UBICC Publishers 2008 Ubiquitous Computing and Communication Journal

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1 UBICC Journal Ubqutous Computng and Communcaton Journal 008 Volume ISSN Specal Issue on Moble Adhoc Networks UBICC ublshers 008 Ubqutous Computng and Communcaton Journal

2 Edted by Usman Tarq.

3 Specal Co-Edtor Dr. Shafque Ahmad Chaudhry Ubqutous Computng and Communcaton Journal Book: 008 Volume 3 ublshng Date: roceedngs ISSN Ths work s subjected to copyrght. All rghts are reserved whether the whole or part of the materal s concerned, specfcally the rghts of translaton, reprntng, re-use of llusons, rectaton, broadcastng, reproducton on mcroflms or n any other way, and storage n data banks. Duplcaton of ths publcaton of parts thereof s permtted only under the provson of the copyrght law 965, n ts current verson, and permsson of use must always be obtaned from UBICC ublshers. Volatons are lable to prosecuton under the copy rght law. UBICC Journal s a part of UBICC ublshers UBICC Journal rnted n South Korea Typesettng: Camera-ready by author, data conversaton by UBICC ublshng Servces, South Korea UBICC ublshers

4 Table of Contents apers. erformance Evaluaton of Deadlne Monotonc olcy over 80. protocol Ines el Korb Impact of Node densty on Cross Layer Desgn for Relable Route Dscovery n Moble Ad-hoc Networks Ramachandran B, Shanmugavel S A Framework for Aggregated Qualty of Servce n Moble Ad hoc Networks Ash Mohammad Abbas

5 erformance Evaluaton of Deadlne Monotonc olcy over 80. protocol Ines El Korb and Lela Azouz Sadane Natonal School of Computer Scence Unversty of Manouba, 00 Tunsa Emals: ABSTRACT Real tme applcatons are characterzed by ther delay bounds. To satsfy the Qualty of Servce (QoS) requrements of such flows over wreless communcatons, we enhance the 80. protocol to support the Deadlne Monotonc (DM) schedulng polcy. Then, we propose to evaluate the performance of DM n terms of throughput, average medum access delay and medum access delay dstrbuton. To evaluate the performance of the DM polcy, we develop a Markov chan based analytcal model and derve expressons of the throughput, average MAC layer servce tme and servce tme dstrbuton. Therefore, we valdate the mathematcal model and extend analytal results to a mult-hop network by smulaton usng the ns- network smulator. Keywords: Deadlne Monotonc, 80. protocol, erformance evaluaton, Medum access delay, Throughput, robablstc medum access delay bounds. INTRODUCTION Supportng applcatons wth QoS requrements has become an mportant challenge for all communcatons networks. In wreless LANs, the IEEE 80. protocol [5] has been enhanced and the IEEE 80.e protocol [6] was proposed to support qualty of servce over wreless communcatons. In the absence of a coordnaton pont, the IEEE 80. defnes the Dstrbuted Coordnaton Functon (DCF) based on the Carrer Sense Multple Access wth Collson Avodance (CSMA/CA) protocol. The IEEE 80.e proposes the Enhanced Dstrbuted Channel Access (EDCA) as an extenson for DCF. Wth EDCA, each staton mantans four prortes called Access Categores (ACs). The qualty of servce offered to each flow depends on the AC to whch t belongs. Nevertheless, the granularty of servce offered by 80.e (4 prortes at most) can not satsfy the real tme flows requrements (where each flow s characterzed by ts own delay bound). Therefore, we propose n ths paper a new medum access mechansm based on the Deadlne Monotonc (DM) polcy [9] to schedule real tme flows over 80.. Indeed DM s a real tme schedulng polcy that assgns statc prortes to flow packets accordng to ther deadlnes; the packet wth the shortest deadlne beng assgned the hghest prorty. To support the DM polcy over 80., we use a dstrbuted schedulng and ntroduce a new medum access backoff polcy. Therefore, we focus on performance evaluaton of the DM polcy n terms of achevable throughput, average MAC layer servce tme and MAC layer servce tme dstrbuton. Hence, we follow these steps: Frst, we propose a Markov Chan framework modelng the backoff process of n contendng statons wthn the same broadcast regon []. Due to the complexty of the mathematcal model, we restrct the analyss to n contendng statons belongng to two traffc categores (each traffc category s characterzed by ts own delay bound). From the analytcal model, we derve the throughput acheved by each traffc category. Then, we use the generalzed Z-transforms [3] to derve expressons of the average MAC layer servce tme and servce tme dstrbuton. As the analytcal model was restrcted to two traffc categores, analytcal results are extended by smulaton to dfferent traffc categores. Fnally, we consder a smple mult-hop scenaro to deduce the behavor of the DM polcy n a mult hop envronment. UbCC Journal, Volume 3, Specal ssue on Moble Ad hoc Networks

