Bit4201 mobile computing

Mount Kenya University
P.O. Box 342-01000 Thika
Email: info@mku.ac.ke
Web: www.mku.ac.ke
DEPARTMENT OF INFORMATION
TECHNOLOGY
COURSE CODE: BIT4201
COURSE TITLE: MOBILE COMPUTING
Instructional manual for BBIT – Distance Learning

TABLE OF CONTENT
TABLE OF CONTENT ......................................................................................................................................2
COURSE OUTLINE..........................................................................................................................................6
CHAPTER ONE: INTRODUCTION TO COMPUTER NETWORKING.................................................................11
Definitions...............................................................................................................................................11
Network Topologies................................................................................................................................16
Network Protocols ..................................................................................................................................20
Open System Interconnection(OSI) Protocol..........................................................................................21
Network Operating Systems...................................................................................................................22
Switching Techniques .............................................................................................................................25
Multiplexing............................................................................................................................................30
Analog and Digital Data transmission.....................................................................................................34
Chapter Review Questions......................................................................................................................37
CHAPTER TWO: INTRODUCTION TO MOBILE COMPUTING AND WIRELESS COMMUNICATION................37
Introduction ............................................................................................................................................38
Definitions...............................................................................................................................................39
Mobile Computing Advantages...............................................................................................................40
Limitations of mobile computing............................................................................................................41
CHAPTER THREE: MOBILE COMPUTING ARCHITECTURE............................................................................45
Introduction ............................................................................................................................................45
Public switched telephone network .......................................................................................................45
Data Communications.............................................................................................................................49
Cellular Digital Packet Data (CDPD) Technology.....................................................................................50
Specialized Mobile Radio........................................................................................................................57

General Packet Radio Service (GPRS) .....................................................................................................58
GPRS Network Architecture...............................................................................................................63
Advanced Mobile Phone System ............................................................................................................66
Digital - Advanced Mobile Phone System (D-AMPS) ..............................................................................68
GSM (Global System for Mobile communication) ..................................................................................69
High-Speed Circuit-Switched Data (HSCSD)............................................................................................87
EDGE (Enhanced Data GSM Environment) .............................................................................................87
CHAPTER FOUR: WIRELESS TECHNOLOGIES ...............................................................................................90
WiFi .........................................................................................................................................................90
WiFi Hotspots..........................................................................................................................................93
Building a Wireless Network...................................................................................................................93
WAP.........................................................................................................................................................95
The Cellular Explosion.............................................................................................................................96
Wireless Markup Language.....................................................................................................................96
Wireless Application Protocol.................................................................................................................97
The Evolution of Wireless Network Security ..........................................................................................99
Wireless Mesh Networks......................................................................................................................102
Wireless Mesh Technology...................................................................................................................104
Applications for Wireless Mesh Networks............................................................................................105
Wireless Internet Cards for Laptops, Desktops and PDAs ....................................................................111
Comparing Wireless Internet Connection Cards ..................................................................................112
Wireless Networks................................................................................................................................113
Chapter Review Questions....................................................................................................................114
CHAPTER FIVE: SATELLITES .......................................................................................................................115

Introduction to Satellites ......................................................................................................................115
Whose Satellite Was the First to Orbit Earth?......................................................................................116
How Is a Satellite Launched into an Orbit?...........................................................................................117
Orbital Velocity and Altitude ................................................................................................................118
What Is a Satellite Launch Window? ....................................................................................................120
How Are Satellite Orbits Predicted? .....................................................................................................123
Satellite Altitudes..................................................................................................................................123
80 to 1,200 miles -- Asynchronous Orbits ........................................................................................123
3,000 to 6,000 miles -- Asynchronous Orbits ...................................................................................124
6,000 to 12,000 miles - Asynchronous Orbits...................................................................................124
22,223 Miles - Geostationary Orbits.................................................................................................126
What Is AMSAT?....................................................................................................................................127
Satellite Internet ...................................................................................................................................128
Global Positioning System (GPS)...........................................................................................................130
CHAPTER SIX: VOICE OVER INTERNET PROTOCOL (VoIP) .........................................................................137
Introduction to VoIP..............................................................................................................................137
Using VoIP.............................................................................................................................................138
Circuit Switching ...................................................................................................................................140
Packet Switching...................................................................................................................................141
Advantages of Using VoIP.....................................................................................................................142
Disadvantages of Using VoIP.................................................................................................................144
CHAPTER SEVEN: BLUETOOTH..................................................................................................................147
Introduction to bluetooth.....................................................................................................................147

How Bluetooth Creates a Connection...................................................................................................148
Why is it called Bluetooth? ...................................................................................................................149
How Bluetooth Operates ......................................................................................................................149
Bluetooth Piconets................................................................................................................................151
CHAPTER EIGHT: SAMPLE PAPERS ............................................................................................................154

COURSE OUTLINE
BIT4201: Mobile Computing
Contact hours 42
Prerequisite: BIT 2203 Introduction to Data Communication and Computer Networks
Purpose: To describe the development of wireless and mobile tools techniques and technologies.
To develop applications that exploits the interface between information and communication
technologies.
Objectives: By the end of the course unit a learner shall be:
 Conversant with computer networking technologies
 Describe wireless and mobile communications.
 Explain the foundations of wireless and mobile technologies.
 Conversant with wireless and mobile application protocols.
 Explain cellular telephony
 Be aware of paging systems.
Teaching methodology
Lectures, tutorials and laboratory exercises
Assessment
CAT’s 30%, End of Semester exam 70%
Required text books
Rogers G.S & Edwards J. S, Wireless technology, Prentice Hall (ISBN 0-13-09486)
Martin J. (2001) Telecommunications and the computer, Prentice Hall International

Course Outline
ONE: INTRODUCTION TO COMPUTER NETWORKING
 Definitions
 Network Topologies
 Network Protocols
 Open System Interconnection(OSI) Protocol
 Network Operating Systems
 Switching Techniques
 Multiplexing
 Analog and Digital Data transmission
 TWO: INTRODUCTION TO MOBILE COMPUTING AND WIRELESS
COMMUNICATION
 Introduction
 Definitions
 Mobile Computing Advantages
 Limitations of mobile computing
THREE: MOBILE COMPUTING ARCHITECTURE
 Introduction
 Public switched telephone network
 Data Communications
 Cellular Digital Packet Data (CDPD) Technology

 Specialized Mobile Radio
 General Packet Radio Service (GPRS)
 GPRS Network Architecture
 Advanced Mobile Phone System
 Digital - Advanced Mobile Phone System (D-AMPS)
 GSM (Global System for Mobile communication)
 High-Speed Circuit-Switched Data (HSCSD)
 EDGE (Enhanced Data GSM Environment)
FOUR: WIRELESS TECHNOLOGIES
 WiFi
 WiFi Hotspots
 Building a Wireless Network
 WAP
 The Cellular Explosion
 Wireless Markup Language
 Wireless Application Protocol
 The Evolution of Wireless Network Security
 Wireless Mesh Networks
 Wireless Mesh Technology
 Applications for Wireless Mesh Networks
 Wireless Internet Cards for Laptops, Desktops and PDAs

 Comparing Wireless Internet Connection Cards
 Wireless Networks
FIVE: SATELLITES
 Introduction to Satellites
 Whose Satellite Was the First to Orbit Earth?
 How Is a Satellite Launched into an Orbit?
 Orbital Velocity and Altitude
 What Is a Satellite Launch Window?
 How Are Satellite Orbits Predicted?
 Satellite Altitudes
 80 to 1,200 miles -- Asynchronous Orbits
 3,000 to 6,000 miles -- Asynchronous Orbits
 6,000 to 12,000 miles - Asynchronous Orbits
 22,223 Miles - Geostationary Orbits
 What Is AMSAT?
 Satellite Internet
 Global Positioning System (GPS)
SIX: VOICE OVER INTERNET PROTOCOL (VoIP)
 Introduction to VoIP
 Using VoIP
 Circuit Switching

 Packet Switching
 Advantages of Using VoIP
 Disadvantages of Using VoIP
SEVEN: BLUETOOTH
 Introduction to bluetooth
 How Bluetooth Creates a Connection
 Why is it called Bluetooth?
 How Bluetooth Operates
 Bluetooth Piconets

CHAPTER ONE: INTRODUCTION TO COMPUTER
NETWORKING
Learning Objectives:
By the end of this chapter the learner shall be able to;
i. Understand the overview of computer networks
ii. Understand network topologies
Definitions
Network - A group of computers connected together in a way that allows information to be
exchanged between the computers.
Node - Anything that is connected to the network. While a node is typically a computer, it can
also be devices such as:
– Mainframes, minicomputers, supercomputers
– Workstations
– Printers, disk servers, robots
– X-terminals
– Gateways, switches, routers, bridges
– Cellular phone, Pager.
– Refrigerator, Television, Video Tape Recorder
Segment - Any portion of a network that is separated, by a switch, bridge or router, from other
parts of the network.
Backbone - The main cabling of a network that all of the segments connect to. Typically, the
backbone is capable of carrying more information than the individual segments. For example,
each segment may have a transfer rate of 10 Mbps (megabits per second: 1 million bits a
second), while the backbone may operate at 100 Mbps.

