Unit 2 Design mobile computing architecture MC1514

MT Unit2 -Design Mobile Computing Architecture
GCEK MobileTechnologies ~Swapnali Pawar Page 1
Swapnali Pawar

Mobile Communication
Mobile Communication is the use of technology that
allows us to communicate with others in different
locations without the use of any physical connection
(wires or cables). Mobile communication makes our life
easier, and it saves time and effort.
A mobile phone (also called mobile cellular network,
cell phone or hand phone) is an example of mobile
communication (wireless communication). It is an
electric device used for full duplex two way radio
telecommunication over a cellular network of base
stations known as cell site.

Characteristics of Mobile
Communication Devices
● Fixed and wired: This configuration describes
the typical desktop computer in an office. Neither
weight nor power consumption of the devices
allow for mobile usage. The devices use fixed
networks for performance reasons.
● Mobile and wired: Many of today’s laptops
fall into this category; users carry the laptop from
one hotel to the next, reconnecting to the
company’s network via the telephone network and
a modem.
● Fixed and wireless: This mode is used for
installing networks, e.g., in historical buildings to
avoid damage by installing wires, or at trade
shows to ensure fast network setup. Another
example is bridging the last mile to a customer by
a new operator that has no wired infrastructure and
does not want to lease lines from a competitor.
● Mobile and wireless: This is the most
interesting case. No cable restricts the user, who
can roam between different wireless networks.
Today’s most successful example for this category
is GSM with more than 800 million users.

Applications of Mobile
Communication
1.Vehicles
2.Emergencies
3.Business
4.Replacement of wired networks
5.Infotainment and more
6.Location dependent services
7.Mobile and wireless devices
1. Vehicles -
Today’s cars already comprise some, but tomorrow’s cars will
comprise many wireless communication systems and mobility
aware applications. Music, news, road conditions, weather
reports, and other broadcast information are received via
digital audio broadcasting (DAB) with 1.5 Mbit/s. For
personal communication, a universal mobile
telecommunications system (UMTS) phone might be
available offering voice and data connectivity with 384 kbit/s.
For remote areas, satellite communication can be used, while
the current position of the car is determined via the global
positioning system (GPS). Cars driving in the same area build
a local ad-hoc network for the fast exchange of information in
emergency situations or to help each other keep a safe
distance. In case of an accident, not only will the airbag be
triggered, but the police and ambulance service will be
informed via an emergency call to a service provider. Cars

with this technology are already available. In the future, cars
will also inform other cars about accidents via the ad-hoc
network to help them slow down in time, even before a driver
can recognize an accident. Buses, trucks, and trains are
already transmitting maintenance and logistic information to
their home base, which helps to improve organization (fleet
management), and saves time and money. Figure 1.1 shows a
typical scenario for mobile communications with many
wireless devices. Networks with a fixed infrastructure like
cellular phones (GSM, UMTS) will be interconnected with
trunked radio systems (TETRA) and wireless LANs (WLAN).
Satellite communication links can also be used. The networks
between cars and inside each car will more likely work in an
ad-hoc fashion. Wireless pico networks inside a car can
comprise personal digital assistants (PDA), laptops, or mobile
phones, e.g., connected with each other using the Bluetooth
technology. This first scenario shows, in addition to the
technical content, something typical in the communication
business – many acronyms. This book contains and defines
many of these. If you get lost with an acronym, please check
the appendix, which contains the complete list, or check the
terms and definitions database interactive (TEDDI) of ETSI
(2002). Think of similar scenarios for air traffic or railroad
traffic. Different problems can occur here due to speed. While
aircraft typically travel at up to 900 km/h and current trains up
to 350 km/h, many technologies cannot operate if the relative
speed of a mobile device exceeds, e.g., 250 km/h for GSM or
100 km/h for AMPS. Only some technologies, like DAB work
up to 900 km/h (unidirectional only).

2 .Emergencies-
Just imagine the possibilities of an ambulance with a high-
quality wireless connection to a hospital. Vital information
about injured persons can be sent to the hospital from the
scene of the accident. All the necessary steps for this
particular type of accident can be prepared and specialists can
be consulted for an early diagnosis. Wireless networks are the
only means of communication in the case of natural disasters
such as hurricanes or earthquakes. In the worst cases, only
decentralized, wireless ad-hoc networks survive. The
breakdown of all cabling not only implies the failure of the
standard wired telephone system, but also the crash of all
mobile phone systems requiring base stations!

3. Business -
A travelling salesman today needs instant access to the
company’s database: to ensure that files on his or her laptop
reflect the current situation, to enable the company to keep
track of all activities of their travelling employees, to keep
databases consistent etc. With wireless access, the laptop can
be turned into a true mobile office, but efficient and powerful
synchronization mechanisms are needed to ensure data
consistency. Figure 1.2 illustrates what may happen when
employees try to communicate off base. At home, the laptop
connects via a WLAN or LAN and DSL to the Internet.
Leaving home requires a handover to another technology, e.g.,
to an enhanced version of GSM, as soon as the WLAN
coverage ends. Due to interference and other factors discussed
in chapter 2, data rates drop while cruising at higher speed.
Gas stations may offer WLAN hot spots as well as gas. Trains
already offer support for wireless connectivity. Several more
handovers to different technologies might be necessary before
reaching the office. No matter when and where, mobile
communications should always offer as good connectivity as
possible to the internet, the company’s intranet, or the
telephone network

4. Replacement of wired networks
In some cases, wireless networks can also be used to replace
wired networks, e.g., remote sensors, for tradeshows, or in
historic buildings. Due to economic reasons, it is often
impossible to wire remote sensors for weather forecasts,
earthquake detection, or to provide environmental
information. Wireless connections, e.g., via satellite, can help
in this situation. Tradeshows need a highly dynamic
infrastructure, but cabling takes a long time and frequently
proves to be too inflexible. Many computer fairs use WLANs
as a replacement for cabling. Other cases for wireless
networks are computers, sensors, or information displays in
historical buildings, where excess cabling may destroy
valuable walls or floors. Wireless access points in a corner of
the room can represent a solution.
5. Infotainment and more Internet
everywhere?
Not without wireless networks! Imagine a travel guide for a
city. Static information might be loaded via CD-ROM, DVD,
or even at home via the Internet. But wireless networks can
provide up-to-date information at any appropriate location.
The travel guide might tell you something about the history of
a building (knowing via GPS, contact to a local base station,
or triangulation where you are) downloading information
about a concert in the building at the same evening via a local
wireless network. You may choose a seat, pay via electronic
cash, and send this information to a service provider
(Cheverst, 2000). Another growing field of wireless network
applications lies in entertainment and games to enable, e.g.,

ad-hoc gaming networks as soon as people meet to play
together.
6. Location dependent services
Many research efforts in mobile computing and wireless
networks try to hide the fact that the network access has been
changed (e.g., from mobile phone to WLAN or between
different access points) or that a wireless link is more error
prone than a wired one. Many chapters in this book give
examples: Mobile IP tries to hide the fact of changing access
points by redirecting packets but keeping the same IP address
(see section 8.1), and many protocols try to improve link
quality using encoding mechanisms or retransmission so that
applications made for ﬁxed networks still work. In many
cases, however, it is important for an application to ‘know’
something about the location or the user might need location
information for further activities. Several services that might
depend on the actual location can be distinguished:
● Follow-on services:
The function of forwarding calls to the current user location
is well known from the good old telephone system. Wherever
you are, just transmit your temporary phone number to your
phone and it redirects incoming calls.2 Using mobile
computers, a follow-on service could offer, for instance, the
same desktop environment wherever you are in the world. All
e-mail would automatically be forwarded and all changes to
your desktop and documents would be stored at a central
location at your company. If someone wanted to reach you
using a multimedia conferencing system, this call would be
forwarded to your current location.
● Location aware services:

