Semester 1 Module 3

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Semester 1 Module 3

• Networking Media

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• Copper cable is used in almost EVERY LAN
• Many types
• Each type has Adv. and Disadv.
• Proper selection of cabling is key to efficient
  network operation
• Copper uses electrical current to transmit info
  thus need to understand some BASICS of electricity

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• Fiber optic (optical fiber) is the MOST
  frequently used medium for the longer, high BW,
  point-to-point transmission required on LAN
  backbone and on WANs
• Uses light to transmit data through thin glass or
  plastic fiber

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Basics of Electricity

• All matter is composed of atoms. The Periodic
  Table of Elements
• Atoms have 3 parts
• neutron
• electron
• proton

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Atoms and Electrons

• Electrons - Particles with a negative charge
  that orbit the nucleus
• Protons Particles with a positive charge
• Neutrons Particles with no charge (neutral)
• Opposite charges attract and like charges repel.
• Neg charges repel other Neg charges
• Pos charges repel other Pos charges
• Pos charges attract Neg charges

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Voltage V

• 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.
• Protons and electrons love each other when you
  separate you get a volt
• Remember the flow of electricity is really the
  flow of electrons
• Voltage is represented by the letter V
• A Volt is the amt of work that is needed to
  separate he charges

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Voltage Also referred to as electromotive force
(EMF)

• The force or pressure caused by the separation of
  electrons and protons
• When measuring voltage with a multimeter the
  setting must be set to AC or DC -- two kinds of
  voltage
• Multimeters can measure voltage, resistance,
  continuity, and some models also measure current

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Direct Current (D.C.)

• Always flows in the same direction, and DC
  voltages always have the same polarity
• One terminal is always positive, and the other is
  always negative
• Ex. car, flashlight battery

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Alternating Current (A.C.)

• Voltage source regularly change to negative and
  positive and back again
• Varies with time by changing polarity, or
  direction, about 60 times per second
• AC flows in one direction, and then reverses its
  direction and repeats the process

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Resistance

• The inability or ability for electron movement
• Material that offers very little, or no,
  resistance, are called conductorscopper, silver,
  gold.
• Flow of electrons is allowed no resistance to
  flow
• Those that do not allow the current to flow, or
  severely restrict its flow, are called
  insulatorsplastic, rubber, air, paper, glass.
• The amount of resistance depends on the chemical
  composition of the materials.

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Resistance

• The letter R represents resistance. The unit of
  measurement for resistance is the ohm (O ). The
  symbol comes from the Greek letter, Omega.
• The term resistance is generally used when
  referring to DC circuits

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Insulators, Conductors, Semiconductors
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• All materials that conduct electricity have a
  measure of resistance to the flow of electrons
  through them.
• These materials also have other effects called
  capacitance and inductance that relate to the
  flow of electrons. Impedance includes resistance,
  capacitance, and inductance and is similar to the
  concept of resistance.

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Current

• Electrical current is the flow of charges created
  when electrons move. In electrical circuits, the
  current is caused by a flow of free electrons.
• When voltage is applied and there is a PATH for
  the current, electrons move from the negative
  terminal to the positive
• Current can be thought of as the AMOUNT OF VOLUME
  OF ELECTRON TRAFFICE THAT FLOWS
• Voltage can be thought of as the SPEED OF
  ELECTRON TRAFFIC
• The combo of amperage (ampere) and voltage equal
  wattage
• It is the current or amperage in an electrical
  circuit that really does the work
• Static electricity has a high voltage can jump
  a gap of an inch or more but has a low amperage
  and as a result can create a shock but not
  permanent injury

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Circuits

• Current flows in closed loops are called
  circuits. These circuits must be composed of
  conducting materials, and must have sources of
  voltage
• Three required parts
• source or battery
• complete path closed loop
• Conducting material

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Copper Media

• Most common medium for signal wiring
• Copper wires are the components of a cable that
  carry the signals from the source computer to the
  destination computer
• Well suited
• Conduct electrical current corrosion resistance
  malleability--easy to shape does not crack can
  be shaped when it is hot or cold strength
• Two types used for networks twisted-pair (2
  types) and coaxial cable

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Factors to know when choosing cable type

• Speeds
• Achievable bit transmission speeds
• Transmission Type
• analog or digital
• Distance
• Maximum distance before fatal attenuation

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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. It can be run longer distances than
  STP and UTP cable without the need for repeaters.
  
