Maagemet of Wireless Sesor etworks usig TCP/IP Markus Awader, Gerald Wagekecht, ad Torste Brau Istitute of Computer Sciece ad Applied Mathematics Uiversity of Ber, Switzerlad Email: {awader, wage, brau}@iam.uibe.ch Abstract To allow remote maagemet of heterogeeous wireless sesor etworks (WSs), the WSs should be coected to the Iteret. To overcome this problem, we propose a commuicatio ifrastructure, which icludes a wireless mesh etwork (WM) operatig as a backboe etwork. I order to realize such itercoectio betwee the WS ad a exteral etwork without ay proxies or middle-boxes, we propose to use TCP/IP as the stadard protocol for all etwork etities, e.g., for cofiguratio ad uploadig applicatio code to the sesor odes. We preset a cross layer desiged commuicatio architecture which cotais a MAC protocol, TCP/IP, ad a protocol called TCP Support for Sesor odes (TSS). The MAC protocol implemets the MAC layer of obeaco-eabled persoal area etworks (PAs) defied i the IEEE 8.. stadard for peerto-peer topologies. TSS is located betwee TCP ad IP ad implemets mechaisms such as cachig ad local retrasmissio of TCP data packets, local TCP ackowledgmet regeeratio, aggressive TCP ackowledgmet recovery, cogestio ad flow cotrol algorithms. We show that our commuicatio architecture icreases the performace of TCP/IP i WSs sigificatly. I. ITRODUCTIO Wireless sesor etworks (WSs) cosist of a large umber of sesor odes. WSs are used for various applicatios such as buildig moitorig, eviromet cotrol, wild-life habitat moitorig, forest fire detectio, idustry automatio, military, security, ad health-care. For such applicatios, the WSs caot operate i complete isolatio. The WS must be coected to a exteral etwork, such as the Iteret, through which moitorig ad cotrollig etities ca reach the WS. MAR- WIS (Maagemet Architecture for Heterogeeous Wireless Sesor etworks) [] supports commo maagemet tasks such as moitorig, (re)cofiguratio, ad updatig program code i a WS. To hadle large heterogeeous WSs it is proposed to subdivide it ito smaller sesor subetworks ad use a wireless mesh etwork (WM) as backboe. TCP/IP is the de facto stadard protocol suite for wired commuicatio. By ruig TCP/IP i the WS, it is possible to directly coect the WS to a wired etwork ifrastructure, without proxies or middle-boxes []. While UDP ca be used to trasmit sesor data to a sik, TCP is used for admiistrative tasks such as sesor ode cofiguratio ad updatig program code. Because of the limited resources of the sesor odes, the high packet loss, ad the iefficiecy i memory ad eergy cosumptio of TCP [], it is rather difficult to implemet TCP/IP o sesor odes. Optimizatios, e.g. distributed cachig of TCP data packets, local retrasmissios, ad regeeratio of TCP ackowledgmet packets ca reduce theses problems []. Usig TCP/IP to maage WSs requires a optimizatio ad harmoizatio of the differet layers, such as physical, data lik, etwork, ad trasport layer. Protocols at the differet layers have to exchage iformatio across the layers. We preset a cross layer desiged commuicatio architecture, which eables the use of TCP/IP to maage heterogeeous WSs. The mai parts of the commuicatio architecture are a MAC protocol, which implemets the MAC layer of obeaco-eabled PAs defied i the IEEE 8.. stadard [] for peer-to-peer topologies, ad the TCP Support for Sesor odes (TSS) protocol [6], which is a ew protocol betwee TCP ad IP. We implemeted the whole protocol stack i OMeT++ [7] usig the IET framework ad a accurate radio model of the CC radio trasceiver (thus the bit error rate is much higher tha i the stadard radio model). We use the cross layer desig paradigm to optimize ad harmoize the protocols at the differet layers. While the origial TSS has bee implemeted o top of a stadard TDMA MAC protocol, we implemeted a 8.. coform MAC protocol. Further, we exted the origial TSS by cachig more tha oe data packet. The size of the buffer ca be cofigured. The simulatios preseted i this paper are more detailed ad performed i more complex scearios as i [6]. The paper is orgaized as follows. Sectio II itroduces the related work regardig trasport protocols ad usig TCP/IP i WSs. I Sectio III we preset a topology of a heterogeeous WS ad itroduce briefly MARWIS, our maagemet architecture for such WSs. I Sectio IV the MAC protocol ad i Sectio V the TSS protocol are preseted. The developed protocols are simulated ad the results are preseted i Sectio VI. Sectio VII cocludes the paper ad gives a outlook. II. RELATED WORK May ew sophisticated trasport protocols for WSs have bee developed. Some of them explicitly focus o reliable trasport of data from sesor odes to base statios, while oly a few protocols support data trasport to the sesor odes. The reliability requiremets differ sigificatly depedig o the applicatio, sice sesor data ofte have some redudacy ad some loss ca be tolerated. However, packet loss caot be tolerated i the case of distributig program code to sesor
