bidirectional search routing protocol for mobile ad hoc networks

International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-

6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 1, January- February (2013), © IAEME

229

BIDIRECTIONAL SEARCH ROUTING PROTOCOL FOR MOBILE AD

HOC NETWORKS

M. Ahmed, S. Yousef, and Sattar J Aboud

Telecommunications Engineering Research Group (TERG)

Faculty of Science and Technology

Anglia Ruskin University, UK

ABSTRACT

Ad hoc Network is self-configurable, infrastructure-less multi-hop wireless networks,

characterized by their frequent topology changes and the need for dynamic routing protocols

capable of coping with these characteristics. A new reactive ad hoc routing protocol is

proposed in this paper, which relies on the Artificial Intelligence Bidirectional Search

Algorithm in discovering routes from source to destination of communication process in a

balanced and mutual search mechanism. This allows both source and destination to

simultaneously discover the routes to each other reducing the discovery time of reactive

routing strategy up to 53% in small and medium scale networks, while this value starts to

decrease by increasing the size of the network. The new Bidirectional Search Routing

protocol then is compared to both Dynamic Source Routing and Ad-hoc On-Demand

Distance Vector Routing in terms of performance metrics of reactive routing strategy such

route discovery time and average delay showing promising results.

Keywords: Routing, Communication system routing, Protocols, MANET.

I. INTRODUCTION

Unlike infrastructure-oriented wireless networks, wherein the wireless devices

internetwork through relying on fixed network infrastructure to bypass, process or route data

packets across the wireless network. Mobile Ad hoc Networks (MANETs) are multi-hop and

self-organized infrastructure-less wireless networks. This means that each network node

should act as both host and router at the same time traversing data packets across the

network. One of the major challenges facing the designers of MANETs is the routing

dilemma. Recently, developing a dynamic routing protocol that can cope with the dynamic

nature of MANETs and simplifies the finding of feasible routes between the communicating

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nodes is the goal behind the extensive research in this field. Such protocol should be able to

handle the shifting characteristics of MANET such as scalability and mobility. Many routing

protocols have been designed and categorized into different categories mainly according to

their working mechanisms [1]. Each of these categories provides partial solutions to one or

more MANET problems. For instance, reactive routing protocols [2] help in minimizing the

bandwidth consumption through their idle behavior until a data packet is needed to be

transmitted over the network, and then the protocol starts its route discovery process on-

demand to find a route to the data packet’s destination. This process which can cause delay

before starting data transmission is solved in proactive routing strategy [3] where the network

nodes keep up to date view of the network topology through exchanging routing information

periodically, which is mostly considered as bandwidth consumer. Most of the enhancements

on routing strategies are carried out as either expansions of the existing mechanisms or

changing of the protocol’s parameters to adapt in new working environments. The goal of

this article is to propose a core-level improvement on the reactive routing strategy, in

particular on the DSR [4]. The Bidirectional Search Routing protocol (BSR) is introduced in

this article. Namely, it relies on using the bidirectional search algorithm in discovering routes

through initiating two simultaneous route discovery processes from both source and

destination nodes that meet in most cases somewhere in the middle of the distance between

these nodes. The bidirectional search’s computational complexity is low compared to

unidirectional search algorithm [5] which makes the former the best candidate to be a partial

solution to the initialization delay in reactive routing strategy. In order to utilize this search

mechanism in MANET routing process, a new approach is proposed to trigger the destination

and inform it to start the backward discovery at the same time of initiating the forward one.

This approach theoretically guarantees big reduction in route discovery time compared to

other reactive routing protocols which decreases an end-to-end delay. The theoretical model

and working mechanism of BSR are introduced. Then the protocol is compared to both DSR

and AODV [6] in terms of performance metrics of reactive routing strategy such as route

discovery time and average delay, while it is compared to the Optimizer Link-State Routing

(OLSR) as a proactive protocol, in addition to the DSR and Zone Routing Protocol (ZRP) as

a hybrid routing protocol in terms of throughput utilization. The rest of the article is

organized as follows. In the following section, the time and space (Scalability of the

algorithm) computational complexity of bidirectional search algorithm is briefly discussed,

followed by implicit delay factors in DSR. The BSR algorithm is described, and results of

performance comparisons to both DSR and AODV are shown. Finally, conclusions are drawn

pinpointing the new features of BSR protocol and its ability to outperform other routing

protocols from the same routing strategy.

