Packet Forwarding Encouragement Scheme in a Wireless Sensor Network

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					                                                                (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                                          Vol. 9, No. 4, 2011

        Packet Forwarding Encouragement Scheme in a
                  Wireless Sensor Network
                     Praveen Kaushik                                                                Jyoti Singhai
                   Department of CSE                                                             Department of ECE
                        MANIT                                                                          MANIT
                      Bhopal, India                                                                  Bhopal, India

Abstract- The most common issue in wireless sensor networks is               lazy nodes and constrained nodes (e.g. energy constrained or
limited availability of energy within network nodes. A widely                field strength constrained). A routing algorithm plays a crucial
used energy-saving technique is to place nodes in sleep mode,                role in transmission of data among nodes. Also dynamic
corresponding to low-power consumption as well as to reduce                  behavior of nodes causes several challenges in design of
operational capabilities. To conserve energy, sometime nodes
may try to maximize the benefits of its own without participating
                                                                             routing scheme. A lot of algorithms have been proposed
in routing services (e.g. without forwarding packets of other                claiming fairness in routing. DSR is most widely adapted
nodes). To conquer with this problem, several schemes have been              algorithm for routing. But the original algorithm is known to
investigated in the literature. In this paper such nodes are                 fail in a scenario containing non cooperative nodes. In [1]
detected and evicted from the network using rating based                     proposed a mechanism for identifying and isolating selfish
multipath dynamic source routing. In our approach after route                nodes to attain fairness. However after decaling a node selfish,
discovery, multiple paths are returned by the destination node,              source node needs to identify alternate path using Route
which are stored by source node in route cache. Once source                  Discovery. This causes a lot many packet drops before it
node identifies such node in its path based on its rating threshold,         identifies alternate path.
an alternative path is selected from the route cache. In sensor
network a node may be overused due to network topology. In
                                                                             Multipath Source Routing [10] can increase performance by
order to mitigate this problem, this paper uses a minimum                    providing applications the liberty to use multiple paths during
battery cost routing (MBCR).The simulation results for rating                packet forwarding. Also it stores multiple paths required. With
based multipath dynamic source routing indicates significant                 Multipath Source Routing data can be forwarded on arbitrary
improvement in aggregate network throughput.                                 routes, which makes it very easy to forward data to multiple
                                                                             paths without use of path using Route Discovery. This causes
    Keywords- minimum cost; multipath ; reluctant node; wireless             a lot many packet drops before it identifies alternate path.
sensor network;
                                                                                                    II.    NODE MODEL
                       I.    INTRODUCTION
                                                                             A. Malicious nodes
A Wireless Sensor Network (WSN) is a collection of low-end
                                                                             Nodes which drops packet with the intention to cause network
devices whose size can range from a few hundred sensors to a
few hundred thousand or possibly more. The sensors do not
rely on any pre-deployed network architecture. The power                     B. Reluctant nodes
supply of each individual sensor is provided by a battery,                    Reluctant nodes try to save their own resources since
whose consumption for both communication and computation                     resources are very constrained in wireless network. Reluctant
activities must be optimized. A WSN may consist of many                      nodes may decide to conserve their resources by not
nodes without any grouping hierarchy. Nodes can                              forwarding data packets for other nodes:
communicate using any wireless technology such as Bluetooth,                   This can be achieved in two ways:
ZigBee or IEEE standards.                                                      1) Reluctant node of type 1: In this model the reluctant
In wireless sensor networks, two nodes can exchange data                     node do not participate in the Route Discovery phase of DSR
when they are located within one another’s communication                     protocol[10] . Such reluctant nodes not only drop packets that
range. In WSN all nodes cooperates and forward packet for                    have a source address or destination address different from
each other as a router. Here it is possible that nodes may not
                                                                             these reluctant nodes but also drop all RREQ packet they
be within the communication range of each other. At this stage,
                                                                             receive or not forward RREP packet to some destination. If the
nodes extend the transmission range by multi hop packet
                                                                             node does not participate in the route discovery process, then
forwarding. In ad hoc network nodes can be of two types’
cooperative nodes and inactive nodes. Cooperative nodes                      there will be no route with that reluctant node. The outcome is
comply with the standard at all times. Inactive nodes include                that these reluctant nodes will be isolated i.e. these nodes will

