Reliable Robust and Real-Time Communication Protocol for Data Delivery in Wireless sensor Networks

Transcription

1 Relable Robust an Real-Tme Communcaton Protocol or Data Delvery n Wreless sensor Networks Deepal Vrman [1], Satbr Jan [2] Abstract [1] Department o computer scence, BPIT, IPU, Delh, Ina [2] Department o computer scence, NSIT, DU, Delh, Ina eepalvrman@gmal.com WSNs can be consere a strbute control system esgne to react to sensor normaton wth an eectve an tmely acton. For ths reason, n WSNs t s mportant to prove real-tme coornaton an communcaton to guarantee tmely executon o the rght actons. In ths paper a new communcaton protocol RRRT to support robust real-tme an relable event ata elvery wth mnmum energy consumpton an wth congeston avoance n WSNs s propose. The propose protocol uses the ault tolerant optmal path or ata elvery. The propose soluton ynamcally ajust ther protocol conguratons to aapt to the heterogeneous characterstcs o WSNs. Speccally, the nteractons between contenton resoluton an congeston control mechansms as well as the physcal layer eects n WSNs are nvestgate. Keywors: Real-tme, relable, robust, congeston, energy consumpton. 1. Introucton The exstng an potental applcatons o WSNs span a very we range, nclung real tme target trackng an survellance, homelan securty, an bologcal or chemcal attack etecton [1]. Realzaton o these currently esgne an envsone applcatons, however, rectly epens on real-tme an relable communcaton capabltes o the eploye sensor/sub-snk network. In ths paper, a relable, robust an real-tme communcaton RRRT protocol s propose to aress the communcaton challenges ntrouce by the coexstence o sensors an sub-snks n WSNs. The RRRT protocol s a novel transport soluton that seeks to acheve relable an tmely event etecton wth

2 mnmum possble energy consumpton. The RRRT uses a ault tolerant optmal path (FTOP) [2] or ata elvery. It nclues a combne congeston control mechansm that serves the ual purpose o achevng relablty an conservng energy. The RRRT protocol operaton s etermne by the current network state base on the elay constrane event relablty an congeston conton n the network. I the elay constrane event relablty s lower than requre, RRRT ajusts the reportng requency o source noes aggressvely to reach the esre relablty level as soon as possble. I the relablty s hgher than requre, then RRRT reuces the reportng requency conservatvely to conserve energy whle stll mantanng relablty. Ths sel congurng nature o RRRT makes t robust to ranom, ynamc topology n WSNs. Furthermore, to aress the erent relablty requrements o sub-snk an sub-snk communcaton, RRRT ncorporates aaptve rate-base transmsson control an (SACK)-base relablty mechansm urng sub-snk an sub-snk communcaton. Perormance evaluaton va smulaton experments shows that RRRT acheves hgh perormance n terms o relable event etecton, communcaton latency an energy consumpton n WSNs. 2. RRRT Protocol Desgn Prncples Unlke tratonal networks, the sensor/sub-snk network paragm necesstates that the event eatures are collaboratvely estmate wthn a certan relablty an real-tme elay boun. To acheve ths objectve wth maxmum resource ecency, the RRRT protocol explots both the correlaton an the collaboratve nature o the network. In the ollowng sectons, we rst escrbe the characterstcs an challenges o both sensor/sub-snk an sub-snk/sub-snk communcaton an then base on these characterstcs, we scuss the man esgn components o the RRRT protocol n etal. 2.1 Relable Event Transport The RRRT protocol s equppe wth erent relablty unctonaltes to aress heterogeneous requrements o both sensor/sub-snk an sub-snk/sub-snk communcaton. Next, the man eatures o these relablty unctonaltes are escrbe.

