ICT - Lecture Notes 5.pdf

LECTURE NOTES 5
Information & Communications Technology

What is a Network?
A network is two or more computers, or other electronic
devices, connected to each other. A network allows
computers to share files, users to message each other, a
whole room of computers to share a single printer, etc.
Network connections between computers are typically
created using cables (wires). However, connections can be
created using radio signals (wireless / wi-fi), telephone
lines (and modems) or even, for very long distances, via
satellite links.
A computer that is not connected to a network is referred
to as a stand-alone computer.

Why do we need a Network?
Using a computer connected to a network allows us to…
- Easily share files and data
- Get access to a huge range of information for research
- Share resources such as printers and Internet connections
- Communicate with other network users (e-mail, instant
messaging, video-conferencing, etc.)
- Store data centrally (using a file server) for ease of access
and back-up
- Make use of on-line services such as shopping (e-
commerce) or banking
- Access different forms of entertainment (games, video,
etc.)
- Join on-line communities (e.g. WhatsApp, Viber, MySpace,
Facebook, etc.)

The negative aspects of a Network?
Using a computer connected to a network means that…
- The computer is vulnerable to hackers
- Your computer can more easily be attacked by a virus
- If the network breaks, many tasks become very difficult
In particular, if we use a computer connected to The
Internet…
- We have to be careful about revealing personal information
- We have to be careful to avoid suspect websites that might
contain malware
- We have to be aware that information found on The Internet
is not always accurate or reliable

Computers in a Network
Computers connected together to create a network fall into two
categories: servers and clients (workstations).
Servers
Servers are special, powerful computers that provide ‘services’
to the client computers on a network.
These services might include:
- Student Management System Server to provide various
academic related services to students
- Backup Server to provide file / data storage area
- E-Mail Server to provide e-mail services
- Firewall Server to screen in-coming and out-going traffic
- Proxy Server to provide internet related services
- Facebook Server to provide Social Network Services

Servers are built to be very reliable. In a small network one
server might provide all of the required services. In a larger
networks there might be many servers sharing the work.
Clients
Client computers, or workstations, are the normal computers
that people sit at to get their work done. These are the
computers that we use to access services from servers.
When you use your Web browser, you are in fact using a Web
client. When you type in the URL (Uniform Resource Locator) of
a web page, you are actually providing the address of a Web
server.
Your Web browser/client asks this server for the web page you
want, and the server ‘serves’ the page back to the
browser/client for you to see.

Types of Network
Local Area Network (LAN)
A Local Area Network is a network confined to one building or
site. Often a LAN is a private network belonging to an
organisation or business.
Because LANs are geographically small, they usually use
cables or low-power radio (wireless) for the connections.

Types of Network
Wireless Local Area Network (WLAN)
A wireless LAN (WLAN) is a LAN that uses radio signals (WiFi)
to connect computers instead of cables.
At the centre of the WLAN is a wireless switch or router - a
small box with one or two antennas sticking out the back - used
for sending and receiving data to the computers. It is much
more convenient to use wireless connections instead of running
long wires all over a building.

Types of Network
However, WLANs are more difficult to make secure since
other people can also try to connect to the wireless
network.
So, it is very important to have a good, hard-to-guess
password for the WLAN connections.
Typically, the range of a wireless connection is about 50m,
but this depends on how many walls, etc. are in the way;
and also the type of access points / radios / routers being
used.

Wide Area Network (WAN)
A Wide Area Network is a network that extends over a
large area. A WAN is often created by joining several LANs
together, such as a business that has offices in different
countries links the office LANs together.
Because WANs are often geographically spread over large
areas and links between computers are over long
distances, they often use quite exotic connections
technologies: optical fibre (glass) cables, satellite radio
links, microwave radio links, etc.
The Internet is an example of a global WAN. In fact it is the
world’s largest WAN.

Types of Network
Wide Area Network (WAN)

Network Interface Card (NIC)
Any computer that is to be connected to a network, needs to
have a network interface card (NIC).
Most modern computers have these devices built into the
motherboard, but in some computers you have to add an extra
expansion card (small circuit board)

Network Cables
To connect together different devices to make up a network, you
need cables.
Cables are still used in most networks, rather than using only
wireless, because they can carry much more data per second,
and are more secure (less open to hacking).

Network Cables
The most common type of network cable in use today looks like
the one shown above, with plastic plugs on the ends that snap
into sockets on the network devices.
Inside the cable are several copper wires (some used for
sending data in one direction, and some for the other direction).

