Performance Enhancement of a Hybrid Extension of OSPF for MANETs

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VSRD
-
IJCSIT, Vol. 2 (8
), 201
2
,
1
-
5



____________________________

1
,2
Research Scholar, Department of Computer Science & Engineering, Lakshmi Narayan College of Science & Technology,
Indore, Madhya Pradesh, INDIA.

*Correspondence :
trivedimahima@yahoo.in

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Performance Enhancement of a Hybrid Extension

of OSPF for MANETs

1
Mahima Trivedi
*

and

2
Sravan Kumar

1.

ABSTRACT

Open shortest path first, abbreviated as OSPF is a
link state routing protocol. It is widely used in both wired as
well as wireless Networks.

Though there are different protocols for these Networks but the reason behind
extending the OSPF only is that the present age of networking has use of both wired and

wireless networks
easily and they are interacting mutually. MPRSP i.e. Multipoint Relay with Smart Peering is an amalgam of two
different extensions of OSPF. In this paper we are going to evaluate the performance of MPRSP OSPF over
other three extensions
and will enhance its performance by reducing Size of hello packet and adjacency set. To
achieve this we would be using MPR selection algorithm.

Keywords :

MPRSP, OSPF, Multipoint Relay, Smart Peering
.

2.

INTRODUCTION

MPRSP
[1]

or Multipoint Relay with Smart P
eering extension of OSPF

is a hybrid extension composed of
Multipoint Relay OSPF and Smart Peering OSPF
.
In this
protocol, the
MPR (Multipoint Relay)

[2]

algorithm is
used for
Control Traffic Flooding and the link selection for
generating
SPT,
adjacency
minimization is through
using Smart peering rule
. In
this
,
nodes discover their close topology and inform their presence by mutually
exchanging hello packets
contain
ing

a list of Their 1
-
hop routers. In this way, each router is aware of its 2
-
hop
neighbor
hood and so they elect their MPRs. These MPRs are intended to be reachable to their all bidirectional
2
-
hop neighbors. In the protocol, the LSAs are distributed in two ways:
Selective Retransmission
, in which a
router transmits LSA only if they are, transmi
tted from one of the r
outer’s MPR selectors. Another
LSDB
Synchronization
in which the adjacency election is performed according to Smart peering and intended to
exchange the associative link state database.

Topology information received from router
-
LSAs a
nd hello packets
are used to reconstruct a sub graph containing following elements: Path MPRs of every router, Adjacencies, 1
-
Mahima Trivedi
et al

/ VSRD
International Journal of CS & IT Vol. 2 (8), 2012


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hop and 2
-
hop neighbors of the router.It has better performance over the other extensions but still there are some
drawbacks. Firs
t is larger Hello Packet and Adjacency Set. Size of hello packet plays a vital role in speed and
timing of the communication. In mprsp it uses larger hello packet that can make it slow and less efficient than
others. Therefore, by reducing the size of the
Hello Packet we can improve its performance and economy.
Adjacency set of a router is set of all routers connected to it. These are used for flooding in the network.
Obviously making and maintaining these adjacency sets needs some computation and memory. I
ncreased
computation and decreased memory is not a good sign. In mprsp it makes less use of these adjacency sets for
flooding. Therefore we can improve memory and computation usage by reducing these adjacency sets. These
Improvisations will definitely incr
ease the performance of the protocol.
We are suggesting enhancing the
Performance of the MPRSP protocol by reducing two parameters i.e. Hello Packet and Adjacency Set as
mentioned above. Fundamentally, the OSPF in the wireless network works similar to the O
LSR as both the
protocols are link state routing. OLSR depends upon the multipoint relay (MPR) selection that has an important
effect on the routing protocol's performances. In fact overhead generated by the protocol and more particularly
the flooding effi
ciency depends upon MPR selection
. The analysis of MPR selection gives quantitative results
and also allows QoS support.

Thus we can achieve our goal by using one or more MPR selection algorithms. In
our research we are going to use two algorithms i.e. MPR

Selection and MPR in Degree Selection. These
algorithms work on same principle but are slender different.

3.