6 The rest of ths paper s organzed as follows. In secton, we revew the state of the art of the IEEE 80. DCF, QoS support over 80. manly the IEEE 80.e EDCA and real tme schedulng over 80.. In secton 3, we present the dstrbuted schedulng and ntroduce the new medum access backoff polcy to support DM over 80.. In secton 4, we present our mathematcal model based on Markov chan analyss. Secton 5 and 6 present respectvely throughput and the servce tme analyss. Analytcal results are valdated by smulaton usng the ns- network smulator [6]. In secton 7, we extend our study by smulaton, frst to take nto consderaton dfferent traffc categores, second, to study the behavor of the DM algorthm n a mult-hop envronment where factors lke nterferences or routng protocols exst. Fnally, we conclude n Secton 8. LITTERATURE REVIEWS. The 80. protocol.. Descrpton of the IEEE 80. DCF Usng DCF, a staton shall ensure that the channel s dle when t attempts to transmt. Then t selects a random backoff n the contenton wndow [0,CW-], where CW s the current wndow sze and vares between the mnmum and the maxmum contenton wndow szes. If the channel s sensed busy, the staton suspends ts backoff untl the channel becomes dle for a Dstrbuted Inter Frame Space (DIFS) after a successful transmsson or an Extended Inter Frame Space (EIFS) after a collson. The packet s transmtted when the backoff reaches zero. A packet s dropped f t colldes after maxmum retransmsson attempts. The above descrbed two way handshakng packet transmsson procedure s called basc access mechansm. DCF defnes a four way handshakng technque called Request To Send/ Clear To Send (RTS/CTS) to prevent the hdden staton problem. A staton S j s sad to be hdden from S f S j s wthn the transmsson range of the recever of and out of the transmsson range of S... erformance evaluaton of the 80. DCF Dfferent works have been proposed to evaluate the performance of the 80. protocol based on Banch s work []. Indeed, Banch proposed a Markov chan based analytcal model to evaluate the saturaton throughput of the 80. protocol. By saturaton condtons, t s meant that contendng have always packets to transmt. Several works extended the Banch model ether to sut more realstc scenaros or to evaluate other performance parameters. Indeed, the authors of [] ncorporate the frame retry lmts n the Banch s model and show that Banch overestmates the S maxmum achevable throughput. The natve model s also extended n [0] to a non saturated envronment. In [], the authors derve the average packet servce tme at a 80. node. A new generalzed Z-transform based framework has been proposed n [3] to derve probablstc bounds on MAC layer servce tme. Therefore, t would be possble to provde probablstc end to end delay bounds n a wreless network.. Supportng QoS over Dfferentaton mechansms over 80. Emergng applcatons lke audo and vdeo applcatons requre qualty of servce guarantees n terms of throughput delay, jtter, loss rate, etc. Transmttng such flows over wreless communcatons requre supportng servce dfferentaton mechansms over wreless networks. Many medum access schemes have been proposed to provde some QoS enhancements over the IEEE 80. WLAN. Indeed, [4] assgns dfferent prortes to the ncomng flows. rorty classes are dfferentated accordng to one of three 80. parameters: the backoff ncrease functon, Inter Frame Spacng (IFS) and the maxmum frame length. Experments show that all the three dfferentaton schemes offer better guarantees for the hghest prorty flow. But the backoff ncrease functon mechansm doesn t perform well wth TC flows because ACKs affect the dfferentaton mechansm. In [7], an algorthm s proposed to provde servce dfferentaton usng two parameters of IEEE 80., the backoff nterval and the IFS. Wth ths scheme hgh prorty statons are more lkely to access the medum than low prorty ones. The above descrbed researches led to the standardzaton of a new protocol that supports QoS over 80., the IEEE 80.e protocol [6]... The IEEE 80.e EDCA The IEEE 80.e proposes a new medum access mechansm called the Enhanced Dstrbuted Channel Access (EDCA), that enhances the IEEE 80. DCF. Wth EDCA, each staton mantans four prortes called Access Categores (ACs). Each access category s characterzed by a mnmum and a maxmum contenton wndow szes and an Arbtraton Inter Frame Spacng (AIFS). Dfferent analytcal models have been proposed to evaluate the performance of 80.e EDCA. In [7], Xao extends Banch s model to the prortzed schemes provded by 80.e by ntroducng multple ACs wth dstnct mnmum and maxmum contenton wndow szes. But the AIFS dfferentaton parameter s lackng n Xao s model. Recently Osterbo and Al. have proposed UbCC Journal, Volume 3, Specal ssue on Moble Ad hoc Networks

7 dfferent works to evaluate the performance of the IEEE 80.e EDCA [3], [4], [5]. They propose a model that takes nto consderaton all the dfferentaton parameters of the EDFA especally the AIFS one. Moreover dfferent parameters of QoS have been evaluated such as throughput, average servce tme, servce tme dstrbuton and probablstc response tme bounds for both saturated and non saturated cases. Although the IEEE 80.e EDCA classfes the traffc nto four prortzed ACs, there s stll no guarantee of real tme transmsson servce. Ths s due to the lack of a satsfactory schedulng method for varous delay-senstve flows. Hence, we need a schedulng polcy dedcated to such delay senstve flows..3 Real tme schedulng over 80. A dstrbuted soluton for the support of realtme sources over IEEE 80., called Blackburst, s dscussed n [8]. Ths scheme modfes the MAC protocol to send short transmssons n order to gan prorty for real-tme servce. It s shown that ths approach s able to support bounded delays. The man drawback of ths scheme s that t requres constant ntervals for hgh prorty traffc; otherwse the performance degrades very much. In [8], the authors proposed a dstrbuted prorty schedulng over 80. to support a class of dynamc prorty schedulers such as Earlest Deadlne Frst (EDF) or Vrtual Clock (VC). Indeed, the EDF polcy s used to schedule real tme flows accordng to ther absolute deadlnes, where the absolute deadlne s the node arrval tme plus the delay bound. To realze a dstrbuted schedulng over 80., the authors of [8] used a prorty broadcast mechansm where each staton mantans an entry for the hghest prorty packet of all other statons. Thus, statons can adjust ther backoff accordng to other statons prortes. The overhead ntroduced by the broadcast prorty mechansm s neglgble. Ths s due to the fact that prortes are exchanged usng natve DATA and ACK packets. Nevertheless, the authors of [8] propose a generc backoff polcy whch can be used by a class dynamc prorty schedulers no matter f ths scheduler targets delay senstve flows or rate senstve flows. In ths paper, we focus on delay senstve flows and propose to support the fxed prorty deadlne monotonc scheduler over 80. to schedule delay senstve flows. For nstance, we use a prorty broadcast mechansm smlar to [5] and propose a new medum access backoff polcy where the backoff value s nferred from the deadlne nformaton. 3 SUORTING DEADLINE MONOTONIC (DM) OLICY OVER 80. Wth DCF all the statons share the same transmsson medum. Then, the HOL (Head of Lne) packets of all the statons (hghest prorty packets) wll contend for the channel wth the same prorty even f they have dfferent deadlnes. Introducng DM over 80. allows statons havng packets wth short deadlnes to access the channel wth hgher prorty than those havng packets wth long deadlnes. rovdng such a QoS requres dstrbuted schedulng and a new medum access polcy. 3. Dstrbuted Schedulng over 80. To realze a dstrbuted schedulng over 80., we ntroduce a prorty broadcast mechansm smlar to [8]. Indeed each staton mantans a local schedulng table wth entres for HOL packets of all other statons. Each entry n the schedulng table of node S comprses two felds ( S j, D j ) where S j s the source node MAC address and D j s the deadlne of the HOL packet of node S j. To broadcast the HOL packet deadlnes, we propose to use the DATA/ACK access mode. When a node S transmts a DATA packet, t pggybacks the deadlne of ts HOL packet. The nodes hearng the DATA packet add an entry for S n ther local schedulng tables by fllng the correspondng felds. The recever of the DATA packet copes the prorty of the HOL packet n ACK before sendng the ACK frame. All the statons that dd not hear the DATA packet add an entry for S usng the nformaton n the ACK packet. 3. DM medum access backoff polcy Let s consder two statons S and S transmttng two flows wth the same deadlne D ( D s expressed as a number of 80. slots). The two statons havng the same delay bound can access the channel wth the same prorty usng the natve 80. DCF. Now, we suppose that S and S transmt flows wth dfferent delay bounds D and D such as D < D, and generate two packets at tme nstants t and t. If S had the same delay bound as S, ' ts packet would have been generated at tme t such ' t t +, where D ( D ). as D D At that tme, S and S would have the same prorty and transmt ther packets accordng to the UbCC Journal, Volume 3, Specal ssue on Moble Ad hoc Networks 3

