Ch 7: Communications and Connectivity Content

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Communications and Connectivity
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Objectives

• Connectivity options
• User connection
• Connection types
• Communication channels
• Data Transmission
• Network, Network Strategy, Network Type

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6.1 Introduction

• Connectivity is the ability to connect a
  microcomputer by telephone or other
  telecommunication links to other computers and
  information sources around the world
• Incredible power on your desk. It has become
  particularly important in business

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6.1 Introduction (cont)

• Data communication systems are
• Electronic systems that transmit data
• Computer to computer
• Within company
• Across country
• International
• Over Telecommunication lines
• Wired or Wireless Communications Channels

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6.2 Communication Connectivity Concepts

• Communication allows microcomputer users to
  transmit and receive data and gain access to
  electronic information resources
• Connectivity is the means to connect your
  computer by telephone or other telecommunication
  links to other computers and information sources
• There are many methods of communication and
  connectivity options.

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6.2 Connectivity Options Available

• Fax
• Email
• Voice messaging
• Video conferencing
• Shared resources
• On-line services

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6.2.1 Fax Machines

• Convert images to signals that can be sent over a
  telephone line to a receiving machine
• Extremely popular in offices
• Scan image of a document and print the image on
  paper
• Microcomputers use fax/modem circuit boards to
  send and receive fax messages

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6.2.2 E-mail

• Electronic mail
• Method of sending an electronic message between
  individuals or computers
• Receive e-mail messages even when you are not on
  the computer
• E-mail messages can contain text, graphics, and
  images as well as sound

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6.2.3 Voice Messaging

• Computer systems linked to telephones that
  convert human voice into digital bits
• Resemble conventional answering machines and
  electronic mail systems
• Receive large numbers of incoming calls and route
  them to appropriate voice mailboxes, which are
  recorded voice messages.
• Forward calls and deliver the same message to
  many people

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6.2.4 Video Conferencing

• Computer systems that allow people located at
  various geographic locations to have in-person
  meetings
• Use specially equipped videoconferencing rooms to
  hold meetings
• Desktop videoconferencing systems use
  microcomputers equipped with inexpensive video
  cameras and microphones that sit atop a computer
  monitor

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6.2.4 Video Conferencing
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6.2.5 Shared Resources

• Communication networks that permit microcomputers
  to share expensive hardware such as laser
  printers, chain printers, disk packs, and
  magnetic tape storage
• Several microcomputers linked in a network make
  shared resources possible
• Connectivity capabilities of shared resources
  provide the ability to share data located on your
  computer or somewhere else

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6.2.6 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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6.2.7 Telecommuting

• Telecommuting - working at home while in
  telecommunication with the office
• A related term is telework, which includes not
  only those who work at least part-time from home
  but also those who work at remote or satellite
  offices called telework centers.

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6.2.8 Virtual Offices

• An often nonpermanent and mobile office run with
  computer and communications technology

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6.2.9 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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6.2.10 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

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6.2.11 On-Line Services

• Business services offered specifically for
  microcomputer users
• Well-known online service providers are American
  Online (AOL), ATT WorldNet, CompuServe, and
  Microsoft Network
• Typical online services offered by these
  providers are teleshopping, home banking,
  investing, travel reservations Internet access

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6.3 User Connection Concepts

• Computer communication takes place over telephone
  lines that send and receive analog signals
• Computers can only send and receive digital
  signals
• Digital signals need to be converted to analog
  signals and vice versa in order to communicate
  over telephone lines
• Modem device is needed to convert signals
• Other means of user connections are standard
  telephone lines, T1,T2, T3 T4 lines, ISDN,
  DSL, cable modems and satellite/air connection
  services

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6.3.1 Modem

• Hardware device that converts computer signals
  (digital signals) to telephone signals (analog
  signals) and vice versa
• Analog - continuous and varying in strength
  and/or quality
• Digital - communications signals or information
  represented in a two-state (binary) way
• Process of converting digital signals to analog
  is called modulation and converting analog
  signals to digital is called demodulation
• Modulation/demodulation is an acronym for modem

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6.3.1 Modem
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6.3.1 Modem (cont)

• Internal, external, wireless
• Speed is typically measured in bits per second
  (bps)
• Most popular speeds for conventional modems are
  36.6 kbps (36,600 bps) and 56 kbps (56,000 bps)
• Modems of speed 36.6 kbps takes 75 seconds

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6.3.1.1 Internal Modem

• Plug-in circuit board inside the system unit
• Telephone cable connects this type of modem to
  the telephone wall jack

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6.3.1.1 Internal Modem (cont)
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6.3.1.2 External Modem

