IT6601 Mobile Computing Unit IV

IT6601 – MOBILE
COMPUTING
UNIT – IV
Mobile Ad-Hoc
Networks
KAVIYA P
Assistant Professor
Kamaraj College of Engineering &
Technology

Ad-Hoc Basic Concepts
• Temporary or ad-hoc networks that are established and maintained on
the fly and work without the support of any form of fixed infrastructure
such as base station, are known as Mobile Ad-Hoc NETworks (MANETs).
• Self-configuring networks set up among the hand-held devices of
mobile users.

How is an Ad Hoc network Set
up without the
Infrastructure Support?
• Mobile device can communicate with each other in
absence of any form of fixed networking
infrastructure such as hubs, routers, base station etc.
• A network can be established through cooperation
among the devices themselves.
• A mobile device wanting to communicate can forward
its packet to its neighbours and the neighbours nodes
in turn can forward those to their neighbours , and so
on until the destination is reached.

A schematic model of a Mobile
Ad-Hoc Network

Why is Routing in a MANET a
complex Task?• In an ad hoc network, such as simple and efficient routing protocol is
difficult to deploy.
• First it is very difficult to have a global identifier assigned a to every
node that would also indicate route to the node.
• This is because the nodes keep on moving and the identity would also
have to change, which would incur an inordinately large overhead.
• If a route between a pair of nodes is somehow determined, routes
become quickly obsolete since they dynamically get built and also get
dissolved.
• Suppose the route has already been determined between a source and
destination and packets are getting transmitted on this route.
• Some nodes forming this route may move away even as the packets
are getting transmitted, thus disrupting the communication.

Why is Routing in a MANET a
complex Task?
• In a nutshell, in a MANET
• Frequent topology changes
• Node failure
• Link breakages
• Depletion of battery energy

Characteristics of
Mobile Ad-Hoc
Networks

Characteristics of Mobile Ad-Hoc
Networks
• Important characteristics of MANETs are described below:
• Lack of fixed infrastructure
 It is the most distinguishing characteristic of a MANET.
 In the absence of any fixed networking infrastructure, a
pair of nodes can either communicate directly when they
are in transmission range of each other or they can
communicate using a multi-hop communication.
 Based on this characteristic alone, Cellular networks and
wireless LANs cannot be considered to be MANETs.

Networks
• Dynamic topologies
The devices in the MANET are allowed to move
arbitrarily, the network topology can change
unpredictably.
The rate of topology change depends on the
speed of movement of the mobile devices.
The speed of movement of a mobile device can
vary greatly with the time of the day and the
specific MANET application being considered.

Networks
• Bandwidth constrained, variable capacity links
Wireless links have lower capacity.
Factors such as fading, noise, and
interference can change the available bandwidth
of wireless link.
Consequently, the bandwidth of a link can change
arbitrarily with time.

Networks
• Energy constrained operation
 The nodes in a MANET rely on battery power.
 Batteries are small and can store very limited
amounts of energy.
 Transmissions and processing required during
routing involve expenditure of substantial amount of
energy causing the batteries to get rapidly drained
out, unless the routing protocol is carefully designed.
 Therefore, energy conservation is usually considered
to be an important objective of MANET routing
protocols.

Networks
• Increased vulnerability
 MANETs are prone to many new types of security
threats.
 These threats arise due to the underlying wireless
transmissions and the deployment of collaborative
routing techniques.
 There are increased possibilities of eavesdropping,
spoofing, denial-of-service attacks.
 Further, it is very difficult to identify the attacker since
the devices keep moving and do not have a global
identifier.
 Nodes are vulnerable to capture and compromise.

Networks

Applications of Mobile
Ad-Hoc Networks

Applications of Mobile Ad-Hoc
Networks

Applications of Mobile Ad-Hoc
Networks
• Emergency Applications
• It can be used immediately after any natural disaster Tsunami,
earth quake, floods, etc.
• Wired network will get damaged after disasters.
• To immediately create a connectivity to all affected regions of
disaster, for the purpose of rescue work, a network is needed.
• It is not possible to restore the damaged wired network.
• So, ad-hoc networks are the only solution here.

