CCNA 1 Module 3

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CCNA 1 Module 3

• Networking Media

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CCNA 1 Module 3 Objectives

• At the conclusion of this module you should be
  able to
• Discuss the electrical properties of matter.
• Define voltage, resistance, impedance, currents
  and circuits.
• Describe the specifications and performances of
  different cable types.
• Describe coaxial cable and its advantages and
  disadvantages over other types of cable.
• Describe shielded twisted-pair (STP) cable and
  its uses.
• Describe unshielded twisted-pair (UTP) cable and
  its uses.
• Discuss the characteristics of straight-through,
  crossover, and rollover cables and where each is
  used.
• Explain the basics in fiber-optic cable.
• Describe how fibers can guide light for long
  distances.
• Describe multimode and single mode fiber.
• Describe how fiber is installed.
• Describe the type of connectors and equipment
  used with fiber.
• Explain how fiber is tested.
• Discuss the safety issues dealing with fiber.

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Atoms and Electrons

• All matter is composed of atoms that consist of
  the following
• Electrons Particles with a negative charge that
  orbit the nucleus.
• Nucleus Center part of the atom, composed of
  protons and neutrons.
• Protons Particles with a positive charge.
• Neutron Particles with no charge (neutral).

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Atoms and Protons (Continued)

• Electrons stay in orbit, even though the protons
  attract the electrons. Electrons have enough
  velocity to keep orbiting and not be pulled into
  the nucleus.
• Protons do not fly apart from each other because
  of a nuclear force thats associated with
  neutrons.
• Electrons in certain atoms, such as metals, can
  be pulled free from the atom and made to flow.
  The movement of the free electrons is called
  electricity.
• Loosened electrons that stay in one place,
  without moving, and with a negative charge are
  called static electricity. If these static
  electrons jump to a conductor, electrostatic
  discharge (ESD) occurs.
• Atoms, or groups of atoms called molecules, are
  referred to as materials.
• Materials are classified as belonging to one of
  three groups insulators, conductors, and
  semiconductors.

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Voltage

• Voltage is sometimes referred to as electromotive
  force (EMF).
• EMF is related to an electrical force, or
  pressure, that occurs when electrons and protons
  are separated.
• Voltage is related to the electrical fields
  emenating from the charges associated with
  particles such as protons, electrons, etc.
• Voltages is represented as the letter V, and
  sometimes E, for electromotive force.
• The unit of measurement is the volt, and is
  defined as the amount of work, per unit charge,
  needed to separate the charges.

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Current

• Electrical current, or current, is the flow of
  charges created when electrons move.
• In electrical circuits, the current is caused by
  the flow of free electrons.
• When voltage, or electrical pressure, is applied
  and there is a path for the current, electrons
  move from the negative terminal to the positive
  terminal.
• A negative terminal repels the electrons, and the
  positive terminal attracts the electrons.
• The letter I represents current, and its unit of
  measurement is Ampere (amp).
• Amp is defined by the number of charges per
  second that pass by a point along a path.

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Resistance and Impedance

• All materials that conduct electricity have a
  measure of resistance to the flow of electrons
  through them.
• The letter R represents resistance, and the unit
  of measurement is the ohm (O).
• Electrical insulators, or insulators, are
  materials that allow electrons to flow with great
  difficulty or not at all. Examples include
  plastic, glass, air, dry wood, paper, rubber, and
  helium gas.
• Electrical conductors, or conductors, are
  materials that allow electrons to flow through
  them very easily. Examples include copper,
  silver and gold.
• Semiconductors are materials where the amount of
  electricity they conduct can be precisely
  controlled. Examples include carbon,
  germanium, and the alloy gallium arsenide. The
  most important semiconductor is of course,
  silicon.

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Ohms Law

• Defines the relationship between characteristics
  of electricity
• VoltsAmpsOhms
• AmpsVolts/Ohms
• OhmsVolts/Amps
• WattsVoltsAmps

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Circuits

• Current flows in closed loops called circuits.
• These circuits must be composed of conducting
  materials and must have sources of voltage.
• Two ways in which current flows are Alternating
  Current (AC) or Direct Current (DC).
• AC and voltages vary over time by changing their
  polarity, or direction.
• DC always flows in the same direction, and DC
  voltages always have the same polarity.

