yuh-jzer joungcommunications communications starting along the information highway
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Yuh-Jzer Joung Communications
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.
Communications and the Cyberspace
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
Three big companies: America Online (AOL) CompuServe Prodigy
Service: People connections--email, bulletin
boards, chat room Research and news Games,entertainment,clubs Travel services Downloading Shopping
Yuh-Jzer Joung Communications
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
aeinstein@phy.princeton.edu.us
User ID at
subdomain
domain
country
domain type
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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
Intranet Internet
Firewall
A Security Program: 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.
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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
How modems work ?
Modulate (converts digital pulses to analog form)
Demodulate(converts analog signalsback to digital form)
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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
The Conduits of Communications Twisted-pair wire Coaxial cable Fiber-optic cable
Microwave and satellite systems Other wireless communications
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One-way: The Global Positioning systems (GPS) Pagers
Two-way: Analog cellular packet radio Cellular Digital Packet Data
Other Wireless Communication
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The next generation of wireless communications
Digital cellular phone Personal communications services Specialized mobile radio Satellite-based systems
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Type of network
Wide area network (WAN) Metropolitan area network (MAN) Local area networks (LANs)
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Advantages of networks
Sharing of peripheral devices Sharing of programs and data Better communications Security of information Access to databases
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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
Some topologies of LANs
Star Ring Bus
Others: Hybrid network FDDI (Fiber Distributed Data Interface) network
Yuh-Jzer Joung Communications
Controversial material & Censorship
Filtering software Browsers with ratings The V-chip
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