A survey of mitigating routing misbehavior in mobile ad hoc networks

International Journal of ComputerComputerand Technology (IJCET), ISSN 0976 – 6367(Print),
International Journal of Engineering Engineering
ISSN 0976 – 6375(Online) Volume 1, Number 2, Sep - Oct (2010), © IAEME
and Technology (IJCET), ISSN 0976 – 6367(Print)
ISSN 0976 – 6375(Online) Volume 1
IJCET
Number 2, Sep - Oct (2010), pp. 106- 117 ©IAEME
© IAEME, http://www.iaeme.com/ijcet.html

A SURVEY OF MITIGATING ROUTING MISBEHAVIOR
IN MOBILE AD HOC NETWORKS
Mrs. S. A. Nagtilak
Department of Computer Engineering
S.C.O.E, Pune, E-Mail: saranagtilak@yahoo.co.in

Prof. U.A. Mande
Asst. Professors, Departments of Computer Engineering
S.C.O.E, Pune, E-Mail: uamande.scoe@sinhgad.edu

ABSTRACT
The operation of MANETs does not depend on preexisting infrastructure or base
stations. Network nodes in MANETs are free to move randomly. Therefore, the network
topology of a MANET may change rapidly and unpredictably. This paper presents the
existing methods to detect misbehavior in MANETs. Routing protocols used in such type
of networks generally based on the assumption that, all participating nodes will be fully
cooperative. But, due to the open structure node misbehavior may exist and packet loss
occurs. Among them one type of misbehavior is that some nodes will take part in routing
establishment processes but they do not respond to forward data packets and simply
dismiss the packets. This paper surveys the methods can be used for the misbehavior
detection of MANET.
Keywords – 2ACK, SACK, S-TWOACK, beans, nuggets
I. INTRODUCTION
MANET mobile ad hoc network as the name suggests consists of a bunch of
entities called as nodes or hosts which communicate with each other exchanging
information with the help of intermediate devices called as routers. The links between
these so called nodes is generally invisible or called as wireless links. The structure of
such networks is not predefined or it does not depend on any base stations lonely but a lot
of other entities are also involved in the entire communication process. The topology of

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International Journal of Computer Engineering and Technology (IJCET), ISSN 0976 – 6367(Print),

such networks keeps on changing mainly due to a factor called as mobility. Network
clients in MANETs may move randomly. Therefore, the network topology of a MANET
can be change unpredictably and speedily. All network activities, for instance forwarding
data packets, and detecting the topologies which concern with nodes themselves for
execution either collectively or individually. Due to this changing topology packet loss is
a common phenomenon. Any wireless network consists of a lot of nodes that interact
with each other exchanging information continuously. As these nodes have the flexibility
of moving from one place to other, there may be cases wherein a particular node which is
a receiver for a particular packet, moves away from the range of sender. However the
sender is not aware of this scenario and it might still keep on sending packets thus leading
to packet and data loss.
The other case is a bit more interesting, whenever communication takes place
between any two nodes there are a lot of nodes involved in this communication process
acting as mediators. All these nodes agree to forward packets during the actual
communication process but one of them actually turns selfish during the data transfer,
this selfish node keeps on dropping packets as when received instead of forwarding it to
the next hop in the communication process. These selfish behavior results in packet loss
and also the source is unaware of such misbehaving node in the path towards the
destination. And there is no such mechanism to detect this misbehaving node.
The structure of a MANET totally depends on application and it can vary from
network to network. For e.g. from a small static network which is highly power
constrained to a large hugely dynamic network. Lots of techniques have been discovered
to avoid the misbehavior or selfishness among nodes.
There has been a lot of improvements in the field of computer and wireless
technologies therefore there has been a lot of development expected in mobile wireless
computing typical applications of which can be used in military scenes, rescue operations
or where it is almost difficult to rely on wired network. MANET's are self organizable
and configurable hence also known as multi hop wireless ad hoc networks, where the
topology of the network keeps on changing continuously.

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A. PACKET LOSS DUE TO ROUTING MISBEHAVIORS
During data transfer in ad hoc networks, all the nodes in the network usually take
part in the communication process in order to increase or maximize the throughput.
Therefore the more the number of nodes greater is the bandwidth and smaller is the
network partition with smaller paths. However it might also happen that a node has
agreed to fully cooperate in the communication process but later refuses to do so resulting
in loss of packets because of its selfishness [14].
A selfish node which acts as selfish by dropping packets does so because it is
unwilling to spend its battery life and CPU cycles and save its bandwidth. Such a
misbehaving node launches a denial of service attack by simply dropping packets.