BACKGROUND

OSPF is
broadly used routing protocol. It is a proactive link state protocol that makes use of Dijkstra algorithm
for choosing correct pat
h or Shortest Path Tree. The shortest path tree is maintained by each router in the
network. For superior communication these router exchange link state database mutually. It has a 2
-
level
hierarchical structure and divides the Autonomous system into diffe
rent areas commonly connected to a
backbone area. Furthermore, it includes different interface types and corresponding protocol behaviors. OSPF
independently does not fit into wireless technologies because of its non transitive nature. Therefore IETF
exten
ded OSPF for MANETS. This is due to the wide usage of Heterogeneous networks. Despite the fact that
there are different routing protocols for both wired and wireless networks OSPF is only extended because it is
widely used and therefore it would be easy to

train system engineer for a single protocol. Extensions of OSPF
for MANET are OSPF
-
MDR, MPR
-
OSPF, OR/SP and MPRSP

OSPF
-
MDR

[3
]

(MANET Designated Router)

is

dependent
on two Connected Dominating Sets (CDS) term
ed
as

MANET Designated Router

(MDR) and backup

MDR. According

to this, MDRs are

only nodes allowed to
flood link state advertisements i.e. LSAs
.
E
ach non
-
MDR router
forms adjacency

t
o other MDRs. LSAs
maintains a list of configurable

subsets of the links of the
initiator primarily including neighbors.

MPR
-
OSPF

(Multi
-
Point Relay)

is dependent

on the multipoint relays (MPR).
In these MPRs of the nodes are
selected among their bidirectional neighbors
, and
using these LSAs are distributed. A router is

adjacent to
its
MPRs as well as the router for whom it
is an MPR. On the basis of

these set of adjacencies, the SPT is
constructed.

Overlapping Relays / Smart Peering

(OR/SP)

[4
]

Like

MPR
-
OSPF d
istributes LSAs through MPR flooding.

Mahima Trivedi
et al

/ VSRD
International Journal of CS & IT Vol. 2 (8), 2012


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of 9


H
ere, adjacencies are selected
using

Smart Peering (SP) rule. According to this

rule a neighbor becomes
adjacent if it is not already reachable through the computing routers SPT. LSAs maintains list of adjacent
neighbors, and might also list additional bidirectional neighbors. Therefore, the SPT is constructed over
adjacencies and a
subset of bidirectional neighbors.

MPRSP
is composed of
the

two techniques i.e.

Multi Point relay and Smart Peering
discussed

above.
Here, the
MPR algorithm is used for
Control Traffic flooding and the link selection for
generating
SPT,
adjacency
minimizat
ion is done using Smart peering rule
. In MPRSP,
nodes discover their close topology and inform their
presence by mutually exchanging hello packets
contain
ing

a list of their 1
-
hop routers. In this way, each router
is aware of its 2
-
hop neighborhood and so

they elect their MPRs. These MPRs are intended to be reachable to
their all bidirectional 2
-
hop neighbors. In the protocol, the LSAs are distributed in two ways:

Selective Retransmission
, in which a router transmits LSA, only if they are, transmitted from

one of the
router’s MPR selectors. Another LSDB

Synchronization
in which the adjacency election is performed
according to smart peering and intended to exchange the associative link state database.

Topology information
received from router
-
LSAs and hello
packets are used to reconstruct a sub graph containing following elements:
Path MPRs of every router, Adjacencies, 1
-
hop and 2
-
hop neighbors of the router.

MPRSP extension of OSPF

is a hybrid extension combination of Multipoint Relay OSPF and Smart Peering

OSPF. It has superior performance over the other extensions however there are some disadvantages. Foremost is
larger Hello Packet and Adjacency Set. In speed and timing of the communication, Size of hello packet plays a
vital role. In mprsp it the size of

hello packet is large. Therefore it becomes slow and less efficient than others.
Thus, by reducing the Hello Packet size we can get better performance and economy. Set of all routers
connected to a router is Adjacency set of the router. These are utilized

for flooding in the network. Clearly,
making and maintaining these adjacency sets needs some computation and memory. Increased computation and
decreased memory is not a good mark. In mprsp adjacency sets are less used for flooding. Consequently we can
imp
rove memory and computation usage by reducing these adjacency sets. These changes will positively
enhance the performance of the protocol.

4.

TOOLS USED

In the perspective of our paper
, we are going to use the Network Simulator3 to evaluate and justify results.
Below is the brief introduction about the tool.

Ns
-
3
[5]

is a discrete
-
event network simulator for Internet systems,
mainly intended
for research and educational
use.
It is free
software
publicly available for research, development, and use
and
licensed under the GNU
GPLv2 license. The
primary objective

of the ns
-
3 project is to develop a preferred, open simulation envi
ronment
for networking research.

5.

PROPOSED MODEL

For
any organization, it is necessary to have a communication efficient in terms of time. A transaction taking
more time may be corrupted or it may be lost. A time efficient communication can be achieved in two ways.
Mahima Trivedi
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/ VSRD
International Journal of CS & IT Vol. 2 (8), 2012


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One way to reduce the elapsed time is to in
crease bandwidth. By increasing bandwidth, we can send even a
large packet in less time. This seems to be a better idea but actually not. In point of fact, increase of bandwidth
leads to increase the noise in the signal. So having a large bandwidth is a ki
nd of complicated issue.

