Priority Enabled Transport Layer Protocol for Wireless Sensor Network

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1 2010 IEEE 24th Internatonal Conference on Advanced Informaton Networkng and Applcatons Workshops Prorty Enabled Transport Layer Protocol for Wreless Sensor Network 1 Atf Sharf, 2 Vdyasagar Potdar Dgtal Ecosystems and Busness Intellgence Insttute, Curtn Unversty of Technology Perth, WA, Australa 1 atf.sharf@postgrad.curtn.edu.au 2 v.potdar@curtn.edu.au A.J.D.Rathnayaka Department of Electronc and Telecommuncaton Engneerng, Unversty of Moratuwa Sr Lanka ajdr03@ent.mrt.ac.lk Abstract Achevng Qualty of Servce (QoS) objectve n Wreless Sensor Network (WSN) handlng the multmeda nformaton has sgnfcantly ganed the mportance lately besdes energy effcent hardware desgnng. Transport layer of the WSN communcaton protocol stack plays a sgnfcant role n meetng the QoS objectve of WSN. Ths paper presents a lght weght transport protocol for WSN that can handle packets from a numbers of sources havng dfferent sensed nformaton and havng dfferent prorty levels. The protocol assgned mddle motes are ntellgent enough to acheve prortzaton n transmsson based on the prorty level and packet s Tme-To- Lve (TTL) nformaton. Extensve smulaton s carred out for the three dfferent modes of the envsaged protocol havng no prortzed enabled storage, complete prortzed enabled storage and dstrbuted prortzed enabled storage. The results reveal that the sgnfcant mprovement s observed n case of dstrbuted prortzed enabled storage, approxmately 3% data loss occurred, n comparson to 7% data loss for wthout prortzed enabled storage mode. Keywords-WSN, transport layer protocol, IEEE , relablty, congeston control I. INTRODUCTION WSN comprsed of energy hungry devces also called motes that are wrelessly nterconnected for communcatng the sensed pece of nformaton from the regon of nterest to the central control staton or snk. For the longevty of the WSN, transport layer protocol plays a vtal role n assurng the relablty and congeston control aspects of the desgn. In general the WSN transport layer protocol may nclude two man functons: congeston control and data relablty or loss recovery. For congeston control n WSN t s frstly mportant to detect whether or not congeston happens and f t s happen then when and where t happens. Congeston can be detected by a number of ways among them ncludes: Montorng ntermedate mote s buffer occupancy, Wreless lnk load capacty, Packet processng tme exceeds the packet nter-arrval tme lmts. The congeston control and relablty features of the WSN transport layer protocol can be addressed n two ways: 1) End-to-End (E-2-E), 2) Hop-by-Hop (H-B-H). The E-2-E approach s qute robust and smple but t wll ncrease the communcaton overhead wth more on-gong control packets n network. Whereas the H-b-H approach would requre to change the mote s behavor n the entre path from the source to snk but t quckly dampens the local hot spots (caused by congeston) wth fewer number of on-gong control packets thus savng consderable mote s energy budget. So when practcally desgnng the WSN s transport layer protocol we should carefully consder the trade-off between E- 2-E and H-b-H approaches for WSN. In WSN there are a number of reasons for data packet loss ncludng: Congeston n the network, hdden mote problem, Poor Sgnal to Nose Rato (SNR) due to bad channel (wreless by nature) qualty, Lnk breakage due to mote falure. In WSN the role of data relablty s to allow a data loss recovery mechansm n order to retreve the correct nformaton. For detectng the data packet loss, n ether E-2-E or H-b-H framework, the WSN transport protocol uses the packet sequencng concept that nvolves the Acknowledgement (ACK)/Not Acknowledgement (NACK) control packets smlar to that used n packet-swtched networks. Also the WSN, targeted for heterogeneous applcaton.e. multmeda and scalar