• Stands apart from the computer
• Connected by a cable to the computers serial
  port
• Another cable is used to connect the modem to the
  telephone wall jack

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6.3.1.3 Wireless Modem

• Similar to the external modem
• Connects to the computers serial port, but does
  not connect to telephone lines
• Uses new technology that receives data through
  the air

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6.4 Connection Types

• Dial-up
• High-speed telephone lines
• Digital subscriber line (dsl)
• Cable modem TV
• Satellite/air

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6.4.1 Dial-Up

• Standard telephone lines and conventional modems
  provide dial-up connection
• Popular but quite slow and inadequate to meet
  many communication needs

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6.4.1 Dial-up (cont)
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6.4.2 High-Speed Telephone Lines

• T1, T2, T3, T4 lines
• Special high-speed lines leased by large
  corporations from telephone companies
• Speed of T1 is 1.5 mbps 26 times faster than
  dial-up service
• Very expensive type of connection
• Supports all digital communications
• Does not require conventional modems
• Provides very high capacity

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6.4.2 High-Speed Telephone Lines (cont)

• ISDN - Integrated Services Digital Network
• Hardware and software that allows voice, video,
  and data to be communicated over traditional
  copper-wire telephone lines
• 128Kbps

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6.4.3 Digital Subscriber Line (DSL)

• Uses existing telephone lines to provide
  high-speed connections as fast as T1
• Presently limited to a few large cities
• DSL costs less than T1 line
• Expected to become widely available in the next
  few years
• 1.5-8.4Mbps

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6.4.4 Cable Modem

• Use existing television cables to provide
  high-speed connections as fast as a T1 or DSL
• Costs less than T1 or DSL
• 100 percent availability of cable modems is
  predicted within the next few years

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6.4.5 Satellite/Air Connection Service

• Use satellites and the air to download or send
  data to users
• Transmission rate is seven times faster than
  dial-up connections
• Users must rely on a dial-up connection to upload
  or send data to satellites with this type of
  connection
• Slower than DSL and cable modem

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6.5 Communication Channels

• The transmission media used in communication are
  called communications channels
• Two ways of connecting microcomputers for
  communication with each other and with other
  equipment is through cable or air
• Channels can be through cable / wired channels,
  through air / wireless channels, long distance
  wireless communications, and short range wireless
  communications

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6.5 Communication Channels (cont)

• Through cable / wired channels
• Twisted pair
• Coaxial
• Fiber-optic
• Through air / wireless channels
• Infrared
• Broadcast Radio
• Microwave Radio
• Communication Satellites

• Long distance wireless communications
• GPS
• Pagers
• Analog cellular
• Digital wireles
• Future wireless
• Short range wireless communications
• Bluetooth
• WiFi
• HomeRF

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6.5.1 Twisted Pair Wire

• Twisted pair cables known as telephone lines
  (1-128 Mbps)
• Two strands of insulated copper wire, twisted
  around each other reduces interference from
  electrical fields
• A single twisted pair culminates in a wall jack
  where you plug your phone
• Had been the standard communication channel for
  both voice and data
• More technically advanced and reliable
  transmission media is now replacing it

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6.5.1 Twisted Pair Wire(cont)
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6.5.2 Coaxial Cable

• High-frequency transmission cable that replaces
  the multiple wires of telephone lines with a
  single solid-copper core
• Insulated copper wire wrapped in a solid or
  braided metal shield, then in an external cover -
  much better at resisting noise
• Over 80 times the transmission capacity of
  twisted pair
• Used to link parts of a computer system in one
  building
• Co-ax is widely used in cable television
• Voice and data up to 200 Mbps

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6.5.2 Coaxial Cable (cont)
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6.5.3 Fiber-Optic Cable

• Transmits data as pulses of light through tubes
  of glass
• Dozens or hundreds of thin strands of glass or
  plastic that transmit pulsating beams of light
  rather than electricity
• Over 26,000 times the transmission capacity of
  twisted pair - 100 Mbps to 2 Gbps
• Tube can be half the diameter of human hair
• Immune to electronic interference and more secure
  and reliable
• Rapidly replacing twisted-pair telephone line

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6.5.3 Fiber-Optic Cable (cont)
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6.5.4 Infrared Transmission

• Infrared transmission (14 Mbps) - the
  transmission of data signals using infrared-light
  waves
• Infrared ports can be found on some laptop
  computers and printers, as well as wireless mice

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6.5.5 Broadcast Radio

• Up to 2 Mbps
• Wireless transmission medium that sends data over
  long distances--between regions, states, or
  countries

