Probabilistic Mechanism to Avoid Broadcast Storm...

Probabilistic Mechanism to Avoid Broadcast Storm

Problem in MANETS

G Parimala1, B Suvarna2, N Rajeswari3 and Venkatesulu Dondeti4

VFSTR University, Guntur, AP, India [email protected], [email protected],

[email protected], [email protected]

Abstract. The overhead of the route discovery can be increased due to frequent

link breakages in the MANTES. This is caused by the high mobility of nodes in

network. Broadcasting is the optimal mechanism for the route discovery in the

MANETS. In this mobile node rebroadcasts the RREQ packet to all the

neighbors blindly. By this the duplicated packets enormously arises in the

network. This causes the broadcast storm problem. Here in our paper by

combining the neighbor coverage based methods with the probabilistic methods

to reduce the routing overhead in the network. By maintain some factors like

rebroadcast delay, additional coverage ratio, and rebroadcast probability the

duplicated packets in the network can be reduced. By combining the area based

methods and the probability based methods the retransmissions can be reduced.

By executing the NCPR routing performance can be increased and reduces the

redundant rebroadcast compared to the AODV and DPR.

Keywords: Broadcast storm problem, Rebroadcast, Neighbor-coverage

methods, Routing overhead.

1 Introduction

In wireless communication systems, maintaining connection between devices is not

necessary because all the objects move freely throughout the network, This advantage

creates some problems in the wireless communication systems. The most attractive

characteristics of the MANETS are:

Mobility: A wireless communication allows users to use the network resources

from anywhere. The devices in the network can move freely from anywhere.

Reach ability: In the mobile communication, the mobile nodes better connected to

people which leads high reach ability.

Simplicity: Wireless communication is much simpler than wired network. Initial

setup of network is very easy compared to wired network.

Maintainability: The maintainability of the mobile communication is bit difficult

compared to the wired communication. The maintenance of the devices in the

network should be under the network.

Roaming services: As it is mobile communication, the services can be provided

from anywhere including trains, busses etc.

Advanced Science and Technology Letters Vol.147 (SMART DSC-2017), pp.479-486

http://dx.doi.org/10.14257/astl.2017.147.67

ISSN: 2287-1233 ASTL Copyright © 2017 SERSC

Wireless network has two types of communicating environments they are 1.

Infrastructure based Ad-Hoc network. 2. Infrastructure-less Ad-Hoc networks. In

Infrastructure based Ad-Hoc network, all the Aps (access points) in the network are

connected to the fixed backbone and all the mobile nodes are free to move. Whereas

in the infrastructure less network, there is no fixed backbone structure, no AP, only

the mobile nodes are present in the network and move freely in the network. A

Mobile nodes in MANET act as both end point and as a routers, as an end point it

receives packet, as a router it forward the packets further. The mobile nodes are

taking care of communication in the network. The communication among nodes is

done by following 3 ways. First: route discovery from source to destination, second:

establishing the optimal route third: forwarding the data packets from source to

destination.

Finding the optimal route between source and destination becomes major challenge

in the MANETs. Various routing protocols are designed for finding the route from

source and destination. Initially the routing protocols are of two types which are

proactive and reactive routing protocols. In proactive routing the routing information

is maintained at all the nodes as a table called as routing table from source to

destination in the network. Whereas in reactive routing the routes in the network is

found on-demand when it is necessary. In reactive routing type of routing mechanism

routes are identified periodically and maintain the routes to every possible destination

in the network.

