Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Communications Starting Along the Information Highway
Document related concepts
no text concepts found
Transcript
Communications Starting Along the Information Highway Yuh-Jzer Joung Communications Communications and the Cyberspace Communications (telecommunications) is the electronic transfer of information from one location to another. Connectivity refers to the ability to connect devices by communications technology to other devices and sources of information. “Cyberspace,” coined by William Gibson in his novel Neuromancer to refer to a futuristic computer network that people use by plugging their brains into it, has come to mean the computer online world and the Internet in particular, and the whole wired and wireless world of communications in general. Yuh-Jzer Joung Communications Telephone-related communications services Fax messages Dedicated fax machines Fax modems Voice mail analog signal → digital signal → analog signal E-mail (Electronic mail) Yuh-Jzer Joung Communications Video/voice communication Videoconferencing & V-mail (video mail) Picture phones Yuh-Jzer Joung Communications Online Information Service Service: People connections--email, bulletin boards, chat room Research and news Games,entertainment,clubs Travel services Downloading Shopping Yuh-Jzer Joung Communications Three big companies: America Online (AOL) CompuServe Prodigy Bulletin board systems (BBSs) An electronic bulletin board (BBS) is a centralized information source and message-switching system for a particular computer- linked interest group. Yuh-Jzer Joung Communications The Internet The internet the world biggest networks, uses a protocol called TCP/IP to allow computer to communicated. TCP/IP, for Transmission Control Protocol/internet Protocol, is the standardized set of guidelines (protocols) that allow different computers on different networks to communicate with each other efficiently. Applications over the Internet:e-mail, FAQ files, FTP, Archie, telnet, gopher, WAIS, Web browsers. Yuh-Jzer Joung Communications Internet Addresses Domain Name system [email protected] country User ID domain at domain type subdomain Yuh-Jzer Joung Communications Features of the Internet E-mail Usenet newsgroups-electronic discussion groups Mailing lists: E-mail-based discussion groups FTP: for copying all the free files you want Telnet : to connect to remote computers Gopher: including Veronica and Jughead : WAIS: ways of searching by content World Wide Web: for multimedia and hypertext information retrieval Yuh-Jzer Joung Communications Shared resources Workgroup Computing & Groupware: Workgroup computing (collaborative computing) enables teams of co-workers to use networks of microcomputers to share information and cooperative projects. Groupware is a software that allows two or more people on a network to work on the same information at the same time. Two popular groupware: Lotus Notes (purchased bu IBM in 1995) Microsoft Exchange Server Electronic Data Interchange (EDI): EDI is the direct electronic exchange between organizations’ computer systems of standard business documents such as purchase orders, invoces, and shipping documents. Intranets: Intranets are internal corporate networks that use the infrastructure and standards of the Internet and the WWW. Yuh-Jzer Joung Communications A Security Program: Firewall Intranet Internet Firewall A firewall is a security program that connects the intranet to external networks such as the Internet. It blocks unauthorized traffic from entering the intranet and can also prevent unauthorized employees from accessing the intranet. Yuh-Jzer Joung Communications Portable Work : Telecommuting and virtual office Telecommuting: working at home with computer and communications connections between office and home. Virtue office: a nonpermanent and mobile office run with computer and communications technology. Yuh-Jzer Joung Communications Information or Internet appliance The TV/PC (picture) The multifaceted Net Telephone on the Net (e.g., internet phone) Radio on the Net (e.g., Real Audio) Television on the Net (e.g., Real Video) 3-D on the Net (e.g., VRML) The information/Internet appliance Set-top box Internet PCs Network PDAs Network Computers Yuh-Jzer Joung Communications Modems Why needs a modem? How modems work? External modem vs internal modem Transmission speed (e.g., 9600, 14,400, 28,800, 56K bps) bps: bits per second Yuh-Jzer Joung Communications Review of analog and digital signals Yuh-Jzer Joung Communications Modifying an Analog Signal Frequency Modulation Amplitude Modulation Yuh-Jzer Joung Communications How modems work ？ Demodulate (converts analog signals back to digital form) Modulate (converts digital pulses to analog form) Yuh-Jzer Joung Communications ISDN lines & Cable modems ISDN (Integrated Services Digital Network) Cable modems How long it takes to send a 1-megabyte Standard phone modem, 28.8 kbps 4.6 minutes ISDN line, 64-128 kbps 2.1 minutes or less Cable modem, 3000 kbps or less 2.6 seconds or less Yuh-Jzer Joung Communications Communications software Error correction: Noise is anything that causes distortion in the signal when it received. Data compression: Data compression reduces the volume of data in a message, thereby reducing the amount of time required in transmission. Remote control: Remote-control software allows you to control a microcomputer from another microcomputer in a different location. Terminal emulation: Terminal emulation software allows you to use your microcomputer to simulate a mainframe’s terminal. Yuh-Jzer Joung Communications Yuh-Jzer Joung Communications Yuh-Jzer Joung Communications The electromagnetic spectrum Yuh-Jzer Joung Communications The Conduits of Communications Twisted-pair wire Coaxial cable Fiber-optic cable Yuh-Jzer Joung Microwave and satellite systems Other wireless communications Communications Microwave & Satellite Systems Satellite systems Microwave systems Yuh-Jzer Joung Communications Other Wireless Communication One-way: The Global Positioning systems (GPS) Pagers Two-way: Analog cellular packet radio Cellular Digital Packet Data Yuh-Jzer Joung Communications Cellular connections Yuh-Jzer Joung Communications The next generation of wireless communications Digital cellular phone Personal communications services Specialized mobile radio Satellite-based systems Yuh-Jzer Joung Communications Type of network Wide area network (WAN) Metropolitan area network (MAN) Local area networks (LANs) Yuh-Jzer Joung Communications Advantages of networks Yuh-Jzer Joung Sharing of peripheral devices Sharing of programs and data Better communications Security of information Access to databases Communications Yuh-Jzer Joung Communications Client/server LAN Yuh-Jzer Joung Communications Peer-to-peer LAN Yuh-Jzer Joung Communications Components of a LAN Connection or cabling system: Microcomputers with interface cards: A network interface card, which is inserted into an expansion slot in a microcomputer, enables the computer to send and receive messages on the LAN. Network operating system: e.g., Novell’s NetWare. Other shared devices Bridges and gateways: A bridge is an interface that enables similar networks to communicate. A gateway is an interface that enables dissimilar networks to communicate, such as a LAN with a WAN. Yuh-Jzer Joung Communications Factors Affecting Data Transmission Transmission rate: frequency, bandwidth Line configurations: point-to-point vs. multipoint. Serial & parallel transmission Direction of transmission: simplex, half-duplex, full-duplex. Transmission mode: asynchronous vs. synchronous. Packet switching: A packet is a fixed-length block of data for transmission. Packet switching is a technique for dividing electronic messages into packets for switching. Multiplexing: Multiplexing is the transmission of multiple signals over a single communications channel. A multiplexer is a device that merges several low-speed transmissions into one high-speed transmission. Protocols: A protocol is a set of conventions governing the exchange of data between sender and receiver in a communication network. Yuh-Jzer Joung Communications Transmission mode Asynchronous transmission Synchronous transmission Yuh-Jzer Joung Communications Some topologies of LANs Star Ring Others: Hybrid network FDDI (Fiber Distributed Data Interface) network Yuh-Jzer Joung Communications Bus Controversial material & Censorship Yuh-Jzer Joung Filtering software Browsers with ratings The V-chip Communications Cyberethics Netiquette (Net etiquette) Controversial Material Censorship :-) Privacy Issues :-( :-O :-/ ;-) Happy face Sorrow or frown Shock Sarcasm Wink :--)% Boy on a skateboard $%...!@#! Yuh-Jzer Joung Communications