Imagine you wanted to print a document sitting in the lobby
of a hotel using your laptop. If you drop the document over
the printer icon, where would you expect the document to be
printed? Certainly not by the printer in your office! However,
without additional information about the capabilities of your
environment, this might be the only thing you can do. For
instance, there could be a service in the hotel announcing that
a standard laser printer is available in the lobby or a color
printer in a hotel meeting room etc. Your computer might then
transmit your personal profile to your hotel which then
charges you with the printing costs.
● Privacy:
The two service classes listed above immediately raise the
question of privacy. You might not want video calls following
you to dinner, but maybe you would want important e-mails
to be forwarded. There might be locations and/or times when
you want to exclude certain services from reaching you and
you do not want to be disturbed. You want to utilize location
dependent services, but you might not want the environment
to know exactly who you are. Imagine a hotel monitoring all
guests and selling these proﬁles to companies for
advertisements.
● Information services:
While walking around in a city you could always use your
wireless travel guide to ‘pull’ information from a service, e.g.,
‘Where is the nearest Mexican restaurant?’ However, a
service could also actively ‘push’ information on your travel
guide, e.g., the Mexican restaurant just around the corner has
a special taco offer.
● Support services:

Many small additional mechanisms can be integrated to
support a mobile device. Intermediate results of calculations,
state information, or cache contents could ‘follow’ the mobile
node through the fixed network. As soon as the mobile node
reconnects, all information is available again. This helps to
reduce access delay and traffic within the fixed network.
Caching of data on the mobile device (standard for all desktop
systems) is often not possible due to limited memory capacity.
The alternative would be a central location for user
information and a user accessing this information through the
(possibly large and congested) network all the time as it is
often done today.
7. Mobile and wireless devices
Even though many mobile and wireless devices are available,
there will be many more in the future. There is no precise
classification of such devices, by size, shape, weight, or
computing power. Currently, laptops are considered the upper
end of the mobile device range.3 The following list gives
some examples of mobile and wireless devices graded by
increasing performance (CPU, memory, display, input devices
etc.). However, there is no sharp line between the categories
and companies tend to invent more and more new categories.
● Sensor:
A very simple wireless device is represented by a sensor
transmitting state information. One example could be a switch
sensing the ofﬁce door. If the door is closed, the switch
transmits this to the mobile phone inside the office which will
not accept incoming calls. Without user interaction, the
semantics of a closed door is applied to phone calls.

● Embedded controllers:
Many appliances already contain a simple or sometimes more
complex controller. Keyboards, mice, headsets, washing
machines, coffee machines, hair dryers and TV sets are just
some examples. Why not have the hair dryer as a simple
mobile and wireless device (from a communication point of
view) that is able to communicate with the mobile phone?
Then the dryer would switch off as soon as the phone starts
ringing – that would be a nice application!
● Pager:
As a very simple receiver, a pager can only display short text
messages, has a tiny display, and cannot send any messages.
Pagers can even be integrated into watches. The tremendous
success of mobile phones, has made the pager virtually
redundant in many countries. Short messages have replaced
paging. The situation is somewhat different for emergency
services
where it may be necessary to page a larger number of users
reliably within short time.
● Mobile phones: The traditional mobile phone only had a
simple black and white text display and could send/receive
voice or short messages. Today, mobile phones migrate more
and more toward PDAs. Mobile phones with full color
graphic display, touch screen, and Internet browser are easily
available.
● Personal digital assistant: PDAs typically accompany a
user and offer simple versions of office software (calendar,
note-pad, mail). The typical input device is a pen, with built-
in character recognition translating handwriting into

characters. Web browsers and many other software packages
are available for these devices.
● Pocket computer: The next steps toward full computers
are pocket computers offering tiny keyboards, color displays,
and simple versions of programs found on desktop computers
(text processing, spreadsheets etc.).
● Notebook/laptop: Finally, laptops offer more or less the
same performance as standard desktop computers; they use
the same software – the only technical difference being size,
weight, and the ability to run on a battery. If operated mainly
via a sensitive display (touch sensitive or electromagnetic),
the devices are also known as notepads or tablet PCs.
The mobile and wireless devices of the future will be more
powerful, less heavy, and comprise new interfaces to the user
and to new networks. However, one big problem, which has
not yet been solved, is the energy supply. The more features
that are built into a device, the more power it needs. The
higher the performance of the device, the faster it drains the
batteries (assuming the same technology). Furthermore,
wireless data transmission consumes a lot of energy. Although
the area of mobile computing and mobile communication is
developing rapidly, the devices typically used today still
exhibit some major drawbacks compared to desktop systems
in addition to the energy problem. Interfaces have to be small
enough to make the device portable, so smaller keyboards are
used. This makes typing difﬁcult due to their limited key size.
Small displays are often useless for graphical display. Higher
resolution does not help, as the limiting factor is the resolution
capacity of the human eye. These devices have to use new
ways of interacting with a user, such as, e.g., touch sensitive
displays and voice recognition. Mobile communication is

greatly influenced by the merging of telecommunication and
computer networks. We cannot say for certain what the
telephone of the future will look like, but it will most probably
be a computer. Even today, telephones and mobile phones are
far from the simple ‘voice transmission devices’ they were in
the past.4 Developments like ‘voice over IP’ and the general
trend toward packet-oriented networks enforce the
metamorphosis of telephones (although voice services still
guarantee good revenue). While no one can predict the future
of communication devices precisely, it is quite clear that there
will still be many fixed systems, complemented by a myriad
of small wireless computing devices all over the world. More
people already use mobile phones than fixed phones
Features of Mobile Communication
The following are the features of mobile communication:
1. High capacity load balancing: Each wired or wireless
infrastructure must incorporate high capacity load
balancing.
High capacity load balancing means, when one access point
is overloaded, the system will actively shift users from one
access point to another depending on the capacity which is
available.

2. Scalability: The growth in popularity of new wireless
devices continuously increasing day by day. The wireless
networks have the ability to start small if necessary, but
expand in terms of coverage and capacity as needed -
without having to overhaul or build an entirely new
network.
3. Network management system: Now a day, wireless
networks are much more complex and may consist of
hundreds or even thousands of access points, firewalls,
switches, managed power and various other components.
The wireless networks have a smarter way of managing the
entire network from a centralized point.