sensor support, the retransmsson of multmeda traffc flow sgnfcantly depletes WSN s allocated energy budget. Sgnfcant effcency n network s energy budget can be acheved by prortzng the source nformaton [1]. So the source packet wth crtcal E-2-E latency lmts (lke audo or vdeo data) would need to be processed frst by the ntermedate motes n comparson to less crtcal scalar nformaton. The rest of the paper s organzed as followng. After ntroducng the problem defnton n secton 2 followed by secton 3 where we descrbe the smulaton setup used for observng the behavor. In secton 4 we wll show the smulaton results we have taken. The dscusson followed by the conclusons wll be presented n the secton 5. II. RELATED WORK Transport protocols are desgned to support specfc optmzaton aspects and/or applcaton scenaros. TCP (Transmsson Control Protocol) [2] and UDP (User Datagram Protocol) [3] are popular transport control protocols extensvely used n Internet, but both of them are not the correct selecton for Wreless Sensor Networks (WSN) due to many lmtatons. Proven transport Protocols for WSNs are dentfed and classfed based on congeston control and/or relablty guarantee n upstream (from sensor motes to snk) or downstream (from snk to sensor motes). Table: 1 contans several transport control protocols classfcatons for WSNs /10 $ IEEE DOI /WAINA

2 TABLE I. WSN TRANSPORT LAYER PROTOCOLS Features Protocol Drecton Congeston Control Support Relablt y Manage ment Support CODA Upstream Yes No ESRT Upstream Passve Yes RMST Upstream No Yes PSFQ Downstream No Yes GARUDA Downstream No Yes STCP Upstream Yes Yes TCPW Upstream Yes No CODA [4] (Congeston Detecton and Avodance) provdes snk/recever based congeston control nvolvng congeston detecton, open-loop H-b-H back pressure and closed loop mult source regulaton. However t does not offer relablty control feature and offers only undrectonal control n forward (fwd) drecton from source to snk. ESRT [5] (Event-to-Snk Relable Transport) protocol smultaneously supports relablty and congeston control features n forward drecton. However, relablty of sngle packet s not guaranteed by ESRT nstead supports only applcaton level relablty. Also t uses hgh power mode for data communcaton over a sngle hop that may nfluence the on-gong data transmsson. RMST [6] (Relable Mult-Segment Transport), protocol uses selectve ACK (SACK) and desgned to run n conjuncton wth drected dffuson. Although RMST offers hgh relablty wth guaranteed delvery and fragmentaton/reassembly however t lacks energy conservaton mechansm and does not support the congeston control feature of transport protocol desgn. PSFQ [7] (Pump Slowly Fetch Quckly) protocol offers the relablty support n the reverse (rev) drecton form snk mote to source motes. It facltates data form snk to source at relatvely slow speed (Pump Slowly). It uses ntermedate storage motes for rapd H-b-H recovery of the lost nformaton by usng NACK. However, PSFQ unable to detect the loss of sngle packet when nformaton s communcated as bulk transmsson of packets and also requre more cashng space at ntermedate motes. GARUDA [8] protocol does not support congeston but ensures relablty n rev drecton from snk mote to sensor motes. It uses WFP (Wat-for Frst -Packet) pulse transmsson and selects core motes located at a hop count of ntegral multple of 3 for storng the packet nformaton that could possbly be used for packet loss recovery usng NACK based control attrbute and two-ter two-stage loss recovery mechansm. STCP [9] (Sensor Transmsson Control Protocol) offers Snk based controlled varable relablty and congeston control features smultaneously. For contnuous and even drven applcatons STCP uses NACK and ACK based control attrbute for assurng E-2-E retransmssons. Relablty s beng dctated by the source mote where as the ntermedate motes are used for detectng the congeston and notfyng t to snk by settng the congeston