Bas Agni 98 Dream

8/22/2019 Bas Agni 98 Dream

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A Distance RoutingS t efa n o B ~ a gn i

Effect AlgorithmI rnr ich Ch lamtac

for Mobility (DREAM)*Violet R . S y rot iuk

B a r r y A. Woodwa rdErik Jonsson School of Engineering and Computer Science

The University of Texas at DallasEmail: {basagni, chlatac, syrotiuk, woodward}~utdallas. edu

Abstract 1 Introductionh this paper we introduce a new routing protocol forad hoc networks built around two novel observations.One, called the distance ef lect , usw the fmt that thegreater the distance separating two nodes, the slowerthey appear to be moving with respect to each other.Accor@gly, the location informat ion in routing tablescan be updated as a function of the distance separatingnodes without compromising the routing accuracy. Thesecond idea is that of triggering the sending of locationupdates by the moving nodes autonomously, based odyon a nodes m ob il i t y r a t e. htuitively, it is clear thatin a direction routing dgorithrn, routing informationabout the slower moving nodes needs to be updated lessfrequently than that about hig~y mobtie nodw. h thisway e~ node can optimize the frequency at which itsends updates to the networks and correspondingly r~duce the bandwidth and energy used, leading to a fullydistributed and self-optimizing system. B~ed on thwerouting tablw, the proposed direction algorithm sendsmessages in the recorded dwectionn of the destinationnode, guaranteeing detivery by following the directionwith a given probability. We show by detailed simda-tion that our protocol always delivers more than 80% ofthe data messages by following the direction computed,without using any recovery procedure. In addition, itmintilzes the overhead used for maintaining routes us-ing the two new principlw of update message frequencyand distance. Lastly, the dgorithrn is fully distributed,provides loop-free paths, and is robust, since it suppfiesmultiple routes.

q This workw supported in part by the ArmyRwearchOfficeundercontract No. DAAG55-97-1-0312.Pemlissiontomakedigitalorhsrdcopiesofallorpartof this\vorkforpersonal or classroomuse is granted without feeprovided that copiesare not mzde or dis~.buted for prolit or commercialad~arrtageand thatcopies bcwrthisnotice andthe full citation on the first page. To copyothm}tise, to republish, to post on senrers or to redistribute to lists,requires prior specificpermission an&ora fee.N1OBICON19SDallasTexas USACop~ghtAChl19981-5S113435-ti9S/10...$00OO 76

Rom a routing perspective, an ad hoc network is apacket radio network in which the mobile nodes performthe routing functions. Generdy, routing is multi-hopsince nodes may not be within the wireless transmissionrange of one another and thus depend on each otherto forward packets to a given destination. Since thetopology of an ad hoc network changes frequently, arouting protocol should be a distributed algorithm thatcomputes multiple, cycle free routes while keeping thecommunication overhead to a minimum (see, e.g., [4]).One way to classify routing protocols in ad-hoc net-works is by when routes are determined. A proactiueprotocol maintains routes on a continuous basis. Thuswhen a sender needs to send a message, the route to theintended destination-generdly, the next hop to itisrdready known and can be used immediately. On thecontrary, in a reactive approach, the sender determinesa route at the time it needs to send a message, i.e.,a route dt i cove~ phase precedes the transmission of amessage.Most of the proactive routing protocols are based onshortest path algorithms adapted to the mobile envi-ronment. This includes, e.g., the protocols presentedin [2, 12], and, more recently, the Wireless RoutingProtocol (WRP) introduced in [9]. h these protocols,routing tables are exchanged among neighboring nodeseach time a change occurs in the topology of the net-work. This impfies update overhead with each exchange(routes have to be recomputed according to the new in-formation) and, since these tables are possibly large, alarge part of the capacity of the network and the energyof the node is spent in their transmission. As a result,when the mobility rate of nodes is high, proactive protocols are infeasible since they cannot keep up with thechanges in the topology.

