Unit 3 - Data Transmission and Networking Media

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UNIT 3

DATA TRANSMISSION

AND NETWORKING

MEDIA 1

Outcomes 1

By the end of this subtopic, student should be able to :

Explain the basic concept of data transmission: 1. Analog and digital signaling

2. Data Modulation

3. Simplex, half-duplex, and full-duplex transmission

4. Multiplexing

5. Point to point Transmission

6. Broadcast Transmission

7. Throughput

8. Bandwidth

9. Baseband and Broadband

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1. SIGNAL

SIGNAL

Digital Analog

ANALOG SIGNAL

Analog

Continuous signal

Examples of analog data is the human voice When somebody speaks, a continuous wave is created in the air

This can captured by a microphone an converted to and analog

signal.

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DIGITAL SIGNAL

Digital

Discrete signal.

Examples of digital data; is data stored in memory of a computer in the form of 0s and 1s.

Digital signal is more reliable than any other signal.

Waveform of analog & digital signal

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Differences between analog &digital

signal

ANALOG SIGNAL DIGITAL SIGNAL

Continuous signal Discrete signal

Examples of analog data is the human voice

(when somebody speaks, a continuous wave is

created in the air).

Examples of digital data is the data stored in

memory of a computer in the form of 0s and

1s or on-off.

Cannot perform high-quality data transmission

(very difficult to remove noise and wave

distortions during the transmission).

Noise and distortions have little effect, making

high-quality data transmission

No security/encryption implemented in

analog cordless products (analog cordless

phone).

Able to encrypt all 1s and 0s during

transmission so your conversation is safe from

eavesdroppers (digital cordless phone).

2. DATA MODULATION

Data modulation is a technology used to modify analog signals to make them suitable for carrying data over a communication path.

In modulation, a simple wave, called a carrier wave, is combined with another analog signal to produce a unique signal that gets transmitted from one node to another. The carrier wave has preset properties (including frequency, amplitude, and phase).

Its purpose is to help convey information; in other words, its only a messenger.

Another signal, known as the information or data wave, is added to the carrier wave. When the information wave is added, it modifies one property of the carrier wave (for example, the frequency, amplitude, or phase). The result is a new, blended signal that contains properties of both the carrier wave and added data. When the signal reaches its destination, the receiver separates the data from the carrier wave.

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2. DATA MODULATION (cont.)

Modulation can be used to make a signal conform to a specific pathway, as in the case of FM (frequency modulation) radio, in which the data must travel along a particular frequency.

In FM (frequency modulation), the frequency of the carrier signal is modified by the application of the data signal.

In AM (amplitude modulation), the amplitude of the carrier signal is modified by the application of the data signal. Modulation may also be used to issue multiple signals to the same communications channel and prevent the signals from interfering with one another.

Figure below depicts an unaltered carrier wave, a data wave, and the combined wave as modified through frequency modulation.

Network+ Guide to Networks, 4e 10

DATA MODULATION

Figure 3-5: A carrier wave modified through frequency modulation

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3. TRANSMISSION

TRANSMISSION

Simplex Full-Duplex

Half-duplex

Simplex transmission: allows data to travel only in a single direction.

Example of simplex transmission: television broadcast.

Simplex

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Simplex (cont)

Another example of simplex communication is a football coach calling out orders to his team through a megaphone.

In this example, the coachs voice is the signal, and it travels in only one directionaway from the megaphones mouthpiece and toward the team.

Simplex is sometimes called one-way, or unidirectional, communication.

Half-duplex transmission: messages can move in either direction , but only one way at a time (walkie-talkie)

Example of half-duplex transmission: walkie-talkie

Half- Duplex

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For example :

intercom system that requires you to press a talk button to allow your voice to be transmitted uses half-duplex transmission.

If you visit a friends apartment building, you press the talk button to send your voice signals to his apartment.

When your friend responds, he presses the talk button in his apartment to send his voice signal in the opposite direction over the wire to the speaker in the lobby where you wait.

If you press the talk button while hes talking, you will not be able to hear his voice transmission.

Full-duplex: signals free to travel in both directions

simultaneously.

Example of full-duplex: telephone conversations.

Full-Duplex

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When signals are free to travel in both directions over a medium simultaneously, the transmission is considered full-duplex.

