lecture 3: network and the internet dr yingchao zhao
TRANSCRIPT
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