4. Role based access control: Role based access
control (RBAC) allows you to assign roles based on what,
who, where, when and how a user or device is trying to
access your network.
Once the end user or role of the devices is defined, access
control policies or rules can be enforced.
o Indoor as well as outdoor coverage options: It is
important that your wireless system has the capability of
adding indoor coverage as well as outdoor coverage.
o Network access control: Network access control can
also be called as mobile device registration. It is essential
to have a secure registration.
Network access control (NAC) controls the role of the
user and enforces policies. NAC can allow your users to
register themselves to the network. It is a helpful feature
that enhances the user experience.
o Mobile device management: Suppose, many mobile
devices are accessing your wireless network; now think
about the thousands of applications are running on those
mobile devices.
How do you plan on managing all of these devices and
their applications, especially as devices come and go
from your business?
Mobile device management can provide control of how
you will manage access to programs and applications.
Even you can remotely wipe the device if it is lost or
stolen.

o Roaming: You don't need to worry about dropped
connections, slower speeds or any disruption in service
as you move throughout your office or even from
building to building wireless needs to be mobile first.
Roaming allows your end-users to successfully move
from one access point to another without ever noticing a
dip in a performance.
For example, allowing a student to check their mail as
they walk from one class to the next.
o Redundancy: The level or amount of redundancy your
wireless system requires depends on your specific
environment and needs.
o For example: A hospital environment will need a higher
level of redundancy than a coffee shop. However, at the
end of the day, they both need to have a backup plan in
place.
o Proper Security means using the right firewall: The
backbone of the system is your network firewall. With
the right firewall in place you will be able to:
o See and control both your applications and end
users.
o Create the right balance between security and
performance.

o Reduce the complexity with:
o Antivirus protection.
o Deep Packet Inspection (DPI)
o Application filtering
o Protect your network and end users against known
and unknown threads including:
o Zero- day.
o Encrypted malware.
o Ransomware.
o Malicious botnets.
o Switching: Basically, a network switch is the traffic
cop of your wireless network which making sure that
everyone and every device gets to where they need to go.
Switching is an essential part of every fast, secure
wireless network for several reasons:
o It helps the traffic on your network flow more
efficiently.
o It minimizes unnecessary traffic.
o It creates a better user experience by ensuring your
traffic is going to the right places.

Advantages of Mobile Communication
o Flexibility:
Wireless communication enables the people to
communicate with each other regardless of location.
There is no need to be in an office or some telephone
booth in order to pass and receive messages.
o Cost effectiveness:
In wireless communication, there is no need of any
physical infrastructure (Wires or cables) or maintenance
practice. Hence, the cost is reduced.
o Speed:
Improvements can also be seen in speed. The network
connectivity or the accessibility was much improved in
accuracy and speed.
o Accessibility:
With the help of wireless technology easy accessibility to
the remote areas is possible. For example, in rural areas,
online education is now possible. Educators or students
no longer need to travel to far-flung areas to teach their
lessons.
o Constant connectivity:
Constant connectivity ensures that people can respond to
emergencies relatively quickly. For example, a wireless
device like mobile can ensure you a constant
connectivity though you move from place to place or
while you travel, whereas a wired landline can't.

A simpliﬁed reference model
This book follows the basic reference model used to structure
communication systems (Tanenbaum, 2003). Any readers
who are unfamiliar with the basics of communication
networks should look up the relevant sections in the
recommended literature (Halsall, 1996), (Keshav, 1997),
(Tanenbaum, 2003), (Kurose, 2003).
Figure 1.6 shows a personal digital assistant (PDA) which
provides an example for a wireless and portable device.
This PDA communicates with a base station in the middle of
the picture. The base station consists of a radio transceiver
(sender and receiver) and an interworking unit connecting the
wireless link with the ﬁxed link.
The communication partner of the PDA, a conventional
computer, is shown on the right-hand side. Underneath each
network element (such as PDA, interworking unit, computer),
the figure shows the protocol stack implemented in the system
according to the reference model.
End-systems, such as the PDA and computer in the example,
need a full protocol stack comprising the application layer,
transport layer, network layer, data link layer, and physical
layer. Applications
on the end-systems communicate with each other using the
lower layer services. Intermediate systems, such as the
interworking unit, do not necessarily need all of the layers.
Figure 1.6 only shows the network, data link, and physical
layers. As (according to the basic reference model) only

entities at the same level communicate with each other (i.e.,
transport with transport, network with network) the end-
system applications do not notice the intermediate system
directly in this scenario. The following paragraphs explain the
functions of each layer in more detail in a wireless and mobile
environment.
● Physical layer:
This is the lowest layer in a communication system and is
responsible for the conversion of a stream of bits into signals
that can be transmitted on the sender side. The physical layer
of the receiver then transforms the signals back into a bit
stream. For wireless communication, the physical layer is
responsible for frequency selection, generation of the carrier

frequency, signal detection (although heavy interference may
disturb the signal), modulation of data onto a carrier
frequency and (depending on the transmission scheme)
encryption. These features of the physical layer are mainly
discussed in chapter 2, but will also be mentioned for each
system separately in the appropriate chapters.
● Data link layer:
The main tasks of this layer include accessing the medium,
multiplexing of different data streams, correction of
transmission errors, and synchronization (i.e., detection of a
data frame). Chapter 3 discusses different medium access
schemes. A small section about the specific data link layer
used in the presented systems is combined in each respective
chapter. Altogether, the data link layer is responsible for a
reliable point-topoint connection between two devices or a
point-to-multipoint connection between one sender and
several receivers.
● Network layer:
This third layer is responsible for routing packets through a
network or establishing a connection between two entities
over many other intermediate systems. Important topics are
addressing, routing, device location, and handover between
different networks. Chapter 8 presents several solutions for
the network layer protocol of the internet (the Internet
Protocol IP). The other chapters also contain sections about
the network layer, as routing is necessary in most cases.

● Transport layer:
This layer is used in the reference model to establish an end-
to-end connection. Topics like quality of service, flow and
congestion control are relevant, especially if the transport
protocols known from the Internet, TCP and UDP, are to be
used over a wireless link.
● Application layer:
Finally, the applications (complemented by additional layers
that can support applications) are situated on top of all
transmissionoriented layers. Topics of interest in this context
are service location, support for multimedia applications,
adaptive applications that can handle the large variations in
transmission characteristics, and wireless access to the world
wide web using a portable device. Very demanding
applications are video (high data rate) and interactive gaming
(low jitter, low latency).

Security Concerns Related to Mobile
Computing
There are mainly five fundamental goals of security used in
the information system to deal with security issues. They are:
Confidentiality
This is used to prevent unauthorized users from gaining
access to any particular user's critical and confidential
information.
Integrity
This is used to ensure that any type of unauthorized
modification, destruction or creation of information cannot be
done.
Availability
The availability is used to ensure that authorized users get the
required access whenever they need it.
Legitimate
This is used to ensure that only authorized, and legitimate
users have access to the services.
Accountability
Accountability is used to ensure that the users will be
responsible for their security-related activities by arranging
the users and their activities in a linked form.
We have to achieve these goals according to the security
policy used by the service providers.

Wireless Security Issues
Wireless security issues are considered as the primary security issues
of mobile computing. These are related to wireless networks. These
issues occur when the hackers intercept the radio signals. Most
wireless networks are dependent on other private networks, which are
managed by others, so after these issues, the users have less control of
security procedures. These security issues are:
Denial of Service (DOS) attacks
The denial of services or DOS attacks is one of the most common
attacks of all kinds of networks and especially in a wireless network.
It prevents users from using network services because the attacker
sends a large amount of unnecessary data or connection requests to
the communication server. It causes a slow network, and therefore the
users cannot get benefitted from using its service.
Traffic Analysis
Traffic analysis is used to identify and monitor communication
between users. In this process, the service provider listens the traffic
flowing in the wireless channel to access the private information of
users affected by the attacker.
Eavesdropping
It specifies that the attacker can log on to the wireless network and
access sensitive data if the wireless network was not secure enough.
This can also be done if the information is not encrypted.
Session Interception and Messages Modification
It specifies that the attacker can intercept the session and modify the
transmitted data in this session. This scenario is called "man in the
middle." It inserts the attacker's host between the sender and receiver
host.