Design Issues &
Routing in Ad-Hoc
Networks

MANET Design Issues
• Network Size and Node density
• Network and node density are the two important parameters of
MANET.
• Network and node density need to be considered while designing
an appropriate routing protocol for a network.
• Network size refers to the geographical coverage area of the
network.
• Network density refers to the number of nodes present per unit
geographical area.
• For large area networks , clustering is essential to keep the
communication overheads low.
• The cluster size as well as a specific clustering solution for
network would , to large extent , depends on node density.

MANET Design Issues
• Connectivity
• The term connectivity of a node usually refers to neighbours it
has.
• Here a neighbour of a node is one that is in its transmission
range.
• The term connectivity between two nodes is also sometimes
used to refer to a link between the to nodes.
• The term link capacity denotes the bandwidth of the link.
• In a MANET , both the number of neighbouring nodes and the
capacities of the links to different neighbours may vary
significantly.

MANET Design Issues
• Network topology
• The topology of a network denotes the connectivity among the
various nodes of the network.
• Mobility of the nodes affects the network topology.
• Due to node mobility ,new links can form and some links may
get dissolved.
• Other than mobility , nodes can become inoperative due to
• discharged batteries or
• hardware failure
and thereby causing changes to the topology.
• The rate at which the topology changes need to be
appropriately considered in the design of an effective network.

MANET Design Issues
• User traffic
• The design of a MANET is carried out primarily based on the
• anticipated node density.
• average rate of node movements.
• the expected traffic.
• The traffic in a network can be of various types.
• A network protocol should leverage the characteristics of
specific traffic types that are expected to improve the
performance.
• The common traffic types are the following
• Bursty traffic.
• Large packet sent periodically.
• Combination of the above two types of traffic.

MANET Design Issues
• Operational environment
• The operational environment of a mobile network is usually
either urban , rural and maritime.
• These operational environment supports the line of sight(LOS)
communication.
• But , there can be significant difference in the node density
and mobility values in different operational environments ,
requiring different design of mobile network suit an
operational environment.

MANET Design Issues
• Energy constraint
• No fixed infrastructure exist in MANET.
• The mobile node themselves store and forward packets.
• This additional role of mobile nodes as routers lead to nodes
incurring perennial routing related workload and this
consequently results in continual battery draining.
• Though this overhead is indispensable if the network is to be
kept operational, the energy spent can be substantially
reduced by allowing the nodes to go into a sleep mode
whenever possible.

Routing
• Packet routing is usually a much more complex task in an ad hoc
network compared to that in an infrastructure based network.
• Main complications arise on account of continual topology changes and
limited battery power of the nodes.
• The purpose of routing is to find the best path between the source and
the destination for forwarding packets in any store and forward network.
• In a traditional network , routing is a relatively easy task because the
routes to nodes can be uniquely and efficiently identified based on the
subnet structure encoded in IP.
• In a MANET, the nodes Making up a route may themselves move or
shutdown down to low battery energy, in the process making the
knowledge about routes at various nodes to quickly become obsolete.
• It is therefore necessary to find a new route each time a node needs to
transmit a message, making routing an expensive and difficult task.

Routing
Based on the above discussions,
•Traditional routing protocols would not be suitable in an ad hoc network.
•Each node in an ad hoc network needs to have routing capability and
also needs to participate in routing to keep the network operational.
Whenever there is an incoming packet in a MANET:
(a) Forward the packet to the next node(hop).
(b) While forwarding the packet, the sender needs to ensure that:
(i) The packet move towards its destination.
(ii) The number of hops/path length is minimized.
(iii) Delay is minimized.
(iv) The packet loss is minimized.
(v) The packet does not move around the network endlessly.

Routing
• Several types of routing protocols have been proposed for
MANETs.
• Different routing protocols essentially implement the above
steps(a) and (b) while meeting the constraints inherent to the
network, such as low energy consumption, through the
deployment of various techniques.

