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CHAPTER 1
INTRODUCTION TO WIRELESS NETWORKS
1.1 Introduction
Computer network consists of two or more autonomous computers that are linked
together in order to share the resources and allow electronic communication to
increase the productivity. There are two broad categories of computer networks,
namely, wired networks and wireless networks. In wired networks the connecting
medium of all computing devices is some kind of cables. Wires are subjected to
physical damage. In wireless network the connecting medium is some form of
wireless facility. The wired networks are slowly getting replaced by wireless
networks. Instead of wired connectivity, telecommunication equipments are
connected with electromagnetic waves in wireless networks.
The advantage of a wireless network is the mobility and freedom from the restriction
of wires or a fixed connection. The signal travels as electromagnetic waves through
the air. Wireless network has made a network extremely portable because of digital
modulation, adaptive modulation, information compression, and access multiplexing.
Rapid advances in mobile devices and wireless networking have converged to enable
ubiquitous computing where mobile devices can access services, run programs, utilize
resources, and harvest computing power anytime and anywhere. Wireless networks
enable the delivery of services that are no longer bound by time or location
barriers [1].
Wireless networks allow the user to use the network devices anywhere
in an office or home. Wireless networking is available in public “hotspots,” such as
businesses, and airports. With the advent of cellular phones, laptops, palmtops and
PDAs, one can get connected to the global internet.
The challenges posed by wireless networks are different from traditional wired
computer networks. Mobile and wireless communication provide greater flexibility
and ease of access, they rely on an open and public transmission media over which
eavesdropping, unauthorized access, user tracking, and other security threats can be
carried out more effectively in comparison with wired networks [2]. The key
differences between the wired network and wireless network are shown in Table 1.1.
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Table 1.1 Differences between wired and wireless network
Sl.
No.
1
WIRED NETWORK
WIRELESS NETWORK
2
3
4
5
6
7
8
9
Communicates through data cables
(i.e., Ethernet-based)
Need more bandwidth
Number of users is usually known
Identity of users is controllable
Less cost
Reliability is high
Performance is very good
Mobility is limited
No interference below network layer
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Inflexible
Communicates through radio waves
Need less bandwidth
Number of users is not predictable
Identity of users is difficult to control
More cost
Reliability reasonably high
Good
Unlimited
Interference can occur at the physical
layer
Flexible (expect a lot of technical
change within the network)
1.2 Components of wireless networks
The wireless networks have a set of components that are different from wired
networks. The components of wireless network are [3, 4]:
Wireless hosts: As in the case of wired networks, hosts are the end-system
devices that run applications. A wireless host might be a laptop, palmtop,
PDA and desktop computer. The hosts themselves may or may not be
mobile.
Wireless links: A host connects to a base station or to another wireless
host through a wireless communication link different wireless link
technologies have different transmission rates and can transmit over
different distances.
Base station: The base station is a key part of the wireless network
infrastructure which has no counterpart in a wired network. It is
responsible for sending and receiving data to and from a wireless host that
is associated with that base station. A base station will often be responsible
for coordinating the transmission of multiple wireless hosts with which it
is associated. When a wireless host is associated with a base station, it
means that the host is within wireless communication distance of the base
station and the host uses the base station to relay data between it and the
larger network.
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1.3 Characteristics of wireless networks
Apart from various characteristics mentioned so far, the wireless networks also have
the following characteristics [5] that make them significantly different from wired
networks.
Dynamic network topology: The network nodes are mobile and thus the
topology of the network may change frequently.
Infrastructure less: Central servers, specialized hardware, and fixed
routers are absent.
Multi-hop: Packets follow multichip routes and pass through different
mobile nodes before arriving at their final destination.
Amorphous: Node mobility and wireless connectivity allow nodes to enter
and leave the network spontaneously, to form and break links
unintentionally. Therefore, the network topology has no fixed form
regarding both its size and shape, i.e., it changes frequently.
Power limitation: Ad hoc enabled mobile hosts are small and lightweight,
and they are often supplied with limited power resources, such as small
batteries.
Memory and computation power limitation: Ad hoc enabled mobile
nodes have limited storage devices and weak computational capabilities.
Consequently, high complex security solution such as symmetric or
asymmetric data encryption, are difficult to implement.
Mobile devices physical vulnerability: Mobile devices used in Mobile Ad
hoc Networks (MANETs) are lightweight and portable. This represents
vulnerability, since the devices and the information stored in the devices
can be easily stolen. Mechanisms for protecting both devices and
information should be employed. [6]
Hostile environment: The devices in an Ad hoc network are autonomous
units, which roam around in a hostile environment. Devices lack physical
protection and are always under the threat of being captured and
compromised. Further, a device is always under the threat of being
attacked by other malicious or compromised devices in the network. This
means that every device should be prepared to operate in a mode that trusts
no peer.
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1.4 Types of wireless network
Wireless networks utilizes spread-spectrum or OFDM depends on the technology
which is using. Wireless network enable a user to move about within a wide coverage
area and still be associated to the network [4, 6, 7].