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An attempt to overcome the tiltations of proactiveprotocols is instead to look for a route in an on-demand fashion, namely, only when it is needed tode~ver a message. This is the basic idea of reactive protocols, such as Johnson and Mdtzs Dynamic SourceRouting (DSR) protocol [6], Park and Corsons Tem-porally Ordered Routing Algorithm (TORA) [10], andPerkins Ad Hoc On-Demand Distance Vector (AODV)routing protocol [11]. b reactive protocols a controlmessage is sent to discover (possibly more than) a routeto a given destination. This kind of control messageis generally shorter than the control messages used inproactive protocols, leaving more bandwidth availablefor the transmission of data messages. However, sincea route has to be entirely discovered prior to the actualtransmission of the message, a sender may experiencea long delay in waiting for the route to be computed.Furthermore, there is no guarantee that the route obtained is usable, since in the meanwhde some of thenodes in the route may have moved out of transmissionrange. Again, the problem becomes more pronouncedwhen the mobitity rate of nodes is high, since the routediscovery mechanism is not able to adapt to the varia-tions of the speed of the nodes. Even route caching, orstiar techniques, used to reduce the delay are ineffec-tive when the mobflty rate is high.A protocol that combinw both a proactive and a r~active approach has been introduced in [3]. Here, theroute discovery phase is divided into an intra zone dis-covery, which involves dl the nodes whose distance fi.e.,number of hops) from the sender is < k fits zone) in aproactive way, and an inter zone discovery, which oper-ates between zones using a reactive approach. The appropriate choice of the zone radius k depends on the m~bfity rate of the nodes and on the message arrid rate(specficdly, the frequency of route requests). However,this choice is static, and therefore there is no possibilityto adapt to changing network conditions. Moreover, theinter zone route discovery messages may loop back intozones aheady queried, =d this must be prevented, oth-erwise more overhead than flooding based approaches isincurred [5].Whether proactive or reactive, existing routing prot~COISor ad hoc networks store route information similarto routing protocols for static networks+ssentidly, theroute is stored as a sequence of nod=. h a proactiveprotocol the sequence is not e~hcit; it corresponds to anext hop table lookup at each node along the route. ka reactive protocol the restit of a route discovery con-trol message is the route given as an exTficit sequenceof nodes to foUow. However, in the randomly chang-ing topology of ad hoc networks, storing a route x asequence of nodes is inadequate for reaching the desti-

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nation, because the movement of any node in the sequence renders the path indd. Thus, a new definitionof routing table entry is needed.h this paper we present a routing protocol based on anew definition of routing information. b our approach,the routing table stored at each node contains locationinformation for any other node in the network (e.g., g%ographic coordinates that can be obtained by the useof GPS [7]). Our protocol can be considered proactive,since we define a new mechanism for the disseminationand updating of location information. When node Awants to send a message m to node B, it uses the 1~cation information for B to obtti Bs direction, andthen transmits m to dl its one hop neighbors in thedwection of B . Each neighbor repeats the same proc~dure, until B , i f possible, is eventudy reached. Thus, aroute is sought in an on-demand f=hion, hke in reactiveapproaches.The probability of finding B in the computed direction,rehes on how the location information is disseminatedthrough the network. b our model, each node transmitscontrol messages bearing its current location to dl theother nodes. The frequency with which these controlmessages are transmitted is determined by:

q considering what we cdl the distance effect i Thegreater the distance separating two nodes, theslower they appear to be moving with respect toeach other. Thus, nodes that are far apart, need toupdate each others locations less frequently thannodes closer together. This is refllzed by associat-ing with each control message an age) which cor-responds to how far from the sender that messagetravels;

q the m obi l i ty r a te: The faster a node moves, themore often it must communicate its location. Thisallows each node to self optimize its disseminationfrequency, thus transmitting location informationonly when needed and without sacrificing the routeaccuracy.