odes. Thus usig, adaptig, ad ehacig stadard trasport protocols such as TCP is a alterative. Reliable Data Trasport i Sesor etworks (RMST) [8], Pump Slowly Fetch Frequetly (PSFQ) [9], ad Cogestio Detectio ad Avoidace (CODA) [] are built o top of Directed Diffusio [], which is a commo data dissemiatio scheme. Evet-to-Sik Reliable Trasport (ESRT) [] provides cogestio cotrol. The use of TCP i wireless etworks causes some serious performace problems. The ed-to-ed ackowledgmet ad retrasmissio scheme requires expesive retrasmissios alog every hop o the path betwee the seder ad the receiver, if a packet is dropped. I [], [] local cachig of TCP segmets ad local retrasmissio at itermediate odes is proposed. A further problem is the eergy cosumptio of TCP []. I [] FEC is used to shield TCP from losses ot caused by cogestio ad helps to improve its throughput. I [] the authors try to improve TCP performace by establishig the optimal TCP widow size. I [6], a eergy-efficiet protocol called E TCP is preseted. It provides a selective ackowledgmet mechaism ad uses header compressio. Approaches for maagemet of WSs ad code distributio does ot support heterogeeous WS eviromets. MAA [7] is a maagemet architecture for WSs, which provides fuctios to establish cofiguratios for WS etities. Tiy- Cubus [8] is a maagemet ad cofiguratio framework for WSs, which focuses o code distributio ad miimizig code fragmets to be distributed i a WS. Multi-hop Overthe-Air Programmig (MOAP) [9] is a code distributio mechaism focused o eergy-efficiet ad reliable code distributio. III. MAAGEMET ARCHITECTURE FOR WIRELESS SESOR ETWORKS To coect a WS to a exteral etwork, such as the Iteret, additioal ifrastructure is required. Oe possible solutio is a wireless mesh etwork (WM), which works as backboe ad supports the coectio to the exteral etwork. I additio, it supports the coectio betwee the differet types of sesor odes i a heterogeeous WS. To operate such a WS the followig devices are required: oe (or more) maagemet statios, several wireless mesh odes ad a rather high umber of heterogeeous sesor odes. A possible sceario is show i Figure. The sesor odes of the differet subetworks are depicted as small circles, triagles ad rhombuses. The mesh odes are depicted as large circles. I [] it is show that subdivisio of a large WS ito smaller sesor subetworks improves the performace of a WS by reducig the umber of hops i a sesor subetwork. The WS is coected to the Iteret usig the WM as backboe. A sesor ode ca be plugged ito a mesh ode via serial iterface such as USB. Such sesor ode operates as gateway betwee the WM ad the WS. The mesh odes commuicate via IEEE 8.b/g/. The WM is coected to the Iteret via Etheret or IEEE 8.. A TCP/IP implemetatio rus o all etities of the etwork ad IEEE 8. mesh ode Fig.. magemet statio sesor odes IEEE 8. Iteret magemet statio Topology of a heterogeeous wireless sesor etwork is used for reliable poit-to-poit coectios. Every sesor ode ad mesh ode has its ow IP address. Thus, the user ca cotrol ad moitor the WS ad every sigle sesor ode via a maagemet statio located i the Iteret. Differet types of sesor odes, which build differet subetworks, ca commuicate to each other. Figure shows the protocols stacks o several etities (maagemet statio, mesh odes, sesor odes). Maagemet Statio Mesh ode Mesh ode Sesor Gateway Sesor ode Sesor ode Applicatio Applicatio Trasport etwork Datalik Physical TCP IP Etheret Fig.. IP Etheret 8. 8. Reliable uicast coectio IP IP IP SLIP SLIP 8.. 8.. 8.. Applicatio TCP TSS TSS TSS Etheret USB CC CC WLA A reliable uicast coectio with TSS IP 8.. The desig of efficiet commuicatio ivolves all layers from physical layer up to the applicatio layer. It is ot sufficiet to develop a protocol i a sigle layer, which is put o the top of aother sigle layer protocol. Thus, it is ecessary to coordiate ad harmoize all affected layers. Importat iformatio ad states have to be kow at all layers immediately. Such a cross layer desig ca obtai a reliable ad efficiet data trasport withi the WS. We provide a cross layer desiged protocol stack o the sesor odes. This cotais a ew MAC protocol for 8.. obeaco-eabled Persoal Area etworks (PAs) ad TSS betwee IP ad TCP. IV. MAC PROTOCOL The MAC protocol at the data lik layer depeds strogly o the uderlyig radio trasceiver ad is specially tailored to it. We are usig the CC radio trasceiver [], which implemets the physical layer of the IEEE 8.. stadard. The proposed MAC protocol implemets the MAC layer of obeaco-eabled PAs defied i the IEEE 8..
