Improving MAC Layer Fairness in Multi-Hop802.11 Networks

M V S Deekshitulu and Sukumar Nandi Atanu Roy ChowdhuryDepartment of Computer Science and Engineering, Software Engineering and Technology Labs

Indian Institute of Technology, Guwahati, Infosys Technologies LtdNorth-Guwahati- 780139, Assam, India. Bangalore- 560100, India

{vsdm, sukumar} @ iitg.ernet.in {atanuschowdhury} @ infosys.com

Abstract- Wireless adhoc networks consist of nodes intercon- access to the media by all nodes. It is imperative that in multi-nected by wireless multi-hop communication paths. Such net- hop wireless networks there should be fair allocation of band-works exhibit simulated mobility, where the topological changes width among different nodes/flows or else the serviceability ofare caused by nodes coming up or going down. These networksalso exhibit complex overlapping of flow paths. This in turn leads the entire network is affected. Although there has been someto severe contention inbetween flows as well as between the sub- research on fairness issues in single-hop wireless networksflows' of the same flow. In this paper, we analyze the unfairness [18], [15], research on multi-hop fairness is rarely addressedof IEEE 802.11, in case it is extended for multi-hop networks. in the literature. The research approaches for single-hop flowsThereafter we demonstrate how a simple, distributed algorithm have manipulated the size of the contention window to controlcan be put in place to approximate an ideal schedular like round-robin and provide fair access to all the flows. Our simulation the flows In case of multi-hop flows, the popular approach iSresults clearly show that such an approach outscores the existing to have a packet scheduling algorithm above the MAC Layer,standard on fairness grounds. Additionally we also gain in terms based on some pre-estimated information [16].of throughput by reducing the number of collisions. In this paper, we present a distributed linear algorithm that

approximates a preemptive round-robin schedular to achieveI. INTRODUCTION global fairness for the entire network. As per our approach,

It is only recently that wireless technologies have matured to individual node are responsible for collecting and maintaininga stage where wireless networks are being considered feasible the information of the contending sub-flows in the network.and getting deployed on a worldwide scale. Although the Whenever a sub-flow has completed its transmission success-

concept of wireless networks exist from the time packet radio fully, the sender in the sub-flow preempts itself. Moreover itnetworks [1], [2] were developed, yet there remains issues schedules its next turn according to the estimate of the con-

like Quality of Service which need to be properly addressed. tention for the media. We argue that the contention estimation

These issues essentially improves on the user experience of a can be done on the basis of information that is locally availablewireless computing environment and is a necessity if we want and that it can be gathered without any extra message passingto enhance its wide scale acceptance. Although the wireless overhead. Effectively we try to minimize the channel idle time,medium has its advantages, it also brings some new challenges but not at the cost of prospective collisions. Finally we also

g take care so that the channel iS not under utilized.like high bit error rate and broadcast nature of media. This ismainlydue to the multi-path fading [4]. The remainder of this paper is organized as follows. In

Anlyher interesting trend has been the increasing demand section II, we explain the basic access mechanism of IEEEAnother interesting trend has been the increasing demand 80 '1DF ntenx ecinw eiwsm Afor real-time streaming traffic flow to support multimedia . . .protocols aimed at providing fairness. Section IV deals withapplications. Therefore the traffic signature of the network prpr g

the unfairness of IEEE 802.11 in multi-hop environments andalso reflects a flow oriented architecture, where the flows often its impacts. In section V, we present our proposed solution andoverlap significantly. This leads to packet queues building up in section VI we demonstrate the simulation results. The lastat various points within the network which in turn increasestheir end-to-end delay and jitter. Unfortunately this affects theuser experience adversely. II. BASIC TECHNIQUES OF IEEE 802.11

Even as multiple flows race for the media, there this remainsthe problem of sub-flows of the same flow contending against CodninFcine(PCF) An D ritoordint,-7obrAli-- A t,-ci--_4rAx7ornt~-nfrv vor~-ic~- ;t ctlr-Coordination Function (PCF) and Distributed Coordinationeach other. As the sub-flow contention increases, it is the Fucin(C)owhholyDFsuednwrlssa-c

original flow that suffers. This brings us to the issue of fair ntok.Te821 A ok ihasnl is-nfrt'Sub-flow a sourc to a detination out (FIFO) transmission queue. The CSMA/CA constitutes a

lSbJo:While the streaming of packets from ditiueMACrc base onadoclsssssenaotteihaneconstitutes a flow, a sub-flow is a link level stream between two intermediate dsrbtdMCbsdooa sesetohhnenodes in theJflow. status. Basically, the CSMA/CA of DCF works as follows:

1-4244-0614-5/07/$20.00 ©2007 IEEE.

