MATH101/MATH102NUME

RICAL & IT LITERACY

Lecture 3: Network and the Internet

Dr Yingchao ZHAO

LECTURE OUTCOMES After this lecture, you should be able to:

be aware of the basic concepts of networknote the basic applications in the Internet

NETWORK

Before we talk about the Internet, we first need to understand the basic terminologies in

network

COMMUNICATIONS Computer communications describes

a process in which two or more computers or devices transfer data, instructions, and information.

Sending device

Communications channel

Receiving device

COMMUNICATIONS Computing facilities help a lot in

communications. Information can be transferred via

computer network (Internet).

COMPUTER NETWORKS A network is a collection of computers

and devices connected together via communications devices and transmission media.

Advantages of using a network include:

Facilitating communicatio

ns

Sharing hardware

Sharing data and

information

Sharing software

Transferring funds

LOCAL AREA NETWORK (LAN) 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.

MAN AND WAN 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).

NETWORK ARCHITECTURE 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 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.

NETWORK TOPOLOGY A network topology refers to the layout

of the computers and devices in a communications network.

Star network

Bus network

Ring network

COMMUNICATIONS DEVICES A wireless access point is a central

communications device that allows computers and devices to transfer data wirelessly amongthemselves or to a wired network.

ROUTER A router connects

multiple computers or other routers together.

It directs the data to go through the correct routes to the destination.

HOME NETWORKS Home networks provide computers with

the following capabilities:

Connect to the Internet at the same time

Share a single high-speed

Internet connection

Access files and programs on

other computers

Share peripherals

HOME NETWORKS Types of wired home networks:

Ethernet•dedicated communications network

Powerline cable•use special power plugs to communicate

Phoneline•use phone lines to transmit data.

HOME NETWORKS

COMMUNICATIONS CHANNEL 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

TRANSMISSION MEDIA

Radiated Media – signal is radiated through the air by means of a transmitter: Cellular radio Microwave Infrared Bluetooth Wi-Fi Satellite

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

NETWORK CABLES

Twisted-pair cable

Coaxial cable

Fiber-optic cable

FIBER OPTICS (OPTICAL FIBER) 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.

WIRELESS TRANSMISSION 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

802.11ac Up to 7Gbps better coverage

802.11ad Up to 7Gbps only LOS connections

The most common one

WI-FI 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!)

WI-FI

WI-FI EXAMPLES Wireless Internet access points allow

people to connect wirelessly to the Internet from home, work, school, and in many public locations

WI-FI EXAMPLES (2) A cybercafé is a coffeehouse, restaurant,

or other location that provides personal computers with Internet access to its customers

CELLULAR NETWORKS Cellular radio is a form of broadcast

radio that is used widely for mobile communications

MICROWAVES Microwaves are radio waves that

provide a high-speed signal transmission (with LOS)

SATELLITES 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 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

AdvantagesCheapEasy to build

DisadvantagesDo not pass solid objects

BLUETOOTH 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

No cable Low power consumption No line of sight required

between devices. Disadvantages

Low speed: only 1Mbps Security: can be access by other

devices, more open to interception and attach

THE INTERNET

Applications

THE INTERNET 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.

THE INTERNET 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 high-speed private network in U.S.

THE INTERNET Many home and small business users

connect to the Internet via high-speed broadband Internet service

Cable Intern

et servic

e

DSL

Fiber to the Premises

(FTTP)

Fixed wirele

ss

Cellular

Radio Network

Wi-Fi

Satellite

Internet

Service

INTERNET APPLICATIONS Many different actions can be done on

the Internet

Blogs Chat rooms E-mail

Fax FTP Instant messaging

Wiki Newsgroups RSS

INTERNET FOR COMMUNICATIONS Users can send and receive messages

using messaging services

INTERNET MESSAGING

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 Instant messaging (IM) is a real-time

Internet communications service

VoIP VoIP (Voice over IP) enables users to

speak to other users over the InternetAlso called Internet telephonyE.g. Skype

QUESTIONS 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.

SUMMARY Computer networks are important for

our communications. Basic applications of the Internet