Figure 1 Scenario for packet dropping and misrouting
In some cases it might happen that the node which is dropping packets might have
fault in the software running at its end. So the need is to focus on how this misbehaving
node in order to decrease the packet loss can be detected [2]. There are a lot of schemes
available in order to detect the routing misbehavior in MANET’s which are as follows:
i) The watchdog technique:
In this scheme misbehaving nodes are detected by overhearing the wireless
medium. The path rater technique, which is based on the watchdog’s output, allows nodes
to avoid the use of the misbehaving nodes in any future route selections. However, the
drawback with watchdog technique is that it depends heavily on overhearing principal;
therefore there is chance that it might fail to identify misbehavior in routing or raise false
alarms in cases where ambiguous collisions, receiver collisions are present, it might also
fail sometimes in cases for limited transmission power.

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ii) ACK and SACK schemes:
They are used to measure the usefulness of the current route and to take
appropriate action. For example, congestion control is based on the reception of the ACK
and the SACK packets.[1]
iii) TWOACK Scheme:
The 2ACK and the TWOACK schemes have the following major differences: 1)
the node which acts as receiver in the 2ACK scheme usually sends 2ACK packets for a
small amount of data packet which it has received, whereas, in the TWOACK scheme,
TWOACK packets are acknowledged for every data packet received at the receivers end.
But, however it was observed that sending acknowledgement for a fraction of data
packets received, improves the performance of 2ACK scheme when it comes to routing
overhead.
iv) (S-TWOACK) scheme or Selective TWOACK:
In this scheme every TWOACK packet will acknowledge or reply the receipt for
number of data packets, whereas in the 2ACK scheme, a 2ACK packet only
acknowledges one data packet. Because of such a small change, the 2ACK scheme gains
easy control on the trade-off that appears between the network performance and the cost
as compared to the S-TWOACK scheme.
II. EXISTING METHODOLOGIES
Routing protocols for MANETs are designed based on the assumption that all
participating nodes are fully cooperative. Misbehaving nodes can be a significant
problem. The presence of selfish or malicious nodes degrades the efficiency of packet
relaying. It increases the packet delivery latency and the packet loss rate. Selfish nodes
lead to network partitioning. Various techniques have been proposed to prevent
selfishness in MANETs. These schemes can be broadly classified into two categories:
credit-based schemes and reputation-based schemes.
A. Credit-Based Schemes
The basic idea of credit-based schemes presented [6] is to provide incentives for
nodes to faithfully perform networking functions. In order to achieve this goal, virtual
(electronic) currency or similar payment system may be set up. Nodes get paid for

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providing services to other nodes. When they request other nodes to help them for packet
forwarding, they use the same payment system to pay for such services. The concept of
nuggets (also called beans) is used for payments for packet forwarding. There are two
models which use nuggets are: the Packet Purse Model shown Figure 2 and the Packet
Trade Model shown in Figure 3. In the Packet Purse Model, nuggets are loaded into the
packet before it is sent. The sender puts a certain number of nuggets on the data packet to
be sent. Each intermediate node earns nuggets in return for forwarding the packet. If the
packet exhausts its nuggets before reaching its destination, then it is dropped. In the
Packet Trade Model, each intermediate node “buys” the packet from the previous node
for some nuggets and “sells” it to the next node for more nuggets. Thus, each
intermediate node earns some nuggets for providing the forwarding service and the
overall cost of sending the packet is borne by the destination.
In another implementation, each node maintains a counter termed the neglect
counter. The counter is decreased when the node sends packets of its own, but
increased when it forwards packets for the other nodes. The counter should be positive
before a node is allowed to send its packet. Therefore, the nodes are encouraged to
continue to help other nodes. Tamper resistant hardware modules are used to keep nodes
from increasing the neglect counter illegally.

Figure 2 Packet purse model.

