Transmission Media - Information Technology

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24 Νοε 2013 (πριν από 4 χρόνια και 7 μήνες)

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Prepared by Miss N. Nembhard

Fundamentals of Information Technology

TOPIC: Telecommunications and Networks


Transmission Media

Communication involves the transfer of information in the form of text, graphic images,
sound or moving pictures from one place to

another. The medium through which this
transfer takes place

transmission media

determines the effectiveness of such
communication. It is important to understand the types of media available, their method
of construction and their advantages and disadv
antages in different situations.

Transmission media

refers to the physical means by which information is transferred. It
does not include books, compact disks, tapes, floppy disks, photographs and slides which
are themselves moved from one site to anothe
r. Transmission media, then, includes
electrical wires, coaxial cables, optical fibers and electromagnetic waves. Transmission
media can therefore be said to be



When choosing the transmission media, the following factors have to be consi

Transmission Rate


Cost and Ease of Installation

Resistance to Environmental


Wired Transmission Media

What is Network Cabling?

Cable is the medium through which information usually moves from one network device
to another.
There are several types of cables, which are commonly used with LANs. In
some cases, a network will utilize only one type of cable, other networks will use a
variety of cable types. The type of cable chosen for a network is related to the network's
y, protocol, and size. Understanding the characteristics of different types of cable
and how they relate to other aspects of a network is necessary for the development of a
successful network.

The following types of wired media might be used to set up a ne

Twisted Pairs

Coaxial Cable

Fiber Optic Cable
Twisted Pairs

Twisted pair cabling comes in two
varieties: shielded and unshielded.
Unshielded twisted pair (UTP) is the
most popular and is generally the best
option for school networks (See fig. 1).

Fig.1. Unshielded twisted pair

Prepared by Miss N. Nembhard

The quality of UTP may vary from
grade wi
re to extremely high
speed cable. The cable has four pairs of
wires inside the jacket. Each pair is
twisted with a different number of twists
per inch to help eliminate interference
from adjacent pairs and other electrical
devices. The tighter the twisting
, the
higher the supported transmission rate
and the greater the cost per foot.

Unshielded Twisted Pair Connector

The standard connector for unshielded
twisted pair cabling is an RJ
connector. This is a plastic connector
that looks like a large telepho
connector (See fig. 2). A slot allows the
45 to be inserted only one way. RJ
stands for Registered Jack, implying that
the connector follows a standard
borrowed from the telephone industry.
This standard designates which wire
goes with each pin

inside the connector.

Fig. 2. RJ
45 connector

Shielded Twisted Pair (STP) Cable

A disadvantage of UTP is that it may be
susceptible to radio and electrical
cy interference. Shielded twisted
pair (STP) is suitable for environments
with electrical interference; however, the
extra shielding can make the cables quite
bulky. Shielded twisted pair is often
used on networks using Token Ring

Coaxial Cab

Coaxial cabling has a single copper
conductor at its center. A plastic layer
provides insulation between the center
conductor and a braided metal shield
(See fig. 3). The metal shield helps to
block any outside interference from
fluorescent lights, moto
rs, and other

Fig. 3. Coaxial cable

Although coaxial cabling is difficult to
install, it is highly resistant to signal
interference. In addition, it
can support
greater cable lengths between network
devices than twisted pair cable. The two
types of coaxial cabling are thick coaxial
and thin coaxial

Fiber Optic Cable

Fiber optic cabling consists of a center glass core
surrounded by several layers of p
materials (See fig. 5). It transmits light rather
than electronic signals eliminating the problem
of electrical interference. This makes it ideal for
certain environments that contain a large amount
of electrical interference. It has also made it


standard for connecting networks between
buildings, due to its immunity to the effects of
moisture and lighting.

Fiber optic cable has the ability to transmit
signals over much longer distances than coaxial
and twisted pair. It also has the capabilit
y to
carry information at vastly greater speeds. This
capacity broadens communication possibilities to
include services such as video conferencing and
interactive services. The cost of fiber optic
cabling is comparable to copper cabling;
however, it is mor
e difficult to install and