Another way is to have the bandwidth unchanged but to have a decreased size of the packet. A reduced packet
size takes less time to reach destination than a large packet. Now the question arises that how to reduce a size of
a packe
t? Answer is inside the packet only. That means, a packet is composed of different fields. Among them,
some fields are mandatory and some are optional and some of these optional fields are rarely used or not used at
all. Cutting down these unused and rarel
y used fields can lead to a compact and efficient packet. A reduced and
compact packet as discussed above reaches earlier than an untrimmed packet and as a result will lead an error
free and efficient communication. Therefore it is an easy and efficient me
thod as compared to bandwidth
reduction. In the context of MPRSP protocol, reduction in the size of hello packet is better choice to improve its
performance in terms of time taken. A hello packet in transaction is exchanged by routers to inform their
prese
nce and start s communication session. Trimming down its
size will not affect its significance.

The objectives discussed in the paper i.e. size reduction of Hello Packet and Adjacency Set can be achieved by
MPR Selection algorithms as mentioned formerly. T
hese two algorithms are MPR Selection and MPR in Degree
Selection. The algorithm will execute the similar result and we will demonstrate the effect on the performance
of MPRSP. These algorithms are shown below.

MPR Selection Algorithm
[6]
:



Fig
.

1

:

MPR
Selection Algorithm

First Phase of this algorithm makes a sufficient use of the fact that no matter what strategy is preferred, One hop
Mahima Trivedi
et al

/ VSRD
International Journal of CS & IT Vol. 2 (8), 2012


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of 9


nodes that are only cover for two hop nodes should be included in MPR set
. For instance in the figure given
below nodes
b, g, and I have only one neighbor among the neighbors of the source, therefore these relevant
neighbors i.e. nodes 5
, 5 and 8 must be a part of MPR
set
.


Fig
.
2

:

MPR Selection
[6]


Complexity of the original MPR selection primarily depends upon the out
-
d
egree of the neighbor nodes of the
source. Because of the intrinsic connectivity, the wireless networks may be highly clustered. In this case, it is
observable that on the contrary the maximum value of the in
-
degree of the two hop nodes is expected to be a

smaller constant.

This remark enabled researcher to set up a variant of the original MPR selection. The changes made in the
original algorithm are highlighted by numbering them.

MPR INDegree Selection Algorithm
[6]
:

Mahima Trivedi
et al

/ VSRD
International Journal of CS & IT Vol. 2 (8), 2012


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Fig.
3

:

MPR

InDegree

Selection Algorithm

These algorithms are used in MPR selection and as we have discussed earlier that the selection of multipoint
relays are directly responsible for the performance of the OLSR

[7
]

protocol and it’s QoS so will be for OSPF.
In our research

work we are intended to improve the performance of MPRSP protocol by reducing hello packet.
These two algorithms will help us in reducing the size of the hello packet which our ultimate goal.

6.

CONCLUSION AND FUTURE WORK

In this paper we have explored the
usage of OSPF in wireless networks. As mentioned above there are different
extensions of OSPF to be applied in the wireless network.

MPRSP is the recent one and we have proposed to
enhance its performance in terms of reduced size of hello packet and reduce
d size of adjacency set. In the future
we are looking forward to implement the above using the tools NS3 under the guidance of our respected guide
Prof. Sharvan.

7.

REFERENCES

[1]

Juan Antonio Cordero,Thomas Clausen, Emmanuel Baccelli
, MPR+SP: Towards a Unified MPR
-
based

MANET Extension for OSPF.

[2]

E. Baccelli, P. Jacquet, D. Nguyen, T. Clausen: RFC 5449, OSPF Multipoint

Relay (MPR) Extension for
Ad Hoc Networks. IETF. February 2009.

[3]

R. Ogier, SRI International,
P. Spagnolo Boeing: RFC 5614, Mobile Ad Hoc Network (MANET) Extension
of OSPFUsing Connected Dominating Set (CDS) Flooding, August 2009.

[4]

A. Roy, Ed.Cisco Systems

M. Chandra, Ed.
:
RFC 5820
Extensions to OSPF to Support Mobile Ad Hoc
Mahima Trivedi
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/ VSRD
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Networking
March 2010
.

[5]

h
ttp://www.nsnam.org/overview/what
-
is
-
ns
-
3/
.

[6]

[Bernard Mans, Approximation Algorithms for Multi
-
Point Relay Selection in Mobile Wireless Networks,
September

2003]

[7]

T. Clausen, P. Jacquet: RFC 3626, Optimized Link State Routing Protocol

(OLSR). IETF. October 2
003
.

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