MANET QoS support without reservations

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1 SECURITY AND COMMUNICATION NETWORKS Secuity Comm. Netwoks (2010) Published online in Wiley InteScience ( SPECIAL ISSUE PAPER MANET QoS suppot without esevations Soon Y. Oh, Gustavo Mafia and Maio Gela Depatment of Compute Science, Univesity of Califonia, Los Angeles, CA 90095, U.S.A. ABSTRACT An inelastic flow is a flow with an inelastic ate, i.e., the ate is fixed, and it cannot be dynamically adjusted to taffic and load condition as in elastic flows like TCP. Real time, inteactive sessions, and video/audio steaming ae typical examples of inelastic flows. Reliable suppot of inelastic flows in wieless ad hoc netwoks is extemely challenging because flows and outes dynamically change and flows compete fo the shaed wieless channel. Bandwidth must be eseved fo inelastic flows at session set up time. To avoid epeated attempts to set up esevations in a volatile netwok and pevent seious netwok capacity degadation due to call set up ovehead, a Call Admission Contol stategy obust to mobility must be developed. In this pape we popose PobeCast, a pobe based call admission contol scheme with QoS guaantees fo inelastic flows. PobCast was designed fo multicast steams but can also wok, by default, fo unicast. In PobeCast, a path (o a tee) is pobed fo capacity availability. If an intemediate link along the pobed path fails to meet the QoS equiement, the flow is pushed back via backpessue upsteam to an intemediate banch o possibly to the souce. The backpessue pinciple is simple; howeve, its implementation equies some cae to avoid unfainess and eventual captue by one of the flows shaing a congested bottleneck. We show that popotional fainess among inelastic contendes will pevent captue. To achieve this, we have developed the Neighbohood Popotional Dop (N-PROD) scheme. N-PROD guaantees fai ejection of unfeasible flows and maintains the same popotional dop ate among suviving flows in the same contention domain. We demonstate the efficacy and obustness of PobeCast fo unicast as well as multicast scenaios using the Qualnet simulation platfom. Copyight 2010 John Wiley & Sons, Ltd. KEYWORDS MANET; QoS; call admission contol; inelastic flow * Coespondence Soon Y. Oh, Depatment of Compute Science, Univesity of Califonia, Los Angeles, CA 90095,U.S.A. soonoh@cs.ucls.edu 1. INTRODUCTION In emegency and tactical wieless Mobile Ad Hoc Netwoks (MANETs), audio and video steaming ae essential equiements fo goup inteopeation. Even commecial MANETs (e.g., vehicula netwoks) will be faced with multimedia steaming because of the populaity of applications such as P2P TV and YouTube. We can expect that futue MANETs will be designed to handle inelastic flows, both uni and multicast with QoS (bandwidth and delay) equiements, in addition to elastic flows such as TCP. Most of the pevious wok on QoS in MANETs is based on esouce esevation on a selected path befoe tansmission can commence [1--5]. Well known limitations of taditional Call Admission Contol (CAC) stategies ae: the complexity of the available bandwidth estimation in a shaed wieless envionment (whee each allocation impacts seveal othe flows in diffeent ways depending on thei elative positions and tansmission anges), the volatility of the available bandwidth estimation due to the apidly changing topology, the need to fequently eallocate esouces due to node mobility, and the ovehead intoduced by the fequent updates. Howeve, if inelastic calls ae accepted without any attempt to veify the availability of esouces, the situation is even wose: congestion will set on and no inelastic calls can get though! As a solution to this dilemma, we popose PobeCast, a pobing based CAC scheme fo inelastic flows that does esouce veification and allocation at the same time without pio esevations. Namely, a new flow fist pobes the availability of esouces, e.g., evaluating packet dop ate at intemediate nodes without any notion of esouce esevation. If an intemediate link fails to meet the QoS equiements, the flow is pushed back by sending a backpessue message upsteam to the souce (o intemediate banch) no time and effot was spent so fa fo esevations. As a esult of backpessue, the incoming flow is eithe eouted o ejected. Once the inelastic flow is established, Copyight 2010 John Wiley & Sons, Ltd.

2 MANET QoS suppot without esevations S. Y. Oh, G. Mafia and M. Gela it cannot be displaced by incoming inelastic flows because of a built in pioity of incumbent vesus incoming flow. The backpessue stategy woks only if the congested link is shaed with popotional fainess among inelastic contendes in the same contention domain. To undestand this concept, note that in the wied Intenet, when a link becomes congested and the queue oveflows, the packet dop ate of each flow is popotional to its ate, namely, the dop pobability is unifom acoss flows. Without loss of geneality, assume all flows ae inelastic. If a new pobing flow finds enough capacity on intemediate links and suffes no loss, it successfully completes the call set up and is pomoted to established flow with highe pioity. If the new flow does not fit in the bottleneck, i.e., it causes congestion, and dops packets, its dop pobability is equal to that of the incumbent flows. By setting a lowe dop pobability theshold on new flow than on incumbent flows, the new flow is automatically disciminated and backpessued, leaving the incumbent flows undistubed; this is exactly the popety we seek in a Call Acceptance Contol scheme. A CAC appoach inspied to pobing was poposed seveal yeas ago fo Intenet VoIP steams [6]. In the Intenet, whee competing flows shae a single common queue in the oute, popotional fainess, and moe geneally esouce allocation ae athe staightfowad. In the wieless medium, thee is no single common queue. In fact, thee ae seveal queues that independently adjust thei MAC paametes (including etansmission ates) in case of loss. Thus, thee is the isk of unfainess and channel captue by big flows and by flows with a elative intefeence gaph advantage when the wieless medium becomes congested. Clealy, a distibuted popotional fainess scheme must be developed fo wieless channels to ovecome the lack of a centalized contol point. To this end, we have complemented the pobing scheme with a distibuted fainess scheme, Neighbohood Popotional Dop (N-PROD) which enfoces unifom dop pobabilities among flows competing in the same contention domain. Each node estimates own packet dop pobability and popagates this infomation by piggybacking to neighbos. As mentioned ealie, in PobeCast, the incoming flow has by design a lowe dop pobability theshold than the incumbent flows. If duing pobing, the