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Cable Specifications

• Some examples of Ethernet cable specifications
  relating to cable
• type include
• 10BASE-T refers to the speed of the
  transmission at 10Mbps. Type of speed is
  baseband, and the T refers to twisted pair.
• 10BASE-5 refers to the speed of the
  transmission at 10Mbps. Type of speed is
  baseband. The 5 represents the capability of the
  cable, allowing the signal to travel approx. 500
  meters, and is also referred to as Thicknet.
• 10BASE-2 refers to the speed of the
  transmission at 10Mbps. Type of speed is
  baseband. The 2 represents the capability of the
  cable, allowing the signal to travel approx. 200
  meters, and is also referred to as Thinnet.

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Coaxial Cable

• Coaxial cable consists of a hollow outer
  cylindrical conductor that surrounds a single
  inner wire made of two conducting elements.
• For LANs, coaxial cable offers several advantages
  running longer distances, and being less
  expensive than fiber.
• When working with coax, its important to
  consider the size.
• The thicker the cable, the more difficult it is
  to work with it.

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STP Cable

• Shielded twisted-pair combines the techniques of
  shielding, cancellation, and twisting of wires.
• Each pair of wires is wrapped in foil, and the
  four pairs is again wrapped in an overall
  metallic foil.
• STP is usually 150-Ohm, and reduces electrical
  noise within the cable and crosstalk.
• The metallic shielding of STP needs to be
  grounded at both ends, otherwise it becomes
  susceptible to major noise problems.

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UTP Cable

• Unshielded twisted-pair cable is a four-pair wire
  medium used in a variety of networks.
• Each of the 8 individual copper wires is covered
  by insulating material, with each pair of wires
  being twisted around each other.
• UTP relies solely on the cancellation effect to
  limit signal degradation caused by EMI and RFI .
• CAT-5 is the most frequently used and implemented
  installation today.
• UTP has many advantages in that it is easy to
  install and less expensive than other types of
  networking media.

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The Electromagnetic Spectrum

• The light used in optical networks is one type of
  electromagnetic energy.
• When an electric charge moves back and forth, or
  accelerates, electromagnetic energy is produced.
• An important property of any energy wave is the
  wavelength.
• The wavelength of an electromagnetic wave is
  determined by how frequently the electric charge
  that generates the wave moves back and forth.
• Electromagnetic waves are generated the same way,
  and share the same properties.
• They all travel at a rate of 300,000 kilometers
  (186,283 miles per second) per second through a
  vacuum.
• Wavelengths not visible to the human eye are used
  to transmit data over optical fiber.

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Optical Media Total Internal Reflection

• A light ray thats being turned on and off to
  send data into fiber must stay inside the fiber
  until it reaches the far end.
• The ray can not reflect into the material wrapped
  around the outside of the fiber because the
  refraction would cause it to lose part of the
  light energy.
• Two conditions must be met for the light rays in
  fiber to be reflected back into the fiber without
  any loss
• The core of the fiber has to have a larger index
  of refraction than the material surrounding it.
  The material surrounding the core is called
  cladding.
• The angle of incidence of the light ray is
  greater than the critical angle for the core and
  its cladding.
• When both conditions are met, the fiber will have
  total internal reflection, giving a light wave a
  guide for data communications.

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Multimode Mode Fiber

• The part of optical fiber through which light
  rays travel is called the core.
• Once the rays enter the core, there is a limited
  number of optical paths that a light ray can
  follow through the fiber.
• These optical paths are called modes.
• If the core is large enough so that many paths
  can be taken by the light, then the fiber is
  known as multimode fiber.
• Single-mode fiber has a much smaller core, and
  therefore allowing light rays to travel along one
  mode inside the fiber.
• Every fiber-optic cable used in networking
  consists of two glass fibers encased in separate
  sheaths.
• One fiber carries data from device A to device B,
  while the other fiber carries data from device B
  to device A making it full-duplex.
• The two types of light sources for multimode
  fiber are LEDs (Infrared Light Emitting Diodes)
  or VCELs (Vertical Cavity Surface Emitting
  Lasers). LEDs are used more often in multimode
  fiber than the VCELs.