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6.5.8 Microwave Radio

• 45 Mbps
• Transmits voice data through the atmosphere as
  super-high-frequency radio waves called microwaves

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6.5.8.1 Microwave

• Transmit data as high-frequency radio waves that
  travel in straight lines through the air
• Cannot bend with the curvature of the earth
• Can only be transmitted over short distances
• Good medium for sending data between buildings in
  a city or on a large college campus
• Microwave transmission over longer distances is
  relayed by means of dishes or antennas
  installed on towers, high buildings, or mountain
  tops

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6.5.9 Satellite

• Used to amplify and relay microwave signals from
  one transmitter on the ground to another
• Orbit about 22,000 miles above the earth
• Rotate at a precise point and speed
• Used to send large volumes of data
• Bad weather can sometimes interrupt the flow of
  data from a satellite transmission
• Intelsat (INternational TELecommunications
  SATellite Consortium), owned by 114 governments
  forming worldwide communications system, offers
  many satellites that can be used as microwave
  relay stations

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6.5.9 Satellites (cont)

• Uplinking downlinking
• Geostationary earth orbit (GEO), medium-earth
  orbit (MEO), low-earth orbit (LEO)

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6.5.10 Global Positioning System

• Global Positioning System (GPS) is one-way
  communications
• Series of earth-orbiting satellites continuously
  transmitting timed radio signals that can be used
  to identify earth locations
• A GPS receiver can pick up transmission from any
  four satellites, interpret the information from
  each, and pinpoint the receivers longitude,
  latitude, and altitude

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6.5.11 Pagers

• Simple radio receivers that receive data (but not
  voice messages) sent from a special radio
  transmitter
• One-way pagers
• Two-way pagers (enhanced paging)
• Acknowledgments from recipient to sender
• Email composition sending
• Messages to other pagers
• Once stereotyped as devices for doctors and drug
  dealers, pagers are now consumer items

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6.5.12 Analog Cellular Phones

• First generation analog cellular services - 1G
• 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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6.5.12 Cellular Connections
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6.5.13 Digital Wireless

• Support digtal cellphones PDA - 2G
• Using a network of cell towers to send voice
  communications data over the airwaves in
  digital form

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6.5.14 Future Wireless Services

• 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
  todays 2G wireless systems
• 2.5G - compromise between 2G and 3G, which is an
  always on version of 2G technology

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6.5.15 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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6.6 Data Transmission

• Technical Matters that affect data
  communications
• Bandwidth
• Line Configurations
• Serial vs. parallel
• Direction of flow
• Modes
• Circuit packet switching
• Multiplexing
• Protocol
• Compression Decompression techniques

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6.6.1 Bandwidth

• The radio frequency spectrum are fields of
  electrical energy and magnetic energy that carry
  communications signals
• A range of frequencies is called a band or
  bandwidth. Bandwidth is a measure of the amount
  of information that can be delivered within a
  given period of time
• For analog signals, bandwidth is expressed in
  hertz (Hz) or cycles per second. For digital
  signals, bandwidth is expressed in bits per
  second (bps)

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6.6.1 Bandwidth (cont)

• The bandwidth is the difference between the
  lowest and the highest frequencies transmitted
• The wider the bandwidth, the faster data can be
  transmitted. The narrower the band, the greater
  the loss of transmission power
• Broadband connections are characterized by very
  high speed. For example, the connections that
  carry broadcast video range in bandwidth from 10
  megabits to 30 gigabits per second

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6.6.1 Bandwidth (cont)

• 3 types
• Voiceband - bandwidth of standard telephone
  lines, 9,600 to 56,000 bps
• Medium band - bandwidth of special leased lines
  used, 56,000 to 264,000,000 bps
• Broadband - bandwidth of microwave, satellite,
  coaxial cable, and fiber-optic, 56,000 to
  30,000,000,000 bps

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6.6.2 Line Configuration

• 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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6.6.3 Serial vs. Parallel

• Data travels in two ways
• Serial
• Parallel

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6.6.3.1 Serial Data Transmission

• Continuous stream of bits
• One after the other
• The way most data is sent over telephone lines
• Used by external modems typically connected to a
  microcomputer through a serial port
• Technical names for such serial ports are RS-232C
  connector or asynchronous communications port

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6.6.3.1 Serial Data Transmission (cont)
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6.6.3.2 Parallel Data Transmission

• Simultaneously flow of bits
• Separate but parallel wires
• Typically limited to communications over short
  distances (not telephone lines)
• Standard method of sending data from a computers
  CPU to a printer

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6.6.3.2 Parallel Data Transmission (cont)
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6.6.4 Direction of Flow