8 80. protocol. Thus, to support DM over 80., each staton uses a new backoff polcy where the backoff s gven by: The random backoff selected n [ 0,CW ] accordng to 80. DCF, referred as BAsc Backoff (BAB). The DM Shftng Backoff (DMSB): corresponds to the addtonal backoff slots that a staton wth low prorty (the HOL packet havng a large deadlne) adds to ts BAB to have the same prorty as the staton wth the hghest prorty (the HOL packet havng the shortest deadlne). Whenever a staton S sends an ACK or hears an ACK on the channel ts DMSB s revaluated as follows: DMSB ( S ) Deadlne( HOL( S ) ) DT ( S ) () mn Where DT mn ( S ) s the mnmum of the HOL packet deadlnes present n S schedulng table and Deadlne( HOL( S ) ) s the HOL packet deadlne of node S. Hence, when S has to transmt ts HOL packet wth a delay bound D, t selects a BAB n the contenton wndow [ 0,CWmn ] and computes the WHole Backoff (WHB) value as follows: ( S ) DMSB( S ) BAB( S ) WHB + () The staton S decrements ts BAB when t senses an dle slot. Now, we suppose that S senses the channel busy. If a successful transmsson s heard, then S revaluates ts DMSB when a correct ACK s heard. Then the staton S adds the new DMSB value to ts current BAB as n equaton (). Whereas, f a collson s heard, S rentalzes ts DMSB and adds t to ts current BAB to allow colldng statons contendng wth the same prorty as for ther frst transmsson attempt. S transmts when ts WHB reaches 0. If the transmsson fals, doubles ts contenton wndow sze and repeats the above procedure untl the packet s successfully transmtted or dropped after maxmum retransmsson attempts. 4 MATHEMATICAL MODEL OF THE DM OLICY OVER 80. S In ths secton, we propose a mathematcal model to evaluate the performance of the DM polcy usng Markov chan analyss []. We consder the followng assumptons: Assumpton : The system under study comprses n contendng statons hearng each other transmssons. Assumpton : Each staton S transmts a flow F wth a delay bound D. The n statons are dvded nto two traffc categores C and C such as: C represents n nodes transmttng flows wth delay bound D. C represents n nodes transmttng flows wth delay bound D, such as D < D, D ( D D ) and ( n + n ) n. Assumpton 3: We operate n saturaton condtons: each staton has mmedately a packet avalable for transmsson after the servce completon of the prevous packet []. Assumpton 4: A staton selects a BAB n a constant contenton wndow [ 0,W ] ndependently of the transmsson attempt. Ths s a smplfyng assumpton to lmt the complexty of the mathematcal model. Assumpton 5: We are n statonary condtons,.e. the n statons have already sent one packet at least. Dependng on the traffc category to whch t belongs, each staton S wll be modeled by a Markov Chan representng ts whole backoff (WHB) process. 4. Markov chan modelng a staton of category C Fgure llustrates the Markov chan modelng a staton S of category C. The states of ths Markov chan are descrbed by the followng quadruplet ( R,, j,d ) where: R : takes two values denoted by C and ~ C. When R ~ C, the n statons of category C are decrementng ther shftng backoff (DMSB) durng D slots and wouldn t contend for the channel. When R C, the D slots had already been elapsed and statons of category C wll contend for the channel.. UbCC Journal, Volume 3, Specal ssue on Moble Ad hoc Networks 4

9 Fgure : Markov chan modelng a category C Staton : the value of the BAB selected by S n [ 0,W ]. ( j ) : corresponds to the current backoff of the staton S. D : corresponds to ( D D ). We choose the negatve notaton D for statons of C to express the fact that only statons of category C have a postve DMSB equal to D. Intally S selects a random BAB and s n one of the states ( ~ C,,, D ), 0.. W. Durng ( D ) slots, S decrements ts backoff f none of the ( n ) remanng statons of category C transmts. Indeed, durng these slots, the n statons of category C are decrementng ther DMSB and wouldn t contend for the channel. When S s n one of the states ~ C,, ( D ),, D.. W and ( ) D th senses the channel dle, t decrements ts D slot. But S knows that henceforth the n statons of category C can contend for the channel (the D slots had been elapsed). Hence, S moves to one of the states ( C,, D, ), D.. W. D However, when the staton S s n one of the ~ C,, j,,.. W, states ( D ) j 0..mn( D, ) and at least one of the ( n ) remanng statons of category C transmts, then the statons of category C wll rentalze ther DMSB and wouldn t contend for channel durng addtonal D slots. Therefore, S moves to the state ( ~ C, j, j, D ),.. W, j 0..mn( D, ). Now, If S s n one of the states,, D,, ( D + ).. W and at ( C D ) least one of the ( ) n remanng statons (ether a category C or a category C staton) transmts, then S moves to one of the states ( ~ C, D, D, ), ( D + ).. W. D 4. Markov chan modelng a staton of category C Fgure llustrates the Markov chan modelng a staton S of category C. Each state of S Markov chan s represented by the quadruplet (,k,d j, D ) where: : refers to the BAB value selected by S n [ 0,W ]. k : refers to the current BAB value of S. D j : refers to the current DMSB of S, j [ 0,D ]. D : corresponds to ( D ). D When S selects a BAB, ts DMSB equals D and s n one of the states (,,D, D ), 0.. W. Durng D slots, only the n statons of category C contend for the channel. If S senses the channel dle durng D slots, t moves to one of the states (,,0, D ), 0.. W, where t ends ts shftng backoff. - UbCC Journal, Volume 3, Specal ssue on Moble Ad hoc Networks 5

