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1 Deakn Research Onlne Ths s the publshed verson: Chellappa Doss, Robn, Chandra, D., Pan, L., Zhou, Wanle and Chowdhury, Morshed 6, Address reuse n wreless sensor networks, n ATNAC, Australan Telecommuncaton Networks and Applcatons Conference, 6., Australan Telecommuncaton Networks & Applcatons Conference, Melbourne, Vc, pp. 9-. Avalable from Deakn Research Onlne: Every reasonable effort has been made to ensure that permsson has been obtaned for tems ncluded n Deakn Research Onlne. If you beleve that your rghts have been nfrnged by ths repostory, please contact drosupport@deakn.edu.au Copyrght : 6, ATNAC

2 Address Reuse n Wreless Sensor Networks R. Chellappa Doss, D. Chandra, L. Pan, W.Zhou, M. Chowdhury School of Engneerng and Informaton Technology Deakn Unversty, Burwood Hwy, Vctora 5, Australa. {rchell, dchandra, ln, wanle, muc}@deakn.edu.au Abstract Sensor Networks have applcatons n dverse felds. Whle unque addressng s not a requrement of many data collectng applcatons of wreless sensor networks, t s vtal for the success of applcatons such as emergency response. Data that cannot be assocated wth a specfc node becomes useless n such stuatons. In ths work we propose a dynamc addressng mechansm for wreless sensor networks. The scheme enables successful reuse of addresses n event-drven wreless sensor networks. It also elmnates the need for network-wde Duplcate Address Detecton (DAD) to ensure unqueness of network level addresses. Keywords Wreless Sensors, System Desgn. I. INTRODUCTION Wreless sensor networks (WSN) represent the next step n the evoluton of wreless communcaton. They are self-organzng networks that do not depend on a fxed communcaton nfrastructure []. An applcaton that s becomng ncreasngly attractve s the use of WSNs for emergency (frst) response n mass casualty ncdents. It s envsoned that these networks wll play a pvotal role n dsaster response and recovery []. WSN applcatons can be categorzed as ether datacentrc or node-centrc applcatons. Whle both categores of applcatons are concerned wth data montorng/collectng, data-centrc applcatons do not requre the node of data generaton to be unquely dentfed. Unlke n data-centrc applcatons, nodecentrc applcatons requre the dentty of the node of data generaton. In such applcatons data that s collected becomes useless f the source (sensor node) cannot be unquely dentfed. An example s vtal-sgn montorng applcatons such as n emergency response [] []. Two levels of nformaton can be dentfed n sensor nodes events and data. Events are defned as crtcal data that s generated by a node [5] (e.g., a patent s vtal sgn measurement falls below a crtcal threshold or enemy movement has been detected). In event-drven sensor networks only events are of nterest and need to be communcated to the snk. In ths work, we propose an On-demand Locaton Aded Addressng mechansm that can enable address reuse by explotng the random nature of event occurrence n large scale WSNs. In secton II we present related work followed by our proposed scheme n Secton III. Analyss of the scheme s presented n Secton IV. We conclude wth fnal comments n Secton V. II. RELATED WORK The need for effcent addressng schemes s well artculated wth varous addressng schemes proposed n lterature [] [5] [6] [7] [8] [9]. In [] an energy-effcent node addressng scheme usng spatal reuse of locally unque addresses s presented. Nodes are organzed n a herarchy of logcal layers and used to satsfy the unqueness condton. TreeCast [5] s a stateless addressng scheme proposed for effcent addressng. It requres the constructon of multple dsjont trees. A smlar scheme [8] s based on the concept of herarchcal levels and repeated patterns and supports self-organzaton n sensor networks. In [] a dstrbuted on-demand addressng mechansm s proposed for assgnment of MAC addresses. It explots spatal reuse of addresses and uses Huffman codng to reduce the address length n the packer header. Event-drven addressng has been proposed n [7]. Local unqueness between mmedate neghbors s amed for wth lnk level addressng whle an on-demand mechansm for network level addressng s proposed. The addressng protocol s coupled wth the routng protocol and employs Duplcate Address Detecton (DAD). In [6], data aggregaton and dluton by modulus addressng s proposed whle an addressng mechansm based on a herarchcal archtecture usng de Brujn graphs s proposed n [9]. All of the above addressng schemes place the complexty of the addressng process on the sensor nodes by nsstng on strct organzaton or by DAD through floodng. In our work the complexty s removed from the sensor nodes to the network control centre (snk). III. DYNAMIC ADDRESSING FOR WSNS The proposed addressng mechansm s an on-demand addressng protocol that employs a lease-based approach for address assgnment. It explots the random nature of event occurrence n event-drven sensor networks. Snce events occur at random, addresses can be assgned and released n a dynamc manner enablng the reuse of addresses. In large scale sensor networks such an approach wll reduce the overhead of addressng qute sgnfcantly. Locaton awareness s a requrement of many WSN applcatons [6]. The proposed mechansm ncorporates locaton awareness and works wth both absolute and relatve levels of awareness. The proposed

