Enhanced Dynamic Source Routing Protocol using On Demand Passive Clustering

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(IJCSIS) International Journal of Computer Science and Information Security,
Vol. 8, No. 5, August 2010

Enhanced Dynamic Source Routing Protocol using
On Demand Passive Clustering
Shobha.K.R and Dr.K.Rajanikanth
M.S.Ramaiah Institute of Technology
Bangalore, India.
shobha_shankar@yahoo.com
principal@msrit.edu

Abstract— In this paper an enhancement technique for Dynamic a peer-to-peer fashion. Two nodes communicate directly if they
Source Routing (DSR) protocol using on demand passive are within transmission range of each other. Otherwise, nodes
clustering is proposed. DSR is a popular reactive protocol in must communicate via a multihop route. To find such a multi-
Mobile Adhoc Networks (MANETs) which uses flooding for hop route, MANETs commonly employ on demand routing
route discovery and route maintenance. Flooding can be easily algorithms that use ﬂooding or broadcast messages. Many ad
restricted using clustering. Clustering restricts the set of hoc routing protocols [12] [13] [26] [27], multicast schemes
forwarding nodes during flooding which in turn reduces the [25], or service discovery programs depend on massive
energy, cost and traffic overhead during routing in dynamic ﬂooding. In ﬂooding, a node transmits a message to all of its
traffic and dynamic topology environment of MANET. Active
neighbors. The neighbors in turn relay to their neighbors and
clustering mechanisms require periodic refresh of neighborhood
information and tend to introduce a large amount of
so on until the message has been propagated to the entire
communication maintenance overhead. This can be overcome network. In this paper, we will refer to such ﬂooding as blind
using passive clustering which executes only when the user has flooding. As one can easily see, the performance of blind
data to transmit. Passive clustering dynamically partitions the ﬂooding is closely related to the average number of neighbors
network into clusters interconnected by gateways. Existing (neighbor degree) in the CSMA/CA network. As the neighbor
Passive Clustering techniques exploit the data packets for cluster degree gets higher, blind ﬂooding suffers from the increase of
formation and thus reduce the periodic exchange of explicit (1) redundant and superﬂuous packets, (2) probability of
control packets. We have proposed an enhanced passive collision, and (3) congestion of wireless medium [1].
clustering technique which makes use of the control packets used Performance of blind ﬂooding is severely impaired especially
for route discovery in DSR to establish a cluster. We have used in large and dense networks [2]. When topology or
the Lowest ID technique and first declaration wins technique to neighborhood information is available, only subsets of
form clusters. We have analyzed the performance of this neighbors are required to participate in ﬂooding to guarantee
technique to reduce flooding by using single cluster head called the complete ﬂooding. We call such ﬂooding as efficient
primary cluster head. Then an analysis has been carried out with ﬂooding. The characteristics of MANETs (e.g., node mobility,
two cluster heads called primary and secondary cluster heads. the limited bandwidth and resource), however, make the
Simulation results on DSR have shown that this enhanced passive periodic collection of topology information difficult and costly
clustering technique can reduce redundant ﬂooding, with (in terms of overhead). For this reason many on-demand adhoc
negligible overhead; - thus making DSR more efficient. routing schemes and service discovery protocols simply use
blind ﬂooding [12] [25]. In contrast with on-demand routing
methods, the proactive adhoc routing schemes by virtue of
Keywords- MANETs; DSR; Flooding; Clustering; Passive periodic route table exchange, can gather topological
clustering; Primary cluster head; Secondary cluster head; information without much extra overhead. Thus, the leading
MANET proactive adhoc routing schemes use route
I. INTRODUCTION aggregation methods to forward routing packets through only a
Mobile Adhoc Networks (MANETs) have recently been the subset of the neighbors [26] [27].
subject of active research because of their unique advantages.
In this paper, we focus on on-demand routing protocols and
MANETs are self-creating, self-organizing and self-
propose a mechanism for efficient ﬂooding based on passive
administrating networks and do not require deployment of any
clustering. Existing passive clustering scheme [10] requires
kind of infrastructure. They offer special beneﬁts and
neither the deployment of GPS like systems nor explicit
versatility for wide range of applications in military (e.g.,
periodic control messages to identify the subset of forwarding
battleﬁelds, sensor networks etc.), commercial (e.g., distributed
neighbors. This scheme makes the following contributions
mobile computing, disaster discovery systems, etc.), and
compared with previous efficient ﬂooding schemes (such as
educational environments (e.g., conferences, conventions, etc.),
multipoint relay, neighbor coverage, etc): (1) it does not need
where fixed infrastructure cannot be easily acquired. With the
any periodic messages. Instead, it exploits existing data
absence of pre-established infrastructure (e.g., no router, no
packets by attaching few more extra fields; (2) it is very
access point, etc.), two nodes communicate with one another in
resource-efficient regardless of the degree of neighbor nodes or

