Telecommunications and Networks

1
Chapter 6

• Telecommunications and Networks

2
Agenda - I

• What Is Telecommunications?
• What Is Data Communications?
• What are the Electromagnetic Waves?
• What is Electromagnetic Signal Frequency?
• What is a Communication Line Bandwidth?
• Digital Versus Analog Data
• Components of Communication Networks
• Contacted and Radiated Media
• Twisted Pair Wire
• Coaxial Cable
• Fiber-Optic Cable
• Broadcast Radio
• Microwave
• Satellite Microwave

3
Agenda - II

• Cellular Radio
• Infrared Transmission
• Selection of Media
• Transmission Modes
• Telecommunications Devices
• Telecommunications Carriers and Services
• Networks LANs and WANS
• Terminal-to-Host, File Server, and Client/Server
  Systems
• Network Topologies
• Star Topology
• Bus Topology
• Ring Topology
• Coordinating Data Communications
• Popular Communication Protocols
• Home and Small Business Networks

4
What Is Telecommunications?

• Telecommunications is the electronic
  transmission of signals for communications
  between a sender and a receiver. The methods
  include telephone, radio, and television, etc.

5
What Is Data Communications?

• Data communications is a specialized subset of
  telecommunications that refers to electronic
  collecting, processing, and distributing of data
  between computer system devices. This definition
  excludes the transmission of data to local
  peripherals such as disk, tape, and printers.
• Data communications is sometimes called
  networking because it involves the transmission
  of data over a network.

6
What are the Electromagnetic Waves?

• The motion of electrically charged particles
  produces electromagnetic waves. These waves are
  also called "electromagnetic radiation" because
  they radiate from the electrically charged
  particles.
• Radio waves, microwaves, visible light, and x
  rays are all examples of electromagnetic waves
  that differ from each other in wave length.
• Electromagnetic waves need no material medium for
  transmission. Light and radio waves can travel
  through interplanetary and interstellar space
  from the sun and stars to the earth. Regardless
  of their frequency and wavelength,
  electromagnetic waves travel at a speed of
  299,792 km (186,282 mi) per second in a vacuum.

7
What is Electromagnetic Signal Frequency?

• Frequency refers to the number of times a current
  (electromagnetic wave) passes through a complete
  cycle. The measure of frequency is a Hertz (Hz),
  which represents one cycle per second.
• Frequencies are represented from a number from 0
  Hertz to 300 GHz (called the electromagnetic
  spectrum).
• KKilo1,000, MMega1,000,000,
  GGiga1,000,000,000

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What is a Communication Line Bandwidth?

• Communication line bandwidth is the difference
  between the minimum and maximum range of
  frequencies allowed by the communication line.
• Bandwidth higher frequency - lower frequency.
  For example A wire transmits in a frequency
  range from 100 Hz to 2,500 Hz. Its bandwidth is
  2,400 Hz.
• Bandwidth is important because it indicates how
  much data can be transmitted over a specific
  channel. A wider bandwidth allows more data to be
  transmitted at a given time.

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Digital Versus Analog Data

• Analog signals are represented by rising and
  falling voltages (waves) such as light, voice,
  video signals that are in a continuous form.
• Digital signals are represented pulse of fixed
  voltages such as binary signals (o or 1) that are
  in a discrete form and can be used by computer.

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Components of Communication Networks

• In order for communication to occur, there must
  be a source, a medium, a receiver and a message.
• The source (sender) is the device that sends the
  message (transmitter) and is any device that can
  be connected to the network like a PC or a
  telephone.
• The medium connects the source with the receiver
  and can be a copper cable, a fiber-optic cable,
  airwaves or another physical path.
• The receiver is the device that accepts the
  message.
• The message can be a file, a request, a response,
  a status message, a control message or
  correspondence. The message must be
  understandable.

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Contacted and Radiated Media

• A Communication network cannot exist without a
  medium to connect the source and receiver. If
  this medium can be seen physically, it is
  considered a contacted medium.
• Radiated media, or wireless media, do not use
  physical wires to transmit data. With radiated
  media, the signal is radiated through the air,
  water and vacuum of space.

12
Twisted Pair Wire

• Twisted pair wire consists of two wires twisted
  together a specific number of times to create a
  magnetic field that reduces the amount of
  interference in the line.
• In shielded twisted pair (STP), the twisted core
  is placed into a cladding shield, which is
  wrapped with wires to absorb any interference.
  Used when you have to pack many wires together in
  a small space or in an environment with a lot of
  electrical equipment. STP wires are reliable in
  high-speed areas.
• In unshielded twisted pair (UTP), the twisted
  core is just covered with the plastic material
  without the use of cladding material. Often used
  in telephone systems. UTP lines are grouped into
  categories based on their quality and use.

