TCP Performance through Simulation and Testbed in Multi-Hop Mobile Ad hoc Network

8/9/2019 TCP Performance through Simulation and Testbed in Multi-Hop Mobile Ad hoc Network

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International Journal of Computer Networks & Communications (IJCNC),Vol.2, No.4, July 2010

DOI : 10.5121/ijcnc.2010.2410 109

TCP Performance through Simulation and

Testbed in Multi-Hop Mobile Ad hoc Network

*Assistant Prof.Chandra Kanta Samal, AND College, University of Delhi, New Delhi, India

[email protected]

ABSTRACT

When a packet is sent through wireless network it can be lost due to either environmental noise or due to

congestion in the network. Traditional TCP protocols do not perform well in the wireless network because

they were designed for wired networks with the assumption that the transmission medium is quite reliable.

This often results in TCPs failure in distinguishing the cause of the packet loss as most of these problems

hinder the throughput of the TCP connections in wireless networks. The work has been carried out to test

the window size, packet size and path length of Multi-Hop Ad hoc Network, the TCP performance in a

straight line, multi hop ad-hoc networks in two ways: the first one network simulator ns-2 and second one

practical testbed, and the results that were obtained from both the models were compared and analyzed.

Keywords:Wireless network, Throughput, Interference, Multi-Hop.

I. INTRODUCTIONI. INTRODUCTIONI. INTRODUCTIONI. INTRODUCTION

A d H o c N e t w o r k s a r e c o m p l e x d i s t r i b u t e d s y s t e m s t h a t c o n s i s t o f w i r e l e s s m o b i l e o r

s t a t i c n o d e s t h a t c a n f r e e l y a n d d y n a m i c a l l y s e l f - o r g a n i z e . I n t h i s w a y t h e y f o r m a r b i t r a r y

a n d t e m p o r a r y A d h o c n e t w o r k s t o p o l o g i e s , a l l o w i n g d e v i c e s t o s e a m l e s s l y

i n t e r c o n n e c t i n a r e a s w i t h n o p r e - e x i s t i n g i n f r a s t r u c t u r e . R e c e n t l y , t h e i n t r o d u c t i o n o f

n e w p r o t o c o l s s u c h a s B l u e t o o t h [ 1 ] , I E E E 8 0 2 . 1 1 [ 2 ] a n d H y p e r l a n [ 3 ] a r e m a k i n g

p o s s i b l e t h e d e p l o y m e n t o f A d h o c n e t w o r k s f o r c o m m e r c i a l p u r p o s e s . A s a r e s u l t ,

c o n s i d e r a b l e r e s e a r c h e f f o r t s h a v e b e e n p u t o n t h i s n e w c h a l l e n g i n g w i r e l e s s

e n v i r o n m e n t .

T h e T C P ( T r a n s m i s s i o n C o n t r o l P r o t o c o l ) [ 4 ] w a s d e s i g n e d t o p r o v i d e r e l i a b l e e n d - t o -

e n d d e l i v e r y o f d a t a o v e r u n r e l i a b l e n e t w o r k s . I n t h e o r y , T C P s h o u l d b e i n d e p e n d e n t o f

t h e t e c h n o l o g y o f t h e u n d e r l y i n g i n f r a s t r u c t u r e . I n p a r t i c u l a r , T C P s h o u l d n o t c a r e

w h e t h e r t h e I n t e r n e t P r o t o c o l ( I P ) i s r u n n i n g o v e r w i r e d o r w i r e l e s s c o n n e c t i o n s . I n

p r a c t i c e , i t d o e s m a t t e r b e c a u s e m o s t T C P d e p l o y m e n t s h a v e b e e n c a r e f u l l y d e s i g n e d

b a s e d o n a s s u m p t i o n s t h a t a r e s p e c i f i c t o w i r e d n e t w o r k s . I g n o r i n g t h e p r o p e r t i e s o f


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w i r e l e s s t r a n s m i s s i o n c a n l e a d t o T C P i m p l e m e n t a t i o n s w i t h p o o r p e r f o r m a n c e . I n d e e d ,

i n m o b i l e o r s t a t i c A d h o c n e t w o r k s l o s s e s a r e n o t a l w a y s d u e t o n e t w o r k c o n g e s t i o n , a s

i t i s m o s t l y t h e c a s e i n w i r e d n e t w o r k s .