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Vol. 8, No. 5, August 2010

the size of network. To our knowledge, passive clustering is node) only when it has neighbors that are not covered by its
the only scheme that provides scalability and practicality for forwarding nodes. While the self-pruning heuristic utilizes
choosing the minimal number of forwarding nodes in the information of directly connected neighbors only, the
presence of dynamic topology changes; (3) it does not dominant-pruning heuristic extends the propagation of
introduce any startup latency; (4) it saves energy if there is no neighbor information two-hop away. The dominant pruning
traffic; (5) it easily adapts to topology and available resource scheme is actually similar to Multipoint Relay scheme (MPR)
changes. [7]. In Multipoint Relay scheme, a node periodically
exchanges the list of adjacent nodes with its neighbors so that
In this paper we propose an enhanced passive clustering each node can collect the information of two-hop away
scheme which uses route request packets (RREQ) instead of neighbors. Each node, based on the gathered information,
data packets for maintaining cluster. This technique reduces the selects the minimal subset of forwarding neighbors, which
flooding efficiently and also reduces the overhead in each and cover all nodes within two-hops. Each sender piggybacks its
every data packet transmitted. We have simulated and tested chosen forwarding nodes (i.e. multipoint relay nodes) on the
this algorithm using DSR routing protocol. outgoing broadcast packet.
The remainder of the article is organised as follows: In
section 2 we discuss the various methods available for
achieving efficient flooding. Section 3 gives an explanation
about the algorithms we are proposing for achieving efficient
flooding .Section 4 discusses the simulation parameters and
results .The main conclusions for this paper are summarized in
section 5.
II. RELATED WORK
Several papers [1] [6] [7] [8] have addressed the limitations
of blind ﬂooding and have proposed solutions to provide
efficient ﬂooding. However, because of the problem of ﬁnding
a subset of dominant forwarding nodes in MANETs, all the
work about efficient ﬂooding has been directed to the
development of efficient heuristics that select a sub-optimal Figure 1. The collision rate of broadcast
dominant set with low forwarding overhead.
Along the same lines, several other schemes have proposed
In [1] [6], the authors propose several heuristics to reduce the selection of a dominant set based on topology [18] [21] [22]
rebroadcasts. More speciﬁcally, upon receiving a ﬂood packet, [23]. All of these schemes, however, again depend on periodic
a node decides whether to relay it or not based on one of the hello messages to collect topological information.
following heuristics: (1) rebroadcast with given probability;
(2) rebroadcast if the number of received duplicate packets is The extra hello messages, however, consume resources and
less than a threshold; (3) distance-based scheme where the drop the network throughput in MANETs [14]. The extra
relative distance between hosts determines the rebroadcast traffic brings about congestion and collision as geographic
decision; (4) location-based scheme where the decision is based density increases [1]. Fig 1[26] depicts the collision probability
on pre-acquired neighbor location information; (5) cluster- of hello messages in a single hop and a two hop network as the
based scheme where only precomputed cluster heads and number of neighbor’s increases. This result clearly shows that
gateways rebroadcast. Our approach, passive clustering, differs the neighbor degree causes the broadcast collision probability
from the above schemes in that it provides a more systematic to increase (note, the collision probability is more than 0.1 with
method based on locally collected information (e.g., neighbor more than 15 neighbors). Moreover, the hidden terminal and
information, cluster states, etc.). Each node participates in exposed terminal problems aggravate collisions in the two hop
ﬂooding based on its role or state in the dynamically network. Note that Fig 1 assumes no data traffic - only hello
constructed cluster architecture instead of depending on local messages.
heuristics or on pre-computed clusters. With user-data packets, the collision probability of hello
Another approach to efficient ﬂooding is to exploit messages will dramatically increase. Thus, it will be hard to
topological information [6] [7] [8] [24] [19]. In the absence of collect complete neighbor topology information using hello
preexisting infrastructure, all the above schemes use a periodic messages. As a consequence, the aforementioned schemes
hello message exchange method to collect topological (e.g., neighbor coverage, MPR, etc.) are not scalable to offered
information. Our approach does not require periodic control load and number of neighbors.
messages. Rather, it exploits on-going Route REQuest Lastly, we consider clustering. Clustering can be described
(RREQ) packets to exchange cluster-related information. The as grouping of nodes. A representative of each group (cluster)
authors of [8] suggest two schemes called self-pruning and is dynamically elected to the role of cluster head based on some
dominant pruning. Self pruning is similar to the neighbor- criterion (e.g., lowest ID). Nodes within one hop of a cluster
coverage scheme in [6]. With self-pruning scheme, each head become associated to its cluster. A node belonging to two
forwarding node piggybacks the list of its neighbors on or more clusters at the same time is called a gateway. Other
outgoing packet. A node rebroadcasts (becomes a forwarding