• More expensive than UTP, but less expensive than
  fiber-optic
• The purpose of the conductive braid around the
  insulator
• Acts as a second wire in the cable
• A shield for the inner conductor
• Reduces the amount of outside interference

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• Comes in several sizes
• General rule -- the more difficult the media is
  to install, the more expensive it is to install
• Largest - 1 cm - thicknet
• Used as Ethernet backbone cable
• Great transmission length and better noise
  rejection
• More expensive than twisted-pair
• Almost never used except for special-purpose
  installs

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Cable Specifications

• 10BASE5
• speed of transmission at 10 Mbps
• type of transmission is baseband
• 5 represents the capability of the cable to allow
  the signal to travel for approximately 500 meters
  before attenuation could disrupt the ability of
  the receiver to appropriately interpret the
  signal being received.
• often referred to as Thicknet

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• Thinnet - .35 cm
• Useful for cable installs that make many twists
  and turns
• Easier to install than thicknet, thus cheaper to
  install (cheapernet)
• Both types must be carefully and properly
  grounded -- increases complexity of the install
• For this reasons, coaxial cable in no longer
  commonly used in Ethernet networks
• Many bus topologies still utilize coaxial
• However, IEEE no longer recommend such
• Nearly all new LANs use Ethernet extended star
  topology and a combo of UTP and fiber

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Cable Specifications

• 10BASE2
• speed of transmission at 10 Mbps
• type of transmission is baseband
• The 2, in 10BASE2, represents the capability of
  the cable to allow the signal to travel for
  approximately 200 meters, before attenuation
  could disrupt the ability of the receiver to
  appropriately interpret the signal being
  received. 10BASE2 is often referred to as
  Thinnet.

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Cable Specifications

• Cables have different specifications and
  expectations pertaining to performance.

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• Twisted for two reasons
• Pairs of wires carry signals in opposite
  directions, so that the two magnetic fields also
  occur in opposite directions and cancel each
  other out -- cancellation twisting the pair
  holds the two wires closer together to ensure
  effective cancellation
• A copy of the data is sent on each wire--copies
  are mirror images of each other
• When the data is received, one copy is inverted
  and the two signals are compared
• Two basic types shielded twisted pair (STP) and
  unsheilded twisted pair (UTP)

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Shielded Twisted-Pair Cable (STP)

• Shielded twisted-pair cable (STP) combines the
  techniques of shielding, cancellation, and
  twisting of wires
• Shielded twisted-pair cable shares many of the
  advantages and disadvantages of unshielded
  twisted-pair cable (UTP). STP affords greater
  protection from all types of external
  interference, but is more expensive and difficult
  to install than UTP
• Must be grounded at both ends for higher freq
  signals
• Reduces internal external interference
• A new hybrid of UTP with traditional STP is
  Screened UTP (ScTP), also known as Foil Twisted
  Pair (FTP)

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Unshielded Twisted-Pair (UTP)

• Four-pair wire medium used in a variety of
  networksCat1-Cat6.
• Pairs carry signals in opposite direction thus
  the magnetic fields also occur in opposite
  directions and cancel each other out
  cancellation twisting the pair holds the two
  wires closer to ensure the cancellation of EMI
  and RFI
• TIA/EIA-568-A contains specifications governing
  cable performance.
• RJ-45 connector
• CAT 5 is the one most frequently recommended and
  implemented in installations today

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Twisting wire pairs limits signal degradation
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STP vs. UTP

• Speed and throughput 10 100 Mbps
• Avg. per node Moderately Expensive
• Media and conductor sizeMedium to Large
• Max. cable length 100m

• Speed and throughput 10 100 1000Mbps
• Avg. per node Least Expensive
• Media and conductor size small
• Max. cable length 100m

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UTP Straight-through Cable
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UTP Cross-over Cable
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UTP Rollover Cable
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Use straight-through cables for the following
cabling(for different devices)

• Switch to router
• Switch to PC (host) or server
• Hub to PC or server

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Use crossover cables for the following
cabling(for similar devices)

• Switch to switch
• Switch to hub
• Hub to hub
• Router to router
• PC to PC
• Router to PC

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The electromagnetic spectrum

• The light used in optical fiber networks is one
  type of electromagnetic energy
• This energy, in the form of waves, can travel
  through a vacuum, the air, and through some
  materials like glass
• Because electromagnetic waves are all generated
  in the same way, they share many of the same
  properties. They all travel at a rate of 300,000
  kilometers per second (186,283 miles per second)
  through a vacuum

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• Human eyes were designed to only sense
  electromagnetic energy with wavelengths between
  700 nanometers and 400 nanometers.
• Wavelengths that are not visible to the human eye
  are used to transmit data over optic
  fiber--infrared light
• Wavelength of the light in optical fiber is
  either 850 nm, 1310 nm, or 1550 nm
• These were selected because they travel through
  optical fiber better than other wavelengths