Full-duplex may also be called bidirectional transmission or, sometimes, simply duplex.

When you call a friend on the telephone, your connection is an example of a full-duplex transmission because your voice signals can be transmitted to your friend at the same time your friends voice signals are transmitted in the opposite direction to you.

In other words, both of you can talk and hear each other simultaneously.

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4. Transmission Direction: Multiplexing

A form of transmission that allows multiple signals to travel simultaneously over one medium is known as multiplexing. To carry multiple signals, the mediums channel is logically separated into multiple smaller channels, or subchannels. Many different types of multiplexing are available, and the type used in any given situation depends on what the media, transmission, and reception equipment can handle.

For each type of multiplexing, a device that can combine many signals on a channel, a multiplexer (mux), is required at the transmitting end of the channel.

At the receiving end, a demultiplexer (demux) separates the combined signals and regenerates them in their original form. Networks rely on multiplexing to increase the amount of data that can be transmitted in a given time span over a given bandwidth.

Network+ Guide to Networks, 4e

5.Relationships Between Nodes

Figure 3-10: Point-to-point VS broadcast transmission

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Point to Point Transmission

When a data transmission involves only one

transmitter and one receiver, it is considered a

point-to-point transmission.

The sender only transmits data that is intended to

be used by a specific receiver.

Broadcast transmission

Broadcast transmission involves one transmitter and multiple, undefined receivers. For example, a TV station indiscriminately transmitting a signal from its tower to thousands of homes with TV antennas uses broadcast transmission.

A broadcast transmission sends data to any and all receivers, without regard for which receiver can use it. Broadcast transmissions are frequently used on both wired and wireless networks because they are simple and quick.

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6.Throughput and Bandwidth

Throughput: measure of amount of data transmitted during given time period

Also called as capacity

Expressed as a quantity of bits transmitted per second, with prefixes used to designate different throughput amounts. For example, the prefix kilo combined with the word bit (as in kilobit) indicates 1000 bits per second.

Bandwidth: difference between highest and lowest frequencies that a medium can transmit

Range of frequencies is directly related to throughput.


7.Baseband and Broadband

Baseband: digital signals sent through direct current (DC)

pulses applied to a wire

Requires exclusive use of wires capacity

Baseband systems can transmit one signal at a time

Ethernet

Broadband: signals modulated as radiofrequency (RF) analog

waves that use different frequency ranges

Does not encode information as digital pulses

broadband transmission is used to bring cable TV to your home.

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Describe common transmission flaws (kecacatan

penghantaran):

Noise

Attenuation

Latency

Outcomes 2

Transmission flaws

1 Attenuation

2 Noise

3 Latency

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1. Attenuation

Attenuation (pengurangan/penyusutan):

the loss of signal strength over long distances

when signals travel along cabling.

Measured in decibels (dB).

Copper cabling has much greater attenuation

than fiber-optic cabling, which makes copper

suitable only for relatively short cable runs.

A digital device, known as a remodulator,

provides better signal quality by removing all of

the accumulated noise and attenuation and

transmitting a cleaned-up signal.

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Loss of signal strength as transmission travel away

from source

Analog signals pass through an amplifier,which

increase not only voltage of a signal but also noise

accumulated.

Noise :

interference in cabling by proximity to electrical equipment that generates electromagnetic interference (EMI).

Any undersirable influence degrading or distorting signal

Noise is generated by all electrical and electronic devices, including : motors

fluorescent lamps

power lines, and office equipment.

2. Noise (Hingar)

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Noise can usually be reduced (but never entirely

eliminated) by using higher-quality components,

lowering the temperature of components, or

using shielded cabling

noise

An analog signal distorted by noise

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A digital signal distorted by noise

Latency (masa pendam):

Delay between transmission and receipt of a signal

Many possible causes: Cable length

Intervening connectivity device (e.g., modems and routers)

3. Latency

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Describe Transmission Media in network

Explain physical characteristics of :

1. coaxial cable,

2. STP,

3. UTP, and

4. fiber-optic media.