I n A d h o c n e t w o r k s , t h e p r i n c i p a l p r o b l e m o f T C P l i e s i n p e r f o r m i n g c o n g e s t i o n c o n t r o l i n

c a s e o f l o s s e s t h a t a r e n o t i n d u c e d b y n e t w o r k c o n g e s t i o n . S i n c e b i t e r r o r r a t e s a r e v e r y

l o w i n w i r e d n e t w o r k s , n e a r l y a l l T C P v e r s i o n s n o w a d a y s a s s u m e t h a t p a c k e t s l o s s e s

a r e d u e t o c o n g e s t i o n . C o n s e q u e n t l y , w h e n a p a c k e t i s d e t e c t e d t o b e l o s t , e i t h e r b y

t i m e o u t o r b y m u l t i p l e d u p l i c a t e d A C K s , T C P s l o w s d o w n t h e s e n d i n g r a t e b y a d j u s t i n g

i t s c o n g e s t i o n w i n d o w . U n f o r t u n a t e l y , w i r e l e s s n e t w o r k s s u f f e r f r o m s e v e r a l t y p e s o f

l o s s e s t h a t a r e n o t r e l a t e d t o c o n g e s t i o n , m a k i n g T C P n o t a d a p t e d t o t h i s e n v i r o n m e n t .

N u m e r o u s e n h a n c e m e n t s a n d o p t i m i z a t i o n s h a v e b e e n p r o p o s e d o v e r t h e l a s t f e w y e a r s

t o i m p r o v e T C P p e r f o r m a n c e o v e r o n e - h o p w i r e l e s s ( n o t n e c e s s a r i l y A d h o c ) n e t w o r k s .

T h e s e i m p r o v e m e n t s i n c l u d e i n f r a s t r u c t u r e b a s e d W L A N s [ 5 , 6 , 7 , 8 ] , m o b i l e c e l l u l a r

n e t w o r k i n g e n v i r o n m e n t s [ 9 , 1 0 ] , a n d s a t e l l i t e n e t w o r k s [ 1 1 , 1 2 ] . A d h o c n e t w o r k s i n h e r i t

s e v e r a l f e a t u r e s o f t h e s e n e t w o r k s , i n p a r t i c u l a r h i g h b i t e r r o r r a t e s a n d p a t h a s y m m e t r y ,

a n d a d d n e w p r o b l e m s t h a t c o m e f r o m m o b i l i t y a n d m u l t i - h o p c o m m u n i c a t i o n s , s u c h a s

n e t w o r k p a r t i t i o n s , r o u t e f a i l u r e s , h i d d e n a n d e x p o s e d t e r m i n a l s . W e n o t e t h a t t h e

f o l l o w i n g T C P v e r s i o n s : T a h o e , R e n o , N e w r e n o , a n d V e g a s p e r f o r m d i f f e r e n t l y i n A d h o c

n e t w o r k s [ 1 3 ] . H o w e v e r , a l l t h e s e v e r s i o n s s u f f e r f r o m t h e s a m e p r o b l e m o f i n a b i l i t y t o

d i s t i n g u i s h b e t w e e n p a c k e t l o s s e s d u e t o c o n g e s t i o n f r o m l o s s e s , d u e t o t h e H i d d e n ,

E x p o s e d s t a t i o n s a n d n e t w o r k p a r t i t i o n o f A d h o c n e t w o r k s a r e c o r r e l a t e d w i t h t h e

t r a n s m i s s i o n r a n g e . B y i n c r e a s i n g t h e t r a n s m i s s i o n r a n g e , t h e h i d d e n t e r m i n a l p r o b l e m

o c c u r s l e s s f r e q u e n t l y . O n t h e o t h e r h a n d , t h e e x p o s e d t e r m i n a l p r o b l e m b e c o m e s m o r e

i m p o r t a n t a s t h e t r a n s m i s s i o n r a n g e i d e n t i f i e s t h e a r e a a f f e c t e d b y a s i n g l e t r a n s m i s s i o n .

II. PROBLEM STATEMENTII. PROBLEM STATEMENTII. PROBLEM STATEMENTII. PROBLEM STATEMENT

A d h o c n e t w o r k s a r e c o m p l e x d i s t r i b u t e d s y s t e m s t h a t c o n s i s t o f w i r e l e s s m o b i l e o r

s t a t i c n o d e s t h a t c a n f r e e l y a n d d y n a m i c a l l y s e l f - o r g a n i z e . T e r m i n a l s t h a t c o m m u n i c a t e

w i t h e a c h o t h e r b y f o r m i n g a m u l t i h o p r a d i o n e t w o r k a n d m a i n t a i n i n g c o n n e c t i v i t y i n a

d e c e n t r a l i z e d m a n n e r . I n t h i s w a y t h e y f o r m a r b i t r a r y , a n d t e m p o r a r y a d h o c n e t w o r k s

t o p o l o g i e s , a l l o w i n g d e v i c e s t o s e a m l e s s l y i n t e r c o n n e c t i n a r e a s w i t h n o p r e - e x i s t i n g

i n f r a s t r u c t u r e . S i n c e t h e n o d e s c o m m u n i c a t e o v e r w i r e l e s s l i n k s , t h e y h a v e t o c o n t e n d


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w i t h t h e e f f e c t s o f r a d i o c o m m u n i c a t i o n , s u c h a s n o i s e , f a d i n g , a n d i n t e r f e r e n c e . E a c h

n o d e i n a w i r e l e s s a d h o c n e t w o r k f u n c t i o n s a s b o t h a h o s t a n d a r o u t e r , a n d t h e c o n t r o l

o f t h e n e t w o r k i s d i s t r i b u t e d a m o n g t h e n o d e s .