3 addressng scheme has fve man phases of operaton. We shall dscuss the operatons of each of these phases n detal below. A. Boot Up Phase The dynamc addressng mechansm s used only for the assgnment of network level addresses. Durng the boot up phase each node self-assgns a lnk-level address that s locally unque. The assgnment of the lnk-level address proceeds along smlar lnes as descrbed n [7]. The negotated lnk-level address s assgned permanently to a node and s only reassgned n the event of the orgnal node dyng or reconfguraton when new nodes jon the network. Durng the boot up phase the Snk (S) broadcasts a confguraton packet that contans the locaton of the snk (x, y co-ordnates). The purpose of ths confguraton packet s to allow each of the sensor nodes to calculate ther dstances from the snk. A sensor node s deemed to have successfully joned the network (booted) only after the recepton of ths confguraton packet. The dstance of the sensor node from the snk, d,sink s calculated accordng to (). Snce the sensor nodes are relatvely statonary, recalculaton of the dstance s not requred after boot up. Each sensor node s assumed to be connected to a locaton devce such as a GPS recever. It s to be noted that the use of GPS measurements s only needed durng the boot up phase and hence the overhead of locaton awareness wll not be sgnfcant (.e., once d,sink has been calculated the GPS recever s turned off to conserve energy). Alternate boot up procedures based on parent nodes and tree-based routng can also be used. d, SINK ( xsink x ) ( ysink y ) () Snce the topology of wreless sensor networks s dynamc, t s possble that new nodes wll jon the network ether to replace nodes that have faled (ded) or to expand the network. To complete self-confguraton a new sensor node jonng the network sends a jon request that s receved by all nodes wthn ts transmsson range. The one-hop neghbours respond to the jon request wth a confguraton packet (they have prevously receved from the snk) that contans the locaton nformaton of the snk. On the recepton of ths confguraton packet the bootup phase s completed. The purpose of the locaton nformaton s to enable energyeffcent forwardng of messages. B. Address Request Phase Once a node has successfully completed the boot up phase t becomes a canddate for address request. A node performs ts data montorng functon wth lmted levels of local processng to generate an event. In order for the event to be communcated relably to the snk a network level address s requred to dentfy the source of the event at the snk (lnk-level addresses are only locally unque). The node generates an address_request packet of the form {Source, Type, event_id, motedst, motedst Source }. Source s the lnk level address of the requestng node, Type denotes the type of packet and doubles as an dentfer for the destnaton of the address request packet (snce all address requests are destned for the snk), event_id s an dentfer for the specfc event generatng the request and s used to map an address allocaton to the correspondng address_request, motedst Source s the dstance of the requestng sensor node from the snk calculated usng () and motedst s the dstance of the forwardng node from the snk. motedst s used by forwardng nodes n ther decson makng process (.e., to decde f a node s closer to the snk than the forwardng node to t). The dstance of the requestng sensor s ncluded n the address request packet as the Snk s not aware of the locaton of the deployed sensors. The event_id carred n the address request packet s generated usng a random functon that takes the lnk-level address of the sensor node as an nput to unquely dentfy the address request and to match the correspondng reply (address allocaton) from the snk to the orgnal address request. Ths s needed as the lnk-level addresses are only locally unque. Forwardng of the address request from the sensor node to the snk s done makng use of lmted-scope floodng. Ths s acheved makng use of the dstance rule. We defne the dstance rule to be a node j forwards an address request from node only f t s closer to the snk than node (.e., the forwardng node to t). The dstance rule has been prevously used n locaton aded routng protocols [] for moble ad hoc networks and s shown to be an effectve