Switch
A switch is a device that connects a number of computers
together to make a LAN.
The typical use of a switch is at the centre of a star network -
the switch has cables plugged into it from each computer.
A switch is normally associated to a LAN and several switches
may be used in one LAN.
There are several types of switches. The most basic type are
normally simply referred to as LAN Switches.
Switches contribute towards reducing network congestion or
bottlenecks by distributing packages of data only to their
intended recipients.

Router
A router is network device designed to receive, analyze and
move incoming data / packets to another network. It may also
be used to convert / modify the packets to suit another
network’s interface, drop them, and / or perform other actions
relating to a network.
A router has a lot more capabilities than other network devices,
such as a hub or a switch that are only able to perform basic
network functions.
Routers facilitate the sharing of a single Internet connection by
multiple computers. A common use of a router is to join a home
or business network (LAN) to the Internet (WAN).
The router will typically have the Internet cable plugged into it,
as well as a cable, or cables to computers on the LAN.

Firewall
A firewall is a network security system, either
hardware- or software-based, that controls incoming
and outgoing network traffic based on a set of rules.
A firewall acts as a barrier between a trusted network
and other entrusted networks -- such as the internet --
or less-trusted networks.
A firewall controls access to the resources of a
network through a positive control model. This means
that the only traffic allowed onto the network is that
which is defined in the firewall policy; all other traffic is
denied.

Firewall
A firewall blocks unauthorised connections being made to your
computer or LAN. Normal data is allowed through the firewall
(e.g. e-mails or web pages) but all other data is blocked.

Setting Up a Small Network
If you were asked to build a small, Internet-connected network from
scratch, what would you need to do?
You would need to buy some hardware:
- One or more switches / hubs - to link devices together
- Network cables to connect devices to the switch, etc.
- A separate wireless access point (or this could be part of the
switch) - to allow wireless devices (e.g. laptops or smart-
phones) to join the network
- A router to connect your LAN to the Internet (WAN)
- A firewall to protect your network from hackers
- Possibly a bridge if you already have a section of network and
you want your new network to connect to it
- Server(s) to manage network functions such as network
security, network file storage, shared resources (such as
printers)

Setting Up a Small Network
You would need to organise some other things:
- Set up an account with an Internet Service Provider (ISP)
- Get an Internet connection installed from the ISP to your
location
- Configure various bits of hardware and software so that
everything worked with the network
For any network that is more complex than a small home
network, there is a lot to do.
It's not just a case of buying the parts and connecting them together...
- Routers and switches have to be configured (settings changed)
- Network devices need to be given network addresses
- Software needs to be configured to use the network
- Etc...

Networks are pretty complex thing to set-up. The people who do this
are called Network Engineers. It's a very interesting technical job, if
you like that sort of thing!

What is the Internet?
The Internet is a worldwide network of networks. It can be
defined as a global network of over a million of smaller
heterogeneous computer networks.
The term Internet is derived from the concept of Interconnected
Networks. The Internet connects millions of people, and
thousands of businesses, governments, schools, universities
and other organisations.
The internet uses a common language whereby dissimilar
computers with various operating systems, are able to
communicate with each other, using a standard set of protocols.
There is nobody who owns Internet or no company called the
“Internet”. Think of the Internet as the Universe and your
computer as a planet, which is a part of that Universe.

Protocols
In information technology, a protocol is the special set of rules
that end points in a telecommunication connection use when
they communicate.
Protocols specify interactions between the communicating
entities. Thus it can be defined as a set of rules of
communication.
For the Internet, the common protocols are TCP and IP.
Commonly referred to as TCP/IP. TCP/IP stands for
Transmission Control Protocol / Internet Protocol.
TCP/IP protocol relies on a series of steps to prepare, transmit
and receive data. Without TCP/IP, devices would be unable to
connect to the Internet or share data.

TCP/IP is the communication protocol used for Internet
and similar networks such as Intranet and Extranet.
It controls and manages the data transmission over
the Internet. It also defines a mechanism through
which every computer on the Internet is identified
separately.
TCP/IP manages the transmission of data on the
Internet by breaking the data into small pieces called
packets.
Each packet contains actual data and address part
i.e. addresses of destination and source.

TCP breaks message or file into smaller packets that
are transmitted over the Internet. It also reassembles
the packets into the original message that are received
from Internet.
IP handles the address part of each packet so that it
can be transmitted to the right destination. Each
gateway on the network checks this address to see
where to forward the message.
Through TCP/IP different types of computer can share
information among them. For example, a personal
computer can exchange data with a mainframe on the
Internet by using TCP/IP.