II. TIME AND SPACE COMPUTATIONAL COMPLEXITY OF BIDIRECTIONAL

SEARCH ALGORITHM

The main idea behind bidirectional search is to simultaneously search both forward

from the initial state (i.e. Source) towards goal and backward from the goal (i.e. Destination)

towards initial state and stop when the two searches meet in – or close to - the middle. For

problems where the branching factor (which is the number of children of each node) is b in

both directions, bidirectional search can make a big difference. Assuming that there is a

solution of depth d, and then the solution will be found in )()2( 2/2/ ddbObO = steps, because



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the forward and backward searches each have to go only half way. For example: let b = 10

and d = 8, breadth-first search[7] spawns )( dbO nodes , and accordingly, the maximum

number of nodes expanded before finding the solution can be given as a result of: 1+

b1 + b

2 + b

3 +... + b

d = 111,111,111 nodes. Whereas bidirectional search succeeds

when each direction is at depth 4 giving the result 2 × (1+ b1 + b

2+ ... + b

d/2), at

which point 22,222 nodes have been produced.

Figure 1 Computational Complexity of Unidirectional Search vs. Bidirectional

Search.

III. IMPLICIT CACHE MANAGEMENT AND ROUTE RECORDING

DELAYS IN DSR

The source routing protocols (such as DSR) experience initialization delay

caused by the time the source node has to wait until it receives a reply from

destination -or any intermediate node holding an up to date route to destination-

confirming that an available route to destination is found. In addition to the delay

added before starting data communications in reactive routing protocols, particularly

in source routing ones, some additional delay values are neglected in most of the

related research works due to the slight effect of these values compared to overall end-

to-end delay (i.e. Request-Reply cycle time).

1. Cache Management Delay (Time-to-Read TTR and Time-to-Check TTC) Caching schemes have only been applied to DSR [8]. There are three main

characteristics of the caching scheme to cope with time aspects of caching: read

policy, write policy, and delete policy. These policies add extra little time during

request-reply cycle. Request-reply cycle time of DSR using cache is compared to the

discovery time of DSR with disabling the cache scheme. This has been done by

building 2 simulation scenarios containing 50 MANET nodes and running DSR

protocol, once with cache enabled, and another disabled. One may argue that the

cache is proposed to decrease the request-reply time if routes to destination exist in the

cache rather than increasing it. However, in the first simulation scenario, the cache is

0

20000

40000

60000

80000

100000

120000

1 2 3 4 5 6 7 8

Ma

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um

a n

um

be

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f

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Depth of search

O(b^d(

O(b^(d/2((



232

partially enabled, i.e. reading entries and checking for cached routes are enabled,

while using cached routes to initiate Route Replies (RREP) is disabled. As a result,

time reduction through using cache is put out of action. A timer is set to 0 when a

node starts destination’s discovery and stopped when the node receives a reply from

destination. While in the second scenario, route caching is disabled and the requests

are propagated directly towards the destination without any cache management

processes.

2. Route Recording Delay (Time-to-Record TTR)

In DSR, when the destination node receives a Route Request (RREQ), it

initiates a RREP back to the source node the intermediate nodes will record route

information included in the traversed packet overhead. Simulation has been performed

in order to validate this theory by building two network scenarios. First scenario is a

50 MANET nodes network running DSR protocol, and with cache enabled for all

nodes. Conversely, similar to time calculation of round-trip, the second scenario is a

simple Flood-Reply network in which the source node broadcast beacons to all

network nodes requesting a reply from a certain node (a same destination in a first

scenario). Any intermediate node role is only to check if it is the desired destination or

not by comparing its IP address with the one indexing the destination tag of the

traversed packet. Neither route recording, nor cache management are involved in the

Flood-Reply mechanism.

IV. THEORETICAL MODEL OF BSR

1. Originating and Processing Propagating Triggers Similar to DSR, when a MANET node originates an application packet to be

sent over the network to a destination, the former have to check its own cache for

available routes to destination and it will use them if there are any. Otherwise it will

broadcast the Propagating Triggers (PT). The PTs are simple beacons that contain

only addresses of source, final target, and broadcast address (255.255.255.255) in

addition to Time-To-live (TTL) value to prevent the PTs from travelling infinitely

across the network. That is, In order to engage the destination of communication

process into the route discovery formula for a balanced bidirectional search, the

destination must be informed in one way or another to start searching backwards.