Outcomes 3

Transmisson Media

Guided

Unshielded Twisted Pair

Cable

Shielded Twisted Pair

Cable Coaxial Cable Fiber Optic

Cabel

Unguided

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Twisted pair cables

Twisted pair cables consist of one or more pairs of insulated copper wires that are twisted together and housed in a protective jacket. Like all copper cables, twisted pair uses pulses of electricity to transmit data.

Data transmission is sensitive to interference or noise, which can reduce the data rate that a cable can provide. A twisted pair cable is susceptible to electromagnetic interference (EMI), a type of noise.

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A source of interference, known as crosstalk, occurs when cables are bundled together for long lengths. The signal from one cable can leak out and enter adjacent cables.

When data transmission is corrupted due to interference such as crosstalk, the data must be retransmitted. This can degrade the data carrying capacity of the medium.

In twisted pair cabling, the number of twists per unit length affects the amount of resistance that the cable has to interference. Twisted pair cable suitable for carrying telephone traffic, referred to as CAT3, has 3-4 turns per foot making it less resistant. Cable suitable for data transmission, known as CAT5, has 3-4 turns per inch, making it more resistant to interference.

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UTP

Unshielded twisted pair (UTP) is the most commonly encountered type of network cable in North America and many other areas. Shielded cables (ScTP and F-UTP) are used almost exclusively in European countries.

UTP cable is inexpensive, offers a high bandwidth, and is easy to install. This type of cable is used to connect workstations, hosts and network devices. It can come with many different numbers of pairs inside the jacket, but the most common number of pairs is four. Each pair is identified by a specific color code.

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Many different categories of UTP cables have been developed over time. Each category of cable was developed to support a specific technology and most are no longer encountered in homes or offices. The cable types which are still commonly found include Categories 3, 5, 5e and 6.

There are electrical environments in which EMI and RFI are so strong that shielding is a requirement to make communication possible, such as in a noisy factory. In this instance, it may be necessary to use a cable that contains shielding, such as Shielded twisted-pair (STP) and Screened twisted-pair (ScTP).

Unfortunately both STP and ScTP are very expensive, not as flexible, and have additional requirements due to the shielding that make them difficult to work with.

All Categories of data grade UTP cable are traditionally terminated into an RJ-45 connector.

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Shielded cables and screened twisted pair are

used almost exclusively in European

countries.

Individual pair are wrapped in a shield and

then the entire four pairs are wrapped in

another shield

Used for data transmission (in a noisy

factory)

Not as flexible (bulky), and have additional

requirements due to the shielding that make

them difficult to work with.

STP & ScTP

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SHIELDED TWISTED PAIR

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Coaxial Cable

Like twisted pair, coaxial cable (or coax) also carries data in the form of electrical signals. It provides improved shielding compared to UTP, so has a lower signal-to-noise ratio and can therefore carry more data. It is often used to connect a TV set to the signal source, be it a cable TV outlet, satellite TV, or conventional antenna. It is also used at NOCs to connect to the cable modem termination system (CMTS) and to connect to some high-speed interfaces.

Although coax has improved data carrying characteristics, twisted pair cabling has replaced coax in local area networking uses. Among the reasons for the replacement is that - compared to UTP - coax is physically harder to install, more expensive, and harder to troubleshoot.

Coaxial cable

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Coaxial cable

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Fiber optic cables

Unlike TP and coax, fiber optic cables transmit data using pulses of light. Although not normally found in home or small business environments, fiber optic cabling is widely used in enterprise environments and large data centers.

Fiber optic cable is constructed of either glass or plastic, neither of which conducts electricity. This means that it is immune to EMI and is suitable for installation in environments where interference is a problem.

In addition to its resistance to EMI, fiber optic cables support a large amount of bandwidth making them ideally suited for high-speed data backbones. Fiber optic backbones are found in many corporations and are also used to connect ISPs on the Internet.

Each fiber optic circuit is actually two fiber cables. One is used to transmit data; the other is used to receive data.

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Multimode

Of the two forms of fiber optic, multimode is the less expensive and more widely used. The light source that produces the pulses of light is usually an LED.

It is referred to as multimode because there are multiple rays of light, each carrying data, being transmitted through the cable simultaneously. Each ray of light takes a separate path through the multimode core.

Multimode fiber optical cables are generally suitable for links of up to 2000 meters. However, improvements in technology are continually improving this distance.