new flow dop ate inceases beyond the theshold, the flow is backpessued towad the souce node and the flow is eouted. If backpessue pushes the flow back to the souce and all altenate outes ae exhausted, PobeCast ejects the incoming flow. The poblem of fai shaing among inelastic multicast flows and the concept of popotional fainess was intoduced in a companion pape that appeaed in MSWIM This pape extends that wok by adding a Call Admission Contol scheme based on backpessue. The majo contibution of PobeCast is to enable CAC and fai allocation of inelastic flows in MANETs, fo both unicast and multicast steams, without equiing pio esouce esevation and thus ovecoming the ovehead limitations of taditional MANET esevation and allocation of CAC schemes. The est of the pape is oganized as follows: Section 2 illustates the elated woks, Section 3 descibes the details of the PobeCast, Section 4 exhibits analytical model of PobeCast, and Section 5 pesents simulation esults. Finally, Section 6 contains conclusions and futue wok. 2. RELATED WORK PobeCast builds upon FaiCast [7] adding a CAC scheme to FaiCast. In fact, FaiCast s ationale is to monito flows and adjust thei ates, locally, so that each flow eceives an acceptable shae of bandwidth. Acceptable means that a sufficient amount of bandwidth is available fo multimedia eo coection schemes to ecove. This may not always be the case, in some cases the bandwidth demand may exceed any netwok and coding capability. PobeCast s contibution, then, is to guaantee a minimum QoS level in the netwok following FaiCast s philosophy of implementing a completely distibuted algoithm. A numbe of ad hoc unicast QoS suppot potocols and algoithms have been poposed in the liteatue, e.g., INSIGNIA [8], SWAN [9], and FQMM [10]. Howeve, elatively few MANET multicast QoS schemes have been intoduced. We classify existing MANET multicast QoS schemes into thee categoies based on thei esouce measuement and esevation methods Bandwidth estimation and esouce esevation Ad hoc QoS Multicasting (AQM) [1,2] achieves multicast QoS suppot by tacking available neighbo nodes esouces. Nodes peiodically boadcast a hello message including own bandwidth usage. Upon eceiving the hello message, nodes ecod neighbo infomation in a neighbohood table which is used to calculate the total bandwidth allocation to existing multicast sessions. When stating a multicast session, a node floods an initiation packet. Intemediate nodes fowad it on feasible links based on the neighbohood table. AQM hello messages intoduce consideable ovehead in a mobile netwok, intefeing with QoS suppot. The Lanten Tee based QoS on-demand Multicast (LTM) [3] elies on a multipath stuctue, called a lantenpath. LTM employs the lanten tee as a outing path in ad hoc multicast and it uses a CDMA-ove-TDMA model at the MAC laye to allow the supeposition of many flows. LTM exploits CDMA othogonal multiuse capability to allocate an exta flow in an aleady occupied netwok. QoS is guaanteed only to the extent that the load is kept in check (else losses escalate). Main implementation dawback is the need fo a non standad CDMA-ove-TDMA MAC with distibuted time synchonization equiements. QoS Multicast Routing Potocol (QMR) [4] is an on-demand mesh based potocol that uses a fowading mesh like On-Demand Multicast Routing Potocol (ODMRP) [11]. QMR defines Fowad Nodes (FNs) which

3 S. Y. Oh, G. Mafia and M. Gela MANET QoS suppot without esevations establish a fowading mesh and povide multiple paths. FNs eseve bandwidth fo a multicast session if they can accept QoS oute equest (QREQ) fom the souce. Upon eceiving data packets fom multicast sessions WITHOUT esevations, they fowad them only if shaed bandwidth is available. To implement this hybid scheme, nodes divide bandwidth into fix eseved and shaed bandwidth. The mesh stuctue can guaantee good delivey atio via edundant fowading. Howeve, flood type edundancy may lead to congestion and excessive ovehead effecting QoS pefomance of eseved flows End-to-End pobing Call Multicast Admission-Potocol fo MANETs (M- CAMP) [12] is an end-to-end pobing potocol in which a souce, befoe tansmitting the data steam floods pobing packets to test bandwidth availability along the multicast tee. Only the eceives paticipate in the CAC decision by submitting an accept/efuse decision to the souce based on the eceived quality. Simila to PCP [6] M-CAMP employs thee pioity levels among packets: eal time, pobe, and best effot. Level 2 pobing packets do not affect existing QoS flows. To cope with mobility, afte topology changes, a new esouce pobing pocess is stated to ebuilds the tee and the allocation. QAMNet [5] establishes a QoS awae mesh using Join-Pobe and Pobe-Response contol packets. QAMNet exploits MAC laye feedback to estimate available bandwidth. Like QMR, a souce floods a Join-Pobe packet when it has packets to tansmit. Intemediate nodes update a bandwidth field in the Join-Pobe packet to eflect minimum available bandwidth along the path. Afte collecting one o moe Join-Pobe packets, a eceive sends a Pobe- Response to souce if a feasible path is found. The common limitation of all the above end to end schemes is the inability to pevent unfainess and captue. In addition, QAMNet incus the buden of local available bandwidth estimation Bandwidth fai shaing As mentioned ealie, Mafia et al. designed an algoithm, called FaiCast [7]. The main focus of FaiCast is congestion contol and bandwidth fai shaing acoss multicast flows. To do this, FaiCast uses local flow inteactions and packet dopping; no end-to-end feedback o backpessue. Each flow has a packet loss theshold that coesponds to the minimum acceptable quality. If a flow expeiences a loss ate that exceeds the desied theshold, it pomptly eacts against the competing flows equesting them to dop at a cetain ate. Flows exchange (piggybacked) loss infomation and employ selective packet dops to equalize thei loss ates. This is called Distibuted Gentleman Ageement (DGA) algoithm [7]. DGA algoithm is appopiate fo ad hoc netwoks and bings the following advantages: no bandwidth is wasted due to end-to-end feedback, flows ae faste in adapting to highly dynamic taffic changes, the solution is fully distibuted, and it achieves popotional fainess in wieless multicast. PobeCast N-PROD potocol enfoces equal dop ates among flows within the collision domain. It is inspied by DGA. Once the loss ate exceeds the theshold, N-PROD stops selective packet dop. At this point, PobeCast initiates back-pessue of selective flows towad the souce to equest ejection o eoute. In FaiCast, DGA also stats packet dop when the loss ate eaches the theshold; howeve, it does not attempt to eoute o eject the flow. Namely, the main diffeence between the two potocols is that FaiCast does not execise Call Admission Contol. 