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(IJCSIS) International Journal of Computer Science and Information Security,
Vol. 8, No. 5, August 2010

members are called ordinary nodes. Various distributed investigation of a new cluster formation protocol called
enhanced passive clustering. While retaining the advantages of
passive clustering, our scheme eliminates much of the control
overhead.
III. ENHANCED PASSIVE CLUSTERING
A. Overveiw of Enhanced passive clustering
The proposed protocol called enhanced passive clustering is
very much similar to passive clustering algorithm except that it
uses RREQ packets for formation of clusters and their
maintenance. RREQ packets are generated only when the
Figure 2. . An example of efficient flooding with clustering. Only cluster topology of the network changes and hence is more suitable for
heads and gateways rebroadcast cluster formation and maintenance in a rapidly changing
network. RREQ packet is transmitted by the node having data
computation techniques can be used to dynamically create to transmit but has no path to forward it. If data packets are
clusters. In the active clustering lowest ID technique [15] each used for cluster formation and maintenance then every data
node attempts to become cluster head by broadcasting its ID to packet carries the overhead of cluster related information thus
neighbors. It will give up only if it hears from a lower ID increasing the overhead transmitted in the network. Our
neighbor. Based on the above definition, any two nodes in a scheme helps in reducing flooding and redundant overhead
cluster are at most 2 hops away [9]. With this clustering transmission effectively.
scheme, the dominant forwarding nodes are the cluster heads
and the gateways, as shown in Figure 2. B. Construction and maintainance
Clustering in ad hoc networks has been extensively studied A node can be in different states during the clustering
for hierarchical routing schemes [9] [5] [3], the master election process, namely: INITIAL, CLUSTER HEAD (CH),
algorithms [4], power control [3], reliable broadcast [20], load ORDINARY NODE, GATEWAY (GW), CH READY, GW
aware schemes [17], efficient broadcast [16] and efficient READY and DISTRIBUTED GW.
flooding [10]. Some clustering schemes are based on the When a node joins the network, it sets its cluster state to
complete knowledge of neighbors. However, the complete INITIAL. Moreover, the state of a floating node (a node does
knowledge of neighbor information in adhoc networks is hard not belong to a cluster yet) also is set to INITIAL. Because
to collect and introduces substantial control overhead caused by enhanced passive clustering exploits RREQ packets, the
periodic exchange of hello messages. Passive clustering [10] is implementation of this clustering resides between layer 3 and 4.
an “on demand” protocol. It constructs and maintains the An additional field in the header (the cluster information field)
cluster architecture only when there are on-going data packets is carried by RREQ packet. This field contains the following
that piggyback “cluster related information”. Each node entries:
collects neighbor information through promiscuous packet
receptions. Passive clustering, therefore, eliminates setup  Node ID: The IP address of the sender node. Not to be
latency and major control overhead of clustering protocols. confused with the source address of the IP packet.
Passive clustering has two innovative mechanisms for the  State of node: The cluster state of the sender node.
cluster formation: First Declaration Wins rule and Gateway  Two cluster heads addresses: If a sender node is a
Selection Heuristic. With the First Declaration Wins rule, a gateway, then there is another field with the two IP
node that first claims to be a cluster head “rules” the rest of addresses of the cluster heads (CHs) which are
nodes in its clustered area (radio coverage). There is no reachable from the gateway.
waiting period (to make sure all the neighbors have been
checked) unlike for all the weight-driven clustering Below, we provide a summary description of the enhanced
mechanisms [3] [5]. Also, the Gateway Selection Heuristic passive clustering algorithm.
provides a procedure to elect the minimal number of gateways
(including distributed gateways) required to maintain the 1) The packet handling:
connectivity in a distributed manner. Upon sending a RREQ packet, each node piggybacks
cluster related information in the cluster info field. Upon a
Passive clustering maintains clusters using implicit timeout. promiscuous packet reception, each node extracts cluster-
A node assumes that the nodes it had previously heard from as related information of neighbors and updates neighbor
dead or out of its locality if they have not sent any data within information table.
timeout duration. With a reasonable offered load, a node can
easily keep track of dynamic topology changes by virtue of this 2) A cluster head declaration:
timeout. A node in INITIAL state changes its state to CH READY
(a candidate cluster head) when a RREQ packet arrives from
Lastly, the existing passive clustering scheme uses another node that is not a cluster head. With the next outgoing
flooding initially till the cluster is formed and each data packet RREQ packet, a CH READY node can declare itself as a
carries cluster formation overhead fields even though the CLUSTER HEAD.
cluster has not changed. These limitations motivated our