notfcaton feld of the transmtted packet. TCPWW [10] (TCP Westwood) [2] s a sender based extenson of the exstng TCP protocol. It refnes the wndow control and back-off process of the exstng TCP desgn thereby achevng greater desgn effcency under sporadc or random data losses. Under congested network condtons TCPWW uses the estmated value of the avalable channel bandwdth for properly settng the congeston wndow and slow start threshold lmts. It also ensures rapd data retreval, by avodng excessvely conservatve reductons of congeston wndow and the slow start threshold lmts. III. PROTOCOL OVERVIEW The proposed transport protocol scheme comprsed of followng functonal modules: 1) Congeston Control a) Congeston Detecton b) Congeston Notfcaton c) Source rate adjustment 2) Relablty or Loss recovery module The purpose of the congeston control module s to detect the congeston n the network, the congeston ndex (C ) s used to measure the severty of the congeston n the network and s gven by Eq (1) [15] C Κ Μ ( Q * T + T T ) = * Γ + N * 1 p ) RTS / CTS + 1 h pr (1) where, K= total avalable free space n ntermedate mote s storage, M=total avalable space n ntermedate mote s storage, N= number of hops between source and snk, Q = Current Queue ndex, T 1-p = Tme to execute one packet, T RTS/CTS =tme delay for RTS/CTS nformaton exchange, T 1-h-pr =tme requred for 1-hop propagaton, Γ = tme to process one packet. Ths C value wll be used along wth the E-2-E packet latency T delay ( E 2 E ) by the envsaged transport protocol and s helpful n decdng the future source rate plan n order to mtgate the congeston n the network. The newly estmated ( E 2 E ) and rate value nvolvng C s gven by [13] T delay ( c ) Tdelay C T ˆ = delay / (2) Hence the new estmated rate value comes to be: ˆ T c Rˆ delay ( ) ( c ) (3) = N Based on the computed C, the snk broadcast the new rate plan to all sources and upon lstenng to ths broadcasted rate value the sources become aware wth the congeston state of the network and mmedately swtch ther sendng rate to newly broadcasted value. 584

3 The software descrpton of the proposed protocol s shown n the Fgure 1. The prortzed packet communcaton ncludng the retransmsson (here we are assumng that lnk s already establshed at the lower layers, below transport level, of the communcaton protocol stack) s done n the followng way: 1. Source sense the nformaton, locally process t and sends the data packet to ntermedate storage mote. 2. The ntermedate mote receves the ncomng packet and wth ACK = NACK = 0 t assumes the new data. If t s frst packet then t clears the storage memory ntally else stores the packet to mmedate locaton. The storage along wth the duraton of storage s done based on some prorty. 3. The ntermedate mote after storng the nformaton wll forward the data packet to the next hop or snk. It wll frst search the prorty ndex and packet wth hgher prorty wll be served frst. Incase f there are multple packets wth same prorty then the decson wll be made on the ndvdual s packet TTL value. 4. Snk, wth ACK=NACK=0, assumes the ncomng new packet and mark ts sequence number and return an ACK (ACK=1, NACK=0) packet to the mmedate ntermedate storage mote, whch on recepton of t delete the correspondng packet entry from ts memory. 5. Snk f msses some packets then upon recept of the newly arrved packet t wll generate a NACK packet wth entres marked wth the mssng sequence numbers and send t to the mmedate ntermedate mote for possble retreval of the mssng sensed nformaton. 6. Upon recevng the NACK packet the ntermedate storage mote search the mssng packets n ts storage and resend the nformaton to the snk wth ACK=NACK=0. 