Specifically, on the way to achieve a mutual search mechanism, the source and

destination nodes have to find a route over which they have to meet and start

communication.

Therefore, if no route to destination is found in the route cache, the source must

broadcast PTs to all over the network. These PT packets are propagated across the

network hop-by-hop checking the intermediate node’s address if it is equal to the

Destination Address value stored in the header of the PT packet, as a result Figure (2)

shows the possible procedures processing the PT afterwards. The PTs have some

characteristics to prevent flooding and to ensure fast network coverage, such as:



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1) The PTs packet option has 4 fields to be filled prior to broadcast, Source Node

Address, Final Destination Address, Broadcast Address (255.255.255.255), and

TTL.

2) The PTs do not record route, nor do they modify or get modified while travelling

across the network except the fact that their TTL decreases by propagating through

the network. As a result, no implicit factors can delay the PTs other than the time

required to check a traversed nodes on a Boolean manner.

3) TTL is statically set for PTs as a constant value, this is vital since the absence of

TTL for PTs might cause the PT packets to travel infinitely across the network.

The same node that initiated the PT should wait certain amount of time known as

Forward Route Request (FRREQ) Jitter before starting the forward route discovery

process, this delay value is optimally chosen according to the network size,

mobility and in a way that assures the BSR in its worst performance to show as no

more delay than in the case of DSR (section V explains the way the jitter is

optimally set).

2. Originating and Processing FRREQ After sending the PT packets by the source node to trigger the destination’s

RRREQ, the former has to wait for FRREQ Jitter which – at most - should be less

than half the time needed for average source-destination discovery time - before

broadcasting FRREQ en route for the destination. The choice of this waiting time

value ensures that even if it was exactly equal to half of the average source-destination

discovery time, the overall discovery time of BSR is guaranteed to be equal to the

discovery time of DSR. The optimal value of FRREQ Jitter according to MANET size

is described later in this paper. FRREQ has some characteristics that can distinguish it

from both PTs and Reverse Route Requests (RRREQ):

1) In the BSR protocol the non-propagating requests which are used in DSR are not

employed, although sometimes this could be inexpensive way to get routes to

destination IF the destination is within the direct neighbors of the source, however

this cannot always be guaranteed in dynamic networks like MANETs. Therefore,

the BSR uses only propagating FRREQ for any kind of destination (direct

neighbors or not), and builds-up the source route in the FRREQ while traversing

across the MANET. Thus it is one-step process for the FRREQ.

2) The FRREQ traverse is delayed each time it passes through an intermediate node

due to the explicit and implicit delay factors mentioned earlier. This will help us

to differentiate between the time needed for FRREQ and PT to travel across the

network between a certain source and destination. Thus it will help in validating

the BSR theory.

3) The BSR’s FRREQ option is encoded in Type-Length- Value (TLV) format.

4) A timer is associated with the transmission process of the propagating FRREQ

after which the source node has to retransmit a FRREQ if it did not receive a

RREP from either the destination node or any other BSR’s supportive node in a

mechanism that will be discussed later in this article.



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Figure.2 Working Flowchart

Generate

Propagating

PT

Addresse

s

No

Yes Retransmit

Initiate

RRREQ,Destroy

PT

Start Data

Address

of D?

No

Discard Yes

Done

Change Status

to RP

RRREQ

Reached

S ?

No

Yes

Pop out the

Destination

Proceed to the

next hop

Done

Generate Forward

Route Request

Wait for FRREQ tter

Yes

Route in

Cache?

No

Address

of S?

No

Discard Yes

Done

FRREQ

Reached

D ?

No

Yes

Initiate Node is

RP?

No

Yes

Append

Address +

Originating

Application

Invert Source

Route and

Start Data

Comm.

Done

S: Source node

D: Destination node

A B

C



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3. Originating and Processing RRREQ As described earlier, in the case of matching the addresses of the receiving node with

the target node in the PT header, the receiving node will instantly use the PT originator’s

address as a target address, and its address as a source address to start backward route

discovery towards the original source of communication.