Topology - The way that each node is physically connected to the network.
Network Types (classification based on Network size)
LAN - Local Area Network - A LAN connects network devices over a relatively short distance.
A networked office building, school, or home usually contains a single LAN, though sometimes
one building will contain a few small LANs (perhaps one per room), and occasionally a LAN
will span a group of nearby buildings.
Metropolitan Area Network - a network spanning a physical area larger than a LAN but
smaller than a WAN, such as a city. A MAN is typically owned an operated by a single entity
such as a government body or large corporation.
WAN - Wide Area Network - As the term implies, a WAN spans a large physical distance. The
Internet is the largest WAN, spanning the Earth. A WAN is a geographically-dispersed
collection of LANs. A network device called a router connects LANs to a WAN.
Basic Components of Network
The most common components of a network are:
Terminal
Over the years, the data terminal market has increased substantially and there are now literally
hundreds of manufactures and many different kinds if terminal. However, the fact is that all of
these terminals have been designed primarily to input and display information in some form or
another. Therefore, even though specific characteristics such as screen size and keyboard layout
may differ, they can generally be categorized into three simple groups.
1. Dumb Terminals

Dumb terminals are those which have limited functions and are driven with information from a
host computer. Normally, they consist of a Cathode Ray Tube (CRT) display screen with a full
alphanumeric keyboard and can be connected directly to a computer system (host computer)
through some sort of communications interface. In most cases, data is transmitted directly
through the communication interface as it is typed on the keyboard.
2. Intelligent Terminals
The category of intelligent or programmable terminals is probably the largest and widest ranging
group. Unlike dumb terminals, intelligent terminals are equipped with a processor that can
support an instruction set to direct the basic functions of the terminal. Like any other type of
computer that has a processor, these terminals normally have additional memory and storage
devices such as disc drives.
Intelligent terminal are, therefore, capable of stand-alone processing and can support a variety of
software applications which, in turn, enable them to support a variety of communications
interfaces through the use of emulation program. This is also means that, unlike dumb terminals,
intelligent terminals are able to use addresses and sophisticated access method to transmit and
receive messages.
3. Graphic Terminals
Graphic terminals are display devices that provide a means not only for displaying data in
graphical form, but also for manipulating and modifying the data presented. Generally, graphic
terminal keyboards have a number of specific or programmable function keys in addition to the
full alphanumeric keys of a normal keyboard and the resolution of the display screen is normally
a lot higher to enable more detailed displays
Workstation
A workstation is a client. More specifically, it is a standalone computer equipped with it‘s own
processor, system and application software. It can perform its functions independent of the
network. To expand its resources and knowledge, it may get connected to a network.
Server

Network plays one of two basic roles at any given moment, the computer is either acting s a
client or as a server. A server is a computer that shares its
Resources across the network, and a client are one that accesses shared resources. Depending on
the size and requirements of the network, servers can be classified as below:
1. File Server
A file server allows user to share files. It several LAN users need access to an application such as
word processing, only one copy of the application software needs to reside on a file server. This
copy can be shared among all the users. When a user requests to start an application, that
application is downloaded into the users workstation.
Consider the saving in disk space in a company having 100 users for application package that
requires 10 MB of disk storage. Storage on the file server requires only 10 MB of disk space for
all users. Storing the same application on 100 users‘ local disk drives will require 1,000 MB of
disk space.
This is only an example of one application. Same logic can be applied when hundreds of
different application programs needed.
2. Database Server
The database server was developed to solve the problem of passing an entire file over the
medium. The most common example of a database server is the SQL server. Structured Query
Language (SQL) is standard database definition, access, and update language for relational
database. An SQL server accepts a database request, accesses all necessary records locally, and
then sends only the result back to the requester (not the whole database).
3. Print Server
Print server allows anyone on the network to have access to a printing service.
4. Disk Server
It is server with large storage. A portion of storage is given to each user to store their files/data. It
is very useful in university where each student is given a user account with password and some
storage space in disk server. Once the student completes the education the same space can be
assigned to new student.

5. Dedicated Vs Non-Dedicated Server
Many networks will let their user run standard programs while their computer is
simultaneously functioning as a server to others. A computer that both runs standard programs
and lets other user see its data at the same time is said to be ―non-dedicated server‖. Non-
dedicated servers can be clever way of setting up a small LAN without having to buy any extra
system. Dedicated server are specially assigned for network management and provided no
general-purpose services.
Network Interface Card
Attaching a computer to a network requires a physical interface between computer and the
networking medium. For PCs, this interface resides in a special network interface card (NIC),
also known as network adapter or a network card that plugs into an adapter slot inside the
computer‘s case. Laptops and other computers may include built-in interface or use special
modular interface such as PC card interface, to accommodate a network adapter of some kind.
For any computer, a NIC performs following crucial tasks:
1. It establishes and manages the computer‘s network connection.
2. it translates digital data( of source computer) into signals (appropriate for the networking
medium) for outgoing messages, and translates from signals into digital computer data for
incoming messages.
3. Converts serial incoming data via cable into parallel data to for CPU, and vice versa.
4. It has some memory, which acts as a holding tank or buffer. It buffers the data to control the
data flow.
Other Network Devices
Network
Component
Functions OSI Model
Modem Puts a message (baseband signal) on a
carrier for efficient transmission; takes
the baseband signal from the carrier.
Physical (Layer 1)
Repeater Receives signal, amplifies it, and then Physical (Layer 1)

(Regenerator) retransmits it.
Bridge Connects networks with different Layer 2
protocols; divides a network into several
segments to filter traffic.
Data Link (Layer 2)
Hub Connects computers in a network;
receives a packet from a sending
computer and transmits it to all other
computers.
Physical (Layer 1)
Switch Connects computers in a network;
receives a packet from a sending
computer and transmits it only to its
destination.
Data Link (Layer 2)
Access Point Connects computers in a wireless
network; connects the wireless network
to wired networks; connects it to the
Internet.
Data Link (Layer 2)
Router Forwards a packet to its destination by
examining the packet destination network
address.
Network (Layer 3)
Residential Gateway Connects a home network to the Internet;
hides all computers in the home network
from the Internet.
Network (Layer 3)
Gateway Connects two totally different networks;
translates one signaling/protocol into
another.
All layers
Network Topologies
A network topology can be physical or logical.
Physical Topology is the actual layout of a network and its connections. Logical Topology is the
way in which data accesses the medium and transmits packets. There are several network
topologies:

Physical Bus Topology
Each node is daisy-chained (connected one right after the other) along the same backbone.
Information sent from a node travels along the backbone until it reaches its destination node.
Each end of a bus network must be terminated with a resistor to keep the packets from getting
lost.
Physical Ring Topology
Similar to a bus network, rings have nodes daisy chained, but the end of the network in a ring
topology comes back around to the first node, creating a complete circuit. Each node takes a turn
sending and receiving information through the use of a token. The token along with any data is
sent from the first node to the second node which extracts the data addressed to it and adds any
data it wishes to send. Then second node passes the token and data to the third node, etc. until it
comes back around to the first node again. Only the node with the token is allowed to send data.
All other nodes must wait for the token to come to them.
Physical Star Topology
In a star network, each node is connected to a central device called a hub. The hub takes a signal
that comes from any node and passes it along to all the other nodes in the network. A hub does
not perform any type of filtering or routing of the data. A hub is a junction that joins all the
different nodes together.
Logical Topologies
There are three logical topologies (bus, ring, and switching) which are usually implemented as a
physical star.
Logical Bus Topology
Modern Ethernet networks are Star Topologies (physically) but logically they are bus topologies.
The Hub is at the centre, and defines a Star Topology. In any network, computers communicate
by sending information across the media as a series of signals. In a logical bus topology, the
signals travel along the length of the cable in all directions until they weaken enough so as not to
be detectable or until they encounter a device that absorbs them. This traveling across the
medium is called signal propagation
When a computer has data to send, it addresses that data, breaks it into manageable chunks, and
sends it across the network as electronic signals
 All computers on a logical bus receive them

 Only the destination computer accepts the data
 All users must share the available amount of transmission time, implying network
performance is reduced
 Collisions are bound to occur since all nodes are sharing same bus.
Logical Ring Topology
Data in a logical ring topology travels from one computer to the next computer until the data
reaches its destination. Token passing is one method for sending data around a ring
Token is a small packet which passes around the ring to each computer in turn.
If a computer (sender) has packets to send, it modifies the token, adds address and data, and
sends it around the ring. The receiver returns an acknowledgement packet to the sender.
Upon receiving the acknowledgement packet, the sender releases the tokens and sends it around
the ring for another sender to use.
Logical ring can be implemented on a physical star. Modern logical ring topologies use “smart
hubs” that recognize a computer‘s failure and remove the computer from the ring automatically.
One advantage of the ring topology lies in its capability to share network resources fairly.
Switching
A switch takes a signal coming from a device connected and builds a circuit on the fly to
forward the signal to the intended destination computer Superior to other logical topologies
because unlike bus and ring, multiple computers can communicate simultaneously without
affecting each other. Switching is the dominant logical topology in LAN design.
Transmission Media
This refers to the mode in which messages are delivered from one node to another over the
network. There are several types of media:
Guided Transmission Media - uses a conductor cable to transmit data e.g. twisted
pair(shielded/unshielded), coaxial cable.
Twisted pair is two insulated copper wires that are twisted around each other to minimize
interference and noise from other wires. Based on the presence of individual shield and overall