7. If the mmedate ntermedate storage mote fals to fnd the mssng sequence number t resend the NACK packet back to the next ntermedate mote on the way towards source untl t wll ACK. 9. Source upon recevng the new rate value wll update ts rate plan and start sendng the scheduled data packets wth ths rate value n order to suppress the congeston n the network. In ths secton we have revewed the envsaged transport layer protocol for WSN. In the next secton we wll dscuss the smulaton setup used for the extensve testng of the envsaged protocol and the possble outcomes of the testng. IV. SIMULATION SETUP AND RESULTS Ths secton descrbes the smulaton setup used for an extensve evaluaton of the proposed transport layer protocol for WSN. Fgure 2 and Table III shows the smulaton setup and network parameters used for an extensve testng of the proposed protocol, where Sources A, B and J are multmeda sensor motes whle Source C, D, E and H are generc scalar sensor motes. The prorty of the multmeda data packet s hgher than of the scalar data packet the source prorty graph s shown n Table II and obeys the followng prorty rule: Pr [A] = Pr [B] = Pr [J] > Pr [C] > Pr [D] > Pr [E] > Pr [H] where, Pr(A) = Prorty of data packet from Source A, Pr(B) = Prorty of data packet from Source B, Pr(C) = Prorty of data packet from Source C, Pr(C) = Prorty of data packet from Source D, Pr(C) = Prorty of data packet from Source E, Pr(H) = Prorty of data packet from Source H, Pr(J) = Prorty of data packet from Source J. TABLE II. SOURCE PRIORITY Mote A B C D E H J Prorty Fgure 2. Network topology used for evaluaton Fgure 1. Software descrpton of the proposed transport layer protocol 8. The snk based on Equatons 1-3 start makng measurement of the C and new rate plan and wll then update the sources wth ths nformaton. The performance of the Prortzaton Capablty enabled Transport Layer Protocol s evaluated based on followng crtera; [1] Performance of the Protocol wthout Prortzaton enabled storages, [2] Performance of the Protocol wth Prortzaton enabled storages at Mote F, G and I, [3] Performance of the Protocol wth Prortzaton enabled storages at Mote I. TABLE III. NETWORK PARAMETERS 585

4 Parameter Values Frequency 914e+6 Range 100 meters Transport Protocol Proposed protocol wthout prorty enabled storage Proposed protocol wth complete prorty enabled storage Proposed protocol wth dstrbuted prorty enabled storage MAC IEEE [11] RX and CS Threshold e-10W e-10 W Routng agent Ad hoc On-Demand Dstance Vector (AODV) [14] Ifqlen (Queue length at MAC 200 packets level) Energy Model Yes: NS-2 based Energy computaton [12] CP Threshold 10 Mote Intal power 1000 W Mote Idle power 712e-6 W Mote Rx power 35.28e-3 W Mote Tx power 31.32e-3W Mote Sleep power 0.001W and E s W, W, W and W respectvely. Fgure 3. Average Throughput comparson A. Performance of the Protocol wthout Prortzaton enabled storages Table IV shows the average packet drop comparson for the selected network. As we can see from the Table IV that hgh prorty sources A, B and J (havng prorty of 5) has a packet drop of 0, 11 and 0. Whereas the packets drop for the Sources C, D, E and H are 3, 6, 5 and 0 respectvely. So on average around 7% of packet drop occurred for ths network topology havng no prortzed enabled storage at the ntermedate motes and among all sgnfcant packet drop occurs for the case of Source B whose total packet drop count s 11. TABLE IV. AVERAGE PACKET DROP COMPARISON Mote No of Send Receved Dropped A B C D E H J Total The average throughput comparson for the same network s shown n Fgure 3. From ths t would be obvous that on average throughput rses to 0.435Mbps and then drops to 0.42Mbps when all sources are actve for sendng wth almost equal contrbuton from every source. Fgure 4. shows the average mote power consumpton for the selected network topology. From the graph t s obvous that on average every source consumes 0.2 Watt (W) of power whereas the ntermedate and snk motes consumes 0.45 W and 0.25 W of power respectvely. So for sources the successful transmsson of every packet consumes W, W, W, W, W, W and W respectvely. Whereas the power (source) consumed n retransmsson of the mssng packets from Sources B, C, D Fgure 4. Average Mote power consumpton comparson B. Performance of the Protocol wth Prortzaton enabled storages at Mote F, G and I Average packet drop comparson for the network wth prortzed enabled storage at motes F, G and I s shown n Table V. From the data gven n the Table V t s obvous that hgh prorty sources A, B and J (havng prorty of 5) has a packet drop of 3, 2 and 0. Whereas the packets drop for the low pror Sources C, D, E and H are 1, 5, 8 and 0 respectvely. So on average around 6% of total packet drop (send =327, receved 308) occurred for ths network topology havng complete prortzed enabled storage at the ntermedate motes and among all sgnfcant packet drop occurs for the case of Source E whose total packet drop count s 8. The average throughput comparson for the same network s shown n Fgure 5. From ths t would be obvous that on average throughput rses to 0.42Mbps and then drops to 0.39Mbps when all sources are actve for sendng wth almost 586

5 equal contrbuton from every source except from Source A and B. TABLE V. AVERAGE PACKET DROP COMPARISON Mote No of Send Receved Dropped A B C D E H J Total consumes W, W, W, W, W, W and W respectvely. Whereas the power (source) consumed n retransmsson of the mssng packets from Sources A, B, C, D and E s W, W, W, W and W respectvely. C. Performance of the Protocol wth Prortzaton enabled storages (Buffdata Agent) at Mote I Now we dscuss the case of dstrbuted prortzed enabled storage where mote I serve the purpose of ntermedate storage. Ths case s smlar to the second case dscussed above but wth only one mote s used for loss recovery and prortzed forwardng whle all other mddle motes act as smple relay motes. The average packet drop comparson for ths network topology s gven n the Table VI. From the Table VI t s obvous that every mote except mote A contrbute the same amount of load nformaton and hgh pror Sources A, B and J has 0% data loss whch s qute a sgnfcant mprovement as compared to the above two cases. Also the low pror Sources C, D, E and H has data loss of 4, 1, 3 and 4 packets respectvely. Overall ths confguraton exhbts a sgnfcant mprovement wth total data loss of only 3% as compared to 7% and 6% for wthout and complete prortzed enabled storage cases dscussed above. TABLE VI. AVERAGE PACKET DROP COMPARISON Fgure 5. Average Throughput comparson Fgure 6. Average Mote power consumpton comparson The Average mote power consumpton for the selected network topology wth prortzed enabled storage s shown n the Fgure 6. From the Fgure 6 t s obvous that on average every source consumes 0.2 W of power whle the ntermedate and snk motes consumes 0.5 W and 0.28 W of power respectvely whch s slghtly hgher than the case havng no prortzed enabled ntermedate storage dscussed above. So for sources the successful transmsson of every packet Mote No of Send Receved Dropped A B C D E H J Total The throughput comparson for the network s shown n the Fgure 7. For ths network topology the peak throughput of 0.465Mbps and mnmum of 0.445Mbps s acheved wth all sources contrbuted equally (51 data packets except for 45 data packets for Source A). Thus havng sngle storage mote that stores nformaton from all ts chld relay motes as well as source motes exhbts hgh throughput n comparson to have no or multple storage motes. The hgh data loss for wthout case s qute obvous where as for multple motes the reason of hgh loss s due to the fact that snce each ntermedate mote serve the purpose of storng so durng peak data transmsson (when all sources contrbutes) t takes long for every mote to store and rearrange the packets n prortzed order and then prortzed retreval of the packets for forwardng. As every ntermedate mote n complete prortzed enabled storage case perform the smlar thng and also the TTL value of every source packet s fxed so there s a chance for some packets to be dropped on ther way towards snk because of ths long delay. The Average mote power consumpton for the selected network topology wth prortzed enabled storage at ntermedate mote I s shown n the Fgure 8. From the Fgure 8 t s obvous that on average every source consumes 0.2 W of power whle the ntermedate and snk motes consumes 0.45 W 587