10 Fgure : Markov chan modelng a category C Staton, other statons of category C have also decremented ther DMSB and can contend for the channel. Thus, S decrements ts BAB and moves to the state (,,0, D ),.. W, only f none of ( n ) remanng statons transmts. When S s n one of the states (,,0, D ) 0.. W, the ( n ) If S s n one of the states (,,0, D ).. W, and at least one of the ( n ), remanng statons transmts, the n statons of category C wll rentalze ther DMSB and S moves to the state (,,D, D ),.. W. 4.3 Blockng probabltes n the Markov chans Accordng to the explanatons gven n paragraphs 4. and 4., the states of the Markov chans modelng statons S and S can be dvded nto the followng groups: ξ : the set of states of S where none of the n statons of category C contends for the channel (blue states n fgure ). ξ ~ C,, j, D, 0.. W, {( ) ( max( 0, ),D )} j 0..mn γ : the set of states of S where statons of category C can contend for the channel (pnk states n fgure ). γ,, D, D, D.. W {( ) } C ξ : the set of states of S where statons of category C do not contend for the channel (blue states n fgure ). ξ,,d j,d, 0.. W, j 0.. {( ) ( D )} γ : the set of states of S, where statons of category C contend for the channel (pnk states n fgure ). γ,,0, D, 0.. W {( ) (,,0,D ),.. W } Therefore, when statons of category C are n one the states of ξ, statons of category C are n one of the states of ξ. Smlarly, when statons of category C are s n one of the states of γ, statons of category C are n one of the states of γ. Hence, we derve the expressons of S blockng probabltes p and p shown n fgure as follows: p : the probablty that S s blocked gven that S s n one of the states of ξ. p s the probablty that at least a staton the other ( n ) statons of gven that ' S of C transmts ' S s n one of the states of ξ. p n ( ) τ (3) where τ s the probablty that a staton of C transmts gven that the states of ξ : τ r ' [ S transmts ξ ] 0 W mn ' S ' S s n one of ( ~ C,0,0, D ) π ( max( 0, ),D ) ( ~ C,, j, D ) π j 0 (4) ( R,, j, D ) π s defned as the probablty of the state (,, j, D ), n the statonary R UbCC Journal, Volume 3, Specal ssue on Moble Ad hoc Networks 6

11 ( R,, j, D ) condtons and Π { π } s the probablty vector of a category C staton. p : the probablty that S s blocked gven that S s n one of the states of γ. p s the probablty that at least a staton the other ( n ) statons of gven that ' at least a staton ' S of C transmts S s n one of the states of γ or S of the n statons of ' C transmts gven that states of γ. p ' S s n one of the n n ( τ ) ( τ ) where τ s the probablty that a staton of C transmts gven that the states of γ. τ r ' [ S transmts γ ] ( C,D,0, D ) π W D ( C,, D, D ) π (5) ' S ' S s n one of and τ the probablty that a staton C transmts gven that states of γ. τ r ' [ S transmts γ ] W 0 ( 0,0,0,D ) π (6) ' S of ' S s n one of the W (,,0,D ) (,,0,D ) π + π (7) (,k,d j, D ) π s defned as the probablty of the state (,k,d j,d ), n the (,k,d D ) statonary condton. Π π j, { } s the probablty vector of a category C staton. In the same way, we evaluate p and p the blockng probabltes of staton S as shown n fgure : p : the probablty that S s blocked gven that S s n one of the states of ξ. p n ( τ ) (8) p : the probablty that S s blocked gven that S s n one of the states of γ. p n ( ) n ( ) τ τ (9) The blockng probabltes descrbed above allow deducng the transton state probabltes and havng the transton probablty matrx, for a staton of traffc category C. Therefore, we can evaluate the state probabltes by solvng the followng system []: Π j Π π j (0) 4.4 Transton probablty matrces 4.4. Transton probablty matrx of a category C staton Let be the transton probablty matrx of the staton S of category C. {, j} s the probablty to transt from state to state j. We have: {( ~ C,, j, D ),( ~ C,, ( j + ), D )} p,.. W, j 0..mn(,D ) {( ~ C,,, D ),( ~ C,0,0, D )}..mn( W,D ) p (), (), D {( ~ C,, D +, D ),( C,, D )} p, D.. W {( ~ C,, j, D ), ( ~ C, j, j, D )} p,.. W, j..mn(, D ) {( ~ C,,, D ), ( ~ C,,, D )} p,.. W (3) (4) (5) {( C,, D, D ),( ~ C, D, D, D )} p, ( D + ).. W (6) {( C,, D, D ),( C,( ),( D ), D )} p, ( D + ).. W {( ~ C,0,0, D ), ( ~ C,,, D )} 0.. W If ( D < W ) then: W, (7) (8) UbCC Journal, Volume 3, Specal ssue on Moble Ad hoc Networks 7

12 {( C, D,0, D ), ( ~ C,,, D )} 0.. W W, (9) By replacng p and p by ther values n equatons (3) and (5) and by replacng and Π n (0) and solvng the resultng system, we can ( R,, j, D ) express π as a functon of τ, τ and τ gven respectvely by equatons (4), (6) and (7) Transton probablty matrx of a category C staton Let be the transton probablty matrx of the staton S belongng to the traffc category C. The transton probabltes of S are: {(,, D j,d ), (,, D ( j + ), D )} p, 0.. W, j 0.. ( D ) {(,, D j, D ), (,,D, D )} 0.. W, j 0.. ( D ) {(,,0, D ),(,,0, D )} p,.. W {(,,0, D ),( 0,0,0, D )} p {(,,0, D ),(,,D, D )} p,.. W {(,,0, D ),(,,D,D )} p, (0) () () (3) p,.. W {(,,0, D ),(,,0, D )} (4) (5) p, (6) 3.. W {( 0,0,0, D ), (,,D, D )}, 0.. W (7) W By replacng p and p by ther values n equatons (8) and (9) and by replacng and Π n (0) and solvng the resultng system, we can (,k,d j, D ) express π as a functon of τ, τ and τ gven respectvely by equatons (4), (6) ( R,, j, D ) and (7). Moreover, by replacng π and (,k,d j, D ) π by ther values, n equatons (4), (6) and (7), we obtan a system of non lnear equatons as follows: ( τ, τ, τ ) ( τ, τ, τ ) ( τ, τ, τ ) τ f τ f τ f under the constrant τ > 0, τ > 0, τ > 0, τ <, τ <, τ < (8) Solvng the above system (8), allows deducng the expressons of τ, τ and τ, and dervng the state probabltes of Markov chans modelng category C and category C statons. 5 THROUGHUT ANALYSIS In ths secton, we propose to evaluate B, the normalzed throughput acheved by a staton of traffc category C []. Hence, we defne: +,s τ r,s, s : the probablty that a staton S belongng to the traffc category C transmts a packet successfully. Let S and S be two statons belongng respectvely to traffc categores C and C. We have: r[ S transmts successfully ξ ] r[ ξ ] [ S transmts successfully γ ] r[ γ ] ( p ) r[ ξ ] + τ ( p ) r[ γ ] + r τ r[ S transmts successfully ξ ] r[ ξ ] [ S transmts successfully γ ] r[ γ ] ( p ) r[ γ ] dle (9) (30) : the probablty that the channel s dle. The channel s dle f the n statons of category C don t transmt gven that these statons are n one of the states of ξ or f the n statons (both category C and category C statons) don t transmt gven that statons of category C are n one of the states of γ. Thus: n n n ( τ ) r[ ξ ] + ( τ ) ( τ ) r[ γ ] dle (3) Hence, the expresson of the throughput of a category C staton s gven by: UbCC Journal, Volume 3, Specal ssue on Moble Ad hoc Networks 8