Since distance and mobifity play a central role in ourprotocol, we name it the D i st an ce R ou t in g E fect A l go-n .t hm f or M obi l it y (DREAM) protocol for ad hoc net-works. Due to the new definition of routing information,we do not have to exchange large amounts of controlinformation m in existing proactive protocols. At thesame time, since no route discovery is needed, we do notsuffer the associated delay typical of reactive solutions.Furthermore, DREAM achieves the following desirableproperties:

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q

q

q

q

it is b an d w i d th a n d en er g y ef i ci en k Each controlmessage carries ordy the coordinates and the iden-tfier of a node, thus being small compared to thecontrol messages used by proactive protocols (thathave to carry routing tabla) and to those usedby reactive protocols (that have to carry an entireroute). Most importantly:a.

b.

The rate of control message generation is determined and optimized according to the m~bfity rate of each node individu~y.Due to the distance effect the number ofhops (radius from the moving node) it flbe allowed to travel in the network beforebeing discarded wi~ only depend on the rela-tive (geographic) distance between the mov-ing node and the location tables being up-dated.

h this way the number of copies as well as the num-ber of hops control messages W travel are bothoptimized (minirni zeal) without sacrificing qutity.This means that with respect to efisting protocols,in D~AM more bandwidth and energy (requiredfor transmission in each mobde node) can be usedfor the transmission of data messages;it is inherently l oop-f ree, since each data messagepropagates away from its source in a spec%c direc-tion;it is rebut, meaning that the data message canreach its intended destination by foUowing possiblyindependent routes;it is a da pt i ve t o m ob il i ty, si n ce the frequency withwhich the location information is disse&nated depends on the mobfity rate.

h the nefi sections, we d~cribe the mechanism of dis-semination of location information, a general model toprobabfisticrdly guarantee how to find a node in a givendirection, and the D~AM protocol in greater detti.The paper concludes with simtiation results that showthe effectiveness of our method, namely, that the prot~COIalways dehvers more than 80% of the data messagesby fo~owing the direction computed,l and that whencompared to a reactive protocol, the average end-t~enddelay decreases considerably.1This percentagerefersto the m=sages deHvereddi~tiy, i.e.,to those mwsages that are delivered by sending them in the di-rection of the recipient node. H a mmage cannot be deliveredbecause its intended destination cannot be found in the expecteddirection,ourprotocol providesa recoveryroutinethat guaranteesthat eventualy that mmage will be delivered.

2 Dissemination of Location In-formation

Consider an ad hoc network with n nodes. We assumethe etistence of a mechanism that flows each nodeto be aware of its own location (given as coordinates)with respect to a predefied positioning system (see,e.g., Global Positioning System as in [7]). These coor-dinates are mchanged between nodes so that each nodeconstantly obtains location information about the othernodes in the network for routing purposes. Specifically,a L ocat ion T abl e (L T ) is maintained at each node Athat records, for each node B, its location, from whichits d i r ect i on B . and distance B , can be computed. Bydirection we mean that B o is the angle of the polarcoordinates of B on a system centered on the currentposition of A ad by distance, we mean that Br is thegeographical distance separating A and B. The entryrelated to a node B, L T(B), dso contains L T , (B ), thetime at which the location information for B w as lastupdated.Since our routing protocol is based on the location tablemaintained at each node, care is required in order to r~duce the eWense of disseminating location informationthrough the network. This is accomplished through thefollowing simple observation: the f~her two nodes aresepaated the less often their location table entries needupdating. htuitively, when two nodes ae moving thesame speed, a closer node appems to be chmging morerapidly than one that is far away. We refer to this observation as the distance effect .Each node, periodic~y broadcasts a control packet con-ttilng its own coordinates with respect to the specificpositioning system considered. To retilze the distanceeffect, we assign each control packet a l i fe t im e that isbreed on the geographicrd distance the packet has trav-eled from its sender. A majority of the packets, willhave a short fife time: these sh od l i ved packets %esent at high frequency, and die after they have trav-eled through the network a short distance from theirsender. Other long lived packets, sent less frequently,travel farther through the network, reatilng the mostdistant nodes.2When a control packet is received by a node A, the nodedetermines how far the packet has traveled by calcula-tingthe distance d between itself and the sender of thepacket. E d is greater than the fife time associated withthe packet, then the packet is no longer forwarded.