(outer) shield, there are three types of twisted pair, i.e. UTP(unshielded twisted pair),
STP(shielded twisted pair), and ScTP(Screened twisted pair). Individual shield encloses a single
twisted pair, while outer shield encloses all twisted pairs in a cable. A shield is a protective
sheath that is made from conductive material (metal) and functions to protect the twisted pair
from external interference. An insulator is made from non-conductive material, such as plastic.
UTP (Unshielded Twisted Pair) is a cable containing several twisted pairs that is only insulated
but not shielded. UTP is the most widely used cable in telephone and computer networks because
it is relatively cheaper than other cables and performs well in normal electrical environment such
as inside an office or a house.
Coaxial cable contains a solid or stranded wire in the core that is insulated with a dielectric layer,
then protected with a solid or braided metallic shield, and covered with an outer insulator.
Electromagnetic wave propagation in a coaxial cable is confined within the space between the
core and the outer conductors. The structure of a coaxial cable makes it less susceptible to
interference, noise, and crosstalk than the twisted pair cable.
Glass or plastic - Uses optical technology to transmit data using light waves e.g. fiber optics
Fiber-optic cable or optical fiber provides a medium for signals using light rather than electricity.
Light waves are immune to electromagnetic interference and crosstalk. Optical fiber can be used
for much longer distances before the signal must be amplified. Data transmission using optical
fiber is many times faster than with electrical methods.
Wireless transmission - Uses air interface to transmit e.g. microwave, satellite. Microwave links
are widely used to provide communication links when it is impractical or too expensive to install
physical transmission media. Two properties of microwave transmission place restrictions on its
use. First, microwaves travel in a straight line and will not follow the earth’s curvature. Second,
atmospheric conditions and solid objects interfere with microwaves. For example, they cannot
travel through buildings.
Satellite transmission is microwave transmission in which one of the stations is a satellite
orbiting the earth. A microwave beam is transmitted to the satellite from the ground. This beam
is received and retransmitted (relayed) to the predetermined destination. Receiver and transmitter
in satellites are known as transponder. The optimum frequency range for satellite transmission is
in the range 1 to 10 GHz. Below 1 GHz, there is significant noise from natural sources,

atmospheric noise, and noise from electronic devices. Above 10 GHz, the signal is attenuated by
atmospheric absorption.
Network Protocols
Communication between devices on a network is governed by a set of rules called protocols.
There are two types of network protocols, TCP/IP and OSI.
TCP/IP Protocol
TCP/IP is responsible for a wide range of activity: it interfaces with hardware, route data to
appropriate nodes, provides error control, and much more. The developers of TCP/IP designed a
modular protocol stack- meaning that the TCP/IP system was divided into separate components
or layers. But why use a modular design? Not only does it aid in the education process, but it
also lets manufacturers easily adapt to specific hardware and operating system needs.
For example- if we had a token ring network and an extended star network, we surely wouldn‘t
want to create entirely different network software builds for each one. Instead, we can just edit
the network layer, called the Network Access Layer, to allow compatibility. Not only does this
benefit manufacturers, but it greatly aids networking students in education. The TCP/IP suite is
divided into four layers.
Network Access Layer – The Network Access Layer is fairly self explanatory- it interfaces with
the physical network. It formats data and addresses data for subnets, based on physical hardware
addresses. More importantly, it provides error control for data delivered on the physical network.
Internet Layer – The Internet Layer provides logical addressing. More specifically, the internet
layer relates physical addresses from the network access layer to logical addresses. This can be
an IP address, for instance. This is vital for passing along information to subnets that aren‘t on
the same network as other parts of the network. This layer also provides routing that may reduce
traffic, and supports delivery across an internetwork. (An internetwork is simply a greater
network of LANs, perhaps a large company or organization.)
Transport Layer – The Transport Layer provides flow control, error control, and serves as an
interface for network applications. An example of the transport layer would be Transmission
Control Protocol (TCP) - a protocol suite that is connection-oriented. We may also use
UDP(User Datagram Protocol)- a connectionless means of transporting data.

Application Layer – Lastly, we have the Application Layer. We use this layer for
troubleshooting, file transfer, internet activities, and a slew of other activities. This layer interacts
with many types of applications, such as a database manager, email program, or Telnet.
Open System Interconnection(OSI) Protocol
The International Organization of Standardization (ISO) defined procedures for computer
communications which was called Open System Interconnection (OSI) Reference Model or OSI
Model for short. The OSI Model describes how data flows from one computer to another
computer in a network.
The OSI Model
The Open System Interconnection Model, more commonly known as simply OSI, is another
model that can help break the TCP/IP suite into modules. Technically speaking, it is exactly the
same as the TCP/IP model, except that it has more layers. This is currently being pushed by
Cisco since it aids in learning the TCP/IP stack in an easier manner.
 Physical Layer – They Physical Layer converts data into streams of electric or analog
pulses- commonly referred to as “1‘s and 0‘s.” Data is broke down into simple electric
pulses, and rebuilt at the receiving end.
 Data Link Layer – The Data Link layer provides an interface with the network adapter,
and can also perform basic error checking. It also maintains logical links for subnets, so
that subnets can communicate with other parts of the network without problem.

 Network Layer – Much like the Transport Layer of the TCP/IP model, the Network
Layer simply supports logical addressing and routing. The IP protocol operates on the
Network Layer.
 Transport Layer – Since we left out the error and flow control in the Network Layer, we
introduce it into the Transport Layer. The Transport Layer is responsible for keeping a
reliable end-to-end connection for the network.
 Session Layer – The Session Layer establishes sessions between applications on a
network. This may be useful for network monitoring, using a login system, and reporting.
The Session Layer is actually not used a great deal over networks, although it does still
serve good use in streaming video and audio, or web conferencing.
 Presentation Layer – The Presentation Layer translates data into a standard format,
while also being able to provide encryption and data compression. Encryption or data
compression does not have to be done at the Presentation Layer, although it is commonly
performed in this layer.
 Application Layer – The Application Layer provides a network interface for
applications and supports network applications. This is where many protocols such as
FTP, SMTP, POP3, and many others operate. Telnet can be used at this layer to send a
ping request- if it is successful, it means that each layer of the OSI model should be
functioning properly.
Network Operating Systems
Any modern Operating System contains built-in software designed to simplify networking of a
computer. Typical O/S software includes an implementation of TCP/IP protocol stack and
related utility programs like ping and traceroute(is a computer network diagnostic tool for
displaying the route (path) and measuring transit delays of packets across an Internet Protocol
(IP) network.). This includes the necessary device drivers and other software to automatically
enable a device's Ethernet interface. Mobile devices also normally provide the programs needed
to enable Wi-Fi, Bluetooth, or other wireless connectivity.
The early versions of Microsoft Windows did not provide any computer networking support.
Microsoft added basic networking capability into its operating system starting with Windows 95
and Windows for Workgroups. Microsoft also introduced its Internet Connection Sharing (ICS)

feature in Windows 98 Second Edition (Win98 SE). Contrast that with Unix, which was
designed from the beginning with networking capability. Nearly any consumer O/S today
qualifies as a network operating system due to the popularity of the Internet.
Network operating systems (NOSs) distribute their functions over a number of networked
computers they add functions that allow access to shared resources by a number of users
concurrently. Client systems contain specialized software that allows them to request shared
resources that are controlled by server systems responding to a client request. The NOS enhances
the reach of the client PC by making remote services available as extensions of the local native
operating system. NOSs also support multiple user accounts at the same time and enables
concurrent access to shared resources by multiple clients. A NOS server is a multitasking system.
Several clients in a network
Choosing a NOS
The main features to consider when selecting a NOS include:
 Performance
 Management and monitoring tools
 Security
 Scalability

 Robustness/fault tolerance
Types
There are two popular competing NOS families. Windows based and Unix based. The former is
proprietary whereas the latter is open source.
Windows NOS
Windows server-based networks that run Windows NT Server or Windows 2000 Server are
based on the concept of the domain. A domain is a group of computers and users that serves a
boundary of administrative authority. Windows NT domains and Windows 2000 domains,
although similar in function, interact with one another differently. In Windows NT 4.0, the
Domain Structure of Windows NT was entirely different from the Domain Structure in Windows
2000.
Instead of Active Directory, Windows NT provides an administrative tool called the User
Manager for Domains. It is accessed from the domain controller and is used to create, manage,
and remove domain user accounts. Each NT domain requires one Primary Domain Controller
(PDC). A domain can also have one or more Backup Domain Controllers (BDCs).
Windows 2000 and 2003 Family of Operating Systems includes:
– Windows 2000 Professional
– Windows 2000 Server
– Windows 2000 Advanced Server
Unix/Linux
Linux is an operating system similar to UNIX. It runs on many different computers and was first
released in 1991. Linux is portable, which means versions can be found running on name brand
or clone PCs. It offers many features adopted from other versions of UNIX.
The UNIX NOS was developed in 1969, and it has evolved into many varieties.
The source code is opened, that is, available at no cost to anyone who wants to modify it. It is
written in C programming language so businesses, academic institutions, and even individuals
can develop their own versions. There are hundreds of different versions of UNIX. Linux is
sometimes referred to as "UNIX Lite", and it is designed to run on Intel-compatible PCs. Linux
brings the advantages of UNIX to home and small business computers.

