PERFORMANCE STUDY AND SIMULATION OF AN ANYCAST PROTOCOL FOR WIRELESS MOBILE AD HOC NETWORKS

International Journal of Wireless & Mobile Networks (IJWMN) Vol. 5, No. 3, June 2013
DOI : 10.5121/ijwmn.2013.5302 19
PERFORMANCE STUDY AND SIMULATION OF AN
ANYCAST PROTOCOL FOR WIRELESS MOBILE AD
HOC NETWORKS
Reza Azizi
Engineering Department, Bojnourd Branch, Islamic Azad University, Bojnourd, Iran
reza.azizi@bojnourdiau.ac.ir
ABSTRACT
This paper conducts a detailed simulation study of stateless anycast routing in a mobile wireless ad hoc
network. The model covers all the fundamental aspects of such networks with a routing mechanism using
a scheme of orientation-dependent inter-node communication links. The simulation system Winsim is used
which explicitly represents parallelism of events and processes in the network. The purpose of these
simulations is to investigate the effect of node’s maximum speed, and different TTL over the network
performance under two different scenarios. Simulation study investigates five practically important
performance metrics of a wireless mobile ad hoc network and shows the dependence of this metrics on
the transmission radius, link availability, and maximal possible node speed.
KEYWORDS
Mobile Wireless Ad Hoc Networks, Network Protocols, Anycast, Simulation, Performance Evaluation
1. INTRODUCTION
Any computer network, which is not connected by the cables and in which data is transmitted
by using radio waves between nodes of the network is called a wireless network. Wireless
networks support mobility, so users have access to network anywhere within the range. Also
installing a wireless network is simpler and faster due to the elimination of cables.
Wireless ad hoc network [1] is a type of wireless network that does not need any existing
infrastructure such as wireless router or access point. An ad hoc network consists of multiple
nodes that are connected through wireless links. Since the transmission range for each node is
limited, if receiver node is not inside the coverage area of sender, each node should participate
in routing as intermediate node by forwarding data to other nodes until it reaches the receiver. It
means every node can work as a router in network to establish a multi-hop wireless link
between sender and receiver. A mobile ad hoc network [2] (MANET) is a decentralized wireless
ad hoc network in which nodes can move arbitrarily in any direction; therefore it results in
frequent changing of links to other nodes. Like in other wireless ad hoc networks, every node
should forward the data which is not related to it, and accordingly act as a router. Due to
dynamic nature of MANETs, they have wide usage in military scenarios to disaster relief
operations or sensor networks. Besides, they are also used increasingly in our everyday life for
transferring the data between wireless devices, and mainly to share internet in home networks or
public places like airports, restaurants.
As mentioned above each node must be able to work as a source, destination, or router and
decide which way to route packets. The act of selecting paths to direct the packets or generally
network traffic is called routing. Routing protocol is the tool used to control all the
transmissions inside the network. It also should be able to handle the topology changes as a

20
result of node’s random movement through the wireless network. Flooding [3] is an algorithm
in which every incoming message is sent to all reachable parts of the network. It is easy to
implement and is used as a part of some routing protocols. Besides, anycasting algorithm is used
to choose the topologically nearest node in a group of possible receivers and forward data
toward it.
Simulation modeling [8] and real-world experiments [4] are two different methods used for
investigation and performance evaluation of wireless ad hoc networks. The simulation method
allows studying the characteristics and manner of MANETs with eligible number of nodes and
desired number of repetitions, in comparison with real-world investigation that requires much
more resource and time and to provide precise and noteworthy information.
A detailed simulation study of stateless anycast routing in a mobile wireless ad hoc network is
conducted. The proposed scheme enables representation of reliability aspects of wireless
communication in a general and flexible way. Using a flooding anycast mechanism, the paper
addresses issue of locating the nearest server from a group of contents-equivalent servers in the
network. The simulation model explicitly represents parallelism of events and processes in the
wireless network. The goal of this study is to investigate an anycast routing protocol
characteristics in wireless ad hoc network under different conditions with use of some
performance metrics. In simulation, the behavior of five fundamental performance metrics -
response ratio, average number of hops, relative network traffic, average response time and
duplicate ratio - was investigated with varying distance of transmission and different
combinations of model parameters.
The rest of the paper is organized in the following way. Section 2 presents system assumptions
and specification of the chosen mobility model in simulation modeling. Section 3 explains the
simulation setup, organization of our conducted simulations, and performance metrics.
Respectively, sections 4 and 5 mention results and their discussions. Finally Section 6 concludes
the study.
2. SIMULATION SYSTEM
Winsim [5] is the simulation system which used for modeling and simulation of wireless ad hoc
network in this paper. Winsim is based on a class of extended Petri nets. It has high level of
programming language possibilities for processing complex data, and provides quick
simulation. More details and examples about extended Petri nets are provided in [6]. The
program was developed based on the prototype program already implemented in [7].
2.1. The System Assumptions
The area of network is assumed to be restricted to a rectangular shape with system configuration
parameters xmin and xmax for horizontal axis, and ymin and ymax for vertical axis. Also the number
of the nodes within this area is fixed and their primary distribution assumed to be random with
uniform probability distribution within the (xmin , xmax ) and (ymin , ymax ) limited areas.
Next assumption is that, nodes have capability to communicate with each other, by using of
bidirectional wireless channels. The transmission radius is assumed to be same in different
directions. Besides, even within this limited coverage area, inter-node connection is not reliable
due to different reliability aspects of wireless communication, like interference, fading, or
climate conditions. Each node has a unique identifier or address.
Another assumption is that, movement of the nodes in the given area is same in form with a
chosen mobility model. A node will bounce and continue moving within the area in a new
direction, if it reaches to the borders.