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Figure 3 Packet trade model.
Another credit-based scheme, termed Sprite, has nodes that keep receipts of the
received/forwarded messages. When the users have a fast connection to a Credit
Clearance Service (CCS), they report all of these receipts. The CCS then decides the
charge and credit for the reporting nodes. In the network architecture of Sprite, the CCS
is assumed to be reachable through the use of the Internet, limiting the utility of Sprite.
The main problem with credit-based schemes is that they usually require some kind of
tamper-resistant hardware and/or extra protection for the virtual currency or the payment
system.
B. Reputation-Based Schemes
The second category of techniques to combat node misbehavior in MANETs is
reputation-based presented by [2]. In such schemes, network nodes collectively detect
and declare the misbehavior of a suspicious node. Such a declaration is then propagated
throughout the network so that the misbehaving node will be cut off from the rest of the
network. The two modules under this category are watchdog and path rater shown in Fig
4. Nodes operate in a promiscuous mode wherein the watchdog module overhears the
medium to check whether the next-hop node faithfully forwards the packet. At the same
time, it maintains a buffer of recently sent packets. A data packet is cleared from the
buffer when the watchdog overhears the same packet being forwarded by the next-hop
node over the medium. If a data packet remains in the buffer for too long, the watchdog
module accuses the next hop neighbor of misbehaving. Thus, the watchdog enables
misbehavior detection at the forwarding level as well as the link level. Based on the
watchdog’s accusations, the path rater module rates every path in its cache and

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subsequently chooses the path that best avoids misbehaving nodes. Due to its reliance on
overhearing, however, the watchdog technique may fail to detect misbehavior or raise
false alarms in the presence of ambiguous collisions, receiver collisions, and limited
transmission power.
The CONFIDANT protocol [7] is another example of reputation-based schemes.
The protocol is based on selective altruism and utilitarianism, thus making misbehavior
unattractive. CONFIDANT consists of four important components—the Monitor, the
Reputation System, the Path Manager, and the Trust Manager. They perform the vital
functions of neighborhood watching, node rating, path rating, and sending and receiving
alarm messages, respectively. Each node continuously monitors the behavior of its
first-hop neighbors. If a suspicious event is detected, details of the event are passed to
the Reputation System. Depending on how significant and how frequent the event is, the
Reputation

Figure 4 Watchdog & Path rater.
System modifies the rating of the suspected node. Once the rating of a node
becomes intolerable, control is passed to the Path Manager, which accordingly controls
the route cache. Warning messages are propagated to other nodes in the form of an Alarm
message sent out by the Trust Manager. The Monitor component in the CONFIDANT
scheme shown in Figure 5 observes the next hop neighbor’s behavior using the
overhearing technique. This causes the scheme to suffer from the same problems as the
watchdog scheme.

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C. End-to-End Acknowledgment Schemes
There are several schemes that use end-to-end acknowledgments (ACKs) to detect
routing misbehavior or malicious nodes in wireless networks.
In the TCP protocol, end-to-end acknowledgment is employed. Such
acknowledgments are sent by the end receiver to notify the sender about the reception of
data packets up to some locations of the continuous data stream. The Selective
Acknowledgment (SACK) technique [3] is used to acknowledge out-of-order data blocks.

Figure 5 CONFIDANT Scheme.
The 2ACK technique differs from the ACK and the SACK schemes in the TCP
protocol in the following manner: The 2ACK scheme tries to detect those misbehaving
nodes which have agreed to forward data packets for the source node but refuse to do so
when data packets arrive. TCP, on the other hand, uses ACK and ACK to measure the
usefulness of the current route and to take appropriate action.
In order to identify malicious routers that draw traffic toward them but fail to
correctly forward the traffic, the secure trace route protocol is proposed. The normal trace
route protocol allows the sender to simply send packets with increasing Time-To- Live
(TTL) values and wait for a warning message from the router at which time the packet’s
TTL value expires. The secure trace route protocol authenticates the trace route packets
and disguises them as regular data packets.
In secure trace route scheme, binary search is initiated on faulty routes.
Asymptotically, log (n) probes are needed to identify a faulty link on a faulty n-hop route.
This technique only works with static misbehaviors and needs to disguise the probing
messages as regular routing control packets. Once a link is identified as faulty, the link
weight is increased so that future link selections will avoid this link.

