Transcript Internet

Lecture 3:
Network and the Internet
Dr Yingchao ZHAO
 After


this lecture, you should be able to:
be aware of the basic concepts of network
note the basic applications in the Internet
Before we talk about the Internet, we first need to
understand the basic terminologies in network
 Computer
communications describes a
process in which two or more computers or
devices transfer data, instructions, and
information.
Sending device
Communications
channel
Receiving
device
 Computing
facilities help a lot in
communications.
 Information can be transferred via computer
network (Internet).
A
network is a collection of computers and
devices connected together via
communications devices and transmission
media.
 Advantages of using a network include:
Facilitating
communications
Sharing
hardware
Sharing software
Sharing data and
information
Transferring
funds
A
local are network
(LAN) is a network
that connects
computers and
devices in a limited
geographical area.
 A wireless LAN
(WLAN) is a LAN that
uses no physical
wires.
A
metropolitan
area network
(MAN) connects
LANs in a
metropolitan area.
 A wide area
network (WAN) is
a network that
covers a large
geographical area
(may connect
multiple MAN).
 The
design of how computers, devices, and
media are combined on a network is
sometimes called the network architecture.
Client/server network
Peer-to-peer network
 P2P
(Peer-to-Peer) describes an Internet
network on which users access each other’s
hard disks and exchange.

E.g., BitTorrent,
Gnutella,
Kazaa,
LimWire, etc.
A
network topology refers to the layout of
the computers and devices in a
communications network.
Bus network
Ring network
Star network
A
wireless access point is a central
communications device that allows
computers and devices to transfer data
wirelessly among
themselves or
to a wired network.
A
router connects
multiple computers or
other routers together.
 It directs the data to
go through the correct
routes to the
destination.
 Home
networks provide computers with the
following capabilities:
Connect to the
Internet at the
same time
Share a single
high-speed
Internet
connection
Play multiplayer
games
Access files and
programs on
other computers
Connect game
consoles to the
Internet
Share
peripherals
Subscribe to and
use VoIP
 Types
of wired home networks:
Ethernet
Powerline cable
• dedicated
communications network
• use special power plugs
to communicate
Phoneline
• use phone lines to
transmit data.
 The
amount of data that can
travel over a communications
channel sometimes is called the
bandwidth
 Latency is the time it takes a
signal to travel from one
location to another on a network
 Transmission media carries one
or more signals
 Broadband media transmit
multiple signals simultaneously
 Data
Communications network can be
broken down into two major classes:

Conducted Media –
media can be
seen physically:



Coaxial Cable
Twisted Pair Wires
Fiber Optics

Radiated Media – signal
is radiated through the
air by means of a
transmitter:






Cellular radio
Microwave
Infrared
Bluetooth
Wi-Fi
Satellite
Twisted-pair cable
Fiber-optic cable
Coaxial cable
 Thin,
non-metallic (typically glass), wire that
is used to transmit optical signals.
 Copper wire cables transmit signals
electrically, whereas fiber-optic cables (光纖
電纜) transmit signals by means of light.

network based on the 802.11 wireless LAN (local area network) standards.

Wireless LAN can be set-up with Wi-Fi access point & Wi-Fi enabled
stations
.
Standard
Transfer Rates
Remarks
802.11
1 or 2 Mbps
Original
802.11a
Up to 54 Mbps
Faded out
802.11b
Up to 11 Mbps
Faded out
802.11g
Up to 54 Mbps
Compatible to b
802.11n
Up to 600 Mbps
Compatible to g
The most
802.11ac
common one
Up to 7Gbps
better coverage
802.11ad
Up to 7Gbps
only LOS connections
 Wireless
local area networks (LANs)
 a Wi-Fi enabled device such as a computer,
smart phone or PDA can connect to the
Internet when in proximity of an access point.
 Advantages


Suitable for outdoor areas and historical
buildings, can host wireless LANs.
Wi-Fi is a global set of standards.
 Disadvantages


Power consumption is fairly high compared to
some other standards
Wi-Fi Access Points typically default to an open
(encryption-free) mode. (You should change that
at once!)
 Wireless
Internet access points allow people
to connect wirelessly to the Internet from
home, work, school, and in many public
locations
A
cybercafé is a coffeehouse, restaurant, or
other location that provides personal computers
with Internet access to its customers
 Cellular
radio is a form of broadcast radio that
is used widely for mobile communications
 Microwaves
are radio waves that provide a
high-speed signal transmission (with LOS)
A
communications
satellite is a space
station that receives
microwave signals
from an earth-based
station, amplifies it,
and broadcasts the
signal over a wide
area.
 Infrared



(紅外線)
Electromagnetic radiation of a wavelength longer
than visible light but shorter than radio wave
Used for short-range.
For television, VCR, or mobile phone
 Advantages


Cheap
Easy to build
 Disadvantages

Do not pass solid objects
 Connect
and exchange information between
devices (mostly handheld)


personal digital assistants (PDAs), mobile phones,
laptops, PCs, printers, digital cameras
a secure, globally unlicensed short-range radio
frequency.
 Advantages


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No cable
Low power consumption
No line of sight required
between devices.
 Disadvantages

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Low speed: only 1Mbps
Security: can be access by other
devices, more open to interception and attach
Applications
 The
Internet is a worldwide collection of
networks that links millions of businesses,
government agencies, educational
institutions, and individuals
A world-wide
interconnected
network of networks.
 Each
organization is responsible only for
maintaining its own network, and share
information to adjacent networks.
 The
Internet Engineer Task Force (IETF)
oversees research and sets guidelines and
standards for the Internet.
 Internet2
connects more than 200
universities and 115 companies via a highspeed private network in U.S.
 Many
home and small business users connect
to the Internet via high-speed broadband
Internet service
Cable
Internet
service
DSL
Fiber to
the
Premises
(FTTP)
Fixed
wireless
Cellular
Radio
Network
Wi-Fi
Satellite
Internet
Service
 Many
different actions can be done on the
Internet
Blogs
Chat rooms
E-mail
Fax
FTP
Instant
messaging
Wiki
Newsgroups
RSS
Video
conferencing
VoIP
Web
Web 2.0
Web folders
Wikis
 Users
can send and receive messages using
messaging services
Text messaging allows users to send and receive short text
messages on a phone or other mobile device or computer
Picture messaging allows users to send pictures and sound
files
Video messaging allows users to send short video clips
Wireless instant messaging allows wireless users to
exchange real-time messages with one or more other users
 Instant
messaging (IM) is a real-time
Internet communications service
 VoIP
(Voice over IP) enables users to speak
to other users over the Internet


Also called Internet telephony
E.g. Skype
 How
many computers do you have in your
home?
 How
can you share your Internet access to all
your home’s computers?
 How
can you set this up?
Notes: ISPs (Internet service providers) in HK
usually provide connections without a modem.
They give you a network cable so that you can
connect it to your computer (or router) directly.
 Computer
networks are important for our
communications.
 Basic applications of the Internet