Transmission media or communication
channels of network meant that connecting
cables or connecting media, The cables that
connect you mean by transmission media
What dotwo or more workstations are the
communication channels. The transmission
media are of mainly two types.
Guided Media is that contain some conducting
material to carry data or signal. Many types of cable and
wires fall under this category. Each of them has its own
characteristics like transmission speed, effects of noise.
Guided media is also known as wired media. In this we will
use wires to send our data from one place to other place.
Types of Guided Media
Radio waves Transmission
Twisted pair consists of two conductors
(normally copper), each with its own plastic
insulation, twisted together.
Twisted-pair cable comes in two forms:
unshielded and shielded
The twisting helps to reduce the interference
(noise) and crosstalk.
UTP and STP
Unshielded twisted pair cable and
shielded twisted pair cable
Any medium can transmit only a fixed range of frequencies!
UTP cable is the most common type of telecommunication medium
in use today.
The range is suitable for transmitting both data and video.
Advantages of UTP are its cost and ease of use. UTP is
cheap, flexible, and easy to install.
The Electronic Industries Association (EIA) has developed
standards to grade UTP.
1.Category 1. The basic twisted-pair cabling used in
telephone systems. This level of quality is fine for voice but
inadequate for data transmission.
2.Category 2. This category is suitable for voice and data
transmission of up to 2Mbps.
3.Category 3.This category is suitable for data transmission of
up to 10 Mbps. It is now the standard cable for most telephone
4.Category 4. This category is suitable for data transmission of
up to 20 Mbps.
5.Category 5. This category is suitable for data transmission of
up to 100 Mbps.
Categories of unshielded twisted-pair cables
< 100 kbps
< 2 MHz
The most common UTP connector is RJ45 (RJ stands for
STP cable has a metal foil or braided-mesh
covering that enhances each pair of insulated
The metal casing prevents the penetration of
Materials and manufacturing requirements
make STP more expensive than UTP but less
susceptible to noise.
Twisted-pair cables are used in telephones lines to provide
voice and data channels.
The DSL lines that are used by the telephone companies to
provide high data rate connections also use the highbandwidth capability of unshielded twisted-pair cables.
Local area networks, such as 10Base-T and 100Base-T, also
used UTP cables.
This type of cable consist of a solid wire core
surrounded by one or more foil or wire shields, each
separated by some kind of plastic insulators.
Inner core carries the signal, and the shield provides
Coaxial cable carries signals of higher frequency
ranges than twisted-pair cable.
Coaxial Cable standards: RG-8, RG-9, RG-11 are used
in thick Ethernet RG-58 Used in thin Ethernet RG-59
Used for TV
Types of coaxial cables
Thicknet : this form of coaxial cables is thinnet.
The thicknet coaxial cable segments (while
joining nodes of a network) can be up to 500
Thinnet : this form of coaxial cable is thinner
and it can have maximum segment length of 185
meters that is using this cables, nodes having
maximum distance of 185 meters can be joined.
Metal cables transmit signals in the form of electric
Optical fiber is made of glass or plastic and transmits
signals in the form of light.
Light, a form of electromagnetic energy, travels at
300,000 Kilometers/second ( 186,000 miles/second), in a
The speed of the light depends on the density of the
medium through which it is traveling ( the higher density,
the slower the speed).
There are two basic types of fiber: multimode fiber
and single-mode fiber.
Multimode fiber is best designed for short
transmission distances, and is suited for use in LAN
systems and video surveillance.
Single-mode fiber is best designed for longer
transmission distances, making it suitable for longdistance telephony and multichannel television
supports two modes for
propagating light along
optical channels, each
requiring fiber with
and Single Mode.
Multimode, in turn, can be
implemented in two forms:
step-index or graded index.
Multimode: In this case multiple beams from a
light source move through the core in different
In multimode step-index fiber, the density of
the core remains constant from the center to the
edges. A beam of light moves through this
constant density in a straight line until it reaches
the interface of the core and cladding. At the
interface there is an abrupt change to a lower
density that alters the angle of the beam’s
In a multimode graded-index fiber the
density is highest at the center of the core and
decreases gradually to its lowest at the edge.
Single mode uses
step-index fiber and a
highly focused source
of light that limits
beams to a small range
of angles, all close to
Optical fibers are
defined by the ratio of
the diameter of their
core to the diameter of
their cladding, both
expressed in microns
Light sources for optical fibers
The purpose of fiber-optic cable is to contain and
direct a beam of light from source to target.
The sending device must be equipped with a light
source and the receiving device with
photosensitive cell (called a photodiode) capable
of translating the received light into an
The light source can be either a light-emitting
diode (LED) or an injection laser diode.
The subscriber channel (SC) connector is used in cable TV. It
uses a push/pull locking system. The straight-tip (ST)
connector is used for connecting cable to networking devices.
MT-RJ is a new connector with the same size as RJ45.
The major advantages offered by fiber-optic cable
over twisted-pair and coaxial cable are noise
resistance, less signal attenuation, and
Noise Resistance: Because fiber-optic
transmission uses light rather than
electricity, noise is not a factor. External light, the
only possible interference, is blocked from the
channel by the outer jacket.
Less signal attenuation
Fiber-optic transmission distance is significantly greater
than that of other guided media. A signal can run for miles
without requiring regeneration.