mechansm. The dstance rule effectvely creates a multcast group towards the snk and hence s dfferent from greedy forwardng (that can suffer from local ma). A forwardng node wll change the value of motedst n the address request packet to ts own motedst j to enable ts neghbours to apply the dstance rule. The value of motedst Source remans unchanged. C. Address Allocaton Phase The snk mantans an address_allocaton table wth a lst of addresses and a correspondng status flag for each address. On the recept of an address_request the snk allocates a free address to the requestng node based on avalablty or alternatvely dscards the request. The snk also has the opton to queue the request untl an address becomes avalable or for a pre-defned tme nterval. In our analyss and smulatons for the sake of tractablty address requests are not queued. On the recept of the address_request packet the snk responds wth an address_allocaton packet of the form {Source Type, event_id, motedst Source, Address, motedst }. Source denotes the lnk level address of the destnaton sensor, Type denotes the packet type and also doubles to dentfy the sender as the Snk, event_id s coped to the address_allocaton packet from the correspondng address_request packet and s used to match the address_allocaton message to the requestng sensor, motedst Source denotes the dstance of the requestng sensor from the snk and s coped from the

4 address request packet. Address denotes the allocated address; motedst denotes the dstance of the node that forwarded the orgnal address_request message to the snk. Lmted scope floodng usng the dstance rule s agan employed to forward the reply to the requestng node. However, some modfcaton s requred to make t effcent. At the frst nstance the address allocaton message s uncast usng motedst and the lnk level address to the node that forwarded the address request message. On recevng ths message the node then employs the dstance rule wth respect to the destnaton sensor. All calculatons are wth respect to the destnaton sensor and are done usng the value of motedst Source. Ths requres that the locaton nformaton (motedst Source ) of the fnal destnaton sensor s ncluded n the reply message generated by the snk. On sendng of the address_allocaton the snk stores the locaton nformaton of the requestng sensor node and the event_id and assocates ths par wth a network level address. SINK Tmer Broadcast packet sent SINK Req_Add pkt rcvd, Resp_Req_Add pkt sent Release_Add pkt rcvd Assgned Addr Released Tmer stopped T Sensor Node Broadcast packet rcvd, Req_Add pkt sent Resp_Req_Add pkt rcvd Release Add pkt sent Fgure. A Typcal Address Request, Allocaton and Release When the snk sends out an address allocaton response t starts a tmer (lease_tmer) that s assocated wth the allocated address. The value of ths tmer s set to T whch s the longest amount of tme that a node s allowed to hold on to an address. We refer to ths tme as a lease. T can be a fxed value. However there s the scope of extendng ths to dfferentate between dfferent classes of events. On the expry of the lease.e., lease_tmer the address becomes avalable for allocaton to a new node requestng an address. Along smlar lnes prorty queung can also be used to servce address requests that have been queued D. Address Release Phase To enable reuse of addresses and optmzaton of the sze of the address space, addresses are not allocated on a permanent bass to each sensor node. Instead, we adopt a lease based approach. Each address s held by a sensor for a perod of tme (less than T ) untl t completes communcaton related to an event. When communcaton s completed the sensor node explctly releases the address enablng the snk to reuse the address (pror to expry of T ) for another node. The success of lease based schemes depends on the Addr. Held effectveness of the lease management mechansm. We adopt a dstrbuted lease management mechansm for our scheme by combnng the snk based lease_tmer wth a node-based address release mechansm. The lease_tmer specfes the mum tme that a node can hold on to an address whle the node based address release mechansm enables release of an address pror to the expry of the lease_tmer. It can be argued that a purely snk-based scheme s preferable to reduce the computatonal load on ndvdual sensors. However, n event-drven networks a dstrbuted approach s more benefcal as t enables effcent reuse of addresses. When a node decdes to release an address t sends an address_release message of the form {Source, Type, motedst, Release_Address} to the snk. Source ndcates the lnk level address of the node, Type dentfes the packet as beng destned to the snk, motedst s the dstance of the forwardng node from the snk and Release_Address s the network level address beng released. The snk on recept of an