stadard for peer-to-peer topologies. To our kowledge it is the first implemetatio i this way. It provides multihop commuicatio. All odes are full fuctio devices (FFD). The MAC protocol holds a buffer to store the icomig frames from the lower layer (radio trasceiver) ad the upper layers (TCP TSS µip). The size of the buffer ca be cofigured. The format of the MAC frame is coform to the IEEE 8.. stadard ad show i Figure. There are o eergy-savig fuctioalities such as sleepig periods implemeted yet. Preamble Sequece Start of Frame Delimiter Sychroizatio Header (SHR) Frame Legth PH Header (PHR) Fig.. to Frame Cotrol Field (FCF) Data Sequece umber MAC Header (MHR) MAC Payload MAC Footer (MFR) - 7 Bytes PH Protocol Data Uit (PPDU) A. Trasmittig ad Receivig Address Iformatio MAC Protocol Data Uit (MPDU) PH Service Data Uit (PSDU) IEEE 8.. MAC frame. Frame payload Frame Check Sequece (FCS) MAC Layer PH Layer The receivig ad trasmissio process is realized as a state machie. The MAC protocol operates accordig to the states of the CC radio trasceiver. We provide two modes for ackowledgmets: a explicit ackowledgmet () ad a implicit ackowledgmet (MAC-). The state machies for trasmittig ad receivig are show i Figure ad work as follows: ) For trasmissio of frames the uslotted CSMA-CA algorithm is used. ) Data comig from the upper layer are writte to the TX buffer of the radio trasceiver. This step depeds o the uderlyig radio trasceiver.this step depeds o the uderlyig radio trasceiver. ) This step cotais the uslotted CSMA-CA algorithm. Two variables are maitaied: B, ad BE. B is the umber of times the CSMA-CA algorithm was required to backoff while attemptig the curret trasmissio. BE is the backoff expoet, which is related to how may backoff periods a device shall wait before attemptig to assess a chael. The MAC protocol delays for a radom umber of backoff periods. Via CCA (Clear Chael Assessmet) the radio trasceiver idicates, whether the chael is free. I case of a busy chael the backoff period is ewly calculated ad the maximum umber of retrasmissio attempts is checked. ) The frame stored i the TX buffer is trasmitted. By a successful trasmissio it deletes the frame. It retrasmits the frame, if there is o cofirmatio ( / MAC-). ) Whe a frame is i the RX buffer, the CC radio trasceiver cofirms it via the SFD ad the FIFO pi. 6) The received frame is processed (CRC) ad hadled accordig the frame type. 7) I the mode the is trasmitted. 8) is delivered to the upper layer. write frame to PH TX-Buffer B = BE = macmibe delay for radom( BE - ) wait backoff period perform CCA chael idle? trasmit frame wait for or /OVER received? success Fig.. uslotted CSMA-CA frameretries = PH TX-Buffer free? wait B = B + BE = mi(be+, macmaxbe) B > macmaxcsma Backoffs failure frameretries > maxframeretries frameretries++ 6 drop hadle MAC Commad hadle wait for flush TX-Buffer write to PH TX-Buffer trasmit CMD State machie of the MAC protocol. B. vs MAC- 7 8 packet received SFD = low FIFO = high get frame form PH RX-Buffer CRC ok Frame Type DATA hadle wait for sed? PH TX-Buffer free? deliver frame to upper layer There are two kids of ackowledgmet modes: ad MAC-. I case of the MAC protocol iitiates the trasmissio of a ackowledgmet. I case of MAC- o ackowledgmet frame is trasmitted. Istead the radio trasceiver listes whether the followig ode forwards the frame. The upper layers get iformed about the state of ackowledgmet (cross layer iformatio). There are three states: The frame has bee successfully trasmitted (cofirmed via or MAC-). The frame has bee trasmitted, but there is o cofirmatio. Frame trasmissio failed. The mode show i Figure works as follows: ) is set after checkig whether the chael is free ad whether there is o Sed Stop active.