21
This model assumes that nodes change position alternatively at discrete steps. This time interval
for each step, is another system configuration parameter, and is defined by τ. Also each node is
moving with a different speed in the range of (0, ∆Vmax(x) ) and (0, ∆Vmax(y) ).
2.2. Mobility Model
A mobility model controls the movement of mobile nodes, and change in their speed and
location. The Random direction mobility model [10] is one of commonly used synthetic models.
In this study, the random direction mobility model is used, but with some modifications. In the
modified version, mobile nodes still continue to select random directions but can change their
direction of movement at the end of any step, with the probability p. So nodes are not forced
anymore to reach the borders to choose a new direction. By using the p probability as another
system configuration, we can demonstrate various motion patterns. The original random
direction model can be reached, if value of p is set to zero in extended version.
A flooding-based [11] simulation system was developed relying on the chosen mobility model.
System is used to localize an anycast server in wireless ad hoc network by employing anycast
service. It is assumed that there are two types of nodes in the network. Simple nodes (clients)
are the first type of nodes, they are sources of anycast requests. Simple nodes (intermediate) re-
transmit anycast requests, which come from source nodes, in multicast mode inside the network
area. Simple nodes are also capable of forwarding unicast replies generated by server nodes.
It is assumed that there is one group of anycast servers in the network with five identical mobile
server nodes. These server nodes are distributed randomly in the network area. In the current
model, there is only one source of requests. Therefore, logically, the system is equivalent to a
finite population queuing system [12] with one client and a few identical servers.
3. SIMULATION SETUP
Simulation experiments were organized and conducted according to the following setup. It is
assumed that the network area is a rectangular (square) of 500 m × 500 m. Such an area is quite
realistic for small and medium-sized ad hoc wireless networks. The network area is populated
by N=50 nodes, having numbers 1, 2, 3,…, N. The first m nodes are anycast servers with
numbers 1, 2, …, m < N. The number of anycast servers, m, is specified in the file of
parameters. The nodes with numbers m+1, m+2, …, N are simple nodes. It is assumed that
m<N-m, i.e. the number of anycast server nodes is less than the number of simple nodes. For
the sake of simplicity, simple node N is the source node that generates anycast requests.
Initial positions of the nodes (simple and servers) are random and different in different
simulation runs with the uniform probability distribution [6] in given area. That is, the network
area with its nodes can be approximated as a point Poisson field [6]. All nodes move from their
initial positions according to the chosen mobility model.
Any anycast server can receive more than one multicast request, but only the first received
multicast request will be accepted and responded. Any simple node can receive more than one
unicast reply from a few servers, but only the first unicast reply will be accepted and forwarded
(if not the source node).
As was mentioned earlier, only one network node was used as a source of anycast request
messages. All other network nodes work as message routers or servers of anycast messages
transmitted by the source node. Correspondingly, the source node discards all requests that can
be transmitted by other nodes since these requests are copies of messages initiated by the source
node. The source node assigns a unique number to each generated packet. Interval between
transmissions of requests by the source node is set to be 500ms. For a small sized or medium

