, so the noe shoul be istribute more message copies. When two noes encounter, we re-allocate the number of message copies they shoul carry accoring to the total number of message copies they carry now. The etaile process are shown in equations (4) an (5), where m is the message for Finally after upating the two encounter time interval, we can ynamically ajust the number of message copies accoring to the following equation (7). L a ( m ) L m ) a ( ) (7) m( ) 3.4. Detaile Routing Algorithm Base on the above schemes, we can finally implement the propose routing algorithm as shown in Fig. 2. Here, we efine the message set of noe a as the follows. 512

4 M ( a) mi 1 i M ( a) (8) As shown in algorithm 2, when two noes encounter, line 1 first exchanges some essential information which are use to upate the numbers of message copies on the two noes. Lines 4-5 recalculate the numbers of message copies that the two noes shoul respectively carry accoring to the total number of message copies they are carrying an the elivery probabilities for estination noe. Then line 6 ajusts the number of message copies base on the real time networ conition. Lines 7-10 upate the number of message copies in the buffer accoring to the calculate La ). Lines forwar message copies to the encountere noe. Algorithm 2. The propose routing protocol Require: When noe a encounters noe b Ensure: 1. exchange P, m an with each other; 2. for message m N o 3. estination noe of m ; 4. compute La ) with equation (4); 5. compute Lb ) with equation (5); 6. upate La ) with equation (7); 7. buffer.get( m ).upate( La ) ); 8. if La ( m ) 0 then 9. buffer.eletemessage( m ); 10. en if 11. if Lb ) && Lb ) then 12. a m into forwarlist; 13. forwarlist.get( m ).upate( Lb ) ); 14. forwarlist.sort(ascening, TTL); 15. forwarlist.sento(; 16. en if 17. en for 4. Simulation Fig. 2. The propose routing protocol. In this section, we use the most popular networ simulator ONE (the Opportunistic Networ Environment evaluator) to implement our propose routing protocol. An extensive simulations have been conucte respectively base on Ranom Wal mobility moel an Ranom Waypoint mobility moel. We compare the routing performance of our propose algorithm, First Contact, Spray an Wait, Epiemic an PROPHET in terms of message elivery ratio, networ overhea ratio, average elivery latency an average hop count. We mostly focus on their ifferent routing performance inifferent buffer sizes an message time-to-live. The etaile simulation settings are shown in Table 1. Table 1. Simulation settings. Parameter Area size Number of noes Ticets Initial topology Transmit raius Message size Message interval Transmit spee Moving spee Noe buffer size Time-To-Live(TTL) Simulation time Movement moel Default value 1000 m x 1000 m Uniform 100 m 500 K 40 s 250 Kbps 0.5 (m/s) 5 M 300 min 5 hours RanomWal an RanomWaypoint 4.1. Vary Buffer Size in Ranom Wal Moel Fig. 3 shows the ifferent simulation results of varying noe s buffer size in the Ranom Wal moel. As shown in the figure, the propose algorithm can get obvious avantages in terms of elivery probability an average latency, which can verify that the propose routing scheme can greatly improve the transmission performance of the entire networ. First Contact only elivers one single message copy in the entire networ, thus it nees more time to finish message transmission. As shown in the figure, the average latency of First Contact is the biggest among the five routing algorithms, an its average hop count is also the most compare to others. But its networ overhea ratio is significantly lower than those of Epiemic an Prophet. So in a conclusion, First Contact is applicable to the application scenario whose loa capacity is low an buffer resource is extremely limite. Epiemic oes not tae any measures to control message reunancy, so it will inevitably create numerous reunant messages in whole networ an consume more networ resource. When noe s buffer resource is insufficient, Epiemic will rop a large number of message pacets, so its message elivery probability is the lowest in this case. Besies, these reunant messages also increase the networ overhea ratio. However, Epiemic can reuce the average latency an average hop count compare to First Contact. Spray an Wait limits the number of message copies, so its overhea ratio can be ept at a very low level. An its average hop count is also the lowest because that it oes not forwar message in the wait perio. But it oes not evaluate noes when istributing message copies, so its message elivery probability is lower than that of our propose algorithm an its average latency is also bigger than that of the propose algorithm. 513