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The 5 Elements of Fiber-Optic Cable

• There are 5 elements of fiber-optic cable.
• Core light transmission element at the center
  of the optical fiber. All light signals travel
  through the core. The core is typically glass
  made of a combination of silica and other
  elements.
• Cladding also made of silica, but with a lower
  index of refraction than the core. Light rays
  traveling through the core reflect off of this
  core-to-cladding interface as they move through
  the fiber. Standard multimode fiber uses a 62.5
  or 50 micron core and a 125 micron cladding
  (62.5/125 or 50/125)
• Buffer material that is usually plastic and
  helps shield the core and cladding from damage.
• Strength material surrounds the buffer,
  preventing the fiber from being stretched when
  installers pull it. Material that is often used
  is Kevlar.
• Outer jacket surrounds the cable to protect the
  fiber against abrasion, solvents, and other
  contaminants. Color of the outer jacket in
  multimode fiber is usually orange.

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Multimode Fiber
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Single Mode Fiber

• Single mode fiber consists of the same parts as
  multimode.
• The outer jacket of single mode fiber is usually
  yellow.
• The major difference between multimode and single
  mode fiber is that single mode allows only one
  mode of light to propagate through the smaller
  core.
• The single mode core is 8 to 10 microns in
  diameter, with 9 micron cores being the most
  common.
• 9/125 indicates that the core of the fiber is 9
  microns, with a 125 micron cladding.
• Infrared laser is used as the light source of
  single mode fiber, resulting in the ray pulses
  being transmitted in a straight line.
• Because of its design, single mode fiber is
  capable of higher bandwidth and greater cable run
  distances than multimode fiber.
• Single mode fiber can carry LAN data up to 3000
  meters, while multimode is only capable of 2000
  meters.

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Single Mode Fiber
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Other Optical Components

• There are other optical components that play a
  necessary role in data
• transmission.
• Transmitter receives data to be transmitted
  from switches and routers. The data is
  electrical signals, and the transmitter converts
  the electrical signals into light pulses.
• Receiver detects the light pulses that arrive
  from the fiber and convert them back into an
  electrical signal.
• Connectors attached to the fiber ends so the
  fibers can be connected to the ports on the
  transmitter and receiver. The connector used for
  multimode fiber is the SC, or Subscriber
  Connector, while the ST, or Straight Tip
  connector is used for single mode fiber.
• Repeaters optical amplifiers that receive
  attenuating light pulses traveling long
  distances.
• Fiber patch panels increase the flexibility of
  the optical network by allowing quick changes to
  the connection of devices like switches or
  routers.

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Fiber Components
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Signals and Noise in Optical Fibers

• Although fiber is the best of all the
  transmission media at carrying large amounts of
  data over long distances, it is not without
  problems.
• When light travels through fiber, some of the
  light energy is lost, the further the light
  travels, the more the signal loses strength.
• This attenuation of the signal is due to several
  factors, one being scattering.
• Scattering is caused by distortions in the fiber
  that reflects and scatters some of the light
  energy.
• Absorption is another cause, making the light
  signal dimmer.
• Dispersion of a light flash also limits
  transmission distances on a fiber, meaning the
  spreading of pulses of light as they travel down
  the fiber.

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Installation, Care and Testing of Fiber

• A major cause of too much attenuation is caused
  by improper installation.
• If fiber is stretched or curved too tightly, it
  can cause tiny cracks in the core that scatter
  the light rays.
• When the fiber has been pulled correctly, it must
  be cut and properly polished to ensure smooth
  ends.
• The connector is then attached to the fiber end.
• Once the fiber optic cable and connectors have
  been installed, then the ends of the fibers must
  be kept clean.
• The ends of the fibers are covered with
  protective covers to prevent damage to the ends.
• Scattering, absorption, dispersion, improper
  installation, and dirty fiber ends diminish the
  strength of the light signal and referred to as
  noise.

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Wireless LAN Organizations and Standards

• A key technology within the 802.11 standard is
  Direct Sequence Spread Spectrum (DSSS).
• DSSS applies to wireless devices operating within
  the 1 to 2 Mbps range.
• 802.11b, or high-speed wireless, refers to DSSS
  systems that operate at 1, 2, 5.5 and 11 Mbps.
  These devices achieve higher data throughput by
  using a different coding technique than 802.11.
• 802.11a covers WLAN devices operating in the 5
  GHz transmission band. Using this range
  disallows interoperability of 802.11b devices.
• 802.11g provides the same throughput as 802.11a,
  but with backwards compatibility for 802.11b
  devices using Othogonal Frequency Division
  Multiplexing (OFDM) modulation technology.