The following are a few of the most popular types:
• Red Hat Linux
• Linux Mandrake
• Caldera eDesktop and eServer
• Debian GNU/Linux
• Corel Linux
• Turbo Linux
• Ubuntu
Other Software and Programs
A popular use of a Linux system is a web server. Web server software uses Hypertext Transfer
Protocol (HTTP) to deliver files to users that request them, using a web browser from their
workstation. A Mail Server is a system that is configured with the proper programs and services
that enable handling the exchange of e-mail sent from one client to another.
Switching Techniques
The main objective of networking is to connect all the devices so that resources and information
can be shared efficiently. Whenever we have multiple devices, we have problem of connecting
them to make one-to-one connection possible. One solution is to install a point to point link
between each pair of devices such as in mesh topology or between a central device and every
other device as in star topology. These methods, however, are impractical and wasteful when
applied to very large network. The number and length of the links require too many
infrastructures to be cost efficient; and majority of those links would be idle most of the time.
A better solution is to uses switching. A switch network consists of a series of inter-linked nodes,
called switches. Switched are hardware and/or software capable of creating temporary
connection between two or more devices linked to switch but not to each other.
Traditionally, three methods of switching have been important:
 Circuit switching

 Packet switching and
 Message switching
Circuit Switching
Communication via circuit switching implies that there is a dedicated communication path
between two stations. The path is a connected sequence of links between network nodes. On
each physical link, a channel is dedicated to the connection. A common example of circuit
switching is the telephone network..
Communication via circuit switching involves three phases:
Circuit Switching Network
1. Circuit Establishment
Before any signals can be transmitted, an end-to-end (station to station) circuit must be
established. For example, station A wants to communicate with station E. station A sends a
request to node 4 requesting a connection to station E. typically, the link from A to 4 is a
dedicated line, so that part of connection already exists. On the basis of routing information and
measures availability and perhaps cost, lets assume that node 4,5, and 6 are used to complete the
connection. In completing the connection, a test is made to determine if station E is busy or is
prepared to accept the connection.
2. Information Transfer

Information now can transmit from A through the network to E the transmission may be analog
voice, or binary data. Generally the connection is full duplex, and signals may be transmitted in
both direction simultaneously.
3. Circuit Disconnection
One the transmission is completed, the connection is terminated, usually by the action of one of
the two station. Signals must be propagated to the nodes 4,5, and 6 to deallocate the dedicated
resources.
Circuit switching can be rather inefficient. Channel capacity is dedicated for the duration of a
connection, even if no data are being transferred. The connection provides for transmission at a
constant data rate. Thus, each of the devices that are connected must transmit and receive at the
same data rate as the other.
Packet Switching
In a packet switching data are transmitted in short packets. A typical packet length is 1000 byte.
If a source has longer message to send, the message is broken up into a series of packets. Each
packet contains a portion (or the entire short message) of the user‘s data plus some control
information. These packets
Packet Switching Networks
Above figure illustrate the basic operation. A transmitting computer or other device sends a
message as a sequence of packets. Each packet includes control information including the

destination station. The packets are initially sent to the node to which the sending station
attaches. As each packet arrives at these nodes, the node stores the packet briefly, and determines
the next available link. When the link is available, the packet is transmitted to the next node. The
entire packet eventually delivered to the intended node.
There are two popular approaches to packet switching: datagram and virtual circuit.
a) Datagram Approach
In the datagram approach to packet switching, each packet is treated independently from all
others and each packet can be sent via any available path, with no reference to packet that have
gone before. In the datagram approach packets, with the same destination address, do not all
follow the same route, and they may arrive out of sequence at the exit point.
Virtual Switching Network
b) Virtual Circuit
In this approach, a preplanned route is established before any packets are sent. Once the route is
established, all the packets between a pair of communicating parties follow this same route
through the network. Each packet now contains a virtual circuit identifier as well as the data.
Each node on the pre-established route knows where to direct such packet. No routing decisions
are required. At any time, each station can have more than one virtual circuit to any other station
and can have virtual circuits to more than one station.
Message Switching

The descriptive term store and forward best know message switching. In this mechanism, a
anode (usually a special computer with number of disks) receives a message, stores it until the
appropriate route is free, then send it along. Note that in message switching the messages are
stored and relayed from the secondary storage (disk), while in packet switching the packets are
stored and forward from primary storage (RAM).
The primary uses of message switching have been to provide high-level network service (e.g.
delayed delivery, broadcast) for unintelligent devices. Since such devices have been replaced,
message switching has virtually disappeared. Also delays inherent in the process, as well as the
requirement for large capacity storage media at each node, make it unpopular for direct
communication.

Multiplexing
Multiplexing is the process of combining separate signal channels into one composite
stream. It is carried out to increase the utilization of transmission channel. In a multiplexed
system, n devices share the capacity of one link. In the following figure, four devices on the
left direct their transmission stream to a multiplexer (MUX) which combines them into a
single stream (many to one). At the receiving end, the stream is fed into a demultiplexer
(DEMX), which separates the stream back into its component transmissions (one to many)
and directs them to their receiving devices.
Frequency Division Multiplexing
FDM is an analogue technique that works by dividing slicing the total bandwidth of a
media into a number of narrow bandwidth units known as channels.

These channels are separated by further narrower slices, known as guard bands, to prevent
inter-channel interface. This actual waste of bandwidth is offset by the lower costs of the
filter (frequency selection device). The closer the channels are together (the narrower the
guard bands (the more critical and expensive the channel filter become.
Bellow figure gives a conceptual view of FDM. In this illustration, the transmission path is
divided into three parts (based on different frequencies), each representing a channel to
carry one transmission.

As an analogy, imagine a point where three separate narrow roads merge to form a three-
lane highway. Each of the three roads corresponds to a lane of the highway. Each car
merging into the highway from one of the road still has its own lane and can travel without
interfering with cars in other lane.
Example: Cable Television
A familiar application of FDM is cable television. The coaxial cable used in a cable
television system has a bandwidth of approximately 500 MHz. An individual television
channel requires about 6 MHz of bandwidth for transmission. The coaxial cable, therefore,
can carry many multiplexed channels (theoretically 83 channels, but actually fewer to allow
for guard band). A demultiplexer at your television allows you to select which of those
channels you wish to receive.
Time Division Multiplexing

In this method, multiplexer allocates the same time slot to each device at all time, whether
or not a device has anything to transmit. IF there are n input line than there must be n time
slots in the frame (time slots are grouped into frames). Time slot (lets say T), for example,
is assigned to device (lets say D) alone and can not be used by any other device. Each time
its allocated time slot comes in (in a round robin fashion), Device D has the opportunity to
send a portion of its data for time slot T. If the device D is unable to transmit or does not
have data to send, its time slot remains empty and no other device can use it, another words
it is wasted.
Asynchronous TDM(Statistical TDM)
Asynchronous TDM provide better utilization of media. Like synchronous TDM,
asynchronous TDM allows a number of lower speed input lines to be multiplexed to a
single higher speed line. Unlike synchronous TDM, however, in asynchronous TDM the
total speed of input line can be greater than the capacity of the media. In asynchronous
TDM the number of slots in the frame are less than numbers of input lines. Slots are not
preassigned, each slot is available to any of the attached input lines that has data to send.
The multiplexer scans the input line, accepts the portion of data until a frame is filed, and
then sends the frame across the link. Since the slots are not pre-assigned for each input line,
line address must be added along with the data to send.

Analog and Digital Data transmission
Analog Signals
A continuously varying electromagnetic wave that may be propagated over a variety of media,
depending on frequency. Examples of media:
 Copper wire media (twisted pair and coaxial cable)
 Fiber optic cable
 Atmosphere or space propagation
Analog signals can propagate analog and digital data

Digital Signals
A sequence of voltage pulses that may be transmitted over a copper wire medium, generally
cheaper than analog signaling, less susceptible to noise interference, Suffer more from
attenuation. Digital signals can propagate analog and digital data

Reasons for Choosing Data and Signal Combinations
Digital data, digital signal - Equipment for encoding is less expensive than digital-to-analog
equipment
Analog data, digital signal - Conversion permits use of modern digital transmission and
switching equipment
Digital data, analog signal - Some transmission media will only propagate analog signals,
Examples include optical fiber and satellite
Analog data, analog signal - Analog data easily converted to analog signal
Analog Transmission
Transmit analog signals without regard to content , Attenuation limits length of transmission
link, Cascaded amplifiers boost signal’s energy for longer distances but cause distortion and
Analog data can tolerate distortion, Introduces errors in digital data

Digital Transmission
Concerned with the content of the signal, Attenuation endangers integrity of data, Digital Signal,
Repeaters achieve greater distance, Repeaters recover the signal and retransmit, Analog signal
carrying digital data, Retransmission device recovers the digital data from analog signal and
Generates new, clean analog signal
Chapter Review Questions
1. Discuss analogue and digital signals
2. Discuss different multiplexing techniques
References
1. Rogers G.S & Edwards J. S, Wireless technology, Prentice Hall (ISBN 0-13-09486)
2. Martin J. (2001) Telecommunications and the computer, Prentice Hall International

CHAPTER TWO: INTRODUCTION TO MOBILE
COMPUTING AND WIRELESS COMMUNICATION
i. Understanding the overview of wireless technologies
ii. Understanding the overview of Mobile Computing
Introduction
Mobile computing is human–computer interaction by which a computer is expected to be
transported during normal usage. Mobile computing involves mobile communication, mobile
hardware, and mobile software. Communication issues include ad-hoc and infrastructure
networks as well as communication properties, protocols, data formats and concrete
technologies. Hardware includes mobile devices or device components. Mobile software deals
with the characteristics and requirements of mobile applications.
Wireless communication is the transfer of information over a distance without the use of
electrical conductors or wires.
The term "Wireless" came into public use to refer to a radio receiver or transceiver (a dual
purpose receiver and transmitter device),today the term is used to describe modern wireless
connections such as in cellular networks and wireless broadband Internet. It is also used in a
general sense to refer to any type of operation that is implemented without the use of wires, such
as "wireless remote control", "wireless energy transfer", etc. regardless of the specific technology
(e.g., radio, infrared, ultrasonic, etc.) that is used to accomplish the operation.
Wireless communications is generally considered to be a branch of telecommunications.