13
Coaxial Cable

• Coaxial cable is composed of a single copper wire
  (the inner conductor), surrounded by a insulating
  cladding material called a shell. The shell is
  then surrounded by a second conductor (usually a
  braided copper shield), which gives the cable the
  ability to transmit much more data than a twisted
  pair wire. Finally, the entire cable is enclosed
  in a rubber outer cladding called the jacket.
• Coaxial cables allow the use of broadband and
  baseband transmission. In broadband transmission,
  a single cable is divided into many channels,
  each of which can carry a different transmission.
  The carrier wave is divided into bandwidths and
  separated by guardbands to prevent interference
  between the signals. In baseband transmission,
  only a single signal is transmitted over the
  cable.
• A single coaxial cable can carry 1,000
  simultaneous voice and data transmissions.

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Fiber-Optic Cable

• Fiber-optic cable uses light to transmit data
  signals. The core of the fiber-optic cable is
  composed of one or more thin tubes of glass or
  plastic. Each tube is called the optical fiber
  and is as thin as the human hair. A
  light-emitting diode (LED) or a laser is used to
  send light through the fibers.

15
Broadcast Radio

• Broadcast radio involves sending signals through
  the air between transmitters, at frequencies from
  30 to 300 MHz.
• Amplitude modulation (AM) radio uses a low
  frequency and allows it to broadcast its signal
  far (530-1605 KHz).
• Frequency modulation (FM) radio uses a higher
  frequency and the signal travels shorter
  distances (87.6-108 MHz).
• Short wave radios transmit signals over long
  distances and utilize specific restricted
  frequency ranges.
• Television stations use the ultra-high frequency
  (UHF) channels and very-high frequency (VHF)
  channels to transmit TV programs in the ranges
  400-900 MHz and 50-225 MHz respectively.

16
Microwave

• Microwave transmission uses very-high frequency
  signals (3,000 MHz to 30 GHz) to transmit signals
  between stations. The high frequency permits
  large amounts of data to be transmitted. Unlike
  broadcast radio signals, which are
  omnidirectional, microwave transmission is
  focused and unidirectional. That means means that
  microwave stations use line-of-sight transmission
  and signals travel in straight line. The two
  types of microwave transmission are terrestrial
  and satellite
• Terrestrial microwave transmissions are sent
  between two microwave stations on the earth
  (earth station). It is the most common form of
  long-distance communication.
• Satellite microwave transmissions involve sending
  microwave transmissions between two or more
  earth-based microwave stations and a satellite.

17
Satellite Microwave

• Most communications satellites are placed into
  orbit 22,300 miles above the earth's surface. The
  earth's gravity keeps the satellite in orbit at
  the same rate as the earth (geosynchronous
  orbit). Such satellites are called geosynchronous
  orbiting satellites (GEOS).
• Low earth orbiting satellites (LEOS) orbit the
  earth at a height of 325-1,000 miles and they
  orbit around the poles (not in a fixed position
  relative to the earth).
• Medium earth orbiting satellites (MEOS) are
  similar to LEOS but are positioned at
  6,000-10,000 miles above the earth.
• Because microwaves use line-of-sight, the
  satellite signal can only reach a part of the
  earth. This area is called a footprint.

18
Cellular Radio

• Cellular telephones actually are radio devices
  that use cellular radio (form of broadcast radio
  with restrictions on how far the signal is
  transmitted) to transmit voice and data. The
  broadcast area of a cellular radio system is
  divided into cells. Here is how it works
• 1. Using a cellular phone, the caller dials a
  number. The signal is sent from the cell phone's
  antenna to the cellular antenna located in cell
  1.
• 2. The signal is sent to the regional cellular
  phone switching office.
• 3. The signal is switched to the local Telephone
  Company switching station.
• 4. The signal is now in the regular phone system
  and the call is switched to the number dialed.

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Infrared Transmission

• Infrareds (IR) transmission involves sending
  light signals at a frequency between visible
  light and radio waves. Commonly used in TV remote
  controls, now is used to provide LAN connections.
• It is a line-of-sight transmission and has a
  maximum coverage of 30 to 80 feet.
• Increasingly, computers and devices such as
  printers come with IrDA ports, which enable the
  transfer of data without the use of cables.

20
Selection of Media

• In developing any network, the designer must take
  into account
• The cost of the medium
• The speed at which it can transmit
• The error rate that should be expected using the
  medium
• The security of the data transmitted over the
  medium
• The transmission distance
• The availability of the medium
• The environmental constraints

21
Transmission Modes

• Signals can be transmitted though
  telecommunications media in a number of different
  ways
• In simplex transmission, data can flow only in
  one direction
• In half-duplex transmission, data can flow in
  both directions but it can only flow in one
  direction at any point in time
• In full-duplex transmission, data can flow in
  both directions at the same time

22
Telecommunications Devices

• Telecommunication devices are hardware devices
  that allow electronic communication to occur.
• Modems translate data from digital to analog and
  vice versa
• Fax devices allow the transmission of text,
  graphs and other digital files via telephone
  lines
• Multiplexers allow several signals to be sent
  over one channel
• Communication processors are computers devoted to
  communications management
• Bridges, Routers, Gateways, and Switches

