Telecommunications

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Chapter 9 Telecommunications
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Telecommunications

• Telecommunications The communication of
  information by electronic means, usually over
  some distance (e.g.. telephone, email)

• Telecommunications system contains
• Sender Receiver
• Message - Data that is transmitted as a signal
  over a
• communications line

• Channel - The medium by which data or voice are
  transmitted
• between sender and receiver (e.g., wire,
  optical cable, air).
• Other equipment (switch, relay, modem, gateway,
  etc.)

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Types of Signals

• Analog signal
• Continuous waveform
• Can get all the ranges
• Use voice communications
• Example cassette tape

• Digital signal
• Discrete waveform
• Two states 0 and 1 (On-off electrical pulses)
• Use data communications
• Example compact disk (CD)

Modem (MOdulation / DEModulation) Converts
digital into analog, and analog into digital
signals
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Transmission Speed

• Total amount of information that can be
  transmitted through a telecommunications channel
  (bits/second)

bpsbits per second Kbpskilobits per
secondMbpsmegabits per second Tbpsterabits
per second
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Telecommunications Technologies Systems

• Telephone
• Oldest and still most pervasive telecommunication
  technology. Based on converting sound into
  electrical signals and signals back to sound.
• Cellular Telephone wireless uses air as the
  channel (radio waves) can access Internet.
• Facsimile (Fax)
• Machine that transforms print content into
  electrical signals and transmits them over
  telephone lines.

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Telecommunications Technologies Systems

• Personal Digital Assistant (PDA)
• Handheld computer, often with built-in wireless
  telecommunications capability
• Satellite
• Part of global telecommunications systems
• A radio relay station in orbit above the earth
  that receives, amplifies and redirects analog and
  digital signals contained within a carrier
  frequency.

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Telecommunications Technologies Systems

• EDI
• Software for transferring electronic documents
  between trading partners. EDI software, computers
  and the channels connecting them make an EDI
  system.
• Teleconferencing
• A telecommunication system supporting oral and
  text-based communication among people at
  different locations (e.g., phone conference call,
  Internet chat, etc.)
• Videoconferencing
• A telecommunication system supporting
  communication based on image and video (computers
  have cameras mounted, and participants see each
  other).

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Networks

• Network - A set of nodes (computers, printers,
  and other equipment) and links among them.
• Types of networks
• Topology (configurations of nodes and links
  e.g., star network)
• Geographic scope LAN vs. WAN
• Data transfer method Circuit vs. Packet

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Star Network

• All computers are connected to a central node
  (e.g. hub, computer, switch, controller).
• All communications between computers must pass
  through the central node.

hub, switch,controller,computer
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Bus Network

• All computers are linked by a single circuit
• All messages are broadcast to the entire network
• No central node messages can travel in both
  directions along the cable.

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Ring Network

• All computers are linked by a closed loop
• Data is passed in one direction from one device
  to another
• Each computer operates independently so that if
  one fails, communication through the network is
  not interrupted

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LAN vs. WAN

• Local Area Network (LAN)
• Network covering a smaller area (one or more
  buildings like campus)

• Wide Area Network (WAN)
• Network covering a larger area (a region, world)
• Examples IBMs SNET, Internet

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Circuit Switching

• Circuit Switching
• Entire message travels from switch to switch
• Used for analog signals
• (classical telephone networks)

Source TechWeb
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Packet Switching

• Packet Switching
• Sender breaks message into small packets
• Packets are routed in the most economical way by
  different routes
• Receiver reassembles the message
• Internet works this way

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Network Hardware

• Bridge
• A device that connects segments of the same or
  similar networks
• Gateway
• A communications processor that connects
  dissimilar networks
• Router, Switch, Hub
• Devices for managing message traffic

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Network Software

• Network Operating System (NOS)
• Routes and manages communications on the network
• Coordinates resources
• Network Protocol
• Set of rules and procedures that govern
  transmission between the components in a network
• E.g., TCP/IP