22
sized ad hoc network, this interval is sufficiently large to complete all activities in a network
related to a request transmitted by the source node before it transmits the next request. As a
result, at any moment of simulation time, the model will handle, at different nodes, messages
with the same identifier. This considerably simplifies the model and its study.
To obtain sufficiently stable statistical results of simulation, the total number of requests
transmitted by the source node is set as Ns = 2000 messages. With this number of messages and
inter-message interval of 500 ms, the simulation interval of each run is 2000 × 500 ms + 1000
ms = 1001000 ms, where 1000 ms is a small margin to provide the clearance of the model at the
end of each simulation run [9].
Starting from a chosen random position, each network node (including the source node) moves
in a random direction with a constant random speed in the given area. The random speed of a
node is set according to uniform probability distribution in the range (0, Vmax), where Vmax is the
maximal speed set as a network configuration parameter.
As it is explained in [13], the inter-node communication is considered as very reliable for nodes,
which are very close to each other. For this reason, in the model, the distance to very close
nodes is assumed to be a random variable which has a lower bound equal to zero and upper
bound being uniformly distributed from 5 to 10 meters. Also when probability of changing
direction is equal to zero, nodes change the direction of their movement randomly at the border
of the network area was used in this mobility model.
One more parameter of the inter-node communication scheme is the interval in which the states
of oriented inter-node communication links are checked. This interval is the same for all
simulation experiments and was set at 2000ms. At the end of this interval, the state of each link
can change.
The simulation experiments were conducted for maximal transmission distances 30m, 60m,
90m, 120m, 150m, 180m and 210m. Obviously, with these distances, the message transmitted
or forwarded by a node can reach only a subset of network nodes in the given area. This is true
for real ad hoc wireless networks.
It is also assumed that each network node, intermediate or destination one, can lose any
message, transmitted by another node, with some probability l. In the simulation experiments, as
parameters, link availability l was used as the message loss probability in the range of 0< l <1.
The value of time-to-leave (TTL) field in generated packets was fixed at seven or four in each
request message.
Two series of experiments were conducted. In the first series, the chosen performance metrics
were studied for maximal node speeds 5 Km/h, 30 Km/h and 50 Km/h. It should be noted that,
with the given value of Vmax, different network nodes will move with different speeds in the
range (0, Vmax). For these series of experiments link availability l=0.7 and probability of
changing direction p=0.0 were used. In both series of experiments, the value of TTL in each
request message was fixed at seven.
In the second series of conducted experiments, the effect of TTL value on the performance
metrics was investigated. For this reason, a set of experiments were performed by setting TTL
to 4 and 7 with link availability l = 0.05, 0.1, 0.3, 0.5 and 0.7 when Vmax was set to 5 Km/h,
probability of changing directions p=0.0 and the maximum transmission distance is varied in the
range (30-210) meters. All the parameters and setup of simulation setup are shown in Table 1.

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Table 1: Parameters of simulation setup
Network area 500 m x 500 m
Number of nodes 50
Total number of requests 2000
Interval between transmission of requests 500ms
TTL (Time-to-leave) 4 and 7
Link availability (l) 0< l <1
Maximal transmission distances, m 30 to 210
Maximal node speed (Vmax) 5 Km/h, 30 Km/h and 50 Km/h
Changing direction probability (p) p = 0
3.1. Performance Metrics
Performance metrics are used to help researchers to investigate the wireless ad hoc networks.
Delivery ratio and average number of hops per delivered packet are the most popular
performance metrics used for this reason. The delivery ratio (referred as response ratio)
characterizes how the network is effective in delivering packets from source nodes to server
(destination) nodes. Average number of nodes that a packet traverses in its way to the source
node is represented as the average number of hops. Both of these performance metrics have
direct relation with the implemented routing algorithm, node mobility models and inter-node
communication links specification.
Response time is another performance metric. Response time is the time interval between the
moments the source node sends a request, until the reception of the reply message. This metric
is important for some real-time applications which need small time interval.
Each packet that is transmitted by a source node will be usually retransmitted by some
intermediate nodes until it is received by server nodes. Relative traffic is the performance metric
that represents the number of times each packet is transmitted by other nodes. As matter of fact,
it is necessary to keep relative traffic as low as possible to have less overloading in the network.
All received replies in source node for a request, after receiving the first reply are taken as
duplicated replies. This characteristic of the network behavior is shown by duplication ratio
performance metric. It has a direct relation with robustness and availability of the network, but
should not be large to have less traffic in the network.
4. RESULTS OF SIMULATIONS
The results of the first series of simulations are presented in Figures 1 – 5. The results of the
second series of simulation are shown in Figures 6 – 15. Afterwards, Figures 16 – 20 represent
the comparison for second series of experiments.