3 2.1.1 Sensor/Sub-snk Transport Relablty In WSNs, sensor/sub-snk transport s characterze by the ense eployment o sensors that contnuously observe physcal phenomenon. Because o the hgh ensty n the network topology, sensor observatons are hghly correlate n the space oman. In aton, the nature o the physcal phenomenon consttutes the temporal correlaton between each consecutve observaton o the sensor. Because o these spatal an temporal correlatons along wth the collaboratve nature o the WSNs, sensor/sub-snk transport oes not requre 100% relablty [3], [4]. The RRRT protocol also consers the new noton o event-to-acton elay boun to meet the applcaton-specc ealnes. Base on both event transport relablty an event-toacton elay boun notons, we ntrouce the ollowng entons: 1. The observe elay-constrane event relablty ( o ) s the number o receve ata packets wthn a certan elay boun at the sub-snk noe n a ecson nterval. In other wors, o counts the number o correctly receve packets complyng wth the applcaton-specc elay bouns an the value o o s measure n each ecson nterval. 2. The esre elay-constrane event relablty ( ) s the mnmum number o ata packets requre or relable event etecton wthn a certan applcaton specc elay boun. Ths lower boun or the relablty level s etermne by the applcaton an base on the physcal characterstcs o the event sgnal beng tracke. 3. The elay-constrane relablty ncator (α) s the rato o the observe an esre o elay-constrane event relabltes,.e (1) Base on the packets generate by the sensor noes n the event area, the event eatures are estmate an o s observe at each ecson nterval to etermne the necessary acton. I the observe elay constrane event relablty s hgher than the relablty boun,.e., o >, then the event s eeme to be relably etecte wthn a certan elay boun. Otherwse, approprate acton nees to be taken to assure the esre relablty level n sensor/sub-snk communcaton.

4 2.1.2 Sub-snk-Sub-snk Transport Relablty In WSNs, a relable an tmely sub-snk-sub-snk a hoc communcaton s also requre to collaboratvely perorm the rght acton upon the sense phenomena [1]. The RRRT protocol smultaneously ncorporates aaptve rate-base transmsson control an (SACK)-base relablty mechansm to acheve 100% packet relablty n the requre a hoc communcaton. To acheve ths objectve, RRRT protocol reles upon new eeback base congeston control mechansms an probe packets to recover rom subsequent losses an selectve-acknowlegments (SACK) to etect any holes n the receve ata stream. These algorthms are shown to be benecal an eectve n recoverng rom multple packet losses n one roun-trp tme (RTT) especally [5]. 2.2 Real-Tme Event Transport To assure accurate an tmely acton on the sense phenomena, t s mperatve that the event s sense, transporte to the sub-snk noe an the requre acton s perorme wthn a certan elay boun. We call ths event-to-acton elay, e2a, whch s specc to applcaton requrements an must be met so that the overall objectve o the sensor/subsnk sub-snk network s acheve. The event-to-acton elay components as outlne below: e2a, has three man 1. Event transport elay ET el : It s manly ene as the tme between when the event occurs an when t s relably transporte to the sub-snk noe. In general, t nvolves the ollowng elay components: (a) Buerng elay ( B el ): It s the tme spent by a ata packet n the routng queue o an ntermeate orwarng sensor noe. It epens on the current network loa an transmsson rate o each sensor noe. (b) Channel access elay ( CA el ): It s the tme spent by the sensor noe to capture the channel or transmsson o the ata packet generate by the etecton o the event. It epens on the channel access scheme n use, noe ensty an the current network loa.

