User:Itpastorn/dko/ccna1-3.1-3

Networking Media

Overview CCNA 1 - Module 1 (3.1)
 * Electrical properties of matter
 * Voltage, resistance, impedance, current, and circuits
 * Different types of cable
 * Coaxial cable
 * STP cable
 * UTP cable
 * Straight-through, crossover, and rollover cables
 * Fiber-optic cable
 * How fiber-optic cables transmit signals
 * Multi-mode optical fiber and Single-mode optical fiber
 * How fiber is installed
 * Connectors and equipment for fiber-optic cable
 * How fiber is tested
 * Safety issues related to fiber optics

Atoms and electrons
All matter is composed of atoms. The Periodic Table of Elements


 * Electrons
 * Protons
 * Neutrons

Nucleus


 * Coulomb's law
 * The Bohr model

Electrons stay in orbit

Electrons in certain atoms, such as metals, can be made to flow. Electricity = flow of electrons.

Static electricity and electrostatic discharge (ESD)

ESD can create serious problems for sensitive electronic equipment.

Atoms, or groups of atoms called molecules, can be referred to as materials.


 * Insulators
 * Conductors
 * Semiconductors

Multimeter

Voltage
Electromotive force (EMF)

Created by:
 * Friction, static electricity
 * Magnetism, electric generators
 * Light, solar cell

Resistance and impedance
Semiconductors:
 * R represents resistance
 * ohm (Ω).
 * carbon (C)
 * germanium (Ge)
 * Gallium arsenide (GaAs)
 * Silicon (Si)

Electrical current

 * Letter I
 * Ampere (A)

Circuits
Closed loops
 * Alternating current (AC)
 * Direct current (DC)

Cable specifications
Considerations:
 * Speed
 * Digital or analog?
 * Digital ≈ basebandtransmission
 * Analog ≈ broadband transmission
 * Signal distrance
 * Attenuation

Coaxial cable
Variants:
 * Copper or aluminum conductor
 * Flexible insulation.
 * Woven copper braid or metallic foil
 * second wire
 * shield
 * reduces outside electromagnetic interference
 * Cable jacket
 * Thicknet - 10Base5
 * Thinnet - 10Base2 (Cheapernet)

Important to properly ground the cable!

STP cable
CCNA has these two: Wikipedia divides the first into two.
 * STP
 * ScTP = FTP

STP (in all variants) need to be grounded at both ends - otherwise noise.

UTP cable
Advantages Disadvantages Variants
 * Cancellation effect produced by the twisted wire pairs. Specifications how many twists are permitted.
 * TIA/EIA-568-B.2
 * Category 5e
 * Category 6
 * RJ45
 * Cheapest of all
 * Easy to install
 * Good quality signals, up to Gbps (or even maybe 10Gbps)
 * Susceptible to interference
 * Max 100 meters
 * Straight-through
 * Crossover
 * Rollover

The electromagnetic spectrum
Light - one type of electromagnetic energy
 * Waves
 * Wavelength

Radio, microwaves, radar, infrared, visible light, ultra violet, x-rays, and gamma rays.

300,000 kilometers per second = the speed of light.

Human eyes sense wavelengths between 700 nanometers and 400 nanometers (nm) = visible lightI

Infrared light:
 * TV remote
 * IR connections on computers, phones, etc
 * Optical fiber
 * 850 nm
 * 1310 nm
 * 1550 nm

"These wavelengths were selected because they travel through optical fiber better than other wavelengths."

Ray model of light

 * Reflection
 * Refraction
 * Index of refraction

Total internal reflection

 * The core has to have a larger index of refraction (n) than the material that surrounds it (the cladding).
 * The angle of incidence greater than the critical angle

Total internal reflection = All light is reflected back

The light will follow a zigzag path through the core of the fiber.


 * The numerical aperture of the fiber = the range of angles of incident light rays entering the fiber that will be completely reflected.
 * Modes – The paths which a light ray can follow inside the fiber.

Multimode fiber
Optical paths through the core are called modes.
 * Multimode - larger core
 * Single-mode - smaller core

Two fibers in separate sheaths - full duplex. Single outer jacket until they reach the point at which connectors are attached.


 * No crosstalk issues with fiber.
 * One cable can many separate fibers
 * Longer distances than electric cables.


 * The core - typically glass made from of silicon dioxide (silica) and other elements. Graded index glass in multimode fiber
 * The cladding - silica but with a lower index of refraction
 * A buffer - usually plastic
 * Loose-tube - usually outside-building installations
 * Tight-buffered - usually inside buildings
 * A strength material (aramid yarn, usually kevlar)
 * An outer jacket - maybe PVC, usually orange; protect the fiber against abrasion, solvents, and other contaminants

Multimode fiber-optic cable is the most common fiber-optic cable in LANs.

Either a 62.5 or a 50-micron core and a 125-micron diameter cladding.
 * 62.5/125
 * 50/125
 * 100/140

Light sources:
 * Infrared Light Emitting Diodes (LEDs)
 * Vertical-cavity surface-emitting lasers (VCSELs)

Single-mode fiber
Advantages to multi mode But it is more expensive!
 * Same parts as multimode
 * Usually yellow
 * One mode
 * Longer distances
 * Less bouncing = faster travel = less latency
 * Higher bandwith

Nine-micron cores are the most common: 9/125.

The infra red light is invisible, but it is strong enough to hurt the eyes! Never look into the end of a cable or into any other equipment.

Other optical components
LED LASER Optical fiber connector You may also see:
 * Transmitter
 * Receiver
 * 850 nm wavelength
 * 1310 nm
 * Cheaper
 * 1310 nm
 * 150 nm
 * Stronger signal
 * Subscriber Connector (SC) (multimode)
 * Straight Tip Connector (ST) (singlemode)
 * Optical communications repeater
 * Fiber patch panels

Signals and noise in optical fibers

 * Scattering
 * Absorption
 * Dispersion (optics)

Installation, care, and testing of optical fiber

 * Macrobends
 * Microbends
 * Interducting

Splicing is hard. Carefully polish, inspect with a microscope!

"The connectors and the ends of the fibers must be kept spotlessly clean."

Optical link loss budget

Optical loss meters and Optical time domain reflectometers

Additional resources (besides Wikipedia)

 * A Brief Overview Of Networking Media at Learn Networking
 * The Difference Between Straight Through, Crossover, And Rollover Cables at Learn Networking
 * CCNA 1 Module 3 Exam Solutions at Learn Networking

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