• There are three directions or modes of data flow
  in a data communications system
• Simplex communication - data travels in one
  direction only. Example point-of-sale terminals
• Half-duplex communication - data flows in both
  directions, but not simultaneously.
  Example electronic bulletin board
• Full-duplex communication - data is transmitted
  back and forth at the same time.
  Example mainframe communications

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6.6.4.1 Simplex
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6.6.4.2 Half-Duplex
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6.6.4.3 Full-Duplex
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6.6.5 Modes of Data Transmission

• Data may be sent over communication channels by
• Asynchronous
• data sent and received one byte at a time
• transmission rate slow
• Synchronous
• several bytes or a block at a time
• coordinated by synchronized clock

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6.6.5.1 Asynchronous Transmission
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6.6.5.2 Synchronous Transmission
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6.6.6 Circuit Packet Switching

• Circuit switching
• Transmitter has full use of the circuit until all
  the data has been transmitted and the circuit is
  terminated
• Best for voice
• Packet switching
• Electronic messages are divided into packets for
  transmission over a wide area network to their
  destination through the most expedient route
• Best for data

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6.6.7 Multiplexing

• Transmission of multiple signals over a single
  communications channel
• Devices
• Multiplexer merges several low-speed
  transmissions into one high-speed transmission
• Concentrator collects data in a temporary storage
  data
• Front-end processor is a smaller computer
  connected to larger computer assists with
  communication functions

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6.6.7 Mutiplexing
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6.6.8 Protocols

• Set of communication rules
• Speeds and modes for connecting one computer with
  another computer
• Network protocols can become very complex
  therefore standards increase
• First was IBM Systems Network Architecture (SNA)
  which only works for IBMs own equipment
• Next Open Systems Interconnection (OSI)
• Different equipment
• Identifies network functions into seven layers

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6.6.8.1 Open Standard Interchange (OSI)
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6.6.9 Compression Decompression

• Compression - a method of removing repetitive
  elements from a file so that the file requires
  less storage space and therefore less time to
  transmit
• JPEG- Joint Photographic Experts Group of the
  International Standards Organization
• Technique looks for a way to squeeze a single
  image, mainly by eliminating repetitive pixels
  (picture-element dots) within the image
• MPEG- Motion Picture Experts Group
• Weeding out redundancies between neighboring
  images in a stream of video

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6.7 Network

• Communications system connecting two or more
  computers that work to exchange information and
  share resources
• Consist only of microcomputers, or it may
  integrate microcomputers or other devices with
  larger computers
• Controlled by all nodes working together equally
  or by specialized nodes coordinating and
  supplying all resources
• May be simple or complex, self-contained or
  dispersed over a large geographical area

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6.7 Networks (cont)

• The Benefits of Networks
• Sharing of peripheral devices printers, disk
  drives, and scanners can be shared.
• Sharing of programs and data People in an
  organization can use the same software and have
  access to the same files
• Better communications Networks make e-mail
  possible, keeping everyone posted about important
  information
• Security of information Information on a network
  is apt to be backed up (duplicated) somewhere.
  Thus, a fire or flood is less apt to destroy
  essential information
•  Access to databases Networks enable users to
  tap into all kinds of databases

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6.7.1 Network Architecture

• Description of how a computer network is set-up
  (configured)
• Strategies are used in the design

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6.7.1.1 Terms

• Node - any device connected to a network
• Client - node that requests and uses resources
  available from other nodes
• Server - node that shares resources with other
  nodes
• Network operating system (NOS) - software to
  control and coordinate activities between
  computers on a network
• Distributed processing - computing power located
  and shared at different locations
• Host computer - large centralized computer,
  usually a mainframe

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6.7.2 Configuration

• A computer network configuration is also called
  its topology
• Topology is the method of arranging and
  connecting the nodes of a network
• Four principal network topologies
• Star
• Bus
• Ring
• Hierarchical

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6.7.2.1 Star Network

• Number of small computers or peripheral devices
  linked to a central unit
• The central unit may be a host computer or file
  server
• All communications pass through the central unit
• Control is maintained by polling
• Used to provide a time-sharing system
• Common for linking microcomputers to a mainframe

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Star network
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6.7.2.2 Bus Network

• Each device handles its own communications
  control
• There is no host computer however there may be a
  file server
• All communications travel along a common
  connecting cable called a bus
• Common arrangement for sharing data stored on
  different microcomputers
• Not as efficient as star network for sharing
  common resources, but is less expensive

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Bus network
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6.7.2.3 Ring Network

