adhoc final
DESCRIPTION
Adhoc FinalTRANSCRIPT
1. INTRODUCTION
In computer networking, an Ad Hoc Network refers to a network connection established for a
single session and does not require a router or a wireless base station.Mobile nodes that are
within each other's radio range communicate directly via wireless links that. Here mobile
nodes are cause the di erent topology in the networks.
FIG 1.1 RADIO STATION
In the above diagram nodes A and D have direct connection between them. In the rst radio
station shows that in same radio stations both A and D are directly connected. But as the
show in the second radio station, when nodes d are goes away from the these station the
connection link was broken between them. But still A and D are connected via nodes A-B-C-
D. So this type of networks connections is held in ad hoc networks. So it is widely used in the
military application and other temporary networks. For example, military units (e.g., soldiers,
tanks, or planes), equipped with wireless communication devices, could form an ad hoc
network when they roam in a battle eld. Ad hoc networks can also be used for emergency,
law enforcement, and rescue missions.
1.1 Characteristics
Operating without a central coordinator
Multi-hop radio relaying
Frequent link breakage due to mobile nodes
Constraint resources (bandwidth, computing power, battery lifetime)
Instant deployment
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1.2 Applications
Military applications
Collaborative computing
Emergency rescue
Mesh networks
Wireless sensor networks
Multi-hop cellular networks
Wireless Community Network
1.3 Major Issues and Challenges
Hidden terminal problem
Exposed terminal problem
Channel e ciency
Access delay and fairness
Di erential service
Realistic mobility modeling
power-aware routing
Constructing virtual backbone
Distinguish contention, packet drop, and noise errors
Security
E cient multicasting
1.4 Ad Hoc versus Infrastructure based Networks
In infrastructure based Networks , communication typically takes place only between the
wireless nodes and the access point , but not directly between the wireless nodes.
Infrastructure Networks contain special nodes called access points(APs), which are con-
nected via existing networks. APs are special in the sense that they can interact with wireless
nodes as well as with the existing wired network. The other wireless nodes , also known as
mobile stations , communicate via APs. The APs also act as bridges with other networks. Ad
hoc LANs do not need any xed infrastructure. These networks can be set up on the y at any
place. Nodes communicate directly with each other or forward messages through other nodes
that are directly accessible. The design of infrastructure based networks is simpler because
most of the network functionality lies within the access point ,whereas the client can remain
quite simple. In Ad hoc networks, the complexity of each node is higher because every node
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has to implement medium access mechanisms to provide certain quality of service.
Infrastructure based networks lose some of the exibility which wireless networks can o er.
They cannot be used for disaster relief in cases where no infrastructure is left, where ad hoc
networks can be used.
2. ARCHITECTURE OF AD HOC NETWORK
The architecture of ad hoc network can be explained by IEEE 802.11 standards.
2.1 IEE 802.11
IEEE 802.11 is a set of IEEE standards that govern wireless networking transmission
methods.
2.1.1 History
802.11 technology has its origins in a 1985 ruling by the U.S. Federal Communications
Commission that released the ISM band for unlicensed use. In 1991 NCR Corporation (now
Alcatel-Lucent and LSI Corporation) invented the precursor to 802.11 in Nieuwegein, The
Netherlands. The inventors initially intended to use the technology for cashier systems; the
rst wireless products were brought on the market under the name WaveLAN with raw data
rates of 1 Mbit/s and 2 Mbit/s. Vic Hayes, who held the chair of IEEE 802.11 for 10 years
and has been called the "father of Wi-Fi" was involved in designing the initial 802.11b and
802.11a standards within the IEEE. In 1992, the Commonwealth Scienti c and Industrial
Research Organisation (CSIRO) obtained a patent in Australia for a method of wireless data
transfer technology based on the use of Fourier transforms to "unsmear" the signal. In 1996,
CSIRO obtained a patent for the same technology in the US. In April 2009, 14 tech
companies selling Wi-Fi devices, including Dell, HP, Microsoft, Intel, Nintendo, and
Toshiba, agreed to pay CSIRO 250 dollors million for infringements on the CSIRO patents .
Mobile terminals can operate in two modes under IEEE 802.11 :
Infrastructure Mode
Ad Hoc Mode
2.2 Ad Hoc Mode
IEEE 802.11 only covers PHY layer and MAC layer
PHY layer is subdivided into
Physical Layer Convergence Protocol (PLCP)
Physical Medium Dependent sub layer (PMD)
PHY management include channel tuning and responsible for higher layer functions (e.g. 3
control of bridging). MAC management controls authentication mechanism and power man-
agement to save battery power.
