A study and comparison of olsr, aodv and zrp routing

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 02 Issue: 08 | Aug-2013, Available @ http://www.ijret.org 370
A STUDY AND COMPARISON OF OLSR, AODV AND ZRP ROUTING
PROTOCOLS IN AD HOC NETWORKS
Hrituparna Paul
1
, Priyanka Sarkar
2
1, 2
Assistant Professor, National Institute of Technology, Agartala
hrituparnanita@gmail.com, priyanka.csenita@gmail.com
Abstract
A mobile ad hoc networks (MANET) is characterized by multihop wireless connectivity consisting of independent nodes which move
dynamically by changing its network connectivity without the uses of any pre-existent infrastructure. MANET offers[1, 2] such
flexibility which helps the network to form anywhere, at any time, as long as two or more nodes are connected and communicate with
each other either directly when they are in radio range or via intermediate mobile nodes. Routing is a significant issue and
challenge in ad hoc networks and many routing protocols have been proposed like OLSR, AODV, DSDV,DSR, ZRP, and TORA, LAR
so far to improve the routing performance and reliability. This research paper describes the characteristics of ad hoc routing
protocols OLSR, AODV and ZRP based on the performance metrics like packet delivery ratio, end–to–end delay, throughput and
jitter by increasing number of nodes in the network. This comparative study proves that OLSR, ZRP performs well in dense networks
in terms of low mobility and low traffic but in high mobility and high traffic environment ZRP performs well than OLSR and AODV.
Keywords: MANET, AODV, OLSR, ZRP, routing
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1. INTRODUCTION:
The rapid increases in the applications of Personal Digital
Assistants (PDAs) devices such as tabs, compact laptops etc
has made popularity of wireless networks. One of the major
types of wireless networks is Mobile Ad-Hoc networks
(MANET). Every node in this network acts as a router or
relay station to forward data to the designated node. In this
network nodes are mobile and constantly change its location
from one MANET to another. The application of this
network is such as emergency situation, disaster recovery,
crowd control, battle fields etc.
Many routing protocols have been proposed for the mobile ad
hoc network and classified as Proactive or Table Driven
routing Protocol, Reactive or On Demand Routing Protocol,
Hybrid Routing protocol.
A. Proactive or Table-Driven Routing Protocols
Proactive routing is also often termed as table- driven
routing. In this type of routing protocols, fresh lists of
destinations and their routes are maintained by periodic
distribution of routing tables throughout the network and this
category of protocol always strives to maintain consistent and
updated routing information at each node [3]. The proactive
routing protocols use link-state routing algorithms which
frequently flood the link information about its neighbors and
the main drawback of proactive routing protocol is that all the
nodes in the network always maintain an updated table.
Destination-Sequenced
Distance-Vector Routing Protocol (DSDV) [4] and Optimized
Link-State Routing (OLSR) [5] are the two common
proactive routing protocols.
B. Reactive or On Demand Routing Protocol
This type of routing is often known as on- demand routing or
source-initiated routing protocol. The main advantage of
reactive protocols is that it imposes less overhead due to route
messages on the network but at the same time, it is also facing
high latency time in route finding process and sometimes
excessive flooding of the communication packets may lead to
network blockage. Unlike table driven protocols, all nodes
need not maintain up-to- date routing information here. Ad-
hoc On- Demand Distance Vector Routing (AODV) [4],
Dynamic Source Routing (DSR) [6] and Temporally Ordered
Routing Algorithm (TORA) [7], are some of the examples of
reactive routing protocol.
C. Hybrid Routing Protocol
Hybrid routing protocol combines the advantages of both
proactive and reactive routing protocols. The routing is
initially established with some proactively prospected routes
and then serves the demand from additionally activated nodes
through reactive flooding. Some of the existing hybrid
protocols are ZRP [8] and TORA [9].

__________________________________________________________________________________________
Figure 1 Classification of MANET routing protocols
The figure 1 shows the prominent way of classifying
MANETs routing protocols. The protocols may be categorized
into two types, Proactive and Reactive. Other category of
MANET routing protocols which is a combination of both
proactive and reactive is referred as Hybrid.