3. PROBECAST In this section, we pesent a detailed desciption of Pobe- Cast Assumptions In PobeCast, a key undelying assumption is that inelastic flows ae potected by some fom of end to end FEC (e.g., easue coding, fountain codes, apto coded, etc.). Namely, a sende adds edundancy to its steam, in the fom of eo coecting code which allows a eceive to detect and coect eos (within some limits) at the expense of some exta delay, without the need fo etansmission. This is citical in MANET multicast sessions since conventional ACK and etansmission techniques between a sende and eceives may cause ACK/NACK implosion. We also assume that inelastic flows ae classified into seveal pioity levels. Each level is given a maximum toleable loss ate which (in the easue code implementation) coesponds to a packet dop theshold. The packet dop theshold is caied in the packet heade. An intemediate node backpessues the flow when the packet dop ate exceeds the theshold. PobeCast is independent of the undelying multicast outing potocols (in ou simulation expeiments we will use ODMRP). PobeCast woks equally well with unicast (a special class of multicast). It can coexist with lowe pioity best effot taffics (e.g., TCP), and will thottle best effot taffics to make oom fo inelastic, highe pioity flows Packet dop pobability PobeCast delives dop pobability infomation via piggybacking in the packet heade. To calculate the packet dop pobability, each intemediate node keeps a time window based evolving count of eceived and lost packets. In addition to the sequence numbe stamped by the souce and used to discad duplicates, each intemediate node keeps tack of flows and assigns local sequence numbes to packets in each flow. Local flow bookkeeping is geneally unacceptable in the wied Intenet because of scalability consideations. In ou case, scalability is not violated due to the athe limited

4 MANET QoS suppot without esevations S. Y. Oh, G. Mafia and M. Gela numbe of simultaneous inelastic flows in a single MANET node. When tansmitting a data packet, an intemediate node updates the local sequence field in the packet heade. Upon eceiving a packet, a down-steam node incements the numbe of eceived packets and monitos the local sequence numbe in the packet heade. If thee is a gap, a packet was lost. A node also tacks the numbe of packets dopped fom its queue. It does not, howeve, attempt to monito packet dops on outgoing links to neighbos. This count is the esponsibility of the downsteam neighbos, which eventually epot the loss to upsteam nodes. Evey time unit, a node estimates its packet dop ate. Since the estimate fluctuates, PobeCast uses a weighted aveage to smoothen fluctuations. Dop pobability computation follows: whee DN i (t) = DqN i (t) + DlN i (t) (1) D i (t) = DN i (t) RN i (t) + DlN i (t) (2) P i (t) = αp i (t 1) + (1 α)d i (t) (3) t is the tth time inteval DN i is the total dopped packet ate at node i, flow DqN i is the dopped packet ate at the queue at node i, flow DlN i is the dopped packet ate on the incoming link to node i, flow RN i is eceived packet ate at node pio to dop i, flow D i is the calculated packet dop ate at node i, flow P i is the packet dop pobability at node i, flow α is the constant value, called step constant Th is the dop pobability theshold fo flow. Algoithm 1 summaizes the Node Dop Pobability computation based on the above fomulas. If a node elays multiple inelastic flows, each flow may have a diffeent packet dop pobability. To educe ovehead, instead of sending all dop pobabilities, it suffices fo a node to popagate just the highest value. Fo convenience, we call this value the Node Dop Pobability heeafte. Upon heaing the neighbo Node Dop Pobability, a node sets own Node Dop Pobability by neighbo s value if neighbo s Node Dop Pobability is highe than its own value. Node Dop Pobability values ae timed out and efeshed to account fo lossy neighbos that move away Neighbohood popotional dop N-PROD allows inelastic flows to acquie esouces in a fai and totally distibuted manne without esouce esevation. It enfoces popotional dop ates among flows competing in the same contention domain. Note that popotional fainess is not geneally desiable in elastic flows such as best effot data sessions contolled by TCP. In Algoithm 1 Calculates the node dop pobability DEFINITIONS: Fo each flow, DqNi is the numbe of dopped packets at the queue in a unit time, DlNi is the numbe of dopped packets on the link, and RNi is the numbe of eceived packets at node i pio to queue dop. Node monitos DqNi, DlN i, and RN i. P i is packet dop pobability of flow at node i. Pob i is the Node Dop Pobability of node i and Thi is the dop theshold of flow. fo each flow in i do D i (t) = DqN i (t)+dln i (t) RN i (t)+dln i (t) P i (t) = αp i (t 1) + (1 α)d i (t) if P i (t) > Th i then Pob i = P i (t) SetBackpessueFalg() else if P i (t) > Pob i o Pob i is timeout then Pob i = P i (t) RecodtheUpdatedTime(Pob i ) end if end fo fact, a popula TCP fainess scheme called NRED [13] enfoces unifom dop pobability so that all the TCP flows in the same contention domain achieve the same thoughput. Popotional dop in N-PROD can enfoce diffeent thoughputs fo diffeent inelastic flows with diffeent nominal ates. Fo example, if flow A and B send 100 Kbps and 60 Kbps, espectively, and N-PROD contol stabilizes at 20% dop pobability, flows A and B thoughputs stabilize at 80 Kbps and 48 Kbps espectively. In contast, TCP fainess stives to equalize flows. In ou implementation Section 3.2, each node eads Node Dop Pobability values fom ovehead packets and adjusts its Node Dop Pobability value. If Node Dop Pobability of the neighbo node is highe than its value, a node eplaces own Node Dop Pobability by neighbo s value; othewise, the node ignoes it. To enfoce dop pobability, befoe fowading a packet, the node geneates a andom numbe to compae it with the taget Node Dop Pobability. If the numbe is smalle than the Node Dop Pobability, the packet is dopped fom the queue; othewise, it is fowaded. As a heuistic exception, the packet is not dopped if it belongs to the flow with highest Node Dop Pobability, in ode not to futhe hut that flow Backpessue The flow packet dop theshold depends on taffic class, encoding ate and age of the flow. Fo example, assume thee inelastic flows have 50%, 40%, and 30% dop thesholds, espectively. The fist flow is moe loss toleant than the othes. It will be moe difficult to eoute o eject it once it is established. By the same agument, a new enteing flow typically has a lowe dop theshold than existing flows and thus it is the fist to be ejected in case of oveload.