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Telecommunications Carriers and Services

• Several companies provide telecommunications
  media, devices and services called
  telecommunications carriers
• Switched lines are standard telephone lines
  provided by telephone companies
• Dedicated lines provide a constant connection
  between two points
• Private Branch Exchange (PBX) is a communications
  system that can manage both voice and data
  transfer within a building and an outside line
• Wide-area Telecommunications Service (WATS) is a
  billing method for heavy users of voiceband media
  (the 1-800 lines)
• Integrated Serviced Digital Network (ISDN) is a
  technology that uses existing common-carrier
  lines to simultaneously transmit voice, video and
  image data in digital form
• Digital Subscriber Line (DSL) uses existing phone
  wires to provide transmission speeds exceeding
  500 Kbps.
• T1 carrier increases the number of voice calls
  through the existing cables

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Networks LANs and WANS

• A Computer Network is a collection of computers
  and peripherals linked together so that they can
  share applications, data, and resources such as
  printers, modems, and CD-ROMs.
• A Local Area Network (LAN) enables computer users
  to transfer files, manipulate data, and share
  resources within the same office or building.
• A Wide Area Network (WAN) ties together large
  geographic regions using microwave, satellite, or
  telephone lines.

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Home and Small Business Networks
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Terminal-to-Host, File Server, and Client/Server
Systems

• In a Terminal-to-Host network, the application
  and database reside on one host computer and the
  user interacts with the application and data
  using a dump terminal.
• In the File and Client/Server model, certain
  machines and devices on the network are dedicated
  to providing services to the network. (cost,
  performance, security, privacy, virus,
  multi-vendor)
• A Peer-to-peer network allows personal computers
  to be linked together to share their resources.
  In such an arrangement, a single peripheral as a
  printer connected to a workstation can be used by
  other network users. Users can also share
  programs and data.

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Network Topologies

• The Topology of the Network is the networks
  physical layout. This is what defines the path
  that information must take to move from one place
  to another on the network. The 3 basic topologies
  are Star, Bus, and Ring

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Star Topology

• In a Star topology, all of the workstations and
  servers are connected to a centrally located
  device called a hub. The hub controls and directs
  messages.

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Bus Topology

• In a Bus or linear network topology, all
  workstations and servers are connected to a
  single cable called the bus. At the ends of the
  network circuit, a device called terminator is
  installed to complete the network circuit.

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Ring Topology

• In a Ring topology, all workstations and servers
  are chained together in much the same way as they
  are in a bus network. The exception is that the
  cables at the ends of the network are connected
  together rather than terminated.

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Coordinating Data Communications

• Polling is a procedure in which the main computer
  checks each device one at a time to see if there
  are any messages waiting to be communicated to
  other network devices.
• Token passing is a technique in which an
  electronic "token" is passed from one device to
  another. If a device has the token and a message,
  the message can be transmitted.
• Contention is a procedure in which a device
  checks to see if a message is currently being
  transmitted. If there are no messages being
  transmitted, the device starts the
  message-sending sequence.

32
Popular Communications Protocols

• Ethernet is the most widely used networking
  protocol in use today, mainly because of the low
  cost of implementing the network and the lack of
  need for centralized control. Ethernet can be
  used to link many different types of computers
  together. Ethernet can run on coax, twisted pair,
  and fiber optic cabling. All cabling schemes
  support 10 Mbps speeds but the latest (10baseF)
  can also support 100 Mbps.
• The Transmission Control Protocol/Internet
  Protocol (TCP/IP) was developed in 1973 for use
  in the APRANet network. Over time, TCP/IP has
  developed to be a suite network protocols that
  will support remote log-in capabilities, file
  transfer, e-mail, and routing. It is most
  commonly associated with the Internet since in
  1983 TCP/IP was adopted as the Internet standard.
• Bluetooth is a communications standard using
  short-range radio wave that defined by Ericsson
  for wireless communications

33
Communications Software

• Network operating system (NOS)
• Network management software
• Simple Network Management Protocol (SNMP)
• Fault detection
• Performance management

34
Points to Remember - I

• What Is Telecommunications?
• What Is Data Communications?
• What are the Electromagnetic Waves?
• What is Electromagnetic Signal Frequency?
• What is a Communication Line Bandwidth?
• Digital Versus Analog Data
• Components of Communication Networks
• Contacted and Radiated Media
• Twisted Pair Wire
• Coaxial Cable
• Fiber-Optic Cable
• Broadcast Radio
• Microwave
• Satellite Microwave

35
Points to Remember - II

• Cellular Radio
• Infrared Transmission
• Selection of Media
• Transmission Modes
• Telecommunications Devices
• Telecommunications Carriers and Services
• Networks LANs and WANS
• Terminal-to-Host, File Server, and Client/Server
  Systems
• Network Topologies
• Star Topology
• Bus Topology
• Ring Topology
• Coordinating Data Communications
• Popular Communication Protocols
• Home and Small Business Networks