This paper is categorized as follows. Section I present the
Introduction and overview of Proactive, Reactive and Hybrid
routing protocols. Section II provides an overview of Routing
protocols. Section III provides description about Metrics for
performance comparison Section IV presents Comparative
Study of Ad Hoc Routing Protocols. Section IV concludes the
paper
2. OVERVIEW OF ROUTING PROTOCOLS:
A. Optimized Link State Routing Protocol
Optimized link state routing [10] is a proactive protocol in
which, each node intermittently broadcasts its routing table,
allowing each node to build an inclusive view of the network
topology. The episodic nature of this protocol creates a large
amount of overhead and in order to reduce overhead, it
limits the number of mobile nodes that can forward
network wide traffic and for this purpose it use multi point
relays (MPRs), which are responsible for forwarding routing
messages and optimization for flooding operation. Mobile
nodes, which are selected as MPRs can forward control traffic
and reduces the size of control messages. MPRs are
chosen by a node, such that, it may reach each two hop
neighbor via at least one MPR, then it can forward packets, if
control traffic received from a previous hop has selected the
current node as a MPR. Mobility causes, route change and
topology changes very frequently and topology control (TC)
messages are broadcasted throughout the network. All mobile
nodes maintain the routing table that contains routes to all
reachable destination nodes. This protocol does not notify the
source immediately after detecting a broken link. Source node
comes to know that route is broken, when the intermediate
node broadcasts its next packets. Thus, by determining the
path through the multipoint relays, it is possible to keep away
the difficulties experienced during the packet transmission
over a uni-directional link.
Fig2:-Multipoint Relays of the OLSR network
Advantages and Limitations:
OLSR is a flat routing protocol and it does not need central
administrative system to handle its routing process. The link is
reliable for the control messages, since the messages are sent
periodically and the delivery does not have to be sequential.
This protocol is best suitable for high density network and
does not allows long delays in the transmission of the packets.
However, as a limitation this protocol needs that each node
periodically sends the updated topology information
throughout the entire network, this increase the protocols
bandwidth usage. But the flooding is minimized by the
MPR’s, which are only allowed to forward the topological
messages.
B. Ad hoc On-Demand Distance Vector
Routing (AODV)
AODV is a up to date routing protocol that adopts a purely
reactive approach and capable of both unicast and multicast
routing: it sets up a route on-demand at the start of a
communication session, and uses it till it breaks, after which a
new route setup is initiate .AODV adopts a very different
mechanism to maintain routing information. It uses traditional
routing tables, one entry per destination [11–15]. Without
source routing, AODV relies on routing table entries to
propagate a route replay (RREP) back to the source and,
subsequently, to route data packets to the destination. AODV
uses sequence numbers maintained at each destination to
determine the freshness of routing information and to prevent
routing loops. All routing packets carry these sequence
numbers. An important feature of AODV is the maintenance
of timer-based states in each node, regarding utilization of
individual routing table entries. A routing table entry is
expired if not used recently. A set of predecessor nodes
is maintained for each routing table entry, indicating the
set of neighboring nodes which use that entry to route data

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packets. These nodes are notified with route error (RERR)
packets when the next hop link breaks. Each predecessor
node, in turn, forwards the RERR to its own set of
predecessors, thus effectively erasing all routes using the
broken link. Route error propagation in AODV can be
visualized conceptually as a tree whose root is the node at the
point of failure and all sources using the failed link [16].
The algorithm’s primary objectives are as follows:
• To broadcast discovery packets only when necessary.
• To distinguish between local connectivity
management Neighborhood detection and general
topology maintenance.
• To disseminate information about changes in local
connectivity to those neighboring mobile nodes that
are likely to need the information.
Advantages and Limitations
The main advantage of AODV protocol is that routes are
established on demand and destination sequence numbers are
used to find the latest route to the destination and it also
supports both unicast and multicast packet transmissions even
for nodes in constant movement. It responds quickly to the
topological changes in the network and updating only the
nodes that may be affected by the change, using the RRER
message. The Hello messages, which are responsible for the
route maintenance, are also limited so that they do not create
unnecessary overhead in the network.
The limitations of AODV protocol is all nodes in the
broadcast medium can detect each other’s broadcasts. It is also
possible that a valid route is expired and the determination of a
reasonable expiry time is difficult. The reason behind this is
that the nodes are in mobility and their sending rates may
differ widely. In addition, as the size of network grows,
various performance metrics begin decreasing. A route
discovered with AODV may no longer be the optimal route
further along in time. This situation can arise because of
network congestion or the fluctuating characteristics of
wireless links.