5 S. Y. Oh, G. Mafia and M. Gela MANET QoS suppot without esevations (A) (B) (C) Flow 2 Flow 2 Flow 2 Backpessue Flow 3 Flow 3 Flow 1 Flow 1 Flow 1 Figue 1. Thee flows in the simple topology. Lowe gaphs show packet delivey atios, pesented by pecentage. (A) Two flows ae pesented both with have high delivey atios ove 90%. (B) Flow 3 stats tansmitting and othe flows delivey atios decease because of channel contention. (C) Flow 3 packet dop ate is exceeded the theshold and backpessue stat. When the packet dop ate is ove the theshold, the flow is backpessued towad its souce. The backpessue mechanism uses piggybacking to educe ovehead. Upon getting a backpessue signal fom a neighbo, the node checks if the neighbo is one of its downsteam fowades fo that flow. If so, it will emove the downsteam node fom the list. It will then check the list to detemine if thee ae any othe downsteam fowades o local eceives fo the flow in question. If thee ae none, the node will fowad the backpessue signal to its upsteam node. This way, all non poductive banches of the multicast tee ae puned. If the backpessue signal eaches the souce, the flow is ejected (i.e., thee is no eceive eady fo it). Altenatively, the souce can attempt to constuct a new multicast tee/mesh by seaching fo lightly loaded paths. Figue 1 illustates an example of new flow ejection via backpessue. In Figue 1 (A), two inelastic flows, Flow 1 and 2, ae initially allocated to two non intefeing paths. In Figue 1 (B), a new flow, Flow 3 is injected by PobeCast. It stats tansmitting packets which intefee with Flow 1 and 2. Thus, Flow 3 shows low delivey atio since it must compete against the othe two flows. Finally, Flow 3 dop ate goes ove the dop theshold and in Figue 1 (C) backpessue and ejection occus. The othe flows ae estoed to thei oiginal ates. 4. PROBECAST OPERATION MODEL PobeCast can be inseted in a simila optimization famewok as authos do fo FaiCast [7]. In fact both potocols ely on the definition of inteaction ules and selective dops. PobeCast is a supeset of FaiCast in which it also implements admission contol (besides poviding fainess among feasible flows of equal pioity) and thus punes unfeasible banches in a multicast distibution gaph. As in Refeence [7], we fomulate the poblem consideing a single multicast communication. Multiple unicast and multiple multicast models can be deived by extending this basic model. In the sequel we will use the following notation: L is the set of links of the netwok, N is the set of nodes, and R i is the set of eceives fo souce i. p loss is a vecto of L ows, fo eceive. Row p loss,l epesents the aveage faction of packets lost, fo eceive, on link l. p loss,0 and x0 ae scalas that both depend fom the data ate and the packet size of flow. x is a vecto of L ows, fo eceive. Row xl epesents the aveage ate of flow on link l. xsouce is a scala. This is the maximum ate at the souce Optimization poblem An in depth desciption of the optimization fomulation and of the techniques used to design the distibuted algoithm can be found in Refeence [7]. We fist descibe the ationale behind the optimization function s design choice and then intoduce the main optimization poblem. Diffeent optimization functions could have been chosen instead of Equation 4: minimize the maximum dop pobability, jointly minimize the aveage dop pobability and the maximum dop s standad deviation, etc. Ou choice can be explained by ou aim at implementing a completely distibuted algoithm. In fact, we tade an optimal solution

6 MANET QoS suppot without esevations S. Y. Oh, G. Mafia and M. Gela fo a distibuted solution. Fo example, the choice of minimizing the maximum dop pobability would have equied a netwok-wide knowledge of each flow s dop ate. In the fomulation of Equation 4, instead, it is possible to elax the poblem and decouple the vaiables so that dop choices ae taken at each node. PobeCast adds a call acceptance contol scheme to FaiCast, theefoe this should be taken in account in PobeCast s model. PobeCast behaves as FaiCast until, though pobing, it discoves that it is not possible to adjust a new flow in the netwok without seveely damaging the othes; we will assume that FaiCast s model holds until the acceptance contol phase does not kick in. We will now concentate on PobeCast s behavio, once PobeCast flows decide that a flow should be shutdown. PobeCast s model can be witten as follows: min 1 T p loss (4) subject to: p loss {0, 1} (5) x 0, R i (6) x R i x souce 1. (7) whee vectos p loss = p,c loss + p,d loss, p,c loss epesents the faction of packets lost due to contention, p,d loss epesents the faction of packets lost due to FaiCast dop decisions. Clealy, p,d loss ae the vaiables in the optimization poblem. As pointed out in Refeence [7], an equation of type xl = F(x, p) is missing. Namely, we lack an accuate analytic model that elates the flow on each link to flows and loss ates in the est of the netwok. As in Refeence [7] we solve this poblem in the numeical optimization pocedue by using data extacted fom simulation. Namely we ae hee defining a Simulation- Optimization poblem, a genealization of a Deteministic Optimization poblem, whee one o moe of the constaints ae obsevable though a stochastic simulation. A simulation optimization appoach is an appoach whee one o moe functions of an optimization poblem ae implemented in simulation. In ou case, QualNet implements the function xl = F(x, p). Obseving p loss at each node, each node sets new values fo p(, d) loss accoding to Algoithms 1 and 2 [14]. We should obseve one impotant fact, the poblem defined in the above equations defines a intege pogam, diffeently than in Refeence [7]. This takes into account the