1. science
2. physics
3. optics

07-May-15
INTRODUCTION TO
COMMUNICATION
Communication Media
• What is communication?
- It is the process of sending information from one
point (transmitter) to another (receiver).
Communication media
• Communication media is the actual physical path or
environment through which data travel as they move
from one component (transmitter) to another
(receiver) and the media connects the network
devices.
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Communication Media
• Types of Communication Media
The transmission media can be classified as:
- guided
or - unguided
Guided media provide a physical path (solid medium)
along which the signals are propagated.
Eg. twisted pair, coaxial cable and optical fiber
Unguided media employ an antenna for transmitting the
information through air, vacuum or water.
Eg. Wireless communication
Communication Media
• Types of Communication Media
The most common types of network media are
– Twisted pair cable
– Coaxial cable
– Optical Fiber cable
&
– Wireless
Guided media
Unguided media
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Communication Media
Frequency Ranges of Communication Media:
Sl No. Media
Frequency Range
1.
Twisted pair
0 to 1 MHz
2.
Coaxial Cable
0 to 500 MHz
3.
Optical Fiber
180 to 370 THz
4.
Wireless
1GHz to 40 GHz
Electromagnetic Spectrum of
Communication Media
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Communication Media
Twisted Pair Cable
- Consists of two insulated copper wires twisted
together to form a pair of a regular spiral pattern.
- A wire pair acts as a single communication link.
- Typically, a number of these pairs are bundled
together into a cable by wrapping them in a tough
protective sheath.
Communication Media
• The twisting tends to decrease the crosstalk
interference between adjacent pairs in a cable.
• Neighboring pairs in a bundle typically have different
twist lengths to reduce the crosstalk interference.
• On long-distance links, the twist length typically
varies from 5 to 15 cm.
• The wires in a pair have thicknesses of from 0.4 to
0.9 mm.
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Communication Media
Twisted pair cables are of two types:
- unshielded
and
- shielded
Unshielded Twisted Pair (UTP)
Cables
UTP cables:
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Unshielded Twisted Pair (UTP) Cables
Advantages of UTP cables
- Least expensive of all the transmission media
- Used for local area networks
- Small in size (diameter of approximately 0.43 cm), so
does not fill up wiring ducts as rapidly as other types
- Easy to install
- UTP can be used with most of the major networking
architectures
- The oldest method of data transmission, trained
manpower are easily available
Unshielded Twisted Pair (UTP) Cables
Disadvantages of UTP cables
- Prone to external electromagnetic interferences
(interference from nearby twisted pair & from noise
generated in the environment)
- The distance between the repeaters is shorter
- Being thin in size, it is likely to break easily
Some features of UTP cable:
–
–
–
–
Speed and throughput—10 to 1000 Mbps
Average cost per node—Least expensive
Media and connector size—Small
Maximum cable length—100 m (short)
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Unshielded Twisted Pair (UTP) Cables
Commonly used types of UTP cables:
Category
Uses/Data rate
Category 1
Used for telephone communications. Not suitable for transmitting data.
Category 2
Capable of transmitting data at speeds up to 4 Mbps.
Category 3
Used in 10BASE-T networks. Can transmit data at speeds up to 10 Mbps.
Category 4
Used in Token Ring networks. Can transmit data at speeds up to 16 Mbps.
Category 5
Can transmit data at speeds up to 100 Mbps.
Category 5e
Used in networks running at speeds up to 1Gbps.
Category 6
Used in networks running at speeds up to 1Gbps.
Category 7
Category 7 cable is currently the fastest standard for UTP.
Shielded Twisted Pair (STP) Cable
STP cables:
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Communication Media
• Shielded Twisted Pair (STP) Cable:
– Each pair of wires is wrapped in a metallic foil.
– The four pairs of wires then are wrapped in an
overall metallic braid or foil.