C. ZRP
ZRP [14] divides the topology into zones and uses different
routing protocols within and between the zones based on their
weaknesses and strengths. Each node in ZRP has a predefined
zone centered at itself.. ZRP maintains a zone around each
node that consists of all nodes within ‘k’ hops away from that
node. Proactive routing is used within the zone whereas
reactive routing is used amongst zones. For data delivery, it is
checked whether the destination node exists within the zone or
not. If yes, data is sent immediately otherwise RREQ packet is
sent to border nodes. Border nodes check within their own
zones for destinations. If found, border node sends RREP on
reverse path otherwise it adds its own address to the packet
and forwards to its own border nodes. Process continues until
packet reaches to the destination itself or to a node having
destination within its zone. Path in the RREP packet is used
for sending data to destinations.
Advantages and Limitations
ZRP tries to combine the advantages of reactive and proactive
routing protocols. With properly configured zone radius, ZRP
may outperform both proactive routing protocols and reactive
routing protocols.
The potential disadvantage is that since hierarchical routing is
used, the path to a destination may be suboptimal.
Furthermore, since each node has higher level topological
information, memory requirement is greater
3. METRICS FOR PERFORMANCE
COMPARISON
MANET has number of qualitative and quantitative metrics
that can be used to compare ad hoc routing protocols. The
table I illustrates the comparison of OLSR, AODV and ZRP
routing protocols. This paper has been considered the
following metrics to evaluate the performance of ad hoc
network routing protocols.
1) End-to-end Delay:
This metric represents average end-to-end delay and indicates
how long it took for a packet to travel from the source to the
application layer of the destination. It includes all possible
delay caused by buffering during route discovery latency,
transmission delays at the MAC, queuing at interface queue,
and propagation and transfer time. It is measured in seconds.
2) Packet Delivery Ratio:
Packet delivery ratio is calculated by dividing the number of
packets received by the destination through the number of
packets originated by the application layer of the source (i.e.
CBR source). It specifies the packet loss rate, which limits the
maximum throughput of the network.
3) Throughput:
It is the measure of the number of packets successfully
transmitted to their final destination per unit time. It is the
ratio between the number of received packets vs sent packets.
4) Packet Jitter:
It is the ratio of transmission delay of the current packet
and the transmission delay of the previous packet. Jitter can
be calculated only if at least two packets have been received

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Low Mobility and Low Traffic
Protocol End
to End
delay
Packet
delivery
ratio
Throughput Jitter
OLSR Low High Good Low
AODV Average High Average High
ZRP Low High Average Low
4. COMPARATIVE STUDY OF AD HOC
ROUTING PROTOCOLS
TABLE 1 COMPARISON OF AD HOC ROUTING
PROTOCOLS
Performance
Constraints
OLSR AODV ZRP
Category Table driven or
Proactive
On Demand
or Reactive
hybrid
Protocol
Type
Link state
scheme
Distance
Vector
Link Reversal
Route
Maintained
Route Table Route Table Route Table
Loop Yes Yes Yes
Route
Philosophy
Flat Flat Flat
Multiple No No Yes
Multicast Yes Yes NO
Message
Overhead
Minimum Moderate Moderate
Periodic
broadcast
Possible Possible Possible
Requires
sequence
No Yes Yes
Route
reconfigurati
on
methodology
Control messages
sent in advance
to
increase the
reactiveness
Erase Route
notify
Source
Link Reversal
and information
stored in link
table
TABLE.2 ROUTING PERFORMANCE IN LOW
MOBILITY
TABLE.3ROUTING PERFORMANCE IN HIGH
MOBILITY
High Mobility and High Traffic
Protocol End
to End
delay
Packet
delivery
ratio
Throughput Jitter
OLSR Low Average Good Low
AODV Average Average Average High
ZRP High Low Average Average
CONCLUSIONS
This paper presents the comparative study and
Performance analysis of various ad hoc routing protocols
(OLSR, AODV and ZRP) on the basis of end-to-end
delay, packet delivery ratio, throughput, jitter performance
metrics. The study of these routing protocols shows that
OLSR is more efficient in high density networks with highly
sporadic traffic. OLSR requires that it continuously have
some bandwidth in order to receive the topology updates
messages. As well, AODV keeps on improving in packet
delivery ratio with dense networks. The performance of all
protocols was almost stable in sparse medium with low traffic.
It has been concluded that performance of ZRP is better for
high mobility and high traffic networks where as the OLSR
and ZRP performs well in low mobility and low traffic
networks. The future work suggested that the effort will be
made to enhance ad hoc network routing protocol by tackle
core issues.
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2000-2001.
[3] Shah, R.C., Rabaey, J.:Energy Aware Routing for Low
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November 1997.
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