fact that, implementing an acceptance contol scheme, PobeCast implements eveything o nothing policy fo its flows. Clealy, the model summaizes the call acceptance contol effect in Equation 5, which defines that a eceive can eithe lose eveything o nothing. In FaiCast, in contast, the flows loss ates can be inceased without limits, until fainess is achieved. Algoithm 2 N-PROD algoithm DEFINITIONS: Di is packet dop ate of flow at node i. Pob i is the Node Dop Pobability of node i and Thi is the dop theshold of flow. pkt and pkt s ae the packet of flow and s, espectively. Node i eceives pkt s fom Node j Node Dop Pobability of i is Pob i NumReceivedPkt = NumReceivedPkt + 1 if Pob j > Pob i and Pob j and Pob i ae diffeent flows then Pob i = Pob j RecodtheUpdatedTime(Pob i ) end if Node i sends pkt Node Dop Pobability of i is Pob i and it is flow s while queue is not empty do if packet is pkt and Pob i is not flow then if Pob i > unifomrandom[0, 1] then PacketDop(pkt ) end if end if pkt DopPob = Pob i PacketSend(pkt ) end while The objective, expessed by Equation 4, is to minimize the faction of packets lost in the netwok. Constaint Equation 5 defines the acceptance contol model. Equations 6 and 7 ae feasibility constaints, whee Equation 7 limits the total ate at eceives to be bound by the ate at souce by the numbe of eceives Convegence discussion In FaiCast and consequently in PobeCast we tade the seach of an optimal solution fo the seach of a distibuted solution. FaiCast conveges to an optimal solution unde two main assumptions. The fist assumption is that the mobility patten and, theefoe, outes between souce destination pais ae stable compaed to the netwok taffic dynamics. The second assumption is that the objective function in Equation (7), the total loss ate in the netwok is convex in the flows, and the constained set is a convex set. The second popety is vey difficult to pove in geneal, given the complexity of the loss ate expession in a multihop wieless envionment. Thus, FaiCast geneally conveges to a sub-optimal solution. Moe details ae found in Refeence [7]. PobeCast s convegence to a local minimum (in tems of aggegate loss ate) deives fom the convegence of FaiCast. Following that path, we can state that PobeCast can each a local minimum in the case the incoming flow is accepted and a steady state solution is eached. If the incoming flow is ejected (o bette, if seveal banches of the

7 S. Y. Oh, G. Mafia and M. Gela MANET QoS suppot without esevations incoming multicast flow ae blocked), PobeCast conveges to the same, stable solution egadless of the contol paametes used in the pobing and backpessue pocedues. Namely, the PobeCast algoithm is stable. PobeCast convegence is also guaanteed if one posed a slightly diffeent poblem and consideed a set of F flows aleady pesent in a netwok, each with diffeent dop theshold depending on pioity and age. If PobeCast is applied to this set, it will dop the same flow egadless of contol paametes. This situation is of pactical impotance in a MANET whee nodes move and netwok capacity changes constantly. In fact, this is whee PobeCast outpefoms taditional, esevation based acceptance contol schemes. The taditional schemes, once they accept a flow, can no longe eject it. PobeCast instead constantly eadjust flow membeship to eflect changes in topology and capacity. Howeve, the caeful eade will note that, if F flows ae competing to ente the same netwok, the final set of accepted flows will depend on the ode in which the flows ae coming in. This is because we tighten the dop theshold fo an incoming flow, making it easie fo it to be dopped. 5. SIMULATIONS In this section, we validate PobeCast using Qualnet v3.9.5 [15], a packet level netwok simulato. To this end we implemented ODMRP, QAMNet, FaiCast, and PobeCast all in Qualnet. Compaison with ODMRP and FaiCast teaches us how PobeCast successfully builds on pio schemes (which ae actually its ingedients) to achieve the desied goals. Compaison with QAMNet gives an indication of how PobeCast faes against competitos. The FaiCast vesion used in this section is based on the N-PROD module. It is a vey close appoximation of the FaiCast scheme published in Refeence [7] Simulation setup We use b with 2 Mbps channel capacity and 376 m effective eception ange. Intefeence ange is not given as input, athe it is geneated by the simulato. It is appoximately twice as lage as the eception ange. Channel popagation model is the two-ay gound eflection model. The packet size is 512 bytes and the maximum queue size is 50 Kbyte (about 100 packets). We use Qualnet default values fo MAC and Physical laye configuation paametes. PobeCast and FaiCast can un on any ad hoc multicast outing potocol. In ou simulation, we chose ODMRP. In ODMRP, a souce peiodically floods a Join Quey packet into the whole netwok. Upon eceiving a non-duplicate Join Quey packet, evey node in the netwok stoes the upsteam node addess fo evese path leaning and eboadcasts it. When the Join Quey eaches a multicast eceive, the eceive ceates and boadcasts a Join Reply packet to its neighbos. This Join Reply packet is elayed all the way back to the souce following the leaned evese path. Nodes on the evese path become the fowading goup. Data is deliveed along the mesh consisting of the fowading goup nodes. We use the ODMRP implementation included in the Qualnet package. The Join Quey efesh inteval is 3 s and the fowade life time is thee times the Join Quey efesh inteval. We chose the ad hoc multicast call admission contol potocol QAMNet as it is epesentative of the QoS taditional esouce esevation appoaches. Moeove, QAMNet is built on ODMRP, making the compaison with PobeCast easie. QAMNet