When a frame (or an MSDU) arrives at the head of the III. RELATED WORKtransmission queue, if the channel is busy, the MAC waitsuntil the medium becomes idle, then defers for an extratime interval, called the DCF Inter frame Space (DIFS). If Bharghavan pioneered the work on addressing the fairnessthe channel stays idle during the DIFS deference, the MAC problem in [13]. In this paper, they exposed the deficienciesthen starts the backoff process by selecting a random backoff of binary exponential backoff (BEB) and suggested a differentcounter (or BC). backoff algorithm called Multiplicative Increase and Linear

Each station maintains a contention window (CW), which Decrease (MILD). Additionally, a "per stream" concept wasis used to select the random backoff counter. The BC is introduced which accords achannel capacity to individualdetermined as a random integer drawn from a uniform dis- streams instead of stations. However, the backoff scheme usedtribution over the interval [0,CW]. How to determine the CW in MACAW works only when congestion is homogeneous,value is further detailed below. If the channel becomes busy which unfortunately is not necessarily the case in multi-hopduring a backoff process, the backoff is suspended. When wireless networks.the channel becomes idle again, and stays idle for an extra Nandagopal proposes a general analytical framework thatDIFS time interval, the backoff process resumes with the comprises of generating flow-contention graph of the network,suspended BC value. The timing of DCF channel access is in [15]. From this graph a resource constraint graph is ex-illustrated in Figure 1. For each successful reception of a tracted. It was shown that achieving fairness in the system isframe, the receiving station immediately acknowledges by equivalent to solving a utility maximization function, subjectsending an acknowledgement (ACK) frame. The ACK frame to transmission constraints in the resource constraint graph.is transmitted after a short IFS (SIFS), which is shorter than Also system-wide fairness can be achieved without explicitthe DIFS. Other stations resume the backoff process after the global coordination so long as individual nodes execute aDIFS idle time. If an ACK frame is not received after the data contention resolution algorithm designed to optimize its localtransmission, the frame is retransmitted after channel sensing, utility function. An interesting feature of the algorithm isDIFS and then random backoff. that it moves the burden of contention adaptation away from

the backoff mechanism and into the persistence mechanism.

DIFS But the flow-contention graph is insufficient to analyze theImmediate access when _ Contention Window contention as for the same contention graph, the receiver andmedium is idel >= DIFS P sender of a flow experience different contentions.

DIFS BUSY SIFS Kanodia et al proposed a distributed scheduling and me-MEDIUM Ba o Window Ne tFrame dia access algorithm, called DWOP [10], targeted to ensure

packets accessing the medium in an order defined by anSlotDTime ideal reference scheduler such as FIFO. Their key technique

Defer Access Select Slot and decrement backoff involved the piggybacking of head-of-line packet prioritiesas long as medium stays idle in IEEE 802.11 control messages so that nodes can assess

Fig. 1. Timing diagram of IEEE 802.11 the relative priority of their own queued packets. With agraph theoretic problem formulation, DWOP was designed toachieve the exact reference ordering in fully connected graphs.

The CW size is initially assigned CWmim, and increases However for multi-hop flows, the interlinked dependencieswhen a transmission fails, i.e., the transmitted data frame has make it difficult to predict the flow-contention graphs.not been acknowledged. After any unsuccessful transmission Zhifei's thesis [17] analyzes the unfairness of IEEE 802.11attempt, another backoff is performed using a new CW value in a systematic way. In his solution for a fair MAC inupdated by 2 x (CW + 1) - 1, with an upper bound multi-hop environments, each node collects some contentionof CWmax. This reduces the collision probability in case information and accordingly decides its mode of contention:there are multiple stations attempting to access the channel. aggressive, normal or restrictive. However the consideredAfter each successful transmission, the CW value is reset topologies are essentially manifestations of single-hop com-to CWmim, and the station that completed the transmission munication.performs another DIFS deference and a random backoff even One of our critical observations from the survey is thatif there is no other pending frame in the queue. This is often although there has been some research on the fairness inreferred to as "post" backoff, as this backoff is done after, not single-hop wireless networks, multi-hop fairness is rarelybefore, a transmission. This post backoff ensures there is at addressed in the literature. Moreover most approaches reliesleast one backoff interval between two consecutive MSDU on overhearing ongoing transmissions for information sharing.transmissions. All of the MAC parameters including SIFS, We can easily observe that this mechanism starts failing whenDIFS, Slot Time, CWmim, and CWmax are dependent on the hopcount exceeds three. It is in this regard that spatialthe underlying physical layer (PHY). Irrespective of the PHY, reuse assumes critical significance and thwarts throughputDIFS is determined by SIFS + 2 x SlotTime, degradation due to exposed terminals.