So what is an IP Address?
It is the means whereby an entity on a network can be
addressed or identified on the network.
This is a string of numbers which identify the device
transmitting the information or receiving the information.
It takes the format indicated below:

Basic IP Addressing
IP Addresses are essentially 32-bit binary numbers;
computer systems and routers do not see any sorts of
divisions within the IP Address space.
To make IP Addresses more human-readable,
however, we break them up into four sections divided
by dots, or periods, commonly called “octets.”
An octet is a set of eight binary digits, sometimes also
called a “byte.” The figure below illustrates the IP
Address Structure.

TCP/IP Protocol
The success of TCP/IP as the network protocol of the Internet is
largely because of its ability to connect together networks of
different sizes and systems of different types.
A subnet mask is used to divide an IP address into two parts.
One part identifies the host (computer), the other part
identifies the network to which it belongs.
To better understand how IP addresses and subnet masks
work, look at an IP (Internet Protocol) address and see how it is
organized.
IP Addresses: Networks and Hosts
An IP address is a 32-bit number that uniquely identifies a host
(computer or other device, such as a printer or router) on a
TCP/IP network.

Hosts, Networks, and Subnetworks
IP addresses are normally expressed in dotted-decimal format,
with four numbers separated by periods, such as
192.168.123.132. To understand how subnet masks are used to
distinguish between hosts, networks, and subnetworks,
examine an IP address in binary notation.
For example, the dotted-decimal IP address 192.168.123.132 is
(in binary notation) the 32 bit number
110000000101000111101110000100. This number may be hard
to make sense of, so divide it into four parts of eight binary
digits.
These eight bit sections are known as octets. The example IP
address, then, becomes
11000000.10101000.01111011.10000100.

This number only makes a little more sense, so for most uses,
convert the binary address into dotted-decimal format
(192.168.123.132). The decimal numbers separated by periods
are the octets converted from binary to decimal notation.
For a TCP/IP wide area network (WAN) to work efficiently as a
collection of networks, the routers that pass packets of data
between networks do not know the exact location of a host for
which a packet of information is destined.
Routers only know what network the host is a member of and
use information stored in their route table to determine how to
get the packet to the destination host's network. After the packet
is delivered to the destination's network, the packet is delivered
to the appropriate host.

For this process to work, an IP address has two parts. The first
part of an IP address is used as a network address, the last part
as a host address. If you take the example 192.168.123.132
and divide it into these two parts you get the following:
192.168.123. Network .132 Host OR
192.168.123.0 - network address. 0.0.0.132 - host address.
Subnet Mask
The second item, which is required for TCP/IP to work, is the
subnet mask. The subnet mask is used by the TCP/IP protocol
to determine whether a host is on the local subnet or on a
remote network.

In TCP/IP, the parts of the IP address that are used as the
network and host addresses are not fixed, so the network and
host addresses above cannot be determined unless you have
more information.
This information is supplied in another 32-bit number called a
subnet mask. In this example, the subnet mask is
255.255.255.0.
It is not obvious what this number means unless you know that
255 in binary notation equals 11111111; so, the subnet mask is:
11111111.11111111.11111111.0000000 Lining up the IP address
and the subnet mask together, the network and host portions of
the address can be separated:
11000000.10101000.01111011.10000100 -- IP address
(192.168.123.132)

11111111.11111111.11111111.00000000 -- Subnet mask
(255.255.255.0)
The first 24 bits (the number of ones in the subnet mask) are
identified as the network address, with the last 8 bits (the
number of remaining zeros in the subnet mask) identified as the
host address.
This gives you the following:
11000000.10101000.01111011.00000000 -- Network address
(192.168.123.0)
00000000.00000000.00000000.10000100 -- Host address
(000.000.000.132)

So now we know, for this example using a 255.255.255.0
subnet mask, that the network ID is 192.168.123.0, and the host
address is 0.0.0.132.
When a packet arrives on the 192.168.123.0 subnet (from the
local subnet or a remote network), and it has a destination
address of 192.168.123.132, your computer will receive it from
the network and process it.
Almost all decimal subnet masks convert to binary numbers that
are all ones on the left and all zeros on the right.
Some other common subnet masks are: Decimal Binary
255.255.255.192 1111111.11111111.1111111.11000000
255.255.255.224 1111111.11111111.1111111.11100000

Network Classes
IP addresses are divided into classes. The most common of
these are classes A, B, and C. Classes D and E exist, but are
not generally used by end users.
Each of the address classes has a different default subnet
mask. You can identify the class of an IP address by looking at
its first octet.
Following are the ranges of Class A, B, and C Internet
addresses, each with an example address:
Class A networks use a default subnet mask of 255.0.0.0 and
have 0-127 as their first octet. The address 10.52.36.11 is a
class A address. Its first octet is 10, which is between 1 and
126, inclusive.

