Transcript Networks : What is a network?

Networks : What is a network?
A Network is formed when 2 or more
computers are linked together.
Every computer or device on a
network can send and receive data
from any of the other computers or
devices connected to the network.
A computer which is not part of a
network is called a stand-alone
computer.
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Networks: Local Area Networks (LANs)
A Local Area Network (LAN) covers a
small geographical area such as a
classroom or school building.
Computers and devices are
connected in a LAN by wired
connections or by wireless
connections. They are connected via
transmission media. Home networks
increasingly are using wireless
transmission media.
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Networks: Advantages of a LAN
The advantages of having an LAN
include:
 Allow you to share data
 Allows you to share expensive
computer peripherals e.g. A
colour laser printer
 Allows communication via email
 Software sharing (subject to the
necessary licences being in place)
 Very fast and reliable data
transmission
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Networks:
Wide Area Network (WAN)
A Wide Area Network (WAN) covers
a larger geographical area than a LAN
– typically a country or a continent.
WAN often connect lots of smaller
LANs.
The Internet is a good example of a
WAN which spans the globe – the
name Internet coming from
Interconnecting Networks.
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Networks: WAN
Transmission Medium
Telecommunication links are used to transmit and receive data in
a WAN.
These links include fibre optic, satellite links and microwave
transmission.
Fibre optic cables for WANs are frequently laid on the seabed.
A single satellite channel is
capable of carrying large
numbers of separate
transmissions.
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Networks: Advantages of a WAN
The advantages of using a WAN:
 Allows businesses to share data.
 Allows users to send messages between offices around the
world.
 Allows access to files from any computer anywhere on the
network
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Networks: The Internet and the WWW
The Internet is a global system of computer
networks that enables computers and
peripheral devices worldwide to connect with
each other using a range of telecommunication
systems.
It can be thought of as many different smaller
networks connect together.
The WWW (world wide web) is millions of web
pages that are stored on computers across the
world. Web pages display different data types :
text, graphics, sounds, animations and video.
The term web comes from the fact that web
pages are linked together using hyperlinks.
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Networks: Search Engines and Browsers
A search engine is a software
system that is designed to search
for information on the WWW. They
help users find their way around
the web by searching web pages
for keywords.
A browser is a program that allow
internet users to view data on the
WWW. Examples are internet
Explorer, Firefox, Google chrome.
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Networks: Network Interface Cards
(NICs)
All computers on a network must
have a either a Network Interface
Card (NIC) or a Wireless Network
Interface Card. This device allows
the computer to connect to the
network and to send and receive
data to and from other devices.
These cards are fitted inside the
computer.
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Networks
Now attempt
Task 1 LANs and WANs
on page 8.
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Networks:
Types of Transmission Media in Wired Networks (1)
There are several type of cables used as transmission media in a
wired local area network.
Twisted pair (copper cabling) : a simple type of
cable made up of two copper wires twisted around
each other. It is used in the school network. It is
relatively cheap cabling and allows fast data
transfer (over 100Mbps).
Coaxial (copper cabling) : the central cable that
transmits the data is surrounded by a shield of
copper braiding which protect the central cable
from interference. Tends to be in factories where
there is a greater chance of interference. It is more
expensive than twisted pair cabling.
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Networks:
Types of Transmission Media in Wired Networks (2)
Fibre optic: fibre optic cable is made up of fine
strands of glass hat carry pulses of light. These
pulses of light carry the data to be transferred. It is
more secure than copper cabling as any break in
the cable can be detected. Fibre optic cable does
not suffer from electromagnetic interference and
can transmit data at very high speeds.
Fibre optic cables is commonly used to connect
buildings together in a LAN although it is very
expensive.
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Networks:
Types of Transmission Media in Wireless Networks
Wireless networks do not need cables. Wireless networks transmits data through
the air using radio waves and microwaves.
Each computer or device needs a transmitter/receiver and the network needs a
control device such as a router to pass data round the network.
The most popular standard for wireless networks id Wi-Fi which
uses radio waves to transmit data through the air.
Wi-Fi can connect devices up to 100m apart and transfer data at a
rate of 60Mbps.
