Transcript Processors

Arab Open University - AOU
T209
Information and Communication Technologies:
People and Interactions
Fourth Session
1
Prepared by: Eng. Ali H. Elaywe
Introduction
 Book S gives a brief overview of Communication
Systems and Computer Systems
 Now it is time to dive a little deeper in the details of
these systems. Book T consists of three parts:
 Part 1: The technology of personal digital assistants  to
be covered in this session (continued…)
 Part 2: The technology of the Internet, e-mail and the
World Wide Web  to be covered in this session
 Part 3: The technology of mobile telephony
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Aims
 We will continue discussing the Part 1 of Book T
 As mentioned in Book S, Systems, the Internet is a
global network which interconnects many subnetworks
of computers
 In Part2 of Book T, three documents will be used to
introduce the students to some principal features of the
internet and two of its major applications, e-mail and
the Web, including accessing the Web while on the
move
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Reference Material
 This
session
references:
is
based
on
the
following
1- Part1 of Book T: Technologies
2- Part2 of Book T: Technologies
Most of the work in this part would be basically discussing the
fundamental issues presented in:
A- Electronic document, “Information and the internet”, by
Ian Johnston (see T209 CD ROM1)
B- “Electronic mail” by John Monk (Book D, Document 7,
page 14)
C- “Wireless Web” by John Lettice (Book D, Document 8,
page 25)
3- Also we refer to the T529 ICT CD-ROM
4- A part of the study is based on
Communication Skills (Sections 3 & 4)
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Book
C:
Topic 1: The Memory Unit
 The Memory Unit in a computer system is
used to store programs and data
 There are two types of memories:
1- Main Memory
2- Secondary Memory
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 1- Main Memory
 Main memory consists of one or more Integrated Circuits or
chips
 As the technology of integrated circuits advances, so more
and more memory can be put on a single chip
 This is one of the advances that have made handheld and
palmtop PDAs possible
 Main memory can be thought of as a set of numbered ‘slots’
called memory locations, or just locations
 The numbers identifying the locations are known as memory
addresses, or just addresses
 All memory locations hold exactly the same number of bits, and
the groups of bits that will fit into data locations are often known as
data words, or just words. Most PDAs use 16-bit or 32-bit data
words
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 Bit: is the smallest information units, hence can not represent much
information
 Byte: is the basic unit which is passed around the computer, hence can
represent more information than a single bit
 Each 8-bit unit is called a byte
 Kilobytes:
 210 = 1024 bytes (Example: a file is 45 Kbytes)
 Megabytes:
 220 = 1,048,576 bytes (1024*1024) (Example: a computer has 256MB of RAM)
 Gigabytes:
 230 bytes (1024*1024*1024) (Example: a computer has 40GB of hard disk)
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 Writing and Reading process
 1- The process of storing data in a particular location in
memory is known as writing

During a write operation the processor first sends to the memory the
address of the location to be written to and then sends the data
word that is to be written into that location. And of course it must ‘tell’
the memory that it is a write operation
 2- The process of retrieving data from a particular location is
known as reading

During a read operation the processor sends to the memory the
address of a location and receives back a copy of the data word
held in that location. And again, it must ‘tell’ the memory that it is a
read operation
 So writing to a memory location overwrites whatever was there
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before, but the data stored in a memory location is unchanged
when it is read
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 Address bus and data bus
 The address bus carries addresses from the processor to the
main memory
 The data bus carries data words between the processor and
the main memory
 The data bus can carry data words in either direction and so is
known as a ‘bidirectional bus’, whereas the address bus
carries addresses in only one direction and so is known as a
‘unidirectional bus’
 Two sorts of memory integrated circuits are used for
main memory, A- ROMs and B- RAMs
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16-bit / 32-bit
How many data words
can be stored in a 10 MB
main memory, knowing
that the system has a 32bit data words?
1
2
Memory locations
or Locations
3
4
10 MB= 10 x 8 x 1024 x
1024
bit=
10 MB=
1080
x 8xx 1000 x
1.048.576
= 83.886.080
1000 bit= 80.000.000
Memory
addresses
or
Addresses
N
83886080
80.000.000/ /3232= =
2.621.440
2.500.000 data words
N+1
Main memory
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How information is transferred in a machine which has 16-bits
long addresses and 16-bit data words?
Bus
1
0
1
0
Processor
Serial
Memory
- DVDs
1
0
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 A- ROMs (Read Only Memory)
 The name refers to the fact that this is a type of memory whose
contents cannot be changed by the processor after the
memory integrated circuit has been installed in the computer
 The processor can examine (read) the ROM’s contents, but not
change (not write to) them (non volatile)
 Example: BIOS
 Computer built-in instructions to load the operating system when the
computer starts up
 On the other hand, there are some sorts of ROM, such as
‘Flash’ ROM, where the user can change the contents (write
to)
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 B- RAM (Random Access Memory)
 RAM, can be both written to and read from by the processor
 This name (Random Access Memory) arises from the fact that
the data in any location in the whole memory can be
accessed just as quickly as the data in any other location