The main challenging issue in the MANET is found to be the route discovery. The

route discovers phase is to find out all the routes from source to destination. In

conventional on-demand routing protocol, for finding the route, the node should

broadcast the Route Request packet (RREQ) packet to all the neighbors which are in

that node’s transmission range in the network. The received nodes simply (blindly)

rebroadcast that RREQ packet until it discovers the route to the destination. This

broadcasting is known as blind flooding. This process continues until destination is

reached. At the end the total number of rebroadcast is N-2. Where ‘N’ is the total

number of nodes in the network. By this flooding mechanism most of the packets are

going waste and bandwidth of the network is wasted by this forwarding of

unnecessary packets. This can leads to excessive redundant retransmissions in the

network. The collision of packets in the network is high and contention of data

occurs. This serious contention, collision and redundant retransmissions lead to

“Broadcast storm problem”. Many solutions are proposed to overcome this broadcast

storm problem.

1.1 Broadcast Schemes

Broadcasting is the most powerful mechanism that can be used to forward the packets

in any mobile communication. As the mobility is very high in the MANETS, mobile

nodes can move from one place to another in the network with respect to time. In this

case broadcasting mechanism is used to forward packets. In this method node

broadcasts the packets to all the nodes which are under the radio range of its node.

That received nodes further rebroadcasts the packets to other neighbors. This process

continues until the destination is reached. The uncovered neighbors are covered when

Advanced Science and Technology Letters Vol.147 (SMART DSC-2017)

480 Copyright © 2017 SERSC

the rebroadcasting is takes place. For this broadcasting different techniques are used.

Different broadcasting schemes are listed below:

a. Unicasting: Forwarding message from one device to other device.

b. Broadcasting: Forwarding message from one device to all the devices in the

network.

c. Multicasting: forwarding message from one device to specified devices.

Basically the broadcasting schemes are classified into five types. They are:

1. Probabilistic based schemes: In this type of schemes, the RREQ packet is

forwarded with some probability. Based on the probability, the transferring

of packets are done.

2. Counter based schemes: In this counter based schemes, the RREQ packet is

transferred based on time. That means, the sender rebroadcasts the packet

when the time expires. In this type of counter based schemes the time factor

is used.

3. Distance based schemes: In this distance based schemes, the distance

between sender and receiver can be measured. Based on the distance the

packet forwarding is takes place. If the distance between sender and receiver.

When the distance between sender and the receiver is high then the

rebroadcasting probability is high.

4. Location based schemes: In this type of location based schemes, the location

of the node can be calculated by Global positioning system (GPS). Based on

that information, the forwarding of the RREQ packets is done.

5. Cluster based schemes: In this scheme, some of mobile nodes form a cluster

and communicate with the other clusters in the network. By introducing this

type of methods bandwidth consumption is less. And the active members in

cluster based schemes are the cluster heads and gateways.

The broadcasting protocols used traditionally are:

1. Flooding

Different approaches are proposed for the broadcasting in the mobile

communications. But there are some problems in those methods. Flooding is the

optimal mechanism for the broadcasting. In this flooding, one node floods the RREQ

packets to all the nodes in the network. That means the main aim of this flooding

mechanism is to cover all the nodes. The process in flooding is one node sends the

RREQ packet to the nodes which are in the radio range. Then it is the responsibility of

the receiving node to forward the RREQ packets further in the network. By this

packet collisions are more. And the bandwidth of the network is wasted. By this

flooding mechanism is not optimal one for the broadcasting in the MANETS. Some

improvements are made for this flooding mechanism.

2. Probabilistic broadcasting scheme based on coverage area & neighbor

confirmation:

This broadcasting is developed by using some other techniques; by appending

probability to the broadcasting some of the problems with the broadcasting can be

reduced. In this approach we use a dynamic probabilistic approach based on the

coverage area and neighbor confirmation. In this mechanism, coverage area concept is

used. If the mobile node is placed near to the sender, then the rebroadcast probability

is low. Whereas the mobile node is placed far from sender then the rebroadcast


Copyright © 2017 SERSC 481

probability is high. In this case the additional coverage area is high. The coverage

area of one broadcast is calculated by measuring the distance between the sender and

receiver. The node position can be measured by global position system (GPS).