IV. UNFAIRNESS IN IEEE 802.11 AND ITS IMPACTS While the impact of long-term unfairness is obvious [11],In this section, we try to expose unfairness in IEEE 802.11 the short-term unfairness at MAC layer also leads to large

and its impacts in multi-hop flow scenarios. The unfairness delays and jitters. This substantially degrades the performanceexhibited by IEEE 802.11 is clearly and systematically of the delay or jitter sensitive traffic (such as real-time mul-explained in [17] and we just present one example of it. For timedia ). Moreover it also affects adaptive traffic like TCP.

each flow, Constant Bit Rate (CBR) traffic is adopted and the For example, in a scenario where a single flow dominates thetraffic rate is large enough for a single flow to occupy the media, the TCP Acks belonging to other flows are transmitted

entire channel capacity as unfairness occurs only when the in a burst. This ACK compression phenomenon is in fact

system is over-loaded. We use the notation F(SA,RA) to noticeable even in wireless LANs [11], where it results in

denote a single-hop flow, A, between two distinct nodes SA packet loss at the congested nodes. Also, the link idle time

and RA- between the TCP Data and ACK packet bursts is significantlyincreased, thereby degrading performance.The short-term unfairness also affects the behavior of on-

demand routing protocols. For example, when a node underS *S 'B*Athe influence of this unfairness fails to deliver a packet, the

- MAC layer discards it and conveys this event to the routingScenario -2 Scenario -3 protocol. The routing protocol may possibly misinterpret the

Fig. 2. Asymmetrical Information Scenarios discarding of a packet as an indication of link-breakage andinitiates a new route discovery process,even though the link isstill available. In an iterative manner the new route discovery

Long-term Unfairness in Asymmetrical Information Scenarios: process adds to the congestion and unfairness in the media.Under these circumstances a flow may face prolonged starva-

In this case a sender who is in the range of the receiver tion. This situation was frequently observed in our simulation,of some other flow is able to get more information about the when AODV is used as the routing protocol.contention in the media than other senders. This has been Short-term unfairness also affects the sub-flows of areferred as the asymmetrical information problem [10] and particular flow. If the sub-flows are starved it naturallyit results in substantial long-term unfairness. For example, leads to bottlenecks of the flow itself and this affects delaywhen SA completes its transmission, it has to race with a and jitter parameters negatively. Thus due to short-termneighboring node SB for the medium. In such a situation, and long-term unfairness under IEEE 802.11 at MACSA wins when RA responds with CTS before SB begins level, multi-hop flows suffers severely in several aspects liketo send out a RTS. Otherwise, SB will definitely win the throughput, fairness and QoS provisioning at end-to-end level.contention, even it sends out the RTS later than SA does.This is obviously unfair for flow A. Now let us consider Reason for Unfairnessthe situation when a packet belonging to flow B is beingtransmitted. It is difficult for Node SA to predict when this The main reasons for this unfairness are:transmission will end. Therefore SA will contend futilely and * The sender not aware of when exactly the contentionin the process keep increasing its CW. This is again an unfair period starts and ends.situation for SA. In summary, after every transmission ( in * Location dependent contention.flow A or B), SA will always be treated unfairly. Note that * Lack of receiver role in contention resolution.though the receivers in the scenario-2 and -3 have differentinformation about the contention, the two scenarios will show V. PROPOSED PROTOCOLthe same performance since the receiver in IEEE 802.11 doesnot play an active role in the contention. Our main aim is to provide fair (equal) access to the medium

for all flows without degrading the effective throughput. ToConcealed Information Problem: achieve this fairness we propose a distributed algorithm that

approximates a round-robin schedular.The main problem leading to unfairness in the CSMA/CA

protocols is that the senders cannot obtain precise informationabout the contention in the medium. In other words, the state --information required for fair contention is concealed from thesender, and therefore it is called the concealed informationproblem. The interested reader can refer to [17] for further

details.-- -- - -- - ---Fig. 3. Scenario 1: Two 5-hop flows

Impact of Unfairness

LExternal LSender LReceiver is the freshness of the entries that get affected. On the otherhand higher values of k are advantageous in scenarios with