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Optical Media

• Ray model of light
• When electromagnetic waves travel out from a
  source, they travel in straight lines. These
  straight lines pointing out from the source are
  called rays
• Light travels at different speeds--slower through
  air, water and glass
• Incident ray - when a light ray crosses the
  boundary from one material to another, some of
  the light energy in the ray will be reflected
  back
• Why you can see yourself in a window glass

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Reflection

• When a ray of light (the incident ray) strikes
  the shiny surface of a flat piece of glass, some
  of the light energy in the ray is reflected
• The angel at which a light ray strikes a
  reflective surface determines the angle that the
  ray will reflect off the surface
• 3.2.3 - figure 2

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Refraction

• When a light strikes the interface between two
  transparent materials, the light divides into two
  parts.
• If a ray strikes the glass at an exact 90 degree
  angle, the ray is NOT bent
• If it is NOT at an exact 90 degree angle, the ray
  is bent when entering the glass
• Bending of the ray is refraction

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Total internal reflection

• A light ray that is being turned on/off to send
  data (1s and 0s) must stay inside the fiber until
  it reaches the far end
• Ray MUST NOT refract into the material wrapped
  around the outside of the fiber
• A design must be achieved for the fiber that will
  make the outside surface of the fiber act like a
  mirror to the light ray moving through the fiber

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Total internal reflection

• The following two conditions must be met for
  light rays in a fiber to be reflected back w/o
  any loss due to refraction.
• The core of the optical fiber has to have a
  larger index of refraction (n) than the material
  that surrounds it. The material that surrounds
  the core of the fiber is called the cladding.
• The angle of incidence of the light ray is
  greater than the critical angle for the core and
  its cladding

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• When both of these conditions are met, the entire
  incident light in the fiber is reflected back
  inside the fiber
• This is total internal reflection
• Foundation upon which optical fiber is
  constructed
• Total internal reflection causes the light rays
  in the fiber to bounce off the core-cladding
  boundary and continue its journey towards the far
  end of the fiber
• Light will follow a zig-zag path through core

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Fiber Optic

• Core - part which rays travel through cladding -
  protective layer around core
• Single-mode vs. Multimode
• Singlemode 8-125 microns
• Rays travel along one path small core
• Higher bandwidth than multimode and greater cable
  run distances--3000 meters
• Multimode many paths that light can take
• 50-125 microns (1st is core size 2nd is
  cladding 3.2.7 figure 2)
• 62.5 125 microns
• 100 140 microns
• Cable run distance 2000 meters

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Fiber Optic Cabling
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Fiber Optic Cabling
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• Every FO cable consists of two glass fibers
  encased in SEPARATE SHEATHs
• One carries transmitted data from device A to B
• The 2nd carries data from device B to A --
  received data
• Similar to two one-way streets going in opposite
  directions
• Provides full-duplex communication
• No light escapes when inside fiber--so there are
  no crosstalk issues

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Warning

• The laser light used with single-mode (vs. LEDs)
  has a longer wavelength than can be seen. The
  laser is so strong that it can seriously damage
  eyes.
• Never look at the near end of a fiber that is
  connected to a device at the far end.
• Never look into the transmit port on a NIC,
  switch, or router.

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Transmission Devices

• FO uses light to send data most data sent over a
  LAN is in the form of electrical signals
• Therefore something is needed to convert the
  electricity to light and at the other end of the
  fiber and convert the light back to electricity.
• transmitter (Tx) - receives data converts
  electrical pulses to light
• receiver (Rx) gets signal ready to send over
  copper wire two types of light used to encode
  and transmit
• LED - infrared light with wavelengths of 850nm or
  1310nm multimode
• Laser - produces a thin beam of intense infrared
  light (1213nm or 1550nm) single-mode extra care

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• Receivers
• Have semiconductor devices call p-intrinsic-n
  diodes (PIN photodiodes)
• When struck by a pulse of light, the PIN
  photodiode quickly produces an electric current
  of the proper voltage for the network
• Connectors are attached to the fiber ends so that
  the fibers can be connected to the ports on the
  Tx and Rx.
• SC connection - multimode
• ST connection - single-mode (3.2.8 figure 2)

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ST and SC Connectors

• The type of connector most commonly used with
  multimode fiber is the Subscriber Connector (SC
  connector).
• On single-mode fiber, the Straight Tip (ST)
  connector is frequently used.

