Transcript Chapter 7: Communications Technology

Communications Technology
Chapter 7
Starting Along the Information
Superhighway
© The McGraw-Hill Companies, Inc., 2000
Overview
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Technology basics
Channels
Factors among devices
Communication
networks
• Local networks
• Networking options
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Computers to Communicate:
Technological Basics
• Communications or
telecommunications
• transfer of data from a
transmitter or source to
a receiver or sink
• may have intermediate
devices to set up a path
or maintain adequate
signal strength
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Analog Signals
• Analog
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called a carrier wave
frequency
amplitude
telephones, radios, televisions
• digital telephones and television broadcasts are
increasing
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Digital Signals
• Uses on/off or
present/absent
electrical or
optical pulses in
discontinuous or
discrete bursts
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Modem
• Analog modem
– modulator/demodulator
– analog modems convert digital signals into an
analog form for telephone lines
– does not actually change digital signals
• rather changes form of the wave to represent 1s and
0s
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Modem
• Digital modems
– cable
– ASDL
• DSL
• G. Lite
– ISDN
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Internal Modems
• Internal
– separate
– ISA or PCI
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External Modems
• External
– does not occupy
additional IRQ
– generally has volume
control
– shows communication
lights
– easily moved to a new
computer
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Additionally
• PCMCIA cards for laptops
– some even have combo modem and
network cards, so that workers who
have to use the network in the office
and yet have access while out of
town on business may do so
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Transmission Speeds
• Faster transmission speeds mean faster
downloads of graphics, video, sound, and
data or program files
• Expressed in bits per second (bps)
• Speeds obtained can be affected by
– line quality, distance from communications
center, line traffic, modem speed at the ISP
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v.90 standard
• By the middle of 2000, most ISPs will have
their modem racks filled with the 56K v.90
standard
• Slower modems can still communicate, but
at a speed slower than v.90
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Communications Software
• Often incorporated
into an operating
system
• Establishes
communication
• Error correction
• Data compression
• Remote control of
another system
• Terminal emulation
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ISDN
• Integrated Services Digital Network
• Uses POT (plan old telephone system)
• Capable of transmitting five times faster than
conventional modems
• Need special ISDN connection box or adapter
card
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ASDL
• Asymmetric Digital
Subscriber Line
• Often good return on costs
compare to ISDN in the
United States
• Runs on POTS
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Cable Modems
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Up to 1000 times faster than POTS
Two-way transmission
Shared cable line with community
Security questions
Can get bogged down, if many
subscribers in the same building or
neighborhood, for instance
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Dishes
• 15 times faster than standard
cable
• Upload currently through ISP
phone modem
• With more low-level satellites,
there is the potential to directly
upload
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Channels
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Twisted-pair
Coaxial cable
Fiber-optic cable
Microwave systems
Satellite systems
Other wireless systems
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Twisted-Pair
• Copper wire
• Most telephone connections
• UTP
– unshielded twisted pair
• STP
– shielded twisted pair
• Most common connection
worldwide
• 16 to 100 Mbps
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Coaxial Cable
• “Co-ax”
• Insulation resists noise, or electronic
interference
• Up to 200 Mbps
• Often many or bundled together
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Fiber-Optic
• Strands of glass transmitting light farther
and with fewer errors
• No effected by electromagnetic interference
• Addition of plastic fiber allows the last 100
feet to install for curb-to-home wiring
• 1 trillion bps per fiber
• Being laid worldwide
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Microwave
• Voice and data as high-frequency radio
waves
• Line-of-sight
• More than half of telephones system use
microwave
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Satellite
• Computer communications satellites are
microwave relay stations
• Normal orbit 22,300 miles above earth
– geo-stationary orbit (GEO)
• Medium-earth orbits
– 5,000 to 10,000 require less power to transmit
• Low-earth orbits
– 400 to 800 miles up
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Other Wireless
• Two-way radio
• Mobile telephones
• Global Positioning system
– GPS
– high accuracy to a few feet
• Local Position Systems (LPS)
– uses radio frequency for tracking
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More Communications
• Pagers
– “beepers”
– radio receivers
– becoming two-way with voice
or prerecorded messages
• Analog cellular phones
– 824 to 894 MHz using groundarea cells
– direct calls through Mobile
Telephone Switching Office
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Other Phones and Radios
• Digital cellular phones
– higher promise of more accurate transmission
– not universal standard
– World Trade Organization (WTO)
• hoping to standardize telecommunications systems
• Packet radio
– useful for mobile workers who need to
communicate frequently with a corporate
database
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Factors Affecting Channel Speed
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Transmission rate
Line configurations
Serial vs. parallel transmission
Simplex, half-duplex, full-duplex
Asynchronous vs. synchronous
Packet switching
Multiplexing
Protocols
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Frequency
• Frequency
– amount of data that can be transmitted on a
channel depends on the wave frequency
– the cycles of waves per second in hertz
– 400 hertz twisted-pair may send 1 kilobyte of
data a second
– 100 megahertz coax may send 10 megabytes
– 200 trillion hertz fiber-optic may send 1 gigabyte
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Bandwidth
• The difference between the highest and
lowest frequencies transmitted
• There maybe several frequencies within a
bandwidth
• Rate of speed expressed in bits per second
(bps), kilobits per second (Kbps), megabits
per second (Mbps)
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Point-to-Point
• Point-to-point line directly connects the
sending and receiving devices
– terminal to central computer
– private (leased) line use
– T1 lines can carry 24 signals on a single set of