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Single Mode

Single mode fiber optic cables are constructed in such a way that light can follow only a single path through the fiber.

The light source for single mode fiber optic cables is usually a LED laser, which is significantly more expensive and intense than ordinary LEDs. Due to the intensity of the LED laser, much higher data rates and longer ranges can be obtained.

Single mode fibers can transmit data for approximately 3000 meters and are used for backbone cabling including the interconnection of various NOCs. Again, improvements in technology are continually improving this distance.

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Test Yourself

FO UTP

A company must provide network connectivity between

three buildings on a single campus. The cables must be run

outside and there is a high probability of lighting storms in

the area.

A company must provide network connectivity between

two buildings located 1 km apart.

3. A company must provide 100Mbps connectivity to users

located in their main office by running cables from the

central switch to the individual desktops. The maximum

distance from the switch to a workstation is 60 meters.


Describe benefit and limitation of different

networking media in terms of :

1. Throughput

2. Noise Immunity

3. Size and Scalability

4. Cost

Outcomes 4

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1.Throughput

Probably most significant factor in choosing transmission

method

Limited by signaling and multiplexing techniques used in given

transmission method

Transmission methods using fiber-optic cables achieve faster

throughput than those using copper or wireless connections

Noise and devices connected to transmission medium can limit

throughput

UTP STP Fiber Optic Coaxial Cable

STP and UTP can both transmit data

at 10 Mbps, 100 Mbps, 1 Gbps,

and 10 Gbps, depending on the

grade of cabling and the

transmission method in use.

Fiber has proved reliable

in transmitting data at

rates that can reach 100

gigabits (or 100,000

megabits) per second per

channel.

Each type of coax is suited to a

different purpose. When discussing

the size of the conducting core in a

coaxial cable, we refer to its

American Wire Gauge (AWG) size.

The larger the AWG size, the

smaller the diameter of a piece of

wire. RG-6 coaxial cables are used,

for example, to deliver broadband

cable Internet service and cable TV,

particularly over long distances.

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2.Noise Immunity

Some types of media are more susceptible to noise than others

Fiber-optic cable least susceptible

Install cabling away from powerful electromagnetic forces

May need to use metal conduit to contain and protect cabling

Possible to use antinoise algorithms


signals transmitted over

UTP may be subject to

filtering and balancing

techniques to offset the

effects of noise.

Because of its shielding,

STP is more noise

resistant than UTP.

Because fiber does not

conduct electrical

current to transmit

signals,

it is unaffected by EMI.

Its impressive noise

resistance is one reason

why fiber can span

such long distances

before it requires

repeaters to regenerate

its signal.

Because of its shielding,

most coaxial cable has a

high resistance to noise.

It can also carry signals

farther than twisted pair

cabling before

amplification of the

signals becomes

necessary (although not

as far as fiber-optic

cabling). On the other

hand, coaxial cable is

more expensive than

twisted pair cable

because it requires

significantly more raw

materials to

manufacture.

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3.Size and Scalability

Three specifications determine size and scalability of

networking media:

Maximum nodes per segment

Depends on attenuation and latency

Maximum segment length

Depends on attenuation, latency, and segment type

Populated segment contains end nodes

Maximum network length

Sum of networks segment lengths


The maximum segment length

for both STP and UTP is 100 m,

or 328 feet, on Ethernet

networks that support data rates

from 1 Mbps to 10 Gbps.

These accommodate a maximum

of 1024 nodes. (However,

attaching so many nodes to a

segment is very impractical, as it

would slow traffic and make

management nearly

impossible.)

Depending on the type of

fiber-optic cable used,

segment lengths vary

from 150 to 40,000

meters. This limit is due

primarily to optical loss,

or the degradation of the

light signal after it travels

a certain distance away

from its source.

The maximum

segment length of 185

meters (or roughly

200).

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4.Cost

Many variables can influence final cost of implementing specific

type of media:

Cost of installation

Cost of new infrastructure versus reusing existing infrastructure

Cost of maintenance and support

Cost of a lower transmission rate affecting productivity

Cost of obsolescence


Inexpensive.

High-grade UTP, can

be expensive too,

however.

For example, Cat 6e

costs more per foot

than Cat 5 cabling

Typically, STP is

more expensive than

UTP because it

contains more

materials and it has a

lower demand. It also

requires grounding,

which

can lead to more

expensive

installation.

