Ad-Hoc Wireless Network

A Seminar
on
Wireless Ad-Hoc
Network

Outline:







Introduction
Advantage and application
Technical challenges and issues
Protocols
Problems
Conclusion
References
1

Introduction
Multi-hop Wireless Networks (MHWNs):
It is defined as a collection of nodes that communicate with each
other wirelessly by using radio signals with a shared common
channel.
Hop
Path, chain or route
Switching UnitHost
2

Introduction
 There are several names for MHWNs; it could be called packet
radio network, Ad-Hoc network or mobile network.
 The
and
nodes here
receivers.
could be named stations or radio transmitters
MHWNs
Ad-Hoc
Networks
Wireless Sensor
Networks
Mesh Networks
3

Introduction



Nodes in the network are mobile in general.
The wireless hosts in such networks, communicate with each
other without the existing of a fixed infrastructure and without a
central control.
 A mobile ad-hoc network canbe connected to other fixed
networks or to the Internet.
Most of the Ad-Hoc networks use the allocated frequencies for
the Industrial, Scientific and Medical (ISM) band.

4

Advantages and Applications:
Ad-hoc networks have several advantages over the traditional
networks, like:





Ad-hoc networks can have more flexibility.
It
It
It
It
is better in mobility.
can be turn up and turn down in a very short time.
can be more economical.
considered a robust network because of its non-hierarchical
distributed control and management mechanisms.
5

There are lots of applications for Ad-Hoc networks, like:
 Group of people with laptops and they want to exchange files and
data without having an access point.
Sharing the internet
Connected to the internet
6

 Incase if we need to exchange information and the network's
infrastructure has been destroyed.
 It is suitable for military communications at battlefield where
there is no network infrastructure.
7

Technical Challenges and Issues:
There are several challenges that Ad-Hoc network faces such as:
•
•
•
•
•
•
Limited wireless range.
Hidden terminals.
Packet losses.
Routes changes.
Devices heterogeneity.
Battery power constraints.
8

Technical Challenges and Issues:
The main challenges face the Ad-Hoc networks are the following:
 Energy conservation: Nodes in Ad-Hoc networks are equipped
with limited batteries.
 Unstructured and/or time-varying network topology: Because of
the nodes mobility, that makes the network topology usually
unstructured and makes the optimizing process a difficult task.
 Scalability: In some cases, there will be a huge number of nodes.
9

Technical Challenges and Issues
 Low-quality communications: In general, wireless networks are
less reliable than the wired networks. In addition to that, the
quality of
factors.
the network can be affected by the environmental
 Resource-constrained computation: The resources in Ad-Hoc
networks such as energy and network bandwidth are available in
limited amounts.
10

Ad-Hoc Wireless Media Access Protocols
MAC Protocols
Synchronous Asynchronous
MAC Protocols
Sender-Initiated Receiver-Initiated
11

Sender-Initiated MAC Protocols:
RTS1
CTS2
ReceiverSender
Data3
12

Receiver-Initiated MAC Protocols:
RTR1
ReceiverSender
Data2
13

Existing Ad-Hoc MAC Protocols:
Multiple Access with Collision Avoidance (MACA):
 It was proposed as a solution for both hidden
exposed node problems.
terminal and
 It has the ability to control the transmitter power for each
packet.
It uses a three-way handshake, RTS-CTS-Data.
 Collisions could
sensing in it.
occur in MCSA, because there is no carrier
14

Ad-Hoc Routing Protocols
There are lots of routing protocols which have been developed for
Ad-Hoc networks. When these protocols have been developed, it
has been
network.
taken in the consideration the limitations of this type of
Ad-Hoc Routing
Protocols
Table Driven /
Proactive
On-Demand-
Driven / Reactive
Hybrid
15

1. Table-Driven Approaches:
 Table-driven routing protocols try to keep the last updated and
stable routing information from each node to the rest of the
nodes in the network.
 In this type of routing
least one table to store
protocol, each node should maintain at
the routing information.
 In case of any change in the network topology, the nodes will
propagate the route updates throughout the network in order to
maintain a stable network view. 16

Destination Sequenced Distance Vector (DSDV):


Wireless Routing Protocol (WRP)
Cluster Switch Gateway Routing (CSGR)
17

1.1. Destination Sequenced Distance Vector (DSDV):
 The main feature in this protocol is the avoidance of the routing
loops.
Each node here maintains a routing table of all destinations
within the non-partitioned network and the number of hops to
these destinations.

 A sequence numbering
distinguish between the
Updates in the routing
routing table up-to-date
system is used in order to be able to
old and bad routes from the new ones.
table are sent periodically to keep the
and consistent.