Spoofing
In this security issue, the attacker impersonates him as an authorized
account of another user and tries to access the sensitive data and
unauthorized services.
Captured and Retransmitted Messages
In this security issue, the attacker can get some of the network
services by getting unauthorized access. After capturing the message,
he/she can reply to it with some modifications to the same destination
or another.
Device Security Issues
Mobile devices are very prone to new types of security attacks and
fraud issues. These issues are not only because of the mobile devices'
vulnerability but also because of the sensitive data that the mobile
devices have stored. These security issues and threats such as Virus,
Spyware and Trojan may damage or destroy the mobile devices and
steal the information stored on them. A virus is a part of malicious
software or spyware that tends to gather information about the user
without his/her knowledge.
Following is a list of some mobile computing security issues we face
using mobile devices:
Push Attacks
In the push attack, the attacker creates a malicious code at the user's
mobile device by hacking it and then he/she may spread it to affect
other elements of the network.
Pull Attacks
The pull attack is a type of attack where the attacker controls the
device and handles it in his/her way. He can decide which emails they
want to receive. In this attack, the user can decide about the obtained
data by the device itself.

Forced De-authentication
In this security issue, the attackers convince the mobile end-point or
the mobile user to drop its connection and re-connection to get a new
signal. Within this process, they insert their device between the
mobile device and the network and steal the information or do the
fraud.
Multi-protocol Communication
The multi-protocol communication provides the ability of many
mobile devices to operate using multiple protocols. For example, A
cellular provider's network protocol. Most of the protocols have some
security loopholes, which help the attacker to exploit this weakness
and access to the device.
Mobility
This security issue may occur because of the mobility of the users and
the mobile devices. You may face these security threats due to a user's
location, so you must replicate the user profiles at different locations
to allow roaming via different places without any concern regarding
access to personal and sensitive data in any place and at any time.
This repetition of sensitive data on different sites can increase seethe
chances of security threats.
Disconnections
These types of security issues occur when mobile devices go to
different places. It occurs in the form of frequent disconnections
caused by external parties resulting in the handoff.

Personnel security issues or insider attacks
These are the non-technical attacks. They are occurred due to the lack of
awareness of security policies. Due to this reason, many times, security
breaches occur. Even though corporate has standard policies for mobile device
security, many employees don't understand its risks. It is found in a study that
most of the security risks and threats (almost 72%) occur because of careless
employees than hackers (28%). It shows the importance of implementing a
strong combination of technology and security awareness within an
organization.
How to handle security issues?
The biggest issue in mobile computing is the credential verification of users.
Because the users share the username and passwords, it may become a
significant threat to security. Due to this sensitive issue, most companies are
very reluctant to implement mobile computing. Some recommendations can be
followed by companies or mobile users to keep their mobile devices and the
data stored in the devices secure.
o The company should hire qualified personnel.
o You should install security hardware and software.
o You should ensure that the data stored in the mobile devices are encrypted and
audited.
o Educate the users on proper mobile computing ethics and security issues.
o You must ensure that the mobile devices are configured with a power-on
authentication to prevent unauthorized access if lost or stolen.
o You must ensure that anti-virus software is installed on mobile devices.
o Make sure that the firewall client is installed on mobile devices.
o Make your mobile devices encrypted with a strong password.
o Encrypt your data stored in the secondary storage devices such as Memory Sticks,
Data card, removable USB etc.
o Ensure that the Bluetooth, Wi-Fi, etc. enabled mobile devices are turned off when you
are not using them.
o Make periodic backups of your mobile devices on a data server.

Guidelines for Mobile Computing Security
Encryption: Mobile devices that do store sensitive data can be protected by
means of encryption systems. Automatic encryption/decryption systems exist,
but are less secure than systems which require the user to enter a password at
the beginning of every session. Both Android and Apple iOS devices can be set
up to utilize encryption capabilities.
External Identification: End users should label their mobile devices with
their name and telephone contact information so lost devices can be returned to
them, even after their battery has gone dead.
Limiting Data Storage: One of the best ways to prevent the compromise or
loss of sensitive data is not to store it on a mobile device. Such data can be
stored in the cloud or accessed from a proprietary server. Naturally, means of
access must be thoroughly secured, or there is no advantage to be gained from
keeping sensitive data off a mobile device.
Lost Device Locator and Data Eraser Systems: Depending on the
mobile device and its operating systems, there are various technologies that
enable end users to locate a lost device (even if it's just between the couch
cushions). Failing that, there are ways to remotely erase sensitive data.
Encourage end users to enroll their devices in a good system, and to learn how
to use it.
Passwords and Timeouts: End users should set a password and a relatively
brief timer to shut down and lock their mobile devices when left idle for even a
few minutes. Passwords and timeouts prevent—or at least delay—unauthorized
users from gaining access to sensitive data not only on lost or stolen devices,
but also on devices left unattended in homes and offices.
Trusted Sources: Mobile devices can add software from a variety of
sources, but end users should rely only on trusted sources, such as the Apple
iTunes Store, Google Play, or the Amazon App Store for Android. Other
sources are less likely to thoroughly search for and prevent software
contaminated by viruses or other malware.
Updates: Hackers and defensive software are engaged in running battles for
superiority, so any delay in updating operating systems and/or security systems

leaves mobile devices particularly vulnerable. Systems should be set to check
automatically for updates, and users should get in the habit of performing
manual updates at regular intervals.
While it may seem like no data is safe in this technological age, users can
greatly decrease the likelihood of a security breach on their devices by adhering
to these mobile computing security guidelines.
What is Middleware?
Middleware is Software that provides a link between separate software
applications. It is a layer that lies between the operating system and
applications.
Use of Middleware:
 Provide interaction with another service or application.
 Filter data to make them friendly usable.
 Make an application independent from network services.
 Make an application reliable and always available.
 Add complementary attributes like semantics.

Types of Middleware:
1. Communication Middleware : Communication Middleware is used to
connect one application with another application. For Example connecting
one application with another application using telnet.
2. Message Oriented Middleware: It supports the receiving and sending of
messages over distributed applications. It enables applications to be
disbursed over various platforms. It makes the process of creating software
applications across many operating systems. It makes network protocols
less complicated. It holds many advantages over middleware alternatives
and is one of the most widely used types of middleware.
3. Object Oriented Middleware : Object Oriented Middleware is also known
as an object request broker. It provides the facility to send objects and
request services via an object oriented system. In short, it manages the
communication between objects.
4. Remote Procedure Call (RPC) Middleware : It provides the facility to
calls procedures on remote systems and is used to perform synchronous or
asynchronous interactions between applications or systems. It is usually
utilized within a software application.
5. Database Middleware: It provides direct access to databases and direct
interaction with databases, There are many database gateways and
connectivity options and you simply have to see what will best work for
your necessary solution. This is the most general and commonly known
type of middleware. This includes SQL database software.
6. Transaction Middleware : This type of middleware includes applications
like transaction processing monitors. It also encompasses web application
servers, These types of middleware are becoming more and more common
today.
7. Embedded Middleware : This type of middleware allows the facility of
communication and integration of services with an interface of software or
firmware. It acts as a liaison between embedded applications and the real
time operating system,
8. Content-Centric Middleware: This type of middleware allows you to
abstract specific content without worry of how it is obtained. This is done
through a simple provide / consume abstraction. It is similar to publish /
subscribe middleware, which is another type of this software that is often
used as a part of web based applications.