Fiber-optic cable is

the most expensive

transmission

medium. Because of

its cost, most

organizations find it

impractical to run

fiber to every

desktop.

In addition, hiring

skilled fiber cable

installers costs more

than hiring twisted

pair cable

installers.

The sheath, which

protects the cable

from physical

damage, may be

PVC or a more

expensive, fire-

resistant plastic.

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5.Connectors and Media Converters

Connectors: pieces of hardware connecting wire to network

device

Every networking medium requires specific kind of connector

Media converter: hardware enabling networks or segments

running on different media to interconnect and exchange

signals

Type of transceiver

Device that transmits and receives signals


STP and UTP use RJ-45

(Registered Jack 45) modular

connectors and

data jacks, which look similar

to analog telephone connectors

and jacks. However, telephone

connections follow the RJ-11

(Registered Jack 11) standard.

With fiber cabling, you can

use any of 10 different types

of connectors.

Most common connector

types:

the ST (straight tip), SC

(subscriber connector or

standard connector), LC

(local connector), and MT-

RJ (mechanical transfer

registered jack).

F-type connectors attach to coaxial

cable so that the pin in the center of

the connector is the conducting

core of the cable. Therefore, F-type

connectors require that the cable

contain a solid

metal core. A BNC connector is

crimped, compressed, or twisted

onto a coaxial cable. It connects to

another BNC connector via a turning

and locking mechanism.

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Explain the best practices for cabling buildings and

work areas.

Outcomes 5

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The best practice for installing cable is to follow the TIA/EIA 568 specifications and the manufacturers recommendations.

Be careful not to exceed a cables bend radius, untwist wire pairs more than one-half inch, or remove more than one inch of insulation from copper wire.

Install plenum-rated cable in ceilings and floors, and run cabling away from where it might suffer physical damage. Maintain clear, comprehensive documentation on your cable plant.

TIA/EIAs 568 Commercial Building Wiring Standard, also known as structured cabling, provides guidelines for uniform, enterprise-wide, multivendor cabling systems.

Structured cabling is based on a hierarchical design that begins with a service providers facilities and end at users workstations.


Cable Design and Management

Cable plant: hardware making up enterprise-wide cabling

system

Structured cabling: TIA/EIAs 568 Commercial Building

Wiring Standard

Entrance facilities point where buildings internal cabling plant

begins

Demarcation point: division between service carriers network and

internal network

Backbone wiring: interconnection between telecommunications

closets, equipment rooms, and entrance facilities

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Cable Design and Management

(continued)

Structured cabling (continued):

Equipment room: location of significant networking hardware, such as servers and mainframe hosts

Telecommunications closet: contains connectivity for groups of workstations in area, plus cross connections to equipment rooms

Horizontal wiring: wiring connecting workstations to closest telecommunications closet

Work area: encompasses all patch cables and horizontal wiring necessary to connect workstations, printers, and other network devices from NICs to telecommunications closet


Installing Cable

Many network problems can be traced to poor cable

installation techniques

Two methods of inserting UTP twisted pairs into RJ-45 plugs:

TIA/EIA 568A and TIA/EIA 568B

Straight-through cable allows signals to pass straight through

between terminations

Crossover cable: termination locations of transmit and receive

wires on one end of cable reversed

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By the end of this subtopic, student should be able to

define the characteristics of wireless transmission 1) Signal Propagation (Penyebaran isyarat)

2) Signal Degradation (Penurunan isyarat)

3) Antenna

4) Narrowband, broadband and spread spectrum signals

5) Fixed and mobile wireless communication

Outcomes 6

Wireless Network?

Networks that transmit signals through the

atmosphere via radio frequency (RF) waves are

known as wireless networks or WLANs (wireless

local area networks).

Wireless transmission media is now common in

business and home networks and necessary in

some specialized network environments.

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The Wireless Spectrum

All wireless signals are carried through the air by electromagnetic waves.

The wireless spectrum is a continuum of the electromagnetic waves used for data and voice communication. On the spectrum, waves are arranged according to their frequencies, from lowest to highest.

The wireless spectrum (as defined by the FCC, which controls its use) spans frequencies between 9 KHz and 300 GHz.