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Wireless Devices and Technologies

• Equipped with wireless NICs, an ad hoc network
  could be established, comparing it to a
  peer-to-peer wired network.
• Both devices act as servers and clients, and
  security is set at a minimum along with
  throughput
• To solve the problem of compatibility, an access
  point is installed to act as the central hub
  for the WLAN.
• The range for an access point is usually between
  300 to 500 feet (91.44 152.4 meters).
• When a client is activated within the WLAN, it
  will start listening for a compatible device so
  it can associate, or scan.

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How Wireless LANs Communicate

• After establishing connectivity to the WLAN, a
  node will pass frames.
• WLANs use three types of frames control,
  management, and data.
• Since radio frequency is a shared medium,
  collisions occur just as on shared medium.
• For that reason WLANs use CSMA/CA, Carrier Sense
  Multiple Access/Collision Avoidance.
• When a source node sends a frame, the receiving
  node returns a positive ACK.
• This overhead when combined with the collision
  avoidance protocol reduces the actual data
  throughput to a maximum of 5.0 to 5.5 Mbps on an
  802.11b WLAN rated at 11Mbps.
• Performance on the network will also be affected
  by signal strength and degradation in signal
  quality due to distance interference. The
  further away from an access point, the lower the
  data rate.

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Authentication and Association

• WLAN authentication occurs at Layer 2, and is the
  process of authenticating the device, not the
  user.
• Authentication and Association Types
• Unauthenticated and unassociated node is
  disconnected from the network and not associated
  with an access point.
• Authenticated and unassociated node has been
  authenticated on the network, but not yet
  associated with the access point.
• Authenticated and associated node is connected
  to the network and able to transmit and receive
  data through the access point.
• Methods of authentication
• Open system open connectivity in which only the
  SSID must match. May be used in secure or non
  secure environments, although the ability of low
  level network sniffers discovering the SSID of
  the WLAN is high.
• Shared key process requires using the Wireless
  Equivalency Protocol (WEP) encryption. The
  access point is configured with an encrypted key
  and nodes attempting to access the network via
  the access point must have the matching key. WEP
  keys do provide a higher level of security than
  open system, but arent totally hack proof.

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Signals and Noise on a WLAN

• When using radio frequency technology many kinds
  of interference must be taken into consideration.
• Narrowband is the opposite of spread spectrum,
  and as the name implies it does not affect the
  entire frequency spectrum of the wireless signal.
• One solution to narrowband interference is
  changing the channel that the access point is
  using.
• Another obvious source of a signal problem is the
  transmitting station and antenna type.
• A higher output station will transmit the signal
  further and a parabolic dish antenna that
  concentrates the signal will increase the
  transmission range..

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Wireless Security

• Where wireless networks exist, there is little
  security.
• New security protocols such as VPN (Virtual
  Private Networking) and EAP (Extensible
  Authentication Protocol) are emerging
• With EAP, the access point does not provide
  authentication to the client, but passes the
  duties to a dedicated server that is designed for
  that purpose.
• Using a dedicated server VPN technology creates a
  tunnel on top of an existing protocol such as IP.
  This provides a Layer 3 connection instead of a
  Layer 2 connection between the access point and
  the sending node.

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Summary

• You should now be able to
• Discuss the electrical properties of matter
• Define voltage, resistance, impedance, currents
  and circuits
• Describe the specifications and performances of
  different cable types
• Describe coaxial cable its advantages/disadvanta
  ges with other cables
• Describe shielded twisted-pair (STP) cable and
  its uses
• Describe unshielded twisted-pair (UTP) cable and
  its uses
• Discuss the characteristics and use of
  straight-through, crossover, and rollover cables
• Explain the basics in fiber-optic cable
• Describe how fibers can guide light for long
  distances
• Describe multimode and single mode fiber
• Describe how fiber is installed
• Describe the type of connectors and equipment
  used with fiber
• Explain how fiber is tested
• Discuss the safety issues dealing with fiber

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Questions???