ode ode ode sed stop delay time slot for Fig.. time slot for ode ) After successfully receivig the frame a is trasmitted immediately (after symbols). ) A is received which is ot addressed for the receiver. It sets the Sed Stop timer, thus correspodig s from the receiver to the seder caot be destroyed. After the timer has expired it ca trasmit regularly. ) The is received withi the time slot for MAC-. ) Collisios ca occur. If CRC checks fail, frames are destroyed. A caot be trasmitted ad after expirig the time slot for the frame is retrasmitted. ode ode ode ode time slot for overhearig Fig. 6. timer for retrasmissio (. * RTT) MAC- o itermediate odes. The MAC- mode is show i Figure 6. There exists o explicit ackowledgmet. The seder listes whe the receiver forwards the frame to the ext hop. The mechaism works as follows: ) The seder trasmits a frame. The receiver forwards the frame ad the seder overhears it (withi the time slot for overhearig). ) Also i the MAC- mode collisios ca occur. Because odes ad odes caot hear each other, they trasmit frames at the same time. Thus frames collide ad overhearig is impossible. ) O expiratio of the time slot for overhearig there are o retrasmissios. The TSS protocol gets the iformatio that the frame is trasmitted, but ot ackowledged (ot overheard). Retrasmissio is iitiated by TSS. C. Cross Layer Support of the MAC Protocol The MAC protocol is resposible to establish a stable lik to the eighbor odes. The commuicatio should be eergy-efficiet. Therefore, the physical layer has to provide additioal iformatio about the trasmissios. The radio trasceiver provides CCA (Clear Chael Assessmet), LQI (Lik Quality Idex), ad RSSI (Receive Sigal Stregth Idicator). CCA provides iformatio whether the chael is used or ot. LQI idicates the quality of a lik betwee two odes ad RSSI provides the sigal stregth. The MAC protocol decides with this iformatio, if a frame ca be trasmitted to a eighbor ode. The exchage of iformatio betwee the MAC protocol ad the TSS protocol is very importat for the reliability mechaisms. The MAC protocol iforms the TSS protocol about the trasmissio state of a frame. It ca be trasmitted successfully or the trasmissio ca fail (e.g. if the chael was busy). Further, the MAC protocol gives iformatio about retrasmissios of segmets ad the traffic betwee the odes i the eighborhood. This iformatio is importat for cogestio cotrol ad avoidace i the TSS protocol. The TSS layer provides the iformatio about the buffer size ad the free space i the buffer. The MAC layer uses this iformatio ad drops a frame (with payload), if the buffer is full. V. TCP SUPPORT FOR SESOR ODES (TSS) To esure a reliable trasport i WSs a ew protocol betwee TCP ad IP, the TCP Support for Sesor etworks (TSS) [6] protocol has bee iserted. This protocol is resposible for the followig tasks: Cachig ad local retrasmissio of TCP data packets Improvig the TCP ackowledgmet mechaism Flow ad cogestio cotrol TSS supports eergy-efficiet operatio of sesor odes by reducig the umber of trasmissios. The TSS protocol holds a buffer to store the icomig frames from the lower layers (radio trasceiver MAC) ad the upper layer (TCP). The reliability mechaisms of TSS have a effect, whe the etwork is overloaded (e.g. because of a high load of packets of other protocols or iterfereces). The MAC protocol must ot be too reliable, because i case of ureliable trasport protocols (such as UDP) there ca be too high overload ad delays. A. TSS Cachig Local Retrasmissios of TCP Data Packets I geeral, TCP is a reliable byte stream protocol desiged for wired etworks. Reliability is provided by positive ackowledgmet with ed-to-ed retrasmissios. I cotrast
