Transcript Communication Systems

Arab Open University - AOU
T209
Information and Communication
Technologies: People and
Interactions
Second Session
Prepared by: Eng. Ali H. Elaywe
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Aims



Introduce the technology of Communication
Systems
Introduce the technology of Computer Systems
Information and Communication Technology
(ICT) System usually comprises of the above 2
systems
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Reference Material
This session is based on the following
references:
1- Chapters 6 to 8 of Book S: Systems
2- A part of the study is based on Book C:
Communication Skills
3- Also we refer to the Book D: Documents
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Topic 1: Communication
Systems
The Communication Systems have become
part of our daily life and people use them to
stay in touch and informed
In this section the following sub - topics will be
discussed:
1- Categories of Communication Systems
2- Block diagram of a Communication System
3- The Mobile Phone Systems
4- The Internet
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Sub Topic 1.1: Categories of
communication systems
1- How many senders and recipients there are??
 A- One-to-one:
 One sender and one recipient
 Examples: A simple telephone call or as in an e-mail to a
single recipient

B- One-to-many:
 One sender and many recipients
 Examples: An individual’s Web page viewed by many
visitors, or as in an e-mail sent to several recipients

C- Many-to-Many:
 Many senders and many recipients
 Examples: Broadcast radio services (where there are
many radio stations broadcasting to many listeners)
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2- Identification of the recipient by the
sender
A- Identification requested: In a telephone
system the recipient’s phone number has to be
supplied by the sender
B- No identification requested: Broadcast TV
or radio no need to identify the recipient
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3- The possibility of message exchange via the
same system
A- One-way connection
If the system does not support message exchange, then the
communication system is said to be one-way. (Another term that is
sometimes used is unidirectional or simplex)
Examples: As in the case of broadcast TV or radio that are noninteractive in nature
B- Two-way connection
Sometimes an interchange of messages is possible using the
same means of conveying the message in both directions, then
the communication system can be said to be two-way. (Another
term that is sometimes used is bidirectional or duplex)
Examples: As in a telephone system
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4- The separation of the sender(s) and
recipient(s) for the message transfer.
They may be:

A- Separated in space but not time
 Example: As in a telephone call

B- Separated in time but not space
 This is fairly rare
 Example: someone leaving a note on someone
else’s desk for later reading

C- Separated in time and space
 Examples: As in a telephone system where a
voicemail message is left, and as in e-mail
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5- Asynchronous Vs. Synchronous
Communications

A- Asynchronous
 In this type of communication the act of
sending and the act of receiving of the
message are separated in time


Example 1: The Email system is asynchronous in
nature and it does not require the sender and receiver of
the email to be using the system at the same moment in
time
Example 2: ATM (Asynchronous Transfer Mode)
systems for telecommunication networks
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
B- Synchronous is the term used for
communication systems the sender and
recipient are not separated in time
 Example 1: Most TDMA systems (e.g., GSM cell
phone system) need to be synchronized in order to
keep track of the slot boundaries etc… in the 8 TDMA
slots
 Example 2: The W-CDMA (3G) system can be
deployed both in an Asynchronous as well as
Synchronous mode of operation. In the Synchronous
mode of operation, the neighboring Base Stations
have to use the same clock timing which can be
generated from a GPS system clock
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Sub Topic 1.2: A diagrammatic
representation of a communication system
In 1948, an American engineer called Shannon
published a paper called ‘A Mathematical Theory
of Communication’
In this paper he presented a diagram of a
communication system (see Figure 1) which is
simple but nevertheless generic
This diagram, and derivations of it, have been
widely used in the subsequent study of
communication systems
For simplification Shannon suppose that his
communication system is: (see Activity 8)
a- one-way (uni-directional)
b- one-to-one system
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Channel
Message
Information
Source
Signal
Transmitter
Received
Signal
Receiver
Message
Destination
Noise Source
Figure 1 The diagram Shannon used in his theory
of communication
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Shannon explained the components of the diagram
as follows:
1- The information source ‘produces a message or
sequence of messages …
2- The transmitter ‘operates on the message in some way
to produce a signal suitable for transmission over the
channel…
3- The channel is ‘the medium used to transmit the signal
from transmitter to receiver…
4- The receiver ‘performs the inverse operation of that done
by the transmitter…
5- The destination is ‘the person (or thing) for whom the
message is intended
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6- Noise is a well-known engineering term, so Shannon
did not need to explain it
Briefly, noise is something which disturbs or distorts a
signal while it is traveling along a communication path. The
hisses and crackles sometimes heard on the radio are
examples of the effects of noise, as is the ‘snow’
sometimes seen on a TV screen
Digital signals are much more resistant to noise than are
analogue signals
In practice, noise could occur anywhere along the channel
(or, indeed, anywhere else in the system, including in the
transmitter or the receiver)
Shannon, however, chose to simplify things by
representing the noise as occurring in just one place: the
channel
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