copper wires
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Multipoint
• A multipoint line is a single
line that connects several
communications devices to
one computer
– often only one communications
device, but can transmit at any
time
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Serial and Parallel Transmission
• In serial transmission, bits are transmitted sequentially
– twisted-pair
– communications lines, modems, many mice
• In parallel transmission, bits are transmitted through
separate lines simultaneously
– faster than serial, but not as efficient after 15 feet
– printer and some scanners
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Asynchronous vs. Synchronous
• Asynchronous
– sent one byte or character in a line
– sent whenever its is convenient for the sender
• Synchronous
– sync bytes transmitted at start and stop of
blocks of data
– best for large amounts of data on large systems
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Packet Switching
• Maximum-fixed-length block of
data for transmission
• Contains instructions about
destination
• Packets arrive at destination,
reassembled
• Used in large networks
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Circuit Switching
• Transmitter has full use of
the circuit until all the data
has been transmitted
• Used by telephone
company for voice network
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Asynchronous Transfer Mode
• ATM
• Combines efficiency of packet switching
with some of circuit switching features
• Handles both data and real-time voice and
video
• Designed to operate on fiber-optic cables
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Multiplexing
• Transmission of multiple signals over a
signal communications channel
• Multiplexer
– merges several low-speed transmissions into
one high-speed transmission
• Concentrator
– similar to multiplexer, but collects data in a
temporary storage area, then sends to a
receiving computer
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Multiplexing
• Front-end processors
– a smaller computer for mainframes and
midframes assists in communication functions
– corrects errors and relieves larger computer of
routing computational tasks
• Sometimes used synonymously with
communications controller
– but this is usually less sophisticated
– in LAN, an adapter does this task
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Protocols
• Rules of data transmission
• A set of conventions governing the
exchanging of data between hardware
and/or software
• OSI, Open Systems Interconnection,
provides a seven-layer look at software
responsibilities
– hope for more universal usage
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Communications Network
• A system of interconnected computers,
telephones, and other communications
devices that can communicate and share
data and applications
• Run through a NOS or Network Operating
System
– NetWare
– Windows NT
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NOS
• May require operating system to function
Ch 7
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Hosts and Nodes
• Host computer
– main computer in a system using
communications link
• Node
– device attached to a network
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Advantages of Networks
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Sharing of peripheral devices
Sharing of programs and data
Better communications
Security of information
Access to databases
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Local Area Network
• Private branch exchange (PBX)
– private or leased switching system connecting
to outside telephone systems
• Newer PBXs can handle not only analog
telephones but also digital equipment
• Local Area Network (LAN)
– “lans” usually require installation of own
communications channels
Ch 7
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Types of LANs
• Client-server
– microcomputer clients using devices that
provide a service, called servers
• Microcomputers connection to AOL
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LAN
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File server
Print server
Application server
Database server
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Peer-to-Peer
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No reliance on server
Can be less expensive than client-server
Backups and recovery more difficult
Systems slow down under heavy use
Can be a mix of peer-to-peer and clientserver
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Components
• Connection or cabling system
• Microcomputer or workstations with
network interface cards (NICs)
• Network operating system
• Other shared devices
– printers, fax machines, scanners,
storage devices
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Bridges, Routers, Gateways
• Bridge is interface to same type of network
– protocol independent
• Router is intelligent device supporting like and unlike
LANs, and LANs and WANs
– protocol reading
• Gateway performs all functions of bridges and routers,
including protocol conversion
– slowest of three
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Topology of LANs
• Star
– central hub
• Ring
– continuous loop
• Bus
– on a network backbone using coax, STP, or UTP
• Hybrid
– combination
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Fast Networks
• FDDI network - “fiddy”
– Fiber Distributed Data Interface with duplex
token ring topology
– transmits 100 to 200 Mbps
– high cost and fragility
– used for high-resolution needs
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Fax Messages
• facsimile transmission
• fax machine
• fax-capable modem
Ch 7
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Voice Mail
• Digitizes incoming
voice messages
• Can then be retrieved
by phone or computers
with proper ID
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Electronic Mail
• E-mail
• Can be linked,
wireless or wired
connections
• Post and read
• Advantage
– quick communication
• Disadvantage
– need to handle junk
mail (spam)
Ch 7
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Video Conferencing and V-Mail
• Television video
• Sound technology
• Limited with the use of
normal telephone lines
• Can lease video
conferencing
• V-mail sent like e-mail
– usually on ISDN
Ch 7
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Workgroup Computing
• Also called
collaborative
computing
• Groupware
• Best known
– Lotus Notes
• many operating systems
• database
• e-mail
Ch 7
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Electronic Data Interchange
• EDI
• Electronic interchange of business
documents
• Standardized format
• Dedicated line
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Intranets and Extranets
• Intranets
– network within the organization
– security behind firewalls
• Extranet
– extended intranets outside to employees such as
salespeople
– extended to suppliers, B-2-B customers, and
alliances
Ch 7
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Telecommuting
• Also called telework
• work from home or at
another office location
– often called telework
centers
• Hoteling
– for businesspeople
who are out of the
office quite a bit
Ch 7
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