(In fact, ROM is also random-access, but the terminology is now so
widespread that it is firmly established, even if not wholly
unambiguous)
 An important point about RAM is that it is usually ‘volatile’,
which means that the data stored in it is lost when the power
supply to the RAM is switched off. This contrasts with ROM and
secondary memory, which are non-volatile
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 Important Notes:
 1- If you look back to the brief specifications of the Palm IIIc and
Psion Revo in Table 1 (in the Third Session), you will see that
each has both ROM and RAM
 2- In these PDAs, which do not have any secondary memory:
 The ROM is used to hold the programs and data supplied by
the manufacturer
 While the RAM is used to hold the user’s own data plus any
additional programs that the user may have been able to
install
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 2- The secondary memory
 It holds data and programs not in active use
 Examples (for the PC): The hard disk, floppy disks, CD-
ROMs and DVDs
 Very few PDAs, however, include any secondary memory as
standard, though some do offer it as an optional extra
 If a PDA does offer secondary memory, the most likely type
is a memory card, also known as a PC card
These small cards can contain additional programs and associated
data and fit into a special slot in the PDA’s housing
 As memory cards can hold several hundred megabytes of program
and/or data (even as much as a gigabyte, at a price!) they offer a
significant increase in the potential number and size of programs in a
PDA, and/or in the amount of data that can be accessed by the PDA

 So the use of such memory cards can greatly increase the
flexibility of a PDA
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Topic 2: Processors
 A processor is the brain of a PDA or any other computer
system
 The job of the processor is to execute programs and to
manipulate data
 In its simplest form, it consists of:
 1- ALU (arithmetic and logic unit) performs the arithmetical
(addition, subtraction, multiplication etc…) and the logical
operations
 2- The control unit as usually concerned with the program
execution and control
 3- The register is a storage element which is part of the
processor itself, as distinct from the locations of main memory.
Also the instructions in the program must refer to the internal
registers (or internal memory) of the processor

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A processor may have anywhere from 8 to 32 registers
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 The program resides in memory and an instruction Fetch-Decode-
Execute cycle is used to describe the process of reading a program
instruction from memory, decoding that instruction and then
performing the task corresponding to that instruction
 Examples of instructions used in processors:
 1- Read a data word from memory location 29 and put it into register 1
 2- Send the data word currently in register 5 to output subsystem 3
 3- Add the number in register 2 to the number in register 1 and put the result in
register 3
 4- jump over the next 5 instructions if the number in register 3 is zero
 Instructions that the processor understands directly are called
Machine/Assembly Language instructions
 Programmers usually write programs in a higher level language such
as C/C++ etc…
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 What does the processor do to add two numbers in M1
and M2 then put the result in M3??
 1- Load AX,M1

Read a data word from memory location M1 and put it into register AX
 2- ADD AX,M2

Add the number in register AX to the number in memory location M2
and put the result in register AX
 3- STORE M3,AX

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Store the result in memory location M3
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 The Instruction sets:
 The term ‘instruction set’ is used to refer to the complete set