In particular, we are not for the moment
interested in the problem of noise, but we
are interested in all of one-to-one, one-tomany and many-to-many systems. We
have therefore adapted Shannon’s
diagram into the one shown in Figure 2
So this diagram of a communication
system is the one that we will work with for
the rest of this book
Continue
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Figure 2 A diagram of a communication system
for this book
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The various blocks of the communication system
block diagram (Figure 2) are briefly described below:
1- Sender: It is the information source that produces a
message to be transmitted. This source could be speech or
data
2- Transmitter: It operates on the message to produce a
signal suitable for transmission over the channel
3- Channel: It is the medium used to transmit the signal.
Examples of channels include:
A- Fixed-wire channels (these are less noisy in nature):
Copper cable
Coaxial cable
Fiber-optics etc…
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B- Wireless channels (these are more noisy in nature
and hence more difficult to design and build. The
mobile wireless channel systems are exceeding
difficult):
Multipath propagation channel (the cellular channel)
Satellite channel etc...
4- Receiver: It performs the inverse of the operations
that occurred at the transmitter. In general, receiver is
the most complicated part of the system and
wireless receiver designs are more challenging than
fixed-wire receiver designs
5- Recipient (or destination): It is the person (or
thing) for whom the message is intended
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Please note that the arrows in the Figure 2
denote electrical signals:
1- These signals are of low frequency (speech or
data) starting at “sender” (also called baseband
signals)
2- And are of high frequency at the output of the
transmitter (also called radio frequency or RF
signals)
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Sub Topic 1.3: The Mobile Phone
System (MPS)

Various communication systems are
differentiated in general by the characteristics of
the channel



In the Mobile Phone System (MPS) (see Figure 3) , the
channel is Wireless in nature and the users have the
additional freedom of movement or mobility
The wireless link in a MPS is usually called the Air
Interface
The three major components of MPS are:



1- Mobile Station (MS): This is the cell phone itself
2- Base Station (BS): This is the fixed station designed
to handle many cell phone calls through a wireless Air
Interface with the MS
3- Network: This is the switching/routing and billing
activities area
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Figure 3 A Mobile Phone System (MPS)
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Activity 9 (self-assessment)
A- The Mobile Phone System (MPS) is:
1- One-to-one
2- two-way (bidirectional)
3- synchronous system
B- The sender and recipient are normally
people, but if the sender has to leave a voicemail
message then the recipient is, temporarily, an
object
Continue
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
Activity 10 (exploratory)
 A- What do you think the ‘transmitter’ and ‘receiver’ of the
Mobile Phone System?


Transmitter: In this case the mobile phone in the user’s hand
is the transmitter while the user is speaking
 It takes the user’s (sender’s) spoken message and
transmits it into the telephone system
Receiver: Remember that not all calls from mobile phones are
to mobile phones! So the receiver may be:
 1- Another mobile phone (whether as a separate device
or as part of a multifunction device)
 2- or it may be a ‘fixed’ phone
 3- It may even be an answering machine
Continue
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 B- What do you think the ‘channel’ might be
here?