13 B Idle,s T Te + s Ts + Idle n,s T c (3) Where T e denotes the duraton of an empty slot, T s and T c denote respectvely the duraton of a successful transmsson and a collson. Idle n,s corresponds to the probablty of collson. Fnally T p denotes the average tme requred to transmt the packet data payload. We have: T s ( T + T + T + T ) ( T + T + T ) + DIFS HY HY ACK MAC D p D + SIFS + (33) For all the scenaros, we consder that we are n presence of n contendng statons wth n statons for each traffc category. In fgure 3, n s fxed to 8 and we depct the throughput acheved by the dfferent statons present n the network as a functon of the contenton wndow szew, ( D ). We notce that the throughput acheved by category C statons (statons numbered from S to S 4 ) s greater than the one acheved by category C statons (statons numbered from S S ). to 4 T ( T + T + T + T ) EIFS (34) c HY MAC p D + Where T HY, T MAC and T ACK are the duratons of the HY header, the MAC header and the ACK packet [], [3]. T D s the tme requred to transmt the two bytes deadlne nformaton. Statons hearng a collson wat durng EIFS before resumng ther backoff. For numercal results statons transmt 5 bytes data packets usng 80..b MAC and HY layers parameters (gven n table ) wth a data rate equal to Mbps. For smulaton scenaros, the propagaton model s a two ray ground model. The transmsson range of each node s 50m. The dstance between two neghbors s 5m. The EIFS parameter s set to ACKTmeout as n ns-, where: ACKTmeout DIFS + Table : 80. b parameters. ( T + T + T ) SIFS HY ACK D + Data Rate Mb/s Slot 0 µs SIFS 0 µs DIFS 50 µs HY Header 9 µs MAC Header 7 µs ACK µs Short Retry Lmt 7 (35) Fgure 3: Normalzed throughput as a functon of D,n 8 the contenton wndow sze ( ) Analytcally, statons belongng to the same traffc category have the same throughput gven by equaton (3). Smulaton results valdate analytcal results and show that statons belongng to the same traffc category (ether category C or category C ) have nearly the same throughput. Thus, we conclude the farness of DM between statons of the same category. For subsequent throughput scenaros, we focus on one representatve staton of each traffc category. Fgure 4, compares category C and category C statons throughputs to the one obtaned wth 80.. Curves are represented as a functon of W and for dfferent values of D. Indeed as D ncreases, the category C staton throughput ncreases, whereas the category C staton throughput decreases. Moreover as W ncreases, the dfference between statons throughputs s reduced. Ths s due to the fact that the shftng backoff becomes neglgble compared to the contenton wndow sze. UbCC Journal, Volume 3, Specal ssue on Moble Ad hoc Networks 9

14 Fnally, we notce that the category C staton obtans better throughput wth DM than wth 80., but the opposte scenaro happens to the category C staton. We propose to evaluate the Z-Transform of the MAC layer servce tme [3], [4], [5] to derve an expresson of the average servce tme. The servce tme depends on the duraton of an dle slot T e, the duraton of a successful transmsson T s and the duraton of a collson T c [], [3],[4]. As T e s the smallest duraton event, the duraton of all events Tevent wll be gven by. Te 6. Z-Transform of the MAC layer servce tme Fgure 4: Normalzed throughput as a functon of the contenton wndow sze (dfferent D values) In fgure 5, we generalze the results for dfferent numbers of contendng statons and fx the contenton wndow sze W to Servce tme Z-transform of a category C staton: Let TS ( Z ) be the servce tme Z-transform of a staton S belongng to traffc category C. We defne: H ( R,, j, ) ( Z ) D : The Z-transform of the tme already elapsed from the nstant S selects a basc backoff n [ 0,W ] (.e. beng n one of the ~ C,,, ) to the tme t s found n the states ( D ) state ( R,, j, ). D Moreover, we defne: suc : the probablty that S observes a successful transmsson on the channel, whle S s n one of the states of ξ. suc n ( n ) ( ) τ τ (36) Fgure 5: Normalzed throughput as a functon of the number of contendng statons All the curves show that DM performs servce dfferentaton over 80. and offers better throughput for category C statons ndependently of the number of contendng statons. 6 SERVICE TIME ANALYSIS In ths secton, we evaluate the average MAC layer servce tme of category C and category C statons usng the DM polcy. The servce tme s the tme nterval from the tme nstant that a packet becomes at the head of the queue and starts to contend for transmsson to the tme nstant that ether the packet s acknowledged for a successful transmsson or dropped. suc : the probablty that S observes a successful transmsson on the channel, whle S s n one of the states of γ. suc + n n ( n ) τ ( τ ) ( τ ) n n τ ( τ ) ( τ ) We evaluate H( R,, j, ) ( Z ) n (37) D for each state of S Markov chan as follows: H ( ~ C,,, D ) ( Z ) ( ) c mn + D,W ( ) Te p suc Z H( ~ C ) ( ),k,, D Z + Ĥ T s ( + ) ( ) + ( ) Te C, D,, D Z sucz p suc Where: W + k + suc Z T Ts Te + Z Tc T e (38) UbCC Journal, Volume 3, Specal ssue on Moble Ad hoc Networks 0