Essentials of
Traditional Routing
Protocols

Essentials of Traditional Routing
Protocols
• The two important classes of routing protocols for traditional
networks are the link state and the distance vector.
• Both are extremely popular in packet-switched networks.
• The shortest path is computed according to some specific cost
metric such as the number of hops in the route.

Approaches to Shortest Path
Routing
1. Link State Routing or Link State Protocol (LSP)
•Each node knows the distance to its neighbors.
•The distance information (=link state) is broadcast to all nodes in
the network.
•Each node calculates the routing tables independently.
2. Distance Vector Routing
•Each node knows the distance (=cost) to its directly connected
neighbors.
•A node sends a list to its neighbors with the current distances to
all nodes.
•If all nodes update their distances, the routing tables eventually
converge.

Link State Routing
• Each node must
• discover its neighbors.
• measure the delay (=cost) to its neighbors.
• broadcast a packet with this information to all other nodes.
• compute the shortest paths to every other router.
• The broadcast can be accomplished by flooding.
• The shortest paths can be computer with Dijkstra’s algorithm.

Link State Routing – Basic
principles
1. Each router establishes a relationship (“adjacency”) with its
neighbors.
2.Each router generates link state advertisements (LSAs) which are
distributed to all routers. The LSA contains
• The identity of the router originating the message
• The identities of all neighbors.
• LSA = (link id, state of the link, cost, neighbors of the link)
3. Each router maintains a database of all received LSAs
(topological database or link state database), which describes the
network has a graph with weighted edges.
4. Each router uses its link state database to run a shortest path
algorithm (Dijikstra’s algorithm) to produce the shortest path to
each network.

A router is connected to other routers
through links

Link State Routing – Properties
• Each node requires complete topology information.
• Link state information must be flooded to all nodes.
• All routers which are connected to the router added to the tree or
in the candidate list.
• The delay in the candidate list to every other router in the tree are
compared
• The shortest delay is moved in to the tree and attached to
appropriate neighbor router and removed from the candidate list.
• The above steps are repeated till there are no more routers left in
the candidate list.
• The network topology has been determined in the form of a
shortest path tree a router forms its routing table and uses it to
find the best route to any destination.

Operation of a Link State
Routing Protocol

Advantages & Disadvantages
Advantages
•Builds a topological map –Full knowledge of the network.
•Fast convergence –Floods LSPs immediately.
•Event-driven updates –LSP sent when there is a change, only
contains information regarding the affected link.
•Hierarchical design –Areas can be used to separate routing traffic.
Disadvantages
•Significant demands on memory and processing resources.
•Requires very strict network design.
•Requires a knowledgeable network administrator.
•Initial flooding can impede network performance.

Distance Vector Routing
• The term vector means that routes are advertised as vector (distance,
direction)Each node maintains two tables:
• Distance is the number of hops between the two nodes and direction is defined
in terms of the next hop router to which the packets need to be forwarded.
• The distance vector protocols are based on well known Bellman-Ford
algorithm.
• The protocol share everything in the network with neighbors by broadcasting
the entire router table.
• Router updates its own routing table by examining the received information
and in turn informs its own neighbors of the changes, called ‘routing by rumor’
• The router do not have knowledge of the entire path, just know the following
vector
• Direction in which a packet should be forwarded.
• Its own distance form the destination.
• The two popular DV routing protocol are RIP(Routing Information Protocol) and
IGRP(Interior Gateway Routing Protocol).

Advantages & Disadvantages
Advantages
•Simple implementation and maintenance.
•Low resource requirements (memory, CPU).
Disadvantages
•Slow convergence (periodic updates).
•Limited scalability.
•Routing loops (due to slow convergence).