2 Forsimplicity,we consideronly twom~ximumagesfor thecontrol pwkets.

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The frequency with which a given node broadcasts con-trol packets is a function of the nodes mobltity: themore mobde the node, the more often it must dissem-inate its location information. The fact that most ofthe pa&ets d be short hved clearly re&es the ideathat the nodes closest to A xe those most in need ofAs location, while nodes farther away need As locationupdated less ofien.As a result, the firther away a destination and theslower the rate of movement of the updating node, theless often a copy of the control packet wifl be sent. Wecu therefore miniize the total number of control pack-ets in the network, while maintaining the same proba-btity of error per route. The dissemination methoddescribed reflects the distance effect and thus maintainsthe same probabtity of routing accuracy w~e distribut-ing control packets proportionately to distance and rateof movement.Overall, th~ dissemination method will therefore havethe fo~owing properties:

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When no movement occurs no bandwidth is wastedon control packets since control packets are initi-ated by moving nodes ody.The update frequency can be optimaUy gaugedsince the decision of the update frequency ties withthe moving node itse~.The total number of control packets (and consequently related transmission energy) can be til-rnized since the aging of control packets capturesthe relative distance between the moving node andthe location table updating node.

A Model for DREAMThe procws of dissemination of location information asdescribed in the previous section, Wows us to detie amodel from which we can derive a probabtistic guar-antee of finding a node in a given direction. When anode S needs to send a m~sage m to a recipient nodeR, it refers to its L T i n order to retrieve location infor-mation about R. Based on this information, S selectsfrom among its neighbors those nodes that are in thedirection of R wd forwards m to them. Each of thesenodes, in turn, do the same, forwarding the messageto those nodes in the direction of R until R, if possi-ble, is reached. It is thus crucial to select the neighborsof a given node in a certain dwection range in such away that it is guaranteed that R can be found with a

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given probab%ty p, O< p to,node S wants to senda message m with node R as the recipient. S mustchoose among dl its one hop neighbors those nodes Awhose direction A. lies within the range [0 a, $ + a].The angle a must be chosen in such a way that theprobabihty of fidmg R i n the sector S is at least p, for agiven p. The sector S is a wedge centered about the Yiesegment connecting S and R, defied by [0 a, # + a].It may be seen from Figure 1 that, in the time inter-val horn to to tl, node R, whose speed is v, cannot beanywhere outside the circle C centered on its originalposition with radius z = (tl to)v. Here we considerthat R can move in any direction ~, uniforrrdy chosenbetween Oand 2n at speed v. Therefore, we want to finda minimum due for a such that the m-um distancez that R can travel in the time tl to at velocity u iswithin the sector S.Clearly, a depends ofly on v (Rs speed). E either theactual or the mtium speed of R is known to S, thedue for Q that guarantees that R is in the direction[0 a, 0 + a] is immediately given by

V(t l to)Q = ~csi nT.

E the distance z that R travels is greater than the dis-tance r separating S and R, then R can be in any di-rection. h this case, we must set a = x.E v is not known, and ody its probability density finc-tion ~(v) is atiable, we can find a specific E so that theprobab~lty of finding R i n the direction [0 E, 8 + E] is> p, for a given p, O < p s 1. More formWy, we wantto determine E such that

P(z s (tl to)v) > p.h this case, since

x T=sin a sin(~ a)and, since when

@a=~itisx=Tsina,

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,,

I,,

, s

Figureh

we want to findE so thati

z is the maximum dkance that the node R can travel in tl to.

P(z s (tl to)v) = P(r Sins< (tl to)v)= (s)

Once the integral is computed, the needed tiue for ais e=fiy obtained.FinWy, the same reasoning appfies when, given a, wewant to determine when the location information of anode R which is & far from S has to be updated inorder to have a probabfistic guarantee to find R i n thedirection defied by a (i.e., we look for a value of tl).That is, we can determine the frequency at which todisseminate location information.

