Classifications of Transmission
Media
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Transmission Medium
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Guided Media
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Communication Fundamentals
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(Contd.)
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Transmission and reception are achieved by
means of an antenna
Configurations for wireless transmission
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Directional
Omnidirectional
Waves are guided along a solid medium
E.g., copper twisted pair, copper coaxial cable, optical
fiber
Unguided Media
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Unguided Media
Physical path between transmitter and receiver
Provides means of transmission but does not guide
electromagnetic signals
Usually referred to as wireless transmission
E.g., atmosphere, outer space
General Frequency Ranges
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Microwave frequency range
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Radio frequency range
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1 GHz to 40 GHz
Directional beams possible
Suitable for point-to-point transmission
Used for satellite communications
30 MHz to 1 GHz
Suitable for omnidirectional applications
Infrared frequency range
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Roughly, 3x1011 to 2x1014 Hz
Useful in local point-to-point multipoint applications
within confined areas
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Terrestrial Microwave
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Description of common microwave antenna
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Description of communication satellite
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Parabolic "dish", 3 m in diameter
Fixed rigidly and focuses a narrow beam
Achieves line-of-sight transmission to receiving
antenna
Located at substantial heights above ground level
Applications
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Satellite Microwave
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Long haul telecommunications service
Short point-to-point links between buildings
Applications
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Broadcast Radio
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Description of broadcast radio antennas
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Omnidirectional
Antennas not required to be dish-shaped
Antennas need not be rigidly mounted to a precise
alignment
Applications
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Broadcast radio
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Microwave relay station
Used to link two or more ground-based microwave
transmitter/receivers
Receives transmissions on one frequency band (uplink),
amplifies or repeats the signal, and transmits it on
another frequency (downlink)
Television distribution
Long-distance telephone transmission
Private business networks
Multiplexing
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Capacity of transmission medium usually
exceeds capacity required for transmission
of a single signal
Multiplexing - carrying multiple signals on
a single medium
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More efficient use of transmission medium
VHF and part of the UHF band; 30 MHZ to 1GHz
Covers FM radio and UHF and VHF television
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Multiplexing
Reasons for Widespread Use of
Multiplexing
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Multiplexing Techniques
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Frequency-division Multiplexing
Frequency-division multiplexing (FDM)
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Cost per kbps of transmission facility
declines with an increase in the data rate
Cost of transmission and receiving
equipment declines with increased data rate
Most individual data communicating
devices require relatively modest data rate
support
Takes advantage of the fact that the useful
bandwidth of the medium exceeds the required
bandwidth of a given signal
Time-division multiplexing (TDM)
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Takes advantage of the fact that the achievable
bit rate of the medium exceeds the required data
rate of a digital signal
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Time-division Multiplexing
Communication Networks
Types of Communication
Networks
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Traditional
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Speed and Distance of
Communications Networks
Traditional local area network (LAN)
Traditional wide area network (WAN)
Higher-speed
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High-speed local area network (LAN)
Metropolitan area network (MAN)
High-speed wide area network (WAN)
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Characteristics of WANs
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Covers large geographical areas
Circuits provided by a common carrier
Consists of interconnected switching nodes
Traditional WANs provide modest capacity
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64000 bps common
Business subscribers using T-1 service – 1.544 Mbps
common
Higher-speed WANs use optical fiber and
transmission technique known as asynchronous
transfer mode (ATM)
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Scope of a LAN is smaller
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LAN interconnects devices within a single
building or cluster of buildings
LAN usually owned by organization that
owns the attached devices
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Like WAN, LAN interconnects a variety of
devices and provides a means for
information exchange among them
Traditional LANs
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High-speed LANS
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Provide data rates of 1 to 20 Mbps
Provide data rates of 100 Mbps to 1 Gbps
10s and 100s of Mbps common
Differences between LANs and
WANs
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Characteristics of LANs
For WANs, most of network assets are not
owned by same organization
Internal data rate of LAN is much greater
The Need for MANs
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Traditional point-to-point and switched network
techniques used in WANs are inadequate for
growing needs of organizations
Need for high capacity and low costs over large
area
MAN provides:
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Service to customers in metropolitan areas
Required capacity
Lower cost and greater efficiency than equivalent
service from telephone company
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Switching Terms
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Switching Nodes:
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Intermediate switching device that moves data
Not concerned with content of data
Stations:
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Switched Network
End devices that wish to communicate
Each station is connected to a switching node
Communications Network:
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A collection of switching nodes
Observations of Figure 3.3
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Some nodes connect only to other nodes (e.g., 5
and 7)
Some nodes connect to one or more stations
Node-station links usually dedicated point-to-point
links
Node-node links usually multiplexed links
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Frequency-division multiplexing (FDM)
Time-division multiplexing (TDM)
Not a direct link between every node pair
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