24
Figure 1: Relative traffic versus transmission radius with link availability l=0.7 and different
maximal node speed.
Figure 2: Response ratio versus transmission radius with link availability l=0.7 and different
maximal node speed.
Figure 3: Duplicate ratio versus transmission radius with link availability l=0.7 and different
maximal node speed.

25
Figure 4: Average number of hops versus transmission radius with link availability l=0.7 and
different maximal node speed.
Figure 5: Average response time versus transmission radius with link availability l=0.7 and
different maximal node speed.
Figure 6: Relative traffic versus transmission radius with different link availability for TTL=4.

26
Figure 7: Response ratio versus transmission radius with different link availability for TTL=4.
Figure 8: Duplicate ratio versus transmission radius with different link availability for TTL=4.
Figure 9: Average number of hops versus transmission radius with different link availability for
TTL=4.

27
Figure 10: Average response time versus transmission radius with different link availability for
TTL=4.
Figure 11: Relative traffic versus transmission radius with different link availability for TTL=7.
Figure 12: Response ratio versus transmission radius with different link availability for TTL=7.

28
Figure 13: Duplicate ratio versus transmission radius with different link availability for TTL=7.
TTL=7.
TTL=7.

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Figure 16: Relative traffic versus transmission radius with different link availability for TTL=7,
and 4.
Figure 17: Response ratio versus transmission radius with different link availability for TTL=7
and 4.
Figure 18: Duplicate ratio versus transmission radius with different link availability for TTL=7
and 4.

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TTL=7 and 4.
TTL=7 and 4.
5. DISCUSSIONS OF THE RESULTS
The following comments and observations can be made using the simulation results:
1. All the performance metrics dependent on the transmission radius, but the character of
this dependence is different for different performance metrics.
2. As Figures 2, 7 and 12 demonstrate, the response ratio is quite low for small values of
transmission radius, but it approaches the highest value of 1 at the transmission radius
of 210m. However, for small link availability l=0.05, the response ratio remains quite
low even at transmission radius of 210m, since a large number of packets are lost on the
path from the source node to server and back.
3. At a small transmission radius of 30 m, the response ratio is low even for high value of
link availability l = 0.7. The reason is that, with N = 50 nodes in the network, there is a
high probability that each transmitting or forwarding node has no neighbors within this

31
transmission radius. This means that a packet transmitted by a node in network area has
a very low chance to be received by at least one other node in this area.
4. Response ratio has direct relation with link availability. Increasing the link availability
results in increment of response ratio, and it becomes more obvious in higher
transmission radiuses (Figures 7 and 12). Also, as you can understand from Figures 2,
and 17 different node speeds, and TTL has no significant effect on this performance
metric.
5. As Figures 4, 9 and 14 show, the average number of hops is quite low at a small
transmission radius. It initially increases with the increase of the transmission radius,
reaching some maximum and then decreases. Such a behavior of this metric can be
explained in the following way. When the transmission radius is small, then, as it was
explained earlier, many transmitted or forwarded packets will be received mainly by a
close neighbor. It means, the packet can reach the destinations if only the destination is
a close neighbor of source, with a low number of hops. On the other hand, with a very
large transmission radius, many nodes will find their destination node in the coverage
area, so packet can be transmitted with only one transmission. This reduces the average
number of hops again.
6. The average number of hops metric was usually varying in the range (1-2) for different
link availabilities and node speeds. Figures 9 and 14 indicate that for small link
availabilities (l=0.05 and 0.1) it shows small changes and always stays close to 1 even
with increasing the transmission radius. This performance metric is the same for
different TTL with small link availability as shown in Figure 19, but it reaches higher
average number of hops for TTL=7. As packets with smaller TTL will be discarded on
their way to destination, it results in a minor increase in this performance metric.
7. The third metric, the relative traffic, can be quite high for a large value of link
availability (Figures 6, and 11), especially at large transmission radius, when more and
more nodes are involved in the retransmission of packets (Figure 1). With variable
values of TTL, the number of nodes involved in packet transmission is reduced. As
shown in Figure 16, a value of TTL=4 has a small impact on the performance of the
pure flooding scheme.
8. As Figures 5, 10 and 15 show, the average response time is quite low at a small
transmission radius. It initially increases with the increase of the transmission radius,
reaches some maximum and then decreases. As explained before, when the
transmission radius is small, less numbers of nodes are involved in the transmission. On
the other hand, with a large transmission radius, many transmitted packets will find
their destination node in the area with only one transmission. This reduces response
time of the packets. Plus, maximum average response time is larger for packets with
bigger TTL as you can see in Figure 20.
9. Figures 3, 8, and 13 show that the duplicate ratio, the last metric, is quite low for a small
transmission radius, but can be high for a large value of link availability (Figures 8, and
13). At the transmission radius of 210m as it approaches the highest value, since more
than one server can be in the range of the transmitted packets and contribute to
duplicate replies.
10. As indicated in Figure 18, in a network with all its nodes having the same link
availability, changing the packet’s TTL doesn’t have a visible effect on the duplicate
ratio.

