Using Information Technology

Chapter 7Telecommunications

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Telecommunications Networks & Communications--The “New Story” in Computing

7.1From the Analog to the Digital Age

7.2The Practical Uses of Communications

7.3Communications Channels: The Conduits of Communications

7.4Factors Affecting How Data Is Transmitted...

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Networks & Communications--The “New Story” in Computing

7.5Networks

7.6The Future of Communications

7.7Cyberethics: Controversial Material, Privacy, & Intellectual Property

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7.1 From the Analog to the Digital Age

Analog - continuous and varying in strength and/or quality

Digital - communications signals or information represented in a two-stat (binary) way

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Purpose of the Modem: Converting Digital Signals to Analog Signals & Back

Sending modem - modulates digital signals into analog signals for transmission over phone lines

Receiving modem - demodulates the analog signals back into digital signals

Modem - short for modulate/demodulate

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7.2 The Practical Uses of CommunicationsVideoconferencing & VideophonesVideoconferencing - the use of television video and sound technology as well as computers to enable people in different locations to see, hear, and talk with one another

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Workgroup Computing & Groupware

Workgroup computing - teams of co-workers use networks of microcomputers to share information and to cooperate on projects

Made possible by networks, microcomputers, & groupware

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Telecommuting

Telecommuting - working at home while in telecommunication with the office

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Virtual Offices

Virtual office - an often nonpermanent and mobile office run with computer and communications technology

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Smart Television

Digital television (DTV) - uses a digital signal, or series of 0s and 1s

High-definition television (HDTV) - high-resolution type of DTV

Standard-definition television (SDTV) - allows broadcasters to transmit more information within the HDTV bandwidth

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Other Practical Uses of Communications

Home network - LAN which allows all the personal computers under the same roof to share peripherals and a single modem and Internet service

Information/internet appliance - a device merging computing capabilities with communications gadgets

TV set-top boxesInternet phonesPDAs

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7.3 Communications Channels: The Conduits of Communications

Communications channel - the path (physical medium) over which information travels in a telecommunications system from its source to its destination

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The Electromagnetic Spectrum, the Radio Spectrum, & Bandwidth

Radio frequency spectrum

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Wired Communications Channels

Twisted-pair wire - two strands of insulated copper wire, twisted around each other

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Wired Communications Channels

Coaxial cable - insulated copper wire wrapped in a solid or braided metal shield, then in an external cover

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Wired Communications Channels

Fiber-optic cable - dozens or hundreds of thin strands of glass or plastic that transmit pulsating beams of light rather than electricity

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Wireless Communications Channels

Infrared transmission - the transmission of data signals using infrared-light waves

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Wireless Communications Channels

Broadcast radio - a wireless transmission medium that sends data over long distances--between regions, states, or countries

Microwave radio - transmits voice & data through the atmosphere as super-high-frequency radio waves called microwaves

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Wireless Communications Channels

Communications satellites - microwave relay stations in orbit around the earth

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Long-Distance Wireless Communications

Global Positioning System (GPS) - a series of earth-orbiting satellites continuously transmitting timed radio signals that can be used to identify earth locations

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Long-Distance Wireless Communications

Pagers - simple radio receivers that receive data (but not voice messages) sent from a special radio transmitter

One-way pagersTwo-way pagers (enhanced paging)

Acknowledgments from recipient to senderEmail composition & sendingMessages to other pagers

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Long-Distance Wireless Communications

Analog cellular phones - designed primarily for communicating by voice through a system of ground-area cells

Cell - hexagonal shape, usually 8 miles or less in diameter, & served by a transmitter-receiving tower

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Long-Distance Wireless Communications

Digital wireless services (2G) - support digital cellphones & PDAs, using a network of cell towers to send voice communications & data over the airwaves in digital form

Broadband wireless digital services (3G) - “always on” technology which can quickly transmit video, still pictures, and music, along with offering better ways to tape into websites than today’s 2G wireless systems

2.5G - compromise between 2G and 3G, which is an “always on” version of 2G technology

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Short-Range Wireless Communications

Bluetooth - a short-range wireless digital standard aimed at linking cellphones, PDAs, computers, & peripherals up to distances of 30 feet

WiFI - a short-range wireless digital standard aimed at helping machines inside offices to communicate at high speeds and share Internet connections at distances up to 300 feet

HomeRF - a separate, incompatible standard designed to network up to 10 PCs & peripherals as far as 150 feet apart