Routing in MANET Vs - Traditional
Networks
The three important ways in which a MANET routing protocol
differs from routing of packets in traditional networks.
•In MANET each node act as a router, whereas ordinary nodes in a
traditional wired network do not participate in routing the packets.
•In MANET the topology is dynamic because of the mobility of the
routing, the routing table become obsolete and routing process
complicated.
•In the simple IP based addressing scheme deployed in wired
networks, the IP address encapsulated in the subnet structures
does not work because of node mobility.
•To cope with the above three impermanent differences, MANET
need to carryout route discovery and route maintenance.

Types of communications
The node initiate the following types of communication.
•Unicast: The message is sent to a single destination node.
•Multicast: The message is sent to a selected subset of the
network nodes.
•Broadcast: The message is sent to all node in the network. Since
unrestrained broadcast can choke a MANET, applications usually
do not use broad cast.

A Classification of Unicast Routing
Protocols

Protocols• Proactive protocols
• Traditional distributed shortest-path protocols
• Maintain routes between every host pair at all times
• Based on periodic updates; High routing overhead
• Little or no delay for route determination
• Consume bandwidth to keep routes up-to-date
• Maintain routes which may never be used
• Example: DSDV (destination sequenced distance vector)
• Reactive protocols
• Determine route if and when needed
• Source initiates route discovery
• Example: DSR (dynamic source routing)
• Lower overhead since routes are determined on demand
• Significant delay in route determination
• Employ flooding (global search)
• Control traffic may be bursty

Protocols
• Hybrid protocols
• Adaptive; Combination of proactive and reactive
• Combine the good features of both the protocols
• To achieve increased scalability by allowing nodes with close proximity to
work together to form some sort of backbone to reduce the route discovery
overheads. – Proactive Routing
• Route discovery strategy - Determining routes to far away nodes
• Example : ZRP (zone routing protocol)

Destination Sequence Distance
Vector Routing Protocol (DSDV)
• DSDV is based on the table driven (Proactive) approach to packet
routing, it extends the distance vector protocol of wired networks
(Bellman-Foard routing algorithm).
• Improvement made is the avoidance of routing loops through the use of
sequence number scheme.
• Each node maintains information regarding routes to all the known
destinations. The routing information updated periodically.
• Full Update or full dump: Send all routing information from own table.
• Incremental Update: Send only entries that has changed. (Make it fit
into one single packet)
• This can be considered shortcoming – traffic overhead and maintain
routes which they may not use.

• Steps in DSDV
• Each router (node) in network collects route information from
all its neighbours .
• The node finds shortest path to destination based on gathered
information .
• A new routing table is generated based on gathered
information .
• Router broadcasts this table to neighbours for updating .
• This process continues till routing information is stable.

• Sequence number: originated from destination. Ensures loop
freeness.
• Install Time: when entry was made (used to delete stale entries
from table)

Dynamic Source Routing (DSR)
• DSR is a source initiated on-demand (or reactive) routing protocol for ad
hoc networks.
• It uses source routing technique in which sender of a packet determines
the complete sequence of nodes through which a packet has to travel.
• The sender of the packet then explicitly records this list of all nodes in
the packet’s header.
• Not exchange the routing table information periodically
• Each mobile node in the protocol maintains a routing cache – which
contains the list of all routes that the node has learnt and maintains a
sequence counter called request id to uniquely identify the last
request it had generated.
• DSR works in two phases:
I. Route discovery
II. Route maintenance

Dynamic Source Routing (DSR)
• Route discovery
• First checks its own routing cache. If there is a valid route, sends the
packet other wise
• It initiate the route discovery by route request
• The route request packet initiates a route reply by the destination
node or by an intermediate node that knows a route to the
destination.
• Route maintenance
• Route maintenance is the process of monitoring the correct operation
of a route in use and taking the corrective action when needed.
• As soon as the source receives the RouteError message, it deletes the
broken-link-route from its cache.
• If it had another route to the destination, it starts to retransmits the
packets using alternative route otherwise it intimates the route
discovery process again.