                                                                                                          ISSN 1947-5500
                                                             (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                                       Vol. 9, No. 4, 2011
never participate in packet forwarding. A reluctant node of this          make a decision whether the node is regular or misbehaved,
type uses the node energy only for its own communication.                 while trust rating is used to choose whether the node is
                                                                          trustworthy or not as a recommender.
  2) Reluctant node of type 2: In this type of model, the                  Michiardi and Molva proposed CORE (Collaborative
reluctant node does not forward packets which are destined to             Reputation mechanism) [3]. It defers from Watchdog and
other nodes[10]. These reluctant nodes participate correctly              CONFIDANT by bringing aging factor with more weight on
in the routing function by advertising available roots. When              past observations and isolating nodes having bad reputation.
this behaviour is chosen, reluctant nodes do not cooperate in             Three types of reputations are used in the CORE.
packet forwarding function. However, a reluctant node that                Subjective reputation of a target node is the reputation
operates complying with this model, participates in the route             calculated directly from a subject’s inspection of the target
discovery and route maintenance phase of the DSR protocol.                node’s behavior. Indirect reputation is evaluated only
                                                                          considering the direct communication between a subject and
The outcome of this type of behaviour is that the reluctant
                                                                          its neighbours. Function reputation is the subjective and
node will save a major amount of energy (battery life) by
                                                                          indirect reputation calculated with respect to different
dropping great no of data packets.
                                                                          functions such as forwarding a data packet, reply route request.
                   III.   RELATED WORK                                    The final reputation information is combined from the three
                                                                          reputations with different weight associated to the functional
A lot of algorithm has been proposed claiming fairness in                 reputation value. CORE consists of two basic components:
routing.L Wang, Y Shu, M Dong, L Zhang proposed a                         Reputation Table (RT) is a data structure stored in each
multipath source routing scheme [9]. This scheme makes use                network entity, keeping the reputation data pertaining to the
of DSR’s route discovery mechanism whereby multiple routes                nodes in the network. The Watchdog mechanism (WD) is used
can be returned. The more alternative routes available in route           to detect misbehaving nodes. With CORE only positive rating
cache, the more possibility that a node can find a perfect route.         factors are distributed among the entities to avoid a
To get multiple route dsr optional feature is enabled. All the            misbehaving entity to distribute false information about other
routes discovered are stored in the route cache with a unique             entities in order to initiate a denial of service (DoS) attack.
route index. Route index is used in selecting multiple paths                 Miranda and Rodrigues classified nodes into friends, foes
from the route cache.                                                     and reluctant but at the cost of memory and message overhead
S. Marti, T. J. Giuli, K. Lai and M. Baker proposed two                   [4]. W. J. Adams, G. C. Hadjichristofi and N. J. Davis used
techniques that improve throughput of a network in the                    Reputation Indexing Windows (RIW) to handle misbehaving
presence of reluctant nodes [1]. The watchdog method is used              nodes [5]. Unlike CORE it emphasised on current feedback
for each node to detect misbehaving nodes in the network.                 items rather than old ones.
When a node sends a packet to next hop, it tries to overhear                 S. Zhong, J. Chen and R. Yang proposed Sprite [13], a
the packet forwarded by next hop. If it hears that the packet is          credit-based system for MANET. As opposed to Nuglets or
forwarded by next hop and the packet matches the previous                 Counter they do not require tamper-proof hardware to prevent
packet that it has sent itself, it considers the next hop node            the fabrication of payment units.
behaves well. Otherwise it considers the next hop node is
misbehaving. The pathrater uses the knowledge about                                      IV.   DYNAMIC SOURCE ROUTING
misbehaving nodes acquired from watchdog to pick the route
that is most likely to be reliable. Each node maintains a trust           A. Overview
rating for every other node. When watchdog detects a node is                  The DSR is an entirely on demand routing protocol which
misbehaving, the trust rating of the node is updated in negative          composed of two parts: route discovery and route maintenance
way. When a node wants to choose a safe route to send                     [6].
packets, pathrater calculates a path metric by averaging the
node ratings in the path.                                                 B. Route Discovery
 S. Marti, T. J. Giuli, K. Lai and M. Baker implemented the                   In DSR, whenever a node needs to send a packet to some
solutions on DSR protocol using ns2 as simulation                         destination for which, it does not currently have a route in its
environment. The simulation result shows the throughput of                route cache, it initiates Route Discovery to find a route. The
the network is increased by up to 27% in a network where                  initiator broadcasts a Route Request packet to its neighbours,
packet drop attack happens. However, routing overhead is also             specifying the target and a unique identifier from the initiator.
increased up to 24%.                                                      Each node receives the route request. If it has recently seen
A lot of work has been proposed on sensor network using                   this request identifier from the initiator, discards the request.
reputation to bring fairness in routing [11]. S. Buchegger and            Otherwise it appends its own node address to a list in the
J.Y. LeBoudec proposed CONFIDANT algorithm using both                     request and rebroadcasts the request. When the route request
direct and indirect observations to measure fairness in                   reaches its target node, the target sends a route reply back to
Dynamic Ad -hoc Networks [2]. CONFIDANT makes a                           the initiator of the request, including a copy of accumulated
distinction trust from reputation. For each node, reputation              list of address from the request. When the reply reaches the
rating signifies how well a node behaves while trust rating               initiator of the request, it caches the new route in the route
stands for how honest a node is. Reputation rating is used to

