Objectives
Explain data transmission concepts including fullduplexing, attenuation, and noise
Describe the physical characteristics of coaxial cable, STP, UTP, and fiber-optic media
Explain the benefits and limitations of different networking media
Identify the best practices for cabling buildings and work areas
Describe the methods of transmitting data through the atmosphere

Transmission Basics
Transmission has two meanings:

Refers to process of issuing data signals on a medium

Refers to progress of data signals over a medium
On a data network, information can be transmitted via one of two methods:

Analog

Digital

Transmission Basics
Both analog and digital signals are generated by electrical current, pressure of which is measured in
In analog signals, voltage varies continuously
In digital signals, voltage turns off and on repeatedly

Transmission Basics
Figure 4-1: Example of an analog signal

Transmission Basics

Measure of a signal’s strength

Number of times a signal’s amplitude changes over a period of time

Expressed in h ertz (Hz)

Distances between corresponding points on a wave’s cycle

Transmission Basics
Phase

Refers to progress of a wave over time in relationship to a fixed point
Figure 4-2: Phase differences

Transmission Basics
Figure 4-3: A complex analog signal representing human speech

Transmission Basics
system encodes using 1s and 0s
can only have a value of either 1 or 0
Eight bits together form a
or any interference that may degrade signals affects digital signals less than analog signals

Transmission Basics
Figure 4-4: Example of a digital signal

Data Modulation
Modem

Name reflects function as modulator/demodulator
Modulation

Technique for formatting signals
Frequency modulation (FM)

Method of data modulation in which frequency of carrier signal is modified by application of a data signal
Amplitude modulation (AM)

Modulation technique in which amplitude of carrier signal is modified by application of a data signal

Data Modulation
Figure 4-5: A carrier wave modified by frequency modulation

Transmission Direction

Signals travel in only one direction

Signals may travel in both directions over a medium but in only one direction at a time

Signals are free to travel in both directions over a medium simultaneously

Also referred to just as duplex

Transmission Direction
Channel

Distinct communication path between two or more nodes
Figure 4-6: Simplex, half-duplex, and full-duplex transmission

Transmission Direction
Multiplexing

Allows multiple signals to travel simultaneously over one medium

To accommodate multiple signals, single medium is logically separated into subchannels

For each type of multiplexing:
Multiplexer (mux) is required at sending end of channel
Demultiplexer (demux) separates the combined signals and regenerates them in original form

Transmission Direction
Time division multiplexing (TDM)

Divides channel into multiple intervals of time
Figure 4-7: Time division multiplexing

Transmission Direction
Wavelength division multiplexing (WDM)



Used only with fiber-optic cable
Data is transmitted as pulses of light
Fiber-optic modem (FOM) is a demultiplexer used on fiber networks that employ WDM
Figure 4-9: Wavelength division multiplexing

Relationships Between Nodes

Transmission involving one transmitter and one receiver

Transmission involving one transmitter and multiple receivers

Broadcast transmission used over the Web

Relationships Between Nodes
Figure 4-10: Point-to-point versus broadcast transmission

Throughput and Bandwidth
is amount of data the medium can transmit during a given period of time

Also called capacity
measures difference between highest and lowest frequencies a media can transmit

Range of frequencies is directly related to throughput

Transmission Flaws
Electromagnetic interference (EMI)

Interference that may be caused by motors, power lines, television, copiers, fluorescent lights, or other sources of electrical activity
Radiofrequency interference (RFI)

Interference that may be generated by motors, power lines, televisions, copiers, fluorescent lights, or broadcast signals from radio or TV towers

Transmission Flaws
Figure 4-11: An analog signal distorted by noise

Transmission Flaws
Figure 4-12: A digital signal distorted by noise

Transmission Flaws
Attenuation


Loss of signal strength as transmission travels away from source
Analog signals pass through an amplifier , which increases not only voltage of a signal but also noise accumulated
Figure 4-13: An analog signal distorted by noise, and then amplified

Transmission Flaws
Regeneration

Process of retransmitting a digital signal
Repeater

Device used to regenerate a signal
Figure 4-14: A digital signal distorted by noise, and then repeated

Consists of central copper core surrounded by an insulator, braiding , and outer cover called a sheath
Coaxial Cable
Figure 4-15: Coaxial cable

Coaxial Cable
Table 4-2: Some types of coaxial cable

Thicknet (10Base5)
Also called
Rigid coaxial cable used on original Ethernet networks
IEEE designates Thicknet as
Ethernet
Almost never used on new networks but you may find it on older networks

Used to connect one data closet to another as part of network backbone

Thicknet Characteristics

According to IEEE 802.3, Thicknet transmits data at maximum rate of 10 Mbps

Less expensive than fiber-optic but more expensive than some other types of coaxial cable