The main task of RRREQ is not only to search for the source node, but also to create

meeting points (Named as Rendezvous Points or RP) where at the FRREQ and the RRREQ

may connect. Explicitly, when a node receives a PT informing it to start reverse discovery,

the node proceeds as follows:

1) It first checks the addresses field in the PT header and copy the addresses to be:

--The Target Address in the received PT becomes Source Address.

--The Source Address in the received PT becomes Target Address.

--The destination address stays as it is, i.e. the broadcast address (255.255.255.255)

2) After processing the addresses field, it instantaneously originates reverse discovery

packets with RRREQ option, this option is identical to the one used for FRREQ except

that in the RRREQ, the Target Address is the Source Address in the FRREQ, while the

Source Address in the RRREQ is the Target Address in the RREQ.

3) The RRREQ packets start traversing across the MANET searching for its target (The

source of the RREQ and PT). On their way:

They build up the Destination Route (Similar to Source Route in the FRREQ). In other

words, the traversed nodes starting from the initiator of the RRREQ until the current node are

being added to the destination route in order to be used whenever both the FRREQ and the

RRREQ meet. The addition mechanism is important for RRREQ as the destination route

should be built up using a stack, the reason behind using stacks is the push and pop order.

That is, instead of reversing the destination route when the FRREQ meets the RRREQ, the

destination route gets popped out so that the last traversed node using RRREQ (the last

pushed entry) becomes the first in the route to destination just after the Rendezvous Point.

As a result, this mechanism will omit the time needed for inversion of the route in

case if First-In-First-Out (FIFO) is used like the case of source route. Change the status of

each traversed node from Normal node to RP. Any intermediate node that receives a RRREQ

changes its own attribute to become a RP which expands the destination territory towards the

source. More details about the characteristics of the RP will be discussed in the next sub-

section. If the RRREQ found the source node while the FRREQ still searching, the source

node will use the destination route contained within the RRREQ header to start data

communication.

Finally, the destination node in this case will be ready to originate RREP even though it

has initiated RRREQ. The reason behind this is to guarantee as exact as DSR’s discovery

time in cases where the coverage of the RP took place on another direction rather than the

source’s direction.

Apart from the similarities between processing a packet containing a FRREQ option and

another containing RRREQ option, the latter generally differs in the way it processes the

receiving node since the receiving node’s attributes get modified the moment it receives a

RRREQ packet, although the checking mechanism for the target node (The source of the

FRREQ) is identical.



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Therefore,

1) If the address of the receiving node is listed in the RRREQ route then discard the packet to

prevent infinite loops. Processing a packet with self address means that the receiving node

has processed this packet previously.

2) If the address of the receiving node matches the address of the source node (The Target

according to the RRREQ) contained in the routing header, this means that the RRREQ

has reached the source node directly providing a destination route which – by popping out

if the stack – can be used by the source node to send application packets through.

3) Otherwise, the status of receiving node will be changed to be a RP and holding the –to the

point – destination route to be ready whenever it gets contacted by a FRREQ. After that

the RRREQ proceeds to the next hop repeating the same procedure.

4. Rendezvous Points

The RP is a normal intermediate MANET node which has been passed trough by a

packet containing RRREQ option. Namely, if a RRREQ passes through a MANET node on

its way towards destination it checks the status of the intermediate node, if it is a RP node, it

will leave it unchanged, and otherwise it will change the status to RP. Accordingly, during its

TTL, if the RP was found by the FRREQ the RP will initiate a RREP back to the source node

carrying the inverted destination route. This is considered as the core of time reduction

mechanism of BSR. Instead of reaching the destination itself to initiate a RREP, it could be

half the distance when reaching an intermediate RP, thus approximately half the time.