                                                                                                     ISSN 1947-5500
                                                                           (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                                                     Vol. 9, No. 4, 2011
cache. The intermediate node also sends a route reply, if it has                        A.       Multipath dynamic source routing
a route to the destination.
                                                                                        B.     Efficient Packet forwarding and load balancing
C. Route maintenance                                                                         (Reputation based) Multipath Dynamic Source Routing
    It is a mechanism by which a node sending a packet along
a specified route to some destination detects if that route has                             Multipath routing makes use of DSR’s route discovery
broken. If after a limited no of local retransmission of the                            mechanism whereby multiple routes can be returned. With
packet a node in the route is unable to make this confirmation,                         standard DSR, a node selects a shortest route to the destination
it returns a route error to the original source of the packet,                          from the route cache. In this mechanism, it works as the more
identifying the link from itself to the next node as broken.                            alternative routes available in route cache, the more possibility
                                                                                        that a node can find a perfect route. To get multiple route DSR
                                                                                        optional features is enabled. All the routes discovered are
                        E                                                               stored in the route cache with a unique route index. Route
                                              G           I                             index is used in selecting multiple paths from the route cache.
                    C                 F                                                           Efficient Packet forwarding and load balancing

            B                                     H                                          Since this mechanism makes use of source routing
                            D                                                           intermediate nodes forwards the packet as the route indicated
                                                                                        in packet’s header. Reputation based packet forwarding to
                                                                                        handle reluctant behaviour. The mechanism counts on the
                                                                                        principle that a node freely evaluates its neighbours based on
                                                                                        the completion of requested service. The core principle is that
                    E                                                                   when a node forwards packet through one of its neighbours, it
                                          G           I                                 holds the neighbour responsible for the correct delivery of the
     A                                                                                  packet to destination. Fig. 2 illustrates the operation of
                C                F
                                                              J                         mechanism.

        B                                     H
                        D                                                                                                   C                   D
                                (b)                                                                                 F               G               H

                    E                                                                                  A
                                          G           I
                                                                                                                        I                   J             K
                C                F
        B                                     H                                                            Figure 2.Sensor network with reluctant node G.

                                (c)                                                          Consider two flows A-F-G-H-E, B-F-G-H-K, in fig.
    Figure 1.Example of Route Request: Node C is source node while Node J                    1    Suppose node G starts acting reluctantly, dropping all
 is destination. (a) Node C broadcasts a route request packet to find a path to
node J. (b) Neighbour nodes broadcasts route request in the same manner but                       the packets that it is likely to forward.
   adding its own address to the packet. In the same manner route request is                 2    Once, neighbour nodes of G will notice that packets
 forwarded throughout the network. (c) J sends back a route reply to C using                      are not being delivered to their intended destinations.
              the path contained in one of the route request packet.