5 (c) Transmsson elay ( T el ): It s the tme spent by the sensor noe to transmt the ata packet over the wreless channel. It can be calculate usng transmsson rate an the length o the ata packet. () Propagaton elay ( P el ): It s the propagaton latency o the ata packet to reach the next hop over the wreless channel. It manly epens on the stance an channel contons between the sener an recever. 2. Event processng elay ( EP el ): Ths s the processng elay experence at the subsnk noe when the esre eatures o event are estmate usng the ata packets receve rom the sensor el. Ths may nclue a certan ecson nterval [3] urng whch the sub-snk noe wats to receve aequate samples rom the sensor noes. 3. Acton elay ( A el ): The acton elay s the tme t takes rom the nstant that event s relably etecte at the sub-snk noe to the nstant that the actual acton s taken. It s compose o the task assgnment elay,.e., tme to select the best set o sub-snks or the task an the acton executon elay,.e., tme to actually perorm the acton. For a tmely acton t s necessary that the ollowng relaton hols: B EP A (2) e2a el el el 2.3 Congeston Detecton an Control Mechansm In WSNs, because o the memory lmtatons o the sensor noes an lmte capacty o share wreless meum, congeston mght be experence n the network. Congeston leas to both waste o communcaton an energy resources o the sensor noes an also hampers the event etecton relablty because o packet losses [3]. Hence, t s manatory to aress the congeston n the sensor el to acheve real-tme an relable event etecton an mnmze energy consumpton. Only the sub-snk noe, an not any o the sensor noes, can etermne the elay-constrane relablty ncator, o an act accorngly. 3. RRRT Protocol Operaton or Sensor-Sub-snk Communcaton

6 In ths secton, we escrbe the RRRT protocol operaton urng sensor/sub-snk communcaton. Recall that n the prevous sectons, base on the elay-constrane event relablty an the event-to-acton elay boun notons, we ha ene a new elay- constrane relablty ncator o,.e., the rato o observe an esre elayconstrane event relabltes. To etermne proper event reportng requency upate polces, we also ene T an T sa, whch are the amount o tme neee to prove elayconstrane event relablty or a ecson nterval an the applcaton specc sensor/sub-snk communcaton elay boun, respectvely. In conjuncton wth the congeston notcaton normaton (CN bt) an the values o, α, T an T sa, the subsnk noe calculates the upate reportng requency, +1, to be broacast to source noes n each ecson nterval. Ths upatng process s repeate untl the optmal operatng pont s oun,.e., aequate relablty an no congeston conton are obtane. In the ollowng sectons, we escrbe the etals o the reportng requency upate polces an possble network contons experence by the sensor noes. 3.1 Early Relablty an No Congeston Conton In ths conton, the requre relablty level specc to applcaton s reache beore the sensor/sub-snk communcaton elay boun,.e., T T sa, an no congeston s observe n the network,.e., CN = 0. However, the observe elay-constrane event relablty,, s larger than esre elay-constrane event relablty, o Ths s because source noes transmt event ata more requently than requre. The most mportant consequence o ths conton s excessve energy consumpton o the sensors. Thereore, the reportng requency shoul be ecrease cautously to conserve energy. Ths reucton shoul be perorme cautously so that the elay-constrane event relablty s always mantane. Thereore, the sub-snk noe ecreases the reportng requency n a controlle manner. Intutvely, we try to n a balance between savng energy an mantanng relablty. Hence, the upate reportng requency can be expresse as ollows: T 1 (3) Tsa

7 3.2 Early Relablty an Congeston Conton In ths conton, the requre relablty level specc to applcaton s reache beore the sensor/sub-snk communcaton elay boun,.e., T T, an congeston s observe n the network,.e., CN = 1. However, the observe elay-constrane event relablty, o, s larger than the esre elay-constrane event relablty, sa.in ths stuaton, the RRRT protocol ecreases reportng requency to avo congeston an save the lmte energy o sensors. Ths reucton shoul be n a controlle manner so that the elay-constrane event relablty s always mantane. However, the reportng requency can be ecrease more aggressvely than the case where there s no congeston an the observe elay-constrane event relablty, elay-constrane event relablty, o, s larger than the esre. Ths s because n ths case, we are arther rom optmal operatng pont. Here, we try to avo congeston as soon as possble. Hence, the upate reportng requency can be expresse as ollows: T T T 1 mn, sa (4) Tsa 3.3 Low Relablty an No Congeston Conton In ths conton, the requre relablty level specc to applcaton s not reache beore sensor-sub-snk communcaton elay boun,.e. T T sa, an no congeston s observe n the network,.e., CN = 0. However, the observe elay-constrane event relablty, s lower than the esre elay-constrane event relablty,. The o RRRT protocol can work wth any o these routng schemes. Thereore, to acheve requre event relablty, we nee to ncrease the ata reportng requences o source noes. Here, we explot the act that the congeston,.e., or max Dr vs relatonshp n the absence o s lnear. In ths regar, we use the multplcatve ncrease strategy to calculate upate reportng requency, whch s expresse as ollows: 1 (5) o