What is Gateway ?
Gateways are required when the networks between the device and the middleware having
different set of protocol.
For Example: an IVR Gateway is used to interface voice with a computer. WAP Gateway is
used to access internet on mobile phones

Making Existing Application Mobile‐Enabled
There are many applications that are now being used within the
intranet or the corporate network. These application need to be made
ubiquitous and mobile computing capable. There are many ways by
which this can be achieved:
 Enhance existing application take the current application.
Enhance the application to support mobile computing.
 Rent an application from an ASP, there are many organizations
who develop ubiquitous application and rent the same at a fee.
 Write a new application, develop a new application to meet the new
business requirement of the mobile computing.
 Buy a packaged solution, there are many companies who are
offering packaged solutions for various business areas starting from
manufacturing to sales and marketing. Buy and install one.
 Bridge the gap through middleware, use different middleware
techniques to facelift and mobile computing enable the existing
application.
 One of these techniques, or any combinations can be used to make an
application ubiquitous. If the enterprise has a source code for the
application, enhancement of the existing application may be a choice.
Writing a new application by taking care of all the aspects described
previously may also be a possibility. Buying a package or renting a
solution from an ASP can also be preferred path for some business
situations. Many of these applications might have been developed
inhouse, but may not be in a position to be enhanced. Some might
have been purchased as products. A product developed by outside
agency cannot be enhanced or changed as desired. In many of such
situations, mobile computing enabling can be done through
middleware. The combination of communication middleware and
application middleware can be used to make an application mobile.
By using a transcoding middleware, the application can be wireless-
enabled and used through WAP, J2ME or even SMS (Short Message
Service). Through middleware, some additional security features can
be added.

Mobile Internet Protocol (or Mobile IP)
Mobile IP
This is an IETF (Internet Engineering Task Force) standard communications
protocol designed to allow mobile devices' (such as laptop, PDA, mobile phone,
etc.) users to move from one network to another while maintaining their
permanent IP (Internet Protocol) address.
Defined in RFC (Request for Comments) 2002, mobile IP is an enhancement of
the internet protocol (IP) that adds mechanisms for forwarding internet traffic to
mobile devices (known as mobile nodes) when they are connecting through
other than their home network.
The following case shows how a datagram moves from one point to another
within the Mobile IP framework.
o First of all, the internet host sends a datagram to the mobile node using
the mobile node's home address (normal IP routing process).
o If the mobile node (MN) is on its home network, the datagram is
delivered through the normal IP (Internet Protocol) process to the mobile
node. Otherwise the home agent picks up the datagram.

o If the mobile node (MN) is on foreign network, the home agent (HA)
forwards the datagram to the foreign agent.
o The foreign agent (FA) delivers the datagram to the mobile node.
o Datagrams from the MN to the Internet host are sent using normal IP
routing procedures. If the mobile node is on a foreign network, the
packets are delivered to the foreign agent. The FA forwards the datagram
to the Internet host.
In the case of wireless communications, the above illustrations depict the use of
wireless transceivers to transmit the datagrams to the mobile node. Also, all
datagrams between the Internet host and the MN use the mobile node's home
address regardless of whether the mobile node is on a home or foreign network.
The care-of address (COA) is used only for communication with mobility
agents and is never seen by the Internet host
Components of Mobile IP
The mobile IP has following three components as follows:
1. Mobile Node (MN)
The mobile node is an end system or device such as a cell phone, PDA
(Personal Digital assistant), or laptop whose software enables network roaming
capabilities.
2. Home Agent (HA)
The home agent provides several services for the mobile node and is located in
the home network. The tunnel for packets towards the mobile node starts at
home agent. The home agent maintains a location registry, i.e. it is informed of
the mobile node's location by the current COA (care of address). Following
alternatives for the implementation of an HA exist.
o Home agent can be implemented on a router that is responsible for the home
network. This is obviously the best position, because without optimization to mobile
IP, all packets for the MN have to go through the router anyway.
o If changing the router's software is not possible, the home agent could also be
implemented on an arbitrary node in the subset. One biggest disadvantage of this
solution is the double crossing of the router by the packet if the MN is in a foreign

network. A packet for the mobile node comes in via the router; the HA sends it
through the tunnel which again crosses the router.
3. Foreign Agent (FA)
The foreign agent can provide several services to the mobile node during its
visit to the foreign network. The FA can have the COA (care or address) acting
as a tunnel endpoint and forwarding packets to the MN. The foreign agent can
be the default router for the MN.
Foreign agent can also provide security services because they belong to the
foreign network as opposed to the MN which is only visiting.
In short, FA is a router that may function as the point of attachment for the
mobile node when it roams to a foreign network delivers packets from the home
agent to the mobile node.
4. Care of Address (COA)
The Care- of- address defines the current location of the mobile node from an IP
point of view. All IP packets sent to the MN are delivered to the COA, not
directly to the IP address of the MN. Packet delivery toward the mobile node is
done using a tunnel. To be more precise, the COA marks the endpoint of the
tunnel, i.e. the address where packets exit the tunnel.
There are two different possibilities for the location of the care of address:
1. Foreign Agent COA: The COA could be located at the foreign agent, i.e.
the COA is an IP address of the foreign agent. The foreign agent is the
tunnel endpoint and forwards packets to the MN. Many MN using the FA
can share this COA as common COA.
2. Co-located COA: The COA is co-located if the MN temporarily acquired
an additional IP address which acts as a COA. This address is now
topologically correct, and the tunnel endpoint is at the mobile node. Co-
located address can be acquired using services such as DHCP. One problem
associated with this approach is need for additional addresses if MNs
request a COA. This is not always a good idea considering the scarcity of
IPv4 addresses.

5. Correspondent Node (CN)
At least one partner is needed for communication. The correspondent node
represents this partner for the MN. The correspondent node can be a fixed or
mobile node.
6. Home Network
The home network is the subset the MN belongs to with respect to its IP
address. No mobile IP support is needed within this network.
7. Foreign network
The foreign network is the current subset the MN visits and which is not the
home network.
Process of Mobile IP
The mobile IP process has following three main phases, which are:
1. Agent Discovery
During the agent discovery phase the HA and FA advertise their services on the
network by using the ICMP router discovery protocol (IROP).
Mobile IP defines two methods: agent advertisement and agent solicitation
which are in fact router discovery methods plus extensions.
o Agent advertisement: For the first method, FA and HA
advertise their presence periodically using special agent
advertisement messages. These messages advertisement can be
seen as a beacon broadcast into the subnet. For this
advertisement internet control message protocol (ICMP)
messages according to RFC 1256, are used with some mobility
extensions.
o Agent solicitation: If no agent advertisements are present or the
inter arrival time is too high, and an MN has not received a
COA, the mobile node must send agent solicitations. These
solicitations are again bases on RFC 1256 for router
solicitations.