T h e f o c u s o f t h i s s t u d y i s o n t h e p e r f o r m a n c e o f T C P o p e r a t i n g i n a d h o c n e t w o r k s .

S i n c e T C P / I P i s t h e s t a n d a r d n e t w o r k p r o t o c o l s t a c k o n t h e I n t e r n e t , i t s u s e o v e r a d h o c

n e t w o r k s i s a c e r t a i n t y . N o t o n l y d o e s i t l e v e r a g e a l a r g e n u m b e r o f a p p l i c a t i o n s , b u t i t s

u s e a l s o a l l o w s s e a m l e s s i n t e g r a t i o n w i t h t h e I n t e r n e t , w h e r e a v a i l a b l e . R e l i a b l e d a t a

t r a n s f e r a n d c o n g e s t i o n c o n t r o l a r e k e y r e q u i r e m e n t s f o r a n y c o m p u t e r n e t w o r k . T C P ,

w h i c h f u l f i l l s b o t h o f t h e s e r e q u i r e m e n t s , i s t h e m o s t w i d e l y u s e d r e l i a b l e t r a n s p o r t

p r o t o c o l i n t o d a y s I n t e r n e t a n d h a s d e m o n s t r a t e d i t s v i a b i l i t y w i t h r e s p e c t t o I n t e r n e t

c o n n e c t i v i t y . F u r t h e r m o r e , T C P i s u s e d t o t r a n s p o r t a s i g n i f i c a n t p o r t i o n o f I n t e r n e t t r a f f i c

s u c h a s e - m a i l ( S M P T ) , f i l e t r a n s f e r s ( F T P ) , a n d W W W ( H T T P ) . T h u s , t h e u s e o f T C P i s

m o b i l e a d h o c n e t w o r k s i s c l e a r l y a d v a n t a g e o u s . B u t t h e c h a r a c t e r i s t i c s o f a d h o c

n e t w o r k s f a c e a p r o b l e m f o r t h e T C P p r o t o c o l , w h i c h w a s p r i m a r i l y d e s i g n e d f o r w i r e l i n e

n e t w o r k s , w h i c h t h e i r t o p o l o g y i s m u c h l e s s d y n a m i c , a n d t h e r e f o r e h a v e m o r e

p r e d i c t a b l e n a t u r e .

M a i n p r o b l e m s t h a t c o m m o n l y a s s o c i a t e d w i t h p e r f o r m a n c e a n a l y s e s o f T C P o v e r

w i r e l e s s a d h o c n e t w o r k s a r e l a c k o f s p e c i a l i z a t i o n / s p e c i f i c a t i o n a n d c o m p l e t e n e s s .

M o s t o f t h e r e s e a r c h o n p e r f o r m a n c e e v a l u a t i o n s o f T C P o v e r a d h o c n e t w o r k s w e r e n o t

s p e c i f i c , a n d a r e g e n e r a l i z e d . M o s t a v a i l a b l e p e r f o r m a n c e e v a l u a t i o n s a r e u s u a l l y

a n a l y z e t h e p e r f o r m a n c e o f a T C P o v e r d i f f e r e n t r o u t i n g p r o t o c o l s a v a i l a b l e [ 1 2 , 1 4 , 1 5 ]

( D S R , D S D V , T O R A , A O D V ) ; o r e l s e c o n s i d e r i n g a l l t h e T C P v e r s i o n s o v e r a s p e c i f i c

r o u t i n g p r o t o c o l w i t h g e n e r a l s c e n a r i o s - r a n d o m m o b i l i t y p a t t e r n s a n d f e w s t u d i e s h a v e

p r o p o s e d i m p r o v e m e n t s . B u t n o s u c h a n a l y s i s h a s b e e n d o n e b a s e d u p o n t h e s t r i n g

t o p o l o g y w i t h s t a t i c n a t u r e d n o d e s . B e c a u s e o f a b o v e r e a s o n s t h i s r e s e a r c h i s m a i n l y

f o c u s e d u p o n t h e p e r f o r m a n c e o f T C P i n m u l t i

t h e p e r f o r m a n c e o f T C P i n m u l t i t h e p e r f o r m a n c e o f T C P i n m u l t i

t h e p e r f o r m a n c e o f T C P i n m u l t i h o p

h o p h o p

h o p M o b i l

M o b i l M o b i l

M o b i l e

ee

e a d h o c n e t w o r k s .