15 H H + Ĥ f Ĥ ( C + ) ( Z ) H( + ) ( Z ), D,, D C, D,, D ( + D ) W ( C, + D,, D ) ( Z ) 0 Otherwse We also have: ( ~ C,, j, D ) ( Z ).. W, j..mn ( C,, D, D ) ( Z ) (39) j ( ( p ) Z ) H( ) ( Z ) suc Z (,D ) Ts Te ~ C,,, D Tc Te suc Z ( p ) (40) D ( ( p ) Z ) H( ) ( Z ) ( p ) ( p ) ZH( ) ( Z ), D.. W H + suc Z C, +, + D, D Ts Te ( C ) ( Z ),W,W D, D D ( ( p ) Z ) H( ) ( Z ) Z ( p ) ~ C,,, D Tc Te suc Z ( p ) ZH( ) ( Z ), D.. W H + suc Ts Te ( ~ C,0,0, D ) ( Z ) mn ~ C,W,W, D Tc Te suc Z C, +, + D, D ( W,D ) ( p ) ZH( ) ( Z ) ( p ) Z H( ) ( Z ) suc Z Ts Te ~ C,,, D ~ C,,, D ( p ) + W suc Z Tc Te (4) (4) (43) If ~ C,0,0, D, the transmsson wll be successful only f none of the ( n ) remanng statons of C transmts. Whereas when the staton S transmsson state s ( C,D,0, D ), the transmsson occurs successfully only f none of ( n ) remanng statons (ether a category C or a category C staton) transmts. S transmsson state s ( ) If the transmsson fals, S tres another transmsson. After m retransmssons, f the packet s not acknowledged, t wll be dropped. Thus: TS + + ( Te ( Z ) Z ( p ) H( ) ( Z ) Te ( p ) H( ) ( Z ) ) Z p H( ) ( Z ) p + Z H Tc Te Ts ( C,D,0, D ) ( Z ) )) ( p H ) C,D,0, D ~ C,0,0, D m 0 Tc ( ~ C,0,0, D ) ( Z ) + ph( C,D,0, D ) ( Z ) ( ~ C,0,0, D (44) 6.. Servce tme Z-transform of a category C staton: In the same way, let TS (Z) be the servce tme Z-transform of a staton S of category C. We defne: H,k,D j, Z : The Z-transform of the ( ) ( ) D tme already elapsed from the nstant S selects a basc backoff n [ 0,W ] (.e. beng n one of the states (,,D, D ) ) to the tme t s found n the state (,k,d j, D ). Moreover, we defne: suc : the probablty that S observes a successful transmsson on the channel, whle S s n one of the states of ξ. suc n ( n ) ( ) τ τ (45) suc : the probablty that S observes a successful transmsson on the channel, whle S s n one of the states of γ. n n suc nτ ( τ ) ( τ ) n n ( n ) τ ( τ ) ( τ ) + We evaluate H (,,D j, ) ( Z ) (46) D for each state of S Markov chan as follows: H (,,D ) ( Z ), 0 W j, D and (47) W H (,,D,D ) ( Z ) T W + c T e ( p ) Z H ( ) ( Z ),.. W T j dec suc suc Z +,,0,D Ts Te To compute H (,,D ) ( Z ) j, D ( Z ), such as: + (48), we defne m+ UbCC Journal, Volume 3, Specal ssue on Moble Ad hoc Networks

16 T 0 dec ( Z ) (49) T j dec ( Z ) for j..d H H So: suc Z Ts Te + ( p ) T c T j ( ) e p Z T ( Z ) Z suc dec j (,,D j,d ) ( Z ) H (,,D j,d ) ( Z ) Tdec ( Z ) W, j..d,(, j ) ( 0,D ) And: (,,0,D ) ( Z ) ( p ) ZH ( ) ( Z ) +,,0,D ( p ) ZH ( ) ( Z ) + suc Z.. W H Ts Te +,,0,D T c T e D ( p ) Z T ( Z ) suc ( W,W,0,D ) ( Z ) ( p ) ZH ( ) ( Z ) suc Z Ts Te + T dec c T e D ( p ) Z T ( Z ) W W,,0,D suc dec (50), (5) (5) (5) TS ( ) Te Z p Z H ( ) ( Z ) Ts Tc ( ) Te ( ) ( ) Te p Z H Z p Z H ( ) ( Z ) 0,0,0,D 0,0,0,D m 0 m+ + Tc 0,0,0,D (54) 6. Average Servce Tme From equatons (43) (respectvely equaton (54)), we derve the average servce tme of a category C staton ( respectvely a category C C staton). The average servce tme of a category staton s gven by: ( X ) TS ( ) (55) Where TS ( ) ( Z ) tme Z-transform of staton, s the dervate of the servce S []. By consderng the same confguraton as n fgure 3, we depct n fgure 5, the average servce tme of category C and category C statons as a functon ofw. As for the throughput analyss, statons belongng to the same traffc category have nearly the same average servce value. Smulaton servce tme values concde wth analytcal values gven by equaton (55). These results confrm the farness of DM n servng statons of the same category. Accordng to fgure and usng equatons (44), we have: H D ( 0,0,0,D ) ( Z ) H ( ) ( Z ) T ( Z ) 0,,0,D dec ( p ) ZH ( ) ( Z ) + suc,,0,d Ts Tc (53) Te T e D Z + ( p suc ) Z Tdec ( Z ) Therefore, we can derve an expresson of S Z-transform servce tme as follows: Fgure 6: Average servce tme as a functon of the contenton wndow sze (D, n8) In fgure 8, we show that category C statons obtan better average servce tme than the one obtaned wth 80. protocol. Whereas, the opposte scenaro happens for category C statons UbCC Journal, Volume 3, Specal ssue on Moble Ad hoc Networks

17 ndependently of n, the number of contendng statons wthn the network. D 4, the probablty that S servce tme exceeds 0.005s equals 0.8%. Whereas, staton S servce tme exceeds 0.005s wth the probablty 5.67%. Thus, DM offers better servce tme guarantees for the statons wth the hghest prorty. In fgure 9, we double the sze of the contenton wndow sze and set t to 64. We notce that category C and category C statons servce tme curves become closer. Indeed, when W becomes large, the BAB values ncrease and the (DMSB) becomes neglgble compared to the basc backoff. The whole backoff values of S and S become near and ther servce tme accordngly. Fgure 7: Average servce tme as a functon of the number of contendng statons 6.3 Servce Tme Dstrbuton Servce tme dstrbuton s obtaned by nvertng the servce tme Z transforms gven by equatons (43) and (54). But we are most nterested n probablstc servce tme bounds derved by nvertng the complementary servce tme Z transform gven by []: X ~ ( Z ) ( Z ) TS (55) Z In fgure 8, we depct analytcal and smulaton values of the complementary servce tme dstrbuton of both category C and category C staton ( W 3). Fgure 9: Complementary servce tme dstrbuton for dfferent values of D (W64) In fgure 0, we depct the complementary servce tme dstrbuton for both category C and category C statons and for values of n, the number of contendng nodes. Fgure 8: Complementary servce tme dstrbuton for dfferent values of D, ( W 3) All the curves drop gradually to 0 as the delay ncreases. Category C statons curves drop to 0 faster than category C curves. Indeed, when Fgure 0: Complementary servce tme dstrbuton for dfferent values of the contendng statons Analytcal and smulaton results show that complementary servce tme curves drop faster when the number of contendng statons s small for both category C and category C statons. Ths UbCC Journal, Volume 3, Specal ssue on Moble Ad hoc Networks 3