The various types of wireless networks are:
1. IEEE 802.11 Wireless LAN (Wi-Fi)
2. IEEE 802.15 Wireless Personal Area Network
2.1
IEEE 802.15.1 (Bluetooth Certification)
2.2
IEEE 802.15.2 (Zigbee Certification)
3. IEEE 802.16 Broadband Wireless Access (WiMax Certification)
4. Mobile Ad hoc Network (MANET)
5. Wireless Sensor Network (Base Network)
6. Wireless Mobile Ad hoc Sensor Network (MASN – Hybrid)
7. Wireless Metropolitan Area Network (WMAN)
IEEE 802.11 Wireless LAN (Wi-Fi) provide wireless network contact using radio
signal instead of traditional network cabling. They provide highest data-transfer rate
with 802.11 terminologies. WLANs offering various benefit for user such as mobility,
condensed Cost-of-Ownership, installation speed and flexibility and scalability.
IEEE 802.15 Wireless Personal Area Network (WPAN) is used to provide
connectivity to personal devices separated by up to 10 meters. This network is a lowpower, short-range, low-rate “cable-replacement” technology for interconnecting
notebooks, peripheral devices, cellular phones and PDAs. Bluetooth belongs to this
network category. Any Bluetooth enabled device could search for other Bluetooth
devices and could communicate with them [5].
IEEE 802.16 Broadband Wireless Access (WiMax Certification) provides full
worldwide interoperability for microwave access, communication technology for
wirelessly delivering high-speed Internet service to large geographical areas. WiMAX
would operate similar to WiFi but at higher speeds, over greater distances and for a
greater number of users. WiMAX has the ability to provide service even in areas that
are difficult for wired infrastructure to reach and the ability to overcome the physical
limitations of traditional wired infrastructure.
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Mobile Ad hoc Network (MANET) is a collection of wireless mobile nodes
dynamically forming a temporary network without the use of existing network infrastructure or centralized administration. Due to the limited transmission range of
wireless network interfaces, multiple network hops may be needed for one node to
exchange data with another across the network. In such a network, each mobile node
operate not only as a host but also as a router, forwarding packets for other mobile
nodes in the network, that may not be within the direct reach wireless transmission
range of each other. Each node participates in an ad hoc routing protocol that allows it
to discover multi hop paths through the network to any other node. The idea of an ad
hoc network is sometimes also called an infrastructure-less networking, since the
mobile nodes in the network dynamically establish routing among themselves to form
their own network on the fly. Some examples of the possible use of ad hoc networks
include students using laptop computers to participate in an interactive lecture,
business associates sharing information during a meeting, soldiers relaying
information for situational awareness on the battlefield, and emergency disaster relief
personnel coordinating efforts after a hurricane or earthquake. MANET the chosen
area of this research is explained in detail in Chapter 2.
Wireless Sensor Network (WSN) is an emerging technology that shows great
promise for various futuristic applications both for mass public and military. The
sensing technology combined with processing power and wireless communication
makes it lucrative for being exploited in abundance in future [8]. The basic idea of
sensor network is to disperse tiny sensing devices; which are capable of sensing some
changes of incidents/parameters and communicating with other devices, over a
specific geographic area for some specific purpose.
Wireless Mobile Ad hoc Sensor Network (WASN) combines the advantages of
sensor networks and MANETs.
Wireless Metropolitan Area Network (WMAN) is fast communicating networks
within the vicinity of a metropolitan area and span up to 50km. WMAN designed for
a larger geographical area than a LAN. The standard of MAN is DQDB which cover
up to 30 miles with the speed of 34 Mbit/s to 155 Mbit/s.
WMAN is
a
certified
name by the IEEE 802.16 that functioning on Broadband for its wireless
metropolitan.
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1.5 Advantages of wireless network
The technical advantages of the wireless networks result in various other
consequential advantages in business and management. A few are listed below:
Reduced cost of installation in the organizations
Flexible configuration that easily accommodate growth, change and
scalability
Allowance of mobile employees
Increased productivity and streamlined processes due to convenient
information access
No need to knock holes in walls
Adaptability as a stand-alone solution or to compliment a traditional wired
network
1.6 Limitations of wireless network
Despite a wide range of technical, organizational, financial and operational
advantages offered by the wireless networks, a few limitations still exist which are
listed below.
The potential for radio interference due to weather, other wireless devices,
or obstructions like walls.
The range of a wireless network is limited and a typical wireless device
will only allow individuals within 150 to 300 feet to access the network.
Wireless networks are typically inexpensive, but can cost up to four times
more to set up a wireless network than to set up a wired network in some
cases.
Wireless networks can be accessed by any computer within range of the
network's signal so information transmitted through the network (including
encrypted information) may be intercepted by unauthorized users.
Wireless networks are typically slower than wired networks, sometimes
even up to 10 times slower.
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1.7 Summary
A wireless network connects the computing devices without wires. Wireless
technologies make use of electromagnetic microwaves in the ultra high frequency
band to send data from one node to another. This chapter discussed the different types
of wireless networks, their characteristics, advantages and limitations.
The domain of the research is Mobile Ad hoc network (MANET) which is a part of
wireless network. The following chapter deals with the MANETs.
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