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3) Becoming a member (Gateway or Ordinary node): becomes a distributed gateway if it has not heard from any
A node becomes a member of a cluster once it has heard or other neighboring distributed gateway belonging to the same
overheard a message from any cluster head. A member node cluster. If an ordinary node has received a packet from a
will serve as a gateway or an ordinary node depending on the distributed gateway and no other gateway is a neighbor node of
information collected from neighbors. Specifically, a member that node, then this node changes to a distributed gateway.
node settles as an ORDINARY NODE only after it has learned Enhanced passive clustering was first implemented using
(i.e., has heard from) enough neighbor gateways. In enhanced one cluster head per cluster in DSR. In this paper this
passive clustering, the existence of a gateway can be found implementation is referred to as Enhanced Dynamic Source
only through overhearing a packet from that gateway. Thus, Routing protocol1 (EDSR1). Enhanced passive clustering was
we define another internal state, GW READY, for a candidate then implemented using two cluster heads per cluster. In this
gateway node that has not yet discovered enough neighbor paper this implementation is referred to as Enhanced Dynamic
gateways. Recall that we develop a gateway selection Source Routing protocol2 (EDSR2). Two cluster heads are
mechanism to reduce the total gateways in the network. A named as primary and secondary cluster heads. Primary cluster
candidate gateway finalizes its role as a GATEWAY upon heads are active as long as they are in the cluster. Once the
sending a packet (announcing its gateway’s role). Note that a primary cluster head moves out of the cluster, instead of
candidate gateway node can be downgraded to ordinary node at
performing reclustering and flooding the network, this
any time after detection of enough gateways. technique makes the secondary cluster head active and
C. Gateway Selection Heuristic promotes it as primary cluster head so that flooding in the
A gateway is a bridge node that connects two adjacent network can be avoided. It is now the responsibility of primary
clusters. Thus, a node that belongs to two or more clusters at cluster head to select secondary cluster head. We have used
the same time is eligible to be a gateway. One can easily see lowest id technique to select secondary cluster head.
that only one gateway is needed for the each pair of adjacent IV. SIMULATION RESULTS
clusters. Following this observation, we have used a gateway
selection mechanism that eventually allows only one gateway The simulations were performed using Glomosim [11]. The
for each pair of neighboring cluster heads. However, it is mobility scenarios were randomly generated using random
possible that there is no potential gateway between two waypoint model. We used distributed coordination function
communicating clusters. For instance, suppose that two cluster (DCF) of IEEE 802.11 for wireless LANs as the MAC layer
heads are mutually reachable not by a two-hop but a three-hop protocol.
route. Then the clustering scheme should select the two In our simulation, 100 nodes move in a 1000x1000 meter
intermediate nodes as distributed gateways (DISTR GW). rectangular region for 600 seconds simulation time. Initial
The gateway selection mechanism can be summarized as locations of the nodes are obtained using a uniform