18 means that all statons servce tme ncreases as the number of contendng nodes ncreases. 7 EXTENTIONS OF THE ANAYTICAL RESULTS BY SIMULATION The mathematcal analyss undertaken above show that DM performs servce dfferentaton over 80. protocol and offers better QoS guarantees for hghest prorty statons Nevertheless, the analyss was restrcted to two traffc categores. In ths secton, we frst generalze the results by smulaton for dfferent traffc categores. Therefore, we consder a smple multhop and evaluate the performance of the DM polcy when the statons belong to dfferent broadcast regons. 7. Extenson of the analytcal results In ths secton, we consder n statons contendng for the channel n the same broadcast regon. The n statons belong to 5 traffc categores where n 5m and m s the number of statons of the same traffc category. A traffc category C s characterzed by a delay bound D, and Dj D D j s the dfference between the C j deadlne values of category C and category statons. We have: D j ( j )K (53) Where K s the deadlne multplcty factor and s gven by: D +, D + D K (53) Indeed, when K vares, the deadlne values of all other statons also vary. Statons belongng to the traffc category C are numbered from S to S. m CW max < 04 and K. Analytcal and smulaton results show that throughput values ncrease wth statons prorty. Indeed, the staton wth the lowest delay bound has the maxmum throughput. Moreover, fgure shows that statons belongng to the same traffc category have the same throughput. For nstance, when n s set to 5 (.e. m 3 ), the three statons of the same traffc category have almost the same throughput. Fgure : Normalzed throughput: dfferent statons belongng to the same traffc category In fgure 3, we depct the average servce tme of the dfferent traffc category statons as a functon of K, the deadlne multplcty factor. We notce that the hghest prorty staton average servce tme decreases as the deadlne multplcty factor ncreases. Whereas, the lowest prorty staton average servce tme ncreases wth K. Fgure : Normalzed throughput for dfferent traffc category statons In fgure, we depct the throughput acheved by dfferent traffc categores statons as a functon of the mnmum contenton wndow sze CW mn such as CW mn s always smaller than CW max, Fgure 3: Average servce tme as a functon of the deadlne multplcty factor K In the same way, the probablstc servce tme bounds offered to S (the hghest prorty staton) are better than those offered to staton S 5 (the lowest prorty staton). Indeed, the probablty that S servce tme exceeds 0.0s0.3%. But, staton UbCC Journal, Volume 3, Specal ssue on Moble Ad hoc Networks 4

19 S 5 servce tme exceeds 0.0s wth the probablty of 36%. and D D D 5 slots. Flows F 3 and F 4 are transmtted respectvely by S and S 4 and have the same delay bound. Fnally, F 5 and F 6 are transmtted respectvely by S 5 and S 6 wth delay bounds D and D and D, D D 5 slots. Fgure 6 shows that the throughput acheved by F s smaller than the one acheved by F. Fgure 4: Complementary servce tme dstrbuton (W3, n8) The above results generalze the analytcal model results and show once agan that DM performs servce dfferentaton over 80. and offer better guarantees n terms of throughput, average servce tme and probablstc servce tme bounds for flows wth short deadlnes. 7. Smple Mult hop scenaro In the above study, we consdered that contendng statons belong to the same broadcast regon. In realty, statons may not be wthn one hop from each other. Thus a packet can go through several hops before reachng ts destnaton. Hence, factors lke routng protocols or nterferences may preclude the DM polcy from workng correctly. In the followng paragraph, we evaluate the performance of the DM polcy n a mult-hop envronment. Hence, we consder a 3 node smple mtlt-hop scenaro descrbed n fgure 5. Fgure 6: Normalzed throughput usng DM polcy Indeed, both flows cross nodes 6 and 7, where F got a hgher prorty to access the medum than F when the DM polcy s used. We obtan the same results for flows F 5 and F 6. Flows F 3 and F 4 have almost the same throughput snce they have equal deadlnes. Fgure 7 show that the complementary servce tme dstrbuton curves drop to 0 faster for flow F than for flow F. Fgure 5: Smple mult hop scenaro Sx flows are transmtted over the network. Flows packets are routed usng the AODV protocol. Flows F and F are respectvely transmtted by statons S and S wth delay bounds D and D Fgure 7: End to end complementary servce tme dstrbuton The same behavor s obtaned for flow F5 and F6, where F5 has the shortest delay bound. Hence, we conclude that even n a mult-hop UbCC Journal, Volume 3, Specal ssue on Moble Ad hoc Networks 5