of instructions a processor can execute
The processor come equipped with different sets of
instructions that they are able to execute!
Why, in different processors, we have different numbers of
registers?
Why the processor’s components are interconnected in
different ways?
Why the processors have different sets of instructions?
 The answer is that all of these features significantly affect the
performance of the processor
 and since manufacturer are competing with each others, they try
to find an architecture and instruction set that will give their
processor an advantage on their rivals
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 RISC (Reduced Instruction Set Computer)
 instruction sets of processors were becoming larger and larger. They
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were including more complex instructions which were designed to carry
out more complex tasks
But including these complex instructions in the processors made them
harder to design and more expensive to produce
In fact, some research showed that processors spent around 80% of their
time executing only around 20% of the instructions in the instruction set
So there was a fresh look at the design of processor architectures and
instruction sets. This fresh look led to RISC (Reduced Instruction Set
Computer) processors
RISC processor have a small and simple set of carefully chosen
instructions
RISC processor is faster and consumes less power than its more
complex cousins
PDAs usually use RISC processor
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 The speed of the processors
 Manufacturers often quote the ‘speed’ of their
processors in megahertz (MHz) or gigahertz (GHz)
 This ‘speed’ figure is an indication of how many
instructions the processor can execute per second
 Why we did not need higher speed processors in the
PDA??
 1- High speeds are not needed for the simpler, more limited
tasks of a PDA
 2- Faster processor would significantly increase the costs
 3- Faster processors deplete a battery faster and so reduce
battery life
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 Does it imply that the speed of 30 MHz would perform a
particular task faster than another processor at speed of 25
MHz?
 On the face of it, you might well assume that a processor with a quoted
speed of 30 MHz would perform a particular task faster than another
processor with a quoted speed of 25 MHz
 But things are not so simple!!!! remember, the architecture and
instruction set of a processor significantly affect its performance
 So the 25 MHz processor may have a well-designed architecture
and instruction set, then can perform any given task just as fast as
the 30 MHz processor
 In fact, all that the number of megahertz really tells you is
how fast instructions are fed to the processor, not how
fast the processor will perform a given task!!!
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Topic 3: PDA Software
 The software for a PDA (or any other computer
system) can be divided into two types:
 1- Operating Systems
 2- Application Programs
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Sub-Topic 3.1: Operating Systems
 Which are the basic set of programs without which
the computer becomes difficult
 Operating system enables the computer to respond
to the user’s inputs and to provide outputs to the
user (I/O functions)
 The application programs’ are also handled by the
operating system
 When a program needs to collect some data from the user
it does not itself include the computer instructions to
collect this data; instead it refers the task to the operating
system, and the operating system performs the task on
behalf of the application program
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 So an operating system must take into account the
particular processor that will be used, its architecture
and its instruction set
 If there is any secondary memory then the operating
system must take care of the transfer of data between
the processor and that secondary memory
 Example 1: Operating System for the PCs
 The best known operating system for PCs is Windows
 Example 2: Operating Systems For PDAs
 There are two operating systems for PDAs: EPOC32 and
PalmOS
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 Activity 1.15 (exploratory)
 Can you think of any reasons why this is a good way of doing
things? ( the advantages of the operating systems)
 1- Make the user interface more friendly
 2- It saves storage space in the memory. If each individual
application program had to include the instructions for
collecting data from the user then each program would take up
more memory space and the memory would hold several
copies of the same list of instructions. If all application
programs call on the operating system to perform the task
then the instructions are held only once in the memory. This
is an important consideration in PDAs where memory space is
at a premium
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 3- This advantage is perhaps more relevant to desktop and
notebook computers than to PDAs, is that if the hardware of
the computer is changed – a new printer, perhaps – only the
details of the operating system need to be changed. If each
individual application program contained instructions for
sending material to the printer then every application program
would need to be updated when a new printer was installed – a
very difficult task!
 4- co-ordinate all the activities of the various components of
the computer system, and making sure that they are
scheduled appropriately and there are no conflicts between
them, Failure to do this will cause the system to crash!!
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Sub-Topic 3.2: Application programs
 These enable computer systems to perform particular
tasks
 Example 1: Application Programs for PC:
 Wordprocessor, spreadsheet, database, Web browsers etc…
 A user can also write his own application programs using a
computer programming language such as C/C++
 Example 2: Application programs for PDAs:
 An electronic address book
 An electronic diary
 An electronic ‘to do’ list
 An electronic notepad
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 Activity 1.18 (Journal)
 Here is an activity to prompt you to begin to work on ‘bringing it all
together’ for small computer systems like PDAs. I suggest you
write your answer in the Workbook section of your Journal. You
may even want to write two versions of your answer, one to give
an overview and the other to go into more detail
 Imagine that you have a PDA with a full keyboard and a
monochrome LCD screen. You have the address book program
running and you have just typed in the name of a new friend,
John Smith, (without making any errors and so having to press
the ‘delete’ key). Describe as fully as you can what activities
have had to go on inside the PDA and in appropriate input and
output peripherals while you were doing this. Also describe what
will end up in the PDA’s RAM
Try to do this activity by your self
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Topic 4: Introduction to the technology of the
Internet, e-mail and the World Wide Web
 Activity 2.1 (self-assessment / revision)
 It is possible to think of all of the data transmitted
around the Internet as being composed of bytes or
octets of data. In the context of computers and the
Internet, what are
 (a) a bit

A bit is a binary digit. That is, it is either 1 or 0
 (b) a byte

A byte is a group of 8 bits. (e.g., 00110011)
 (c) an octet

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An octet is another name for a byte. (The term ‘byte’ is more
often used in computing contexts, the term ‘octet’ in
communications contexts)
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 Activity 2.2 (self-assessment / revision)
 Compression is a process that is often used when files
are transferred across the Internet (and sometimes when
they are stored, as well)
 (a) What is compression and, in outline, what happens during
the compression process?
Compression is a process of recoding binary data into a more
compact form. During the compression process portions of
redundant data are detected and removed (so it also be called
data reduction)
 Compression is widely used in multimedia, digital
broadcasting, some forms of digital recording, and in virtually
all commercial software delivery and storage
 It is important in the Internet is to send large files (multimedia
applications)
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
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
There are two main reasons for using compression:
o 1- a compressed file takes up less storage space than the
uncompressed version. Hence more data can be stored on a given
disk or in a particular memory
o 2- a compressed file can be transferred more quickly. This may
be important, for example, when loading files from the Internet, or
when digital sound or video has to be transferred in ‘real time’

There are two main disadvantages of using compression:
o 1- Compression and decompression require additional hardware
or software – at the very least, an additional coder and a decoder,
as shown in Figure 1
o 2- Compression and decompression also take time to perform,
because of the necessary processing operations
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Figure 1 Compression and subsequent decompression require a coder
and decoder
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 (b) What are the two main classes of Data compression
techniques?