to a wired coectio, a wireless etwork possesses a high bit error rate. This leads to may ed-to-ed retrasmissios. These extra packets reduce the throughput ad icrease the roud-trip-time (RTT). The extra eergy for retrasmissios also reduces the lifetime of the idividual sesor odes. Oe of the basic ideas of TSS is to cache a TCP-DATA packet i the WS util the packet is ackowledged (show i Figure 7): ) The ode caches TCP-DATA ad forwards it. ) The receiver ackowledges TCP-DATA by trasmittig +. ) The itermediate ode receives + ad deletes TCP-DATA. I geeral, it ca delete all TCP- DATA packets with a lower sequece umber tha. be i the etwork at the same time. The order of the packets is preserved. Figure 9 shows a packet loss i that case: ) TCP-DATA ad TCP-DATA + are cached o itermediate odes ad get lost. ) TCP-DATA + reaches the receiver, which ackowledges the packet. ) The ode recogizes that TCP-DATA is lost. It forwards the ackowledgmet, because it does ot have TCP-DATA cached. ) Itermediate ode has TCP-DATA i the buffer, forwards it ad deletes the. ) This packet is ackowledged ad TCP-DATA + is retrasmitted (from ode 6). The ext packet is requested by trasmittig +. SEDER Fig. 7. cache TCP data packet + ode drop cached TCP data packet Basic idea of TSS: cachig of TCP data packets. The case of a packet loss is show i Figure 8 ad works as follows: ) The ode caches TCP-DATA ad forwards it. ) After forwardig a TCP-DATA packet, the ode expects the ackowledgmet () withi. * RTT. Otherwise, the cached packet is retrasmitted. ) After receivig + it deletes TCP-DATA (ad all lower TCP-DATA packets) from the buffer. SEDER Fig. 8. retrasmit packet ode. * RTT + Basic idea of TSS: retrasmissio of lost TCP data packets. Too log retrasmissio timeouts cause retrasmissios by the seder. Simulatios i [6] show that a retrasmissio timeout of. * RTT is adequate to also retrasmit multiple losses of TCP-DATA packets without triggerig ed-to-ed retrasmissio. The RTT is measured betwee the ode ad the destiatio. The RTT coefficiet (. i this case) ca be cofigured. Both ideas above assume that oly oe TCP-DATA packet ca be cached o every itermediate ode ad oly oe packet is i the etwork at the same time. If it is assumed that every itermediate ode ca buffer more tha oe packet the retrasmissio mechaisms ca be exteded ad optimized. The throughput ca be icreased, because of more packets ca SEDER + + cache drop Fig. 9. ode ode 6 drop + cache + + Packet loss i a exteded sceario. B. TSS Ackowledgmet Mechaisms + + Because of the limited memory, oly a few packets ca be cached ad a efficiet cachig algorithm is required. A ode caches a packet util it kows that the successor ode has successfully received the packet. This ca be discovered by receivig a ackowledgmet o the data lik layer or through overhearig a implicit ackowledgmet (show i Figure ): ) ode receives, caches, ad forwards TCP-DATA ad +. The MAC protocol iforms the TSS protocol that forwardig has failed. ) ow ode tries to retrasmit TCP-DATA. After cofirmatio it deletes it from the buffer. ad trasmits TCP-DATA +. TSS passes oly oe packet to the MAC protocol (directed through the IP) ad waits afterwards for cofirmatio. There are three states after packet trasmissio: The packet has bee trasmitted successfully to the ext hop, ad it is cofirmed through or MAC-. The packet has bee trasmitted, but the has ot bee received or the forwardig of the packet could ot be overheard (MAC-). The MAC protocol was ot able to trasmit the packet, because of e.g. chael was busy or some other reasos.