Network Classes
Class B networks use a default subnet mask of 255.255.0.0 and
have 128-191 as their first octet. The address 172.16.52.63 is a
class B address. Its first octet is 172, which is between 128 and
191, inclusive.
Class C networks use a default subnet mask of 255.255.255.0
and have 192-223 as their first octet. The address
192.168.123.132 is a class C address. Its first octet is 192,
which is between 192 and 223, inclusive.
In some scenarios, the default subnet mask values do not fit the
needs of the organization, because of the physical topology of
the network, or because the numbers of networks (or hosts) do
not fit within the default subnet mask restrictions.

Network Classes
If we have 150 hosts and we are allocated the class C network
of 192.168.123.0. It means that we can use the addresses
192.168.123.1 to 192.168.123.254 for the 150 hosts.
Two addresses that cannot be used in our example are
192.168.123.0 and 192.168.123.255 because binary addresses
with a host portion of all ones and all zeros are invalid.
The zero address is invalid because it is used to specify a
network without specifying a host. The 255 address (in binary
notation, a host address of all ones) is used to broadcast a
message to every host on a network.
Just remember that the first and last address in any network or
subnet cannot be assigned to any individual host. It means we
can allocate IP addresses to a maximum of 254 hosts.

The Internet
- You may compare or view the internet to a highway
system. Imagine complex network of roads. It consists of
superhighways, highways, to the small roads on the
countryside, all connected to each other in one way or the
other. The nature of the internet is much similar to this.
- There is no central computer to control the internet. There
is no particular person, group or organization owns the
whole Internet. However, there are some standards for
Internet technologies, policies and protocols that manage
the operations on internet.
- The Internet is the world's largest computer network, a
distinction it has earned by virtue of being a "network of
networks.”

The Router
The routers determine where to send information from
one computer to another. Routers are specialized devices
that send your messages and those of every other Internet
user speeding to their destinations along thousands of
pathways. In doing this, the following are achieved:
- It ensures that information doesn't go where it's not
needed. This is crucial for keeping large volumes of
data from clogging the connections of "innocent users."
- It makes sure that information does make it to the
intended destination.

A router is extremely useful in dealing with two separate
computer networks. It joins the two networks, passing
information from one to the other.
It also protects the networks from one another, preventing
the traffic on one from unnecessarily spilling over to the
other.
Regardless of how many networks are attached, the basic
operation and function of the router remains the same.
Since the Internet is one huge network made up of tens of
thousands of smaller networks, its use of routers is an
absolute necessity.

Intranet
An intranet is the name given to a private network that provides
similar services to The Internet: e-mail, messaging, web pages, etc.
However, these services are only for the users of the intranet – they
are private, not public (unlike Internet services which are generally
public).
Businesses and other organisations often have intranets for use by
their employees.
Typical uses of an intranet would be:
- Viewing internal web pages (e.g. company calendars, etc.)
- Internal e-mail and instant-messaging between workers
- Sharing of internal documents
Ideally, the Intranet would be used and only accessible by employees
belonging to that particular organization.

Extranet
An extranet is a computer network that allows controlled access from
the outside, for specific business or educational purposes. In a
business-to-business context, an extranet can be viewed as an
extension of an organization's intranet that is extended to users
outside the organization, usually partners, vendors and suppliers; in
isolation from all other Internet users.
What Can We Use the Internet For?
The Internet provides the network connections that links computers
together. There are many ways that we can use these connections.
The services that are available on the Internet can however be
classified into two categories:
- Communication Services
- Information Retrieval Services

Some of the common systems / services through the Internet
Technology include the following:
1) E-mail Communications (Sending and Receiving e-mail messages)
2) Remote Login
3) File Transfer
4) View Web Pages on the WWW (World Wide Web)
5) Live Chatting
6) Discussion Forums
7) File Sharing and Cloud Storage - Google Drive, Dropbox,
MicroSoft OneDrive, Box.Net, FilesAnywhere, OpenDrive,
SkyDrive, Adrive, FreeDrive, MediaFire, etc
8) Voice Over Internet Protocol (VOIP) and Text Over Internet
Protocol (TOIP) Solutions (Skype, Viber, WhatsApp, Google Talk,
Windows Live Messenger, Yahoo Messenger, Twitter, Facebook,
Linkedln, etc)
9) Teleconferencing (Video, Audio, Telephone, Phone, Web, etc).
10) YouTube Video Clips.
11) Listening to streamed music or watching streamed video

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