Wireless communications encompasses various types of fixed, mobile, and portable two way
radios, cellular telephones, personal digital assistants (PDAsWireless computer mice, keyboards
and headsets, satellite television and cordless telephones.
The term "wireless" has become a generic and all-encompassing word used to describe
communications in which electromagnetic waves or RF carry a signal over part or the entire
communication path. Common examples of wireless equipment in use today include:
 Global Positioning System (GPS)
 Cordless Computer Peripherals
 Cordless Telephone Sets
 Satellite Television
 Wireless Gaming
The term "wireless" should not be confused with the term "cordless", which is generally used to
refer to powered electrical or electronic devices that are able to operate from a portable power
source (e.g., a battery pack) without any cable or cord to limit the mobility of the cordless device
through a connection to the mains power supply.
Wireless communication can be via;
 Radio frequency
 Microwave (i.e. long-range and line-of-sight via antennas or short range
communications)
 GSM
 GPRS
 3G
 GPS
 ZigBee
Definitions
Mobile computing is "taking a computer and all necessary files and software out into the field."

"Mobile computing: being able to use a computing device even when being mobile and therefore
changing location. Portability is one aspect of mobile computing."
"Mobile computing is the ability to use computing capability without a pre-defined location
and/or connection to a network to publish and/or subscribe to information ." Uwe Vieille,
ACM.org
Mobile Computing is a variety of wireless devices that has the mobility to allow people to
connect to the internet, providing wireless transmission to access data and information from
where ever location they may be.
Mobile Computing is a modified and new way of interacting with the computer device and to
facilitate the other computing capabilities being present at different mobile locations.
Wireless telecommunications is the transfer of information between two or more points that are
not physically connected. Distances can be short, such as a few metres for television remote
control, or as far as thousands or even millions of kilometres for deep-space radio
communications. It encompasses various types of fixed, mobile, and portable two-way radios,
cellular telephones, personal digital assistants (PDAs), and wireless networking. Other examples
of wireless technology include GPS units, Garage door openers or garage doors, wireless
computer mice, keyboards and Headset (audio), headphones, radio receivers, satellite television,
broadcast television and cordless telephones.
Mobile Computing Advantages
The following are the advantages of mobile computing: -
 Location Flexibility: You no longer need to stay plugged in (literally!) to a specific
location for performing computing activities. Mobile computing allows you
unprecedented flexibility to move about and perform computing activities at the same
time! This is, indeed, the chief among all other benefits of portable computing. Traveling
abroad for work and missing family and friends? Mobile computing enables you to
connect with near and dear ones while you're in transit, thanks to evolution of the mobile
technology!
 Saves Time: Doesn't it get boring when you're on a 12 hour-long flight across the globe?
Don't you feel you could use some of these 12 hours to get some office work done?

Mobile computing technology is just the thing to use such transit time more effectively! It
also allows to instantly connect with your family anywhere and anytime. Missing your
parents during the college tour? Not any more! You can connect with them over Internet
using portable computing devices such as Internet phones and share the fun!
 Enhanced Productivity: Increased work flexibility is directly proportionate to enhanced
work productivity - the fact that you can do your work from any place you want, without
waiting for, and making efforts to, get access to computing facility translates into people
being able to do more work with greater flexibility. This is the reason why most
companies these days offer home-computing access to employees. Suppose a national
emergency is declared or any natural calamity occurs (or any other reason) due to which
offices stay closed, work can still go on as people are no longer dependent upon office
computing systems to get their work done!
 Ease of Research: Mobile computing and the flexibility offered by it enable students as
well as professionals to conduct in-depth research on just about any topic or subject even
when on the go!
 Entertainment: Nowadays, with the advent and advance of mobile communication
technology, no time is wasted time anymore! Getting bored is so last-decade now what
with zillions of entertainment options available on mobile communication and computing
devices these days - games, movies, music, videos, you name it!
 Improved decision making: Mobile Computing lets you conduct business at the point of
activity. The ability to collect, access and evaluate critical business information quickly
and accurately means better decision making that can have a far-reaching effect on your
company's ability to compete successfully
 Improved customer relations: The success of a business can often be measured by its
ability to satisfy customers. Mobile computers gives your field worker the ability to
answer customer questions, check order status and provide other services anytime their
customers need them from wherever they happen to be.
Limitations of mobile computing
The following are the limitations of mobile computing: -

 Insufficient bandwidth: Mobile Internet access is generally slower than direct cable
connections, using technologies such as GPRS and EDGE, and more recently HSDPA
and HSUPA 3G networks. These networks are usually available within range of
commercial cell phone towers. Higher speed wireless LANs are inexpensive but have
very limited range.
 Security standards: When working mobile, one is dependent on public networks,
requiring careful use of VPN. Security is a major concern while concerning the mobile
computing standards on the fleet. One can easily attack the VPN through a huge number
of networks interconnected through the line.
 Power consumption: When a power outlet or portable generator is not available, mobile
computers must rely entirely on battery power. Combined with the compact size of many
mobile devices, this often means unusually expensive batteries must be used to obtain the
necessary battery life.
 Transmission interferences: Weather, terrain, and the range from the nearest signal point
can all interfere with signal reception. Reception in tunnels, some buildings, and rural
areas is often poor.
 Potential health hazards: People who use mobile devices while driving are often
distracted from driving and are thus assumed more likely to be involved in traffic
accidents. (While this may seem obvious, there is considerable discussion about whether
banning mobile device use while driving reduces accidents or not.) Cell phones may
interfere with sensitive medical devices. Questions concerning mobile phone radiation
and health have been raised.
 Human interface with device: Screens and keyboards tend to be small, which may make
them hard to use. Alternate input methods such as speech or handwriting recognition
require training.
Portable computing devices
The following is a list of mobile computing devices: -
 A portable computer is a general-purpose computer that can be easily moved from place to
place, but cannot be used while in transit, usually because it requires some "setting-up" and

an AC power source. The most famous example is the Osborne 1. Portable computers are
also called a "transportable" or a "luggable" PC.
 A tablet computer that lacks a keyboard (also known as a non-convertible tablet) is shaped
like a slate or a paper notebook. Instead a physical keyboard it has a touchscreen with some
combination of virtual keyboard, stylus and/or handwriting recognition software. Tablets
may not be best suited for applications requiring a physical keyboard for typing, but are
otherwise capable of carrying out most of the tasks of an ordinary laptop.
 A personal digital assistant (PDA) is a small, usually pocket-sized, computer with limited
functionality. It is intended to supplement and to synchronize with a desktop computer,
giving access to contacts, address book, notes, e-mail and other features.
 A PDA with a web browser is an Internet tablet, an Internet appliance in tablet form. It does
not have as much computing power as a full tablet computer and its applications suite is
limited, and it can not replace a general purpose computer. Internet tablets typically feature
an MP3 and video player, a web browser, a chat application and a picture viewer.A
 An ultra mobile PC is a full-featured, PDA-sized computer running a general-purpose
operating system.
 A smartphone has a wide range of features and installable applications.
 A carputer is installed in an automobile. It operates as a wireless computer, sound system,
GPS, and DVD player. It also contains word processing software and is bluetooth
compatible.
 A Fly Fusion Pentop Computer is a computing device the size and shape of a pen. It
functions as a writing utensil, MP3 player, language translator, digital storage device, and
calculator.
 A laptop computer is a personal computer for mobile use. A laptop utilizes most of the same
components as a desktop computer, including a display, a keyboard, a pointing device such
as a touchpad (also known as a trackpad) and/or a pointing stick, and speakers into a single
unit. A laptop is powered by mains electricity via an AC adapter, and can be used away from
an outlet using a rechargeable battery. Laptops are also sometimes called notebook
computers, notebooks or netbooks.
 Netbooks are a category of small, lightweight, legacy-free, and inexpensive laptop
computers. At their inception in late 2007 as smaller notebooks optimized for low weight and

low cost netbooks omitted certain features (e.g., the optical drive), featured smaller screens
and keyboards, and offered reduced computing power when compared to a full-sized laptop.
Over the course of their evolution, netbooks have ranged in size from below 5" screen
diagonal to 12". A typical weight is 1 kg (2–3 pounds). Often significantly less expensive
than other laptops. In the short period since their appearance, netbooks grew in size and
features, and converged with smaller, lighter notebooks and subnotebooks. By August 2009,
when comparing a Dell netbook to a Dell notebook, CNET called netbooks "nothing more
than smaller, cheaper notebooks," noting, "the specs are so similar that the average shopper
would likely be confused as to why one is better than the other," and "the only conclusion is
that there really is no distinction between the devices."However, by 2011, the increasing
popularity of tablet computers, particularly the iPad, had led to a decline in netbook sales.
Chapter Review Questions
i. Define Mobile Computing
ii. what are the advantages of mobile computing
References
1. Rogers G.S & Edwards J. S, Wireless technology, Prentice Hall (ISBN 0-13-09486)
2. Martin J. (2001) Telecommunications and the computer, Prentice Hall International