SEDER + remove cached packet ode Overhearig Overhearig Overhearig Overhearig first sed cache & + Overhearig Overhearig + Overhearig Overhearig that it has already received the packet (ad successfully forwarded). Thus, it does ot forward it ad deletes it from the buffer. SEDER loger tha. * RTT ode ode ode 7 Overhearig history list Delay + Fig.. Cross layer support of the MAC protocol. Overhearig + Accordig to these three states of the cofirmatio the ode ca retrasmit the packet or ot. I the first case the packet is ormally deleted from the buffer. Thus, o retrasmissio is possible, eve if there is o withi. * RTT. If the packet is still i the buffer (accordig to the basic idea of TSS show i Figure 7), the packet is retrasmitted after. * RTT. I the case of a egative cofirmatio (missed or MAC-), we ca retrasmit the packet immediately after the egative cofirmatio by the MAC protocol, or we have to wait for. * RTT ad retrasmit it the. I the third case, we ca try immediately to retrasmit the packet or to wait a short time util the chael is ot busy aymore. As log as a cached packet has ot bee successfully delivered to the ext hop, later received packets of the same coectio are ot forwarded. Thus, the order of the packets are ot chaged. It happes that a packet has successfully bee trasmitted to the ext hop, but the ackowledgmet or the overhearig has ot bee discovered by the seder (show i Figure ). I such case the seder duplicates the packet ad retrasmits it. To avoid duplicated packets, every ode holds a small history list with the idetificatio umbers of received TCP packets ad their ackowledgmets. I case of a detected duplicate, it is dropped. The history list is the mai elemet of the ackowledgmet mechaism. The source ad destiatio address, ports, sequece umber, ad whether the packet is ackowledged with a or are stored for each packet. With this iformatio TSS ca calculate the RTT, ad assig s to TCP-DATA packets. Further curret TCP-DATA sequece umbers ca be calculated ad retrasmissios ca be recogized. The mechaism is show i Figure ad works as follows: ) The ode caches ad forwards TCP-DATA. However, the MAC protocol cofirms that it does trasmit the packet but does ot receive a. ow the ode waits. * RTT for a. ) The ext ode forwards the packet ad the receiver ackowledges it. + is delayed, e.g. because of much traffic i the eighborhood, ad does ot arrive at ode withi. * RTT. ) The RTT timer expires ad the ode retrasmits TCP- DATA. The ext ode recogizes with the history list, Fig.. History list to avoid packet duplicatios i the WS I TSS, the s are very importat to estimate the RTT, RTT timers, cachig, etc. Experimets i [6] show that the loss of s may have severe impact o the amout of TCP-DATA packet trasmissios. Two mechaisms reduce the cosequeces of lost s: local TCP ackowledgmet regeeratio ad a aggressive TCP ackowledgmet recovery (show i Figure ). SEDER ode ode ode 7 Local TCP regeeratio discover forwardig of Aggressive TCP regeeratio history list + + drop packet recover TCP- + from history list Fig.. Two mechaisms to reduce the cosequeces of lost TCP ackowledgmets The local TCP ackowledgmet regeeratio is used to drop duplicated TCP data packets, which are already ackowledged by the receiver. Because of the history list, a itermediate ode ca discover a already ackowledged packet. The duplicated packet is dropped ad a TCP ackowledgmet with the highest ackowledgmet umber see so far is regeerated ad trasmitted. A sceario is show i ) of Figure ). The aggressive TCP ackowledgmet recovery becomes active whe a sesor ode caot esure by that the TCP- has bee successfully trasmitted to the ext hop. Usig, the retrasmissio ca be eforced directly. It is show i ) of Figure. VI. SIMULATIO AD EVALUATIO We implemeted TCP/IP, TSS preseted i Sectio V, ad the MAC protocol preseted i Sectio IV i OMeT++ [7] ad ru a umber of simulatios. We compared ad MAC- as well as we evaluated TCP/IP