2.2.1 Medium Access Control Layer
The basic servies provided by the MAC layer are the mandatory "Asynchronous data service"
and an optional "Time bounded service". while 802.11 only o ers the Asynchronous data
service in ad-hoc mode,both service types can be o ered using an Infrastructure based
network. The following three mechanisms for IEEE 802.11 : The mandatory basic method
based on a version of CSMA/CA, an optional method avoiding the hidden terminal
problem,and nally a contention free polling method for time bounded service. The rst two
methods are also summarized as "Ditributed Coordination Function(DCF)", the third method
is called "Point Coordination Function(PCF)". The MAC Mechanisms are also called
"Distributed Foundation Wireless Medium Access Control(DFWMAC)".
2.2.2 Basic DFWMAC-DCF using CSMA/CA
The mandatory access mechanism of IEE 802.11 is based on Carrier Sense Multiple Access
with Collision Avoidance(CSMA/CA) ,which is random access scheme with carrier sense
and collision avoidance through random backo . The basic CSMA/CA mechanism shown in
gure 2.1:
FIGURE 2.1: COTENTION WINDOW AND WAITING TIME
If medium is idle for at least the duration of DIFS , a node can access the medium at
once.This allows for short access delay under light load. If medium is busy , nodes have to
wait for the duration of DIFS , entering a contention phase afterwards. Each node now choose
a random back o time within a contention window and delays medium access for this random
amount of time. The node cntinues to sense the medium. As soon as a node senses the
channel is busy , it has lost this cycle and has to wait for the next chance. But if the
randomized additional waiting time for a node is over and the medium is still idle ,the node
can access the medium immediately. The basic CSMA/CA mechanism is not
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fair.Independent of the overall time a node has already waited for transmission;each node has
the same chances for transmitting data in the next cycle.To provide fairness , IEEE 802.11
adds back o timer. Each node selects random amount of waiting time within the range of
contention window. If certain station does not get access to the medium in rst cycle, it stops
its back o timer , waits for the channel to be idle again for DIFS and starts the counter again.
As soon as the counter expires, the node accesses medium. This means that de ered stations
do not choose a randomized backo time again, but continue to countdown. Stations that have
waited longer have the advantage over stations that have just en-tered,in that they only have
to wait for the remainder of their backo timer from the previous cycle.
2.2.3 DFWMAC-DCF with RTS/CTS
Hidden terminal problem may occur in 802.11, if one station can receive two others, but
those cannot receive each other. To deal with this problem, mechanism using two control
packets , RTS and CTS. After waiting for DIFS , the sender can issue a request to send (RTS)
control packet. Every node receiving this RTS now has to set its net allocation vector (NAV)
in accor-dance with the duration eld The NAV than speci es earliest point at which the station
can try to access the medium. If the receiver receives the RTS , it answers with the clear to send
(CTS) waiting for SIFS.
This CTS packet contains duration eld and receivers have to adjust their NAV. Now all
nodes within receiving distance around sender and receiver are informed that they have to
wait more time before accessing the medium. This mechanism reserves the medium for one
sender exclusively. It is also called a Virtual Reservation Scheme.
3. ROUTING IN AD-HOC NETWORKS
3.1 Requirement of the Routing
It should be fully distributed, as centralized routing involves high control
overhead and hence is not scalable. Distributed routing is more fault-tolerant than
centralized routing, which involves the risk of single point of failure.
It must be adaptive to frequent topology changes caused by the mobility of nodes.
It must be localized, as global state maintenance involves a huge state propagation
control overhead.
It must be loop-free and free from stale routes.
It must converge to optimal routes once the network topology becomes stable. The
convergence must be quick.
It must optimally use scare resources such as bandwidth, computing power,
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memory and battery power.
It should be able to provide a certain level of quality of service (Qos) as demanded
by the applications,and should also o er support for time-sensitive tra c.
The ooding must be less.
3.2 General Issues for Ad Hoc Network Routing
Secure delivery and the capability to handle constant connectivity are the most important
issues for routing protocols in wireless mobile ad hoc networks. Once the path will establish
between the source end destination, the source will send message to the destination without
worried.If the connectivity of any two nodes changes and routes are a ected by this change,
the routing protocol should be able to recover if an alternate path exists.
