Transcript Computer network - Kim Young Jun SIS IGCSE1 Coordinated Subject

By Kim Young Jun IGCSE1
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Computer network
Common types of network
Ring, bus, star and tree
Local are networks
Wide are networks
Wireless LANs (WLANs)
Network device
The internet
Intranet
Network security
Communication methods
Most computer systems are now connected
together in some way to form what is known as
a network.
This ranges from the basic school/home network
of only a few computers to large network such
as the internet which effectively allows any
computer connected to it to communicate with
any other computer similarly connected.
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File servers, which allows users to save and
load data/files.
Application servers, which deal with the
distribution of applications software to each
computer.
Printer servers, which ensure printing from
devices on the network is done in a queue.
Proxy servers, which are used as a buffer
between WANs and LANs.
Ring networks
Being less popular. Every computer in the
network is connected in a ring, including
server.
Bus networks
Each computer or device is connected to a
common central line. Data travels along this
central line until it reaches the computer or
device that requires it.
Star networks
With a star network, each computer or device is
connected via a central hub or switch. Data is
sent to the hub which then sends out data
along every cable to every computer or device.
Tree network
A tree network has a central line connecting
together a series of star networks. The sever is
also connected to this central line. Because of
flexibility.
A local area network (LAN) is usually within on e
building or certainly not over a large
geographical area. A typical LAN will consist of a
number of computers and devices which will be
connected to hubs or switches.
A wide area network (WAN) is basically formed by a
number of LANs being connected together
through either a router or a modem. Some
companies will set up private WANs. This is
expensive but comes with the advantage of much
enhanced security. It is more common to use an
internet service provider (ISP) for connections to
the internet and communicate via this network
system.
WLANs are similar to LANs but there are no wires
or cables. They provide wireless network
communications over fairly short distances.
Modem means modulator and is a device which
converts a computer’s digital signal into an
analogue signal for transmission over an existing
telephone line. It also does the reverse process, in
that it converts analogue signals from a telephone
line into digital signals to enable the computer to
process the data.
Network hubs are hardware devices that can have a
number of devices/computers connected to them.
Its main task is to take any data received via one of
the ports and then send out this data from all of
the ports.
Switches are similar to hubs but are more efficient
in the way they distribute data. Data packets sent
to the switch will have a mac address giving the
source and giving the source and receiving device.
Routers inspect the data packages sent to if from
any computer on any of the networks connected to
it. The router is able to send the data package to
the appropriate switch and it will then be delivered
using the mac destination address in the data
packet.
Bridges are device that connect one LAN to another
LAN that use the same protocol. They decode
whether a message from a user is going to another
user on the same LAN or to a user on a different
LAN.
The internet is worldwide collection of networks
which allows a subscriber to send and receive
emails, chat (using text or voice) or browse the
world wide web.
The world wide web (WWW or web) is the part of
the internet which the user can access by way of a
web browser.
The web is made up of millions of these websites
and millions of web pages. Web pages are
documents on a computer screen which may
consist of text, pictures, sounds animation or
video.
There are three common ways of accessing the
internet offered by service providers:
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Dial-up internet access
Cable internet access
Digital subscriber line (DSL) (broadband)
internet access.
Many companies use an intranet as well as the
internet. The simple definition of an intranet is
a computer network based on internet
technology that is designed to meet the
internal needs for sharing information within a
single organization/company.
The security problems when using networks such
as the internet are well documented. There are
various security threats to networks and there are
many equally varied ways of combating the threat.
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User ID
Password
Encryption
Authentication techniques
When logging on to any network system, a user
will be asked to type in a user ID. This assigns
the user privileges once the logon procedure is
successful, who is able to set passwords,
delete files from the server, etc. whilst a user
privilege may only allow access to their own
work area.
After keying in the user ID user will then be
requested to type in their password. This
should be combination of letter and numbers
which would be difficult for somebody else to
guess. When the password is typed in it often
shows on the screen as******* so nobody
overlooking can see what the user ca see what
the user has typed in.
Encryption is the converting of data into a code
by scrambling it or encoding it. This is done by
employing encryption software. Since the data
is all jumbled up it appears meaningless to a
hacker or anyone who illegally accesses the
data.
This is called authentication, and type of
authentication is used in the banking example
that follows.
Most systems adopt the following
authentication logic:
 Something you know-e.g. PIN/password
 Something belonging to you-e.g. your bank
card
 Something unique to you-e.g. your
fingerprints.
Many methods of communication using
networks exist.
These include fax, email, video conferencing
and VOIP.
The term fax is short for the word facsimile. With
the this system, documents are scanned
electronically and converted into a bit map image.
This is transmitted as a series of electrical signals
through the telephone network. The receiving fax
machine converts this electronic image and prints
it out on paper.
This is an electronic method for sending text
and attachments from one computer to
another over a network.
This is a method of communication between
people at two separate locations. This is done in
real time and makes use of a LAN, if internal, or
through a WAN.
The system also uses special software such as:
CODEC, which converts and compresses analogue
data into digital data to send down digital lines.
Echo cancellation software, which allows talking in
real time and synchronises communications.
Voice over internet protocol (VOIP) is a method
used to talk to people using the internet. VOIP
converts sound into discrete digital packets
which can be sent to their destination via the
internet.
The most prominent security issues over VOIP are:
 Identity and service theft
 Viruses and malware
 Spamming
 Phishing attacks