8 3.4 Low Relablty an Congeston Conton In ths conton, the requre relablty level specc to applcaton s not reache beore sensor-sub-snk communcaton elay boun,.e., T T sa, an congeston s observe n the network,.e., CN = 1. However, the observe elay-constrane event relablty, o, s lower than the esre elay-constrane event relablty, Ths stuaton s the worst possble case, snce esre elay-constrane event relablty s not reache, network congeston s observe an thus, lmte energy o sensors s waste. Hence, the RRRT protocol aggressvely reuces reportng requency to reach optmal reportng requency as soon as possble. Thereore, to assure sucent ecrease n the reportng requency, t s exponentally ecrease an the new requency s expresse by: o ( X ) 1 (6) Where x enotes the number o successve ecson ntervals or whch the network has remane n the same stuaton nclung the current ecson nterval,.e. x 1. Here, the purpose s to ecrease reportng requency wth greater aggresson, a network conton transton s not etecte. 3.5 Aequate Relablty an No Congeston Conton In ths conton, the network s wthn β tolerance o the optmal operatng pont,.e., an, 1 1 an no congeston s observe n the network. Hence, the max reportng requency o source noes s let constant or the next ecson nterval: 1 (7) Here, our am s to operate as close to 1 as possble, whle utlzng mnmum network resources an meetng event elay bouns. For practcal purposes, we ene a tolerance level, β, or optmal operatng pont. The entre RRRT protocol operaton s presente n the pseuo-algorthm gven n Fgure 1

9 x=1 ; RRRT() I (Congeston) I ( 1) /* Low Relablty an Congeston */ o ( X ) 1 ; x x 1 ; else ( 1) /* Early Relablty an Congeston */ x 1 ; T mn, Tsa en; T T 1 sa ; else (No Congeston) x 1; ( 1 ) /* Low Relablty an No Congeston */ 1 ; o else ( 1 ) /* Early Relablty an No Congeston */ 1 T T sa ; en; en; en; else 1 1 /* Aequate Relablty an No Congeston */ 1 ; Fgure 1 Algorthm o RRRT

10 4. RRRT Protocol Operaton or Sub-snk/Sub-snk Communcaton In ths secton, we escrbe the protocol operaton o RRRT urng Sub-snk/Sub-snk communcaton. The protocol operaton s compose o two man states: ) Start-up state, ) Steay state. In Fgure 2, the RRRT protocol state agram or Sub-snk/Sub-snk communcaton s shown. The operatons at each state are escrbe n etal. 1. Start-Up State: When establshng new connecton between sener an recever, the sener transports a probe packet towars the recever to capture the avalable transmsson rate quckly. Each ntermeate noe between the sener an recever ntercepts the probe packet an upates the bottleneck elay el o the probe packet, the current value o elay normaton s hgher than that o the ntermeate noe. Start up State t = RTT Hol CN=0 R_ R_c bk CN =1 Probe R_>R_c Increase No_bk Decrease CN=1 Fgure2 RRRT protocol state agram or Sub-snk/Sub-snk communcaton

