Transcript CCNA1_Ch03

CCNA 1 Module 3
Networking Media
By
Your Name
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Objectives
• Copper media
• Optical media
• Wireless media
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Electricity Basics
The basic unit of all matter is an atom.
• Nucleus – center part of the atom (protons and
neutrons)
• Protons – particles that have positive charge
• Neutrons – particles that have no charge
(neutral)
• Electrons – particles that have negative charge
and orbit the nucleus
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Electricity Basics
• Creating Stable Atoms
– Electrons in certain atoms can be pulled free from the
atom and made to flow – this is electricity (a free flow
of electrons).
• Static Electricity
– Loosened electrons that stay in one place, without
moving and with a negative charge.
– Can create electrostatic discharge, which can create
serious problems for computers.
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Types of Electrical Materials
• Insulators
– Electrons flow poorly
– Plastic, paper, rubber, dry wood, air, and glass
• Conductors
– Electrons flow well
– Copper, silver, gold, solder, water with ions, humans
• Semiconductors
– Electrons flow can be controlled precisely
– Carbon, germontum, gallium arsenide, silicon
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Measuring Electricity
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Voltage
Resistance and impedance
Current
Alternating current
Direct current
Circuits
Cable specification and termination
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Current Flow
A 6-volt
flashlight
uses a
simple
circuit.
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Electrical Grounds
Surge
suppressors,
uninterruptible
power
supplies, and
wall outlets all
connect to a
transformer
and to the earth
ground.
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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.
• It can be run without as
many boosts from
repeaters, for longer
distances between
network nodes than
either STP or UTP cable.
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Shielded Copper Cable
• Shielded twisted-pair cable (STP) combines the
techniques of shielding, cancellation, and
twisting of wires.
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Unshielded Twisted Pair
• Unshielded twisted-pair cable (UTP) is a fourpair wire medium used in a variety of networks.
Each of the 8 individual copper wires in the UTP
cable is covered by insulating material.
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Optical Media
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Electromagnetic Spectrum
• Electromagnetic Energy
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Radio
Microwaves
Radar
Visible light
X-rays
Gamma rays
• If all the types of electromagnetic waves are
arranged in order from the longest wavelength
down to the shortest wavelength, a continuum
called the electromagnetic spectrum is created.
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Ray Model of Light
• When electromagnetic waves travel out from a
source, they travel in straight lines called rays.
• Light travels at different slower speeds through
materials like air, water, and glass.
• When a light ray called the incident ray, crosses
the boundary from one material to another,
some of the light energy in the ray will be
reflected back.
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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 angle between the incident ray and a line
perpendicular to the surface of the glass at the
point where the incident ray strikes the glass is
called the angle of incidence.
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Refraction
• When a light strikes the interface between two
transparent materials, the light divides into two
parts.
• Part of the light ray is reflected back into the first
substance, with the angle of reflection equaling
the angle of incidence.
• The remaining energy in the light ray crosses
the interface and enters into the second
substance.
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Total Internal Reflection
• A light ray that is
being turned on and
off to send data (1s
and 0s) into an optical
fiber must stay inside
the fiber until it
reaches the far end.
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Laws of Reflection
• The following two conditions must be met for the
light rays in a fiber to be reflected back into the
fiber with out any loss due to refraction:
– The core of the optical fiber has to have a larger index
of refraction than the material that surrounds it (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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Multimode Fiber
• If the diameter of the core
of the fiber is large
enough so that there are
many paths that light can
take through the fiber, the
fiber is called “multimode”
fiber.
• Single-mode fiber has a
much smaller core that
only allows light rays to
travel along one mode
inside the fiber.
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Single-Mode Fiber
• The major difference between
multimode and single-mode
fiber is that single-mode
allows only one mode of light
to propagate through the
smaller, fiber-optic core.
• Single-mode fiber is capable
of higher rates of data
transmission and greater
cable run distances than
multimode fiber.
• Single-mode fiber can carry
LAN data up to 3000 meters.