Bluetooth is another wireless network standard which uses short
wavelength microwaves to transmit data. It is commonly used for
mobile phones and peripheral devices. Bluetooth has a range of
10m and data transfer rate of 721Kbps.
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Networks:
Wireless Networks
Wireless networks also exist for WANs.
Microwaves dishes are positioned in high
places and pointed towards another
microwave tower to form a relay. This form of
communication is capable of transferring
extremely large quantities of data very
quickly.
One disadvantage of wireless communication is security. Data has to be
encrypted to prevent hackers from accessing networks without
authorisation. Encryption means coding the data using a special key.
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Networks: Client/server Networks
A client-server network is formed when the
client (workstation) is connected to and makes
use of the resources available on the server(s).
A workstation may be a desktop or laptop computer with a network
interface card installed to allow communication to the server or a
workstation may be a tablet with Wi-Fi capabilities.
Servers are responsible for security on the network. Users working at
client workstations are usually required to log in. This will identify the
user to the server and different levels of access can be allocated.
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Networks: Server types – File Server
A file server is used on a
client/server network to
provide centralised
storage. Every user will
have their own allocated
storage space.
Characteristics of a file server include: large amount of RAM and
backing storage and fast multiple processors – so that users can
access their data quickly.
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Networks: Server types – Print Server
A printer server is used to allow
all the clients (workstations) on a
network access to printers
controlled by the printer server.
The printer server also provides a facility for queuing up
printing requests so that they are printed out in turn.
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Networks: Server types – Mail server
A mail server allows users to send
emails and have them stored on
the server hard drives.
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Networks: Server types – Web server
A web server connects to
the Internet via a security
system called a firewall. A
firewall is software that
prevents unauthorised
access to the network. It
also allows frequently
accessed web pages to be
cached on the server’s hard
disk so that they can be
accessed faster.
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Networks: Server types –Application server
An application server allows
programs (applications) to be stored
centrally on a server and loaded
from there into the Ram of the
individual client workstations.
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Networks:
Advantages() and Disadvantages()
of Client/Server Networks
Centralised control of resources and data
Easier to back up all network files at regular intervals
Network operating system will have built in security
measures
Accessibility – the server can be accessed remotely and
across different platforms (Apple, Microsoft, Sun and so on)
Expensive to setup
Administrator required to maintain the server
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Networks: Peer to Peer Networks
Peer to peer networks allow users to share resources
and files located on their computers.
On peer to peer networks all computer are considered
to be equal.
Peer to peer networks are designed for small LANs
with typically up to 6 machines.
Home networks and very small offices are typically
peer to peer.
Peer to peer networks work better in an environment
where users trust each other
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Networks:
Advantages() and Disadvantages ()
of Peer to Peer Networks
Cheaper to set up as there is no need for dedicated servers
Easy to set up as most modern operating systems can be set
up for peer to peer networking.
No easy centralised back up as all files are stored locally
Security of data harder to implement as files are not stored
centrally
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Networks
Now attempt
Task 2 Comparison of Peer to Peer and
Client/Server Networks
on page 13.
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Networks: Cloud Computing
Cloud computing is the use of hardware
and software to deliver services over a
network – mainly the internet.
Companies selling cloud services use banks
of servers and hard disk drives.
Services include:
 Online Data storage
 Software hosting
 Virtual Servers
Cloud services can be accessed by any
device that has Internet access.
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Networks: Local Versus Cloud
Advantages of Cloud
Advantages of Local
Users pay for storage space on servers
and can decide how much they need.
Users can access a wide range of
application software
Users do not need to buy expensive
systems so no large initial layout.
Some users may not have the expertise
to set up the facilities offered by a
cloud provider.
Users are billed for either the time they
spend using the service or on a
monthly quarterly basis.
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There will be a difference in speed of
data transfer compared. Local will be
much faster and is NOT limited by the
speed of the user’s internet
connection.
Security concerns about hacking into
online cloud storage.
Users may prefer an initial payment
to purchase hardware and software
rather than subscribing to a monthly
payment.
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Networks
Now attempt
Task 4 How much storage do
cloud companies offer users?
on page 14.
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