On the other hand, the other possibility is to initiate a RREP is from any RP that

contains the route to the Final Target. In this case, the addresses from the RP to the Source

node in addition to the Addresses from the RP to the Destination form the whole route from

source to destination. That is,

(Address [Target], Address [Target-1]... Address [RP]) + (Address [RP-1], Address [RP-

2]... Address [Source])

V. OPTIMAL FRREQ JITTER

There are different situations wherein the timing of initiating the FRREQ after

broadcasting the PTs plays an effective role in reducing discovery time between a source and

its destination and also in the scalability of MANETs. Although these delay values –in small

to medium scale network with 5 m/s mobility speed for example – may vary between 0.01

and 0.3 milliseconds respectively, therefore, choosing the right delay value for a certain

network size and mobility model is an important issue that guarantees the best performance

of the BSR. In addition to that, the wrong choice of the delay value will show how the

protocol would collapse to the DSR if the delay value was set around 0.01 or 0.3 milliseconds

in the same example. In order to investigate the way through which the delay should be set,

simulations have been performed on the 3 possibilities below through choosing 3 time

intervals for the FRREQ Jitter statically: in the first case (the immediate FRREQ initiating),

the delay is set to uniform distribution between 0 and 0.01 milliseconds. The second case

where the bounds of the uniform distribution are between 3-4 milliseconds is considered the

late FRREQ originating. Lastly, according to that, the bounds of the distribution are set to be

between 0.01 and 3 milliseconds for optimal delay value for medium size networks as a case

study of the investigation.



237

1. Immediate FRREQ Initiating The smallest the FRREQ Jitter, the closer to destination the connecting RP will be.

That is, if the delay values between initiating the PT and the FRREQ are statically set as

small as 0-0.01 milliseconds in a medium size MANET (200 nodes) with a 5 m/s speed of

mobile nodes, the FRREQ will be directly following the PT towards the destination

shortening the path the RRREQ should use to create a balanced bidirectional search. In this

case, the delay times are very similar to the case of source routing because in most cases, the

RRREQ does not spread enough to form a bidirectional search while the FRREQ is the

dominator in the search process, the result is that the BSR will collapse to DSR in its working

mechanism.

2. Late FRREQ Initiating In this case, the source node waits more time before originating the FRREQ which

causes the PT to arrive to the destination and initiates the RRREQ before the FRREQ leaves

the source node. This makes the rendezvous points to spread further than the previous case,

and since the RRREQ does not use route cache as in the case of FRREQ, the destination node

has to do route discovery towards the source which takes more time than FRREQ cycle due

to the time added for the PT to arrive to destination, and thus more delay than in the previous

case. In this case, the BSR will collapse to DSR with more delay added for the process of

initiating the RRREQ.

3. Optimal FRREQ Jitter Considering the scale of the network and the mobility of its nodes as key factors in

determining the delay value that must be set as waiting time between originating the PTs and

then the FRREQ, the effect of this waiting time has been investigated. The simulation runs

show that the bidirectional mechanism is optimized when the value of the FRREQ Jitter is

between 0.01 and 3 milliseconds for a medium size network with a 5 m/s speed of network

nodes, therefore, this attribute’s default value for BSR is set to uniform distribution of lower

bound of value 0.01 milliseconds, and upper of value 3 milliseconds.

Figure 3: Shows the effect of FRREQ Jitter on the scalability of MANETs through the

relation between the FRREQ Jitter and the average End-to-End Delay while varying the

network density, increasing the mobile nodes’ pause time, and using relatively fixed number

of traffic sources for each scenario. The number of traffic sources started as 5 sources per 50

nodes in the first scenario, then 10 in the second, 15 for the third and finally 20 traffic sources

per 200 MANET nodes in the forth scenario. The percentage will be always 10% of the

network size to keep a relatively fixed number of sources for all scenarios. It is obvious from

the example that increasing the number of nodes within a medium scale MANET is less

effective when the FRREQ Jitter is 0.01-3 milliseconds as the increasing percentage of the

average value of all the end-to-end delay values from the 50 nodes MANET case to the 200

nodes case is 272.8%, while it is 523.3% for the immediate FRREQ initiating, and 579.8%

for the late FRREQ initiating. This makes the uniform distribution of 0.01-3 milliseconds the

optimal value of the FRREQ Jitter for BSR in in the above example.