Multicast Routing Protocols for
MANET• Multicast is the delivery of a message to a group of
destination nodes in a single transmission as shown in figure.
• Providing Efficient bandwidth, Reducing communication cost,
Efficient delivery of data, Supporting dynamic topology Multiple
unicast.
• Minimizing network load, Providing basic support for reliable
transmission, Designing optimal routes, Providing robustness,
efficiency, and adaptability.
• There are two main categories of multicast routing
protocols: Tree-based protocols, and Mesh-based protocols.

Multicast Routing Protocols for
MANET• Tree-based protocols: Establish a single path between any
two nodes in the multicast group. Minimum number of copies
per packet to be sent in the tree. Bandwidth efficient .
• Example: Multicast Ad hoc On-Demand Distance Vector (MAODV)
routing protocol
• Mesh-based protocols: Establish a mesh of paths that
connect the sources and destinations. They are more
resilient to link failures as well as to mobility.
• Drawback – Multiple copies of the same packet are
disseminated through the mesh., resulting in reduced packet
delivery and increased overhead under highly mobilized
conditions.
• Example: On-Demand Multicast Routing Protocol (ODMRP)

Vehicular Ad Hoc networks(VANET)
• VANET is a special type of MANET in which moving automobiles
from the nodes of the network
• Vehicle can communicate with other vehicle that are within a
range of about 100 to 300 meters – Multi- hop communication.
• Any vehicle that goes out of the signal range in the network
excluded from the network.
• A vehicle come in the range of a vehicles of a VANET can come in
the range can join the network.
• A VANET can offer a significant utility value to a motorist.
• It can help drivers to get information and warnings from a nearby
environment via message exchange.
• It can help disseminate geographical information to drivers as he
continues to drive.

Vehicular Ad Hoc networks(VANET)
• The driver can get road condition ahead or a warning about the application
of emergency electronic brake by a vehicle ahead in the lane.
• Drivers may have the opportunity to engage in other leisurely tasks, VoIP
with family, watch news and participate in an office video conference etc.
• Two vehicles are involved in a collision. The trailing vehicle get advance
notification of the collision ahead on the road. The scenario shown in figure.

MANET Vs VANET
MANET VANET
A mobile ad-hoc network (MANET)
is a self-configuring
infrastructure- less network of
mobile devices connected by
wireless.
Vehicular Ad hoc Network (VANET)
is a subclass of mobile Ad Hoc
networks (MANETs).
Each device in a MANET is free to
move independently in any
direction, and will therefore
change its links to other devices
frequently.
These networks have no fixed
infrastructure and instead rely
on the vehicles themselves to
provide network functionality.
Dynamic topologies
• variable capacity links
• Energy constrained operation
• Limited physical security
The very high speed of the
nodes.
Vehicles that are not subjected
to the strict energy, space and

Security issues in MANETs
MANETs are much more vulnerable to attack than wired network. This is because of the
following reasons :
•Open Medium - Eavesdropping is more easier than in wired network.
•Dynamically Changing Network Topology – Mobile Nodes comes and goes from the
network, thereby allowing any malicious node to join the network without being detected.
•Cooperative Algorithms - The routing algorithm of MANETs requires mutual trust
between nodes which violates the principles of Network Security.
•Lack of Centralized Monitoring - Absence of any centralized infrastructure prohibits
any monitoring agent in the system.
•Lack of Clear Line of Defense
The important characteristics of ad hoc networks that can be exploited to cause security
vulnerabilities
•Lack of physical boundary – difficult to deploy firewalls or monitor the incoming traffic.
•Low power RF transmission – signal jamming lead to denial of service(DoS) attack
•Limited computational capabilities - Inability to encrypt messages – spoofing and
routing attacks.
•Limited power supply – attacker attempt exhaust batteries.

Characteristics of secure ad hoc
networksA secure ad hoc network should have the following characteristics:
•Availability – able to survive denial of service(DOS).
•Confidentiality - Prevent unauthorized users to access
confidential information.
•Integrity - no tampering of transmitted messages.
•Authentication – Guarantee about the true identity of peer node.
• Non-repudiation- Should ensure that a node having sent a
message can not deny it.

