Chapter 3
 All
transmissions must be carried by some
medium, whether it be copper, glass, or radio
or light waves in space.
 Each
medium has a capacity and each has a
susceptibility to noise.
 Noise
is any unwanted, detectable signal that
coexists with the intended signal.


Radio Frequency Interference (RFI)
Electromagnetic Interference (EMI)
2

A communications circuit is a path over which a
signal can travel.

Circuits are generally thought of as something
physical, like wire or radio wave.

A channel is the actual path for the signal and may
occupy the total circuit or be a portion of it.
Chapter 3
3

Electrical uses direct or alternating current to
carry a signal on a conductive medium.

Electromagnetic circuits use rapidly varying
(high-frequency) current to carry the signal.

Photonic circuits use light as the data carrier on
a transparent media.
Chapter 3
4
 Crosstalk
is the radiation of signals from
one circuit to another.
5
is the reduction of signal strength (or voltage) as
the signal propagates along the circuit.
This means the voltage level of the signal is lowered
as the signal moves down the wire.
To keep the signal at acceptable levels, a repeater or
amplifier is placed along the circuit to amplify the
signal.
6
+
Signal strength
Attenuation
B
A
Noise level
0
Distance
A
Signal/Noise ratio = B/A
A
A
A
= Amplification
7
Twistedpair copper
Coaxial
cable
Radio
Photonic
Microwave
Fiber optic
Satellite
Infrared
Omnidirectional
Chapter 3
8
Guided media provides a physically limited path for the
signals.
A signal travelling along the media is directed &
contained by the physical limits of the medium.
The simplest & most common type of guided media.
Made of 2 insulated copper wires & twisted together
to reduce the effect of electrical interference.
There are 2 forms: shielded & unshielded.
suitable for transmitting data & voice.
consists of 2 copper conductors, each with its own
coloured plastic insulation.
Twisted-pair copper wire is the most used, lowest
cost media.
 A loop formed with a single wire going from the
sender to the receiver and back.
 Seen as a pair of wires.

1.
2.
3.
4.
5.
22-26 gauge copper
Low bandwidth
Used for virtually all local loops
Low installation cost
Susceptible to noise
Chapter 3
11
STP Cable has a metal foil / braided-mesh covering that
encases each pair of insulated conductors.
The metal casing prevents the penetration of electromagnetic
noise & eliminate crosstalk (during telephone conversation).
More expensive than UTP.
Less susceptible to noise.
Unshielded
Double Shield Foil and Braid
Chapter 3
Single Shield
Individually Shielded Pair
13
Coaxial Cable carries higher-frequency ranges of signals.
It has a core central conductor of solid / stranded copper wire
enclosed in an insulating sheath.
The outer metallic wrapping shield against noise & becomes
the 2nd conductor which completes the circuit.
Outer conductor enclosed in an insulating sheath.
The whole cable protected by a plastic cover.

External
wrapping
Conductor
Coaxial cable is similar to
a pair of copper wires
except that one wire is a
sheath that encompasses
the other wire and shields Insulator
it from noise.
Outer conductor
(shield)
1.
2.
3.
4.
5.
6.
7.
Ground is shielded (immune to interference)
Bandwidth of 300MHz, 500 MHz, 750 MHz
Up to 10,800 voice conversations
Amplifiers every mile
50-100 analog TV channels/cable
Cable tapped easily; low to medium security
Any analog channel can be digitized with modems with a
bandwidth of 27 Mbps.
Chapter 3
15
1.63 mm
Solid wire
Stranded wire
The two wires above have the same capacity
 Both are 14 gauge and are 1.63 mm thick
 Stranded wire is composed of a group of smaller
solid wires.
 Stranding makes the wire more flexible

16
Made of glass or plastic
Difficult to splice/merge
Secure
Very high speed
Unidirectional strand
Difficult to split signal
Immune to RFI, EMI , crosstalk
Most expensive, greatest bandwidth = low cost/bit
Chapter 3
17
Fiber optic cables are made
up of very small one-way
glass stands that have the
greatest bandwidth of any
media used.
 Circuits often begin and end
with some other media.

Glass core
Protective coating
(jacket)
Glass
cladding
Protective coating
(jacket)
Coherent light
beam
Glass
cladding
Chapter 3
Glass core
18
 Dense
Wave Division Multiplexing (DWDM) is a
fiber optic transmission technique that
employs multiple light wavelengths to transmit
data.
 Allows
for the better use of the full bandwidth
of a fiber strand.
Chapter 3
19
 Hybrid
Fiber/Coax Service (HFC) makes use of
the installed CATV (Community Access
Television) network in the neighborhood and
uses fiber for high-speed, high-quality
distribution to the neighborhood.
 Fiber-To-The-Curb
(FTTC)
has
greater
bandwidth and lower noise than HFC, but will
be very expensive to run all the way to the
premise.
Chapter 3
20
Circuit Media
Analog Bandwidth (MHz)
Twisted pair
1
Coaxial cable
350, 500, and 750
Microwave radio
30 (1 channel)
Satellite radio
6 (per channel)
Omni-directional radio
0.010 AM, 0.2 FM
Television
6 (per channel)
Telephone channel
0.004
Chapter 3
21
 Broadband
is high speed or wide bandwidth.
 Generally meaning an analog path that is
frequency division multiplexed to create
several channels.
 Baseband
uses all bandwidth of a circuit as one
channel.
 A narrow band, generally not subdivided into
channels
 Often describing a digital circuit.
Chapter 3
22
sends information in the form of an analog signal.
 Each transmission is assigned to a portion of the
bandwidth, hence multiple transmissions are
possible at the same time.
 Communication is unidirectional, so in order to
send and receive, two pathways are needed.

data is sent as digital signals through the media as
a single channel that uses the entire bandwidth of
the media.
 Communication is bi-directional, which means that
the same channel can be used to send and receive
signals.