4 Distace Routing Effect Algo-rithm for Mobility (DREAM)k this section we describe our Distance Routing EffectNgorithm for Mobfity (D~AM) b~ed on the use oflocation information as informdy described in the pr+vious section. The fo~owing is a high-level algorithmic

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dmcription of the procedures Send(m) and Receive(m)of DWAM executed at eachnode S to sendor receiveamessagem, respectively.Weusethe fo~owingnotation:q

q

q

q

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q

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m.sender, m.recipient, m.type and mid: are thefieldsofthe messagem that contain the sender andthe recipientnode ~s, the type ofmessagem (dataor ack) and ms unique message identfier (at thesender). A message of type ack has no addltiondfields;Timeo: returns the current value of the clock atthe node executing the procedure;R is a temporal threshold value;Recov e~ (m ) : is a recovery procedur~F i n d Nei gh bor s (L T ( R)) : is a function that returnsa fist of the one hop neighbors of S whose directionis in the range [ti-a, ti+a] that depends on LT(R).U no neighbor is found in the given range the vrduereturned is til. Here we sssume that the m=imumvelocity of each node is known to d nodes;Ransmit(m, fist): is the procedure by which m issent to W the neighbors specified in lisfiset/clear T i m e-ou t (i ) : sets/cleas a timer msoci-ated with a message m with mid= i;my~: is the identifier of the node executing theprocedure.

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men a node S wants to send a message m to a nodeR, it cfls the procedure Send(m) below. It is assumedthat the fields of m are set on entry to the procedure.

procedwe Send(m)begin

R:= m.recipient;if L T(R) = ni l or T im eo L T.(R) >7then Recovery(m)eke beginNeighbors:= F indNeighbors (LT(R)) ;if Neighbors= nil

then R em ue~ (m )eke begin

if m.type = datathen set Time-out (mid);~ansmii(m, Neighbors)endend

en~The procedure Send(m) executed at node S starts bylooking in Ss location table to &d the current expecteddirection of R. E no location information is atiablefor R findicated by L T (R) = t i l ) or that informationcannot be considered tid (based on LT.(R)), then arecovery procedure must be executed in order to reachR. Here, the tidity of the location information of nodeR is based on the time that has passed since L T(R) w aslast updated: if this time (T i m eo L T T ( R)) is greaterthan a certain threshold T then Rs location informationis considered obsolete. The choice of the value T is acrucial one: in case of slow moving networks it maybe a constant; otherwise, it may be a function of thegeographical distance of R, L Tr (R) (and, in this case,it is stored in another field of the location table).men the direction of R is vtid, S sets a timer r~lated to the message m and then sends m to d the onehop neighbors returned by the function Find_Neighbors.Notice how, given the nature of the wireless channel,the procedure Transmi t is rewed as a single transmis-sion of m to multiple recipients. These are the neigh-bors of S that are within a certain direction rage,as defined in the previous section. Thus, the functionF i ndNei ghbors (LT (R )) is assumed to implement themethod for choosing nodes in a given direction rangesuch that the probab~lty of finding R in a given direc-tion is greater than or equal to a given p, O< p ~ 1. Thedesired probabfity p can be either a constant local tothe function Find3eighbors or it may be passed to thefinction as a parameter. H Findf le ighbors returns nil~.e., if no one hop neighbor exists within the dwectionrange specified) a recovery procedure is again in order.

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The reception of a message m triggers the execution ofthe procedure Receive(m).procedwe Receive(m)beginif my~ = m.recipientthen if m.type = ack

then cle~ Time-out (mid)else beginreply .type := ack;reply.id := mid;reply.sender := my~;reply .recipient := m.sendqSend(repl~)endeke begin