with ad without TSS. We use three differet scearios to evaluate our cross layer desig commuicatio architecture. First, we arrage the sesor odes i a lie (lie sceario, show i Figure ) ad establishs a TCP coectio betwee ode ad ode 6 which trasmits bytes (accordig to a cofiguratio task) or bytes (accordig to a code updatig task). o eergy-savig fuctios such as sleepig cycles are implemeted, because the focus lies o the trasmissio performace. The cofiguratio ad updatig task should be processed as fast as possible. 6 7 9 6 6 6 6 6 66 6 6 67..................6...7 mode are the same as for the overhearig period of ms. The size of the MAC frame is 8 bytes (8.. coform). The average error rate betwee two eighbor odes is approximately % to %, if there are o iterfereces by other odes. Figure shows the trasmissio time of bytes (typical code updatig task) i the three scearios with TSS ad without TSS usig ( left poits) or MAC- ( right poits). Trasmissio time with TSS is % of pure TCP i case of the lie sceario ad % i case of the cross sceario. Usig is faster tha usig MAC-. Figure 6 shows the same scearios trasmittig bytes (typical cofiguratio task). Here the effect of TSS is eve bigger ( times better performace i case of cross sceario i the mode), because there are just oe TCP-DATA packet trasmitted. I the bytes sceario 9 data packets are eeded. Fig.. Sesor odes arraged i a lie. Secod, we arrage the sesor odes i a cross grid ad establish TCP coectios show i Figure. I the parallel sceario oe coectio goes from ode to ode 6 ad oe coectio from ode 7 to ode. The cross sceario is also based o the cross grid ad establish oe TCP coectio ode to ode ad oe coectio from ode to ode 6. Also i these scearios bytes ad bytes are trasmitted over a coectio. time [s]... Trasmissio time with TSS ( Byte) Fig.. time [s] Trasmissio time without TSS ( Byte) Trasmissio time ( byte sceario). 6 7 9 6 7 9...7 6... 67 7...6 66 7... 6...... 7 6 7......... 6 6 7 9... 7 6......9 69 9 8...8 68... 7 6...6 66 7...... 6 7... 6... 7 69 9... 6... 6 8...9 7......8 7 68 6 6 9 6 67......7 time [s]..... Trasmissio time with TSS ( Byte) time [s] 7 6 Trasmissio time without TSS ( Byte) (a) Parallel Sceario Fig.. (b) Cross Sceario Sesor odes arraged i a cross grid. We evaluate the TSS protocol compared with a pure TCP implemetatio the i lie, parallel, ad cross sceario usig the mode or the MAC- mode. We measure the trasmissio time, the umber of the total trasmitted bytes, ad the umber of total trasmissios i the etwork. The trasmissio time is the duratio for trasmittig bytes or bytes over the TCP coectio (time betwee establishig ad closig the coectio). The umber of total trasmissios gives the umber of set frames. It meas ot the umber of successfully trasmitted frames. The parameters for the mode are: TCP widow size 78, RTT coefficiet. (cf. [6]), TSS buffer size, MAC buffer size, radom backoff time µs, ad the umber of retrasmissio attempts. The parameters for the MAC- Fig. 6. Trasmissio time ( byte sceario). Figure 7 shows the umber of real trasmitted bytes comparig TSS with pure TCP usig or MAC- i the byte sceario. TSS reduces the umber of total trasmitted bytes by reducig the of retrasmissios sigificatly. The MAC- mode eeds less trasmitted bytes tha the mode usig TSS. I case of usig pure TCP, eeds less trasmitted bytes tha MAC-. The same effect ca be see i the byte sceario show i Figure 8. Figure 9 shows the umber of trasmissios comparig TSS with pure TCP usig or MAC- i the byte sceario. Figure shows the results i the byte sceario. The umber of total trasmissios icreases, if TSS is ot used. I case of the bytes sceario the effect is stroger, because of overhead of TCP coectio establishmet.