0-1 7 5 high contention among the subflows. Thus we can use large1-2 value of We to cope with the under estimation problem. In7-8 our simulations, we found that the following values are better

suitedTABLE I

ACTIVE SUB-FLOW LIST AT NODE 6, FOR SCENARIO 1 W 2 x ne when n<4 (1)e- I3 x nte ~~~when n/

B. Incorporating Receiver CooperationAs part of its bookkeeping each node is required to maintain We note that the active sub-flows that are exclusively in the

3 lists LExternali LSender and LReceiver as explained below, transmission range of the receiver also affect the transmissionAn illustrative example is also presented in Table I for the of the sub-flow. Therefore we propose a mechanism calledscenario in Figure 3. receiver feedback to cope with this problem. The sender of a

LExternal: This list maintains the IDs of active sub-flows prospective sub-flow is being informed about the contentionof which the node is not a participant. This is the information at the receiver through the acknowledgement packet. Theregarding external contention. contention at the receiver is expressed in equation 2

LSender: This list maintains the IDs of active sub-flows for N = LExternal + LSender + LReceiver - LSR (2)which the node is the sender.

where LS represents the sub-flows in which the corre-LReceiver: This list maintains IDs of active sub-flows for SR p

which the node is the receiver. sponding node that requires cooperation is acting as sender.Thus the contention at the receiver N is being represented

A. Estimation of number of Active sub-flows (n) as the sum of the number of active sub-flows in which the nodeWhenever a node hears or overhears a frame is not taking any part (LExternal), the number of active sub-

(RTS/CTS/DATA/ACK), it inserts the corresponding sub- flows for which the node is sender (LSender) and the numberflow ID into the corresponding list along with a timestamp. of active sub-flows for which the node is receiver (LReceiver)Duplicate entries are refreshed with the latest timestamps. excluding the sub-flows in which the corresponding sender

Note that the entries are based on header information that requires cooperation is acting as sender(LSR).only, so that even encrypted packets are read. However at C Scheduling Algorithmany instant ne, the current estimate of n can be over orunderestimated leading to bandwidth wastage. Specifically, Using the estimation algorithm proposed in previouswhen over-estimation occurs, the stations would be in a subsection, the sender as well as the receiver of a sub-flowwaiting state and thus the channel remains idle and under obtains the number of active sub-flows currently conflictingutilized. On the other hand, when under-estimation occurs the with it. We leverage this information to propose a mediumnumber of nodes contending for the channel at that instant contention resolution algorithm. In our approach, the senderwould be more, increasing the likelihood of collisions. decides to contend for the medium or refrain from contention

In order to cope with the over-estimation problem in the based on the information collected at both the sender andfirst case, a mechanism called inactive notification is proposed. receiver of the sub-flow. We define a set of rules that a senderWhenever a flow sends out its last packet in its queue should follow while contending for an idle medium.the sender should inform the other nodes that the flow isbecoming inactive. Moreover the receiver also piggybacks this Rule 1: If the node is the intended recipient of theinformation in the responding frames CTS/ACK, as some ACK frame, it should compute its mode of contention.nodes may not overhear the RTS/Data. All the nodes thathear the notification should delete this flow ID from their The mode of contention is computed by checking whethercorresponding list. it has transmitted a packet for each of the active sub-flows

In spite of these instruments, it is possible that a node does for which it is acting as sender. If not, then the node remainsnot detect the termination of a flow. However the stale entries in active contention mode.need to be deleted after a timeout. This timeout period is longenough to transmit a certain number (say We) of packets, Rule 2: If the node has transmitted the required number ofproportional to the number of active subflows. Therefore We = packets, then it should be in restrictive mode, restricting itselfk x m$3. Obviously k 7t 1, as this case leads to the deletion from contention for a calculated duration.Of an entry if it was not involved in any of the previous m/eoverhead subflows. Clearly this window is too small and so Let the current estimate of contention at the potential senderwe consider values of k > 2 only. For higher values of k it node be The, computed as in equation 3. We note that the

amount of contention is the total number of active sub-flows The assumptions made in our simulations are as follows:in which either the node is acting as receiver or has no role. . A link can participate in at most in one flow.

The LExte al + LReceiver (3) . The traffic in the network is of CBR type.. We have not incorporated multi-priority traffic.

