This document summarizes a research paper that proposes a Stable and Reliable Route Identification (SRRI) scheme to improve the Dynamic Source Routing (DSR) protocol for mobile ad hoc networks. The SRRI scheme aims to improve route stability by periodically updating node transmission ranges and improve reliability by considering bandwidth availability. Simulation results show that SRRI achieves higher packet delivery ratios and lower routing overhead compared to the existing Expected Link Expiration Time (ELET) scheme, especially with increased node mobility. SRRI also helps minimize bandwidth consumption by maintaining route bandwidth histories in node caches.

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Stable and Reliable Route Identification Scheme for Efficient DSR
Route Cache in Mobile Ad Hoc Networks
S. Sathish, K. Thangavel, M. Padmapriya,
Assistant Professor, Professor, Research Scholar,
Department of Computer Department of Computer Department of Computer
Science, Science, Science,
Periyar University, Salem, Periyar University, Salem, Periyar University, Salem,
Abstract - Reactive routing protocol, rate in multi-radio range transmission
DSR in MANET, discover routes based of mobile ad hoc network using NS-2
on demand with route cache random mobility model. The
mechanism. DSR adapts source performance of the proposed SRRI
routing and aggressive utilize of route scheme is measured in terms of
caches. DSR lacks in determining reliable and stable routes for the ad
route validity in route caches using hoc network, with node mobility rate,
fixed time interval for cache bandwidth consumption, routing
invalidation. Entry in cache is only for a overhead, packet delivery ratio.
specified time and removed when time
expired. Existing work presented a Keywords: MANET, DSR, Route
dynamic mechanism to enhance cache Cache, SRRI
strategies for reducing number of stale
route entries and their dissemination I .INTRODUCTION
with Expected Link Expiration Time
(ELET) and updated route reply A mobile ad hoc network is a
method is used to prevent mobile, multi-hop wireless network
dissemination of stale routes. In with no stationary infrastructure.
dynamically changing ad hoc mobile Dynamic topologies due to mobility
scenario, route stability and the and limited bandwidth and battery
reliability of the route becomes a major power make the routing problem in ad
concern in DSR. However, existing hoc networks more challenging than
work lacked in addressing the issues traditional wired networks. A key to
of route stability and reliability factors. designing efficient routing protocols for
The proposed work presents a Stable such networks lies in keeping the
and Reliable Route Identification routing overhead minimal. A new class
(SRRI) scheme for DSR protocol. of on-demand routing protocols (e.g.,
Route stability is achieved with node DSR, AODV, TORA) attempt to reduce
transmission range control procedure. routing overhead by only maintaining
Route reliability is maintained in terms routes between nodes taking part in
of bandwidth requirement to discover data communication. In these
the required route. In addition the protocols, the source discovers routes
routing overhead for the bandwidth on-demand by initiating a route
consumption is minimized with pre discovery process.
cache history vector of route
bandwidth maintained in node caches. A. Route Discovery in DSR
Simulation is carried out with varied
number of nodes and different mobility
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cache (Figure 2) rather than
forwarding the route request. If the
When a source node originates a new destination node receives the multiple
packet addressed to a destination RREQ propagated from different
node, it will search its Route Cache for routes, it replies to all RREQ by RREP.
a source route. If no route is found in As a result of single route discovery to
the cache, the sender initializes Route a destination node leads to multiple
Discovery by broadcasting a Route routes for it. The RREP can be
Request (RREQ) packet (Figure. 1), delivered to the initiator by simply
containing destination node address, reversing the node list, by using a
unique request identification, and an route to the initiator in its own cache,
initial empty list which together or “piggybacking” the packet on a new
uniquely identify this Route Discovery. Route Request to the original initiator.
When the initiator receives the RREP,
it adds the source route in its route
cache for use in sending subsequent
packets to the destination and for
future use.
Figure 1: Node N1 Sends RREQ
B. Route Reply in DSR
A node receiving the RREQ [1],
if it is not the intended destination,
appends its address to the node list
and forwards the packet. However, Figure 2: Nodes N5, N3 Sends RREP
first it checks whether it has recently
seen another RREQ from the same C. Caching Mechanism
source node with the same request
identification and target address, or The majority of work related to
whether its own address has already route caches in mobile ad hoc
presented in the traveled node list of networks focused on Dynamic Source
this RREQ. If either check is true, the Routing (DSR). DSR is an on-demand
node silently drops this packet. When protocol that uses source routing and
the RREQ packet reaches the makes aggressive use of route
destination node, this node returns a caches. The current specification of
Route Reply (RREP) to the source DSR lacks a mechanism to determine
node (Fig. 2) with a copy of the node the validity of routes in the route
list from the RREQ. If an intermediate caches. DSR uses fixed time interval
node receiving the RREQ contains the for cache invalidation, i.e., entry in
route to the destination in its Route cache appoints a fixed time and
Cache then this node returns a RREP removed when time expired. This
to the source node from its own route mechanism is not efficient as waiting
too long to invalidate route introduces
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information and does not require any
external support.