International Journal of Computer Engineering and Technology (IJCET), ISSN 0976

6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 1, January

Figure 3: Delay Increasing Percentage for different network sizes

Setting the FRREQ jitter statically will result either collapsing the BSR to become a

source routing protocol if the jitter is below a certain threshold, or collapsing to destination

routing protocol if the jitter is above a certain

value statically, self-configurable jitter setting is used. In [10], the way through which the

Zone Routing Protocol (ZRP) sets its own attributes dynamically relying on the network

environment was used. Similarly, we have utilized

FRREQ jitter dynamically, by measuring certain attributes such as network size and mobility

model, the more the network size, the longer the FRREQ jitter and vice versa. The following

simulation scenarios concluded th

the form of:

FRREQ Jitter = 1/m x (Network Size / C),

m is the mobility represented by the speed of nodes in the

m/s. The mobility plays a vital role in determining how long the delay should be for the

reason that the faster the nodes move in the network, the shorter the delay should be and vice

versa.

VI. PERFORMANCE COMPARISON

1. Simulation Model

Optimized Network Engineering Tool (OPNET

testing BSR, in addition to performing all the experiments and comparisons in this paper.

Constant Bit Rate (CBR) traffic sources have been used for all the simulation scenarios with

512-byte data packets and 3 packets/second packet rate.

Point (RWP) mobility model is used with different specifications in each experiment such as

varying ground speed of nodes and changing the pause time of moving nodes. This means

that the nodes travel at the speed on which the nodes were configured to travel, and then

when they reach their destinations, they stop for pause time. After the pause times the nodes

start to travel again towards a random destination and on the same ground s

rectangular field with 2000m x 500m configuration is used and the number of nodes in fixed

network sizes is 100 nodes, while this number varies in the networks where altering the

number of network nodes is part of the experiment.

International Journal of Computer Engineering and Technology (IJCET), ISSN 0976

6375(Online) Volume 4, Issue 1, January- February (2013), © IAEME

238

Delay Increasing Percentage for different network sizes



routing protocol if the jitter is above a certain threshold. In order to avoid setting the jitter

configurable jitter setting is used. In [10], the way through which the


was used. Similarly, we have utilized this successful method in setting the

, by measuring certain attributes such as network size and mobility


concluded the relation between the network size and the FRREQ jitter in

FRREQ Jitter = 1/m x (Network Size / C), (where C is constant).

is the mobility represented by the speed of nodes in the network, and varying form 0.1

The mobility plays a vital role in determining how long the delay should be for the


PERFORMANCE COMPARISON

Engineering Tool (OPNET) has been used in designing and



ckets and 3 packets/second packet rate. For mobility scenarios,

(RWP) mobility model is used with different specifications in each experiment such as


t the nodes travel at the speed on which the nodes were configured to travel, and then


start to travel again towards a random destination and on the same ground speed and so on. A



number of network nodes is part of the experiment.


ary (2013), © IAEME



avoid setting the jitter

configurable jitter setting is used. In [10], the way through which the


this successful method in setting the

, by measuring certain attributes such as network size and mobility


e relation between the network size and the FRREQ jitter in

, and varying form 0.1-20

The mobility plays a vital role in determining how long the delay should be for the


) has been used in designing and



For mobility scenarios, Random Way

(RWP) mobility model is used with different specifications in each experiment such as


t the nodes travel at the speed on which the nodes were configured to travel, and then


peed and so on. A





239

2. Observations Key performance metrics of BSR protocol are examined through a set of simulation runs

in different scenarios and different MANET environments. Some of the performance metrics

which have been evaluated are scalability, adaptability to mobility and traffic intensity, and

comparability to other routing protocols.

2.1 Discovery Time for Different Size Networks

Generally, the time to discover a route to a specific destination is the time when a route

request was sent out to discover a route to that destination until the time a RREP is received with

a route to that destination. This term is only used by reactive routing protocols as they should

discover the available routes to destinations on demand. Theoretically, the BSR aims to reduce

the discovery time in reactive routing strategies up to 50%-60% of the time consumed in other

protocols such as DSR and AODV. This can be achieved by distributing the route discovery load

on the source and destination simultaneously instead of relying on the source only to find its route

to the destination as in the case of DSR. On the other hand, 4 network scenarios have been

designed to examine the BSR algorithm’s ability in reducing the discovery time compared both

DSR and AODV in different size MANETs and 8% CBR traffic sources of the overall number of

nodes.