CHAPTER THREE: MOBILE COMPUTING
ARCHITECTURE
i. Understand the cellular telephony
ii. Understand the Mobile computing architecture
Introduction
Mobile Computing : A technology that allows transmission of data, via a computer, without
having to be connected to a fixed physical link. Mobile voice communication is widely
established throughout the world and has had a very rapid increase in the number of subscribers
to the various cellular networks over the last few years. An extension of this technology is the
ability to send and receive data across these cellular networks. This is the principle of mobile
computing. Mobile data communication has become a very important and rapidly evolving
technology as it allows users to transmit data from remote locations to other remote or fixed
locations. This proves to be the solution to the biggest problem of business people on the move -
mobility.
Public switched telephone network
The public switched telephone network (PSTN) is the network of the world's public circuit-
switched telephone networks. It consists of telephone lines, fiber optic cables, microwave
transmission links, cellular networks, communications satellites, and undersea telephone cables,
all inter-connected by switching centers, thus allowing any telephone in the world to
communicate with any other. Originally a network of fixed-line analog telephone systems, the
PSTN is now almost entirely digital in its core and includes mobile as well as fixed telephones.
The technical operation of the PSTN utilizes standards created by the ITU-T. These standards
allow different networks in different countries to interconnect seamlessly. There is also a single

global address space for telephone numbers based on the E.163 and E.164 standards. The
combination of the interconnected networks and the single numbering plan make it possible for
any phone in the world to dial any other phone.
PSTN History
The first telephones had no network but were in private use, wired together in pairs. Users who
wanted to talk to different people had as many telephones as necessary for the purpose. A user
who wished to speak whistled into the transmitter until the other party heard.
Soon, however, a bell was added for signalling, and then a switch hook, and telephones took
advantage of the exchange principle already employed in telegraph networks. Each telephone
was wired to a local telephone exchange, and the exchanges were wired together with trunks.
Networks were connected in a hierarchical manner until they spanned cities, countries,
continents and oceans. This was the beginning of the PSTN, though the term was unknown for
many decades.
Automation introduced pulse dialing between the phone and the exchange, and then among
exchanges, followed by more sophisticated address signaling including multi-frequency,
culminating in the SS7 network that connected most exchanges by the end of the 20th century.
The growth of the PSTN meant that traffic engineering techniques needed to be deployed to
deliver quality of service (QoS) guarantees for the users. The work of A.K. Erlang established
the mathematical foundations of methods required to determine the capacity requirements and
configuration of equipment and the number of personnel required to deliver a specific level of
service.
In the 1970s the telecommunications industry began implementing packet switched network data
services using the X.25 protocol transported over much of the end-to-end equipment as was
already in use in the PSTN.
In the 1980s the industry began planning for digital services assuming they would follow much
the same pattern as voice services, and conceived a vision of end-to-end circuit switched
services, known as the Broadband Integrated Services Digital Network (B-ISDN). The B-ISDN
vision has been overtaken by the disruptive technology of the Internet.

At the turn of the 21st century, the oldest parts of the telephone network still use analog
technology for the last mile loop to the end user. Digital services have been increasingly rolled
out to end users using services such as DSL, ISDN, FTTx and cable modem systems.
Several large private telephone networks are not linked to the PSTN, usually for military
purposes. There are also private networks run by large companies which are linked to the PSTN
only through limited gateways, like a large private branch exchange (PBX).
Cellular Network Architecture
Mobile telephony took off with the introduction of cellular technology which allowed the
efficient utilisation of frequencies enabling the connection of a large number of users. During the
1980's analogue technology was used. Among the most well known systems were the NMT900
and 450 (Nordic Mobile Telephone) and the AMPS (Advanced Mobile Phone Service). In the
1990's the digital cellular technology was introduced with GSM (Global System Mobile) being
the most widely accepted system around the world. Other such systems are the DCS1800
(Digital Communication System) and the PCS1900 (Personal Communication System).
A cellular network consists of mobile units linked together to switching equipment, which
interconnect the different parts of the network and allow access to the fixed Public Switched
Telephone Network (PSTN). The technology is hidden from view; it's incorporated in a number
of tranceivers called Base Stations (BS). Every BS is located at a strategically selected place and
covers a given area or cell - hence the name cellular communications. A number of adjacent cells
grouped together form an area and the corresponding BSs communicate through a so called
Mobile Switching Centre (MSC). The MSC is the heart of a cellular radio system. It is
responsible for routing, or switching, calls from the originator to the destinator. It can be thought
of managing the cell, being responsible for set-up, routing control and termination of the call, for
management of inter-MSC hand over and supplementary services, and for collecting charging
and accounting information. The MSC may be connected to other MSCs on the same network or
to the PSTN.

Mobile Switching Centre
The frequencies used vary according to the cellular network technology implemented. For GSM,
890 - 915 MHz range is used for transmission and 935 -960 MHz for reception. The DCS
techology uses frequencies in the 1800MHz range while PCS in the 1900MHz range.
Each cell has a number of channels associated with it. These are assigned to subscribers on
demand. When a Mobile Station (MS) becomes 'active' it registers with the nearest BS. The
corresponding MSC stores the information about that MS and its position. This information is
used to direct incoming calls to the MS.
If during a call the MS moves to an adjacent cell then a change of frequency will necessarily
occur - since adjacent cells never use the same channels. This procedure is called hand over and
is the key to Mobile communications. As the MS is approaching the edge of a cell, the BS
monitors the decrease in signal power. The strength of the signal is compared with adjacent cells
and the call is handed over to the cell with the strongest signal.
During the switch, the line is lost for about 400ms. When the MS is going from one area to
another it registers itself to the new MSC. Its location information is updated, thus allowing MSs
to be used outside their 'home' areas.

Data Communications
Data Communications is the exchange of data using existing communication networks. The term
data covers a wide range of applications including File Transfer (FT), interconnection between
Wide-Area-Networks (WAN), facsimile (fax), electronic mail, access to the internet and the
World Wide Web (WWW).
Mobile Communications Overview
Data Communications have been achieved using a variety of networks such as PSTN, leased-
lines and more recently ISDN (Integrated Services Data Network) and ATM (Asynchronous
Transfer Mode)/Frame Relay. These networks are partly or totally analogue or digital using
technologies such as circuit - switching, packet - switching e.t.c.

Circuit switching implies that data from one user (sender) to another (receiver) has to follow a
prespecified path. If a link to be used is busy , the message can not be redirected , a property
which causes many delays.
Packet switching is an attempt to make better utilisation of the existing network by splitting the
message to be sent into packets. Each packet contains information about the sender, the receiver,
the position of the packet in the message as well as part of the actual message. There are many
protocols defining the way packets can be send from the sender to the receiver. The most widely
used are the Virtual Circuit-Switching system, which implies that packets have to be sent
through the same path, and the Datagram system which allows packets to be sent at various paths
depending on the network availability. Packet switching requires more equipment at the receiver,
where reconstruction of the message will have to be done.
The introduction of mobility in data communications required a move from the Public Switched
Data Network (PSDN) to other networks like the ones used by mobile phones. PCSI has come up
with an idea called CDPD (Cellular Digital Packet Data) technology which uses the existing
mobile network (frequencies used for mobile telephony).
Mobility implemented in data communications has a significant difference compared to voice
communications. Mobile phones allow the user to move around and talk at the same time; the
loss of the connection for 400ms during the hand over is undetectable by the user. When it comes
to data, 400ms is not only detectable but causes huge distortion to the message. Therefore data
can be transmitted from a mobile station under the assumption that it remains stable or within the
same cell.
Cellular Digital Packet Data (CDPD) Technology
Today, the mobile data communications market is becoming dominated by a technology called
CDPD.
There are other alternatives to this technology namely Circuit Switched Cellular, Specialised
Mobile Radio and Wireless Data Networks. As can be seen from the table below the CDPD
technology is much more advantageous than the others.

Cellular Digital
Packet Data
(CDPD)
Circuit
Switched
Cellular
Specialized Mobile
Radio (Extended)
Proprietary
Wireless Data
Networks
Speed best best good good
Security best better good better
Ubiquity best best good better
Cost of Service best better better good
Cost of
Deployment
best best better good
Mobility best good better good
Interoperability best good good better
CDPD's principle lies in the usage of the idle time in between existing voice signals that are
being sent across the cellular networks. The major advantage of this system is the fact that the
idle time is not chargeable and so the cost of data transmission is very low. This may be regarded
as the most important consideration by business individuals.
CDPD networks allow fixed or mobile users to connect to the network across a fixed link and a
packet switched system respectively. Fixed users have a fixed physical link to the CDPD
network. In the case of a mobile end user, the user can, if CDPD network facilities are non-
existent, connect to existing circuit switched networks and transmit data via these networks. This
is known as Circuit Switched CDPD (CS-CDPD).