(i) lossless compression
o Is a process which compresses the original binary data
in such a way that it can be reconstructed exactly later
on with no loss

(ii) lossy compression
o Is a process which compresses the original binary data
in such a way that it cannot be reconstructed exactly
later on
o This means that some of the original data is lost, but this
may well not matter in the particular application where
lossy compression is being used
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
and what are their relative advantages and
drawbacks?
o The relative advantage of lossy compression over
lossless compression is that usually (though not
always) it is possible to achieve greater
compression of the data
o The advantage of lossless compression over lossy
is that it is possible to reconstruct the original data
exactly
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 (c) Name two examples each of
 (i) a lossless compression method



1- Run-length encoding (read more about it)
2- Variable-length lossless codes (read more about it)
o The file formats that are saved using the LZ algorithm
o Used in ZIP compression (e.g., PKZIP)
3- GIF (graphical interchange format) coding
 (ii) a lossy compression method
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1- Block-based compression
2- JPEG (Joint Pictures Experts Group) - For still images
3- MPEG (Motion Pictures Experts Group) coding - For video
4- MP3 (MPEG Audio Layer 3) coding - For sound
5- H.320 coding - For video conferencing
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 Example 1: (Important)
 One of the simplest forms of compression of
digital data is run-length coding. This involves
detecting sequences (runs) of 0s or 1s, and
replacing each sequence with a number signifying
how many times that digit is repeated in the
sequence. Given the 100-bit message 0001111 …
1111, where the dots stand for continuous 1s.
 (a) What is the compressed version of this
message?
 (00000011) 0 (01100001) 1
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 (b) What is the compression ratio in this case?
 The compression ratio = the number of bits in the original
message / the number of bits in the compressed message
 So the compression ratio = 100 / 18 = 5.55
 (c) Is this a lossless compression or a lossy
compression?
 Lossless compression
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 Example 2: (Important)
 Run-length coding is used in many compression
algorithms. This involves detecting sequences of
0s or 1s in a stream of bits and replacing each
sequence with a number that specifies the number
of zeros or ones that are in sequence. Assume that
we have a stream of 82 bits, the first 8 are 1s and
the 63 that follows are 0s and the last 11 are again
1s.
 (a) What is the compressed version of this
message?
 In binary: (00001000) 1 (00111111) 0 (00001011) 1
 In decimal: 8(1) 63(0) 11(1)
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 (b) What is the compression ratio in this case?
 The compression ratio = the number of bits in the original
message / the number of bits in the compressed message
 So the compression ratio = 82 / 27 = 3.04
 (c)
Is it a lossless compression or a lossy
compression? And why?
 It is lossless compression
 Because after decompression of the received message we
will recover the original message without any change to
the content
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Topic 5: The Internet
 Most of the work in this section would be basically
discussing the fundamental issues presented in
electronic document, “Information and the
internet”, by Ian Johnston (see T209 CD ROM1)
 What is the Internet?
The Internet is a global network made up of many millions of
interconnected computer networks (see Figure 2).
Messages can pass between any computers connected into
this network, thus enabling rapid transfer of data between
computer users
 LAN (Local Area Network):
 It’s a network covering a small geographical area, such as an
individual workplace or university. (between 10m and 1 KM)
 WAN (Wide Area Network):
 It’s a network covering a large geographical area; (>100 KM). WAN
is usually used to connect LANs together
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Anyone with a computer can interconnect to the
Internet provided they have an Internet Service
Provider (ISP):
1- For computer users at home, a modem and a phone
connection are also needed
2- The users’ computers at work are usually connected into
the employer's (local-area network LAN) via a network
card (e.g., Ethernet card), and the network is then
interconnected to the Internet (see Figure 2)
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Figure 2 : The Internet
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 Where did the Internet come from?
What we now know as the Internet grew out of a research project
started by the United States Department of Defense in the 1960s