Broadcasting is done based on some probability of the RREQ packet. The main aim

of this scheme is to reduce the number of rebroadcasts; by this the bandwidth of the

network is not wasted. By this dynamic based probabilistic broadcasting scheme the

rebroadcast probability is less and the network resources are not wasted compared to

the previous method.

3. Scalable broadcast algorithm:

In this algorithm the main aim is to reduce the cost of the rebroadcast. Mobile node

need not to rebroadcast when all the neighbors is covered by this broadcast. In this

algorithm is divided in two phases. First it needs to find out the neighbors list of the

node. By periodically sending hello packets, each and every node maintains the

neighbor list. Each and every node maintains the topology information of 2 hop

neighbors. When broadcasting is takes place, then the receiver checks which

neighbors are covered by this broadcast by checking into the neighbor information.

Then those covered nodes are added into the broadcast coverage nodes list. Then any

rebroadcast decision is made, it checks into that list. If all its neighbors are covered,

the rebroadcast id canceled. By this Scalable broadcast algorithm, the redundancy of

rebroadcast is decreases. It saves the duplicate packets by compared to the flooding.

4. Probabilistic schemes by calculating delay

This NCPR is the protocol for the routing in the network which has minimum

routing overhead. This NCPR requires one-Hop neighbors of the node. Some

parameters used in this NCPR, which are rebroadcast delay, uncovered neighbor sets,

rebroadcast probability. The above methods have less overhead compared to the

flooding. But in the case of number of nodes are high then the overhead is also high.

When the routing is started, first the source node sends the RREQ packet to the

nodes which are in the transmission range of that source node. Then the nodes which

received that RREQ packets need to resend the RREQ packets further to the nodes

until it reaches the destination node. In this process the packet overhead is increased.

1. NCPR

In this NCPR first the mobile need to identify the 1-Hop neighbors. There after it

calculates the uncover neighbors list.

a. Uncovered neighbor list:

First the mobile node sends the RREQ packet to the all 1-Hop neighbors. After that

it calculates the uncovered neighbors list of that broadcast.

𝑈𝐶(𝑎) = 𝑁(𝑎) − [𝑁(𝑎) ∩ N(b)] − {b} Where UC(a) is the Uncovered neighbors of the node a. N(a) is the neighbors set of

the node a. N(b) is the neighbor set of the node b. here node b is the source node and

the node a is the neighbor of the node b.

b. Rebroadcast delay:

By calculating this rebroadcast delay, the routing overhead can be reduced. If the

node ‘a’ has more common neighbors uncovered by the RREQ packet from the node

b. then the delay of that node is low. If the packet is rebroadcasted through the lower

delayed node, then the more common neighbors can know the RREQ packet in the

network. The rebroadcast delay of the node can be defined as follows:



𝐷𝑟 = 1 −|𝑁(𝑏) ∩ 𝑁(𝑎)|

𝑁(𝑏)

𝐷 = 𝑀𝑎𝑥. 𝑑𝑒𝑙𝑎𝑦 ∗ 𝐷𝑟

Where 𝐷𝑟 is the delay ratio of the neighbor node. N(b) is the neighbor list of the

source node. N(a) is the neighbor list of node a. and D is the rebroadcast delay of the

node neighbor node. Max.Delay is the smallest constant delay.

c. Additional coverage ratio:

For the rebroadcast delay timer should be set. If the timer expires then the final

uncovered neighbor set of the RREQ packet finalized by the node. After getting the

final uncovered neighbors set, then the rebroadcast probability of the node should be

calculated. For this the additional coverage ratio of the node should be defined.

Additional coverage ratio is the ratio of the number of nodes that are additionally

covered by this broadcast to the total number of nodes in the network.

𝑅(𝑎) =𝑈𝑁(𝑎)

𝑁(𝑎)

Where R(a) is the additional covered ratio. UN(a) is the uncovered neighbors of

node a. N(a) is the neighbors set of node a.

d. Connectivity factor

The connectivity of the network should reach 1 at any time. To keep this the

measure which is connectivity factor should be maintained. In the [16] reference the

connectivity metric is derived as 5.1774 log n. Where n is the number of nodes in the

network.