Fig.5. Fiber optic cable
Prepared by Miss N. Nembhard

Transmission Media Comparison Chart


| M


| Twisted | Inexpensive | Sensitive to noise |

| Pair | Well understood | Short distances |

| Cable | Eas
y to add nodes | Limited bandwidth |

| | | Security

easily tapped |


| Coaxial | High bandwidth |


| Cable | Long dist
ances | Security

easily tapped |

| | Noise immunity | |


| Optical | Very high bandwidth | Connections |

| Fiber | Noise immunity |

T splitters |

| Cable | Long distances | |

| | High security | |

| | Small size | |


Wireless Transmission Media

Wireless LANs

Not all networks are connected with cabling;
some networks are wireless. Wireless LANs use
high frequen
cy radio signals, infrared light
beams, or lasers to communicate between the
workstations and the file server or hubs. Each
workstation and file server on a wireless network
has some sort of transceiver/antenna to send and
receive the data. Information is
relayed between
transceivers as if they were physically connected.
For longer distance, wireless communications
can also take place through

cellular telephone

microwave transmission

or by


Wireless networks are great for allowing lap
computers or remote computers to connect to the
LAN. Wireless networks are also beneficial in
older buildings where it may be difficult or
impossible to install cables.


The two most common types of
communications used in schools are
scattered broadcast
. Line
communication means that there must be an
unblocked direct line between the workstation
and the transceiver. If a person walks within the
sight while there is a transmission, the
information woul
d need to be sent again. This
kind of obstruction can slow down the wireless

Scattered infrared communication is a broadcast
of infrared transmissions sent out in multiple
directions that bounces off walls and ceilings
until it eventually hits the

receiver. Networking
communications with laser are virtually the same
as line
sight infrared networks.

Wireless LANs have several disadvantages.
They provide poor security, and are susceptible
to interference from lights and electronic
devices. They ar
e also slower than LANs using


An extremely high frequency (1 GHz or higher)
"line of sight" radio link carries a point
signal, which is accurately focused using dish
antennas. Since it is a line of sight transmission,
towers need to be located about every
35 km. In a microwave radio system,
telecommunications traffic is transmitted in the
Prepared by Miss N. Nembhard

form of directed beams of microwaves.
Microwaves are a kind of electromagnetic
radiation like light or like the radio waves used
in o
rdinary broadcasting, but of a frequency
intermediate between these.

Microwave transmission

refers to the technique
of transmitting information over a

Since microwaves are highly susceptible to
attenuation by the atmosphere (especially dur
wet weather), the use of microwave transmission
is limited to a few contexts.

microwave link

is a transmission

allows video / audio / data to be sent using
radio waves between two locations from just a
few feet to several miles apart. It

is commonly
used by television broadcasters to transmit a
programme across the country. For instance,
from an Outside Broadcast back to a studio.
Mobile units can be camera mounted and are
used to allow cameras the freedom to move
around without trailing
cables. Often seen on the
touchline of field sports games on a


Microwave systems have sufficient bandwidth
capacity to support a large number of voice
channels and one
or two television channels and
can achieve high bit rates over moderately long
distances. They have been used extensively in
inner city data systems where cabling would be
very expensive.

Uses of Microwave


In communication between the
Satellites and base


As a backbone carrier for Cellular


In short range indoor communications

Each base station u
ses two forms of technology
to function. GSM radio signals connect mobile
handsets to a tower, while microwave
transmission links one tower to another in a
linear network.

This worker is taking a compass reading to make
sure a tower's antenna is pointing
in the correct



are a special application of a
microwave system. Here, ground stations with
large dishes direct information to a
communications satellite in geostationary orbit
above the Equator. Originally these satellite
were passive objects but the modern satellite
captures the signal, amplifies it using a
transponder, and relays it back to Earth or on to
another satellite. Each channel is managed by a
transponder, which can support thousands of
speech channels and abou
t four television
channels simultaneously. Despite their high cost
of construction and launch, satellites have
become part of our way of life for live television,
international telephone and data links


is a specification for the use of low
radio communications to wirelessly link phones,
computers and other network devices over short

tooth technology was designed
primarily to support simple wireless networking
of personal consumer devices and peripherals,
including cell

phones, PDAs, and wireless
headsets. Wireless signals transmitted with Blue

tooth cover short distances, typically up to 30
feet (10 meters). Bluetooth devices generally
communicate at less than 1 Mbps.


Fi (short for "wireless fidelity"),it


industry name for wireless LAN (WLAN)
communication technology related to the IEEE
802.11 family of wireless networking standards.

Although the Blue tooth standard utilizes the
same 2.4 Ghz range as, Blue tooth technology is
not a suitable Wi
Fi repl
acement. Compared to
Fi, Bluetooth networking is much slower, a
bit more limited in range, and supports many
fewer devices.