employs distibuted esouce pobing and admission contol as well as adaptive ate contol of elastic flows in ad hoc multicast. The design of QAMNet is based on existing appoaches: mesh based ad hoc multicast potocol ODMRP and ad hoc unicast QoS potocol SWAN [9]. Like ODMRP, QAMNet is on-demand style and peiodically efeshes the oute, e.g., evey 3 s, exchanging contol packets which include available esouce infomation as well as oute infomation. Bandwidth availability estimation at the local node is calculated simila to SWAN. Namely, a new inelastic flow is admitted duing the fist multicast oute establishing peiod and the admitted flow bypasses a local ate contolle to guaantee equied QoS. If esouces ae insufficient, the inelastic flow is classified as a non-admitted flow and is degaded to elastic status. Taffic ates of elastic flows and non-admitted inelastic flows ae contolled by the local ate contolle which uses Additive Incease Multiplicative Decease (AIMD) algoithm to achieve fainess and efficiency in allocating esouces. Evey T seconds, the ate contolle monitos local MAC laye backoff delay of packets and adjusts the taffic ate. Fo example, if the contolle detects excessive delay, the taffic ate deceases multiplicatively; othewise the ate additively inceases. This AIMD algoithm is inspied by SWAN ate contol scheme. Fom the above we note that QAMNet is not stictly a CAC mechanism since it does not eject unfeasible flows. In ou compaison we use fou metics: Thoughput is the total eceived data bits divided by the total simulation time, Packet Delivey Ratio is the faction of eceived data, End-to-end delay is the aveage delay fom the souce to eceives, and Numbe of Packet Sent is the aggegated numbe of packets sent by a souce. All numbes ae aveaged ove 100 simulation uns except fo the Numbe of Packet Sent and confidence level is Thee even unicast inelastic flows We fist tested the fou potocols using thee paallel flow topology shown in Figue 2. In the pocess, we also show the diffeence between unifom and popotional fainess. The scenaio is that thee inelastic flows in Figue 2 use disjoint paths, but they still intefee with each othe. Fo each flow, the souce and the destination ae located out of each othes tansmission ange and communicate only with intemediate nodes, moe pecisely node F1, F2, and

8 MANET QoS suppot without esevations S. Y. Oh, G. Mafia and M. Gela S3 Flow 3 F3 R3 S2 Flow 1 F2 Flow 2 F1 S1 Figue 2. Thee paallel inelastic flows topology example. Intemediate nodes, F1, F2 and F3 ae within adio ange and they compete with each othe. Souces, S1, S2, and S3 ae outside of othe s adio ange. Figue 3. Thoughput of thee inelastic flows. Unifom nominal ate = 500 Kbps. F3. The distances between node F1, F2, and F3 ae 350 m and thus they hea each othe and compete fo the medium. The flows ae inelastic; the souces, S1, S2, and S3, send data at a constant, unifom ate = 500 Kbps. Flow 1 stats tansmitting data 1 s afte simulation initialization. Flow 2 and 3 stat data sending T = 10 s and 20 s, espectively. Because node F2 is located within F1 and F3 s tansmission ange, Flow 2 packets ae at a disadvantage and ae dopped at F2 at a highe ate than the othe flows. As a esult, only a few Flow 2 packets each the destination. This behavio is clealy exhibited by ODMRP in Figue 3. The application of FaiCast estoes fainess as shown in Figue 3. This esult is vey simila to the esult epoted in pape [13]. This is not supising since with unifom inelastic ates, FaiCast is equivalent to NRED. PobeCast and QAMNet exhibit a behavio that esembles that of ODMRP in Figue 3. The main diffeence, howeve, is the way they deal with Flow 2. Recall that ODMRP does not have admission and ate contol mechanism, thus S2 tansmits packets as 500 Kbps ate. Howeve, Flow 2 is intefeed by Flow 1 and 3 so that most of packets ae dopped. Since thee is not enough bandwidth, QAMNet does not admit Flow 2 so R2 R1 Figue 4. Accumulated total thoughput in the netwok in thee inelastic flows case. Unifom nominal ate = 500 Kbps. that it becomes a non-admitted flow. Its ate is contolled by S2 and F2 without ejection. Thus, in QAMNet Flow 2 thoughput is less than in ODMRP while it is highe than in PobeCast fo the eason discussed next. In PobeCast, in fact Flow 2 is ejected. When Flow 2 stats, PobeCast ties to balance Flow 1 and Flow 2 dop ate, but Flow 2 dop ate exceeds the theshold due to lack of bandwidth. Figue 1 pesents Flow 2 situation just befoe ejection. Figue 4 shows total aggegate thoughputs. As aleady noted in Refeence [13], fainess comes at the cost of degaded total thoughput. PobeCast and QAMNet ejects/contols Flow 2 taffic and thus Flow 1 and 3 ean bandwidth. Consequently, aggegate thoughput fo the latte is the same as ODMRP. Figue 5 illustates end-to-end delay espectively. End-to-end delays of ODMRP, FaiCast, and PobeCast ae aound 20 ms consistently fo all thee flows. In QAMNet end-to-end delay is highe than fo the othe schemes. In paticula, Flow 2 and 3 end-to-end delays ae extemely high: Flow 2 delay is ove 2 s and Flow 3 delay is ove 0.1 s. The eason is that ODMRP, N-PROD, and PobeCast have no taffic ate contol so that packets ae dopped at intemediate nodes. This packet dop does not affect end-to-end delay. On the contay, QAMNet contols taffic ate if the flow is not accepted. In Figue 2, since Flow 2 is non-admitted flow, S2 and F2 contol taffic ate. Channel is busy and thus MAC laye backoff inceases at S2 and F2. Due to AIMD algoithm, taffic ate deceases and Flow 2 end-to-end delay inceases enomously. Moeove, Figue 5. End-to-end delay of thee inelastic flows. Unifom nominal ate = 500 Kbps. (QAMNet Flow 2 delay is ove 1 s so it is emoved fom the gaph).