2. Registration
The main purpose of the registration is to inform the home agent of the current
location for correct forwarding of packets.
Registration can be done in two ways depending on the location of the COA.
o If the COA is at the FA, the MN sends its registration request containing the COA to
the FA which is forwarding the request to the HA. The HA now set up a mobility
binding containing the mobile node's home IP address and the current COA.
Additionally, the mobility biding contains the lifetime of the registration which
is negotiated during the registration process. Registration expires automatically
after the lifetime and is deleted; so a mobile node should register before
expiration. After setting up the mobility binding, the HA send a reply message
back to the FA which forwards it to the MN.
o If the COA is co-located, registration can be very simpler. The mobile node may
send the request directly to the HA and vice versa. This by the way is also the
registration procedure for MNs returning to their home network.
3. Tunneling
A tunnel is used to establish a virtual pipe for data packets between a tunnel
entry and a tunnel endpoint. Packets which are entering in a tunnel are
forwarded inside the tunnel and leave the tunnel unchanged. Tunneling, i.e.,
sending a packet through a tunnel is achieved with the help of encapsulation.
Tunneling is also known as "port forwarding" is the transmission and data
intended for use only within a private, usually corporate network through a
public network.

2.2 Mobile IP
Mobile IP is a communication protocol (created by extending
Internet Protocol, IP) that allows the users to move from one network
to another with the same IP address. It ensures that the
communication will continue without user’s sessions or connections
being dropped.
Terminologies:
 Mobile Node (MN):
It is the hand-held communication device that the user caries e.g. Cell
phone.
 Home Network:
It is a network to which the mobile node originally belongs to as per its
assigned IP address (home address).
 Home Agent (HA):
It is a router in home network to which the mobile node was originally
connected
 Home Address:
It is the permanent IP address assigned to the mobile node (within its home
network).
 Foreign Network:
It is the current network to which the mobile node is visiting (away from its
home network).
 Foreign Agent (FA):
It is a router in foreign network to which mobile node is currently
connected. The packets from the home agent are sent to the foreign agent
which delivers it to the mobile node.
 Correspondent Node (CN):
It is a device on the internet communicating to the mobile node.
 Care of Address (COA):
It is the temporary address used by a mobile node while it is moving away
from its home network.

Working:
Correspondent node sends the data to the mobile node. Data packets contains
correspondent node’s address (Source) and home address (Destination).
Packets reaches to the home agent. But now mobile node is not in the home
network, it has moved into the foreign network. Foreign agent sends the care-
of-address to the home agent to which all the packets should be sent. Now, a
tunnel will be established between the home agent and the foreign agent by the
process of tunneling.
Tunneling establishes a virtual pipe for the packets available between a tunnel
entry and an endpoint. It is the process of sending a packet via a tunnel and it
is achieved by a mechanism called encapsulation.
Now, home agent encapsulates the data packets into new packets in which the
source address is the home address and destination is the care-of-address and
sends it through the tunnel to the foreign agent. Foreign agent, on other side of
the tunnel receives the data packets, decapsulates them and sends them to the
mobile node. Mobile node in response to the data packets received, sends a
reply in response to foreign agent. Foreign agent directly sends the reply to the
correspondent node.

Key Mechanisms in Mobile IP:
1. Agent Discovery:
Agents advertise their presence by periodically broadcasting their agent
advertisement messages. The mobile node receiving the agent
advertisement messages observes whether the message is from its own
home agent and determines whether it is in the home network or foreign
network.
2. Agent Registration:
Mobile node after discovering the foreign agent, sends registration request
(RREQ) to the foreign agent. Foreign agent in turn, sends the registration
request to the home agent with the care-of-address. Home agent sends
registration reply (RREP) to the foreign agent. Then it forwards the
registration reply to the mobile node and completes the process of
registration.
3. Tunneling:
It establishes a virtual pipe for the packets available between a tunnel entry
and an endpoint. It is the process of sending a packet via a tunnel and it is
achieved by a mechanism called encapsulation. It takes place to forward an
IP datagram from the home agent to the care-of-address. Whenever home
agent receives a packet from correspondent node, it encapsulates the packet
with source address as home address and destination as care-of-address.
Route Optimization in Mobile IP:
The route optimization adds a conceptual data structure, the binding cache, to
the correspondent node. The binding cache contains bindings for mobile
node’s home address and its current care-of-address.
Every time the home agent receives a IP datagram that is destined to a mobile
node currently away from the home network, it sends a binding update to the
correspondent node to update the information in the correspondent node’s
binding cache. After this the correspondent node can directly tunnel packets to
the mobile node.

How Mobile IP Works
Mobile IP enables routing of IP datagrams to mobile nodes. The mobile node's
home address always identifies the mobile node, regardless of its current point
of attachment to the Internet or an organization's network. When away from
home, a care-of address associates the mobile node with its home address by
providing information about the mobile node's current point of attachment to the
Internet or an organization's network. Mobile IP uses a registration mechanism
to register the care-of address with a home agent.
The home agent redirects datagrams from the home network to the care-of
address by constructing a new IP header that contains the mobile node's care-of
address as the destination IP address. This new header then encapsulates the
original IP datagram, causing the mobile node's home address to have no effect
on the encapsulated datagram's routing until it arrives at the care-of address.
This type of encapsulation is also called tunneling. After arriving at the care-of
address, each datagram is de-encapsulated and then delivered to the mobile
node.
The following illustration shows a mobile node residing on its home network,
Network A, before the mobile node moves to a foreign network, Network B.
Both networks support Mobile IP. The mobile node is always associated with its
home network by its permanent IP address, 128.226.3.30. Though Network A has
a home agent, datagrams destined for the mobile node are delivered through the
normal IP process.
Figure 1–2 Mobile Node Residing on Home Network
The following illustration shows the mobile node moving to a foreign network,
Network B. Datagrams destined for the mobile node are intercepted by the
home agent on the home network, Network A, encapsulated, and sent to the

foreign agent on Network B. Upon receiving the encapsulated datagram, the
foreign agent strips off the outer header and delivers the datagram to the mobile
node visiting Network B.
Figure 1–3 Mobile Node Moving to a Foreign Network
The care-of address might belong to a foreign agent, or might be acquired by
the mobile node through Dynamic Host Configuration Protocol (DHCP) or
Point-to-Point Protocol (PPP). In the latter case, a mobile node is said to have a
co-located care-of address.
The mobile node uses a special registration process to keep its home
agent informed about its current location. Whenever a mobile node moves from
its home network to a foreign network, or from one foreign network to another,
it chooses a foreign agent on the new network and uses it to forward a
registration message to its home agent.
Mobility agents (home agents and foreign agents) advertise their presence
using agent advertisement messages. A mobile node can optionally solicit an
agent advertisement message from any locally attached mobility agents through
an agent solicitation message. A mobile node receives these agent
advertisements and determines whether they are on its home network or a
foreign network.
When the mobile node detects that it is located on its home network, it operates
without mobility services. If returning to its home network from being
registered elsewhere, the mobile node deregisters with its home agent.