There are some other issues related to routing in wireless ad hoc networks. For example:
overhead is particularly important in a wireless network with limited bandwidth.
Power consumption may also be a problem in an ad hoc network with battery-
powered nodes.
Quality of service may be required in an ad hoc network supporting delay
sensitive applications such as video conferencing .
A routing protocol may need to balance tra c based on the tra c load on links.
Scalability of routing protocols is an important issue for large networks .
The routing protocol may need to implement security to protect against attacks, such as sni
er, man-in-the-middle. Routing protocols may rely on information based on other layers. For
example, the Global Positioning System (GPS) can be used in wireless ad hoc networks
deployed in battle elds or connecting vehicles. Mobility prediction can improve routing in
wireless networks with known movement patterns, such as the IRIDIUM system satellite
network . Information from the medium access control layer may be propagated to the
network layer so that neighbours can be detected via MAC layer protocols. The power of
received signals from a neighbouring node can be used to decide whether neighbour is
moving closer or further away .
4. ROUTING PROTOCOLS
4.1 Classification
Routing protocols for ad hoc wireless networks can be classi ed into several types based on di
erent criteria. The routing protocols for ad hoc wireless networks can be broadly classi ed
into four categories base on :-
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� Routing Information update mechanism
� Use of Temporal information for routing
� Routing Topology
� Utilization of speci c resources
4.1.1 Based on the routing information update mechanism.
� Proactive or table-driven routing protocols
� Reactive or on demand routing protocols
� Hybrid routing protocols
4.1.2 Based on the use of Temporal information for Routing
Since ad hoc wireless networks are highly dynamic and path breaks are much more frequent
than in wired networks, the use of temporal information regarding the lifetime of the wireless
links and the lifetime of the path selected assumes signi cance.
Routing protocols using past temporal information
Routing protocols that use future temporal information
4.1.3 Based on Routing Topology
Routing topology being used in the Internet is hierarchical in order to reduce the state
information maintain at the core routers.
Flat topology routing protocols
Hierarchical topology routing protocols
4.1.4 Based on the Utilization of speci c Resources
� Power aware routing
� Geographical information assisted routing
4.2 Proactive or table-driven routing protocols
These protocols are extension of the wired network routing protocols. They maintain the
global topology information in the form of the tables at every node. These tables are updated
frequently in order to maintain consistent and accurate network state information. The
distance-vector routing protocol (DSDV),wireless routing protocol (WRP),source-tree
adaptive routing protocol (STAR),and cluster-head gateway switch routing protocol (CGSR)
are some example for the protocols that belong to this category.
4.2.1 Destination sequenced distance-vector protocol
This protocol also called as the DSDV routing protocol. It is the enhanced version of the
distributed Bellman-Ford algorithm where each node maintains a table that contains the
shortest distance and the rst node on the shortest path to every other node in the network. It
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incorporate table update with increasing sequence number tag to prevent loops, to counter to
the count-to-in nity problem, and for faster convergences. As describe this is the table driven
so that at nite interval the tables of the each node exchange to update and which are reachable
from all the nodes. If the topologies of the network are change then all tables are forwarded
to their neighbor. Here in the table updating, we have two types:- One is the full dump in
which done either when the local topology changed signi cantly or when a more incremental
change required in the table. Second is the incremental update in which node does not
observe change in the topology. Here one example is given for table updating and node table
creation.
FIGURE 4.1: DSDV PROTOCOL
Desination Next Hop Distance
A A 0
B B 1
C C 1
D D 1
E D 2
F D 2
TABLE 4.1: ROUTING TABLE OF DSDV PROTOCOL
Here consider the example, here node A is the source node and F is the destination node.
Here in the table rst Column is destination node which is all nodes in the network. Second
Column is the next node in the shortest path to the source path. Third column is the distance
between two nodes- source to destination. And fourth column is the sequence number of each
packet to be received by them. Here routing table for node A is indicating that the shortest
path to the destination node F is available through node D and the distance to it is two. And
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the packets to be received at that place which has number as shown in table. If any link
between two node is broken then the distance is assign in nite to that node and update the all
node's routing table.
Advantages
The availability of the routers to all destination at all times implies that much less
delay is involved in the route setup process.
