User:Itpastorn/dko/ccna1-3.1-3

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Networking Media

Overview CCNA 1 - Module 1 (3.1)

Copper Media[edit]

Atoms and electrons[edit]

All matter is composed of atoms. The Periodic Table of Elements

Nucleus

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.

Multimeter

Voltage[edit]

Electromotive force (EMF)

Created by:

Resistance and impedance[edit]

  • R represents resistance
  • ohm (Ω).

Semiconductors:

Electrical current[edit]

  • Letter I
  • Ampere (A)

Circuits[edit]

Closed loops

Cable specifications[edit]

Considerations:

  • Speed
  • Digital or analog?
    • Digital ≈ basebandtransmission
    • Analog ≈ broadband transmission
  • Signal distrance

Coaxial cable[edit]

Variants:

Important to properly ground the cable!

STP cable[edit]

CCNA has these two:

  • STP
  • ScTP = FTP

Wikipedia divides the first into two.

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

UTP cable[edit]

Advantages

  • Cheapest of all
  • Easy to install
  • Good quality signals, up to Gbps (or even maybe 10Gbps)

Disadvantages

  • Susceptible to interference
  • Max 100 meters

Variants

  • Straight-through
  • Crossover
  • Rollover

Optical Media[edit]

The electromagnetic spectrum[edit]

Light - one type of electromagnetic energy

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[edit]

  • Reflection
  • Refraction
    • Index of refraction

Reflection[edit]

Refraction[edit]

Total internal reflection[edit]

  • 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[edit]

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:

Single-mode fiber[edit]

  • Same parts as multimode
  • Usually yellow
  • One mode

Advantages to multi mode

  • Longer distances
  • Less bouncing = faster travel = less latency
  • Higher bandwith

But it is more expensive!

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[edit]

  • Transmitter
  • Receiver

LED

  • 850 nm wavelength
  • 1310 nm
  • Cheaper

LASER

  • 1310 nm
  • 150 nm
  • Stronger signal

Optical fiber connector

  • Subscriber Connector (SC) (multimode)
  • Straight Tip Connector (ST) (singlemode)

You may also see:

Signals and noise in optical fibers[edit]

Installation, care, and testing of optical fiber[edit]

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

Wireless Media[edit]

Wireless LAN organizations and standards[edit]

Wireless devices and topologies[edit]

How wireless LANs communicate[edit]

Authentication and association[edit]

The radio wave and microwave spectrums[edit]

Signals and noise on a WLAN[edit]

Wireless security[edit]

Extra topics (in addition to CCNA)[edit]

Additional resources (besides Wikipedia)[edit]

Navigation[edit]

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