R:= m.recipien~if L T(R) #ni l and T i m e{) L T.(R) < ?then begin

Neighbors:= F indNeighbors (LT(R));if Neighbors # nil

then Transmit(m, Neighbors)end

endend;Upon receiving a message m, a node A first checks tosee if it is the recipient of the message. H it is the in-tended recipient, it then looks at the message type. Ethe message is an acknowledgement for a data messagepreviously sent, then the corresponding timer is cleared(and thus if it has not expired, it til no longer be con-sidered). Otherwise, if A h~ just received a data mes-sage, it sends an acknowledgement to the originator ofm .H A is not the recipient of m , then it simply forwards mto dl the nodes (if any) that, according to its L T, ar e inthe direction of R. Notice that if, for any reason, thelocation information is not up to date or if no neighborexists in the required direction, then no message is sent.This allows the timer corresponding to the message toexpire which wotid trigger the recovery procedure.Some comments are in order:

q

q

E A receives more than one copy of the same mes-sage m, then, for each copy, it sends an acknowl-edgement: this increases the possibility that thesender receives an acknowledgement for m whichin turn, increases the robustness of the protocol;The reception of an acknowledgement related to adata message for which an acknowledgement hasalready been received, or for which the timeouttriggered the recovery procedure, hm no effect;

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q The timeout mechanism and the use of acknowl-edgements are important: the sender has to knowif m has reached the recipient. hdeed, in our ap-proach, it is possible that there is one (or even morethan one) route to the recipient but its location in-formation does not Wow us to reach it. Thus, anexpKcit recovery procedure for this case has to beprovided.

RecoveryHa sender S has no location information either availableor up to date for a specific recipient, and dso whenevera timer expires, an alternative method to defiver a mes-sage must be used. These situations are handed byour Recove~ (m) procedure. Its actual implementationmay vary, depending on the characteristi~ of the net-work. For instance, the mwsage m cotid be partiflyflooded, or flooding can be used to determine a route (ifany) to the recipient.

5 Simulations ResultsWe have simulated our DREAM protocol usingM~~, a discret~event simtiator developed at UCLA[1], by placing n = 30 nodes randody on a grid of size100 x 100. For each node A, the speed is given in gridunits per 100 ticks of the simdation clock (here we ~-sume that each node has the same speed and we indicateit by V), and the transmission range tZA is given in gridunits. Two nodes A and B in the network are neighborsif the Euchdean distance d between their coordinates inthe grid is less than the minimum between their trans-mission ratil (i.e., d(A, B) < fi {tZA, tz~ }). At everytick of the simdation clock, each node determines itsdirection randotiy, by choosing it unifordy betweenO and 2r. Ea& node til then move in that directionaccording to its current speed. When a node reachesthe grid bound~, it bounces back with an angle deter-mined by the incoming direction. The find position ofthe nodm is a function of its initial position and of itscurrent speed.We consider three kind of messages: contr ol messages,data messages, and acknowledgments (ack) . Controlmessages carry only the location information, namely,the coordinates of the node that transmits them (herethey wfl be the coordinates on the grid) and its iden-tifier. Hence, they have &ed length, and their time oftransmission is very short. The transmission time of anack is short = we~, since it carries no data. Data mes-sages are considered two orders of magnitude larger thancontrol messages (with respect to their number of bits),

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and therefore their transmission is accordingly longer.The rate of transmission of each node is considered uni-form dl over the network.The arrival rate, namely, the frequency with which eachnode generates and transmits a data message, hm beencomputed as fo~ows. Each rdm ticks of the simdationclock each node picks a number p randomly and uni-fordy, O < p < 1. H p < A, then a data message mis generated and queued for transmission. The desti-nation for m is chosen randomly and uniformly amongdl the other nodes of the network. h our simdations,each node has the same transmission range, which r~mains fied at 40. This value guarantees good networkconnectivity, i.e., fewer than 10% of the data messagescannot be defivered to their bd destination due to thelack of a physical connection (no route &sts betweenthe two nodes and therefore no routing protocol cansuccessfly de~ver messages in this case).Each rcm ticks of the simulation clock every node Abroadcasts a short lived control message with its cur-rent coordinates. This message is dehvered to dl thosenodes whose Euctidean distmce from A is less thm Kgrid units. Fmdy, one long tived control message istransmitted to d the nodes in the network for each pshort tived control messages.k dl the simulation results presented in this paper wehave chosen 0.05 < ~ S 0.4, Td~ = 300 and K = 40.When the speed of a node A is 2, we have chosen Tcm =125 and p = 10. Each time the speed of the nodesincreases by 2 units, we decrease rc m by 3070.Figure 2 shows that always more than 80% of the datamessages de~vered have reached their find destinationwithout resorting to a recovery routine (here impl+mented by flooding). The three curves correspond tothree different node speeds, nmnely, V =2,4 and 6.b the following figures we compare DREAM with thereactive DSR protocol incorporating route caching aspresented in [6]. Here, we have compared the two prot~COISwith respect to the average end-to-end delag definedx fo~ows: if M is the set of rdl the messages detivered,and for each m ~ Jf, t~ and t~ correspond to thetime when m is generated at the sender and queued fortransmission, and received at the destination, respec-tively, then the average end-teend delay is computedas follows: .