follows: distribution. We assume that each node moves independently
with the same average speed. With the random waypoint
1) Gateway mobility model, a node randomly selects a destination from the
A node that belongs to two or more clusters at the same physical terrain and moves in the direction of the destination
time is a candidate gateway. Upon sending a RREQ packet, a with a uniform speed chosen between the minimal and
potential gateway selects two cluster heads among the known maximal speed. After it reaches its destination, the node stays
cluster heads. This node will serve as an intermediate node there for a pause time and then moves again. In our simulation,
between those chosen cluster heads. It cannot be the the minimal speed was 0m/s and maximal speed was 16m/s and
intermediate gateways for any two other cluster heads that have pause time was varied from 0 to 10seconds. The simulated
already been announced by another neighbor gateway node. If traffic was constant bit rate (CBR).
the node finds a unique pair of cluster heads, then it finalizes its
role as a gateway and announces the pair of cluster heads to We have analyzed the variation in the number of control
neighbors. packets by varying the density of the network at different pause
time (i.e. mobility) of 0s, 5s and 10s.
If a gateway has received a packet from another gateway
which has announced the same pair of CHs, then this node The simulation results shown below compares the
compares the node ID of itself with that of the sender. If this performance of standard DSR, DSR with passive clustering
node has the lower ID, it keeps its role as the gateway. (PDSR) and DSR with enhanced passive clustering EDSR1 and
Otherwise, it selects another pair of CHs (that it has heard EDSR2.
from) or changes its state to ordinary node. The graphs in Fig 3, 4 and 5 show that in EDSR1, the
number of control packets used in routing reduces as the
2) Distributed gateway
number of nodes increases at a fixed mobility, compared to
Enhanced Passive clustering uses distributed gateway to
DSR and PDSR. This is because we have used RREQ packets
provide connectivity among cluster heads which are 3 hops
for clustering which limits flooding within the cluster. The
away. Moreover, distributed gateways are common at the
number of control packets drastically reduces in the middle
boundary of the cluster structure. A node that belongs to only
region of the graph as more number of RREQ packets is
one cluster can be an ordinary node only if at least two
generated when the number of nodes increases and hence
(distributed) gateways are known to this node. Otherwise, it
clusters are maintained efficiently. But there is slight increase
keeps the candidate gateway state. A candidate gateway node
in the control packets with increased mobility. This is because

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of reclustering which causes more control packets to be flooded
in the network. But the graphs for EDSR2 shows reduced
number of control packets irrespective of the density and
mobility of the network. As expected EDSR2 shows reduced
number of control packets compared to EDSR1 even when the
mobility of the node is high as reclustering is avoided. Thus we
can say that using two cluster heads in passive clustering we
can reduce flooding in DSR to a great extent
We have also analyzed the variation in the number of route
request packets by varying the density of the network at
different pause time (i.e. mobility) of 0s, 5s and 10s.