32
11. As graphs in Figures 1-5 demonstrate, change of the maximum possible node speed in
the range from 5 Km/h to the medium speed of a car in a city of 50 Km/h does not result
in considerable change of all performance metrics.
6. CONCLUSIONS
In this work, an anycast flooding simulation model of mobile ad hoc networks was used to
investigate practically important performance metrics. The dependence of practically important
performance metrics on the transmission radius, link availability and maximal possible node
speed was investigated by conducting a large number of simulation studies. These metrics are
the delivery ratio, the average number of hops, the relative traffic, the response time and the
duplicate ratio.
Simulation results show that changing the maximum node speed has small effect on
performance of the network. For the small link availabilities performance metrics remain quite
low even at transmission radius of 210m. On the other hand, decreasing the TTL can result in
less traffic when other performance metrics are nearly same.
In summary, the present simulation results together with the simulation model can be used for
better and closer understanding toward anycasting in ad hoc wireless networks.
REFERENCES
[1] Wu S.L. & Tseng Y.C., (2007) Wireless Ad Hoc Networking, Auerbach Publications, ISBN
978-0-8493-9254-2.
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[3] Ho C., & Obraczka K., & Gene T., & Viswanath K., (1999) “Flooding for reliable multicast in
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algorithms and methods for mobile computing and communications(DIALM).pp 64-71.
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[5] Kostin A. & Ilushechkina, L., (2004) Winsim: A tool for performance evaluation of parallel and
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Scientific Publishing. Co.
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Networks”, Mobile Networks and Applications 9, Kluwer Academic Publishers, pp.333-342.
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hamburg.de/TGI/PetriNets/tods/quick.html.
[10] Royer E., & Melliar-Smith P.M., & Moser L.(2001) “An analysis of the optimum node density
for ad hoc mobile networks”. In Proceedings of the IEEE International Conference on
Communications (ICC).
[11] Obrachzka, K., & Viswanath, K. (2001).” Flooding for reliable multicast in multi-hop ad hoc
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33
[13] Haci H., (2010) “Performance investigation of simulation models of wireless mobile ad hoc
networks” , Thesis (M.S.), Eastern Mediterranean University, Institute of Graduate Studies and
Research, Dept. of Computer Engineering, Famagusta, Cyprus.
Author
Reza Azizi was born in Bojnourd, Iran in 1983. He received the BS degree in
Software Engineering from Islamic Azad University of Shirvan, Iran, a MS
degree in Computer Engineering from Eastern Mediterranean University,
Cyprus. He has been employed as a research assistant at computer
engineering department, where he has been involved in multiple A class
projects. He is currently working as Lecturer at Islamic Azad University of
Bojnourd and a joint member of Educational Center of Applied-Science
and Technology. Research interests: Simulation, Performance Evaluation
and Optimization of Wireless Sensor and Mobile Ad-Hoc Networks.

PERFORMANCE STUDY AND SIMULATION OF AN ANYCAST PROTOCOL FOR WIRELESS MOBILE AD HOC NETWORKS

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