Figure 4-A. Average Route Discovery Time for Different MANET sizes

As the traffic starts to flow (i.e. after 100 simulation seconds) the protocols – according to

the reactive strategy – start to discover the routes to destinations to which the application

packets should be transmitted. The BSR shows promising performance in the chosen network

intensities and close to what it is supposed to be theoretically. Figure 4-A describes the low

discovery time of BSR compared to both DSR and AODV where average discovery time of

BSR reaches 53.3% of the DSR’s over 700 seconds of simulation time. This is due to the

bidirectional mechanism which guarantees a simultaneous route discovery from both source

towards destination and vice versa. Additionally, the reasons that prevent the BSR of achieving

exactly half of DSR’s discovery times are because of the time needed to initiate and traverse

the PTs, and the FRREQ Jitter which at its maximum must not exceed 10 milliseconds as

described later in this article. As the network intensity all the values of discovery time shift up

which is logical because the RREQs need to travel further and discover more nodes. In the case

of BSR, its discovery time similarly increases as the number of nodes increases where the

discovery time in the case of 100 nodes network is 60.1% of it for DSR. The discovery time

value keeps linearly increasing as we increase the number of nodes in the network for all

protocols including BSR as shown in Figure. 6-A therefore the BSR’s discovery time value

reaches 72.4% of it for DSR in the case of 150 nodes, and finally 65.5% in the case of 200

nodes MANET.



240

2.2 Average End-to-End Delay for Different Mobility Patterns

The MANETs are known by their dynamic and stochastic nature that is caused by

the mobility of nodes under unexpected conditions and to uncertain destinations in

addition to their limited wireless coverage. These factors affect the overall performance

of MANET in a way that makes it difficult for routing protocols – the reactive ones in

particular - to handle the basic control overhead needed for reactive routing management

in addition to the overhead needed to maintain the routes in high mobility scenarios. This

experiment is to examine the stability of BSR in different mobility scenarios, compared to

DSR only as the AODV reacts to link breakage by initiating new RREQ since it

originally has at most one route per destination in its routing table, therefore it is affected

by mobility more than DSR which tends to check its cache for routes in case of link

breakage instead of initiating RREQs which makes DSR more stable than AODV in most

of the mobility scenarios. In this experiment two factors are used to determine the

stability of the protocols which are the speed of moving nodes and the pause times. These

factors can take different values to control the mobility of nodes as the more the pause

time value and the lower speed of nodes’ value the lower the mobility of nodes is. Four

scenarios of 100 nodes are designed to measure the average delay of BSR and DSR with

respect to increasing the nodes speed every time, and in each time the pause time will be

varied from 0 (constant mobility) to 750 simulation seconds (low mobility).

Figure 4-B Average delay for different mobility patterns

At low ground speed (0.1-5 m/s), the DSR and BSR perform very similarly with

maximum average delay of around 0.99 seconds when the traffic sources start to flow,

then it decreases slightly with increasing the pause time with a gap of 5.8% between the

average delay values of DSR and BSR in favor of the latter. This gap starts to increase

while increasing the ground speed of nodes to become 13.6% in the case of 8 m/s ground

speed, then it becomes 14.6% in the case of 12 m/s, and finally it gets smaller to 11.2% in

the case of 16 m/s ground speed. This means that the average delay of both protocols

increases almost equally by increasing the mobility of nodes as shown in Figure.4-B.

However, the increasing ratio of the average delay of BSR in the 16 m/s case to it in the 4

m/s case is 160% while this value in the case of DSR is 170% which means that the DSR

is more to get affected by mobility changes than BSR.



241

VII. CONCLUSION

Motivated by the accelerated research and development of MANET routing

protocols and inspired by DSR. A new reactive MANET protocol has been proposed

which utilizes the AI’s bidirectional search algorithm to reduce the route discovery

time and therefore reduce the end-to-end delay in MANETs. BSR uses a new

approach in order to inform the destination of communication process to start its

backward search (RRREQ) towards the source at the same time of the forward search

towards the destination through broadcasting small packets called Propagating

Triggers which travel across the network check for destination only. After a small

jitter called FRREQ jitter, the source has to start its normal forward discovery process

(FRRREQ) searching either the destination itself or any Rendezvous Point created by

the RRREQ. This work shows that there are some implicit delay values in DSR that

have been neglected due to their slightness compared to the overall route discovery

time. These values have been shown to explain the way in which the PTs travel faster

than normal route requests across the network. By guaranteeing the faster network

coverage by the PTs followed by the FRREQs, both FRREQ and RRREQ should meet

at around the middle of the distance between the source and the destination.