address_release message deallocates the specfc address whch allows for the address to be reused by other nodes n the network. The release of the address s controlled entrely by the sensor nodes whle the address allocaton s controlled entrely by the snk nodes. The advantage of centralsed address allocaton controlled at the snk s that DAD can now be done at a central pont. In comparson, other schemes perform DAD by floodng the entre network to see f a duplcate address exsts across the network. Fgure llustrates a typcal address request, allocaton and release wth no packet loss. SINK Tmer Extended Broadcast packet sent Req_Add pkt rcvd, Resp_Req_Add pkt sent Rebndng Add OK Rebndng_ACK sent SINK T Release_Add pkt rcvd Tmer stopped Assgned Add Released T Sensor Node Broadcast packet rcvd, Req_Add pkt sent Event # Resp_Req_Add pkt rcvd Event # Occurs Rebndng_Addr pkt sent Rebndng_ACK pkt rcvd Release_Add pkt sent Fgure. A Typcal Address Rebnd and Address Release E. Address Rebnd Phase In order to further ncrease the reuse of addresses and reduce the overhead nvolved n address allocaton we allow nodes to also rebnd an address. The overhead of rebndng an address s much less n comparson to the overhead nvolved n address request/allocaton. The condton for the extenson of a lease s the occurrence of a new event pror to the release (.e., expry of the lease) of the current address. On the occurrence of a new event the sensor node sends out an address_rebnd message of the form {Source, Type, event_id, Address, motedst }. The felds have the same meanng as n earler phases. Addr. Held/Extended

5 Forwardng nodes employ the dstance rule usng motedst. When the snk receves the address_rebnd message t checks to see that the address has not already been released on the Snk (.e., the lease_tmer has expred). If the address s stll bound on the snk t responds wth an acknowledgement (rebnd_ack) message of the form {Source, Type, Address, motedst, motedst Source }. Address represents the address that has been rebound and mote_dst Source, Source and event_id are used for forwardng and to dentfy the destnaton sensor node. When the snk receves an address_rebnd t resets the lease_tmer and the address s held for a perod T from the tme of rebnd. We reset the lease_tmer as falure to do ths can result n the address beng released on the Snk pror to release on the sensor node. It s also mperatve that the lease_tmer s assocated wth the current event. A sensor node assumes a successful rebnd only after the recept of a rebnd_ack message. The arrval of the rebnd_ack message does not have to be pror to completon of communcaton assocated wth the prevous event. However, f communcaton of the prevous event s completed pror to the recept of rebnd_ack then an address_release message s not sent. Instead on completon the node sends an address_request message. The ratonale behnd ths desgn s that n the event of a rebnd_ack arrvng after the completon of the communcaton assocated wth the prevous event the address s stll usable as t has been bound (for a perod T ) on the Snk. There s also not a need to explctly release the address n the event of the address_rebnd message beng lost as ths s addressed by the use of the lease_tmer (worst case scenaro). Further, the duplcate address_request wll be gnored by the snk. A typcal address rebnd scenaro wth no packet loss s presented n Fgure. IV. PROBABILITY OF ADDRESS ALLOCATION Our dynamc addressng protocol ssues and renews a network level address wth respect to a sensor s request; and, every allocated address wll be recycled by the snk on a gven tmeout value T. We assume a mal message loss rate s observable across the network. n n- n n- n- n- n- Fgure. State Machne of A Snk wth n Address Suppose a snk has n addresses, we then construct a state machne consstng of n state - states n to guarantee the address allocaton/renewal and state means denal of request. For each address n, two transtve actons - and are assocated wth address release/tmeout events and address allocaton/renewal events respectvely. Accordng to the defnton of Markov Chan [], the above state machne corresponds to the followng equaton of a probablty functon set P(t) and a transton matrx Q(t): P P( t) Q(t) () where P [ P, P,, P ] and Q( t) n ( ) n ( ) ( ) ( ) () For n, we get these two equatons after matrx multplcaton: P P P P P ( ) P P ( ) t () At any gven tme t, the snk ether ssues an address or denes the request,.e., Pn Pn P. At the ntal moment t after the Boot Up phase, the snk has n address, so P n () and P (). The sensor network reaches state f most addresses are allocated and many request and/or rebndng messages arrve smultaneously. On any stablzed network, the dervatve of the probabltes of each state tends to be zero. Therefore, we have P P P ( ) P P ( t) (5) Solvng these dfferental equatons, we wll get the soluton for the possblty of successfully acqurng an address from the snk P(t) P (t) P P P P P P Hence, we derve the lmt of P ( ) when t as: lm P t n t (6) (7) The successful possblty of address acquston,.e., the sum of possbltes of all states other than state, s equal to