Each type of wireless service can be associated with one area of the wireless spectrum.

AM broadcasting, for example, sits near the low-frequency end of the wireless communications spectrum, using frequencies between 535 and 1605 KHz.

Infrared waves belong to a wide band of frequencies at the high-frequency end of the spectrum, between 300 GHz and 300,000 GHz.

Most cordless telephones and many wireless LANs use frequencies around 2.4 GHz. Other wireless LANs use a range of frequencies near 5 GHz.

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The Wireless Spectrum

Figure 3-37: The wireless spectrum

1. Signal propagation

A wireless signal would travel directly in a straight line from

its transmitter to its intended receiver. This type of

propagation, known as LOS (line-of-sight), uses the least

amount of energy and results in the reception of the clearest

possible signal.

When an obstacle stands in a signals way, the signal may pass

through the object or be absorbed by the object, or it may be

subject to any of the following phenomena: reflection,

diffraction, or scattering. (Pantulan, pembelauan, atau berselerak.)

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Phenomena 1 : Reflection

Reflection in wireless signaling is no different from reflection of other electromagnetic waves, such as light. The wave encounters an obstacle and reflectsor bounces backtoward its source.

A wireless signal will bounce off objects whose dimensions are large compared to the signals average wavelength. In the context of a wireless LAN, which may use signals with wavelengths between one and 10 meters, such objects include walls, floors, ceilings, and the Earth. In addition, signals reflect more readily off conductive materials, like metal, than insulators, like concrete.

Phenomena 2 : Diffraction

In diffraction, a wireless signal splits into

secondary waves when it encounters an

obstruction. The secondary waves continue to

propagate in the direction in which they were

split.

If you could see wireless signals being diffracted,

they would appear to be bending around the

obstacle. Objects with sharp edgesincluding

the corners of walls and deskscause diffraction.

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Phenomena 3 : Scattering

Scattering is the diffusion, or the reflection in multiple different directions, of a signal. Scattering occurs when a wireless signal encounters an object that has small dimensions compared to the signals wavelength.

Scattering is also related to the roughness of the surface a wireless signal encounters. The rougher the surface, the more likely a signal is to scatter when it hits that surface. In an office building, objects such as chairs, books, and computers cause scattering of wireless LAN signals. For signals traveling outdoors, rain, mist, hail, and snow may all cause scattering.

Because of reflection, diffraction, and scattering,

wireless signals follow a number of different

paths to their destination. Such signals are known

as multipath signals.

Figure below illustrates multipath signals caused

by these three phenomena.

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Network+ Guide to Networks, 4e Figure 3-39: Multipath signal propagation

2. Signal degradation

No matter what paths wireless signals take, they are bound

to run into obstacles.

When they do, the original signal issued by the transmitter

will experience fading, or a change in signal strength as a

result of some of the electromagnetic energy being

scattered, reflected, or diffracted after being issued by the

transmitter.

Because of fading, the strength of the signal that reaches the

receiver is lower than the transmitted signals strength. This

makes sense because as more waves are reflected, diffracted,

or scattered by obstacles, fewer are likely to reach their

destination.

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Attenuation is not the most severe flaw affecting

wireless signals.

Wireless signals are also susceptible to noise

(more often called electromagnetic interference

or simply, interference, in the context of wireless

communications).

Interference is a significant problem for wireless

communications because the atmosphere is

saturated with electromagnetic waves.

For example, wireless LANs may be affected by cellular phones, mobile phones, or overhead lights. Interference can distort and weaken a wireless signal in the same way that noise distorts and weakens a wired signal. However, because wireless signals cannot depend on a conduit or shielding to protect them from extraneous EMI, they are more vulnerable to noise.

The extent of interference that a wireless signal experiences depends partly on the density of signals within a geographical area. Signals traveling through areas in which many wireless communications systems are in usefor example, the center of a metropolitan areaare the most apt to suffer interference.

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3. Antenna

Just as with wired signals, wireless signals originate from electrical current traveling along a conductor. The electrical signal travels from the transmitter to an antenna, which then emits the signal, as a series of electromagnetic waves, to the atmosphere. The signal propagates through the air until it reaches its destination.

At the destination, another antenna accepts the signal, and a receiver converts it back to current. Figure below illustrates this process.