Mobile IP With Reverse Tunneling
The previous description of Mobile IP assumes that the routing within the
Internet is independent of the data packet's source address. However,
intermediate routers might check for a topologically correct source address. If
an intermediate router does check, you should set up a reverse tunnel. By setting
up a reverse tunnel from the mobile node's care-of address to the home agent,
you ensure a topologically correct source address for the IP data packet. A
mobile node can request a reverse tunnel between its foreign agent and its
home agent when the mobile node registers. A reverse tunnel is a tunnel that
starts at the mobile node's care-of address and terminates at the home agent. The
following illustration shows the Mobile IP topology that uses a reverse tunnel.
Figure 1–4 Mobile IP With a Reverse Tunnel
Limited Private Addresses Support
Mobile nodes that have private addresses which are not globally routable
through the Internet require reverse tunnels. Solaris Mobile IP supports only
privately addressed mobile nodes. See Overview of the Solaris Mobile IP
Implementation for the functions that Solaris Mobile IP does not support.
Enterprises employ private addresses when external connectivity is not required.
Private addresses are not routable through the Internet. When a mobile node has
a private address, the mobile node can only communicate with a correspondent
node through a reverse tunnel. The privately addressed correspondent node
must belong to the same home agent's administrative domain. The following
illustration shows a network topology with two privately addressed mobile
nodes that use the same care-of address when registered to the same foreign
agent.

Figure 1–5 Privately Addressed Mobile Nodes Residing on the Same Foreign Network
Because both privately addressed mobile nodes belong to the same
administrative domain, the home agent knows how to route data packets
between the two mobile nodes. Also, the foreign agent's care-of address and the
home agent's IP address must be globally routable addresses.
It is possible to have two privately addressed mobile nodes with the same IP
address residing on the same foreign network. This situation is only possible
when each mobile node has a different home agent. Also, this situation is only
possible when each mobile node is on different advertising subnets of a single
foreign agent. The following illustration shows a network topology that depicts
this case.
Figure 1–6 Privately Addressed Mobile Nodes Residing on Different Foreign Networks
Because both privately addressed mobile nodes have the same IP address and
because these mobile nodes belong to different home agent domains, the two
nodes cannot communicate with each other. However, each node can
communicate with nodes in its corresponding home agent's administrative
domain through the reverse tunnel. For example, Mobile Node 2 can
communicate with Correspondent Node 2 in the previous illustration.

A satellite is an object that revolves around another object. For example, earth
is a satellite of The Sun, and moon is a satellite of earth.
A communication satellite is a microwave repeater station in a space that is
used for telecommunication, radio and television signals. A communication
satellite processes the data coming from one earth station and it converts the
data into another form and send it to the second earth station.
How a Satellite Works
Two stations on earth want to communicate through radio broadcast but are too
far away to use conventional means. The two stations can use a relay station
for their communication. One earth station transmits the signal to the satellite.
Uplink frequency is the frequency at which ground station is communicating
with satellite. The satellite transponder converts the signal and sends it down to
the second earth station, and this is called Downlink frequency. The second
earth station also communicates with the first one in the same way.
Advantages of Satellite
The advantages of Satellite Communications are as follows −
 The Coverage area is very high than that of terrestrial systems.
 The transmission cost is independent of the coverage area.
 Higher bandwidths are possible.
Disadvantages of Satellite
The disadvantages of Satellite Communications are as follows −
 Launching satellites into orbits is a costly process.
 The bandwidths are gradually used up.
 High propagation delay for satellite systems than the conventional
terrestrial systems.
Mobile Communication Via Satellite

Satellite Communication Basics
The process of satellite communication begins at an earth station. Here an
installation is designed to transmit and receive signals from a satellite in orbit
around the earth. Earth stations send information to satellites in the form of
high powered, high frequency (GHz range) signals.
The satellites receive and retransmit the signals back to earth where they are
received by other earth stations in the coverage area of the satellite. Satellite's
footprint is the area which receives a signal of useful strength from the
satellite.
The transmission system from the earth station to the satellite through a
channel is called the uplink. The system from the satellite to the earth station
through the channel is called the downlink.
Satellite Frequency Bands
The satellite frequency bands which are commonly used for communication are
the Cband, Ku-band, and Ka-band. C-band and Ku-band are the commonly
used frequency spectrums by today's satellites.
It is important to note that there is an inverse relationship between frequency
and wavelength i.e. when frequency increases, wavelength decreases this helps
to understand the relationship between antenna diameter and transmission
frequency. Larger antennas (satellite dishes) are necessary to gather the signal
with increasing wavelength.
Earth Orbits
A satellite when launched into space, needs to be placed in certain orbit to
provide a particular way for its revolution, so as to maintain accessibility and
serve its purpose whether scientific, military or commercial. Such orbits which
are assigned to satellites, with respect to earth are called as Earth Orbits. The
satellites in these orbits are Earth Orbit Satellites.
The important kinds of Earth Orbits are −
 Geo-synchronous Earth Orbit
 Geo-stationary Earth Orbit
 Medium Earth Orbit
 Low Earth Orbit

Geo-synchronous Earth Orbit (GEO) Satellites
A Geo-synchronous Earth orbit Satellite is one which is placed at an altitude of
22,300 miles above the Earth. This orbit is synchronized with a side real
day (i.e., 23hours 56minutes). This orbit can have inclination and
eccentricity. It may not be circular. This orbit can be tilted at the poles of the
earth. But it appears stationary when observed from the Earth.
The same geo-synchronous orbit, if it is circular and in the plane of equator, it
is called as geo-stationary orbit. These Satellites are placed at 35,900kms
(same as geosynchronous) above the Earth’s Equator and they keep on rotating
with respect to earth’s direction (west to east). These satellites are
considered stationary with respect to earth and hence the name implies.
Geo-Stationary Earth Orbit Satellites are used for weather forecasting, satellite
TV, satellite radio and other types of global communications.
The above figure shows the difference between Geo-synchronous and Geo-
Stationary orbits. The Axis of rotation indicates the movement of Earth.
The main point to note here is that every Geo-Stationary orbit is a Geo-
Synchronous orbit. But every Geo-Synchronous orbit is NOT a Geo-stationary
orbit.

Medium Earth Orbit (MEO) Satellites
Medium earth orbit (MEO) satellite networks will orbit at distances of about
8000 miles from earth's surface. Signals transmitted from a MEO satellite
travel a shorter distance. This translates to improved signal strength at the
receiving end. This shows that smaller, more lightweight receiving terminals
can be used at the receiving end.
Since the signal is travelling a shorter distance to and from the satellite, there is
less transmission delay. Transmission delay can be defined as the time it takes
for a signal to travel up to a satellite and back down to a receiving station.
For real-time communications, the shorter the transmission delay, the better
will be the communication system. As an example, if a GEO satellite requires
0.25 seconds for a round trip, then MEO satellite requires less than 0.1 seconds
to complete the same trip. MEOs operates in the frequency range of 2 GHz and
above.
Low Earth Orbit (LEO) Satellites
The LEO satellites are mainly classified into three categories namely, little
LEOs, big LEOs, and Mega-LEOs. LEOs will orbit at a distance of 500 to
1000 miles above the earth's surface.
This relatively short distance reduces transmission delay to only 0.05 seconds.
This further reduces the need for sensitive and bulky receiving equipment.
Little LEOs will operate in the 800 MHz (0.8 GHz) range. Big LEOs will
operate in the 2 GHz or above range, and Mega-LEOs operates in the 20-30
GHz range.
The higher frequencies associated with Mega-LEOs translates into more
information carrying capacity and yields to the capability of real-time, low
delay video transmission scheme.
High Altitude Long Endurance (HALE) Platforms
Experimental HALE platforms are basically highly efficient and lightweight
airplanes carrying communications equipment. This will act as very low earth
orbit geosynchronous satellites.
These crafts will be powered by a combination of battery and solar power or
high efficiency turbine engines. HALE platforms will offer transmission
delays of less than 0.001 seconds at an altitude of only 70,000 feet, and
even better signal strength for very lightweight hand-held receiving devices.