Attacks on Ad Hoc Networks
• MANET attacks are classified into passive and active attacks.
• Passive attacks:
• Target to monitor and steal the data exchanged in the network without
disrupting the network operations.
• Very difficult to identify since these do not have any perceivable symptoms.
• Can be reduced by using suitable encryption techniques.
• Active attacks:
• Destructive and disturbs the normal functionality of the network.
Passive
attacks
Active
attacks
Snooping,
eavesdroppi
ng, traffic
analysis,
monitoring
Wormhole,
black hole,
grey hole,
resource
consumption
, routing
attacks
Layer Attacks
Application
Layer
Malicious code, repudiation, data corruption
Transport Layer Session hijacking, SYN flooding
Network Layer Wormhole, black hole, fabrication attack, grey
hole
Data link layer Resource consumption
Physical layer Traffic analysis, monitoring, disruption,
jamming, interceptions, eavesdropping

• Routing loop
• By sending tampered routing packets, an attacker can create a routing
loop.
• Data packets being sent endlessly, consuming bandwidth and causing
dissipation of power for a number of nodes.
• As a result, the packets are prevented from reaching their intended
recipients.
• Type of Denial-of-service (DoS) attack.
• Malicious code attack
• A malicious code can be a virus, worm, spyware, or a Trojan.
• An attacker can propagate malicious code and can slow down the
nodes, overload the network, or even crash the nodes.
• Repudiation attack
• Refers to the denial of participation in a communication.
• A malicious user can deny a credit card or bank transaction.

• SYN flooding attack
• An attacker creates a large number of half-opened TCP connections with the
victim nodes by sending a large number of SYN packets to them.
• This causes the victim nodes to overflow.
• Session hijacking
• The attacker can spoof the IP address of a node that has just started a
session and hijack the session from the victim and perform a DoS attack.
• Fabrication attack
• A malicious node sends a false route error message to the packet to the
sender, even when the next hop link is not broken.
• Black hole
• A node can set up a route to some destination via itself, and when the
actual data packets are received from other nodes are simply
dropped.
• This node forms a black hole, to which data packets enter but never
leave.

• Grey hole
• Special case of black hole attack.
• The attackers selectively drops some kinds of packets that pass through it.
• More difficult to detect this attack.
• Partitioning
• The attacker partitions a network by causing some nodes to spilt up from the
other nodes.
• One set of nodes is not able to communicate with other set of nodes.
• By analyzing the network topology the attacker can choose to make the
partitioning between the set of nodes that causes the most harm to the system.
• Blacklist
• This attack tries to exploit a loophole in security mechanisms.
• Keeping a list of perceived malicious node to tackle this problem.
• Each node has a blacklist of bad nodes and thereby avoids using them when
setting up routing paths.
• An attacker might try to get a good node blacklisted, causing the other
good nodes to add this node to their respective blacklists and so avoid it.

• Wormhole
• A direct link (tunnel) between the two nodes is established. – wormhole link
• Through the wormhole link, one node eavesdrops messages at one end,
and tunnels them through the wormhole link to the other node which then
replays them.
• The tunnel essentially emulates a shorter route through the network
and so naïve nodes prefer to use it rather than the alternative longer routes.
• Once a wormhole is established, a malicious node an use it for traffic
analysis or make a denial-of-service attack by dropping certain data
or control packets.
• Dropping routing traffic
• In an Ad-Hoc network, all nodes participate in the routing process.
• A node may act selfishly and process only the routing information
that is related to itself either maliciously or to conserve energy.
• This attack can create network instability or can even segment the
network.

Security Attack
Countermeasures
Layer Attacks
Data link layer Use of spread spectrum transmission and
directional antennae.
Network Layer Use of authentication measures and keeping track
of the trust nodes.
Transport Layer Securing and authenticating end-to-end
communications through data encryption
techniques.
Application
Layer
Detection and prevention of virus, worms,
malicious code through code analysis.

IT6601 Mobile Computing Unit IV

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IT6601 Mobile Computing Unit IV