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Each type of wireless service requires an antenna specifically designed for that service.

The services specifications determine the antennas power output, frequency, and radiation pattern. An antennas radiation pattern describes the relative strength over a three-dimensional area of all the electromagnetic energy the antenna sends or receives.

A directional antenna issues wireless signals along a single direction. This type of antenna is used when the source needs to communicate with one destination, as in a point-to-point link. A satellite downlink (for example, the kind used to receive digital TV signals) uses directional antennas.

In contrast, an omnidirectional antenna issues and receives wireless signals with equal strength and clarity in all directions. This type of antenna is used when many different receivers must be able to pick up the signal, or when the receivers location is highly mobile.TV and radio stations use omnidirectional antennas, as do most towers that transmit cellular telephone signals.

The geographical area that an antenna or wireless system can reach is known as its range. Receivers must be within the range to receive accurate signals consistently. Even within an antennas range, however, signals may be hampered by obstacles and rendered unintelligible.

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4. Narrowband, broadband and spread

spectrum signals.

Narrowband : A transmitter concentrates the signal energy at a

single frequency or in a very small range of frequencies.

Broadband : Uses a relatively wide band of the wireless

spectrum. Broadband technologies, as a result of their wider

frequency bands, offer higher throughputs than narrowband

technologies.

Spread-spectrum : The use of multiple frequencies to transmit

a signal is known as spread-spectrum technology (because the

signal is spread out over the Wireless spectrum).

In other words, a signal never stays continuously

within one frequency range during its transmission.

One result of spreading a signal over a wide

frequency band is that it requires less power per

frequency than narrowband signaling. This

distribution of signal strength makes spread-

spectrum signals less likely to interfere with

narrowband signals traveling in the same frequency

band.

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Wireless

Communication

Fixed and mobile wireless communication

Fixed VS Mobile?

In fixed wireless systems, the locations of the transmitter and receiver

do not move. The transmitting antenna focuses its energy directly

toward the receiving antenna. This results in a point-to-point link.

One advantage of fixed wireless is that because the receivers location

is predictable, energy need not be wasted issuing signals across a large

geographical area. Thus, more energy can be used for the signal.

Fixed wireless links are used in some data and voice applications.For

example, a service provider may obtain data services through a fixed

link with a satellite. In cases in which a long distance or difficult

terrain must be traversed, fixed wireless links are more economical

than cabling.

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However, many types of communications are unsuited to

fixed wireless, For example, a waiter who uses a wireless

handheld computer to transmit orders to the restaurants

kitchen could not use a service that requires him to remain

in one spot to send and receive signals. Instead, wireless

LANs, along with cellular telephone, paging, and many

other services use mobile wireless systems.

In mobile wireless, the receiver can be located anywhere

within the transmitters range. This allows the receiver to

roam from one place to another while continuing to pick up

its signal.

Fixed VS Mobile?


Summary

Information can be transmitted via two methods: analog or digital

In multiplexing, the single medium is logically separated into multiple channels, or subchannels

Throughput is the amount of data that the medium can transmit during a given period of time

Baseband is a form of transmission in which digital signals are sent through direct current pulses applied to the wire

Noise is interference that distorts an analog or digital signal

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Summary (continued)

Analog and digital signals may suffer attenuation

Cable length contributes to latency, as does the presence of any

intervening connectivity device

Coaxial cable consists of a central copper core surrounded by a

plastic insulator, a braided metal shielding, and an outer plastic

cover (sheath)

Twisted-pair cable consists of color-coded pairs of insulated

copper wires

There are two types of twisted-pair cables: STP and UTP


Summary (continued)

There are a number of Physical layer specifications for Ethernet

networks

Fiber-optic cable provides the benefits of very high throughput,

very high resistance to noise, and excellent security

Fiber cable variations fall into two categories: single-mode and

multimode

Structured cabling is based on a hierarchical design that divides

cabling into six subsystems

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Summary (continued)

The best practice for installing cable is to follow the TIA/EIA

568 specifications and the manufacturers recommendations

Wireless transmission requires an antenna connected to a

transceiver

Infrared transmission can be used for short-distance

transmissions

Documents

Unit 3 - Data Transmission and Networking Media