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Compression & Decompression: Putting More Data in Less Space

Compression - a method of removing repetitive elements from a file so that the file requires less storage space and therefore less time to transmit

Lossless vs. lossy

Standards

JPEGMPEG

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7.4 Factors Affecting How Data Is Transmitted

Transmission rate - a function of two variables:

Frequency - the cycles of waves per second

Bandwidth - the range between the highest & lowest frequencies

Higher frequency => greater transmission rateLarger bandwidth => greater transmission rate

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Factors Affecting How Data Is Transmitted

Line configurations

Point-to-point line - directly connects the sending & receiving devices

Multipoint line - a single line that interconnects several communications devices to one computer

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Factors Affecting How Data Is Transmitted

Serial vs. parallel transmission

Serial data transmission - bits are transmitted sequentially, one after the other

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Factors Affecting How Data Is Transmitted

Serial vs. parallel transmission

Parallel data transmission - bits are transmitted through separate lines simultaneously

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Factors Affecting How Data Is Transmitted

Direction of transmission: simplex, half-duplex, & full-duplex

Simplex transmission - data can travel in only one direction

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Factors Affecting How Data Is Transmitted

Direction of transmission: simplex, half-duplex, & full-duplex

Half-duplex transmission - data travels in both directions but only in one direction at a time

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Factors Affecting How Data Is Transmitted

Direction of transmission: simplex, half-duplex, & full-duplex

Full-duplex transmission - data is transmitted back and forth at the same time

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Factors Affecting How Data Is Transmitted

Asynchronous transmission - data is sent one byte at a time, with each string of bits making up the byte bracketed with special control bits

Transmission mode: asynchronous vs. synchronous

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Factors Affecting How Data Is Transmitted

Synchronous transmission - data is sent in blocks, with start and stop bit patterns (synch bytes) at the beginning and end of the blocks

Transmission mode: asynchronous vs. synchronous

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Factors Affecting How Data Is Transmitted

Circuit switching - transmitter has full use of the circuit until all the data has been transmitted and the circuit is terminated

Packet switching - electronic messages are divided into packets for transmission over a wide area network to their destination through the most expedient route

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Factors Affecting How Data Is Transmitted

MultiplexersConcentratorsFront-end

processors

Multiplexing - transmission of multiple signals over a single communications channel

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Factors Affecting How Data Is Transmitted

Protocol - a set of conventions governing the exchange of data between hardware and/or software components in a communications network

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7.5 Networks

Benefits of networks:

Sharing of peripheral devices

Sharing of programs and data

Better communications

Security of information

Access to databases

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Types of Networks

Wide area network (WAN) - a communications network that covers a wide geographical area, such as a country or the world

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Types of Networks

Metropolitan area network (MAN) - a communications network covering a city or a suburb

Local area network (LAN) - connects computers and devices in a limited geographical area

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Types of Networks

Host computer - a mainframe or midsize central computer that controls the network

Node - any device that is attached to a network

Backbone - a high-speed network that connects LANs and MANs to the Internet

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Types of LANs

Client/server LAN:

Clients - microcomputers that request data; and

Server - a powerful microcomputer that manages shared devices

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Types of LANs

Peer-to-peer LAN - all microcomputers on the network communicate directly with one another without relying on a server

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Components of LANs

Connection or cabling system

Microcomputers with network interface cards

Network OS

Other shared devices

Routers, bridges, and gateways

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Topology of LANs

Star network - one in which all microcomputers and other communications devices are connected to a central server

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Topology of LANs

Ring network - one in which all microcomputers and other communications devices are connected in a continuous loop

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Topology of LANs

Bus network - one in which all communications devices are connected to a common channel

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Intranets, Extranets, & Firewalls

Intranet - an organization’s internal private network that uses the infrastructure and standards of the Internet and the WWW

Extranets - private intranets that connect not only internal personnel but also selected suppliers and other strategic parties

Firewalls - a system of hardware and software that blocks unauthorized users inside and outside the organization from entering the intranet

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7.6 The Future of Communications

Satellite-based systems

Beyond 3G to 4G

Photonics: optical technologies at warp speed

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7.7 Cyberethics

Controversial material & censorship:

Blocking software

Browsers with ratings

The V-Chip

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Cyberethics

Privacy - the right of people not to reveal information about themselves

Cookie - a file that the web server stores on your hard-disk drive when you visit a website