Figure 5. Number of nodes v/s control packets

The graphs in Fig 6, 7, and 8 show that the number of route
requests required in the enhanced passive clustering technique
is lesser than standard DSR and PDSR. This is mainly because
this technique chooses the sub-optimal dominant forwarding
nodes. In normal DSR we can see from the graph that there is a
slight increase in the number of RREQ packets as mobility
increases, this is because new routes have to be found as the
position of the nodes change. Whereas in EDSR1 the graph
shows that the number of RREQ packets is less for different
mobilities as the routes need to be found only between cluster
heads and flooding is limited to that of cluster. But in EDSR2
the number of route request packets reduces further as the
Figure 3. Number of nodes v/s control packets secondary cluster head replaces the primary cluster head and
route requests are not required to find the route between
secondary cluster head as the routes will already be known
during the previous transmissions.

Figure 4. Number of nodes v/s control packets Figure 6. Number of nodes v/s Route request packets

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clustering. Clearly, no proactive flood enhancement scheme
would make sense in this environment, as it would introduce
undesirable, periodic background traffic.
Existing passive clustering scheme uses data packets for
cluster formation and hence introduces lot of overhead in data
transmission. So the key issue here was to evaluate the
improvement introduced by enhanced passive clustering versus
the original protocol version. We have applied enhanced
passive clustering to the most popular reactive routing protocol
DSR. Enhanced passive clustering consistently reduces the
flooding overhead and improves the performance and
scalability as shown by the results. This technique can also be
applied to AODV, ODMRP etc.

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(IJCSIS) International Journal of Computer Science and Information Security,
Vol. 8, No. 5, August 2010

[20] E. Pagani, G.P. Rossi, “ Reliable broadcast in mobile multihop packet AUTHORS PROFILE
networks, ” Mobicom 97 (1997)
[21] J. Wu and H. Li, “On calculating connected dominating set for efficient Shobha.K.R received M.E degree in Digital
routing in ad hoc networks, ” DIAL M. 1999 communication from Bangalore University and is
[22] B. Chen, K. H. Jamieson, and R. Morris, “ An energy-efficient currently working towards the Ph.D. She is currently
coordination algorithm for topology maintenance in Ad Hoc wireless working as Assistant Professor with the department of
networks, ”Mobicom, 2001 Telecommunication Engineering, M.S.Ramaiah Institute
[23] Y. Xu, J. Heidemann and D. Estrin,“Geography-informed Energy of Technology, Bangalore,India. She had served as a
Conservation for Ad Hoc Routing, ” Mobicom, 2001 teaching faculty at BMSCE, Bangalore for 5 years up to 1999. Her
research areas include Routing protocols in Mobile Adhoc Networks and
[24] M. Seddigh, J. Solano and I. Stojmenovic, “Internal nodes based Wireless Networks.
broadcasting algorithms in wireless networks, ” Proceedings of the 34th
Annual HICSS 2001.
[25] S.-J. Lee,W. Su, and M. Gerla On-Demand Multicast Routing Protocol
(ODMRP) for Ad Hoc Networks, Internet Draft, draft-ietf-manetodmrp- Dr.K.Rajanikanth received M.E in Automation and
02.txt, Jan. 2000. Ph. D degrees from Indian Institute of Science,
[26] T. Clausen, P. Jacquet, A. Laouiti, P. Minet, P. Muhlethaler, A.Qayyum, Bangalore, India. Areas of interest are software
L. Viennot Optimized Link State Routing Protocol, Internet Draft, draft- engineering, Object Technology, Embedded Systems.
ietf-manet-olsr-05.txt, Nov. 2001. Currently working as Professor and Principal at M S
Ramaiah Institute of Technology, Bangalore.
[27] R. G. Ogier, F. L. Templin, B. Bellur, M. G. Lewis Topology Broadcast
Based on Reverse-Path Forwarding (TBRPF), Internet Draft, draft-ietf-
manet-tbrpf-03.txt, Nov. 2001.

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