a d h o c n e t w o r k s . a d h o c n e t w o r k s .

a d h o c n e t w o r k s . I n t h i s

t o p o l o g y e v e r y n o d e i n o n e r e g i o n c o m m u n i c a t e s w i t h n o d e i n o t h e r r e g i o n . M a n y

e x p e r t s h a v e d o n e a n e x t e n s i v e r e s e a r c h o n t h e p e r f o r m a n c e o f t h e T C P o v e r a d h o c

n e t w o r k s [ 1 2 , 1 4 ] w i t h s i m u l a t i o n a n d h a v e s u g g e s t e d m a n y i m p r o v e m e n t s b u t v e r y l e s s

r e s e a r c h h a s b e e n d o n e o n e x p e r i m e n t a l o r p r a c t i c a l a p p r o a c h f o r e v a l u a t i o n o f T C P

p e r f o r m a n c e t h r o u g h p u t o v e r a d h o c n e t w o r k w i t h a s t r i n g t o p o l o g y , n o r e s e a r c h h a v e

t a k e n p l a c e i n b o t h e n v i r o n m e n t w h i c h h e l p i n m o r e a c c u r a t e a n a l y s i s o f T C P o v e r A d

h o c n e t w o r k s , s o r e s e a r c h i n t e s t b e d o r p r a c t i c a l a p p r o a c h i s n e e d e d .


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H e r e t h e e x p e r i m e n t s w e r e d o n e i n b o t h e n v i r o n m e n t s ( s i m u l a t i o n a n d t e s t b e d ) t h e

r e s u l t s o b t a i n e d f r o m s i m u l a t i o n , t e s t b e d w e r e c o m p a r e d a n d a n a l y z e d . I t w i l l o b s e r v e

w h e t h e r t h e r e i s a c o - r e l a t i o n b e t w e e n r e s u l t s t h a t w e r e o b t a i n e d , w h e t h e r t h e r e i s r e a l l y

a n a d v a n t a g e i s t h e r e w i t h s i m u l a t i o n s o r n o t , c r i t i c s o f b o t h m e t h o d s ( s i m u l a t i o n a n d

t e s t b e d ) w i l l b e a n a l y z e d , t h e r e a s o n s f o r l e s s p e r f o r m a n c e i n s t a t i c n a t u r e w e r e

o b s e r v e d .

III METHODOLOGYThe work consists of finding TCP performance over ad hoc networks on specified conditions with

specified straight-line topology, on both simulator and test bed environments and also consists of

studying ns-2 simulator, implementation of simulation, and implementation of testbed and finally

the comparison of both the results that were obtained

3.1 TOPOLOGY

Ad hoc network is a collection of wireless mobile nodes forming a temporary network withoutthe use of any existing networks infrastructure or centralized administration. Each node in a

wireless ad hoc network functions as both a host and a router, and the control of the network is

distributed among the nodes. Ad hoc networks can be single-hop or multi-hop networks. The

most basic Single-hop ad hoc network consists of two stations which communicate directly with

each other. An example for a single-hop can be found in Figure 3.1 and for a multi-hop ad hoc

network in Figure 3.2.

Figure 3.1: Single-hop ad hoc network Figure 3.2: Two hop/Multi-hop ad hoc network

In our research we focus on the straight line, multi hop topology which looks like as given figure 3.3.

Figure 3.3: Topology

In this topology nodes may communicate directly if they are within the transmission range of

each other. The dotted lines denote transmission range .Since we are trying to isolate the effect of

hop count. Nodes are not mobile and they are static. For example the nodes 1 and three

communicate through node 2 only, assuming if node 2 is not present then there is no

communication at all in between node 1 and all other nodes, this is called as a straight-line

communication.


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IV RESULTSTestbed experiments were carried out under MS Windows XP (with SP2), and Simulation

experiments were carried under Red Hat Linux (kernel 2.4.0) environment, using NS2-2.28

simulator.

4.1 SIMULATION RESULTSAfter running ns-2 simulations, it mainly generates two files, trace file and nam files of sizes 30

Mb each approximately, and the formats of files are as followsSample formats of NAM file data

+ -t 0.000000000 -s 0 -d -1 -p tcp -e 40 -c 2 -a 0 -i 0 -k AGT

- -t 0.004411734 -s 0 -d -1 -p DSR -e 32 -c 2 -a 0 -i 1 -k RTR

h -t 0.004646734 -s 0 -d -1 -p DSR -e 84 -c 2 -a 0 -i 1 -k MAC

r -t 0.005319563 -s 1 -d -1 -p DSR -e 32 -c 2 -a 0 -i 1 -k MAC

Sample formats of trace file data

r 82.565144931 _1_ RTR --- 1 DSR 24 [0 ffffffff 2 800] ------- [2:255 3:255 32 0] 1 [1 1] [0 1 0 0-

>0] [0 0 0 0->0]r 82.626314559 _5_ RTR --- 0 tcp 544 [a2 5 2 800] ------- [2:0 3:1 32 5] [0] 1 2

f 82.626314559 _5_ RTR --- 0 tcp 544 [a2 5 2 800] ------- [2:0 3:1 32 3] [0] 1 2

When a nam file was given as input to NAM, it will generate NAM visualizations, as shown in

figure 4.1 and 4.2. Figure 4.1 gives information about NAM developers, and NAM source. Figure4.2 is an example of a NAM screen shot of 2 nodes when they are in communication.