They were faced with two problems:
1- Many different computer systems were in use which
communicated in different ways
2- Existing communications systems were highly vulnerable to
attack. Nuclear attack was, of course, their particular fear
To deal with these problems a networking system was created
with two fundamental characteristics:
1- A common protocol (IP), implemented on all machines:
This meant that machines made by different manufacturers could 'talk' to
each other directly
This protocol was called the InterNetwork Protocol, from which came the
terms Internet for the collection of computers joined in this way and IP for
Internet Protocol, the basic communications standard
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2- Dynamic routing of information
Information is not transmitted as a continuous stream over
the Internet
Instead it is separated into chunks, called packets
Each packet contains the destination address and a small
amount of information
No route is prescribed by the sender; each packet effectively
creates its own route through the network. This is done by
'routers' - computers
It is therefore possible for the packets which make up a
message to take different routes (so it is packet switched
network)
It is in fact one of the biggest advantages of the Internet
Protocol (IP)
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 What is TCP/IP?
TCP/IP is the name used to refer to a family of
communications protocols used by the Internet.
The two most common protocols, which are used
together, are:
1- TCP (Transmission Control Protocol)
2- IP (Internet Protocol)
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 What are the jobs of TCP and IP when sending and
receiving messages??
 1) The role of TCP at the sending end is to divide messages into
small chunks, called packets. Each packet consists of 64
kilobytes Data and has a unique identifier. TCP then passes the
packets to the IP, which will send them across the network
 2) The role of TCP at the receiving end is therefore to reassemble the packets (which may arrive out of order) into the full
message, to acknowledge correctly received packets and to
request retransmission of lost or corrupted packets (TCP is
robust to failures)
 3) The role of IP: deals with the problem of uniquely identifying
all the computers connected to the Internet, by means of an 'IP
address'. This address is used to route the data from its source to
its destination. IP, though, only makes 'best efforts' to transmit all
the packets in a message. IP cannot deal with problems caused
by congestion on the network or corruption of packets. That
is the role of TCP!!
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 Activity 2.5 (self-assessment)
Explain what TCP/IP are, what an IP address is and why
the original IP addressing system had to be amended (see
types of IP address)?
Transmission of data across the Internet follows a set of rules,
known as a protocol. TCP and IP are the two major protocols
used, and they are usually referred to as TCP/IP
1- IP job is to route data between computers, but it doesn’t
check if the data has been received correctly, or even if it has
been received at all
2- TCP makes sure that all the data that has been sent has
been received, and received correctly
All machines connected into the Internet have a unique number,
the IP number or IP address
Now Lets see the types of IP address??
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The types of IP address:
1- IP version 4 (IPv4)
Until recently, IP addresses all consisted of a group of four
1-byte numbers between 0 and 255 (IPv4 used 4 bytes or
32-bits long)
Internet addresses can be in the range 0.0.0.0 to
255.255.255.255
IPv4 therefore allows a maximum of some 4295 million
individual IP addresses, and in practice rather fewer are
actually available
So an IP address might be, for example, 100.1.20.255
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The numbers towards the left indicate the network while those
towards the right indicate a particular machine on the network.
Where the division between 'left side' and 'right side' numbers falls
depends on the size of organization which runs the network in
question:
1- Small organizations will use 3 of the 4 numbers to describe the
network, and the remaining number to describe individual
machines on the network - giving 256 possible machine
addresses
2- Large organizations may have 2 number (125.108) or, in a very
few cases, one-number (125) network addresses, leaving a larger
number of possible addresses for machines within the organization
Example: In IPv4, for example, the Open University has a 2number network, called a Class B network, so all IP numbers in
the OU start with (137.108). One of the FirstClass servers, for
example, has the address 137.108.143.49
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IP address