The BSR is compared to both DSR and AODV in different simulation

scenarios by varying traffic sources, mobility patterns, and network intensity. BSR

shows promising performance compared to other reactive routing protocols such as

DSR and AODV in terms of route discovery time, average end-to-end delay and other

performance metrics which will be presented in future work such as packet delivery

fraction, routing load, and others. The BSR shows up to 47% reduction in discovery

time compared to DSR in small to medium scale networks. This is due to the

bidirectional mechanism which guarantees a simultaneous route discovery from both

source towards destination and vice versa. Additionally, the reasons that prevent the

BSR of achieving exactly half of DSR’s discovery times are because of the time

needed to initiate and traverse the PTs, and the FRREQ Jitter which at its maximum

must not exceed 10 milliseconds. The BSR then shows less reaction to changing the

mobility patterns through changing the ground speed and pause time of moving nodes

than DSR. Both protocols show similar average delay on low node speeds with a gap

of 5.8% between the average delay values of DSR and BSR in favor of the latter. This

gap starts to increase slightly as we increase the ground speed of nodes to reach 11.2%

in favor of BSR.

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AUTHORS’ INFORMATION

M. AHMED (M’08) Assistant professor at the Middle East University (MEU) Maamoun

received his BSc in Computer Engineering from Mu’tah University, Jordan in 2004; he

started his career right after that and worked for the Jordan’s e-Government as a core system

administrator assistant for a year. In 2005 he has joined the TERG at Anglia Ruskin

University in UK and in 2009 he received his PhD degree in computer engineering. His

research interests are in designing routing protocols for Ad-hoc networks, modeling and

simulation, and Artificial Intelligence applications. Ahmed is a member of IEEE and the

British Computer Society (BCS) since early 2008.

S. YOUSEF Graduated in 1978 as Electrical Engineer. Worked for 18 Years in the

Telecommunication Corporation of Jordan as Operation & Maintenance engineer, and then as

head of Transmission. He moved to Anglia Ruskin University (ARU) in 1993 to gain his

MSc in Telecommunication Systems Management. In 1994 he was Offered studentship from

EPSRC to complete his PhD at ARU on ATM modeling and queuing which has been

achieved in 1998. He worked as a research fellow at ARU from 1998 until 2002 and then

promoted to a senior lecturer. He established and headed the Telecommunication

Engineering Research Group (TERG) since year 2003 which currently hoists 28 MPhil/PhD

students. His main theme of expertise is telecommunication networks in their wired and

wireless status. Most of the research is performed recently on mobile communications at

different generations through considering quality of service, security, physical layer

measurements of fading, modulation techniques, noise cancellation, coding theory, Ad Hoc

mobile networks, knowledge transfer management, 4th

generation mobile networks issues and

all electronic engineering relevant designs. Dr. Yousef has published around 80 papers

covering all the aforementioned fields and he is a member of editorial committees of many

journals, keynote speaker and chair in many conferences around the globe and external

examiner to PhD students and postgraduate degrees in many universities. TERG has to

become a research centre of excellence in Mobile and security research. TERG has wide

international links through the European consortium for bidding to FP7 fund and to Tempus

Fund.

SATTAR J ABOUD is currently a visitor professor in Telecommunications Engineering

Research Group at Anglia Ruskin University in Britain. He received his education (PhD and

Master) in 1982 and 1988 respectively from Britain. He worked in various academic places

and research centres cross the continents. During this long period he has gathered wide and

very rich experiences in both teaching, researching fields and in quality assurance in

university education areas. Thus, he awarded the Quality Assurance Certificate of

Philadelphia University, Faculty of Information Technology in 2002, and also the Iraqi

Council of Representatives medal, for organizing the first International Conference for Iraqi

Expatriates Scientists & Qualifiers, Baghdad-Iraq in 2008. His research interests include the

areas of both symmetric and asymmetric cryptography, area of verification and validation, and

performance evaluation.

bidirectional search routing protocol for mobile ad hoc networks

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