Figure 4.1: NAM source information

Figure 4.2: NAM screen shot

The given figure 4.2 was the simple screen shot of NAM.When two nodes are in communication

range of each other and are able to send packets between each other. In which we can observe the

communication range, packet forwarding, packet dropping, etc

Simulationresults for 2 nodesAs it mentioned above, after running simulation scripts on ns-2, ns-2 generates trace file, on


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giving the trace file as input to trace graph, Trace graph generates different types of outputs like

trace information (figure 4.3), network information (figure 4.4), and graphs of two and three

dimensions (figure 4.5, figure 4.6). Trace graph generates trace information as shown in figure

4.3. and it gives information about packet type, packet size, source trace level, destination trace

level sent packet type, acknowledge type, simulation start time, simulation end time, number of

node information. The information generated for the our simulations were packet type was TCP,

source trace level was AGT, packet size starts from 28, sent packet type, ACK packet types weregiven as TCP, simulation time was given as 300 seconds. As the simulations run were to observe

TCP information.

Figure 4.3: Two nodes Trace graph information

Network information generated by Trace graph was given in figure 4.4. the information generated

was about simulation time, total number of nodes, number of sending nodes, number of receiving

nodes, no of generated packets, no of sent packets, no of forwarded packets, no of dropped

packets, minimum packet size, maximum packet size, average packet size, no of sent bytes, no of

forwarded bytes, no of dropped bytes,

Figure 4.4: Two nodes Network information


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number of dropped nodes, and the above mentioned all parameters information was also given for

current node, and also maximum delay, minimum delay, average delay, minimum RTT, maximum

RTT, average RTT and etc, were given as shown in figure4.4. In figure 4.4 network information is

for 2 nodes were given , as it was for 2 nodes, the sending nodes were 2, receiving nodes were 2,

and dropped nodes were also 2 because the dropping may takes place at source side or

destination side.

In the simulations the first set of results were to observe the cumulative sum of generated bytes,

cumulative sum of send bytes, cumulative sum of received bytes, cumulative sum of dropped

bytes, and cumulative sum of forwarded bytes corresponds to the simulation time, as shown in

figure 4.5.

Figure 4.5: Cumulative sum of diff. Types vs. Simulation time

the second set of results were to observe the throughput of generated bytes, throughput of sendbytes, throughput of received bytes, throughput of dropped bytes, throughput of forwarded

bytes corresponds to the simulation time as shown in figure 4.6

Figure 4.6: Throughput of diff. Types vs. Simulation time


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Simulationresults for 3 nodesThree nodes trace graph information was given in figure 4.7, the information that was given byTrace graph: packet type was TCP, source trace level was AGT, packet size

Figure 4.7: Three nodes Trace graph information

starts from 28, sent and ACK packet types were TCP, current node is 0, and nodes participated

were 0, 1, and 2.

The network information for three nodes was given in figure 4.8 , as its for 3 nodes its given that

the sending nodes were 3, receiving nodes were 3, and dropped nodes were also 3 because the

dropping may be at source node or destination node or at forwarding node , number of generated

packets were given as 36794, and the number of sent packets were also 36794 generally these

should be same, number of forwarded packets were 4516, as the number of forwarded packets

were very less as compared with sent packets cause less throughput, and the packet size varies

from 28 bytes to 7812 where as the average packet size is 1040.2847, and we can also observe

sent bytes, forwarded bytes, dropped bytes and so on.

Figure 4.8: Three nodes Network information


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for three nodes the first set of results were to observe the cumulative sum of generated bytes,

cumulative sum of send bytes, cumulative sum of received bytes, cumulative sum of droppedbytes, cumulative sum of forwarded bytes corresponds to the simulation time. as shown in figure

4.9 it mainly useful for the comparison cumulative sum of generated bytes, cumulative sum of

send bytes, cumulative sum of received bytes, cumulative sum of dropped bytes, cumulative

sum of forwarded bytes according to the time.

