end to end communicatio in adhoc netowrk

8/9/2019 End to End Communicatio in Adhoc Netowrk

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Ci)a- 500.c"5 400a-"00 300CD

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---.... - - - - .single-connection/stream multi-connection/stream(0", __ ~ W __ ,,10

0250m0 0.-----.flow!

Fig. 1. Network topology for preliminary exper iments .

If a service uses one connection and another does severalconnections, the throughput per service is different betweenthem. That is, unfair sharing can be experienced.On the other hand, SCTP has a mechanism called multistream, which manages several data transfers through oneconnection (called association in SCTP.) The SCTP congestioncontrol is based on association, so the multiple transfer withinan association and only one transfer within an association is

managed fairly even when they interfere with each other.As a preliminary experiment, the mutual interference amongflows is evaluated for TCP and SCTP through simulationexperiments with the topology depicted in Figure 1. The circlesin Figure 1 mean nodes, and the figure in a circle shows thenode number. The two flows, flow 1 from node 1 to node 6and flow 2 from node 2 to node 7, share the link betweennode 3 and node 5. In this experiment, we set the number

of data transferred by flow 1 to one and set that by flow 2as the range between one and four, in order to estimate theeffect of multiple data transfers. The performance is evaluatedin terms of goodput and fairness. Here, we define the goodputas the amount of received unique data per unit time, so itis different from the throughput which includes retransmitteddata. In this paper, we evaluate the fairness of communicationflows in terms of fairness index. The fairness index is definedas expression (1), where N means the number of flows and X imeans the goodput of the i-th flow. The fairness index rangesfrom 0 to 1, and the higher value close to 1 shows that thefairness is high.

(1)

The results observed by simulation experiments are shownin Figure 2 and Table I. From Figure 2, it is observed thatthe goodput of flow 2 increases when the number of multipledata transfers becomes large. However, the goodput of flow1 decreases by the increment of goodput of flow 2, and itis also confirmed by the result in Table I that fair sharingis not achieved. On the other hand, the goodput of eachSCTP flow remains steady even when the number of multipledata transfers increases. Thus, SCTP can realize high fairnessamong flows.

. ,! . . "- - - - - - - - - - - - - - - - - - - - - - - l - : - : - : - : - ; - ; - - ~ .... -------r-------------------------

. - - : :-----------:-;- ...--------r--------------------------r-------------------------

TCP f1ow1 ----

: ~ ~ ~ : ~ ~ ~ ~ :::::::::::::::::::1::::::::::::::::::::::::o 1 234umber of data streamsFig. 2. The effect of number of data streams on goodput.

TABLE IFAIRNESS INDEX.

B. Route Failure Caused by Node MovementWhen some nodes move and a route composed of them issplit, we cannot transfer the application data till a new route iscreated. Especially when the node speed is high, the number ofroute failures tends to be large, so the data transfer allowabletime becomes short and the throughput gets lower. Moreover,when designing the transport layer mechanism without notification from the lower layer, we cannot determine when torestart data transfer. The delay in noticing the route recreated

also reduces the effective throughput. TCP and SCTP havesimilar RTO (Retransmission Time Out) backoff proceduresto avoid the congestion collision. The RTO is multiplied bytwo each time a retransmission time out occurs successively.As a result, the data transfer restart is delayed from the routerestoration.C. Packet Collision within a Wireless ChannelGenerally speaking, a packet can collide with another packetbecause a node uses the same wireless channel both to sendand to receive packets. Since reliable transport protocols suchas TCP and SCTP use acknowledgement packets to assure thecomplete file transfer, they are possible to collide with the data

packets sent in the opposite direction within the same wirelesschannel.III. PROPOSED IMPROVEMENT ONSCTP

In this paper, we add Fixed-RTO and dynamic delayedacknowledgmentmechanisms to SCTP to address route failureand packet collision problems.A. Fixed-RTOTCP-Fixed RTO [6] has been proposed to detect the routerestoration immediately and to address the above-mentioned

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Base_TSN = I n i t i a l TSN; / * (a) */DataCnt = 0 ;

Time(b) FixedRTO

restart ofdata transmissionV while (Connection_ESTABLISHED) {.. .if (Da t a Pa c k e t Re c e i v e d) {~ ~ RTO n = receivedTSN - Base_TSN ;

~ m i f (n < L1) d = 1;w::..._________ e l se i f (n < L2) d = 2;e l se i f (n < L3) d = 3;e l se d = 4; / * (b) * /

Time(a) TCP,SCTP

X: retransmission restart of ' Q;I m " ~ : " ~ lw w

Fig. 3. Retransmission behavior of existing TCP and TCP-FixedRTO.

sender I receiver) sender Ib:- I receiver Ii f (Da t a Pa c k e t I n t e r v a l > T &&UpdatedCummulativeTSN )Base TSN = cummulativeTSN; / * (c ) */

i f (++Da t a Cnt >= d I I f as t t imer t imeout )GenerateSACK () ;DataCnt = 0;

........-SACK Chunk------ ..