Orbital Slots
Here there may arise a question that with more than 200 satellites up there in
geosynchronous orbit, how do we keep them from running into each other or
from attempting to use the same location in space? To answer this problem,
international regulatory bodies like the International Telecommunications
Union (ITU) and national government organizations like the Federal
Communications Commission (FCC) designate the locations on the
geosynchronous orbit where the communications satellites can be located.
These locations are specified in degrees of longitude and are called as orbital
slots. The FCC and ITU have progressively reduced the required spacing down
to only 2 degrees for C-band and Ku-band satellites due to the huge demand for
orbital slots.

2.2 Satelite communication
Types of Satellite Systems
Satellites have been put in space for various purposes and their placement in
space and orbiting shapes have been determined as per their specific
requirements.
Four different types of satellites orbits have been identified.
These are:
o GEO (Geostationary Earth Orbit) at about 36,000km above
the earth's surface.
o LEO (Low Earth Orbit) at about 500-1500km above the
earth's surface.
o MEO (Medium Earth Orbit) or ICO (Intermediate Circular
Orbit) at about 6000-20,000 km above the earth's surface.
o HEO (Highly Elliptical Orbit)

1. GEO (Geostationary Earth Orbit)
o If a satellite should appear in fixed in the sky, it requires a period of 24
hours. Using the equation of distance earth and satellite, r =
(g.r2
/2.r.f)2
)1/3
and the period of 24 hours f = 1/24 h. the resulting distance
is 35,786 km. the orbit must have an inclination of 0 degree.
o Geostationary satellites have a distance of almost 36,000 km to the earth.
Examples are almost all TV and radio broadcast satellites, any weather
satellites and satellites operating as backbones for the telephone network.
o Objects in GEO moves around the earth at the same speed as the earth
rotates. This means geostationary satellites remain in the same position
relative to the surface of earth.
Advantages of GEO satellite
o Three Geostationary satellites are enough for a complete coverage of
almost any spot on earth.
o Receivers and senders can use fixed antenna positions, no adjusting is
needed.
o GEOs are ideal for TV and radio broadcasting.
o Lifetime expectations for GEOs are rather high, at about 15 years.
o Geostationary satellites have a 24 hour view of a particular area.
o GEOs typically do not need handover due to the large footprints.
o GEOs don't exhibit any Doppler shift because the relative movement is
zero.
Disadvantages of GEO satellite
o Northern or southern regions of the earth have more problems receiving
these satellites due to the low elevation above latitude of 60 degree, i.e.
larger antennas are needed in this case.
o Shading of the signals in cities due to high buildings and the low elevation
further away from the equator limits transmission quality.
o The transmit power needed is relatively high (about 10 W) which causes
problems for battery powered devices.
o These satellites can't be used for small mobile phones.

o The biggest problem for voice and also data communication is high latency
of over 0.25s one way-retransmission schemes which are known from fixed
networks fail.
o Transferring a GEO into orbit is very expensive.
2. LEO (Low Earth Orbit)
o As LEOs circulate on a lower orbit, it is obvious that they exhibit a much
shorter period (the typical duration of LEO periods are 95 to 120 minutes).
Additionally, LEO systems try to ensure a high elevation for every spot on
earth to provide a high quality communication link.
o Each LEO satellite will only be visible from the earth for about ten minutes.
o A further classification of LEOs into little LEOs with low bandwidth
services (some 100 bit/s), big LEOs (some 1,000 bit/s) and broadband LEOs
with plans reaching into the Mbits/s range can be found in Comparetto
(1997).
o LEO satellites are much closer to earth than GEO satellites, ranging from
500 to 1,500 km above the surface. LEO satellites do not stay in fixed
position relative to the surface, and are only visible for 15 to 20 minutes each
pass.
Advantages of LEO satellite
o Using advanced compression schemes, transmission rates of about 2,400
bit/s can be enough for voice communication.
o LEOs even provide this bandwidth for mobile terminals with omni-
directional antennas using low transmit power in the range of 1 W.
o A LEO satellite smaller area of coverage is less of a waste of bandwidth.
o Using advanced compression schemes, transmission rates of about 2,400
bit/s can be enough for voice communication.
o A LEO satellite's proximity to earth compared to a Geostationary satellite
gives it a better signal strength and less of a time delay, which makes it
better for point to point communication.
o Smaller footprints of LEOs allow for better frequency reuse, similar to the
concepts used for cellular networks.

Disadvantages of LEO satellite
o The biggest problem of the LEO concept is the need for many satellites if
global coverage is to be reached.
o The high number of satellites combined with the fast movement's results in a
high complexity of the whole satellite system.
o The short time of visibility with a high elevation requires additional
mechanism for connection handover between different satellites.
o One general problem of LEO is the short lifetime of about five to eight years
due to atmospheric drag and radiation from the inner Van Allen belt.
o The low latency via a single LEO is only half of the story.
o Other factors are the need for routing of data packets from satellite to
satellite (or several times from base stations to satellites and back) if a user
wants to communicate around the world.
o A GEO typically does not need this type of routing, as senders and receivers
are most likely in the same footprints.
3. MEO (Medium Earth Orbit)
o A MEO satellite situates in orbit somewhere between 6,000 km to 20,000 km
above the earth's surface.
o MEO satellites are similar to LEO satellites in the context of functionality.
o MEO satellites are similar to LEO satellite in functionality.
o Medium earth orbit satellites are visible for much longer periods of time than
LEO satellites usually between 2 to 8 hours.
o MEO satellites have a larger coverage area than Low Earth Orbit satellites.
o MEOs can be positioned somewhere between LEOs and GEOs, both in
terms of their orbit and due to their advantages and disadvantages.
Advantages of MEO
o Using orbits around 10,000km, the system only requires a dozen satellites
which is more than a GEO system, but much less than a LEO system.
o These satellites move more slowly relative to the earth's rotation allowing
a simpler system design (satellite periods are about six hours).

o Depending on the inclination, a MEO can cover larger populations, so
requiring fewer handovers.
o A MEO satellite's longer duration of visibility and wider footprint means
fewer satellites are needed in a MEO network than a LEO network.
Disadvantages of MEO
o Again due to the larger distance to the earth, delay increases to about 70-
80 ms.
o The satellites need higher transmit power and special antennas for smaller
footprints.
o A MEO satellite's distance gives it a longer time delay and weaker signal
than LEO satellite.
4. HEO (High Earth Orbit)
o The High Earth orbit satellite is the only non-circular orbit of the four
types.
o HEO satellite operates with an elliptical orbit, with a maximum altitude
(apogee) similar to GEO, and a minimum altitude (perigee) similar to the
LEO.
o The HEO satellites used for the special applications where coverage of
high latitude locations is required.

Unit 2 Design mobile computing architecture MC1514

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Unit 2 Design mobile computing architecture MC1514