11 Intally, the elay value o probe packet s assgne to zero. Thereore, ater one roun-trp-tme, the sener gets estmate rate eeback rom the recever, whch results n quck convergence to avalable transmsson rate. Furthermore, ths probng mechansm o start up phase s also apple ater route changes. 2. Steay State: Ths state conssts o our sub states: ) Increase, ) Decrease, ) Hol an v) Probe. In the ollowng, we escrbe the RRRT protocol operatons n each sub state: (a) Increase: In ths state, the sener ncreases ts transmsson rate accorng to the eeback comng rom the recever. Once an ncrease ecson or sener transmsson rate s taken, only m racton o the erence between transmsson rate eeback (R_ ) an sener current transmsson rate (R_c) s perorme. The approprate racton value ( m ) or the transmsson rate ncrease s obtane as ollows: I the hop count along the ata path s greater than or equal to 4 or that connecton, m s set to 4. Otherwse, the hop count s less than 4, then m s set to the actual hop count value along the path. The nherent spatal reuse property o unerlyng CSMA/CA base MAC protocol requres ths normalzaton n transmsson rate. (b) Decrease: In ths state, the sener reuces ts transmsson rate accorng to the eeback comng rom the recever. Note that the transmsson rate s ecrease untl the mnmum transmsson rate (R mn ) s reache. R mn represents the mnmum transmsson rate requrement to transer a certan amount o ata wthn event-toacton elay boun. R mn can be calculate as ollows: R mn B re2a where B represents the amount o packets that shoul be transmtte to the sub-snk an re2a s remanng event-to-acton ealne. (c) Hol: In ths state, the requre transmsson rate s reache. Sener oes not change the transmsson rate unless route alure or congeston occurs n the network.

12 () Probe: In ths state, the sener sens a probe packet to the recever so as to montor the avalable transmsson rate n the network as n start up phase. Overall, the RRRT protocol ynamcally shapes ata trac base on both elay bouns an the current contons o the network. Note that, n the protocol operaton, the sener ajusts ts transmsson rate n response to the rate eebacks rom the recever, whch are sent wth the pero ot bk. To prevent the sener rom over loong the network n case all the eeback packets rom the recever are lost, the RRRT protocol also perorms a multplcatve ecrease o transmsson rate or each eeback peros, n whch the sener oes not receve eeback rom the recever up to a maxmum o two eeback peros. Ater the secon eeback pero, the sener stll oes not receve any eeback packet, t enters nto probe state so as to montor the avalable transmsson rate n the network. In ths respect, the peros o eeback T bk an probe packets T p shoul be larger than one roun-trp-tme (RTT) an small enough to capture the network ynamcs. 5. RRRT Perormance Evaluaton 5.1 Sensor/Sub-snk Communcaton To evaluate the perormance o the RRRT protocol urng sensor-sub-snk communcaton, we evelope an evaluaton envronment usng J-Sm [6]. For sensor/sub-snk communcaton scenaro, the number o sources, sensor/sub-snk elay boun an tolerance level were selecte as n 81, 1s an 5%, respectvely. The event raus was xe at 45m. We run 10 experments or each smulaton conguraton. Each ata pont on the graphs s average over 10 smulaton runs. Moreover, n ths smulaton scenaro, the sub-snk noes, whch receve ata packets rom sensors, stop ther movements once they start to receve ata. To urther nvestgate RRRT protocol convergence results, we have compare RRRT protocol, ESRT [3], ATP [5], SPEED [7] protocols n terms o convergence tme to (Aequate relablty, No congeston) conton an total energy consumpton. The reason or comparson wth ESRT an ATP s that both o them are base on event transport relablty noton unlke the other transport layer protocols aressng conventonal ento-en relablty n WSNs. SPEED are a well known real tme communcaton protocol.

13 Convergence tme Energy consumpton(j) As shown n gure 3 an gure 4, the convergence tme an total energy consumpton o the RRRT protocol are much smaller than those o ESRT, ATP an SPEED or erent ntal network contons. Ths s because ESRT an ATP o not conser applcatonspecc elay bouns whle avong network congeston an ajustng reportng rate o sensor noes ESRT ATP SPEED RRRT ATP ESRT SPEED RRRT Frequency Frequency Fgure 3 Convergence tme Fgure 4 Energy Consumpton 5.2 Sub-snk/Sub-snk Communcaton For sub-snk/sub-snk communcaton scenaro, the perormance o the RRRT protocol s evaluate an compare aganst ESRT [3], ATP [5] an SPEED [7]. The man perormance metrcs that we employ to measure the perormance o the RRRT protocol are aggregate throughput an average packet elay. Here, the aggregate throughput relects the number o packets successully receve at the estnaton. By average packet elay, we reer to average latency o ata packets urng sub-snk/sub-snk communcaton. All the smulatons last or 1000 s. We run 10 experments or each smulaton conguraton an each ata pont on the graphs s average over 10 smulaton runs. In Fgure 5, we present the aggregate throughput results o the RRRT protocol an other a hoc transport protocols,.e. ATP, ESRT an SPEED. In terms o aggregate throughput, the RRRT protocol outperorms other transport protocols uner comparson, snce RRRT ynamcally shapes ata trac accorng to the channel conton an ntermeate noe eebacks. In Fgure 6, we also show the average packet elay results