                                                                                                                            C                   D
                   SOURCE ROUTING
                                                                                                                    F               G               H
   In this work we try to find a hybrid approach that reduces
packet drops caused by identification and isolation of reluctant
nodes using algorithm proposed by [9] with the help of                                                                  I                   J             K
multipath source routing. Reputation based multipath dynamic
mechanism has two elements –

                                                                                                                                ISSN 1947-5500
                                                                         (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                                                   Vol. 9, No. 4, 2011

                             C                D                                      Ci is the remaining battery capacity of node. As the battery
                                                                                   capacity decreases, the value of cost function for node n will
                                                                                   increase. Therefore to find a route with maximum remaining
  B                                                                                battery capacity we should select a route π that has minimum
                    F               G             H                                battery cost
                                                                                    C π = min{Ci | i Є A} where A is the set containing all
                                                                                   possible routes. Since battery capacity is directly incorporated
      A                                                                            into the routing protocol, this metric prevent hosts from being
                         I                    J              K                     overused, thereby increasing their lifetime and the time until
                                                                                   the network is partitioned

                                                                                                            VI.   ALGORITHM
      Figure 3.Reluctant node G dropping packets forwarded from node F             1. During route discovery a source node sends a RREQ packet
                                                                                      to its neighbouring nodes. RREQ message must contain
                                                                                      source address, destination address, hop count, sequence no.
   3      Node F will reduce the reputation index it assigns to G
          twice due to G’s effect on both flows.                                   2. The intermediate nodes after appending their addresses
   4      Immediate neighbours of node F and H will in turn                           again broadcast RREQ to the hop-2 neighbours. This
          reduce the reputation index; they give to node F and H.                     process continues until RREQ get to the destination node.
   5      Once G’s reputation index goes below a certain
                                                                                   3. Destination node sends a route reply back to the source node,
          threshold, a new path is selected from the route cache.
                                                                                      including a copy of accumulated list of address from the
In a network of nodes N = {1,2,...,n}, each node i maintains a
reputation table where a reputation index Rij is stored for each                   4. When the reply reaches the initiator of the request, it caches
of the node’s immediate neighbours j. A node credits a                                the new route in the route cache. Here multiple paths are
reputation index to each of its neighbours based on successful                        returned to source node. All the routes discovered are stored
delivery of packets forwarded through that neighbour. On the                          in the route cache with a unique route index. Route index is
other hand delivery failures penalize such neighbours by                              used in selecting multiple paths from the route cache.
decreasing the reputation index. Success or Failure is decided                        During data transfer, when a node receives a data packet, it
based on feedback obtained from the destination.                                      checks if received packet is a retransmission. If data packet
 In this mechanism, each node maintains a lookup table to                             is a retransmission then node decrements the reputation
keep information about data packets forwarded through it. It                          index of the neighbour through which the original packet
stores source and destination IP, port number, sequence                               was forwarded.
number and the next hop address. Each node also maintains a
                                                                                   5.        If Rik be the reputation index of previous hop k and
reputation table in which, a node stores two thing neighbour
                                                                                        rthrash be the reputation threshold then -
node id and its reputation. Following algorithm illustrates the
operation of mechanism.                                                            6. if (Rik < Rthrash )

Load balancing                                                                     7. drop the packet
                                                                                   8. else
In order to perform load balancing this paper uses Minimum
Battery Cost Routing [7] in MP-DSR where accumulated path                          9. store related information and forward the packet
cost is used. If length of path P is L then its accumulated path                   10.     If a node receives acknowledgement packet, it
cost is:                                                                           increments the reputation of its neighbour node.