Data Chunk- .. -_ ..----------_... -........--_. -

T200ms ..------.. .... ..----

- " - - - j T200ms Fig. 5. Dynamic delayed acknowledgment algorithm suitable for MANETs.

Fig . 4 . Behavior of dynamic delayed acknowledgment.

issues. This mechanism counts the number of successiveretransmission timeout events, and it fixes the RTO value evenif some retransmission timeout events follow after the countexceeds a certain threshold. Figure 3(b) shows an exampleof Fixed-RTO behavior when the threshold is set to three.As shown in Figure 3(b), since the RTO value is fixed afterthree successive retransmission timeout events, the FixedRTO mechanism can restart data transfers immediately afterthe route restoration. Fixed RTO eliminates the unnecessarywaiting time to achieve higher performance, while it has riskof making the congestion worse when the timeout is causedby the congestion in the network.B. Dynamic Delayed Acknowledgment Suitable for MANETSCTP manages chunks (like segments in TCP) as transferunit and checks the data receipt by SACKs. We propose adynamic delayed acknowledgment scheme to avoid collisionswithin a wireless channel by decreasing the SACKs in number[7]. The data receiver infers the current network condition

from the receiving interval of data chunks according to theTSN (Transmission Sequence Number), and the SACK interval d is changed between one and four dynamically to adapt tothe speculated network condition. Here, d means the maximumnumber of acknowledgements organized into one ACK packet.If the sequence number away from the beginning n satisfiesn < L1 then d = 1, if L1


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Fig . 7 . Average goodput of each flow in the grid topology.

Row1 Row2 Row3 Row4 Row5 Row6ID TCP DTCP-FR DSCTP PROPOSAL I

TABL E IIS IMULATION ENVIRONMENT.

Simulator QualNet verA.O.IMAC protocol 802.llb

Bandwidth [Mbps] IIRouting protocol DSR [8], AODV[IO], OLSR[9]

Simulatoin time [sec] 300Data packet size [byte] 1024Received buffer in 16

transport layer [Kbyte]Transmission range [m] 250Number of experiments 50Confidence interval [%] 95

flow4 flowS flow6QQQ~ 6 c12somflOW30 '? '? '? -0f lOW20 $ $ $ -0f lOW10 $ $ $ -0666

140012001000'"..0 800...:JD- 6000000 4002000

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-- rEm TmmfJi T n -- - - T-r- -- -- - -- - - -- - -r - - -

1200m0- D_ ~ 0_ _ .9__ ' :0_ 9- 9 -0- > e000000 0o 0 0 00- - - - _0::. - - - - .D_ - - - - -0 - - -> e000000 0 0 0O - - - - - - O - O - - - - c r - - - - ~ > eo 0 0 0 0 0o sender (fixed) receiver (fixed)o forward ing node - - -> data flow

Fig . 6. Grid topology.

into account the beginning phase of the data transfer. As anexception, if the data receiver finds a packet reorder, a SACKmust be returned immediately.As mentioned above, the dynamic delayed acknowledgmentmechanism reduces the SACK sending interval when the data

receiving interval is large, and it extends the SACK sendinginterval to reduce packet collisions within a wireless channelwhen data chunks are delivered continuously.

IV. SIMULATION EVALUATIONIn order to show the effectiveness of the proposal regardless

of routing protocols for MANETs, we have evaluated TCP,TCP-Fixed RTO (TCP-FR), SCTP, and the proposal throughsimulation experiments. We use QualNet as a simulator andapply QualNet SCTP Module[5] to it.A. Simulation Experiment IWe have conducted simulation experiments using the gridtopology as shown in Figure 6. Table II shows the parametersused in the simulation experiments. In the grid topology, thenumbers of data streams in flows I , 2, and 3 are set to one,and the data streams in flows 4, 5, and 6 are evaluated in casesthat the numbers of data streams are set to three, respectively.Figures 7 shows the average goodput of each flow in thegrid topology. As shown in Figure 7, in case that the multi

connection mechanism is introduced in TCP, the goodputs of

Fig. 8. Network topology in simukation experiment II.

flows 4, 5, and 6 increase whereas those of flows I, 2, and 3decrease. The goodput of the proposal becomes 8.3 % morethan that of SCTP.B. Simulation Experiment 11We show the simulat ion environment in Table II. Figure