bytes 7 6 Total set bytes with TSS ( Byte) bytes Total set bytes without TSS ( Byte) trasmissios 8 6 Total trasmissios with TSS ( Byte) trasmissios 6 8 6 Total trasmissios without TSS ( Byte) Fig. 7. Total set bytes ( byte sceario). Fig.. Total umber of trasmissios ( byte sceario). 7 6 Total set bytes with TSS ( Byte) 7 6 Total set bytes without TSS ( Byte) Cotiki operatig system to build a real world sceario of a heterogeeous WS. bytes Fig. 8. bytes Total set bytes ( byte sceario). Without the TSS protocol, oly about 6% of byte scearios, ad about 8% of the scearios are successful. The rest of the trasmissios are aborted by TCP timeout after reachig the retrasmissio limit. VII. COCLUSIO AD OUTLOOK We preseted a commuicatio architecture based o cross layer desig cotaiig a IEEE 8.. MAC protocol i the obeaco-eabled mode for peer-to-peer topologies, TCP/IP, ad TCP Support for Sesor odes (TSS). Reliability mechaisms such as local cachig ad retrasmissio of TCP data packets, ad ackowledgmet mechaisms i the MAC protocol ad the TSS protocol are described. We showed that usig the additioal TSS protocol icrease the performace of TCP i WSs dramatically. The total trasmissio time of pure TCP is reduced to %. Also the the trasmitted bytes ad trasmissio cout is cosiderably reduced by TSS. The ext steps icludig the extesio of the protocol with a cogestio ad flow cotrol algorithm ad the desig of eergy-savig fuctios. Further the commuicatio architecture should be itegrated i the µip stack of the trasmissios 8 6 Total trasmissios with TSS ( Byte) Fig. 9. trasmissios Total trasmissios without TSS ( Byte) Total umber of trasmissios ( byte sceario). REFERECES [] G. Wagekecht, M. Awader, T. Brau, T. Staub, J. Matheka, S. Morgethaler: MARWIS: A Maagemet Architecture for Heterogeeous Wireless Sesor etworks, WWIC8, Tampere, Filad, May 8. [] A. Dukels, T. Voigt, J. Aloso, H. Ritter, J. Schiller: Coectig Wireless Sesorets with TCP/IP etworks, WWIC, Frakfurt/Oder, Germay, Feb [] M. Zorzi ad R. R. Raot: Is TCP eergy efficiet?, MoMuC99, Sa Diego, CA, USA, ov 999. [] A. Dukels, T. Voigt, J. Aloso, H. Ritter: Distributed TCP Cachig for Wireless Sesor etworks, MedHocet, Bodrum, Turkey, Ju. [] IEEE 8..: Wireless Medium Access cotrol (MAC) ad Physical Layer (PH) Specificatios for Low-Rate Wireless Persoal Area etworks (WPAs), IEEE Computer Society, Feb 6. [6] T. Brau, T. Voigt, A. Dukels: TCP Support for Sesor etworks, WOS7, Obergurgl, Austria, Ja 7. [7] OMeT++: Discrete Evet Simulatio System, Website: http://www.ometpp.org. [8] F. Sta, J. Heidema: RMST: Reliable Data Trasport i Sesor etworks, SPA, Achorage, AK, USA, May. [9] C.. Wa, A. T. Campbell, L. Krishamurthy: PSFQ: A Reliable Trasport Protocol for Wireless Sesor etworks, WSA, Atlata, GA, USA, Sep. [] C.. Wa, S. B. Eisema, A. T. Campbell: CODA: Cogestio Detectio ad Avoidace i Sesor etworks, SeSys, Los Ageles, CA, USA, ov. [] C. Itaagowiwat, R. Govida, D. Estri, J. Heidema, F. Silva: Directed Diffusio for Wireless Sesor etworkig, Trasactio o etworkig, ():-6, Feb. []. Sakarasubramaiam, Ö. B. Aka, I. F. Akyildiz: ESRT: Evetto-sik Reliable Trasport i Wireless Sesor etworks, MobiHoc, Aapolis, MD, USA, Ju. [] H. Balakrisha, S. Sesha, E. Amir, R. H. Katz: Improvig TCP/IP Performace over Wireless etworks, Mobicom9, Berkeley, CA, USA, ov 9. [] C. Barakat, E. Altma: Badwidth Tradeoff betwee TCP ad Lik-level FEC, Computer etworks, 9():-, Ju. [] Z. Fu, P. Zerfos, H. Luo, S. Lu, L. Zhag, M. Gerla: The impact of Multihop Wireless Chael o TCP Throughput ad Loss, IFOCOM, Sa Fracisco, CA, USA, Apr. [6] L. Dockers, P. J. M. Haviga, G. J. M. Smit, L. T. Smit: Eergy Efficiet TCP, AMOC, Lagkawi Islad, Malaysia, May. [7] L. B. Ruiz, J. ogueira, A. Loureiro: Maa: A Maagemet Architecture for Wireless Sesor etworks. IEEE Commuicatios, ():6-, Feb. [8] P. J. Marró, A. Lachema, D. Mider, J. Häher, M. Gauger, O. Saukh, K. Rothermel: TiyCubus: A Flexible ad Adaptive Framework for Sesor etworks. EWS, Istabul, Turkey, Ja. [9] T. Stathopoulos, J. Heidema, D. Estri: A Remote Code Update Mechaism for Wireless Sesor etworks. Techical Report CES-TR-, Uiversity of Califoria, Los Ageles, USA, ov. [] CC: Datasheet for the Chipco CC. GHz IEEE 8.. compliat RF Trasceiver, Olie, Mar 7.