Currently, data rates and bandwidth utilization over fiberoptic cable are limited not by the medium but by the signal
generation and reception technology available.
The main disadvantages of fiber optics are
cost, installation/maintenance, and fragility.
Cost. Fiber-optic cable is expensive. Also, a laser light
source can cost thousands of dollars, compared to
hundreds of dollars for electrical signal generators.
Fragility. Glass fiber is more easily broken than
wire, making it less useful for applications where hardware
portability is required.
Radio waves Transmission
•The Radio waves have frequencies between
•Radio waves are Omni direction
•Radio waves can penetrate buildings easily,
so that are widely use for communication
both indoors outdoors.
•They also absorbed by rains
•At high frequency, radio wave tends to
travel in straight line and bounces off the
Radio technology considers the earth as surrounded by
two layers of atmosphere: the troposphere and the
The troposphere is the portion of the atmosphere
extending outward approximately 30 miles from the
The troposphere contains what we generally think of as
air. Clouds, wind, temperature variations, and weather in
general occur in the troposphere.
The ionosphere is the layer of the atmosphere above the
troposphere but below space.
Micro waves Transmission
•Micro waves electromagnetic waves having
frequency between 1 GHZ and 300 GHZ.
•There are two types of micro waves data
communication system : terrestrial and satellite
•Micro waves are widely
used for one to one
sender and receiver,
cellular phone, satellite
networks and in wireless
It does not contain the signal in some
physical conductor or metal. Rather, it transport
electromagnetic signal through air. It is also known as
wireless media. Because in this we are not using any
king of cable.
Electromagnetic waves having frequencies from 300 GHz to 400 THz are
called IR waves or Infrared waves.
IR waves are used for short range communication and use line of sigh
Infrared waves cannot pass through solid objects, like walls and be easil
contained in a room.
They are cheap, easy to build and do not require any government license
to use them.
IR waves offer very bandwidth
This type of transmission use thin laser to transfer data up to few kilometers.
Laser beams are unidirectional, therefore this type of transmission system
use line of sight propagation.
In such a transmission system, a photo detector and laser is set on both
sender and receiver side.
Such a system offer very high band width at a very low cost.
Other disadvantage is that on hot sunny days these waves are affected by hot
turbulent air and miss the detector.
The major problem in this transmission system is that laser beams cannot
penetrate rain or thick fog.
WHAT DO YOU
THIS MEANS THAT A FORMAL
DESCRIPTION OF MESSAGE FORMATS AND
THE RULES THAT TWO OR MORE
MACHINES MUST FOLLOW TO EXCHANGE
HTTP : (Hypertext Transfer Protocol) is the set of rules
for transferring hypertext (i.e., text, graphics , image
sound ,video etc.) on WWW (World Wide Web).
FTP : (File Transfer Protocol) is a standard for the
exchange of files across internet.
TCP/IP : (Transmission Control Protocol / Internet
protocol) is the base communication protocol of the
internet. IP part of TCP/IP uses numeric IP addresses
to join network segments and TCP part of TCP/IP
provides reliable delivery of messages between
SLIP/PPP : SLIP (Serial Line Internet Protocol) is for
delivering IP packets over dial-up lines; PPP (Point to
Point Protocols) is for transmitting IP packets over
Wireless communication : Wireless communication is
simply data communication without the use of
Mobile computing : Mobile computing means that the
computing device is not continuously connected to the
base or central network.
WIRELESS VS MOBILE
Notebook is hotel
Wireless LANs in historic buildings
Personal Digital Assistant (PDA)
Smart phones, pagers
Wireless/ Mobile Computing Technologies
GSM : (Global System for Mobile) GSM uses narrow
band TDMA (Time Division Multiple Access) , which
allows 8 simultaneous calls on the same radio
frequency. To connect to the specific service providers
in these different countries , GSM uses simply switch
subscriber identification module (SIM) cards.
CDMA : (Code- Division Multiple Access) uses a
spread-spectrum technique where data is sent in small
pieces over a number of discrete frequencies available
for use. Each users signal is spread over the entire band
width by unique spreading code. At the receiver
and, the same unique code is used to recover the signal.
WLL : (Wireless in Local Loop) is a system that
connects subscribers to the public switched telephone
network (PSTN) using radio signals as a substitute for
other connecting media.
3G and EDGE : (3rd Generation) and (Enhanced Data
rates for Global Evolution) 3G mobile
communications technology is a broadband, packetbased transmission of text, digitized voice, video and
multimedia at data rates up to and possibly higher than
2 megabits per second (Mbps), offering a consistent set
of services to mobile computer and phone users no
matter where they are located in the world. EDGE is
considered an intermediate step in the evolution of 3G
WCDMA (Wideband CDMA ),although some carriers
are expected to stop short of that final step
SMS : (Short Message Service) is the transmission of
short text messages to and from a mobile phone , fax
machine and/or IP address. Once a message is sent, it
is received by Short Message Service Center (SMSC),
which must then get it to the appropriate mobile
E-mail : (Electronic Mail) is sending and receiving
messages by computer.
Voice Mail : The voice-mail refers to e-mail systems
that supports audio.
CHAT : Online textual talk, in real time, is called
Video Conferencing : A two-way videophone
conversation among multiple participants is called