Can include a few different types of connectors, which are very different from those used on modern networks

Thicknet Characteristics
N-series connector (or n connector)

Screw-and-barrel arrangement securely connects coaxial cable segments and devices
Figure 4-18: N-Series connector

Thicknet Characteristics

Because of its wide diameter and excellent shielding, has the highest resistance to noise of any commonly used types of network wiring

Because of its high noise resistance, it allows data to travel longer than other types of cabling

Thinnet (10Base2)
Also known as thin Ethernet
Characteristics:



Throughput
Can transmit at maximum rate of 10 Mbps
Cost
Less expensive than Thicknet and fiber-optic cable
More expensive than twisted-pair wiring
Connectors
Connects wire to network devices with BNC T-connectors
A seen in Figure 4-19, BNC barrel connectors are used to join two Thinnet cable segments together

Thinnet (10Base2)
Characteristics
(cont.):


Size and scalability
Allows a maximum of 185 m per network segment
(see Figure 4-20)
Noise immunity
More resistant than twisted-pair wiring
Less resistant than twisted-pair wiring
Figure 4-19: Thinnet BNC connectors

Thinnet (10Base2)
Signal bounce



Caused by improper termination on a bus network
Travels endlessly between two ends of network
Prevents new signals from getting through
Figure 4-20: A 10Base2 Ethernet network

Twisted-Pair (TP) Cable
Color-coded pairs of insulated copper wires twisted around each other and encased in plastic coating
Twists in wire help reduce effects of crosstalk

Number of twists per meter or foot known as twist ratio
Alien Crosstalk

When signals from adjacent cables interfere with another cable’s transmission
Figure 21: Twisted-pair cable

Shielded Twisted-Pair (STP)
STP cable consists of twisted wire pairs that are individually insulated and surrounded by shielding made of metallic substance
Figure 4-22: STP cable

Unshielded Twisted-Pair
Consists of one or more insulated wire pairs encased in a plastic sheath
Does not contain additional shielding
Figure 4-23: UTP cable

Unshielded Twisted-Pair
To manage network cabling, it is necessary to be familiar with standards used on modern networks, particularly
Category 3 (CAT3) and Category 5
(CAT5)
Figure 4-24: A CAT5 UTP cable

Comparing STP and UTP
Throughput

Both can transmit up to 100 Mbps
Cost

Typically, STP is more expensive
Connector

Both use RJ-45 connectors (see Figure 4-27) and data jacks
Noise immunity

STP is more noise-resistant
Size and scalability

Maximum segment length for both is 100 meters

RJ-45 Connector
Figure 4-27: An RJ-45 connector

Fiber-Optic Cable
Contains one or several glass fibers at its core

Surrounding the fibers is a layer of glass called cladding
Figure 4-28: A fiber-optic cable

Fiber-Optic Cable
Single-mode fiber

Carries light pulses along single path
Multimode fiber

Many pulses of light generated by LED travel at different angles
Figure 4-29: Single-mode and multimode fiber-optic cables

Fiber-Optic Cable
Throughput

Reliable in transmitting up to 1 gigabit per second
Cost

Most expensive type of cable

Fiber-Optic Cable

Unaffected by either EMI or RFI

Network segments made from fiber can span
100 meters

Signals transmitted over fiber can experience optical loss

Fiber-Optic Cable
Two popular connectors used with fiber-optic cable:

ST connectors

SC connectors
Figure 4-30: ST and SC fiber connectors


networks use infrared light signals to transmit data through space

depends on transmitter and receiver remaining within line of sight

In
, signals can bounce off of walls, ceilings, and any other objects in their path


Radio frequency (RF) transmission relies on signals broadcast over specific frequencies

Two most common RF technologies:
Narrowband
Spread spectrum

Chapter Summary
Information can be transmitted via analog or digital methodology
Throughput is the amount of data a medium can transmit during a given period of time
Noise is interference that distorts an analog or digital signal
Costs depend on many factors
There are three specifications that dictate size and scalability of networking media
Connectors connect wire to the network device

Chapter Summary
Coaxial cable consists of central copper core surrounded by an insulator and a sheath
Thicknet cabling is a rigid coaxial cable used for original Ethernet networks
Both Thicknet and Thinnet coaxial cable rely on bus topology and must be terminated at both ends with a resistor
Twisted-pair cable consists of color-coded pairs of insulated copper wires, twisted around each other and encased in plastic coating

Chapter Summary
STP cable consists of twisted pair wires individually insulated and surrounded by a shielding made of metallic substance
UTP cabling consists of one or more insulated wire pairs encased in a plastic sheath
Fiber-optic cable contains one or several glass fibers in its core
On today’s networks, fiber is used primarily as backbone cable