What’s
an
IP address
why do Host
we use it?
Class
A:
B: Network
C:
Network
Network
Host and
Network
Host
Host
The first bit of the first byte is always off:
0xxxthe
xxxx
on and
second
The first two8 bits
of
the
first
byte
are
always
on
and
the
bits10xx8xxxx
bits
8 bits
8 bits
bit
is
always
off:
Example:
* 200.off:20.16.245
 127
200.20.16 Network address

Network
address
between
0 and
third
bit isB:
always
110x
xxxx
Class
Network
Network
Host
Host
 Network Address between 128 and 191
and
245
Host address
 Network address between: 192
223
21
14 = 2,097,152
Network addresses:
126
2
16,384 10
* 10.10.200.6
Network address
IP address
24-2
Host
addresses:
2816
-2==Network
254
65,534
16.777.214
Network
HostHost address

10.200.6
Class
Example:
C: Network
200.
20.16.245
10.10.200.6
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2- IP version 6 (IPv6)
Many computers are now on the Internet that it’s running out of
spare IP addresses!!
So a new version of IP, known as IP version 6 or IPv6 (IPv6 uses
128-bit), is being introduced
Why do we need IPv6?
A- IPv6 uses such long IP addresses that there is no fear of
them running out in the foreseeable future!!
B- IPv6 also has the advantage of being able to provide
different standards of service for different users. For
instance, a user wanting to send real-time video could ask for
a higher standard of service than one who simply wants to
send occasional e-mail messages. IPv6 is therefore said to
offer 'quality of service (QoS)‘
Although IPv6 is beginning to be used, new software and
sometimes hardware is needed for it and so not all Internet users
are willing to change yet. Many are still using IPv4
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 Relating IP Names and Numbers:
 There is no correlation between IP numbers and
Internet names
 IP numbers are allocated for the Internet as a whole,
without geographical considerations, in both IPv4 and
IPv6
 So in IPv4 123.18.52.xxx might be the network of a
company in Siberia and 123.18.53.xxx a university
in Japan
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 DNS (Domain Name Server / Service)
 DNS stands for Domain Name Service/Server; It allows us to
relate an IP address to a name. In fact it is used to translate
Internet name (which is easier to use) to an IP address
 All addresses are used - by the packets finding their way around in the form of IP numbers. The names are simply to give us
something easier to remember
 No single computer know all the Internet address, In fact DNSs
are in contact with each other. If one doesn’t know he will ask his
neighbour; if the neighbour also doesn’t know he will ask his
neighbour and so on until the answer is answered (the IP address)
 Example:

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Suppose I am trying to access a Web site at cyclops.sydney.ac.au;
the first thing that my computer would need is the IP address, so it
would ask the Open University nameserver computer (DNS). (I'll
use IPv4 numbers for simplicity):
o 123.34.84.29
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 Transmitting Information:
 Plain Text (read more about it)
 Formatted Text 1-By Instruction (read more about it)
 Formatted Text 2-By Description: (read more about it)
 1- Sending a Facsimile
 2- Sending Graphics
 3- Sending Animation and Video
 4- Sending Speech
 5- Sending High Fidelity Music
 6- Computer Control

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MIDI (Musical Instrument Digital Interface) is the standard for
controlling instruments by computer
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Topic 6: The World Wide Web (WWW)
 Activity 2.7 (self-assessment)
 People sometimes use the terms ‘the Internet’ and ‘the Web’
as if they meant the same thing. But they don’t. What is the
difference between them?
The Internet is a worldwide network which is made up of a very
large number of networks of computers. So it’s a physical entity.
You could think of it as hardware
 The Web is an application that uses the Internet. It consists of a
very large number of pages of hypertext information stored on
computers connected into the Internet and retrievable via other
computers connected into the Internet. Although it is not
software, it is much more like software than it is like hardware
 So the Web is a way of using the Internet to distribute 'rich text'
files - referred to as Web Pages
o The 'rich text' format used is called HyperText Markup
Language (HTML)

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 Hyper text Transfer Protocol (HTTP)
 This is the client-server protocol
 Used on the Web for the exchange of web pages
 It defines how the four stages of a web transaction
connection, request, reply and end should be done
 Similar to FTP protocol’s concept
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 Hypertext Mark-up Language (HTML)
 This represents a uniform way of structuring documents on
the web

The language of the Web
 It is considered as the document format used on the WWW

HTML files end with .html or .htm extensions
 What’s a tag?






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HTML page is composed instructions "tags" which tell the browser
how the text should look on the screen
the tag <p> indicates that a new paragraph is starting
the tag <b> indicates that the following text is to be in bold typeface
the tag </b> indicates the end of the text that is to be in bold
the tags <h1>, <h2>, <h3>, etc... indicate that headings (at various
levels) are starting
the tags </h1>, </h2>, </h3>, etc... indicate the end of headings
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 Activity 2.8 (self-assessment)
 The main difference between HTML (Hyper Text
Markup Language) and XML (eXtensible Markup
Language) are:
 HTML (Hyper Text Markup Language)
 1- HTML has predefined and fixed (rigid) tags in nature
 2- HTML includes instructions (tags) that govern a Web
page's appearance. But the tags do not give any
indication about the nature of the page's content
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 XML (eXtensible Markup Language)
 1- XML allows new tags to be defined inside the document
itself
So it is infinitely extensible  In theory XML can cater for any new
features that are needed in future
 This makes XML more like a programming language than simply a
way to mark-up pages
 It is much more flexible and powerful

 2- The idea of XML is that its tags will be used to define the
nature of the content

XML uses tags to indicate what the document is about, or even
what different portions of it are about
 For example, in an electronic version of a newspaper article,
tags will indicate which bits are the heading, the sub-heading,
the author, as well as what sort of content it has
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 Why is this (XML) important?
 The usefulness of this is that it will make searching the Web easier,
as search engines (e.g., Google and Yahoo) will be able to search
not just for particular words, but for types of content