The mechanism of incremental updates with sequence number tags makes the
existing wired network protocol adaptable to ad hoc networks. Hence wired
network protocol can be applied to the ad hoc network by less modi cation.
Disadvantages
A small network with high mobility or a large network with low mobility can
completely choke the available bandwidth. Hence this protocol su ers from excessive
control overhead that is proportional to the number of nodes in the network.
In order to obtain information about a particular destination node, a node has to wait
for a table update message initiated by the same destination node.
4.2.2 Wireless routing protocol
The WRP protocols is the basically same as the DSDV protocols, but it is di er from it only in
the their routing protocol. The routing table contain the up-to-date view of the network for
the network for all known destination. The routing table keeps the shortest distance, the
predecessor node and ag indicating the status of the path. The path status may be a simple
path(correct) ,or a loop(error) ,or the destination node not marked(null). The LTC(Link cost
table) contain the cost of relaying message through each link. The MRL(Message
transmission list) contains an entry for the every update message that is to be retransmitted
and maintain the counter for the each entry. When a node detects a link break, it sends an
update message to its all neighbors with the link cost is in nite (?). And that all neighbors nd
the alternate path to reach the destination and resend the message.
Advantages
� It is the faster convergence and involves fewer table updates.
Disadvantages
Complexity of maintenance of multiple tables demands a larger memory and
greater processing power from the nodes.
At the high mobility, the control overhead involved in updating table entries is
almost the same as DSDV. So it is not suitable for highly dynamic and also for
very large ad hoc networks.
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4.2.3 Cluster head Gateway Switch Routing protocol
The CGSR protocol uses a hierarchical network topology that employs at topologies. CGSR
organizes nodes into clusters, with coordination among the member of each cluster instructed
nodes named "cluster head". This cluster head selected dynamically by employing a least
cluster change (LCC) algorithm. According to this algorithm ,nodes creates to be a cluster-
head only if it comes under the range of another cluster-head, where tie is broken either using
the lower ID or highest connectivity algorithm. CGSR protocol creates a xed region in the
network. Each node in the cluster region is known as cluster member and they all are
connected with pivot node which is called cluster-head .Two cluster region are connected via
node which are place in intersection region of two cluster region and called cluster-gateway.
FIGURE 4.2: CGSR PROTOCOL
Here in the gure three cluster area are shown ,the all are overlapped in each other .so between
their intersection one node is placed as the gateway which transfer the information of one
cluster area to the other.
Advantages
CGSR is a hierarchical routing scheme which enables partial coordination between
nodes by electing cluster-heads. Hence , better bandwidth utilization is possible.
It is easy to implement priority scheduling scheme with token scheduling and gateway
code scheduling.
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Disadvantages
It increases in path length and instability in the system at high mobility when the
rate of change of cluster-heads is high.
To avoid gateway con icts, more resources are required.
The power consumption at the cluster-head node is also a matter of concern
because the battery-draining rate at the cluster-head is higher than that at a normal
node.
4.3 On-Demand routing protocols
This type of protocols execute the path nding process and exchange routing information only
when path is required by the node to communicate with a destination. There some of the
routing protocols like Dynamic Source Routing Protocol (DSR) , Ad Hoc On-Demand
Distance Vector Routing Protocol (AODV) .
4.3.1 Dynamic Source Routing Protocol
This type of routing protocol is design to restrict the bandwidth consumed by control packets
in ad wireless networks by eliminating the periodic table-update message required in the table
driven approach. In this routing protocol does not require periodic 'hello' packet transmission,
which are used by a node to inform its neighbors of its presence. The basic approach of this
protocol during the routing construction phase is to establish a route by ooding Route-
Request packets in the network. The destination node, On receiving a Route-Request packet,
respond by sending Route
FIGURE 4.3: DSR PROTOCOL
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Here shown in the gure, the node 1 is the source node and the node 5 is the destination node.
when 1 has data packet to sent to the node 5, it initiate a Route-Request as BLUE arrow in
gure ,and sent it to all its neighbors or ooded. Each node receiving this request packet check
if it is the destination then it generate Reply packet and send to sender. If it is not proper
destination then again that node send request packets to their neighbor until destination node
not found. Each packet has unique sequence number so that in the network while ooding loop
will not generate. If duplicate the packet at any node then it will discarded by the particular
node where redundancy will observe.
