T. Sangeetha ET AL.
Copyright © 2013 SciRes. CN
reliance on peri odic a dverti sem ents . Their sim ulati on shows
that on-demand route establishment with AODV is quick
i.e., and accurate. AODV is a reactive routing protocol,
meaning that it provides a route to a destination only on
demand. Because AODV does not require global period-
ic routing advertisements, the demand on the overall
available bandwidth to the mobile nodes is substantially
less than in those protocols that do necessitate such ad-
vertisements.
The main difference between AODV and DSR [5,11]
stems out from the fact that DSR uses source routing in
which data packet carries the complete path to be tra-
versed. In AODV, the source node and the intermediate
packet nodes store the next hop information correspond-
ing to each flow for data packet transmission. In this
protocol, the source node floods the Route Request pack-
et in the network when a route is not available for the
desired destination. When an intermediate node receives
a request for route, it either forwards the request or pre-
pares a reply for that route if it has a valid route to the
destination. The validity of a route at the intermediate
node is determined by comparing the sequence number at
the intermediate node with the destination sequence num-
ber in the Route Request packet. It may thus obtain mul-
tiple routes to different destinations from a single Route
Request. Multiple Route Reply packets in response to a
single Route Request packet lead to heavy control over-
head. AODV avoids the counting-to-infinity problem of
other distance-vector protocols by using sequence num-
bers on route updates. AODV has the ability for both
unicast and multicast routing. But considering this case
the AODV protocol not perform well in shadow fading
environments its proved in our simulations.
3.2. QoS Routing Solutions
In this paper titled “A Survey of QoS routing solutions
for Mobile Ad Hoc Networks”, Apr-June 2007 the au-
thors L. Hanzo II and R. Tafazolli have presented a QoS
routing solutions that is suitable for use with ad-hoc
networks [10,13].
This paper offers an up-to-date survey of most major
contributions to the pool of QoS routing solutions for
MANETs published. It includes a thorough overview of
QoS routing metrics, bandwidth, factors affecting per-
formance and classify the protocols found in the litera-
ture. The aim of MAC protocol was to provide a basic
best-effort level of service to ensure network operation in
the face of an unpredictable and shared wireless commu-
nication medium and to maintain a network topology
view and routes in the face of failing links and mobile
devices. QoS routing protocols play a major part in a
QoS mechanism, since it is their task to find which nodes,
if any, can serve an application’s requirements. Therefore,
the QoS routing protocol also plays a major part in Ses-
sion Admission Control (SAC), since that is dependent
on the discovery of a route that can suppo rt the requ ested
QoS.
The majority of the solutions proposed in this litera-
ture till now have focused on providing QoS based on
two metrics: throughput and delay. Of these, the more
common is throughput. This is most likely because as-
sured throughput is somewhat of a “lowest common de-
nominator” requirement; most voice or video applications
require some level of guaranteed throughput in addition
to their other constraints. The proposed protocol will im-
prove the QoS based on the above two metrics.
4. Protocol Implem ent at ion
In this section, we describe the implementation of pro-
posed protocol, which exploits the knowledge of alterna-
tive or backup routes to a source’s destination in order to
improve the robustness of throughput-QoS assurances in
the face of route failures. The main goal of this paper is
to improve the Packet Delivery Ratio (PDR) in shadow
fading environments. Thus by using the proposed proto-
col Quality of Service (QoS) can be improved as much as
possible. Hence in the following sections we are going to
use the name as QoSAR (Qos Aware Routing) for the
propose d protoc ol .
In shadow fading environments, it is difficult to achieve
high PDR only with the use of primary routes from source
to destination. Idea behind QOSAR is to find multiple
routes between source and destination. Hence it improves
PDR as well as it gives solution to the route failures.
In the newly proposed QoSAR protocol, once the ses-
sion is ready to transmit, a backup route for that session
must be found. We have considered two mechanisms to
find multiple routes as follows:
1) Link Disjoint Paths
2) Node Disjoint Paths
4.1. Link Disjoint Paths
Link disjoint paths are paths between sources to destina-
tion which have no overlapping links. The backup route
is selected in such a way they are “sufficiently disjoint”
i.e., it includes no more than half of the links in the cur-
rent/primary route [12].
In Figure 1 three paths (shown in red color) between
sources to destination are called as link disjoint paths. If
the primary and backup routes are selected in such a way
that, they are sufficiently link disjo int then the route fail-
ure is minimized.
If a new backup route must be discovered, the search
packet, referred to as RReq backup carries a copy of the
session’s primary route. To avoid fully flooding the net-
work with the RReq-backup, once the RReq backup has
traveled at least half of the length of the primary route,