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The Best-effort Fault-Tolerant Routing (BFTR) scheme [16] also employs end-to-
end ACKs. The BFTR scheme continuously monitors the quality (i.e., packet delivery
ratio) of the path in use. This is compared with the predefined expected behavior of good
routes. If the behavior of the route in use deviates from the behavior of good routes, it is
marked as “infeasible” and a new route is used. Since BFTR throws out the entire route
before detecting the misbehaving nodes, the newly chosen route may still include the
same misbehaving nodes. Even though the new route will be detected as infeasible by the
source after a period of observation time, data packet loss will occur in traffic flows when
using protocols such as UDP. Such a repeated detection process is inefficient. In contrast
with BFTR, it is try to identify such misbehaving links in this work. Therefore, more
accurate information on routing misbehavior can be obtained in the 2ACK scheme.
III. COMPARISON WITH THE EXISTING SCHEMES
Compared with the above schemes, the 2ACK scheme doesn’t depend on end-to
end acknowledgment. Instead, the 2ACK scheme tries to detect misdemeaning links as
the links are being used. Such a proactive detection approach results in quicker detection
and identification of misdemeaning links. In such a combined scheme, the Multi-Hop
transmission and the monitoring processes are turned on only when routing carry outface
degrades. It will further reduce the routing overhead of the 2ACK scheme.
A scheme to choose routes based on the reliability index of each outgoing
neighbor has each node maintaining a table of reliability indices of its neighbors. This
type of reliability index indicates the previous success or failure experience of packet
transmissions through neighboring nodes. For example, a successful point-to-point
transmission will give output in an increase of the reliability index of the neighbor
associated with the route. When selecting path for data transmissions, nodes prefer those
rooted at the neighbors with higher reliability indices. Since a sender searches all possible
path from its immediate neighbors, the overall reliability of the selecting path depends on
how the neighbors select the rest of the route.
As compared to the watchdog, the 2ACK scheme has the following advantages:
Ambiguous Collisions: Ambiguous or doubtful collisions may occur at node N1.
When a well behaved node N2 forwards the data packet toward N3, it is possible that N1

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cannot overhear the transmission due to another concurrent transmission in N1's
neighborhood. The 2ACK technique solves this problem by requiring N3 to send a Multi-
Hop packet explicitly.
Receiver Collisions: Receiver or acceptor collisions take place in case of
overhearing techniques when N1 overhears the data packet being forwarded by N2, but
N3 fails to get the packet due to collisions in its neighborhood. The data packets will not
be retransmitted by a misbehaving N2 because retransmission requires extra energy.
Again, due to the explicit Multi-Hop packets our 2ACK scheme overcomes this problem.
Limited Transmission Power: A misbehaving N2 may engineer its transmission
power in such a way that N1 can overhear its transmission but not N3 such that, this
problem matches with the Receiver Collisions problem. It goes to a level of threat only
when the distance between N1 and N2 is less than the distance between N2 and N3. The
2ACK scheme does not suffer from limited transmission power problem.
Limited Overhearing Range: In order to transmit data to N3 a well-behaved N2
could apply low level of power transmission. Due to N1's limited overhearing range, it
will not overhear the transmission successfully and will thus infer that N2 is
misbehaving, causing a false alarm. Both this problem occur due to the potential
asymmetry between the communication links. The 2ACK scheme is not affected by
limited overhearing range problem.
The 2ACK scheme of detecting routing misbehavior is different from the
TWOACK and SACK schemes present in the TCP protocol in the following manner:
The 2ACK technique identifies misbehaving nodes which had agreed to forward
data packets originating from the source node but later refuse to do so during actual data
transfer. On the other side, the TCP protocol uses SACK and ACK to find the benefit of
the current route and to take the required action. 2ACK scheme does not depend on end-
to-end acknowledgment. Such a 2ACK scheme may not exist in some traffic flows for
instance UDP protocol. Such a proactive approach of detection results in faster detection
of misbehaving links.

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IV. CONCLUSION
The 2ACK scheme which helps detect misbehavior by a two hop
acknowledgement. The 2ACK scheme is a network-layer technique to detect
misbehaving links and to mitigate their effects. The 2ACK scheme detects misbehavior
through the use of a new type of acknowledgment packet, termed 2ACK. A 2ACK packet
is assigned a fixed route of two hops (three nodes N1, N2, N3), in the opposite direction
of the data traffic route. This technique identifies misbehaving nodes which had agreed to
forward data packets originating from the source node but later refuse to do so during
actual data transfer and it helps to reduce the routing overhead.
V. FUTURE WORK
The 2ACK scheme can be implemented which helps detect misbehavior by a two
hop acknowledgment. The 2ACK scheme for detecting routing misbehavior is considered
to be network-layer technique for mitigating the routing effects. The 2ACK scheme
identifies misbehavior in routing by using a new acknowledgment packet, called 2ACK
packet. The 2ACK technique is based on a simple 2-hop acknowledgment packet that is
sent back by the receiver of the next-hop link. The 2ACK scheme can be used as an add-
on technique to routing protocols such as OLSR in MANETs.
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A survey of mitigating routing misbehavior in mobile ad hoc networks

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