Advantages
Do not exchange routing update periodically, so overhead transmission is greatly
re-duced Can refer to cache for the new route when link fails.
Disadvantages
Scalability problem: High route discovery latency for large network.
High mobility problem: although the packet dropped may not be substantional, the
overhead tra c will increase a lot.
4.3.2 Ad Hoc On-Demand Distance Vector Routing Protocol
The Ad hoc On-demand Distance Vector (AODV) routing protocol is a reactive protocol.
Similar to DSR,AODV broadcasts a route request to discover a route in a reactive mode. The
di erence is that in AODV, a eld of the number of hops is used in the route record, instead of
a list of intermediate router addresses. Each intermediate router sets up a temporary reverse
link in the process of a route discovery. This link points to the router that forwarded the
request. Hence, the reply message can nd its way back to the initiator when a route is
discovered. When intermediate routers receive the reply, they can also set up corresponding
forward routing entries. To prevent old routing information being used as a reply to the latest
request, a destination sequence number is used in the route discovery packet and the route
reply packet. A higher sequence number implies a more recent route request.
We use the example topology shown in Figure to illustrate the discovery procedure of
AODV. Note that Routers A and C are disconnected from each other while both of them
connect to B. When Router A starts a route discovery to C, a route request is broadcast. The
request packet contains the requested destination sequence number, which is 1 greater than
the one currently kept at A. The intermediate routers reply to the source if they know the
route to that destination with the same or higher destination sequence number. We assume
that B does not have a record for a route to C. Therefore, B rst sets up a temporary link
pointing back to A. In the second step, it increases the number of hops by 1 and rebroadcasts
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the request. When C receives that request, it creates a new destination sequence number. A
route reply with that new sequence number is sent by C. The initiator and all intermediate
routers build routing entries associated with this new sequence number when they receive the
reply. The number of hop values can be used to nd a shorter path if a router receives two
replies with the same destination sequence number.
FIGURE 4.4: AODV PROTOCOL
Advantages
� AODV is loop-free due to the destination sequence numbers associated with routes.
Therefore, it o ers quick convergence when the ad hoc network topology changes which,
typically, occurs when a node moves in the network
Disadvantages
� Poor scalability is a disadvantage of AODV.
4.4 Hybrid routing protocols
4.4.1 Zone Routing Protocol
The Zone Routing Protocol (ZRP) is a prototype routing protocol. ZRP is formed by two sub-
protocols, the Intrazone Routing Protocol (IARP) and the Interzone Routing Protocol (IERP).
IARP is "a limited scope proactive routing protocol used to improve the performance of
existing globally reactive routing protocols". It relies on the service of a certain neighbor
discovery protocol (NDP) to provide neighbor information. IARP may use a scheme based on
the time-to-live (TTL) eld in IP packets to control the zone range. IERP is the reactive
routing component of ZRP. This scheme is responsible for nding a global path. It avoids
global queries for destinations that would be sent to surrounding hop neighbors. When global
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queries are required, "the routing zone based broadcast service can be used to e ciently guide
route queries outward, rather than blindly relaying queries from neighbor to neighbor".
ZRP tries to combine the advantages of reactive and proactive routing protocols. The
potential disad-vantage is the lack of route optimization. We use the example network in
Figure to brie y show the concept of ZRP. The range of the zone is set to one. So routers in
Subnets I and II use proactive IARP to nd routes to other routers in the same subnet. For
routes to the other subnet, reactive IERP is used.
FIGURE 4.5: ZONE ROUTING PROTOCOL
Advantages
� By combining the best features of proactive and reactive routing scheme, ZRP reduce the
control overhead compared to the Route-Request ooding mechanism employed in on-
demand approaches and the periodic ooding of routing information packets in table-driven
approaches.
Disadvantages
� In absence of a query control ,ZRP tends to produce higher control overhead than the
aforementioned schemes. This can happen due to the large overlapping of nodes' routing
zones. The query control must ensure that redundant or duplicate Route-Request are not
forwarded.
� The decision on the zone radius has a signi cant impact on the performance of the protocol.