14 Throughput(Kbps) Average Delay(s) o the RRRT an the other transport protocols. As shown n Fgure 6, or all smulaton conguratons, the average packet elay values o RRRT are much lower than those o other protocols, snce RRRT captures the avalable banwth n the network quckly an oes not allow a burst o packet transmssons wth explct congeston notcaton an rate eeback base mechansms ATP ESRT SPEED RRRT ATP ESRT SPEED RRRT Maxmum Spee Maxmum Spee Fgure 5 Throughput Fgure 6 Average Delay 6. Conclusons In ths paper a real-tme an relable transport RRRT protocol was propose to aress the communcaton challenges ntrouce by the coexstence o sensors/sub-snks n WSNs. The RRRT protocol s a novel transport soluton that seeks to acheve relable an tmely event etecton wth mnmum possble energy consumpton. It nclues a combne congeston control mechansm that serves the ual purpose o achevng relablty an conservng energy. The RRRT protocol operaton s etermne by the current network state base on the elay-constrane event relablty an congeston conton n the network. The RRRT uses a ault tolerant optmal path or ata elvery. I the elay-constrane event relablty s lower than requre, RRRT ajusts the reportng requency o source noes aggressvely to reach the esre relablty level as soon as possble. I the relablty s hgher than requre, then RRRT reuces the reportng requency conservatvely to conserve energy whle stll mantanng relablty. Ths sel congurng nature o RRRT makes t robust to ranom, ynamc topology n WSANs. Furthermore, to aress the erent relablty requrements o sub-snk-sub-

15 snk communcaton, RRRT ncorporates aaptve rate-base transmsson control an (SACK)-base relablty mechansm urng sub-snk-sub-snk communcaton. Perormance evaluaton va smulaton experments shows that RRRT acheves hgh perormance n terms o relable event etecton, communcaton latency an energy consumpton n WSNs. Reerences [1] Akylz, I. F., Meloa, T., an Chowhury, K., A Survey on Wreless Multmea Sensor Networks, Computer Networks (Elsever), vol. 51, pp , March [2] Vrman,D., Jan,S., Fault Tolerant Optmal Path or Data Delvery n Wreless Sensor Networks, Acm Dgtal Lbrary, o: / ,pp-7-12, June [3] Akan, O. an Akylz, I. F., Event-to-Snk Relable Transport n Wreless Sensor Networks," IEEE/ACM Transactons on Networkng, vol. 13, pp , October [4] Vuran, M. C., Akan, O. B., an Akylz, I. F., Spato-Temporal Correlaton: Theory an Applcatons or Wreless Sensor Networks," Computer Networks Journal (Elsever), vol. 45, pp , June [5] Sunaresan, K., Anantharaman, V., Hseh, H.-Y., an Svakumar, R., ATP: A Relable Transport Protocol or A-hoc Networks," n Proceengs o ACM MOBIHOC 2003, (Annapols, MD USA), June [6] The Java Network Smulator, J-sm-2. January [7] Tan He, John A Stankovc, Chenyang Lu, an Tarek Abelzaher. SPEED: A stateless protocol or real-tme communcaton n sensor networks. Internatonal Conerence on Dstrbute Computng Systems (ICDCS 2003) May 2003.