TELECOMMUNICATIONS AND NETWORKS

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CHAPTER 4

• TELECOMMUNICATIONSAND NETWORKS

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Basic Definitions

• Telecommunications the electronic transmission
  of signals for communications
• Telecommunications medium anything that carries
  an electronic signal and interfaces between a
  sending device and a receiving device

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The Components of Telecommunications Systems

• Hardware
• Sending/receiving unit
• Computers, Telephones, Fax, Radio sets, TV sets
• Telecommunications devices
• Telecommunications media
• Telecommunications network

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The Components of Telecommunications Systems
(cont)

• Communications software
• Communications protocols
• Communications applications
• E-mail
• Facsimile
• EDI, EFT.
• Communications provider

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The Components of Telecommunications Systems
Telecommunications Device
Telecommunications Device
Receiving Unit
Sending Unit
Communications Channels and Media
Receiver
Transmitter
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Data and Signals

• Data
• Raw facts
• Static
• Signals
• Transmit data
• Dynamic
• Data and signals may be digital or analog

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Digital and Analog Data

• Analog data is represented as continuous waveform
• Example audio tape
• Digital data is computer data sequence of
  binary 0s and 1s
• Example data stored on the hard drive

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Analog vs. digital signals
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Signals

• Analog signals
• Amplitude height of wave above or below a
  reference point
• Frequency a number of oscillations per time
  unit
• Phase determines the shift in time when wave
  obtains maximal value
• Digital signals
• Baud rate

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Data Transmission

• Digital data using digital signals
• Encoding
• Digital data using analog signals
• Modulation
• Analog data using digital signals
• Pulse code modulation
• Analog data using analog signals
• AM, FM radio, broadcast television

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Telecommunications Devices

• Modem
• an analog network is used to transmit digital
  data
• Fax modem
• Transmits images via standard telephone line
• Multiplexer
• an electronic device that allows a single
  communications channel to carry data transmitted
  simultaneously from many sources
• Private Branch Exchange
• a private telephone network used within an
  organization. Users of the PBX share a certain
  number of outside lines for making telephone
  calls external to the PBX.

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Media for Data Transmission

• Conducted (cable) media
• Twisted-pair wire
• Coaxial cable
• baseband transmission a single signal is used
• broadband transmission available medium is
  divided into multiple channels.
• Fiber optic cable
• Wireless transmitting

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Wireless Media
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Wireless Media (continued )

• Terrestrial microwave
• Satellite - digital transmission
• Geostationary earth orbit (GEO) - 22,300 miles
• Medium earth orbit (MEO) - 6,000 miles
• Low earth obit (LEO) - 400 to 1,000 miles
• Radio
• High bandwidth

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Wireless Media (continued )

• Cellular radio technology
• transfers calls from one cell to another
• Mobile computing
• occurs on radio-based networks that transmit data
  to and from mobile computers
• Personal communications services
• use lower-power and higher-frequency means
• Infrared
• commonly used in remote control units

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Data Communications Links

• Switched Lines
• Telephone lines
• Message is routed by switches from a sender to a
  receiver
• Dedicated Lines
• provide a constant connection between two devices
  and require no switching or dialing

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Telecommunications Carriers

• Local exchange carrier (LEC) a public telephone
  company that provides service to homes and
  businesses within its defined geographical area
• Competitive local exchange carrier (CLEC) a
  company that is allowed to compete with the LECs,
  such as a wireless, satellite, or cable service
  provider
• Long-distance carrier a traditional
  long-distance phone provider, such as ATT,
  Sprint, or MCI

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Telecommunications Services

• Telephone and Dialing Services
• Integrated Services Digital Network (ISDN)
• transfer data in different formats simultaneously
• Digital Subscriber Lines (DSL)
• provide high-speed, digital data transmission
• Cable modem
• T1
• Very fast broadband service
• Wireless data communications

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Networks

• Personal Area Networks interconnect IT devices
  within 33 feet
• Local Area Networks connect two or more
  communications devices within 2,000 feet
• Metropolitan Area Networks networks that serve an
  area of 3 to 30 miles
• Wide Area Networks large networks that serve
  large geographical regions
• International Networks link systems between
  countries

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Computer Networks

• Computer network computers and the
  communications media, devices, and software
  needed to connect two or more computer systems or
  devices
• Network nodes the computers and/or devices on
  the networks

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Network Communications Software

• Functions
• Message formatting
• Error checking
• Communications log
• Data security
• Translation
• Main groups
• Network Operating Systems
• Protocols
• Network Management Software

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Protocols

• NOS refers to a protocol to implement data
  transmission
• Protocol set of rules for data exchange
• Main conceptual components
• Syntax
• Semantics
• Timing

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Protocol Functions

• Line access
• To avoid collisions
• Device identification in the communications path
• Detection of transmission errors
• Recovery after errors
• Verification of correct transmission

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OSI Model

• Open Systems Interconnection network
  architecture model
• Consists of layers
• Each layer describes the services provided.

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Seven Layers of the OSI Model
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A mnemonic for remembering the layers of the OSI
Model
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Devices Connecting Networks

• Bridges connect LANs of the same type
• Switches rout incoming signals from input ports
  to output ports
• Routers connect LANs and WANs, route messages
  through the network
• Hubs receive signals from a sending unit and
  retransmit the signals to all connected units
• Gateways connect dissimilar networks

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Types of Data Processing in Organizations

• Centralized processing all processing occurs in
  a single location or facility
• Decentralized processing processing devices are
  placed at various remote locations
• Distributed processing computers are placed at
  remote locations but connected to each other via
  a network

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Types of Distributed Data Processing in the
Organizations

• Terminal-to-Host Processing
• Peer-to-peer processing
• File Server Processing
• Client/Server Architecture and Processing

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Client/Server Configuration