Er. Isha Nagpal
Assistant professor,DCSE, PPIMT,Hisar
Learning Objectives:
·
Introduction to Mobile
Ad hoc Network
·
Types of Routing In
MANET
·
Traditional
Approach of Data Transfer in Unicast Transferring
·
Security
Requirements of Mobile Ad-Hoc Network
Introduction
Mobile ad hoc networks (MANETs)
consists of a collection of wireless mobile nodes which dynamically exchange
data among themselves without the reliance on a fixed base station or a wired
backbone network. The ad-hoc network provides lack of secure boundaries. An ad
hoc network is the cooperative engagement of a collection of mobile nodes
without the required intervention of any centralized access points i.e. no
access points passing information between participants act as LAN which is
built spontaneously as devices connected instead of relying on base stations to
coordinate the flow of messages to each node in a network.
In MANETs communication
between nodes is done through the wireless medium. Because nodes are mobile and
may join or leave the network. MANETs have a dynamic topology. Nodes that are
in transmission range of each other are called neighbours. Neighbours can send data
directly to each other. However, when a node needs to send data to another non-neighbouring
node, the data is routed through a sequence of multiple hops, with intermediate
nodes acting as routers.
Types of Routing in
MANET
1.1 Unipath Routing in MANET
In
unipath routing, only a single route is used between a source and destination
node. Routing protocols are used to find and maintain routes between source and
destination nodes.
Two
main classes of ad hoc routing protocols are table-based and on-demand
protocols:
a) Table Based
Protocols: Each node maintains a routing table
containing routes to all nodes in the network. Nodes must periodically exchange
messages with routing information to keep routing tables up-to-date. Therefore,
routes between nodes are computed and stored, even when they are not needed.
b)
On Demand Protocols: Nodes only
compute routes when they are needed. On-demand protocols consist of the
following two main phases:
1. Route discovery: It is the process of finding a route
between two nodes.
2. Route maintenance: It is the process of repairing a
broken route or finding a new route in
the presence of a route failure.
Two of the most widely used
protocols are the Dynamic Source Routing (DSR) and the Ad hoc On-demand
Distance Vector (AODV) protocols. AODV and DSR are both on-demand protocols.
Dynamic Source Routing:
DSR is an on-demand routing protocol for
ad hoc networks. Like any source routing protocol, in DSR the source includes
the full route in the packets’ header. The intermediate nodes use this to
forward packets towards the destination and maintain a route cache containing
routes to other nodes.
Route discovery: If the source does not
have a route to the destination in its route cache, it broadcasts a route
request (RREQ) message specifying the destination node for which the route is
requested. The RREQ message includes a route record which specifies the sequence
of nodes traversed by the message. When an intermediate node receives a RREQ,
it checks to see if it is already in the route record. If it is, it drops the
message. This is done to prevent routing loops. If the intermediate node had
received the RREQ before, then it also drops the message. The intermediate node
forwards the RREQ to the next hop according to the route specified in the
header. When the destination receives the RREQ, it sends back a route reply
message. If the destination has a route to the source in its route cache, then
it can send a route response (RREP) message along this route. Route maintenance: When a node detects a broken link
while trying to forward a packet to the next hop, it sends a route error (RERR)
message back to the source containing the link in error. When an RERR message
is received, all routes containing the link in error are deleted at that node.
Ad Hoc On Demand
Distance vector: AODV is an on-demand
routing protocol for ad hoc networks. AODV uses hop-by-hop routing by
maintaining routing table entries at intermediate nodes.
Route Discovery: The route discovery
process is initiated when a source needs a route to a destination and it does
not have a route in its routing table. To initiate route discovery, the source
floods the network with a RREQ packet specifying the destination for which the
route is requested. When a node receives an RREQ packet, it checks to see
whether it is the destination or whether it has a route to the destination. If
either case is true, the node generates an RREP packet, which is sent back to
the source along the reverse path. When the source node receives the first
RREP, it can begin sending data to the destination.
Route Maintenance: When a node detects a
broken link while attempting to forward a packet to the next hop, it generates
a RERR packet that is sent to all sources using the broken link. The RERR
packet erases all routes using the link along the way. If a source receives a
RERR packet and a route to the destination is still required, it initiates a
new route discovery process.
1.2 Multipath Routing in MANETs
Standard routing protocols in ad
hoc wireless networks, such as AODV and DSR, are mainly intended to discover a
single route between a source and destination node. Multipath routing consists
of finding multiple routes between a source and destination node.
1.2.1 Route Discovery and Maintenance: Route discovery and route maintenance consists of finding multiple
routes between a source and destination node. Multipath routing protocols can
attempt to find node disjoint, link disjoint, or non-disjoint routes. Node
disjoint routes, also known as totally disjoint routes, have no nodes or links
in common. Link disjoint routes have no links in common, but may have nodes in
common. Non-disjoint routes can have nodes and links in common. From a fault
tolerance perspective, more reliable paths should be selected to reduce the
chance of routes failures. Path selection also plays an important role for QoS
routing. In QoS routing, only a subset of paths that together satisfies the QoS
requirement is selected.