6 n P n n n The value of success probablty of address allocaton ncreases provded a bgger rato of the product of over the product of, when the success probablty value approaches to ; and vce versa, a smaller rato of the product of over the product of gves a success probablty close to. The value of depends on the frequences of address release events and tmeout events; and the value of depends on the frequences of address request events and rebnd events. The rato of / s affected by message loss rate of the network - the loss of request and rebnd messages decreases and the loss of release messages ncreases, and the ncrement of the rato depends on whch loss rate s domnant. Suppose N ndependent events occurs at a frequency of /t mn and each lasts t, together wth n avalable addresses and the tmeout value T at the snk, we derve the rato of / n the followng scenaros: (8) No loss transmsson assumes no packet loss across the network. Thus, N request events, n rebnd events, release events and tmeout events occur at frequences of /t mn, / T t, /t and /T on the network respectvely. The rato of / becomes n n t T (9) N n t T t mn Symmetrc loss transmsson assumes consstent packet loss across the network at the rate c. So, ( c)(n ) request events, ( c)(n ) rebnd events and release events occur at frequences of /t mn, / T t and /t respectvely. The n tmeout events are not affected by the transmsson loss and occur at the frequency of /T. Therefore, the rato of / becomes n n t ( c) T () N n t T t mn Asymmetrc loss transmsson assumes messages are lost at dfferent rates - c from the snk to nodes, c from nodes to the snk. So, ( c c )(N ) request events, ( c c )(n ) rebnd messages and ( c )(n ) release messages occur at frequences of /t mn, / T t and /t respectvely. The n tmeout events are not affected by the transmsson loss and occur at the frequency of /T. Therefore, the rato of / becomes ( c ) ( n ) n t T () ( c c ) ( N ) ( c c ) ( n ) t mn T t Formula (9) () () suggest that the success rate of n address allocaton, essentally n ncreases when T t or t mn ncreases, or t or T decreases. Because t mn and t are determned by the events, the only vable approach s to confgure T, so that the address can be tmed out mmedately after events fnsh, whch s the focus of our future work on adaptve lease mechansms. V. CONCLUSIONS AND FUTURE WORK In ths work we have presented an addressng mechansm that s capable of achevng address reuse. Intal smulaton results (not presented due to space lmtatons) show the scheme to offer an address reuse factor of more than.5 wth mnmal address allocaton delays (around.6secs). In our future work we hope to evaluate the performance of the scheme through more detaled smulatons and nvestgate adaptve leases. REFERENCES []. K Lorncz et al., Sensor Networks for Emergency Response: Challenges and Opportuntes, IEEE Pervasve computng, Volume (), Oct-Dec, pp 6-. []. Vjay Kumar et al., Robot and Sensor Networks for Frst Responders, IEEE Pervasve computng, Volume (), Oct-Dec, pp -. []. M. Al and Z. A. Uzm, An Energy-Effcent Node Address Namng Scheme for Wreless Sensor Networks, Proceedngs of the IEEE Internatonal Networkng and Communcatons Conference (INCC ), June. []. C. Schurgers, G.Kulkarn, M.B. Srvastava, Dstrbuted On- Demand Address Allocaton n Wreless Sensor Networks, IEEE Transactons on Parallel and Dstrbuted Systems, Volume (), Oct, pp [5]. S. PalChaudhur et al., TreeCast: A Stateless Addressng and Routng Archtecture for Wreless Sensor Networks, Proceedngs of the 8 th Internatonal Parallel and Dstrbuted Processng Symposum (IPDPS ),. [6]. E. Cayrc, Data Aggregaton and Dluton by Modulus Addressng n Wreless Sensor Networks, IEEE Communcaton Letters, Volume 7(8), August. [7]. S. Moteg et al., Implementaton and Evaluaton of On-Demand Address Allocaton for Event-drven Sensor Network, Proceedngs of the 5 Symposum n Applcatons and the Internet (SAINT 5), January 5. [8]. J. Jobn et al., A Scheme for the Assgnment of Unque Addresses to Support Self-Organsaton n Wreless Sensor Networks, Proceedngs of the 6 th Vehcular Technology Conference (VTC ), September. [9]. T. Huynh and C. Hong, A Novel Addressng Archtecture for Wreless Sensor Network, th IEEE Performance Computng and Communcatons Conference (PCCC 5), Aprl 5. [].Y. B. Ko and N. H. Vadya, Locaton Aded Routng (LAR) n Moble Ad Hoc networks, Proceedngs of ACM/IEEE MOBICOM 98, Oct.998, pp [].John G. Kemeny and J. Laure Snell, Fnte Markov Chans, Publshed Prnceton, N.J.: Van Nostrand, 96,