5. WIRELESS AD HOC NETWORK
A wireless ad hoc network is a decentralized type of wireless network., The network is ad
hoc because it does not rely on a pre existing infrastructure, such as routers in wired networks
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or access points in managed (infrastructure) wireless networks. Instead,
each node participates in routing by forwarding data for other nodes, so the determination of
which nodes forward data is made dynamically on the basis of network connectivity. In
addition to the classic routing, ad hoc networks can use flooding for forwarding data. An ad
hoc network typically refers to any set of networks where all devices have equal status on a
network and are free to associate with any other ad hoc network device in link range. Ad hoc
network often refers to a mode of operation of IEEE 802.11 wireless networks. It also refers
to a network device's ability to maintain link status information for any number of devices in
a 1-link (aka "hop") range, and thus, this is most often a Layer 2 activity. Because this is only
a Layer 2 activity, ad hoc networks alone may not support a routeable IP network
environment without additional Layer 2 or Layer 3 capabilities.
The earliest wireless ad hoc networks were the "packet radio" (PRNETs) from the 1970s,
sponsored by DARPA after the ALOHAnet project.
5.1 Application
The decentralized nature of wireless ad hoc networks makes them suitable for a variety of
applications where central nodes can't be relied on and may improve the scalability of
networks compared to wireless managed networks, though theoretical[3] and practical[4] limits
to the overall capacity of such networks have been identified. Minimal configuration and
quick deployment make ad hoc networks suitable for emergency situations like natural
disasters or military conflicts. The presence of dynamic and adaptive routing protocols
enables ad hoc networks to be formed quickly.
Wireless ad-hoc networks can be further classified by their application:
mobile ad hoc networks (MANET)
5.2 Technical requirements
An ad hoc network is made up of multiple “nodes” connected by “links.”
Links are influenced by the node's resources (e.g., transmitter power, computing power and
memory) and behavioral properties (e.g., reliability), as well as link properties (e.g. length-of-
link and signal loss, interference and noise). Since links can be connected or disconnected at
any time, a functioning network must be able to cope with this dynamic restructuring,
preferably in a way that is timely, efficient, reliable, robust, and scalable. The network must
allow any two nodes to communicate by relaying the information via other nodes. A “path” is
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a series of links that connects two nodes. Various routing methods use one or two paths
between any two nodes; flooding methods use all or most of the available paths.
5.3 Medium-access control
In most wireless ad hoc networks, the nodes compete for access to shared wireless medium,
often resulting in collisions (interference). Using cooperative wireless
communications improves immunity to interference by having the destination node combine
self-interference and other-node interference to improve decoding of the desired signal.
5.4 Mathematical models
In recent years mathematical models have been proposed to study various types of wireless
ad hoc networks. One class of models involves using stochastic processes to represent the
placement of the nodes in the ad hoc network. More specifically, stochastic geometry models
of wireless networks have been proposed and studied.
5.5 Security
Microsoft does not allow advanced encryption and security protocols for wireless Ad hoc
networks on Windows. In fact, the security hole provided by Ad hoc networking is not only
the Ad hoc network itself, but the bridge it provides into other networks (see Ad hoc
networks in the article Wireless security).
5.6 Simulation of wireless ad hoc networks
One key problem in Wireless Ad Hoc networks is foreseeing the variety of possible situations
that can occur. As a result, Modeling and Simulation using extensive parameter sweeping and
what-if analysis becomes an extremely important paradigm for use in ad hoc networks.
Traditional M&S tools include NS2,(and recently NS3), OPNET Modeler, and NetSim.
However, these tools focus primarily on the simulation of the entire protocol stack of the
system. Although this can be important in the proof-of-concept implementations of systems,
the need for a more advanced simulation methodology is always there. Agent-based modeling
and simulation offers such a paradigm. Not to be confused with multi-agent systems and
intelligent agents, agent-based modeling[6] originated from social sciences, where the goal
was to evaluate and view large-scale systems with numerous interacting "AGENT" or
components in a wide variety of random situations to observe global phenomena. Unlike
traditional AI systems with Intelligent agents, agent-based modeling is similar to the real
world. Agent-based models are thus effective in modeling bio-inspired and nature-inspired
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systems. In these systems, the basic interactions of the components the system, also
called Complex Adaptive System, are simple but result in advanced global phenomena such
as emergence.
6. MOBILE AD HOC NETWORK
A mobile ad hoc network (MANET) is a self-configuring infrastructureless network of
mobile devices connected by wireless. Ad hoc is Latin and means "for this purpose". Each
device in a MANET is free to move independently in any direction, and will therefore change
its links to other devices frequently. Each must forward traffic unrelated to its own use, and
therefore be a router. The primary challenge in building a MANET is equipping each device
to continuously maintain the information required to properly route traffic. Such networks
may operate by themselves or may be connected to the larger Internet.