9 S. Y. Oh, G. Mafia and M. Gela MANET QoS suppot without esevations Figue 6. Delivey atio of uneven thee inelastic flows case. Flow 1, 2, and 3 ae 800 Kbps, 400 Kbps, and 200 Kbps, espectively. QAMNet sometimes seems to accept all thee flows o does not admit Flow 3 instead of Flow 2 due to incoect and uneliable esouce monitoing. In these cases, Flow 3 end-to-end delay inceases significantly (above Flow 1) because of contention and taffic contol at F3 as shown in Figue 5. The abnomal delays of QAMNet ae a definite cause of concen in the suppot of inelastic flows (such as video steaming, say) with impotant delay constaints Thee uneven unicast inelastic flows In the next simulation expeiment, we use the same layout but now the inelastic flows send data packets at diffeent ates. Namely, Flow 1 = 800 Kbps, Flow 2 = 400 Kbps, and Flow 3 = 200 Kbps. Like in the pevious expeiment, Flow 1 stats tansmitting data at T = 1 s. Flow 2 and 3 stat tansmissions at T = 10 s and T = 20 s, espectively. Figue 6 shows packet delivey atios of potocols and Figue 7 illustates thoughputs of flows. In ODMRP, without fainess o admission mechanism, Flow 1 and 3 captue the channel and Flow 2 is staved. Consequently, Flow 3 thoughput, about 180 Kbps, is highe than Flow 2 thoughput, 55 Kbps, while S2 sends packets with highe ate than S3 in Figue 7. With FaiCast, each flow dops packets popotionally to its demand. Thus, dop pobabilities ae unifom and achieved thoughputs ae staggeed as the demands (in the atios Figue 7. Thoughput of uneven thee inelastic flows case. Flow 1, 2, and 3 ae 800 Kbps, 400 Kbps, and 200 Kbps, espectively. Figue 8. Accumulated total thoughput in the netwok of uneven thee inelastic flows case. Flow 1, 2, and 3 ae 800 Kbps, 400 Kbps, and 200 Kbps, espectively. 8:4:2) as shown in Figue 7. This esult is clealy diffeent fom the unifom thoughputs achieved with NRED. As we expected, Flow 2 is ejected in PobeCast while QAM- Net Flow 2 delivey atio is aound 17%. In QAMnet, Flow 1 is often non-admitted since its ate is 800 Kbps and channel bandwidth is only 2 Mbps. As a esult, Flow 1 thoughput is lowe than ODMRP and PobeCast Flow 1 thoughput in Figue 7. Since Flow 2 and 3 ae usually accepted by QAMNet, thei thoughputs ae simila to ODMRP. Even though Flow 1 is a non-admitted flow, Flow 1 taffic ate additively incease since Flow 2 ate is low, 400 Kbps. Figue 8 epesents total thoughput in the netwok. In spite of the fact that individual thoughputs ae now popotional to demands, it appeas that the total thoughputs ae athe insensitive to the actual distibution of demands. Like pevious case, ODMRP, PobeCast, and QAMNet total thoughput is vey close while FaiCast loses total thoughput to achieve fainess. End-to-end delays show the same patten to the pevious expeiment, Figue 5, but Flow 1 delay is much highe than Flow 2 and 3 in all potocols since contention is vey high (high queuing delay) due to high taffic ate, 800 Kbps Mobile thee even unicast inelastic flows In the pevious expeiments, we use a static topology. In this section, we evaluate expeiment esults when thee flows in Figue 2 ae moving. At the beginning of the simulation, flows ae apat enough to emove intefeence and thus all flows ae admitted. They stat packet tansmission at the same time, T = 1 s, with unifom ate = 500 Kbps and Flow 1 and 3 move towad Flow 2. Finally, they fom Figue 2 at simulation time T = 100 s and stop moving. When flows appoach inside the adio ange, FaiCast stats popotional packet dop to achieve fainess among flows and PobeCast stats admission contol. PobeCast ejects Flow 2 since it exceeds the dop theshold due to intefeence. Figue 9 pesents Flow 1 and 3 achieve moe than 450 Kbps thoughput in PobeCast and flow fainess in N-PROD is vey high. The eason why PobeCast though-

10 MANET QoS suppot without esevations S. Y. Oh, G. Mafia and M. Gela Figue 9. Thoughput of thee inelastic flows when they ae moving. Unifom nominal ate = 500 Kbps. put in Figue 9 is highe than the thoughputs in Figue 3 is Flow 2 esponds quickly to the netwok congestion. In Figue 3, Flow 2 stats tansmission afte Flow 1 and befoe Flow 3 stating tansmission so that Flow 2 competes with Flow 1. Howeve, in Figue 9, Flow 1 and 3 intefee in Flow 2 at the same time. When Flow 1 and 3 come inside the intefeence ange, Flow 2 dop ate suddenly inceases and PobeCast ejects it exceeding the theshold. Theefoe, Flow 1 and 2 thoughputs incease in Figue 9 while Flow 2 thoughput is lowe than Figue 3. Contaily, QAM- Net ecods simila esult to ODMRP without thoughput gain. QAMNet has dynamic egulation mechanism to cope with false admission and available bandwidth fluctuation. Fo example, if moe esouces ae actually consumed than eseved, a node andomly selects one of its inelastic flows and contols taffic ate of that flow. In ou scenaio, howeve, flows do not spend moe esouces than eseved so that no flow becomes falling back into a non-admitted flow. In ou scenaio, flows suffe fom available bandwidth deceasing, but Refeence [5] does not clealy descibe this case. Consequently, all thee flows ae admitted and they compete captuing channel when they come inside the intefeence ange. As a esult, QAMNet thoughput is almost same to ODMRP s. In Figue 10, total thoughputs illustate the same patten to pevious esults, Figue 4. PobeCast and FaiCast thoughputs incease significantly, 70 Kbps and 110 Kbps, espectively. ODMRP thoughput, howeve, inceases only 10 Kbps and QAMNet thoughput has no thoughput gain. Figue 11. Thee multicast sessions in the 1000 m by 1000 m aea. Each session has one souce and thee membes. End-to-end delays of fou potocols ae aound 20 ms so we skip the delay gaph hee PobeCast in multicast scenaio In the pevious expeiment, the topology was simple and was specifically chosen to illustate the diffeence between unifom and popotional dopping and the impotance of the latte in the suppot of nonunifom inelastic flow. Moeove, the scenaio was unicast. In this section, we epot on multicast expeiments with PobeCast. Figue 11 is the topology example we used. Thity nodes ae andomly distibuted in a 1000 m by 1000 m aea; thee multicast sessions ae established. Each multicast session has one souce and thee eceives and no common node belongs to two sessions. Howeve, intefeence occus at intemediate fowading nodes in the field. Inelastic data ates ae unifom fo simplicity, namely, 500 Kbps fo each flow. These sessions can toleate up to 50% of packet loss (that is dop theshold is 50%). Multicast session 1 stats tansmitting at T = 1 s and session 2 and 3 stat at T = 1 s and 20 s, espectively. In Figue 12, we epot the esult fo an expeiment with only two multicast sessions (session 1 and 2). We pefomed seveal simulation uns changing seed numbes. In almost all the uns, both sessions suvive and manage to tansmit thei Figue 10. Accumulated total thoughput in the netwok in thee inelastic flows when they ae moving. Unifom nominal ate = 500 Kbps. Figue 12. Two multicast sessions can be simultaneously suppoted.

