M1 Cp 02 Networking Media

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CCNA2: Networking MediaCopper Media

Cable specifications

Coaxial cable

STP cable

UTP cable

Optical Media

Multimode fiberSingle-mode fiber

Other optical components

Signals and noise in optical fibers

Installation, care, and testing of optical fiber

Wireless Media

Wireless LAN organizations and standards

Wireless devices and topologiesHow wireless LANs communicate

Authentication and association

The radio wave and microwave spectrums

Signals and noise on a WLAN

Wireless security


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Cable Specifications

Cables have different specifications and expectations pertaining toperformance:

What speeds for data transmission can be achieved using a particular typeof cable? The speed of bit transmission through the cable is extremelyimportant. The speed of transmission is affected by the kind of conduit

used. What kind of transmission is being considered? Will the transmissions

be digital or will they be analog-based? Digital or baseband transmissionand analog-based or broadband transmission are the two choices.

How far can a signal travel through a particular type of cable beforeattenuation of that signal becomes a concern? In other words, will the signalbecome so degraded that the recipient device might not be able toaccurately receive and interpret the signal by the time the signal reachesthat device? The distance the signal travels through the cable directlyaffects attenuation of the signal. Degradation of the signal is directlyrelated to the distance the signal travels and the type of cable used.


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Coaxial Media

Shielding allows signal to travel 500m

unrepeated

Relatively inexpensive

Medium difficulty to install

Limited to 10Mbps

Relatively unreliable

Only usable in bus topologies

Not the easiest to install

Not the least expensive medium

Coaxial Pros and Cons


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Shielded Twisted Pair

In shielded cable, shielding material protects the data signal from external sources of noise and

From noise generated by electrical signals within the cable.Benefits of shielding

protects the inner conductor from external electrical noise

keeps the transmitted signal confined to the cable

protects each wire pair from noise generated by the other pairs


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Unshielded Twisted Pair

Inexpensive media

Supports speeds up to 1 Gbps

Easiest medium to install

Most widely used for workstation

connections, telephone, etc.

Signal can only travel 100m because of

no shielding (50m if used for Gigabit

Ethernet)

Highly susceptible to outside

interference

UTP Pros and Cons


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Optical Media

Light is one type of electromagnetic

energy

Electromagnetic energy is produced when

an electric charge moves back and forth,or accelerates

This energy in the form of waves can

travel through a vacuum, the air, andthrough some materials like glass


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Ray Model of Light

Wavelengths that are not visible to the human eye are used totransmit data over optical fiber.

These wavelengths are slightly longer than red light and are calledinfrared light

Think of light rays as narrow beams of light like those produced bylasers. In the vacuum of empty space, light travels continuously in astraight line at 300,000 kilometers per second


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Optical Media

Light travels at different, slower speeds

through other 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.

That is why you can see yourself in windowglass. The light that is reflected back is called

the reflected ray


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Refracted ray

Refracted ray- light energy in the incidentray that is not reflected will enter the glass.

The entering ray will be bent at an angle from

its original path. How much the incident light ray is bent

depends on the angle at which the incident

ray strikes the surface of the glass & the

different rates of speed at which light travelsthrough the two substances


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Angle of incidence

Angle of incidence : 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


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Refraction

Index of Refraction - ratio of the speed of light in amaterial to the speed of light in a vacuum

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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Total internal reflection

Total Internal Reflection- 2 conditions

Core of the optical fiber has to have a larger index of

refraction (n) than the material that surrounds it.

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

Multimode Fiber

diameter of the core of the fiber is large

enough so that there are many paths that light

can take through the fiber

Single-mode fiber

smaller core

light rays to travel along one mode


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Fiber optic


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Fiber optic 2 glass fibers encased in separate sheaths

One fiber carries transmitted data from device A to device B.

The second fiber carries data from device B to device A.

The fibers are similar to two one-way streets going in

opposite directions.

Full-duplex communication link


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Multimode fiber (62.5/125)

Five parts make up each fiber-optic cable core

cladding

buffer

strength material

outer jacket

Carry data distances of up to 2000 meters (6,560 ft)

2 types of light source Infrared Light Emitting Diodes (LEDs)

Vertical Cavity Surface Emitting Lasers (VCSELs)


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Single-mode Fiber

Single-mode fiber consists of the same parts as multimode. core fiber has a diameter of9 microns and the surrounding cladding

is 125 microns in diameter.

infrared laser is used as the light source


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Single-mode Fiber

single-mode allows only one mode of light to

propagate through the smaller, fiber-optic

core.

3000 meters

More expensive

Used for inter-building connectivity


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Single-mode Fiber

Warning: The laser light used with single-mode has a

longer wavelength than can be seen. The laser is so

strong that it can seriously damage eyes.

Neverlook at the near end of a fiber that is connected toa device at the far end.

Neverlook into the transmit port on a NIC, switch, or

router. Remember to keep protective covers over the

ends of fiber and inserted into the fiber-optic ports of

switches and routers. Be very careful.


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Transmission Devices

Optical fiber links use light to send data

To convert light into electricity, you need a

transmitter & receiver

There are 2 types of light sources used to

encode and transmit the data through the

cable

LEDs

LASERS


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Signals & Noise in Optical Fibers

Advantages

not affected by the sources of external noise

no problem with crosstalk


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Signals & Noise in Optical Fibers

Disadvantages

Scattering

Absorption Attenuation

Dispersion


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Scattering

Reflects and scatters some of the light

energy


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Absorption

cause of light energy loss

When a light ray strikes some types of

chemical impurities in a fiber, the impurities

absorb part of the energy.