Because there is so much information on the Web that human beings
cannot find it all; we have to use machines to help us. And machines would
be able to find relevant information more efficiently if they could look for
tags - tags that the creators of a Web page have embedded to describe
the sorts of information it includes
 When - or maybe if - XML is used extensively, then all items of a certain
type, such as book titles or definitions of terms or abstracts of articles
from journals, would have a tag that labels them as such. Further, all
pages of a certain type, such as data sheets or advertisements or
teaching text, would also have a tag that labels them as such
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Topic 7: Electronic Mail (e-mail)
 Most of your work for this section consists of studying
an article called Electronic mail by John Monk
(Book D, Document 7, page 14). The article is
considered difficult to read
 Study Note: Section 2.3 in Book C,
Communication skills, is designed to help you to
read a challenging article like this one
 Try to do the Journal activity 2.12 in Book T
Activity 2.11 (reading
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 Activity 2.13 (self-assessment)
 Is an e-mail system
 (a) one-to-one, one-to-many or many-to-many?
In essence, an e-mail system is one-to-one: one sender to one
recipient. And the recipient must be specified by an e-mail
address. But of course one of the conveniences of e-mail is that a
sender can specify several recipients for a message, making the
system perhaps more properly described as one-to-few. Note,
however, that one-to-many is a better description of an e-mail
system when it is used to post messages on ‘bulletin boards’
as in that case no specific recipient or recipients are given; the
message is ‘addressed’ to a single place where many people
can read it
 (b) one-way or two-way?
 The system is two-way (bi-directional)

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 (c) separated in space only, separated in time only or
separated in space and time?

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Usually the sender and the recipient are separated in
space and in time: they are in different places and the
recipient reads the message some time (maybe only a
short time) after the sender sends it
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 The standard laid down in the Internet RFC 822 document
(Crocker, 1982) allows the characters in an e-mail
message to be selected from a set of only 128 characters
 This is severely limiting, and in practice it is got around by the
sender’s software using a translation program to translate the
message to be sent into the 128 permitted characters and the
recipient’s software using a corresponding translation program
to translate back again
 So an e-mail message must conform to an agreed format
such as that in RFC 822
 E-mail address:
 The e-mail address must consist of two parts the Mailbox
names before (LHS) the @ symbol and Domain name after
(RHS) the @ symbol, example:
 [email protected]
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A
domain name identifies a computer in a
department, a company or a school etc… The DN is
related to an IP address
 The Electronic Mail Service:
 The Electronic Mail facility is provided in the form of a
Electronic Mail Service
 This service consists of User Agents, Mailbox
Names and Message Transfer Agents (MTAs) etc...
 Electronic mail is prepared using user agents and
 Sent to the recipient using Message Transfer Agents (MTAs)
 These are software programs that are part of the
mail service
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 User Agents:
 A User Agent is a computer program that is linked
to mail service. They help the user in the use of the
mail service
 User agent software for electronic mail, from
different suppliers provides different kinds of services
in addition to the basic service of sending and
receiving e-mail. Some user-agent software
includes simple word-processing facilities that help
composing and recording the text of a message
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 Protocols:
 Some of the protocols associated with E-mail are
the POP (Post Office Protocol) and the SMTP
(Simple Mail Transfer Protocol)
 SMTP is used by the MTAs
 In an Internet mail system, a user agent can
establish a TCP connection with an MTA and the
MTAs then relay the mail across the Internet using
the SMTP
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 Activity 2.16 (exploratory)
 Figure 3 is a simple diagram for a general communication
system (taken from Book S, Systems)
 (a) Amend this diagram to show the user agents and
message transfer agents in an e-mail system

See Figure 4(a). Notice that the users interact with user agents,
and that the ‘channel’ of Figure 3 must contain at least one
Message Transfer Agents (MTA) (though exactly how many
cannot be predicted; as you have seen, routes are determined
‘on the fly’ and, indeed, some packets of a particular message
may go by one route and others by another)
o So the user agents help to prepare new messages and display
received messages
o And the MTA used for passing the messages along as they travel
across the Internet
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Figure 3 A generic diagram for a communication system
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Figure 4 (a) An e-mail communication system showing user transfer
agents and message transfer agents (MTAs); (b) also shows the
domain name server
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 (b) How might you show a domain name server in your
diagram?
See Figure 4(b), where I have shown the domain name server
to which the user agent refers. It has to be thought of as being
off to one side, because the message never goes to or
through it; instead it is a resource the user agent needs to refer
to in order to translate the domain name to the IP address
 The MTAs along the route may refer to other domain name
servers, which would be similarly shown off to one side of the
MTAs