Figure 4.9: Cumulative sum of diff. Types vs. Simulation time

the second set of results were taken to observe the throughput of generated bytes, throughput of

send bytes, throughput of received bytes, throughput of dropped bytes, throughput of forwarded

bytes corresponds to the simulation time, as shown in figure 4.10. In which the comparison of

throughput of generated bytes, throughput of send bytes, throughput of received bytes, throughputof dropped bytes, and throughput of forwarded bytes can be done easily.

Figure 4.10: Throughput of diff. Types vs. Simulation time


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The effect of Window size on TCP throughput

Figure 4.11: Throughput Vs Window Size

Here the experiments were conducted in such a manner to observe the effect of window size on

throughput, in which the packet size was kept constant to 1024 bytes, varying window size from

64 bytes to 2048 bytes, throughput was taken as average of both the receiving nodes because itstwo way communication with 2 TCP flows, the graph was drawn between window size (bytes)

Vs. throughput (AVG bytes per second) as shown in figure 4.11

The effect of Packet size on TCP throughput

0

20000

40000

60000

0 2000 4000 6000 8000 10000

Packet Size

Throughput

Figure 4.12 Throughput Vs Packet size

Here the experiments were conducted in such a manner to observe the effect of packet size on

throughput, so window size was kept constant to 32 bytes, varying packet size from 512 bytes to

7680 bytes, throughput was taken as average of both the receiving nodes because its two way

communication with 2 TCP flows, the graph was drawn between packet size (bytes) Vs.

throughput (AVG bytes per second) as shown in figure 4.12.

The effect of Path length on TCP throughput (full duplex)Here the experiments were conducted in such a manner to observe the effect of path length on

throughput, so packet size and window were kept constant, packet size was taken as 7680 bytes,

42800

43000

43200

43400

43600

0 500 1000 1500 2000 2500Window Size (Units per byte)

Throughput


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window size taken as 128 bytes, the reason for taking 7680 bytes for packet size and 128 bytes

for window size is that from the above experiments it is observed that throughput is maximum at

128 bytes of window size and there after increasing the window size havent shown any change in

throughput. And in the case of packet size also same, that the throughput is maximum at 7680

bytes of packet size, throughput was taken as average of both the receiving nodes because its two

way communication with 2 TCP flows, the graph was drawn between no of hops Vs. throughput

(AVG bytes per second), and is shown in figure4.13 which is for full duplex communication link,and figure 4.14 was for half duplex link.

0

20000

40000

60000

0 1 2 3 4 5 6 7 8

Hopcount

Throughput

Figure 4.13: Throughput Vs Hop Count

The effect of Path length on TCP throughput (half duplex)

0

20000

40000

60000

80000

100000

120000

0 1 2 3 4 5 6 7 8Hopcount

Throughput

Figure 4.14: Throughput Vs Hop Count

4.2 Observation of unfairnessWhen two nodes were communicating with each other, with two different TCP half duplex

connections in a same environment for a specified simulation time with the same parameters

specified, then the received bytes at both the nodes should be same and TCP throughput at both

nodes should be same, but its observed that the received bytes at the both nodes were not same

and throughput at both the nodes was not same and it shows unfairness.

Unfairness when window size is varyingWith 1024 bytes fixed packet size and varying the window size from 32 bytes to 2048 bytes the

throughput was taken at both nodes, the blue line shows the throughput at node 0 and the pinkline shows the throughput at node 1, the throughput was bytes per second and window size was

bytes. The graph was to observe the throughput at node 0 and throughput at node 1. The figure

4.15 was the graph drawn between throughput (bytes per second) Vs window size (bytes), in

which the comparison of throughput at the both the nodes can be easier.

Unfairness when packet size is varyingBy keeping the window size 32 bytes as a constant and varying the packet size from 512 bytes to

7680 bytes the throughput was taken at both the nodes, and the blue line shows the throughput at


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node 0 and the pink line shows the throughput at node 1, the throughput was bytes per second and

packet size was bytes. The graph was to observe the throughput at node 0 and throughput at node

1. The figure 4.16 was the graph drawn between throughput (bytes per second) Vs window size

(bytes), in which the comparison of throughput at the both the nodes can be easier.

20000

40000

60000

0 500 1000 1500 2000 2500

Windowsize

Throughput

Throughput @ node 0 Throughput @ node1

Figure 4.15: Comparison of Throughput at node 0 and at node 1

0

30000

60000

90000

120000

0 2000 4000 6000 8000 10000

Packetsize

Throughput

Throughput @ node 0 Throughput @ node1

Figure 4.16: Comparison of Throughput at node 0 and at node 1

4.3 TESTBED RESULTS

Incase of Testbed model the experiments are performed in an indoor environment. Sending and

receiving buffer sizes of 32768 bits were taken. A straight line topology is considered here in

which one node communicate with another node in the other region, if they are with in the

communicating range to each other. 200 x 200 meter network topography was used. To have a

test bed setup we have taken three systems and were made to have a straight line topology.