Circuit Switched CDPD
Service coverage is a fundamental element of providing effective wireless solutions to users and
using this method achieves this objective. Where CDPD is available data is split into packets and
a packet switched network protocol is used to transport the packets across the network. This may
be of either Datagram or Virtual Circuit Switching form.
The data packets are inserted on momentarily unoccupied voice frequencies during the idle time
on the voice signals. CDPD networks have a network hierarchy with each level of the hierarchy
doing its own specified tasks.

CDPD Overview
The hierarchy consists of the following levels :
 Mobile End User Interface - Using a single device such as a Personal Digital Assistant or
personal computer which have been connected to a Radio Frequency (RF) Modem which
is specially adapted with the antennae required to transmit data on the cellular network,
the mobile end user can transmit both data and voice signals. Voice signals are
transmitted via a mobile phone connected to the RF Modem Unit. RF Modems transfer
data in both forward and reverse channels using Gaussian Minimum Shift Keying (MSK)
modulation , a modified form of Frequency Shift Keying (FSK) at modulation index of
0.5 .
 Mobile Data Base Station (MDBS) - In each cell of the cellular reception area, there is a
Mobile Data Base Station (MDBS) which is responsible for detection of idle time in
voice channels, for relaying data between the mobile units and the Mobile Data
Intermediate Systems (MDIS), sending of packets of data onto the appropriate

unoccupied frequencies as well as receiving data packets and passing them to the
appropriate Mobile end user within its domain.
o Detection of idle time -This is achieved using a scanning receiver(also known as
sniffer) housed in the MDBS. The sniffer detects voice traffic by measuring the
signal strength on a specific frequency, hence detecting an idle channel.
o Relaying data packets between mobile units and networks - If the sniffer detects
two idle channels then the MDBS establishes two RF air-links between the end
user unit and itself. Two channels are required to achieve bidirectional
communications. One channel is for forward communication from the MDBS to
the mobile units. This channel is unique to each mobile unit and hence
contentionless. The reverse channels are shared between a number of Mobile units
and as a result, two mobile units sharing a reverse link cannot communicate to
each other.
Reverse channels are accessed using a Digital Sense Multiple Access with
Collision Detection (DSMA - CD) protocol which is similar to the protocol used
in Ethernet communication which utilises Carrier Sense Multiple Access with
Collision Detection (CSMA - CD). This protocol allows the collision of two data
packets on a common channel to be detected so that the Mobile unit can be alerted
by the MDBS to retry transmission at a later time.
Once a link is established, the MDBS can quickly detect if and when a voice
signal is ramping up (requesting) this link and within the 40ms it takes for the
voice signal to ramp up and get a link, the MDBS disconnects from the current
air-link and finds another idle channel establishing a new link. This is known as
channel hopping.
The speed at which the MDBS hops channels ensures that the CDPD network is
completely invisible to the existing cellular networks and it doesn't interfere with
transmission of existing voice channels.

When the situation occurs that all voice channels are at capacity, then extra
frequencies specifically set aside for CDPD data can be utilised. Although this
scenario is very unlikely as each cell within the reception area has typically 57
channels, each of which has an average of 25 - 30% of idle time.
 Mobile Data Intermediate Systems (MDIS) - Groups of MDBS that control each cell in
the cellular network reception area are connected to a higher level entity in the network
hierarchy, the Mobile Data Intermediate Systems. Connection is made via a wideband
trunk cable. Data packets are then relayed by MDBS to and from mobile end users and
MDIS.
These MDIS use a Mobile Network Location Protocol (MNLP) to exchange location
information about Mobile end users within their domain. The MDIS maintains a database
for each of the M-ES in its serving area. Each mobile unit has a fixed home area but may
be located in any area where reception is available. So, if a MDIS unit recieves a data
packet addressed to a mobile unit that resides in its domain, it sends the data packet to the
appropriate MDBS in its domain which will forward it as required. If the data packet is
addressed to a mobile unit in another group of cells, then the MDIS forwards the data
packet to the appropriate MDIS using the forward channel. The MDIS units hide all
mobility issues from systems in higher levels of the network hierarchy.
In the reverse direction, where messages are from the Mobile end user, packets are routed
directly to their destination and not necessarily through the mobile end users home
MDIS.
 Intermediate Systems (IS) - MDIS are interconnected to these IS which form the
backbone of the CDPD system. These systems are unaware of mobility of end-users, as
this is hidden by lower levels of the network hierarchy. The ISs are the systems that
provide the CDPD interface to the various computer and phone networks.
The IS's relay data between MDIS's and other IS's throughout the network. They can be
connected to routers that support Internet and Open Systems Interconnection
Connectionless Network Services (OSI-CLNS), to allow access to other cellular carriers
and external land- based networks.

CDPD Network
CDPD Network Reliability
There are some actions that are necessary in order to obtain reliability over a network.
 User Authentication - The procedure which checks if the identity of the subscriber
transferred over the radio path corresponds with the details held in the network.
 User Anonymity - Instead of the actual directory telephone number , the International
Mobile Subscriber Identity (IMSI) number is used within the network to uniquely
identify a mobile subscriber.
 Fraud Prevention - Protection against impersonation of authorised users and fraudulent
use of the network is required.
 Protection of user data - All the signals within the network are encrypted and the
identification key is never transmitted through the air. This ensures maximum network
and data security.
The information needed for the above actions are stored in data bases. The Home Location
Register (HLR) stores information relating the Mobile Station (MS) to its network. This includes
information for each MS on subscription levels , supplementary services and the current or most
recently used network and location area. The Authentication Centre (AUC) provides the
information to authenticate MSs using the network , in order to guard against possible fraud ,

stolen subsciber cards , or unpaid bills. The Visitor Location Register (VLR) stores information
about subscription levels , supplementary services and location for a subscriber who is currently
in, or has very recently been ,in that area. It may also record whether a subscriber is currently
active , thus avoiding delay and unnecessary use of the network in trying to call a switched off
terminal.
The data packets are transmitted at speeds of typically 19.2 Kilobits/second to the MDBS, but
actual throughput may be as low as 9.6 Kilobits/second due to the extra redundant data that is
added to transmitted packets. This information includes sender address, reciever address and in
the case of Datagram Switching, a packet ordering number. Check data is also added to allow
error correction if bits are incorrectly recieved. Each data packet is encoded with the check data
using a Reed-Solomon forward error correction code. The encoded sequence is then logically
OR'ed with a pseudo-random sequence, to assist the MDBS and mobile units in synchronisation
of bits. The transmitted data is also encrypted to maintain system security.
CDPD follows the OSI standard model for packet switched data communications. The CDPD
architecture extends across layers one, two and three of the OSI layer model. The mobile end
users handle the layer 4 functions (transport) and higher layers of the OSI model such as user
interface.
Specialized Mobile Radio
Specialized Mobile Radio (SMR) may be an analog or digital trunked two-way radio system,
operated by a service in the VHF, 220, UHF, 700, 800 or 900 MHz bands. Some systems with
advanced features are referred to as an Enhanced Specialized Mobile Radio, (ESMR).
Specialized Mobile Radio is a term defined in US Federal Communications Commission (FCC)
regulations. The term is of US regulatory origin but may be used in other regions to describe
similar commercial systems which offer a radio communications service to businesses.
Compatibility and purpose
Any company, such as a taxi service, towing service, or construction company, may use an SMR
service. These concerns may rent radios from the SMR operator or may buy compatible radios.
SMR systems use differing protocols, frequency ranges, and modulation schemes: not every
radio is compatible with every SMR system.

These systems generally consist of one or more repeaters used to maintain communications
between a dispatch fleet of mobile or hand-held walkie talkie radios. One- to five-channel
systems may be conventional two-way radio repeaters. More than five channel systems must be
trunked.
Fees
The radio system is operated by a commercial service. Paying a fee allows users to utilize the
radio system backbone, increasing their range. Some SMR systems offer telephone interconnect.
This allows telephone calls to be made from the mobile radio or walkie talkie. Some systems
may also offer selective calling, allowing customers to communicate with individual radios or
segments of their entire radio fleet. Users are charged a fee for some combination of:
 Air time (the amount of time any of the user's radio units is talking).
 A monthly fee covering site lease costs, engineering, maintenance, and overhead.
 Rental of radio units, in some cases.
General Packet Radio Service (GPRS)
GPRS is a packet oriented mobile data service on the 2G and 3G cellular communication
system's global system for mobile communications (GSM). GPRS was originally standardized
by European Telecommunications Standards Institute (ETSI) in response to the earlier CDPD
and i-mode packet-switched cellular technologies. It is now maintained by the 3rd Generation
Partnership Project (3GPP). GPRS usage is typically charged based on volume of data. This
contrasts with circuit switching data, which is typically billed per minute of connection time,
regardless of whether or not the user transfers data during that period. GPRS data is typically
supplied either as part of a bundle (e.g., 5 GB per month for a fixed fee) or on a pay-as-you-use
basis. Usage above the bundle cap is either charged per megabyte or disallowed. The pay-as-you-
use charging is typically per megabyte of traffic.
GPRS is a best-effort service, implying variable throughput and latency that depend on the
number of other users sharing the service concurrently, as opposed to circuit switching, where a
certain quality of service (QoS) is guaranteed during the connection. In 2G systems, GPRS