1.2.2 Split Multipath Routing: Split Multipath Routing (SMR) proposed is an on-demand multipath source routing
protocol. SMR is similar to DSR, and is used to construct maximally disjoint
paths. Unlike DSR, intermediate nodes do not keep a route cache, and therefore,
do not reply to RREQs. This is to allow the destination to receive all the
routes so that it can select the maximally disjoint paths. Maximally disjoint
paths have as few links or nodes in common as possible. Duplicate RREQs are not
necessarily discarded.
2. Security Issues in Mobile Ad hoc Network
As the data is
transmitted over the adhoc there is no centralized manager for the adhoc
network, because of this the chances of Intruder attach increase. The Attack
can be in case of Unipath routing or in multipath, Even the topology is dynamic
still it has many flaws in terms of security.
The Intruder attack is
on the algorithmic approach of data transfer.
Some of the common attacks on security are:
1. Attacks using modification- False Sequence number
Malicious nodes can
cause redirection of network traffic and DoS attacks by altering control
message fields. In AODV, any node may divert traffic through itself by advertising
a route to a node with a desti_sequence_num greater than the authentic value.
2. Attacks using modification – False hop counts.
AODV uses the hop count
field to determine a shortest path Malicious nodes can set hop count to zero.
DSR uses source routes in data packets DoS attack can be launched in DSR by
altering the source routes in the packet headers.
3.Attacks using modification tunneling
A tunneling attack is
where two or more nodes may collaborate to encapsulate messages between them.
Traditional Approach of Data Transfer in Unicast Transferring
According to a standard
approach of communication between two nodes it is always based on the shortest
path. The shortest path gives number of benefits like Easy implementation, Fast
and reliable data transfer between nodes. One of the common algorithm for
selecting the path is given below:
Path(A,n)
/* A is the Weighted
graph of n size to represent the Ad hoc Network*/
{
Step 1. Generate the neighbour list for the source node and put it in
the matrix.
Step
2 .Starting from the first neighbour generate the next neighbour.
Step
3. Check if that neighbour already exist in the list if yes than it is a
loopback and go to end;
Step
4. Generate the route from all the neighbours for the destination and
continue on that path.
Step
5. Generate the route to destination from all neighbours where ever possible.
Step
6. Compare the route length generated by all the possible routes. Compare all
the routes in the distance matrix and choose the path to destination which has
the lowest path length.
}
This
approach of data transfer is very common in case of dynamic topology like the
sensor network. But as the intruder
attacks according to the same approach it gives the very high chances of Data
hack.
In this diagram, there
are number of possible paths and as a reliable and fastest path , the client
will always select the shortest path .But this approach has some problems based
on security and reliability. Some of them are as follows:
1. Select One Shortest
path
- Use of wireless
links in shortest path susceptible to link attacks
- Relatively poor
protection as in Battlefields.
- Passive
eavesdropping
- Attacks from
compromised attacks.
2. Multi Path
- Flooding:
As an incoming packet is sent on all incoming links,it limit the number of
hops to avoid infinite loops or forward packets only once using a packet
ID or only on selected links in the right direction
- Multicasting:
Terribly expensive in terms of resource utilization and results in minimum
delay
We are suggesting the alternate path approach
that is close to the shortest path and more reliable and secure.
Security Requirements of Mobile Ad-Hoc Network
Requirements of Ad-Hoc
Network are:
• Route signalling
can’t be spoofed
• Fabricated routing
messages can’t be injected into the network
• Routing messages
can’t be altered in transit
• Routing loops can’t
be formed by through malicious action
• Routes can’t be
redirected from the shortest path by malicious action
• Unauthorized nodes
should be excluded from route computation and discovery.
Path A to B
/* A is the Adjacency
matrix representation of given network, n is the no of nodes and a,b are two
nodes between we have to transfer data*/
Step 1. Give the range
of the network node and set all other elements that are outside the range to 0.
Step 2. Find the
Neighbour of Each node of network starting from node a to node b.
Step 3.Find the
shortest path from source to destination and store it in an array called array[
].
Step 4. Search the neighbour
list and pick a random node from the list and put that node in the array.
Step 5. Compare the
random node with all the elements of the shortest path array. If the array[top]
element matches with any of the elements in the list then Make the entry
corresponding to that node in neighbour array.
Step 6. Compare the neighbour
list of the generated node with all the elements of array otherwise pick a
random node from the list and put it in the array
}
Finally we get the list
of nodes that provide a safe path in case of unicast, this pass is very closer
to the shortest path but does not include any node from the shortest path list
because of this it provide the secure transmission on the algorithm
implementation attack of the Intruder.
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