You can probably deduce that the signal leaves the
mobile phone as a radio signal in the air, but after
that you may know nothing about how the signal
gets to the recipient’s phone – nor are you
expected to know, at this stage of the module
But when you come to study the mobile telephone
system in some depth in Part 3 of Book T,
Technologies, you may well be surprised at how
complex the answer is, involving some or all of
cables, optical fibres and various telephone
exchanges
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
Now Lets label the arrows between the sender and
the recipient (in Figure 3) to know the types of
signals:




A- There is an acoustical signal or sound signal passing
from the sender to their phone
B- The task of the mobile phone is to convert this acoustical
signal into a suitable radio signal for the channel
C- At the other end of the channel, the signal must be in the
form of another radio signal if the recipient is using a mobile
phone, or an electrical signal in wires if the recipient is using
a ‘fixed’ phone
D- Finally, the recipient’s phone converts this signal back into
an acoustical signal for the recipient. Figure 4 shows this
diagrammatically
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Figure 4 A mobile telephone system, indicating what passes
between the components
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
Switching Center:
 One key role it must play is to select the route
for the signal, to ensure that it reaches the
correct recipient
 This means that there must be at least one
switching center somewhere in the channel
 This switching center receives the incoming
signal and arranges for it to be transmitted
along the appropriate path to its destination

If necessary – and it often is – it will also convert the
signal in some way, perhaps from one physical
form to another
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Activity 11 (Summarizing)

Figure 5 shows typical tasks performed by the
components of communication systems. Find all the
different sorts of task shown on the diagram and
make a list of them. As you do so, make sure that
you understand how these tasks relate to this
particular example of a communication system: a
Mobile Phone System (MPS)
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Figure 5 A mobile telephone system, indicating the tasks performed by
the components
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The tasks in your list should read as follows:
receive signals
generate signals
convert signals from one form to another
transmit signals
select routes for signals
This list of tasks is typical of all communication
systems. You should therefore note this list
carefully
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Activity 12 (Journal)

This system-level overview of mobile
telephone systems may perhaps have
raised questions in your mind about this
particular type of communication system. If it
has, note them in the Workbook section of
your Journal. When you read Part 3 of Book
T, refer back to the questions and try to use
that part of the book to answer them
 Try to do this activity before the next session
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Sub Topic 1.4: The Internet
The Internet is a global network which interconnects
many subnetworks of computers
Users access the Internet via some type of computer
equipped with appropriate software (e.g., netscape
navigator or internet explorer)
The computer also needs to be equipped with either a
network card (e.g., Ether net card) , for those who have
an office network of computers through which they can
access the Internet, or a modem (it stands for
Modulation and Demodulation), for those who must use
a phone line for Internet access
In both cases, the user also needs an Internet Service
Provider (ISP), though in the case of an office computer
this may simply be the employer
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In the case of mobile devices like the
multifunction
device,
also
appropriate
software (e.g., microbrowsers) and a suitable
modem or an internal modem card allow the
device to transmit data to or receive data from
the user’s ISP and so access the Internet
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Old Speech Communication systems were Circuit
Switched in nature. But The Internet uses Packet
Switching for Data Communication and hence such
networks are called IP Networks

Developers are trying to transmit speech in packet form as well and
hence such networks are called Voice Over IP networks (VOIP)
The Protocols
For Data Communication purposes computers usually use a set of
agreed upon rules called a Protocol
The most famous protocol for Internet is called the TCP/IP
(transmission control protocol/internet protocol)
TCP/IP is a Layered Protocol
Application - TCP - IP, The lowest layer is called the physical layer:
which is a communication medium/system (e.g., fixed-wire for fixed
Internet and cellular/wireless for mobile/wireless Internet (e.g., 3G))
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Note:


Although the terms are sometimes used as if they
meant the same thing, the Internet is not the same as
1- e-mail or the 2- World Wide Web
Instead, 1- e-mail and the 2- World Wide Web (Web
for short) are two different applications which both
make use of the Internet
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Sub-Topic 1.4.1: The e-mail
communication system
The basic block diagram of a Data Communication
system for fixed or Mobile Internet (e.g., 3G) is
essentially similar with major difference of the Channel
being wireless in the later case (Mobile Internet)
Hence mobile internet design is much more challenging
due to the Cellular/Wireless nature of the channel
Figure 6 shows one possible scenario of a cellular
wireless internet access in which a mobile phone user
is requesting service from a computer
Please note that the mobile phone must have the data
communication capability (e.g., 3G) in order to perform
this cellular wireless internet access
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Figure 6 An e-mail communication system: mobile phone
user interacting with a computer and modem
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Figure 7 An e-mail communication system, indicating what passes
between the components
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Figure 8 An e-mail communication system, indicating the tasks
performed by the components
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The similarities and differences between Mobile
Phone System (MPS) and an e-mail system

1- The Similarities:
 The striking similarities between Figures 6 to 8 and
Figures 3 to 5 arise because both a Mobile Phone
System and an e-mail system are two-way (bidirectional) and one-to-one

2- The Differences:
 The biggest difference is that the Mobile Phone
System is synchronous whereas the e-mail system is
asynchronous
 And you will note that the mobile phone, computers and
channel in the e-mail system are shown as performing
the task of storing information, something that was
not necessary in the Mobile Phone System
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Sub Topic 1.4.2: The web communication
system
Activity 14 (Exploratory)


I shall now turn my attention to the Web, and to the case where a
user of an Web-enabled mobile phone is a recipient of Web
pages
Who or what is the sender in this case?
 The answer could be either ‘the person or people who created the
Web pages’ or ‘the computer on which the Web pages are stored’
 First, I shall include the creator(s) of the Web pages in the system,
and so my diagram for the World Wide Web system (with a mobile
recipient) is as in Figure 9
 Although this system is one-way (uni-directional) and one-tomany (or, perhaps, few-to-many, given that Web pages may well
be created by a team), because many Internet users can access
and download the Web pages in question, I have simplified things
here by showing just the one recipient with their mobile device
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Figure 9 A Web communication system drawn to include the creator(s) of
the Web pages
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Activity 15 (self-assessment)

Using Figure 9 as your starting point, draw
diagrams similar to Figures 7 and 8 (and 4 and 5)
for the Web communication system with a
mobile recipient
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Figure 10 A Web communication system, indicating what passes
between the components
Figure 11 A Web communication system, indicating the tasks
performed by the components
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Important Notes !!

1- You may have been surprised to note that in both
Figure 8 and Figure 11 – that is, in both the e-mail
communication
system
and
the
Web
communication system – one of the channel’s
tasks is to store. This has to do with the way that
the signal is transmitted over the channel in the
Internet
 We discuss this in Part 2 of Book T, Technologies, when
we look in more detail at the Internet
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2- The creator(s) of the web pages is included in
Figure 9, but as you saw in the answer to Activity 15
this led to something of a problem in drawing the
diagrams (Figures 10 – 11) for the communication
system, as some tasks are likely to be performed at a
very different time from others

So what would the diagram have looked like if the creator(s)
of the Web pages is omitted and considered the computer on
which the web pages are stored as the ‘sender’? This is a
perfectly legitimate way of defining the system boundary, and
in many ways a more convenient one (see Figure 12)
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Figure 12 A Web communication system with the computer that holds
the Web pages considered as the sender
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Activity 16 (Journal)

This system-level overview of the Internet,
e-mail and the Web may perhaps have
raised questions in your mind about this
particular type of communication system.
If it has, note them in the Workbook
section of your Journal. When you read
Part 2 of Book T refer back to the
questions and try to use that part of the
book to answer them
 Try to do this activity before the next session
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Topic 2: Computer Systems
In this section the following sub - topics will
be discussed:
1- Categories of Computer Systems
2- Block Diagram of a Computer System
3- Personal Digital Assistant (PDA)
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Sub Topic 2.1: Categories of Computer
Systems
1- General purpose versus dedicated computer
systems (Potential Use):

A- General-purpose computer system
 is one where the user can determine, at least to some extent, the
tasks the computer is to perform by buying and installing
appropriate software (application software packages), and
perhaps by buying some additional hardware
 This type of computer system is programmable in nature