Also let the estimate of contention at the receiver, informed . There is no consideration for random mobility or channelthrough the ACK frame, be nm. The actual contention of the error.sub-flow is given by the maximum of ne and nm. This allowsus to use the concept of spatial reuse, where the sub-flowsinvolving either the sender or the receiver exclusively can ___access the medium simultaneously.The waiting period Twait, for which the node should be ____ _ ____-__

restricted itself from contention is calculated as in equation 4.

Twait =Tnax(ne:)XTUCS (4)Twant max(me, Thr)XTSUCCESS(4)Fig. 4. Scenario 2: Two 7-hop flows

Where TSUCCESS is the time needed for successfultransmission of a packet when the number of total activesub-flows in the system is one.

Rule 3: The other nodes, overhearing the ACK packet,should start contending for the medium if they are not in 0.95 -

restrictive mode.0.9

Rule 4: Whenever a node receives an ACK packet, themode of the flow is recomputed. If the node is to be in 0.85restricted mode, then the duration must necessarily be 80Parecomputed. 0.8 11

15 1617 18 ~~ ~~~~~19 20

Thus every sub-flow attempts to restricts itself from con- Fig. 5. Fairness index for scenario 2tention after availing its chance of accessing the channel.This self-preempting feature allows the nodes to schedulethemselves in a round robin fashion and prevents any sub- Iflow or flow from dominating for a prolonged duration. Thus Throughput PP 802.11the mechanism achieves the objective of fairness. Moreover, at |FO7 81 94any instant of time, we are successful in reducing the number58of nodes contending for the medium. This in turn reduces the F(8-15) 59.76 39.99probability of collision. Total 117.95 79.47

VI. SIMULATION RESULTS AND PERFORMANCE TABLE IIEVALUATION THROUGHPUT RESULTS FOR SCENARIO 2

In this section, we present simulation results of our algo-rithm over various topologies to compare with IEEE 802.11standard. All simulations have been performed in ns-2.27. The In scenario 2, two 7-hop parallel flows are being considered.simulations are measured over fairness, throughput and QoS The simulation results of fairness are shown in Figure 5parameters like delay and jitter. The well known Jaus index and throughput results in Table II. This scenario is meantis used to measure the fairness provided by the protocols. The to highlight the effect played by subilows on the overallJams index is defined as follows: performance of the flow. Although the fairness of IEEE 802.11

is relatively high, it is the subflow contention that brings theN N throughput down. In this case our proposed protocol uses

Fj (, /i )2/(N S 2 (5) spatial reuse to provide a 50% jump in the overall throughput.i=1 i=1 Tables III and IV also show the effects of unfairness on delay

where N is the total number of flows that share the medium and jitter parameters of 802.11.andthY is the bandwidth utilized by the flow i over a certain In scenario 3, five 4-hop parallel flows are being considered.amount of time. Here we consider the bandwidth utilization As before, he simulation results of fairness are shown in Figurein terms of number of packets transmitted by that flow. In the 7 and throughput results in Table V. This scenario illustratesresults, the units for throughput are in Kbps, delay and jitter the effects of severe short term unfairness on the throughputare in seconds. of IEEE 802.11. Unlike the previous scenario, the 4-hop flows

1.

0.9

0.8

E 0.7

0.6

0.5

PP802.11 X

0.415 16 17 18 19 20

simulation time

Fig. 7. Fairness index for scenario 3

Fig. 6. Scenario 3: Five 4-hop flows

Delay PP | 802.11

do not leave much room for spatial reuse. However, it does F(0-4) 0.0912 0.0516ensure that the effective contention for all the sub-flows is F(5-9) 0.0360 2.5365same and is approximately equal to that of previous scenario. F(10-14) 0.1447 0.3202Even then, by reducing the unfairness we have been able toobtain a 60% improvement in throughput. F(15-19) 0.5461 0.0489

Scenario 4 describes four 4-hop anti-parallel flows, with F(20-24) 0.0245 0.5290the fairness and throughput results shown in Figure 9 and Average 0.1685 0.6972Table VIII respectively. In the case of IEEE 802.11 the antiparallel nature of flows dictate that the winning flow dominates TABLE VIthe media, thereby leading to severe unfairness. As in the DELAY RESULTS FOR SCENARIO 3previous scenario, we are able to generate a 26% increasein the throughput by simply resolving excessive unfairness.