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• Other equipment
• Repeaters and fiber patch panels
• Repeaters are optical amplifiers - receive fading
  out light pulses and restore them to their
  original shape, strength, timing
• Patch panels - 3.2.8 figure 5

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Signals and noise in FO

• Fiber-optic cable is not affected by the sources
  of external noise that cause problems on copper
  media because external light cannot enter the
  fiber except at the transmitter end
• the transmission of light on one fiber in a cable
  does not generate interference that disturbs
  transmission on any other fiber. This means that
  fiber does not have the problem with crosstalk
  that copper media does
• When electrical noise on the cable originates
  from signals on other wires in the cable
• Primary cause electrical noise from other wires
  in a cable

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Signals and noise in FO

• FO is not w/o problems
• Some of the light energy is lost
• The farther a light signal travels through fiber,
  the more signal loss strength
• Why does is lose strength
• Scattering of light in the fiber
• Absorption -
• Manufacturing irregularities or roughness in the
  core-to-cladding boundary
• Any microscopic imperfections in the thickness or
  symmetry of the fiber will cause problems
• Dispersion - spreading of pulses as they travel
  down the fiber

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Install, care, and testing of FO

• A major cause of too much attenuation
  (degradation of signal) in fiber-optic cable is
  improper installationnot easy to install. If the
  fiber is stretched or curved too tightly, it can
  cause tiny cracks in the core that will scatter
  the light rays
• When the fiber has been pulled, the ends of the
  fiber must be cleaved (cut) and properly polished
  to ensure that the ends are smoothnot easy to
  terminal ends of cable
• Install Connectors
• Cleave Polish Ends
• Protect Connectors From Dirt Damage

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Testing fiber links

• When a FO link is planned the amt of signal
  power loss that can be tolerated must be
  calculated
• Referred to as the optical link loss budget
• The decibel (dB) is the unit used to measure the
  amt of power loss
• Tells what of the power that leaves the Tx
  actually enters the Rx.
• Testing is extremely important and records of the
  results of these tests must be kept - very
  detailed

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Testing fiber links

• Two of the most important instruments for testing
  equipment are Optical Loss Meters and Optical
  Time Domain Reflectometers (OTDRs)
• Both test optical cable to ensure that the cable
  meets the TIA standards for fiber
• Also test to verify that the link power loss does
  not fall below the optical link loss budget
• OTDRs can provide much additional detailed
  diagnostic information about a fiber link. They
  can be used to trouble shoot a link when problems
  occur.

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Wi-Fi - network w/o wires

• Wi-Fi is known formally as 802.11
• Three standards
• 802.11a, 802.11b and 802.11g
• Differ in speed
• Most people have 802.11b
• Wi-Fi runs at 11 megabits per second (Mbps)
• Advertised rate
• Only get 50 of that rate

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Wireless LAN organizations and standards

• 802.11 Direct Sequence Spread Spectrum (DSSS)
  applies to wireless operating within 1 to 2 Mbps
  range
• 802.11a - covers WLAN devices operating in the 5
  GHZ transmission band
• Using 5 GHZ disallows interoperability of 802.11b
  because they operate w/i 2.4 GHZ
• Capable of supplying data throughput of 54 Mbps
  has achieved 108 Mbps

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Wireless LAN organizations and standards

• 802.11b - may also be called Wi-Fi or high-speed
  wireless and refers to DSSS systems that operate
  at 1, 2, 5.5 and 11 Mbps
• Backward compliant - support 802.11
• Extremely important as it allows upgrading of the
  wireless network w/o replacing the NICs or access
  points
• Achieves a higher data throughput by using a
  different coding from 802.11
• Generally function at 2 to 4 Mbps

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Wireless LAN organizations and standards

• 802.11g - provides the same throughout 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 topologies

• A wireless network may consist of as few as two
  devices peer to peer network
• Many times NICs from different manufacturers are
  not compatible
• To solve the problem of compatibility, an access
  point (AP) is commonly installed to act as a
  central hub for the WLAN "infrastructure mode
• AP is hard wired to the cabled LAN
• APs are equipped with antennae

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Disadvantages of Wireless

• Security
• Compatibility of NICs
• Access Point (AP) commonly installed to act as
  a hookup to the wirelss NIC
• Devices that are attached to a WLAN act as
  servers and clients

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What equipment is needed for a wireless LAN?
Wireless NICs, Access Point, ST cables, switch
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How WLANs communicate

• When a client is actived in WLANs
• It listens for compatible device to associate
  called scanning
• This is either active or passive
• Active scanning caused a probe request to be sent
  from the wireless node seeking to join the
  network
• The probe request will contain the Service Set
  Identifier (SSID) of the network it wishes to
  join
• When an AP with the same SSID is found, the AP
  will issue a probe response. The authentication
  and association steps are now completed