Advantages of STP cables:
– STP reduces electrical noise within the cable (pair
to pair coupling and crosstalk)
– STP reduces electrical noise from outside the
cable (EMI and RFI)
Shielded Twisted Pair (STP) Cable
Disadvantages of STP cables:
– More expensive than UTP cables
– Physically larger
– Difficult to install
– More difficult to connect to a terminating block
Some features of STP cable
– Speed and throughput—10 to 100 Mbps
– Average cost per node—Moderately expensive
– Media and connector size—Medium to large
– Maximum cable length—100 m (short)
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Coaxial Cable
• Coaxial Cable
Coaxial Cable
• In a Coaxial cable, a copper wire is surrounded by a
layer of flexible insulation
• Over this insulating material is a woven copper braid
or metallic foil that acts both as the second wire in
the circuit and as a shield for the inner conductor
• This second layer or shield can help reduce the
amount of outside interference
• The shield is covered by a cable jacket
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Coaxial Cable
• Advantages of Coaxial Cable
– It has better shield against electromagnetic
interference
– It can span longer distance at higher data bits per
second (bps)
– It can be used for both analog and digital data
transmissions
– Easy to handle
– Coaxial cable emits less radiation, so less
interference with the communication equipment
Coaxial Cable
• Disadvantages of Coaxial Cable
– More expensive to install compare to twisted pair
cable
– The thicker the cable, the more difficult to work
with
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Optical Fiber Cable
• An optical fiber is a cylindrical dielectric
waveguide (no conducting waveguide) that
transmits light along its axis, by the process
of total internal reflection.
• An optical fiber is a flexible, transparent fiber
made of extruded glass (silica) or plastic,
slightly thicker than a human hair.
Optical Fiber Cable
• Structure of an Optical Fiber
– The fiber consists of a core surrounded by
a cladding layer, both are made of dielectric
materials
– The refractive index of the
core is greater than the
refractive index cladding
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Optical Fiber Cable
• Types of Optical Fiber
– Single mode
– Multi mode
Multimode fiber
– has a 62.5 microns or larger in diameter
– Usually used for short distance transmissions
Single-mode fiber
– has a small core of 8 to 10 microns in diameter
– Used for long distance transmissions
Optical Fiber Cable
• Advantages
– It can handle much higher bandwidth
– Low attenuation,
– Required repeaters spacing 30 Km
– Fiber is not affected by electromagnetic interference,
or corrosive chemicals in the air, so ideal for factory
environments where electrical interference is very
high
– Fiber is lighter than copper
– Difficult to tap, high security
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Optical Fiber Cable
• Disadvantages
– Optical fiber is an unfamiliar technology requiring
skills which may not be easily available
– Optical fiber interfaces cost more than electrical
interfaces
Components of a Communication
System
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Highway Scenario
GSM, 3G, WLAN,
Bluetooth, ...
PDA, laptop, cellular phones,
GPS, sensors
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Trends on Wireless Communications
Making a Call
1.
2.
3.
4.
5.
Scan Control Channels: Your cell phone needs to use the "closest" base
station because that's the one with the strongest signal and the one that
will give the best connection. To find the closest base station, your phone
checks all 21 control channels and determines which has the strongest
signal.
Choose Strongest: Your cell phone chooses the strongest signal and decides
to use that one for placing the call.
Send Origination Message: Your cell phone now transmits a very short
message (about 1/4 second) that contains the MIN (Mobile Identification
Number, aka your cell phone number), its ESN (Electronic Serial Number),
and the number you just dialed.
Get Channel Assignment: After the cellular service provider verifies that
you are a valid, paying customer (based on the MIN and ESN your phone
sent), the base station sends a Channel Assignment message to your phone
(also a short 1/4-second burst). This message tells your phone where (that
is, on which channel) the conversation will take place.
Begin Conversation
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Wireless Networks Compared to
Fixed Networks
•
•
•
•
•
•
Higher loss-rates due to interference.
Limited availability of useful spectrum.
Low transmission rates.
Higher delays.
Lower security, simpler active attacking.
Always shared medium.
Cellular Data Networks
Some terms:
• SMS
•
•
•
•
Short Message Service
MMS
Multimedia Message Service
GPRS
General Packet Radio Service
HSCSD
High Speed Circuit Switched Data
EDGE
Enhanced Data Rates for Global Evolution
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Wireless Data
•
•
•
•
IEEE Standard*: 802.11x
Bluetooth
ZigBee
Ultra Wide Band
WHAT ARE STANDARDS?
• Standards are published documents that establish specifications
and procedures designed to maximize the reliability of the
materials, products, methods, and/or services people use every
day. Standards address a range of issues, including but not
limited to various protocols to help maximize product
functionality and compatibility, facilitate interoperability and
support consumer safety and public health.
Thank You
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