𝑐𝑓(𝑎) =𝑁𝑐

|𝑁(𝑎)|

Where cf(a) is the connectivity factor of the neighbor node. 𝑁𝑐 is the 5.1774 log n.

here in this connectivity factor the denominator is greater than the numerator then the

cf(a) is less than 1. That means node a is in the dense area of the network. The part of

neighbors of node a sends the RREQ packets further. Then only the network

connectivity keeps constant. Otherwise cf(a is ) greater than 1. That means the node is

the sparse are of the network. Then the node a should send the RREQ packets to keep

the connectivity factor.

e. Rebroadcast probability

By combining the additional coverage ratio and connectivity factor the rebroadcast

probability of node can be obtained. By this rebroadcast probability the decision is

made whether the RREQ packet is further rebroadcast or not.

𝑅𝐵𝑃 = 𝑅(𝑎) ∗ 𝑐𝑓(𝑎)

2 Implementation of NCPR

To implement the proposed protocol the AODV code is modified to reduce the

routing overhead in the network. To evaluate the performance of the proposed

protocol, it should be compared with some other protocols in NS2. DPR is the optimal

mechanism for the RREQ packet broadcasting in MANETS. This can be compared

with the NCPR. The simulation is started in the 1500×1500 area. The number of



nodes in the network can be any number. The Max. Delay in the above formula

should be set to 0.01 s. The performance of the routing protocol can be measured

based on following metrics.

MAC collision rate: The number of packets dropped at MAC layer.

Routing overhead: The routing overhead when the packet is transferring

form source to destination.

Packet delivery ratio: The ratio of number of data packets successfully

received by the destination to the number of packets generated by the source.

End-to-End delay: Average delay of successfully delivered packets from

source to the destination.

Fig. 1. Routing overhead with varied number of nodes

The NCPR protocol reduces the routing overhead in case of large number of nodes

during route discovery phase.

Fig. 2. Packet delivery ratio with varied number of nodes

NCPR protocol can increase the packet delivery ratio with varied number of nodes

because it reduces the collisions in the network.

0

0.5

1

1.5

2

2.5

0 50 100 150 200 250 300 350

No

rmal

ize

d

Ro

uti

ng

ove

rhe

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Number of nodes

NCPRDPR

65

70

75

80

85

90

95

100

0 100 200 300 400

Pac

ket

de

live

ry r

atio

%

Number of nodes

NCPRDPRAODV



Fig. 3. End-to-End delay with varied number of nodes

The NCPR protocol decreases the end-to-end delay with varied number of node

compared to the AODV and DPR.

Fig. 4. Routing overhead with varied number of CBR connections

NCPR reduces the routing overhead with number of CBR connections increased

compared to the AODV and DPR.

4 Conclusion

In this paper the proposed NCPR protocol works optimal when compared to the

AODV and other broadcasting schemes. NCPR reduces the routing overhead with

varied number of nodes. The broadcast storm problem can be reduced by calculating

rebroadcast delay. By that the broadcasting order can be calculated. By combining

additional coverage ratio and connectivity factor the rebroadcast probability cane be

calculated. According to that rebroadcast probability, sending of the packet further

can be decided. The NCPR protocol reduces the retransmissions compared to the

AODV. The simulation results show that the proposed protocol reduces the routing

overhead when the network density is high.

0

0.2

0.4

0.6

0.8

0 50 100 150 200 250 300 350

Ave

rage

en

d t

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d

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Number of nodes

NCPRDPRAODV

0

0.5

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1.5

10 12 14 16 18 20No

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d r

ou

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g o

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Number of CBR connections

NCPR

DPR



4 Future Enhancement

NCPR reduces the routing overhead in the network. And the broadcast storm

problem can be resolved by this NCPR. In future this NCPR is designed to reduce the

energy consumption.

References

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