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 data and information Sharing software 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 networkPeer-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. Star network Bus network Ring 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 Access files and programs on other computers Share peripherals Play multiplayer games Connect game consoles to the Internet Subscribe to and use VoIP

 Types of wired home networks: Ethernet dedicated communications network Powerline cable 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

 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

Twisted-pair cable Coaxial cable Fiber-optic 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 wireless LAN (local area network) standards.  Wireless LAN can be set-up with Wi-Fi access point & Wi-Fi enabled stations. StandardTransfer RatesRemarks or 2 MbpsOriginal aUp to 54 MbpsFaded out bUp to 11 MbpsFaded out gUp to 54 MbpsCompatible to b nUp to 600 MbpsCompatible to g acUp to 7Gbpsbetter coverage adUp to 7Gbpsonly LOS connections The most common one

 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  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

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 high- speed 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 BlogsChat rooms Fax FTP Instant messaging WikiNewsgroups RSS Video conferencing VoIPWeb Web 2.0Web foldersWikis

 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