18

 The broadcasts of the new route will contain:
•
•
•
Destination address.
Number of hops to the destination.
Sequence number of the information received
destination.
New sequence number unique to the broadcast.
regarding the
•
 Each route is labeled with a sequence number and the route
with the highest sequence number will be used.
 If there are two updates have the same sequence number, then
the route with the smaller hop count will be used.
19

1.2. Wireless Routing Protocol (WRP):
 Each routing node
hop
in WRP communicates the distance and
thesecond-to-last
network.
information for all destinations in
 The WRP is classified as one of the path-finding algorithms, but
here the count-to-infinity problem has been avoided by making
each node check the consistency of the predecessor information
reported by its neighbors.
 In WRP, each nodes learns about its neighbors from the
acknowledgments and the other messages it's receives.
20

 In case if the node does not have any data to send, it should
send a HELLO message in a specified periodic time to make sure
that the connectivity information is properly reflected.
Hello
New Node Existing Node
RoutingTable
Routing Table
21

1.3. Cluster Switch Gateway Routing (CSGR):
 Nodes in CSGR are grouped in clusters and each cluster has a
cluster head which can control a group of
Each time a cluster head moves away,
selected.
By using the least cluster change (LCC)
Ad-Hoc hosts.
a new cluster head is
 algorithm, the cluster
head will be changed either if two cluster heads come into
contact or if the node moves away from all other cluster heads.
CSGR is based on the DSDV, but with a little difference that CSGR
uses a hierarchical cluster-head-to-gateway routing approach.

23

Here, the routing protocols create routes only when requested
by the source node.
A route discovery process is initiated by the source node.
This process is considered done either after:
• finding a route to the destination.
• after examined all the possible route permutations.
Once the route is established, it will be maintained by some
form of route maintenance procedure until either the
destination becomes inaccessible or the route is no longer
desired.
2. Source-Initiated On-Demand Approaches:



25

Ad-Hoc Routing Protocol
Dynamic Source Routing (DSR)
Ad-Hoc On-Demand Distance Vector Routing (AODV)
Temporally Ordered Routing Algorithm (TORA)



26

2.1. Dynamic Source Routing (DSR):
 The DSR protocol is based on the concept of source routing,
where each node is required to maintain route caches that
contain the source routes of which the mobile is aware.
 There are two phases in this protocol:
•
•
The route discovery phase.
The route maintenance phase.
 When node has data to send, it first checks its route cache to see
if it already has an unexpired route to the destination. 27

Propagation of the route request messages:
N1 -N2 N1 -N2-N5
N1
N1 –N3-N4
N1 –N3-N4
N1 –N3-N4-N7
N1-N3
N1
N1 –N3-N4-N6N1 –N3-N4
28

Propagation of the route replay with the route record :
N1 -N2-N5-N8 N1 -N2-N5-N8
N1 -N2-N5-N8
29

2.2. Ad-Hoc On-Demand Distance Vector Routing (AODV):
 The AODV routing protocol is based on the DSDV algorithm.
 It can minimize the number of required broadcasts by creating
routes on an on-demand basis.
 It is considered as a pure on-demand route acquisition system.
30

3. Location Aided Routing (LAR):
 One of the LAR protocol concepts, that it
GPS)
uses the location
information (e.g. by utilizing the to enhance the
performance of the Ad-Hoc network.
 There are two defined zones in LAR:
•
•
The expected zone.
The request zone.
33

Concepts of request zone and expected zone in LAR :
34

Providing Quality of Service in Ad-Hoc Networks
 The QoS is defined as a set of measurable pre-specified service
requirements need to be met by the network while transferring
packets from source to destination.
 It could
network
be defined as an agreement or a guarantee that the
will provide a set of measurable service performance
such as end-to-end delay, delay variance (jitter), available
bandwidth, probability of packet loss, cost of transport, total
network throughput, etc.
36

Providing Quality of Service in Ad-Hoc Networks
There are lots of problems in Ad-Hoc network when providing QoS
such as:
1. Routing problem: It can be defined as the process of finding a
loop free route from the source to the destination which should
also support the requested level of QoS.
Maintenance problem: It can be described as how to make sure
that the network will continue support the agreed level of QoS
in case if any change happened in the network topology.
Variable resource problem: It deals with the changes in the
available resources and how to react to these changes.
2.
3.
37

Conclusion
Mobility in the wireless networks is very popular nowadays. Many peoples in
the street walk and are using small devices like PDA, laptops, or phone to
communicate, listening a music, write SMS, exchanging data with other people
near them, etc.
The rapid developments in the field of ad hoc networking allows the nodes to
form a self-creating, self-organizing and self-administering wireless network.
The presence of ad hoc networks covers the infrastructure’s weakness.
Since the ad hoc networks are independent from infrastructure, the nodes must
be able to work together to establish a greater network.
38
Its intrinsic flexibility, lack of infrastructure, ease of deployment, auto
configuration, low cost and potential applications makes it an essential part of
future pervasive computing environments.

References:



39
https://books.google.com.sg/books/about/Wireless_ATM_and_Ad_Hoc
_Networks.html?id=0hMfAQAAIAAJ&redir_esc=y&hl=en
https://www.pearson.ch/HigherEducation/PrenticeHall/EAN/97801300
78179/Ad-Hoc-Mobile-Wireless-Networks-Protocols-and-Systems
https://www.researchgate.net/profile/Morteza_Mohammadi_Zanjireh/
publication/274638337_A_Survey_on_Centralised_and_Distributed_Cl
ustering_Routing_Algorithms_for_WSNs/links/552444b80cf2b123c517
3968.pdf

Ad-Hoc Wireless Network

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