11 S. Y. Oh, G. Mafia and M. Gela MANET QoS suppot without esevations Figue 13. Thee multicast sessions ae pesent. Session 2 is ejected. full ates. Howeve, when all thee sessions ae injected, the esults epoted in Figue 13 show that one of thee sessions is consistently ejected. At the beginning the sessions ty to balance dop ates and patially succeed. Howeve, as time pogesses, this balance collapses. One session stats dopping packets in busts and packet dop ate suddenly skyockets, exceeding the theshold and tiggeing backpessue on the newcome (with lowe dop theshold) Audio and video steams in a mobile scenaio In this expeiment, 30 nodes ae unifomly distibuted in 1000 m by 1000 m aea and nodes ae moving based on andom mobility model in which the maximum speed is 10 m/s with no pause time. Two inelastic flows ae established: multicast session 1 is 200 Kbps video steam with nine eceives stated at 0 s and session 2 is 40 Kbps audio steam with thee eceives stated at 10 s. The model is epesentative of a seach and escue opeation with two teams communicating with audio and video means. Some of the membes ae motoized, othes ae on foot, justifying the andom way point motion patten. Figue 14 is a snapshot of the topology. An issue is the ability of the two flows, audio and video, to faily compete and coexist. In paticula, we ae inteested in veifying that PobeCast can Figue 15. Thoughput of ODMRP. Two multicast sessions: one is 200 Kbps video steam with nine eceives and the othe is 40 Kbps audio steam with thee eceives. indeed execise pope Acceptance Contol and kill one of the steams (in this case the audio steam) when bandwidth is inadequate. If nodes ae static, channel captue is vey seious in Refeence [7]. Howeve, in this scenaio, nodes ae moving so that unfainess is modeated. Fo example, in the static topology example discussed in Refeence [7], multicast session 1 always captues the channel so that most packets in session 2 ae dopped o lost. In ou mobile scenaio, the topology keeps changing and thus session 2 has a chance to delive packets without seious contention. With ODMRP, in Figue 15, the audio steam delivey atio is aound 45% while video successfully tansmits about 58% packets. Clealy this is unacceptable, audio should be impoved o othewise ejected. In the static expeiment [7], ODMRP delivey atio gap between audio and video is about 50% (session 1 is 80% and session 2 is 30%). In the mobile envionment Figue 16, FaiCast does slightly bette, inceases audio thoughput up to 31 Kbps as well as video thoughput to 125 Kbps. FaiCast alleviates packet collision while focing packet dop so that both multicast session thoughput inceases compaing to ODMRP thoughput. Like we aleady obseved in subsection 5.4, QAMNet pefoms the same as ODMRP, in Figue 17. QAMNet stategy to downgade inelastic flows to elastic when esouces ae inadequate instead of ejecting them does depive video of useful exta bandwidth. PobeCast Figue 14. Topology example of 30 nodes and two multicast flows which ae audio and video steaming. Figue 16. Thoughput of FaiCast. Two multicast sessions: one is 200 Kbps video steam with nine eceives and the othe is 40 Kbps audio steam with thee eceives.

12 MANET QoS suppot without esevations S. Y. Oh, G. Mafia and M. Gela Figue 17. Thoughput of QAMNet. Two multicast sessions: one is 200 Kbps video steam with nine eceives and the othe is 40 Kbps audio steam with thee eceives. Figue 18. Thoughput of PobeCast. Two multicast sessions: one is 200 Kbps video steam with nine eceives and the othe is 40 Kbps audio steam with thee eceives. does the ight thing, consideing the fact that audio cannot be guaanteed adequate bandwidth. It kills the audio while inceasing video thoughput to an impessive 140 Kbps, shown in Figue 18. This is exactly what we expect fom an efficient Acceptance Contol Scheme. The audio will esume afte the video session is ove Inelastic and elastic flow coexistence The final expeiment is about elastic and inelastic flow coexistence and ability of the inelastic flow to gab enough esouces fom the elastic flow to suvive. We will see that PobeCast enables an inelastic flow to gab bandwidth fom an elastic flow (say TCP) by popely execising the popotional dop theshold. Figue 19 epesents a vey 300 m Flow 2 Flow 1 S2 S1 TCP Flow F2 F1 Inelastic Flow Figue 19. Two flows: Flow 1 is an inelastic flow and Flow 2 is an elastic flow. R2 R1 The Numbe of Packets The Numbe of Packet Sent Time (s) TCP Inelastic TCP only Figue 20. The numbe of packet sent by the inelastic and the elastic souces. simple netwok topology whee an inelastic video steam flow coexists with an elastic TCP flow. The TCP sende, S2, stats at t = 1 s and the inelastic flow sende, S1, stats at t = 10 s. Video steam ate is 500 Kbps. S1, S2, F1, and F2 ae all within adio sensing ange so that they intefee with each othe but cannot decode each othe tansmissions. R1 and R2, howeve, ae assumed fa apat to educe hidden teminal collisions (i.e., R1 is not intefeed by F2 and vice vesa). Note that the typical esevation based CAC scheme such as QAMNet does not wok in this situation. When S1 monitos the channel fo available bandwidth, it finds none. In fact, it cannot tell that the intefee is a lowe pioity best effot flow since distance exceeds eception ange. On the othe hand, the TCP flow (due to its geedy natue) completely fills the channel. Theefoe, the inelastic flow is ejected. In contast, PobeCast lets the inelastic flow in, causing an incease in packet loss that in tun foces TCP to back off and leave enough oom fo the inelastic flow to achieve full ate. It is inteesting to note that the TCP souce will backoff and educe the taffic ate even though it does not undestand the packet heade enty that PobeCast adds (i.e., cuent packet dop ate). The intefeence and subsequent loss ate will suffice to slow down TCP. Figue 20 shows the numbe of sent packet at flow souces and Figue 21 illustates eceive s packet dop ate of the inelastic flow, R1. In Figue 20, the middle line (tiangle makes) epesents the numbe of packet sent by TCP when Packet Dop Ratio (%) Packet Dop Rate Time (s) Figue 21. The packet dop atio at the inelastic flow eceive in the two inelastic and elastic flow case.