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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