Chapter 3
23
Wireless is the driving technology of the 21st
century.
 Wireless is the absence of physical channels.
 A wired circuit means the user is tethered to the
point of connection.
 Fixed wireless is designed to be a point-to-point
like and is not designed to be movable.
 Offers the potential of bypassing the expense for
new providers of having to install the last mile.
 Potentially faster to install.
 Fixed wireless is a direct replacement for a wired
circuit.

Chapter 3
24
Forms of wireless connectivity:
• Fixed node
• desktop machines and servers
• Moveable node
• laptops that are carried from point-to-point
• Moving node
• wireless PDAs and palmtop computers
Chapter 3
25
Radio is a medium that has become more
valuable for new wireless applications.
 Use omnidirectional transmitters and receivers.

Chapter 3
26
High Definition Television (HDTV) increases the
information-carrying capacity of the TV channel
but required greater bandwidth.
 HDTV can be in the analog or digital environment.

Internet TV means user can see any station’s
programming anywhere on the globe.
 As bandwidth of the Internet increases and delays
decrease, this generally “free” resource
continues to evolve.
 Can make a local provider a global competitor.

Chapter 3
27
1. 4-28 GHz voice circuits in a 30-MHz-wide
channel.
2. Line of sight – 20 to 30 miles between towers
3. Mostly used for analog.
4. Subject to interference by rain.
5. Must have an FCC license, regulated.
6. No right-of-permit required; great for buildingto-building within a city.
Chapter 3
28
In terrestrial microwave, the distance coverable depends on
the height of antennas
the taller the antennas, the longer the sight distance.
Microwave signals propagate in 1 direction at a time.
Repeater is installed with each antenna, will broadcast the
regenerated signal.
Terrestrial microwave with repeaters provide the basis for
most
contemporary
telephone
systems
worldwide.
1. Uplink and downlink each 22,300 miles
(geosynchronous orbit).
2. Footprint is one-third of earth.
3. Propagation delay = 44,600 miles/186 mps =
.2398 seconds
4. Most common carriers have left satellite for
terrestrial.
5. Only security is encryption.
Chapter 3
30
Satellite Communication
• Satellite transmission → principle same as terrestrial microwave with
satellite is like the antenna with a repeater.
• Satellite microwave → provide transmission capability to & from any
location on earth.
• Creates high-quality communication.
• Extremely expensive.
1.
2.
3.
4.
Wireless – replaces wires and cables.
Passes through walls.
Very localized.
Easy to install; easy to move.
1.
2.
3.
4.
5.
6.
Limited to within a set of walls (room).
Omni-directional.
Low speed.
Easy to install; easy to move.
Not secure.
Very localized.
Chapter 3
32

Cellular telephone is one of the fastest growing areas
in telecommunications.

An air-medium technology.

It is the replacement for mobile radio-telephones and
the precursor of PCS.

PCS (Personal Communications System) is digital
telephone plus paging.

All cellular phones use analog carrier signals; the
voice may be digital, as in the case of PCS.

Call phones do not have dial tones, they send a data
packet to request the desired party.
33
To PSTN
BS
BS
BS
BS
BS
MSC
BS
BS
BS = Base Station
MSC = Mobile Switching Center
34

Microwave radio circuits are special air-medium, highfrequency, line-of-sight radio systems that send signals
from one transmitting station to one receiving station.

Generally 20-30 miles apart.

Transmission is unidirectional (simplex).
 Portable
(or cordless) telephone

Use two FM radio transmitter-receivers to replace
wire from handset to base station.

Transmitters operate at different frequencies to
provide full duplex.

Newest phones use spread spectrum technology.
Chapter 3
35

Same as microwave radio except sending station
transmits to a satellite relay station 22,300 miles
above earth.

Signal is relayed down to another earth station.

Satellite is in a geosynchronous orbit.

Three satellites can cover earth’s surface.

Problem is propagation delay.
Chapter 3
36
Geosynchronous Satellite moves at the same speed of the
earth, therefore it seems to remain fixed above a certain
spot.
Only 1 orbit can be geosynchronous
Orbital speed is based on distance from the planet.
37
Direct broadcast satellites use VSAT (Very Small Aperture
Terminal) antennas which provide competition for CATV
(Community Access TV) providers.
Also called wireless Cable TV.
Signal is usually all digital.
Allows getting information from the Internet on cellular
telephones, pagers, or PDAs.
Aspects of wireless Internet access:
• Information to a portable device.
• Wireless access to a stationary computer.
38
Up to 3 Mbps
Full Duplex
up to 20-mile range
Point-to-point transmission of synchronous data
39
802.16
Base station
s
Cable TV
802.11b
High-speed
wireless
Ethernet
Home
p
Mb
13
96
4M
bp
s
32 Mbp
s
802.16
Intra-building
wireless link
802.16
Subscriber
station
Office
building
802.11
Wireless
Ethernet
School
40