5 Prophet uses the elivery probability to evaluate every encountere noe, so it can great improve the message elivery probability an control overhea ratio compare to Epiemic. Besies, it can also improve the accuracy of routing selection by using the eliver probability as the metric, thus reucing the cost of message transmission. the overhea ratio of our propose algorithm is much lower than those of Epiemic an Prophet. Finally from the whole figure, we can mae a conclusion that our propose routing algorithm can outperform the other four algorithms in terms of message elivery probability an elivery latency in the Ranom Wal moel base networ, thus proviing a higher message elivery probability Vary Message time-to-live in Ranom Wal Moel Fig. 4 escribes the ifferent simulation results of varying message s TTL in the Ranom Wal moel. As shown in figure, our propose routing algorithm can still get the highest message elivery probability an the lowest average elivery latency among the five algorithms, which proves once again that our propose algorithm can greatly improve networ routing performance. When message TTL is more than 250, the message elivery probabilities of the five algorithms can remain stable, but the elivery probability of our propose algorithm is obviously higher than that of the other four algorithms. Besies, Epiemic still gets the lowest message elivery probability in this case. When increasing ifferent message TTL constantly, the overhea ratio of our propose algorithm can be ept a low level compare to Epiemic an Prophet. Finally from the whole figure, we can see that our propose routing algorithm can outperform the other four algorithms in ifferent message TTL in Ranom Wal moel base networ, thus proviing a goo routing performance Vary Buffer Size in Ranom Waypoint Moel Fig. 3. Deliveryprobability, overhearatio, averagelatency, average hop count vs. buffer size in Ranom Wal moel. Our propose routing algorithm ynamically istributes message copies accoring the elivery probability, which is more sensible an can greatly improve message elivery probability. So as shown in the figure, it can get the highest message elivery probability an the lowest average latency. Besies, Fig. 9 escribes the ifferent simulation results of varying buffer size in the Ranom Waypoint moel. As shown in the figure, our propose routing algorithm can still outperform the other four algorithms in terms of message elivery probability an average elivery latency, an Epiemic is still unacceptable In a Ranom Waypoint moel base networ, noe mobility can help to improve message elivery probability. So in this case, the message elivery probabilities of our propose algorithm, First Contact an Spray an Wait are much higher than that of Epiemic an Prophet. First Contact still gets the most average hop count an the biggest average elivery latency, but also it gets a very low networ overhea ratio. In aition, when noe mobility is enhance, our propose routing algorithm can still get the highest message elivery probability an the lowest elivery latency, which can prove that our propose routing algorithm can also improve routing 514

6 performance in the Ranom Waypoint moel base networ. Finally from the whole Fig. 5, we can see that our propose routing algorithm can efficiently improve routing performance, thus proviing a higher message elivery probability. algorithm still get the highest message elivery probability an the lowest average elivery latency, an Epiemic is still unacceptable in terms of message elivery probability an networ overhea ratio. Fig. 4. Delivery probability, overhea ratio, average latency, average hop count vs. TTL in Ranom Wal moel Vary Message time-to-live in Ranom Waypoint Moel Fig. 6 shows the ifferent simulation results of varying message TTL in the Ranom Waypoint moel. As shown in the figure, our propose Fig. 5. Deliveryprobability, overhearatio, averagelatency, average hop count vs. buffer size in Ranom Waypoint moel. When varying message TTL, the message elivery probabilities of our propose algorithm, First Contact an Spray an Wait are still bigger than that of Epiemic an Prophet, an their networ overhea 515

7 ratios are also lower than that of Epiemic an Prophet. This can inicate that noe mobility can improve routing performance. So in this case, we recommen choosing our propose routing algorithm, First Contact or Spray an Wait. unsymmetrical spray routing. Besies, base on the real time networ conition, we can ynamically ajust the number of message copies to get a better routing performance. Extensive simulations have been conucte in both Ranom Wal moel base networ an Ranom Waypoint moel base networ, an the results emonstrate that our propose routing algorithm can outperform First Contact, Spary an Wait, Epiemic an Prophet in terms of message elivery probability an average elivery latency, thus proviing a better routing performance. Our future wor will focus on the social networs. In recent years, DTN moel is increasingly use in civilian areas, an the social networs are closely relate with the public life. So DTN moel in such networ tens to have broa application prospects. Our future wor will focus on this, an we will also try to fin the opportunity to eployment our propose routing algorithm in this paper. Acnowlegements This research is supporte in part by Founation research project of Qingao Science an Technology Plan uner Grant No (14)-jch an Natural Science Founation of Shanong Province uner Grant No. ZR2013FQ022. Reference Fig. 6. Delivery probability, overhea ratio, average latency, average hop count vs. message TTL in Ranom Waypoint moel. 5. Conclusion an Future Wor In most DTNs, the buffer resource is extremely limite. So in this case, uncontrolle flooing schemes are unacceptable. On the contrary, controlling the number of message copies tens to be more acceptable. An it is more sensible that we istribute these message copies accoring to the elivery probability, thus implementing efficient [1]. M. Demmer, K. Fall, DTLSR: elay tolerant routing for eveloping regions, in Proceeings of the Worshop on Networe Systems for Developing Regions, 2007, Article No. 5. [2]. H. Wu, R. Fujimoto, R. Guensler, M. Hunter, MDDV: Mobilitycentric ata issemination algorithm for vehicular networs, in Proceeings of the ACM SIGCOMM Worshop on Vehicular A Hoc Networs (VANET), [3]. P. R. Pereir A. Casac J. J. P. C. Rorigues, V. N. G. J. Soares, J. Triay, C. Cervello-Pastor, From elay-tolerant networs to vehicular elay-tolerant networs, IEEE Communications Survive Tutorials, Vol. 14, No. 4, 2012, pp [4]. V. N. G. J. Soares, J. J. P. C. Rorigues, F. Farahman, GeoSpray: A geographic routing protocol for vehicular elay-tolerant networs, Information Fusion, November 2011, pp [5]. Alberto Cerp Jeremy Elson, Deborah Estrin, Lewis Giro, Michael Hamilton, Jerry Zhao, Habitat monitoring: application river for wireless communications technology, in Proceeings of the ACM SIGCOMM Worshop on Data Communications, April [6]. Z. Guo, B. Wang, J.-H. Cui, Generic preiction assiste single-copy routing in unerwater elay tolerant sensor networs, A Hoc Networs, Vol. 11, Issue 3, January 2013, pp [7]. K. Fall, A elay-tolerant networ architecture for challenge internets, in Proceeings of the International Conference SIGOMM 03, August [8]. M. Chuah, L. Cheng, B. Davison, Enhance isruption, fault tolerant networ architecture for 516

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