Laptops, desktops were used for our experiments with D-Link wireless NICs which provide data

rates up to 11 Mbps.

HARDWARE AND SOFTWARE REQUIREMENTS:

COMPAQ 1 Intel Pentium4, 1.8 GHz, 256 MB, D-Link DWL650+COMPAQ 2 Intel Pentium4, 1.8 GHz, 256 MB, D-Link DWL650+

TOSHIBA Intel Pentium4, 1.6 GHz, 256 MB, Net Gear

DELL Inspiron Intel Pentium4, 1.8GHz, 512 MB, Intel Pro2200g

On Desktops and Laptops, MS Windows XP (with SP2), VC++ IDE, Network Simulator (ns-2.28), Network Animator, Trace Graphs were used.Testbed experiments were carried out under

MS Windows XP (with SP2). Combined source and sink program were developed to generate and

transfer traffic from the source to destination. The sink listens to a port, receives packets,


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accounts them, and drops them. Program was developed in such a manner that the same program

will work as sender and receiver. Packet size, send and receiver buffer sizes can be specified and

the TCP throughput can be calculated. The source can send packets of certain size as fast as it can

but the actual rate would depend on the kernel protocol stack bandwidth. To study the effects on

the throughput of TCP in testbed, through put of TCP was found between two communicating

nodes using MS visual studio 6.0 as a programming language. Effect of packet size, Window size,

and path length were examined on TCP throughput. The results that were obtained from both(simulation and testbed) were compared. It will observe whether there is a co-relation between

results that were obtained, whether there is really an advantage is there with simulations or not,

critics of both methods (simulation and testbed) will be analyzed, the reasons for less

performance in static nature were observed.

The effect of Buffer size on TCP throughputThe experiment was conducted with sending, receiving buffer sizes varying from 1 kb to 64kb,

packets with TCP payload of 1460 bytes and actual size on the air of 1500 bytes.TCP throughput

was taken.

0

0.5

1

1.5

2

2.5

3

3.5

4

0 10 20 30 40 50 60 70

Buffer size

Throughput

Figure 4.17: Throughput (Mbps) Vs buffer size (KB)

The effect of Packet size on TCP throughputTo observe the effect packet size on the TCP throughput, Packet size was varied gradually up to

1460 bytes only. As expected, the throughput increases with packet size as shown in Figure 4.18.As it explained above, including IP header of 20 bytes and TCP header of 20 bytes, with MTU of

1460 bytes, it attains a maximum TCP throughput at around 1500. So experiments were

conducted using packets with TCP payload 1460 bytes and actual size on the air of 1500 bytes.

0

1

2

3

4

5

6

7

8

0 200 400 600 800 1000 1200 1400 1600

Packet size

TCPthroughp

Figure 4.18: Throughput (Mbps) Vs Packet size (bytes)

The effect of Path length on TCP throughputThe experiment was stabilized with sending, receiving buffers of sizes 32768 bytes and packets

with TCP payload of 1460 bytes and actual size on the air of 1500 bytes. The throughput was

taken for 1 hop for 2 nodes, and for 2 hops for three nodes to observe the path length effect on

TCP throughput. The effect of path length on TCP throughput was shown in figure 7.19.


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0

0.5

1

1.5

2

2.5

3

3.5

4

0 1 2 3

Hopcount

Throughput

Figure 4.19: Throughput (Mbps) vs. Hop length

CONCLUSIONCONCLUSIONCONCLUSIONCONCLUSION

Advantages of SimulationAdvantages of SimulationAdvantages of SimulationAdvantages of Simulation

1 . S i m u l a t i o n s p r o v i d e a d v a n c e d s i m u l a t i o n e n v i r o n m e n t s t o t e s t a n d d e b u g a n y k i n d o f

n e t w o r k i n g p r o t o c o l s , i n c l u d i n g w i r e l e s s a p p l i c a t i o n s .

2 . T o c o n d u c t d i f f e r e n t e x p e r i m e n t s o r t o s t u d y d i f f e r e n t p a r a m e t e r s e f f e c t , t h e r e a r e l o t s

o f p a r a m e t e r s w h i c h c a n b e c h a n g e d i n C + + i m p l e m e n t e d c o d e a n d a s w e l l a s i n T C L

c o d e w h i c h m a k e t o s t u d y d i f f e r e n t s e t t i n g s w i t h d i f f e r e n t p a r a m e t e r s , s i m u l a t i o n s t u d y i s

m o r e f l e x i b l e a s c o m p a r e d w i t h e x p e r i m e n t a l s t u d y , a n d i t s n o t a l w a y s p o s s i b l e t o

c h a n g e r e q u i r e d p a r a m e t e r s i n t e s t b e d / e x p e r i m e n t a l s t u d y

3 . C o n d u c t i n g p r a c t i c a l / t e s t b e d e x p e r i m e n t s w e r e n o t a l w a y s p o s s i b l e b e c a u s e w h e n w e

t a k e l a r g e n u m b e r o f n o d e s w i t h m o b i l i t y i t s r e a l l y d i f f i c u l t t o c o n d u c t e x p e r i m e n t s .