The user can program it himself by using a suitable programming
language
 Example: Desktop PC
Continue
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
B- A dedicated (or special purpose) computer
system
 The user cannot modify the tasks the computer performs by changing
either the software or the hardware
 This is usually pre-programmed or pre-designed computer) to
perform a specific task or set of tasks – although the user may need
to supply data for these tasks (e.g., dates and times for a diary alarm
function)
 Examples: an inexpensive PDA, an aircraft’s flight control system
etc…
Continue
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2- Visible versus invisible computer systems
(Visibility):

A- Visible computer system:


Example: the PC ( Desktop or laptop)
B- Invisible computer systems:


Examples: Embedded computer systems in microwave
ovens, car break control systems, washing machines,
cameras etc…
The mobile phone can be also considered as invisible
computer system
Continue
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3- Stand-alone versus networked computer systems:

A- Stand-alone computer system:
 An example of the this category is a PDA without any Internet
access

B- Connectable to a network (Networked) computer system:
 An example of this category is a PDA with Internet access

C- Permanently connected to a network (permanently
networked) computer system:
 The Internet access is not used all the time, but the PDA is
connectable should the user want to access the Internet
 Examples of this category have until recently normally occurred on
business premises where employees’ computers may need to be
permanently connected into the company’s network in order to be
usable at all
 The situation is beginning to change, however, and some mobile
devices (e.g., 3G) are beginning to be permanently connected, as
you will see in Book T
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Sub Topic 2.2: A diagrammatic representation
of a computer system
.
Figure 13 A diagrammatic representation of a generic
computer system, including the user
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
A- The Processor Unit:
 It is the heart (or the brain) of every computer system
 This is where the main intelligent decision making tasks are
performed
 Examples:

1- The simple computer systems like PDAs tend to have only
one simple processor


This processor executes the application program the user asks for –
a diary, perhaps, or a calculator
2- Some computers have sophisticated processor like the
ARM processor for a cell phone or the very sophisticated Intel
80x86 series for a PC system
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

3- The supercomputers will have many processors
which share out a particular task and then work in parallel
to perform the task very quickly
4- Desktop computer systems have one ‘master’
processor and a small number of subsidiary
processors
 The ‘master’ processor executes the application
programs, and in doing so it will delegate certain
specific subtasks to the subsidiary processors
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
B- The memory Unit:
 1- The main memory:




It holds the program the processor is executing (or, at least, an
appropriate portion of the program)
It also provides storage space for any needed data that is
associated with that program
And thirdly it holds some essential programs (boot-up
programs) that enable the computer to start up and keep going
Examples: RAM and ROM
 2- The secondary memory


It holds data and programs not in active use (except for the
essential programs mentioned above, which stay in main
memory)
Examples: The hard disk, floppy disks, CD-ROMs and DVDs
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
Notice that the secondary memory often takes
the form of several different physical
components, and some of it may well be
removable from the computer (a fact made use of
when back-ups are taken)
 In a PDA there may be little or no
secondary memory, with all the programs
and data held in main memory at all times.
Some PDAs do, however, have memory
cards which act as secondary memory
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
C- The Input/Output (I/O) Unit:
 1- The input peripherals


Are the means by which users get their inputs into the computer
system
Examples: Keypad, keyboard, mouse, microphone, a trackball, a
joystick, a tiny video camera, etc…
 2- The output peripherals


Are the means by which users get outputs from the computer system
Examples: Screen, monitor (screen), printer and loudspeaker(s)...
 3- Input and output peripherals


May take signals from or provide signals to other systems
Example: Modem …
 Which receives signals from the Internet via the telephone
system and sends signals back into these same systems
 So it is called an input–output peripheral
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 4- The input subsystem:
 Each input subsystem consists of whatever may be needed

between a particular input peripheral and the processor for them
to be able to work together
Sometimes the input subsystem is minimal; at other times it can
be quite extensive
 It may even contain a dedicated processor. For instance, on
desktop computers the keyboard normally contains a
processor dedicated to detecting keypresses and sending
appropriate data to the ‘master’ processor
 5- The output subsystem:


Each output subsystem is whatever may be needed between the
processor and a particular output peripheral to enable them to
work together
This subsystem may contain a dedicated processor, as is the case
with many printers
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Important Notes!!
 Figure 13 also shows the signals that
may arrive at or leave the computer
system in other ways than via the user –
for example via a network card or
modem
 Figure 13 is designed to depict the
hardware of the system, and software
does not fit easily into it
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Figure 14 A diagram of a computer system showing the tasks
performed by some of the components
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Activity 20 (exploratory)

By indicating the tasks performed by the secondary memory, the
output peripherals and the output subsystems, complete Figure
14
 See Figure 15. Notice that the task of the output subsystems is
the exact reverse of that of the input subsystems; an output
subsystem takes the data and converts it into a suitable signal
that will be recognized by the corresponding output peripheral (a
screen, a loudspeaker, etc…)
 Similarly, the output peripherals receive this signal and either
convert it into outputs which they present to the user (characters
on the screen, sounds) or convert it into a form ready for
transmitting into a communication system
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Figure 15 A diagram of a computer system showing the tasks
performed by the components
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Sub Topic 2.3: Personal Digital Assistant (PDA)
Figure 16 The PDA being described
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Activity 21 (self-assessment)

(a) Use the information in the box ‘Thumbnail
sketch of the user interface of a PDA’,
including Figure 16, to list
 (i) the input peripherals

The input peripherals are the four buttons and the
touch-sensitive screen (with stylus)
 (ii) the output peripherals

The output peripherals are the screen and the buzzer
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
(b) To which of the components on Figure 15
does the docking cradle correspond?
 The docking cradle enables the PDA to exchange
data with a desktop computer. It is therefore an
input–output peripheral, and so it can best be
thought of as corresponding to both the input and
the output peripherals of Figure 15. (In this it is
rather like a modem)
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Activity 22 (self-assessment)


This activity asks you to relate Figure 15 to the box
‘Thumbnail sketch of the user interface of a PDA’
(a) Consider the input functions of the touchsensitive screen. What task or tasks does it perform?
What task or tasks does its input subsystem
perform?
 The touch-sensitive screen converts the physical motions
of the user (taps, tracing of stylized characters, etc…) to
electrical signals
 Its input subsystem converts these electrical signals to
suitable data forms for the processor to use
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
(b) Now consider the buzzer. What task or
tasks does this output peripheral perform?
What task or tasks does its output subsystem
perform?
 The buzzer converts the electrical signal sent to it
by its output subsystem to an acoustical signal –
that is, appropriate sounds
 Its output subsystem takes data from the
processor and turns it into the electrical signals
the buzzer can use
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Activity 23 (summarizing)

(a) Figure 15 shows the tasks performed by a
computer system. Find all the different tasks shown
on the diagram and make a list of them
 accept inputs from user - convert inputs to signals - receive
signals - convert signals from one form to another - convert
signals to suitable data forms - manipulate data - execute
programs - store data - store programs - convert data to
signals - transmit signals - convert signals to outputs present outputs to user

(b) Assume that the PDA has one processor and no
secondary memory
 See Figure 17
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Figure 17 A diagram of a PDA showing the tasks performed by the
components
Continue
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Activity 24 (Journal)

This high-level overview of computer
systems
may
perhaps
have
raised
questions in your mind. If it has, note them in
the Workbook section of your journal.
When you read Part 1 of Book T, refer back
to the questions and try to use that part of the
book to answer them
 Try to do this activity before the next session
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Activity 25 (exploratory)


At the end of Section 6.3 (in Book S) I indicated that
many mobile phones offer ‘nice to have’ features
which are more like those found in a computer
system than those found in a communication
system. Look back to this paragraph (it’s the next to
the last one in Section 6.3) and try to relate these
additional features to the components and tasks in
Figure 15
Comment
 Try to discuss your thoughts on the conferencing system
or in a tutorial
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Topic 3: Preparation for Next Session
1) Read Book S
2) Do all activities in Book S including links to
Book C and Book D
3) Complete the Journal items related to Book S
4) Skim Part 1 (The Technology of the PDA) of
Book T
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