                                                                 (1)               11.      Once a node’s reputation index goes below a certain
                                                                                   threshold, a new path is selected from the route cache using
Where, C {Di, Di+1} implies that the link cost in path P from                      MBCR (minimum battery cost routing.) and data is sent
Di to Di+1 for linkl .                                                             through new path.
To consume the energy in a more balance manner, an intuitive
technique is to utilize cost function based on the node's                                VII.    SIMULATION SETUP AND EVALUATION
remaining battery capacity. In Minimum Battery Cost Routing                           Using ns-2[14] we study the performance of our mechanism.
(MBCR) [8] the battery cost C for a particular route π with n                      In our simulation we placed 20% nodes randomly in 670×670
nodes is defined as:                                                               area. Each node has a transmission range of 250m and moves
                                                                                   at a speed of 10m/s. We randomly generate CBR (Constant

                                                                                                                  ISSN 1947-5500
                                                          (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                                    Vol. 9, No. 4, 2011
Bit Rate) TCP flows. Neighbours identified as reluctant (i.e.
whose reputation index is below threshold). All route requests
(RREQs) and route replies forwarded by such neighbours will
be ignored. Simulation parameters are shown in table I.

                  Table I. SIMULATION PARAMETER
          Parameter                      Value

       Number of nodes                     20
       Routing scheme                     DSR
          Packet size                   512 bytes
        Traffic model                     CBR
         Propagation                 Two Ray Ground                          Figure 4.Total Number of packet drop in DSR vs. Number of packet
                                                                                         dropped in reputation based multipath DSR
     Max speed of nodes                  15 ms
                                                                       As shown in the above graph x axis indicates Simulation time
     Initial energy of node            1000 joules                     and y axis indicates number of packets received. Red line
       Simulation Time                   200 sec                       indicates number of packet received vs. simulation time for
                                                                       original method. Blue line indicates number of packet received
                                                                       vs. simulation time. From the above graph it is observed that
                                                                       number of packet recieved in original method is notably less.
A. Simulation result                                                   In above graph initially for 10 seconds both lines are touching
The impact of reluctant nodes was measured in terms of total           x axis because in the network traffic flow starts at 10 second.
number of packet dropped, number of packet received, packet
delivery ratio and network throughput. The measurements of
the network were made using a AWK script that parses and
analyse the trace file output provided by ns-2 software. The
trace file gives information about a ser of defined events
which occurred in the simulation such as routing events and
agent event. Through agent event trace not only it is possible
to estimate the total no packet sent by every node of the
MANET but also the total number of packets which have been
 Aggregate Network throughput (AGT) is the ratio of total
number of bits received to the total number of bits sent
AGT = Total number of received bits / Total number of sent
Packet delivery ratio (PDR) is the ratio of total number of
packets sent the total number of packet received.                           Figure 5.Total Number of packet received in original DSR vs. Number
                                                                                    of packet received in reputation based multipath DSR.
PDR = Total number of sent packets / Total number of
                                                                                        Table II. AGGREGATE NETWORK THROUGPUT

                                                                          Parameter       % reluctant nodes           DSR           RB-

                                                                           Aggregate              25                  33.04         43.06

                                                                                                       ISSN 1947-5500
                                                                     (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                                               Vol. 9, No. 4, 2011
   In wireless sensor network, due to limited energy of nodes,
some nodes may do not participate in routing functions. This                                    Dr. Jyoti Singhai is Associate professor in Maulana
paper deals with detection and isolation of such nodes. The                                     Azad National Institute of Technology (MANIT),
proposed method has certain limitations such as in proposed                                     Bhopal, India. She holds Ph..D degree from MANIT
method cooperative nodes may be accused of reluctant                                            India. Her general research interests include wireless
                                                                                                communication, image processing, WSN and network
behaviour on account of packet drop due to collision, memory                                    security.
overflow, energy. Currently we are working to mitigate these

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                                   AUTHORS PROFILE
                 Mr. Praveen Kaushik is Assistant Professor in Maulana
                 Azad National Institute of Technology (MANIT) Bhopal,
                 India. He is pursing PhD in WSN. His general research
                 interests include WSNs, Ad hoc Network and Wireless

                                                                                                           ISSN 1947-5500

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