DisadvantagesDisadvantagesDisadvantagesDisadvantagesofofofofsimulationsimulationsimulationsimulation

S o m e d i s a d v a n t a g e s o f N S - 2 f r o m i t s o p e n s o u r c e n a t u r e . F i r s t , d o c u m e n t a t i o n i s o f t e n

l i m i t e d a n d o u t o f d a t e w i t h t h e c u r r e n t r e l e a s e o f t h e s i m u l a t o r . F o r t u n a t e l y m o s t

p r o b l e m s m a y b e s o l v e d b y c o n s u l t i n g t h e h i g h l y d y n a m i c n e w s g r o u p s a n d b r o w s i n g t h e

s o u r c e c o d e . T h e n c o d e c o n s i s t e n c y i s l a c k i n g a t t i m e s i n t h e c o d e b a s e a n d a c r o s s

r e l e a s e s . F i n a l l y , t h e r e i s a l a c k o f t o o l s t o d e s c r i b e s i m u l a t i o n s c e n a r i o s a n d a n a l y z e o r

v i s u a l i z e s i m u l a t i o n t r a c e f i l e s . T h e s e t o o l s a r e o f t e n w r i t t e n w i t h s c r i p t i n g l a n g u a g e s .

T h e l a c k o f g e n e r a l i z e d a n a l y s i s t o o l s m a y l e a d t o d i f f e r e n t p e o p l e m e a s u r i n g d i f f e r e n t

v a l u e s f o r t h e s a m e m e t r i c n a m e s , t h e l e a r n i n g c u r v e f o r N S - 2 i s s t e e p a n d d e b u g g i n g i s

d i f f i c u l t d u e t o t h e d u a l C + + / O T c l n a t u r e o f t h e s i m u l a t o r . A m o r e t r o u b l e s o m e l i m i t a t i o n

o f N S - 2 i s i t s l a r g e m e m o r y f o o t p r i n t a n d i t s l a c k o f s c a l a b i l i t y a s s o o n a s s i m u l a t i o n s o f

a f e w h u n d r e d t o a f e w t h o u s a n d o f n o d e s a r e u n d e r t a k e n


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Advantages of testbed:Advantages of testbed:Advantages of testbed:Advantages of testbed:

I t i s i m p o r t a n t t o c o n d u c t r e a l e x p e r i m e n t s i n s t u d y i n g w i r e l e s s m u l t i h o p a d h o c

n e t w o r k i n g s y s t e m s . S u c h e x p e r i m e n t s c a n p r o v i d e a v a l u a b l e b a s e l i n e t o i d e n t i f y

i m p o r t a n t i s s u e s , p r o v i d e r e f e r e n c e v a l u e s f o r s i m u l a t i o n s t u d i e s , a n d b e u s e d t o s e t

p a r a m e t e r s o f p r o t o c o l s a p p r o p r i a t e l y t o o p t i m i z e p e r f o r m a n c e . S i n c e t h e s e s y s t e m s a r e

d y n a m i c a n d d i f f i c u l t t o m o d e l a c c u r a t e l y , p u r e l y s i m u l a t i o n s t u d i e s c o u l d b e q u i t e

r e m o v e d f r o m r e a l i t y . H e r e t h e a c c u r a c y w i l l b e m o r e a n d t h e r e q u i r e d s t e p s t o i m p r o v e

p e r f o r m a n c e c a n b e p e r f o r m e d a t t h e o b s e r v a t i o n p o i n t , a n d t h i s l e a d s t o a c h i e v e b e s t

o u t p u t s .

Disadvantages of testbed:Disadvantages of testbed:Disadvantages of testbed:Disadvantages of testbed:

Its not always possible to change required parameters in testbed/experimental

study; Conducting practical/testbed experiments were not always possible

because when we take large number of nodes with mobility its really difficult to

conduct experiments.

REFEREFEREFEREFERENCESRENCESRENCESRENCES

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[14] IEEE Computer Society LAN/MAN Standards Committee. Wireless LAN medium access control

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Author:

B.Sc and M.C.A from Utkal University, Orissa, India, M.TECH (Computer

Science),

PhD (Computer Science (MANET) (Pursuing)) Jawaharlal Nehru University, New Delhi, India.

Presently working as Assistant Professor AND College, University of Delhi, New Delhi, India.

Documents

TCP Performance through Simulation and Testbed in Multi-Hop Mobile Ad hoc Network