where IMI is the total number of messages transmitted.Figures 3 and 4 show that the average end-t~end delayof the DSR protocol is from 25% to 250% larger thanthe delay obtained by DREAM protocol (the two figures

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id 6q ..*__ V-4 -

w -

m -

70 -

m -

m 0 oG5 01 tils &2&b 02s 03 Us a4

Figure 2: Percentage of messagm defivered without r~sorting to the recovery procedure, when the nodes havethree ~erent speeds.

Figure 3: Average delay vs. arriti rate for D~AMand DSR when each node has speed V = 2.

correspond to two different node speeds, V = 2 and 6).Furthermore, the average delay for D~AM remainsessenti~y constant for W arrid rates.The cofidence level of W our restits is 95%, and theirprecision is within 5%.

6 Conclusionsb this paper we have presented a new dwectiond rout-ing protocol for ad hoc networks using a novel mecha-nism for the dissemination of location information. Theproposed solution can be used to minimize the amountof bandwidth and transmission power used to maintainrouting tables without pentizing the accuracy of the

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01 J0 0.G 0.1 0.15 025 wA2h!4 03 0.4Figure 4: Average delay vs. arrid rate for D~AMmd DSR when each node has speed V = 6

routing tables. Based on these routing (location) ta-bles a probabilistic method for selecting the direction inwhich a given node maybe found was proposed. Simula-tion resdts showed that with over 80% probability thismethod can &d a route (if any etists) to a given nodein the direction computed by DMAM w~e the aver-age end-t~end delays with respect to the DSR reactiveprotocol are substantially lower. FinWy, the D~AMprotocol provides loopfree routes, and is robust in pr~vidmg mdtiple routes to a given dwtination.

References[1]

[2]

[3]

[4]

BAGRODIA, R. L., AND LIAO, W.-T. Maisie: alanguage for the design of efficient discret~eventsimdations. I E EE f ian sact ion s on Sof tw ar e E ngi -neering 20, 4 (April 1994), 225238.CHENG, C., RILEY, R., KUMAR, S. P. R.,AND GARCIA-LUNA-ACEVES, J. J. A loopfieeetiended be~an-ford routing protocol withoutbouncing effect. Computer Communication Review19,4 (September 1989), 224-236.HAAS, Z. J . A new routing protocol for the recon-figurable wireless network. h P r oceed i n gs of t h e1997 I E EE 6t h I n ter nat ion al Con fer en ce on Uni-v er sa l P er son al C om m u n i ca ti on s, I C U PC 97 (S anDiego, CA, 12-16 October 1997), pp. 562-566.HAAS, Z. J. Panel report on ad hoc networksMllcom97. M obi l e C om p ut i n g and Communica-t i ons Review , M C2R, a publ icat i on of the ACMSI GM OB IL E 2, 1 (January 1998), 15-18.

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[5] HAAS, Z. J., ANDPEARLMAN, M. R. The zonerouting protocol (ZRP) for ad hoc networks. ~-TERNET DRAFT-Mobile Ad hoc Networking(MANET) Working Group of the bternet Engi-neering Task Force (ETF), November 1997. To beconsidered Work in Progress. See dso [8].[6] JOHNSON, D., AND MALTZ, D. A. Dynamicsource routing in ad hoc wireless networks. h

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