MANETs are a kind of Wireless ad hoc network that usually has a routable networking
environment on top of a Link Layer ad hoc network. The growth of laptops and 802.11/Wi-
Fi wireless networking have made MANETs a popular research topic since the mid-1990s.
Many academic papers evaluate protocols and their abilities, assuming varying degrees of
mobility within a bounded space, usually with all nodes within a few hops of each other.
Different protocols are then evaluated based on measures such as the packet drop rate, the
overhead introduced by the routing protocol, end-to-end packet delays, network throughput
etc.
6.1 Types
Vehicular Ad hoc Networks (VANETs) are used for communication among vehicles and
between vehicles and roadside equipment
Internet based mobile ad hoc networks (iMANETs) are ad hoc networks that link mobile
nodes and fixed Internet-gateway nodes. In such type of networks normal adhoc routing
algorithms don't apply directly.
Intelligent vehicular ad hoc networks (InVANETs) are a kind of artificial intelligence that
helps vehicles to behave in intelligent manners during vehicle-to-vehicle collisions,
accidents, drunken driving etc.
A mobile ad-hoc network (MANET) is an ad-hoc network but an ad-hoc network is not a
MANET.
6.2 Simulations
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There are several ways to study MANETs. One solution is the use of simulation tools
like OPNET, NetSim and NS2.
6.3 Data monitoring and mining
MANETS can be used for facilitating the collection of sensor data for data mining for a
variety of applications such as air pollution monitoring and different types of architectures
can be used for such applications. It should be noted that a key characteristic of such
applications is that nearby sensor nodes monitoring an environmental feature typically
register similar values. This kind of data redundancy due to the spatial correlation between
sensor observations inspires the techniques for in-network data aggregation and mining. By
measuring the spatial correlation between data sampled by different sensors, a wide class of
specialized algorithms can be developed to develop more efficient spatial data mining
algorithms as well as more efficient routing strategies. Also researchers have developed
performance models for MANET by applying Queueing Theory.
6.4 Security
A lot of research has been done in the past but the most significant contributions have been
the PGP (Pretty Good Privacy) and trust based security. None of the protocols have made a
decent trade off between security and performance. In an attempt to enhance security in
MANETs many researchers have suggested and implemented new improvements to the
protocols and some of them have suggested new protocols.
Attack classifications
These attacks on MANETs challenge the mobile infrastructure in which nodes can join and
leave easily with dynamics requests without a static path of routing. Schematics of various
attacks as described by Al-Shakib Khan [1] on individual layer are as under:
Application Layer: Malicious code, Repudiation
Transport Layer: Session hijacking, Flooding
Network Layer: Sybil, Flooding, Black Hole, Grey Hole. Worm Hole, Link Spoofing,
Link Withholding, Location disclosure etc.
Data Link/MAC: Malicious Behavior, Selfish Behavior, Active, Passive, Internal
External
Physical: Interference, Traffic Jamming, Eavesdropping
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7. CONCLUSION
It was revealed that ad hoc mobile devices can be highly mobile, powerful (in terms of
computation and memory capacity), and heterogeneous. Ad hoc wireless networks are not
limited to a homogeneous group of laptops. They can consist of a group of minute sensors,
communicating to each other and gathering environmental information.
Ad hoc networks need to possess self-organizing characteristics, and they must perform
routing and packet-forwarding functions. The topology of an ad hoc wireless network is
dynamically changing since devices are not tied down to specific locations over time. The
fact that nodes are not static implies that centralized media access is not entirely applicable.
Routing protocols in ad hoc networks need to deal with the mobility of nodes and constraints
in power and bandwidth. Multicasting in ad hoc wireless networks needs to be efficient since
using flooding will only result in a massive consumption of available bandwidth and degrade
battery life. Ad hoc devices rely on batteries to operate; hence, any inefficiency in
communication protocols can drastically shorten the uptime of these devices. Current
transport protocols are not designed for wireless ad hoc networks. In particular, TCP is an
end-to-end protocol that cannot distinguish the presence of mobility from congestion. Finally,
new methods are needed to faciliate service location, provision, and access in ad hoc wireless
networks. In summary, many challenging technical issues have arisen that demand our
attention and investigation.
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