• Each device is connected to two other devices,
  forming a ring
• No central file server or computer
• Messages are passed around the ring until they
  reach their destination
• Often used to link mainframes, especially over
  wide geographical areas
• Useful in a decentralized organization called a
  distributed data processing system

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Ring network
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6.7.2.4 Hierarchical Network

• Hybrid network
• Consists of several computers linked to a central
  host computer
• Similar to a star
• Other computers are also hosts to other, smaller
  computers or to peripheral devices in this type
  of network
• Allows various computers to share databases,
  processing power, and different output devices
• Useful in centralized organizations

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Hierarchical network
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6.8 Network Strategy

• Way of coordinating sharing
• Resources
• Information
• Most common
• Terminal system
• Peer-to-peer system
• Client/Server system
• Enterprise computing

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6.8.1 Terminal System

• Processing power is centralized in one large
  computer, usually a mainframe
• Star and hierarchical networks are typical
  configurations of terminal strategy with the UNIX
  operating system
• Terminal strategy is commonly used in airline
  reservation systems

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6.8.2 Peer-to-Peer System

• Nodes can act as both servers and clients
• Bus network is a typical configuration for this
  type of system
• Common network operating systems for peer-to-peer
  strategy include Novell NetWare Lite, Microsoft
  Windows NT, and Apple Macintosh Peer-to-Peer LANs
• Inexpensive and easy to install
• Work well for small systems with less than ten
  nodes

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6.8.2 Peer-to-Peer LAN
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6.8.3 Client/Server System

• One powerful computer coordinates and supplies
  services to all other nodes on the network
• Provide access to centralized resources such as
  databases, application software, and hardware
• Server nodes in this type of strategy coordinate
  and supply specialized services
• Client nodes in this type of strategy request
  services from the server

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6.8.3 Client/Server System (cont)

• Common network operating systems for
  client/server strategies include Novell NetWare,
  Microsoft Windows NT, IBM LAN Serer and Banyan
  Vines
• Handle very large networks efficiently through
  network management software
• The installation and maintenance cost of this
  type of strategy is greater than peer-to-peer.

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6.8.3 Client/Server LAN
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6.8.4 Enterprise Computing

• the trend toward integrating or connecting all of
  companys computer resources together
• Different network configurations, operating
  systems, strategies

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6.9 Network Types

• Different types of communications channels allow
  different types of networks to be formed
• Telephone lines may connect communications
  equipment within the same building
• Coaxial cable or fiber-optic cable can be
  installed inside building walls to form
  communication networks
• You can also create you own network in your home
  or apartment
• Three important types of networks, according to
  geographical size are LANs, MANs, and WANs

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6.9 Network Types (cont)
102
6.9.1 LAN

• Local area networks
• Computers and peripheral devices are in close
  physical proximity
• Uses microcomputers in a bus organization linked
  with telephone, coaxial, or fiber-optic cable
• Allows all users to share hardware, software, and
  data on the network
• Minicomputers, mainframes, or optical-disk
  storage devices can be added to the network

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6.9.1 LAN (cont)

• Network bridge device may be used to link a LAN
  to other networks with the same configuration
• Network gateway device may be used to link a LAN
  to other networks, even if their configurations
  are different.

104
Components of LAN

• Connection or cabling system wired or wireless
  connection system
• Two or more microcomputers with network interface
  cards enables message to be send and receive
• Network operating system manages the activity of
  a network Novell NetWare, Microsoft Windows
  NT/2000, Unix, and Linux, is the system software
  that.
• Other shared devices Printers, scanners, storage
  devices, and other peripherals

105
Components of LAN (cont)

• Routers, bridges, and gateways
• A router is a special computer that directs
  communicating messages when several networks are
  connected together.
• A bridge is an interface used to connect the same
  types of networks. An example is the Ethernet.
• A gateway is an interface permitting
  communication between dissimilar networksfor
  example, between a LAN and a WAN.

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6.9.2 Components of LAN (cont)
107
6.9.3 MAN

• Computer network that may be city wide
• Used as a link between office buildings in a city
• Use of cellular phone systems expand the
  flexibility of a MAN network by linking car
  phones and portable phones to the network

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6.9.4 WAN

• Computer network that may be countrywide or
  worldwide
• Uses microwave relays and satellites to reach
  users over long distances
• The widest of all WANs is the Internet, which
  spans the entire globe

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6.9.4 WAN (cont)
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6.9.5 Intranets, Extranets, Firewalls

• Intranet - an organizations 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

111
Web Assignments

• 4G Communication
• ASDL (asymmetric digital subscriber line)
• Measat LEO? MEO? Or GEO?
• Similar connection options provided by Telekom
  and other local providers for both wired
  wireless communication