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How WLANs communicate

• Passive scanning
• Nodes listen for beacon management frames
  (beacons)
• When a node receives a beacon that contains the
  SSID of the network, it attempts to join the
  network
• Passive Scanning
• Continuous process
• Nodes may associate or disassociate with APs as
  signal strength changes

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How WLANs communicate

• Nodes pass frames in same manner as any other
  802.x network
• 3 types of frames
• Management Frames
• Control Frames
• Data Frames
• Since radio frequencies (RF) is a shared medium,
  collision can occur just as they do on wired
  shared medium

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How WLANs communicate

• There is no method to detect a collision
• WLANS use CSMA/CA -- Carrier Sense Multiple
  Access/Collision Avoidance
• Wired networks use CSMA/CD Carrier Sense
  Multiple Access/Collision Detection

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How WLANs communicate

• When a source node sends a frame, the receiving
  node returns a positive acknowledgment (ACK)
• ACKs cause consumption of 50 of the available
  bandwidth
• Combine with the collision avoidance protocol
  (CSMA/CA) the actual data throughput to a MAX is
  5.0 to 5.5 Mbps
• Even on a 802.11b rated at 11Mbps

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Authentication and association

• WLAN authentication occurs at Layer 2
• Data Link (access point, bridge, switch, NIC)
• Client will send an authentication request frame
  to the AP and the frame will be accepted or
  rejected by the AP
• Association (after authentication) is the state
  that permits a client to use service of the AP to
  transfer data

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Authentication and association

• Unauthenticated and unassociated
• The node is disconnected from the network
• Not associated to an access point.
• Authenticated and unassociated
• The node has been authenticated on the network
• BUT has not yet associated with the access point.
  
• Authenticated and associated
• The node is connected, authenticated to the
  network
• Able to transmit and receive data through the
  access point.

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Methods of authentication

• IEEE 802.11 lists two types of authentication
  processes
• Open System This is an open connectivity
  standard in which only the Service Set Identifier
  (SSID) must match. This may be used in a secure
  or non-secure environment although the ability of
  low level network sniffers to discover the SSID
  of the WLAN is high

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Methods of authentication

• The second process is the shared key. This
  process requires the use of Wireless Equivalency
  Protocol (WEP) encryption. WEP is a fairly simple
  algorithm using 64 and 128 bit keys.
• Higher level of security than the open but are
  not hack proof
• Biggest problem of WLAN unathorized entry into
  other WLANs

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Transmission Devices

• WLANs use radio waves to send data most data
  sent over a LAN is in the form of electrical
  signals
• Therefore something is needed to convert the
  electricity to radio waves and convert the radio
  waves back to electricity.
• Radio transmitters
• Receiver must have an antenna
• When radio waves hit the antenna of the receiver,
  electrical currents are generated

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• Radio waves attenuate as they move out from the
  transmitting antenna grow weaker
• In a WLAN, a radio signal measured at a distance
  of just 10 meters (30 feet) from the transmitting
  antenna would be only 1/100th of its original
  strength. Like light, radio waves can be absorbed
  by some materials and reflected by others. When
  passing from one material, like air, into another
  material, like a plaster wall, radio waves are
  refracted. Radio waves are also scattered and
  absorbed by water droplets in the air

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Signals and noise on a WLAN

• When using radio frequency technology many kinds
  of interference must be taken into consideration
• Distance AND Interference
• A device that is often overlooked as causing
  interference is the standard microwave oven
• Leakage from a microwave of as little as one watt
  into the RF spectrum can cause major network
  disruption.
• Wireless phones operating in the 2.4GHZ spectrum
  can also cause network disorder

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Ways to send data signals

• Electrical voltages copper
• Light patterns fiber optic
• Modulated electromagnetic waves wireless - AIR

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Wireless security

• A number of new security solutions and protocols,
  such as Virtual Private Networking (VPN) and
  Extensible Authentication Protocol (EAP) are
  emerging

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Wireless security cont.,

• EAP-MD5 Challenge Extensible Authentication
  Protocol is the earliest authentication type,
  which is very similar to CHAP password protection
  on a wired network.
• LEAP (Cisco) Lightweight Extensible
  Authentication Protocol is the type primarily
  used on Cisco WLAN access points. LEAP provides
  security during credential exchange, encrypts
  using dynamic WEP keys, and supports mutual
  authentication.
• User authentication Allows only authorized
  users to connect, send and receive data over the
  wireless network.
• Encryption Provides encryption services further
  protecting the data from intruders.
• Data authentication Ensures the integrity of
  the data, authenticating source and destination
  devices.

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Path of least resistance

• GROUND Equipment!!!

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• THE
• END