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 Activity 2.17 (exploratory)A
 Is it possible to have an e-mail system where the
recipient is not specified by the sender?
 It is very hard to imagine an e-mail system where the recipient is
not specified by the sender. Even items of junk mail need an
address!!
 In fact, an important characteristic of communication systems
which are essentially one-to-one is that the recipient needs to be
identified: if you want your message to have one unique recipient
(or a set of unique recipients) then you will have to specify the
recipient(s)
 In e-mail this is done through an e-mail address. (In telephone
systems, which are also one-to-one, it is done via the phone
number – which of course does not so much identify the recipient
as the phone where the sender hopes the recipient is)
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Topic 8: Accessing the Internet while on
the move
 This is an introduction to next part (part3) of Book T
 Most of your work for this section consists of studying
an article called “Wireless Web” by John Lettice
(Book D, Document 8,page 25)
 What are the GSM (Global System for Mobile
Communication) mobile phones?
 These are the digital mobile phones used in Europe, the Far
East and some of the US (at the time the article was written) for
Cellular Speech Communication purposes
 What about Cellular Data Communication (or Mobile
Internet)??
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 Activity 2.19 (exploratory)
 1- One problem is that the normal GSM data transfer
rate of only 9.6 kilobits per second is rather slow for
convenient Web access??
 This problem is being overcome by using Mobile Phones for
Speech and Data (Mobile Internet):
 A- In the short term by an upgrade to GSM called General
Packet Radio System (GPRS) (see Part 3 of book T)

2.5G: The GSM/GPRS (General Packet Radio System) mobile
phone system
 B- As an aside, it will be overcome in the longer term by the
new type of mobile telephone system (see Part 3 of book T)

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3G: These are proposed 3rd Generation systems for data
communication
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 2- Another problem is that most Web pages were (at
the time the article was written) configured only for
reading on a standard display screen as found on a
desktop or notebook computer, not on the small
screens of PDAs or mobile phones??
 This was being overcome by preparing Web pages in XML and
then translating them either to the format used by standard
browsers for general users (HTML Format) or to the format
used by ‘microbrowsers’ for mobile users (WML (Wireless
Markup Language) Format)(see Figure 5)
 Of course, this also implies that WAP (Wireless Application
Protocol) – (WAP is a protocol designed for micro
browsers) had to be available for, and supplied on, mobile
phones
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Figure 5 How to translate web pages in XML format to the format used
by standard browsers for general users (HTML Format) or to the format
used by ‘microbrowsers’ for mobile users (WML Format)
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Sub-Topic 8.1: What is WAP ?
 WAP (Wireless Application Protocol) is the de facto
standard for providing Internet services to mobile
phones and other types of wireless devices
 There are two aspects to WAP:
 1)
WAP specifies a transport protocol (application
protocol??) for sending e-mail messages and Web pages
(web applications) between mobile devices and the Internet
 2) WAP specifies a mark-up language called Wireless Markup Language (WML) in which Web pages are prepared (or
created) for use on a mobile device with a small screen, such
as a small PDA or a mobile phone. The ‘microbrowsers’ in
these mobile devices will need to be able to decode pages in
WML in order to display the Web pages on the screen
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 Example: How some can access the web through the WAP-
enabled mobile phone? (or How WAP works?)
 1) People who wish to use e-mail and/or access the Web while out and
about can buy themselves a WAP-enabled mobile phone (or a combined
PDA and mobile phone that is WAP-enabled)
 2) Then when they wish to access a Web page they simply send the URL
(Universal Resource Locator) of the page to their mobile operator. The
mobile operator will have a ‘gateway’ to the Internet (or to that part of it
that the operator wishes to make available), and one task of this gateway is
to translate the request into TCP/IP and send it into the Internet
 3) When the Web page (in WML) comes back, the gateway translates it to
WAP format – which includes compression for efficient transmission – and
sends it back to the user’s mobile device, where the microbrowser displays
the page
 4) The WAP specification includes optional security encryption which
mobile operators may choose to provide as part of their service
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 Important Notes:
 1- Pages in WML are called DECKS. Decks are
constructed as a set of CARDS
 2- Some larger PDAs with a more generous screen
size may be able to display normal HTML Web
pages sufficiently clearly. Such PDAs have no need
for special WML Web pages and hence need not be
WAP-enabled, but they do need to be equipped with
a modem which is compatible with the mobile
telephone system
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 3- You should note that WAP is only a transitional technology,
introduced in 2000 to bring Internet access to mobile users with
GSM phones. It is not an ideal solution to the problem of
accessing the Internet on the move, and indeed by the end of
2000 it was receiving a great deal of criticism for its slowness
and poor security, as well as for the fact that mobile devices
using WAP could only display a few lines of text, usually
monochrome and in plain fonts. But WAP was never intended to
rival PCs for browsing the Web;
 4- In the longer term, people who want Internet access on the
move via their mobile phones will probably transfer to the new
so-called ‘third-generation’ mobile phones (see Part 3 of
book T)
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Topic 9: Preparation for Next Session
 1) Read Part1 of Book T
 2) Do all activities in Part 1 of Book T including links to





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Book C and Book D
3) Do activity 1.18 (Journal)
4) Read Part 2 of Book T
5) Do all activities in Part 2 of Book T including links
to Book C, Book D, Electronic document,
“Information and the internet”, by Ian Johnston
(see T209 CD ROM1) and T529 ICT CD-ROM
6) Complete the Journal items related to Part 1 and Part2
of Book T
7) Skim Part 3 of Book T
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