Yuh-Jzer JoungCommunications Communications Starting Along the Information Highway

Yuh-Jzer Joung Communications

Communications

Starting Along theInformation Highway


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


Telephone-related communications services

Fax messages Dedicated fax machines Fax modems

Voice mail analog signal → digital signal → analog signal

E-mail (Electronic mail)


Video/voice communication

Videoconferencing & V-mail (video mail)Picture phones


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


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.


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.


Internet Addresses

Domain Name system

[email protected]

User ID at

subdomain

domain

country

domain type


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


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.


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.


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.


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


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


Review of analog and digital signals


Frequency Modulation

Modifying an Analog Signal

Amplitude Modulation


How modems work ？

Modulate (converts digital pulses to analog form)

Demodulate(converts analog signalsback to digital form)


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


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.




The electromagnetic spectrum


The Conduits of Communications Twisted-pair wire Coaxial cable Fiber-optic cable

Microwave and satellite systems Other wireless communications


Microwave systems

Microwave & Satellite Systems

Satellite systems


One-way: The Global Positioning systems (GPS) Pagers

Two-way: Analog cellular packet radio Cellular Digital Packet Data

Other Wireless Communication


Cellular connections


The next generation of wireless communications

Digital cellular phone Personal communications services Specialized mobile radio Satellite-based systems


Type of network

Wide area network (WAN) Metropolitan area network (MAN) Local area networks (LANs)


Advantages of networks

Sharing of peripheral devices Sharing of programs and data Better communications Security of information Access to databases



Client/server LAN


Peer-to-peer LAN


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.


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.


Transmission mode

Asynchronous transmission Synchronous transmission


Some topologies of LANs

Star Ring Bus

Others: Hybrid network FDDI (Fiber Distributed Data Interface) network


Controversial material & Censorship

Filtering software Browsers with ratings The V-chip


Netiquette (Net etiquette) Controversial Material Censorship

Privacy Issues

Cyberethics

:-) Happy face

:-( Sorrow or frown

:-O Shock

:-/ Sarcasm

;-) Wink

:--)% Boy on a skateboard

$%...!@#!

Documents

Yuh-Jzer JoungCommunications Communications Starting Along the Information Highway