20 envronment, the DM polcy performs servce dfferentaton over 80. and provdes better QoS guarantees for flows wth short deadlnes. 8 CONCLUSION In ths paper we frst proposed to support the DM polcy over 80. protocol. Therefore, we used a dstrbuted backoff schedulng algorthm and ntroduced a new medum access backoff polcy. Then we proposed a mathematcal model to evaluate the performance of the DM polcy. Indeed, we consdered n contendng statons belongng to two traffc categores characterzed by dfferent delay bounds. Analytcal and smulaton results show that DM performs servce dfferentaton over 80. and offers better guarantees n terms of throughput, average servce tme and probablstc servce tme bounds for the flows havng small deadlnes. Moreover, DM acheves farness between statons belongng to the same traffc category. Then, we extended by smulaton the analytcal results obtaned for two traffc categores to dfferent traffc categores. Smulaton results showed that even f contendng statons belong to K traffc categores, K >, the DM polcy offers better QoS guarantees for hghest prorty statons. Fnally, we consdered a smple mult-hop scenaro and concluded that factors lke routng messages or nterferences don t mpact the behavor of the DM polcy and DM stll provdes better QoS guarantees for statons wth short deadlnes. 9 REFERENCES [] G. Banch: erformance Analyss of the IEEE 80. Dstrbuted Coordnaton Functon, IEEE J-SAC Vol. 8 N. 3, (March 000). [] H. Wu, Y. eng, K. Long, S. Cheng, J. Ma: erformance of Relable Transport rotocol over IEEE 80. Wreless LAN: Analyss and Enhancement, In roceedngs of the IEEE INFOCOM`0, June 00. [3] H. Zha, Y. Kwon, Y., Fang: erformance Analyss of IEEE 80. MAC protocol n wreless LANs, Wreless Computer and Moble Computng, (004). [4] I. Aad and C. Castellucca, Dfferentaton mechansms for IEEE 80., In roc. of IEEE Infocom 00, (Aprl 00). [5] IEEE 80. WG: art : Wreless LAN Medum Access Control (MAC) and hyscal Layer (HY) specfcaton, IEEE (999). [6] IEEE 80. WG, Draft Supplement to art : Wreless Medum Access Control (MAC) and physcal layer (HY) specfcatons: Medum Access Control (MAC) Enhancements for Qualty of Servce (QoS), IEEE 80.e/D3.0, (January 005). [7] J. Deng, R. S. Chang: A prorty Scheme for IEEE 80. DCF Access Method, IEICE Transactons n Communcatons, vol. 8-B, no., (January 999). [8] J.L. Sobrnho, A.S. Krshnakumar: Real-tme traffc over the IEEE 80. medum access control layer, Bell Labs Techncal Journal, pp. 7-87, (996). [9] J. Y. T. Leung, J. Whtehead: On the Complexty of Fxed-rorty Schedulng of erodc, Real-Tme Tasks, erformance Evaluaton (Netherlands), pp , (98). [0]K. Duffy, D. Malone, D. J. Leth: Modelng the 80. Dstrbuted Coordnaton Functon n Non-saturated Condtons, IEEE/ACM Transactons on Networkng (TON), Vol. 5, pp (February 007) []L. Klenrock: Queung Systems,Vol. : Theory, Wley Interscence, 976. []. Chatzmsos, V. Vtsas, A. C. Boucouvalas: Throughput and delay analyss of IEEE 80. protocol, n roceedngs of 00 IEEE 5th Internatonal Workshop on Networked Applances, (00). [3].E. Engelstad, O.N. Osterbo: Delay and Throughput Analyss of IEEE 80.e EDCA wth Starvaton redcton, In proceedngs of the The IEEE Conference on Local Computer Networks, LCN 05 (005). [4].E. Engelstad, O.N. Osterbo: Queueng Delay Analyss of 80.e EDCA, roceedngs of The Thrd Annual Conference on Wreless On demand Network Systems and Servces (WONS 006), France, (January 006). [5].E. Engelstad, O.N. Osterbo: The Delay Dstrbuton of IEEE 80.e EDCA and 80. DCF, n the proceedng of 5th IEEE Internatonal erformance Computng and Communcatons Conference (ICCC 06), (Aprl 006), USA. [6]The network smulator ns-, [7]Y. Xao: erformance analyss of IEEE 80.e EDCF under saturaton condtons, roceedngs of ICC, ars, France, (June 004). [8]V. Kanoda, C. L: Dstrbted rorty Schedulng and Medum Access n Ad-hoc Networks, ACM Wreless Networks, Volume 8, (November 00). UbCC Journal, Volume 3, Specal ssue on Moble Ad hoc Networks 6

21 Impact of Node Densty on Cross Layer Desgn for Relable Route Dscovery n Moble Ad-hoc Networks B.Ramachandran S.Shanmugavel Dept. of Electroncs & Communcaton Engg. Dept. of Electroncs & Communcaton Engg. S.R.M. Unversty Anna Unversty Chenna Chenna profbram@yahoo.com ssv@annaunv.edu Abstract : The moble nature of nodes and dynamc topology of Moble Ad-hoc Networks (MANETs) lead to route falures and requrng the transmsson of control packets. It s mportant to reduce the number of control packets to save resources and to mprove the overall performance of the network. Ad-hoc Ondemand Dstance Vector (AODV) s appealng as an effcent on demand routng protocol because of low routng overhead and hgh performance. However, AODV s not robust aganst topology varatons as t uses weak lnks due to long hops ntroduced by shortest path metrc. In ths paper we propose a moblty adaptve cross layer desgn to enhance the performance of AODV routng protocol by establshng stable routes. The adaptve decson makng accordng to the speed of moble nodes on Route Request (RREQ) packet forwardng results n stable routes. We also test the mpact of node densty n the network on our algorthm, to tell, when to nvoke the our cross layer desgn n moble ad-hoc networks. To demonstrate the effcency of our protocol and ts mpact on network connectvty, we present smulatons usng network smulator, GloMoSm. Keywords: Moble Ad-hoc Networks, AODV, Routng Overhead, Stable Route, and Cross Layer Desgn. I. Introducton Recent growng nterest on potental commercal usage of MANETs has led to the serous research n ths energy and bandwdth constraned network. It s essental to reduce control packet overhead as they consume resources. Routng n MANETs s non trval. Snce moble nodes have lmted transmsson capacty, they mostly ntercommuncate by mult-hop relay. Mult-hop routng s challenged by lmted wreless bandwdth, low devce power, dynamcally changng network topology, and hgh vulnerablty to falure and many more. To meet those challengeous, many routng protocols have been proposed for MANET []. They are categorzed as proactve and reactve protocols. roactve protocols such as DSDV perodcally send routng control packets to neghbors for updatng routng tables. Reactve routng protocols such as AODV and DSR send control packets only when route dscovery or route mantenance s done. When a route s created or repared, the control packets, partcularly RREQ packets flooded by source s network wde broadcast. Moreover, the number of control packets ncreased rapdly wth network sze and topology changes. The prmary goal of an ad-hoc network routng protocol s correct and effcent route establshment between a par of nodes so that messages may be delvered n a tmely manner. Route constructon should be done wth a mnmum of overhead and bandwdth consumpton. The on-demand routng protocols create route only when desred by the source node. When a node requres a route to a destnaton, t ntates a route dscovery process wthn the network. Ths process s completed once a route s found or all possble route permutatons have been examned. Once a route has been establshed, t s mantaned by a route mantenance procedure or untl the route s no longer desred. The Ad-hoc On-Demand Dstance Vector routng protocol bulds on the Destnaton Sequenced Dstance Vector (DSDV) algorthm. It s an mprovement on DSDV because t typcally mnmzes the routng load by creatng routes on a demand bass. AODV [] s a pure on-demand route acquston system, snce node that are not on a selected path do not mantan routng nformaton or partcpate n routng table exchanges. When a source node desres to send a message to some destnaton and does not already have a vald route to that destnaton, t ntates a route dscovery process to locate the destnaton. It broadcasts a route request packet to ts neghbours, whch then forward to ther neghbours and so on, untl ether the destnaton or an ntermedate node wth a fresh enough route to the destnaton s located. Durng the process of forwardng the RREQ, the ntermedate nodes record n ther route tables the address of the neghbor from whch the frst copy of the broadcast packet s receved thereby establshng a reverse path. If addtonal copes of the same RREQ are later receved, these packets are dscarded. Once the RREQ reaches the destnaton or an ntermedate node wth a fresh enough route, the destnaton / UbCC Journal, Volume 3, Specal ssue on Moble Ad hoc Networks 7