Multimode is only capable of
carrying up to 2000 meters.
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Other Optical Components
• Optical fiber links use light to send data.
• A transmitter is needed to convert the electricity
to light and at the other end of the fiber convert
the light back to electricity.
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Other Optical Components (cont.)
• The semiconductor devices that are usually
used as receivers with fiber-optic links are called
p-intrinsic-n diodes (PIN photodiodes).
• Connectors are attached to the fiber ends so
that the fibers can be connected to the ports on
the transmitter and receiver.
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Signals and Noise in Optical Fibers
• The farther a light signal travels through a fiber, the more
the signal loses strength. This attenuation is due to
several factors involving the nature of fiber itself.
– Scattering of light in a fiber is caused by microscopic nonuniformity (distortions) in the fiber that reflects and scatters some
of the light energy.
– Absorption makes the light signal a little dimmer.
– Another factor that causes attenuation of the light signal is
manufacturing irregularities or roughness in the core-to-cladding
boundary.
• Graded index multimode fiber is designed to
compensate for the different distances the various
modes of light have to travel in the large diameter core.
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Installation, Care, and Testing of
Optical Fiber
• If the fiber is stretched
or curved too tightly, it
can cause tiny cracks
in the core that will
scatter the light rays.
• Bending the fiber in
too tight a curve can
change the incident
angle of light rays
striking the core-tocladding boundary.
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Installation, Care, and Testing of
Optical Fiber (cont.)
• Interducting protects the
fiber, makes it easier to
pull, and ensures that the
bending radius (curve
limit) of the fiber is not
exceeded.
• Two of the most important
testing instruments are
Optical Loss Meters and
Optical Time Domain
Reflectometers (OTDRs).
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Wireless Media
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WLAN Organizations and Standards
• A key technology contained within the 802.11 standard is
Direct Sequence Spread Spectrum (DSSS).
• 802.11a covers WLAN devices operating in the 5 GHZ
transmission band.
• 802.11b increases transmission capabilities to 11Mbps.
• 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.
• Cisco has developed an access point that permits
802.11b and 802.11a devices to coexist on the same
WLAN.
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Wireless Devices and Topologies
• An access point (AP) is
commonly installed to act
as a central hub for the
WLAN "infrastructure
mode".
• The AP is hard wired to the
cabled LAN to provide
Internet access and
connectivity to the wired
network.
• APs are equipped with
antennae and provide
wireless connectivity over
a specified area referred to
as a cell.
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Access Points
• To service larger areas,
multiple access points
may be installed with a
degree of overlap.
• A 20-30% overlap is
desirable.
• When a client is activated
within the WLAN, it will
start "listening" for a
compatible device with
which to "associate".
• This is referred to as
"scanning" and may be
active
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How WLANs Communicate
• After establishing
connectivity to the WLAN,
a node will pass frames
similarly to any other 802
network.
• WLANs do not use a
standard 802.3 frame.
• WLANs use CSMA/CD
• When a source node
sends a packet, the
receiving node returns a
positive acknowledgment
(ACK).
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Authentication and Association
• IEEE 802.11 lists two types of authentication
processes.
– Open system – only the SSID must match
– Shared key – requires WEP
• Association permits a client to use the services
of the AP to transfer data.
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Radio Wave and Microwave Spectrums
• Computers send data
signals electronically.
Radio transmitters
convert these electrical
signals to radio waves.
• Changing electric
currents in the antenna
of a transmitter generates
the radio waves.
• Changing electric
currents in the antenna of
a transmitter generates
the radio waves.
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Signals and Noise on a WLAN
• The most obvious source of a signal problem is
the transmitting station and antenna type.
• Leakage from a microwave of as little as one
watt into the RF spectrum can cause major
network disruption.
• Fog or high moisture conditions can affect
wireless networks.
• Lightning can also charge the atmosphere and
alter the path of a transmitted signal.
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Wireless Security
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VPN
EAP-MD5 Challenge
LEAP (Cisco)
User authentication
Encryption
Data authentication
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