6 and 0.3 W of power respectvely. So for sources the successful transmsson of every packet consumes W, W, W, W, W, W and W respectvely. Whereas the power (source) consumed n retransmsson of the mssng packets from Sources C, D, E and H s W, W, W and W respectvely. Fgure 7. Average Throughput comparson Fgure 8. Average Mote power consumpton comparson V. CONCLUSIONS The exstng WSN transport layer protocols are desgned for ether congeston control or ensurng the data relablty parameter of the desgn, and none of them smultaneously handles the congeston control and data relablty except for STCP. Source prortzaton s also another mportant aspect whch s seldom addressed n conjuncton wth congeston control and data relablty. In the followng paper we have dscussed a transport layer protocol scheme for WSN whch guarantees congeston control, data relablty and source data prorty smultaneously. Stochastc framework for computng the E-2-E delay of source data packet nvolvng the congeston ndex parameter wll be used n fndng the updated rate plan for sources and prortzed forwardng of the data packets. Dstrbuted prortzed enabled storage (whch stores data packet for some defned nterval of tme and enables prortzed forwardng of the data packets based on the source prorty and ts TTL value) s used to acheve the E-2-E relablty of the data packets thus ensurng the applcaton specfc QoS. Dstrbuted prortzed enabled storage and data forwardng showed better results n-terms of average throughput, average data packet drop n comparson to wthout and complete prortzed enabled storage and forwardng. In the next step we wll ncorporate the crosslayer feature to the exstng desgn and ths sets our future research drecton. REFERENCES [1] I.F. Akyldz, T. Meloda, and K.R. Chowdhury, A Survey on wreless multmeda sensor networks, Computer Networks (Elsever) J., vol. 51, pp , [2] TCP, Aug [3] UDP, Aug [4] C. -Y. Wan, S. B. Esenman, and A. T. Campbell, CODA: Congeston detecton and avodance n sensor networks, n Proceedngs of ACM Sensys 03, Nov. 5-7, 2003, Los Angeles, Calforna, USA. [5] Y. Sankarasubramanam, O. B. Akan, and I. F. Akyldz, ESRT: Event -to-snk relable transport n wreless sensor networks, ACMMobhoc 03, Jun. 1-3, 2003, Annapols,Maryland, USA. [6] F. Stann and J. Hedemann, RMST: Relable data transport n senor networks, IEEE SNPA 03, May 11, 2003, Anchorage, Alaska, USA. [7] C.-Y. Wan, A. T. Campbell, PSFQ: A relable transport protocol for wreless sensor networks, n Proceedngs of ACM WSNA 02, September 28, 2002, Atlanta, USA. [8] R. Anantharangachar, C. Reddy and D. Ranganathan, GARUDA: A Case Study of Servce Orented Applcaton Integraton Framework, HP Inda. [9] Y. G. Iyer, S. Gandham, and S. Venkatesan, STCP: A generc transport layer protocol for wreless sensor networks, IEEE ICCCN 2005, Oct , San Dego, Calforna, USA. [10] S. Mascolo, C. Casett, M. Gerla, M. Y. Sanadd, and R. Wang TCP Westwood: Bandwdth Estmaton for Enhanced Transport over Wreless Lnks, ACM SIGMOBILE 01, Rome, Italy, 2001 [11] IEEE P802.11, Man General Info Page, Aug [12] The Network Smulator NS-2, July [13] F.L. Lews, L. Xe and D. Popa, Optmal and Robust Estmaton wth an ntroducton to Stochastc Control Theory, Second Edd, CRC Press, 6000 Broken Sound Parkway, NW (2008). ch 1-4, pp [14] C.E. Perkns, E.B. Royer and S. Das, Ad hoc On-Demand Dstance Vector (AODV) Routng, RFC 3561, July [15] A.Sharf, V. Potdar, A.J.D Rathnayaka and T. Dllon, Relable Transport Protocol for WSN wth Congeston Avodance usng Stochastc Control Framework, Submtted to ETRI Journal, Dec