stale route cache and its
dissemination. Also not waiting long This paper has been organized
enough removes the routes from as follow, section II describes the
cache which are still valid and causes related work, section III describes the
unnecessary retransmission of route proposed work, section IV illustrates
request and route reply. The weakness the results and discussions and finally
of this scheme is that it cannot adapt section V concludes the paper.
to the change of the network topology.
Because of these, setting the timeout
close to the expected link expiration II. RELATED WORK
time is considered to improve the
performance. Since the actual lifetime In paper[5], the authors
of a link highly depends on node proposes a novel MANETs routing
mobility, to achieve good performance, protocol by using a link lifetime based
dynamic caching schemes are desired. multipath mechanism to improve route
stability, which is called Link lifetime
D. Expected Link Expiration Time based Backup Routing protocol (LBR).
During the local backup paths setup,
Existing Work suggested LBR conduct a local optimization,
scheme to develop and analyze which guarantees the backup path to
enhanced cache strategies for have the maximum lifetime in local
reducing number of stale route entries area. These mechanisms predict the
and their dissemination. The basic timeout of a route cache using pre
idea of the scheme is to use the determined parameters. However,
Expected Link Expiration Time (ELET) predetermined value of timeout may
[6] as its cache timeout and preventing work for certain scenarios but may not
the distribution of stale information by work well for all. In [3], a smart packet
updated route reply. The ELET is a is generated periodically which travels
measure of time duration in which a through the network, collects topology
node will become out of transmission information, and the nodes update
range of another node. ELET is their route caches. Route entries then
determined dynamically by the contain new routes reflecting the most
Enhanced DSR (EDSR) when it recent topology changes. In [6] the
receives RREQ from nearby node authors presented a cross-layer
using the cross layer information. approach for predicting the route
Cross layer design refers to protocol cache lifetime. The author assigns
stack that intercommunicate the useful timeouts of individual links in route
information to collectively achieve the cache by utilizing RSSI values
desired optimization goal by allowing received from physical layer. This
the different protocols to share scheme requires RSSI thresholds for
information related to the network link timeout on every node of the ad
status. Therefore, cross layer based hoc network. In this method the
cache mechanism in which DSR timeout value directly depends on
computes timeout value of individual thresholds value selected. In [4], the
links by utilizing received signal authors developed a caching strategy
strength from physical layer. This that permits nodes to update their
method uses locally available network cache, when the topology of the
network changes. To achieve it, all
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between strong and weak channels.
Each channel is characterized as
reachable nodes that have cached a strong or weak by the average signal
broken link are notified when it fails. strength at which packets are
Based on it, the proposed algorithm exchanged between the hosts at either
notifies all reachable nodes that have end of the channel. In SRRI based
cached the link in a distributed DSR route discovery, a source initiates
manner. In this work, timeout for route a route discovery request when it has
cache entry is not used, thus if nodes data to send to a destination which is
become unreachable in some cases not in the routing table. The route-
then they will not remove the stale search is broadcast to all neighboring
route from their caches. hosts. These hosts propagate the
broadcast if (1) it is received over a
III. PROPOSED WORK strong channel and (2) the request has
not been propagated previously (to
Proposed work present a Stable avoid looping). The route-search
and Reliable Route Identification packet stores the address of each
(SRRI) scheme for DSR protocol in intermediate host in the route taken.
extremely dynamic mobile node The destination chooses the route
communication setting. Route stability recorded in the first arriving request,
is accomplished with node since this route is probably shorter and
transmission range control process, in less congested than routes for slower
which transmission range of every arriving requests. The destination
node in DSR cache is updated returns the route-reply along the
occasionally to discover the node selected route, and each intermediate
accessibility for link broadcast with node includes the new next-hop,
other nodes. Route reliability is destination pairs in its routing table.