This light energy is converted to a small

amount of heat energy.

Absorption makes the light signal a littledimmer


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Attenuation

Due to manufacturing irregularities or roughness in the core-to-claddingboundary


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Dispersion

limits transmission distances on a fiber

Dispersion is the technical term for the

spreading of pulses of light as they travel

down the fiber


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Installation, care, and testing of optical fiber

Too much attenuation

improper installation. Fiber stretched or curved too tightly

cause tiny cracks in the core that will scatter the light rays.

Bending the fiber changes the incident angle of light rays striking the core-to-

cladding boundary

Connectors and the ends of the fibers must be kept spotlessly clean.


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Fiber noise

Fiber noise- diminishes the strength of the

light signal

Types of fiber noise

Scattering

absorption

dispersion

improper installation dirty fiber ends


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Wireless LANs


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Wireless Networking

Increasingly important as computing devices

become smaller and more mobile

Laptops

Handhelds

Cell phones

Important Concerns

Bandwidth

Security

Interoperability


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Wireless LAN Standards

802.11 General Standards Number

802.11b 11 Mbps WEP

Security:

64-bit or

128-bit

encryptio

n

Uses same

frequency range as

some cordless

phones (2.4 Ghz)

802.11a 54 Mbps Not interoperablewith otherstandards uses

higher frequency

range (5 GHz)

802.11g 54 Mbps Interoperable with802.11b because it

uses the same

frequency range


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Wireless Network Adapters


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Wireless Access Point (WAP)


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Wireless Access Point

WAP


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Wireless Range

As range from WAP increases, negotiated speed is reduced toensure data integrity.

Typical Range is300-500 feet.


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Authentication & Association

Who has access to your network and where?

WLAN Authentication occurs at Layer 2 and identifiesthe DEVICE not the USER

Authentication keys must match on the WAP and theWireless NIC

ASSOCIATION means that your wNIC communicatesthrough a particular WAP. This assignment can bechanged manually, or automatically as he user movesthrough the WLAN. Association can also be restrictedbased on MAC address.


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WLAN Communications Process

Client probes, finds a WAP

Client transmits authentication key

WAP accepts/rejects key, notifies client ofresult

Client is associated with the WAP

All other network processes begin (i.e.

dynamic IP address assignment, networklogin, etc.)


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Two Types of WLANs: Ad-Hoc

Ad-hoc system

Also known as an Independent Basic Service

Set (IBSS) or Wireless Peer-to-Peer network

All clients communicate directly with one

another via their wireless adapters

No WAP is used, and there is no access to a

wired network infrastructure


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Two Types of WLANS: Infrastructure

Uses a WAP to provide access to a wired

network

Technical Term: Basic Service Set (BSS)

Multiple WAPs can be used to form

microcells with overlapping coverage

areas

Technical Term: Extended Service Set (ESS)

Allows the user to roam


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Roaming and WAPs

As client moves closerto another WAP, it re-authenticates and re-associates.

This process occurs inthe background and istransparent to the user.


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WLAN Roaming

Network Admin configures multiple WAPs with

overlapping coverage, each one set to a

different radio channel

When client probes, it chooses a WAP based onsignal strength and error rates

If signal strength weakens, client will search for

another WAP and re-tune to a new frequency,

then authenticate and associate with the new

WAP


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Antennae

Unidirectional- emits signal

in one direction only.

Omnidirectional- emits signal

equally in all directions.


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NoiseNoise

Noise related to communications refers to undesirable signals.

Noise can originate from natural and technological sources, and

is added to the data signals in communications systems

Here are some possible sources of noise:

Nearby cables which carry data signals Radio frequency interference (RFI), which is noise from

other signals being transmitted nearby

Electromagnetic interference (EMI), which is noise from

nearby sources such as motors and lights

Laser noise at the transmitter or receiver of an optical signal


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AttenuationAttenuation

Attenuation is the decrease in signal amplitude over

the length of a link (cable)

Causes:

Long cable lengths

High signal frequencies

resistance of the copper cable

leaks through the insulation

impedance caused by defective connectors


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Impedance

Impedance is a measurement of the resistance of the cable toalternating current (AC) and is measured in ohms

Cat5 cable is 100 ohms

A connector improperly installed will have a different impedance

value than the cable

This is called an impedance discontinuity or an impedance

mismatch


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Impedance DiscontinuitiesImpedance Discontinuities

Impedance discontinuities cause attenuation because a portion

of a transmitted signal will be reflected back

This effect with other discontinuities create echoes making it

difficult for the receiver to accurately detect the signal.

This is called jitter and results in data errors

The effects of signal attenuation and impedance mismatch on a

communications link is called insertion loss


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Noise on Copper Media

TIA/EIA-568-B certification of a cable now requires testing for a

variety of types of noise.

Crosstalk involves the transmission of signals from one wire to a

nearby wire

Alien crosstalk is caused by a signal on another cable

There are three distinct types of crosstalk (noise):

Near-end Crosstalk (NEXT)

Far-end Crosstalk (FEXT)

Power Sum Near-end Crosstalk (PSNEXT)


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M1 Cp 02 Networking Media

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