Scenario 5 demonstrates the case where a single subflow To summarize our comparison we observe that the perfor-acts as a bottleneck for each flow. As before the fairness

mance of IEEE 802.11 is inconsistent. It shows a good degreeand throughput results are shown in Figure 11 and Table of fairness in low contention topologies, which degrades inXI respectively. As there is only one subflow in contention,therefore both IEEE 802.11 and our proposed protocol perform high cntiontopologies Ou pre pro to prormbetter in this count. Secondly we are also able to improvefairly well with respect to fairness. We can also notice that in

on system throughput considerably.Finally we also experiencethe absence of severe unfairness there is not much difference . . .in thethoughputf either rotocol.an improvement in the QoS parameters like delay and jitterin the throughput of either protocol. because we are able to reduce collisions and channel idle time.

VII. CONCLUSIONDelay PP [ 802.11 In this paper, we have identified the reasons for the un-

F(0-7) 0.0186 0.0137 fairness being caused and proposed a novel solution targetingtowards achieving global fairness and providing end-to-end

F(8-15) 0.3777 1.3312 QoS in multi-hop flow scenarios. Our basic idea is to entrustAverage 0.1981 0.6725

TABLE IIIIIT1TABLE III [~~~~~~~~~~Throughput |PP |802.11DELAY RESULTS FOR SCENARIO 2 Thogpt__821

F(0-4) 58.19 34.91

PP ~~~~~~ ~ ~~~~~ ~~~F(5-9)57.31 27.12

Jitter|_ P 802.11 F(10-14) 56.80 35.10

F(0-7) 0.0259 0.0228 F(15-19) 51.34 38.63

F(8-15) 0.0245 0.2179 F(20-24) 61.82 41.56

[Average T0.0252 T0.1209 lTotal 285.47 177.33

TABLE IV TABLE VDELAY RESULTS FOR SCENARIO 2 THROUGHPUT RESULTS FOR SCENARIO 3

Jitter pp [ 802.11 1

F(0-4) 0.0066 0.1173 0.9 -

F(5-9) 0.0689 0.0883 x0.8

F(10-14) 0.0619 0.1169 U, 0.7

F(15-19) 0.0937 0.1059 0.6

F(20-24) 0.0086 0.0405.5 --

Average 0.0479 0.0738 0l802.PP0.4

12 13 14 15 16 17 18 19 20

TABLE VII simulation time

JITTER RESULTS FOR SCENARIO 3 Fig. 9. Fairness index for scenario 4

Throughput PP 802.11 Jitter PP 802.11F(0-4) 0.1750 0.0972

F(0-4) 43.23 53.203F(5-9) 0.1566 0.1410

F(5-9) 28.63 5.08F(10-14) 0.0904 0.1185

F(10-14) 44.19 22.31F(15-19) 0.0854 0.1223

F(15-19) 54.76 54.28Total 0.1268 0.1197

Total 170.81 134.87TABLE X

TABLE VIII JITTER RESULTS FOR SCENARIO 4

THROUGHPUT RESULTS FOR SCENARIO 4

poorly in terms of fairness.individual nodes with the responsibility to collect informationabout the active sub-flows in its contention region. Thereafter REFERENCESthe sender and receiver of a prospective subflow combine

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Delay PP 802.11

F(0-4) 0.1794 0.0534

:- F(5-9) 0.4371 1.5381

F(10-14) 0.1446 1.0559

F(15-19) 0.0957 0.1035

Xa ~~~~~ ~ ~~~~~~Total0.2143 0.6877

- -- -- - - -- - - -- - --- - ---TABLE IX

Fig. 8. Scenario 4: four anti-parallel flows DLYRSLSFRSEAI

Delay PP 802.11

F(0-4) 0.0274 3.8962

F(5-9) 0.4651 0.0325

F(10-13) 0.0205 0.1177

Average 0.1710 1.3488

TABLE XIIFig. 10. Scenario 5: three flows 14 nodes

DELAY RESULTS FOR SCENARIO 5

Throughput PP [ 802.11

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TABLE XITHROUGHPUT RESULTS FOR SCENARIO 5

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. --->_

Jitter PP 802.11

S098 F(0-4) 0.0215 2.61180.97 F(5-9) 0.0946 0.0251

0.96 F(10-13) 0.0217 0.0369

0.95 Average 0.0459 0.8913PP

802.11X12 13 14 15 16 17 18 19 20 TABLE XIII

simulation time

Fig. 11. Fairness index for scenario 5 EA EUT FRSEAI