sustained in terms of bandwidth
requirement to determine the required
route with enhanced DSR as is B. Reliability Based DSR Routing In
justified in the existing work. MANET
Furthermore the routing overhead for
the bandwidth consumption is reduced In order to reduce the broadcast
with pre cache account vector of route storm and routing overhead, an
bandwidth preserved in node caches. intermediate node can re-broadcast a
second RREQ packet only if it has
A. Stability Based DSR Routing In higher reliability and stability than the
MANET first RREQ packet, otherwise the
RREQ will be discarded. When the first
A new routing paradigm can be RREQ packet enabled reaches the
obtained by considering the route destination node, the node starts the
stability as routing metric. Stability timer interval and during that time it
based routing aims at choosing routes examines the reliability and stability of
which are more stable in time. The every arrived RREQ packet. When the
Signal Stability based Routing timer interval expired, the destination
performs on demand route discovery node selects the RREQ packet that
by selecting longer-lived routes based has the highest QOS function and
on signal strength and location sends the route reply (RREP) packet
stability. The signal strength criteria carrying the route information to the
allow the protocol to differentiate source node. When another RREQ
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bandwidth consumption is minimized
with pre cache history vector of route
packet with the same preference bandwidth maintained in node caches.
arrives after the threshold time interval,
it will not be considered and do not
process it further. D. PROCEDURE FOR SRRI
C. Stable and Reliable Route SRRI Procedure
Identification (SRRI)
Procedure SRRI (For each node
We have developed an ad hoc from source to Destination)
routing protocol by introducing a For Node 1 to Total Number
Stable and Reliable Route of Nodes Do
Identification (SRRI) scheme to the If GT = 1 & GR = 1
widely used DSR routing protocol. This
routing metric is concerned with finding
optimal paths between the source and
the destination nodes that can avoid
the congested regions in the network. Else
It focuses on multiple objectives to be Error
optimized, such as Bandwidth End If
consumption (which refers to the End
number of bits per second (bps) that
can be sent along the path between For Node 1 to Total Number
the source and the destination nodes) of Nodes Do
and signal strength.
In this modification, we include
the local availability of the bandwidth End
at a node in addition to the hop count End
metric to maximize the end-to-end  TR  Transmission Range
throughput in MANETs and at the
 PT  Power of Transmitter
same time to control the end-to-end
 GT  Gain of Transmitter
delay time. SRRI helps the routing
protocol to determine the available  GR  Receiver Gain
bandwidth at the node in order to  HT  Height of Transmitter
improve the network performance by  HR  Height or Receiver
avoiding routing traffic through the  D  Distance between two
congested areas. consecutive nodes at time T
Route stability is achieved with  L  Signal Loss
node transmission range control  P  Power
procedure, in which transmission  R  Success Rate
range of every node in DSR cache is  T  Time
updated periodically to identify the
node availability for link transmission IV. RESULTS AND DISCUSSION
with other nodes. Route reliability is
maintained in terms of bandwidth We chose the popular network
requirement to discover the required simulator NS2 as the simulator
route with enhanced DSR as is primarily to implement methods
explained in the existing work. In because it is widespread use in the
addition the routing overhead for the academic community and the
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comprehensive manuals and tutorials
that are freely available. It is possible
to simulate a mobile multi-hop ad hoc
wireless network in ns-2 using
simulated 802.11 MAC layer.
A. Packet Delivery Ratio
Packet delivery ratio is the ratio of the Figure 4: Mobility Vs Routing Overhead
number of data packets received by a
destination over the number of data The above Figure 4 shows the
packets delivered by the routing overhead of SRRI and ELET
corresponding source. with different number of mobile nodes
and mobility speeds, respectively. As
shown in Figure 4 routing overhead
increases as the number of mobile
nodes or the mobility speed increases.
The routing overhead for ELET is
higher than SRRI.
C. Bandwidth Consumption
The number of packets can be
sent along the path between the
Figure 3: Mobility Vs Packet Delivery source and the destination nodes.
Ratio These metrics was chosen due to
these performance metrics was well
The Figure 3 shows the packet known in showing the routing
delivery ratio of SRRI and ELET with performance of the selected protocol.
different number of mobility speeds.
We can observe that SRRI transmits
and receives more data packet than
ELET. The ELET path may break
easily. SRRI will always choose the
most stable and reliable path, the
chance of link breakage for SRRI is
lower than ELET since ELET didn’t
consider the stability of the selected
path.
B. Routing Overhead
Routing Overhead can be termed as
the total number of overhead packets Figure 5: Mobility Vs Bandwidth-
is transmitted per second. This metric Consumption
indicates the routing cost.
The Figure 5 shows the
bandwidth consumption of SRRI and
ELET with different number of mobility
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