8 shows the network topology in MANETs, where the fieldsize is l200m x 300m and the total number of nodes in thenetwork is 50. In the field , six nodes which serve as a sourcenode and a destination node are fixed at both sides , and theother nodes are always moving around the network accordingto the random waypoint modes [II]. The number of SD pairsis 3 and the maximum node moving speed varies from I to10 (m/s).Wehave evaluated transport protocols, which are TCP, TCP

FixedRTO (TCP- FR), SCTP, and Proposal using AODV OLSRand DSR as a routing protocol in each case.Figure 9 shows the average goodput in case of AODV,OLSR, and DSR.At first , we focus on the impact of routing protocols on the

goodput. As shown in Figure 9, in any transport protocols ,DSR has the highest goodput, whil e OLSR has the lowestgoodput. Since OLSR periodically broadcasts control packet tomaintain the routing table and control packets collide with datapackets frequently, data delivery ratio decreases. On the otherhand, since AODV and DSR create routes only when a route



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D TCP OTCP-FR DSCTP II'I PROPOSAL

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- - - -- - - -- - - -- - - -- - - -

Node p ~ e d [rn/ s](a) AODV

10 Node p ~ e d lm / sl(b) OLSR

Fig. 9. Average goodput.

10 Node [m/ 5](c) DSR

10

request is invoked, they have fewer control packets and controlpackets do not often collide with data packets. The reason whyDSR has the highest goodput is that it does not have identicalroutes from the source node to the destination node and viceversa. Therefore, control packets and data packets does notoften collide on the route between the source node and thedestination node.Next , we focus on the impact of transport protocols onthe goodput. As shown in Figure 9, in case of AODV andOLSR, the goodput of TCP-FR becomes higher than that ofTCP because Fixed-RTO efficiently works. Besides, since thegoodput of the proposal becomes higher than that of otherschemes, both Fixed-RTO and the dynamic delayed acknowledgement mechanism are efficiently working. However, incase that the node moving speed is 10 mis, goodputs of theproposal and TCP-FR do not make any difference. It seemsthat the windows size does not extend and the dynamic delayedacknowledgement mechanism does not work because the route

break often occurs due to the node movement and packetcollision.In case of DSR, since goodputs of TCP and TCP-FR donot make any difference, it seems that Fixed-RTO does notwork efficiently. This is because packet collision does not oftenoccur and retransmission time out is not invoked comparedto AODV and OLSR. On the contrary, the dynamic delayedacknowledgement mechanism is efficiently working becausethe proposal has higher goodput than the other schemes.From simulation experiments, DSR gets the highest goodputin routing protocols and the proposal gets the highest goodputin transport protocols. Consequently, we can say that the

proposal works efficiently.C. Simulation Experiment IIIWe evaluate the fairness in case of multi-connection communication. Figure 10 shows the network topology in simulation experiments. In the field, three fixed nodes which serveas a source node send data packets to one destination node,and the other nodes are always moving around the network.All flows perform the singe connection transfer in case of thesingle connection, while two flows except for the central flow

TABLE IIIFAIRNESS IND EX IN CASE OF SINGLE CONNECTION .

Node moving speed [m/sec]1 5 10TCP 0.9872 0.9890 0.9959TCP-FR 0.9810 0.9891 0.9963SCTP 0.9914 0.9971 0.9898PROPOSAL 0.9830 0.9871 0.9889

perform the multi-connection transfer in case of the multiconnection. In this experiment, DSR is adopted as a routingprotocol because it has the highest goodput.Tables III and IV show the values of FairnessIndex incase of the single connection communication and mutliconnection communication, respectively. As shown in Table III,in case of the single connection, the FairnessIndex values ofall transport protocols do not make any difference. As shownin Table IV, in case of multi-connection, the FairnessIn dexvalues ofTCP and TCP-FR reduce in comparisonwith the case

of single connection. However, the FairnessIndex values ofSCTP and the proposal are the same as the case of singleconnection. As a result, we can say that SCTP and the proposalcan manage each flow fairly in comparison with TCP andTCP-FR.Figure II shows the average goodput in case of the singleconnection and multi-connection communications. Comparedwith the case of single connection, the average goodputs of

TCP and TCP-FR significantly decrease in case of multiconnection due to the unfair communication. In addition, theaverage goodput of SCTP and the proposal does not have thebig difference between the case of single connection andmulticonnection because of the multi-stream mechanism.Consequently, multi-stream mechanism of SCTP is efficiently working in mobile ad hoc network environment andprovides the fair communications among flows. We can saythat the proposal can not only provide the fair communicationamong flows but also obtain higher goodput.



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end to end communicatio in adhoc netowrk

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