provides data rates of 56–114 kbit/second. 2G cellular technology combined with GPRS is
sometimes described as 2.5G, that is, a technology between the second (2G) and third (3G)
generations of mobile telephony. It provides moderate-speed data transfer, by using unused time
division multiple access (TDMA) channels in, for example, the GSM system. GPRS is integrated
into GSM Release 97 and newer releases.
General Packet Radio Service, more commonly known as GPRS, is a new non-voice, value
added, high-speed, packet-switching technology, for GSM (Global System for Mobile
Communications) networks. It makes sending and receiving small bursts of data, such as email
and web browsing, as well as large volumes of data over a mobile telephone network possible. A
simple way to understand packet switching is to relate it to a jigsaw puzzle. Imagine how you
buy a complete image or picture that has been divided up into many pieces and then placed in a
box. You purchase the puzzle and reassemble it to form the original image. Before the
information is sent, it is split up into separate packets and it is then reassembled at the receivers
end.
GPRS offers a continuous connection to the Internet for mobile phone and computer users.
Experience has shown that most data communication applications do not require continuous data
transfer. Users may need to be connected to a data communication network (such as a LAN,
WAN, the Internet, or a corporate Intranet), but that does not mean they are sending and
receiving data at all times. Data transfer needs are not generally balanced. In the majority of
cases, users will tend to send out small messages but receive large downloads. Therefore, most of
the data transfer is in one direction.
GPRS is expected to provide a significant boost to mobile data usage and usefulness. It is
expected to greatly alter and improve the end-user experience of mobile data computing, by
making it possible and cost-effective to remain constantly connected, as well as to send and
receive data at much higher speeds than today. Its main innovations are that it is packet based,
that it will increase data transmission speeds, and that it will extend the Internet connection all
the way to the mobile PC – the user will no longer need to dial up to a separate ISP.
GPRS History

Like the GSM standard itself, GPRS will be introduced in phases. Phase 1 became available
commercially in the year 2000/2001.Point to Point GPRS, which is sending information to a
single GPRS user, was supported, but not Point to Multipoint which is sending the same
information to several GPRS users at the same time. GPRS Phase 2 is not yet fully defined, but is
expected to support higher data rates through the possible incorporation of techniques such as
EDGE (Enhanced Data rates for GSM Evolution), in addition to Point-to-Multipoint support. See
Figure below for a timeline history of GPRS.
DATE MILESTONE
Throughout
1999-2000
Network operators place trial and commercial contracts for GPRS
infrastructure.
Incorporation of GPRS infrastructure into GSM networks.
Summer of 2000 First trial GPRS services become available.
Typical single user throughput is likely to be 28 kbps.
For example, T-Mobil is planning a GPRS trial at Expo2000 in
Hanover in the Summer of 2000.
Start of 2001 Basic GPRS capable terminals begin to be available in commercial
quantities.
Throughout 2001 Network operators launch GPRS services commercially an roll out
GPRS.
Vertical market and executive GPRS early adopters begin using it
regularly for nonvoice mobile communications.
2001/2002 Typical single user throughput is likely to be 56 kbps.
New GPRS specific applications, higher bitrates, greater network
capacity solutions, more capable terminals become available, fueling
GPRS usage.
2002 Typical single user throughput is likely to be 112 kbps.

GPRS Phase 2/EDGE begins to emerge in practice.
2002 GPRS is routinely incorporated into GSM mobile phones and has
reached critical mass in terms of usage. (This is the equivalent to the
status of SMS in 1999)
2002/2003 3GSM arrives commercially.
GPRS Shortcomings
 LIMITED RADIO RESOURCES - There are only limited radio resources that can be
deployed for different uses – use for one purpose precludes simultaneous use for another.
For example, voice and GPRS calls both use the same network resources.
 SPEEDS MUCH LOWER IN REALITY - Attaining the highest GPRS data transmission
speed of 171.2 kbps would require a single user taking over all eight timeslots; therefore,
maximum GPRS speeds should be compared against constraints in the GPRS terminals
and networks. It is highly unlikely that a GSM network operator would allow all
timeslots to be used by a single GPRS user. The initial GPRS terminals are expected to
only support one to three timeslots, which will be severely limiting to users. The reality is
that mobile networks are always likely to have lower data transmission speeds than fixed
networks. Mobile cellular subscribers often like to jump on the fact that a certain
technology has high data transmission speeds, when the figure in all reality could be a
theoretical number that is based on the perfect situation. Consumers should, therefore,
compare all available mobile services and use the one that bests suits their needs.
 NO SUPPORT OF MOBILE TERMINATED CALLS - There has been no confirmation
by any mobile phone provider that initial GPRS terminals will support mobile terminated
GPRS calls (receipt of GPRS calls on the mobile phone).When a mobile phone user
initiates a GPRS session, they are agreeing to pay for the content to be delivered by the
GPRS service. Internet sources originating unsolicited content may not be chargeable. A
worst case scenario would be that a mobile user would then be made responsible for
paying for the unsolicited junk content that they received. This is one main reason why

mobile vendors are not willing to support mobile terminated GPRS calls in their
terminals.
 SUBOPTIMAL MODULATION - GPRS is based on a modulation technique known as
Gaussian minimum-shift keying (GMSK). EDGE is based on a new modulation scheme
that allows a much higher bit rate across the air interface – that is called eight-phase-shift
keying (8 PSK) modulation. Since 8 PSK will also be used for 3GSM, network operators
will need to incorporate it at some stage to make the transition to third generation mobile
phone systems.
 TRANSIT DELAYS - GPRS packets are sent in many different directions to reach the
same destination. This makes room for the possibility for some of the packets to get lost
or damaged during the transmission over the radio link. The GPRS standards are aware of
this issue regarding wireless packet technologies and have worked to integrate data
integrity and retransmission approaches to solving these problems. The result of this
leads to possible transit delays.
 NO STORE AND FORWARD - Currently, there is not a storage mechanism integrated
into the GPRS standard.
Method Of Operation
GPRS gives GSM subscribers access to data communication applications such as e-mail,
corporate networks, and the Internet using their mobile phones. The GPRS service uses the
existing GSM network and adds new packet-switching network equipment. GPRS employs
packet switching, which means that the GPRS mobile phone has no dedicated circuit assigned to
it. Only when data is transferred is a physical channel created. After the data has been sent, it can
be assigned to other users. This allows for the most efficient use of the network.
When packet-switched data leaves the GPRS/GSM network, it is transferred to TCP-IP networks
such as the Internet or X.25.Thus, GPRS includes new transmission and signaling procedures as
well as new protocols for interworking with the IP world and other standard packet networks.
Figure below is a diagram of the GPRS Network Architecture.

GPRS Network Architecture
User Features
 SPEED - The maximum speed of 171.2 kbps, available through GPRS, is nearly three
times as fast as the data transmission speeds of fixed telecommunications networks and
ten times as fast as the current GSM network services.
 INSTANT CONNECTIONS – IMMEDIATE TRANSFER OF DATA - GPRS will allow
for instant, continuous connections that will allow information and data to be sent
whenever and wherever it is needed. GPRS users are considered to be always connected,
with no dial-up needed. Immediacy is one of the advantages of GPRS (and SMS) when
compared to Circuit Switched Data.High immediacy is a very important feature for time
critical applications such as remote credit card authorization where it would be
unacceptable to keep the customer waiting for even thirty extra seconds.
 NEW AND BETTER APPLICATIONS - General Packet Radio Service offers many new
applications that were never before available to users because of the restrictions in speed
and messaged length. Some of the new applications that GPRS offers is the ability to

perform web browsing and to transfer files from the office or home and home
automation, which is the ability to use and control in-home appliances.
 SERVICE ACCESS - To use GPRS, the user will need:
o A mobile phone or terminal that supports GPRS (existing GSM phones do not
support GPRS)
o A subscription to a mobile telephone network that supports GPRS – use of GPRS
must be enabled for that user. Automatic access to the GPRS may be allowed by
some mobile network operators, others will require a specific opt-in
o Knowledge of how to send and/or receive GPRS information using their specific
model of mobile phone, including software and hardware configuration (this
creates a customer service requirement)
o A destination to send or receive information through GPRS.(Whereas with SMS
this was often another mobile phone, in the case of GPRS, it is likely to be an
Internet address, since GPRS is designed to make the Internet fully available to
mobile users for the first time.
Network Features
GPRS offers many new network features to mobile service operators. These include packet
switching, spectrum efficiency, Internet aware, and the support of TDMA and GSM.
 PACKET SWITCHING - From a network operator perspective, GPRS involves
overlaying packet based air interference on the existing circuit switched GSM network.
This gives the user an option to use a packet-based data service. To supplement a circuit
switched network architecture with packet switching is quite a major upgrade. The GPRS
standard is delivered in a very elegant manner – with network operators needing only to
add a couple of new infrastructure nodes and making a software upgrade to some existing
network elements.
 SPECTRUM EFFICIENCY - Packet switching means that GPRS radio resources are
used only when users are actually sending or receiving data. Rather than dedicating a

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