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Wireless Networks
Instructor: Fatima Naseem
Computer Engineering Department,
University of Engineering and Technology,
Taxila
Course Books

“Wireless Communications and Networks” by
William Stallings, Second edition.
Reference Book:
 “Wireless Communications” by T.S Rappaport,
2nd Edition Pearson Education
 Refered papers will be given as course will
proceed.
Contact

Fatima Naseem
Room # 17, CED.
[email protected]

Student meeting time:
Course Timeline
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Week 1: Chapter 2,3
Week 2: Chapter 4,5
Week 3 : Chapter 6
Week 4 : Chapter 6
Week 5 : Chapter 7
Week 6 : Chapter 7
Week 7 : Chapter 8
Week 8 : Chapter 8
Course Timeline
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Week 9: Intro to Wireless Networks & Its Types
Week 10:Intro to Wireless LAN
Week 11:802.11
Week 12:Cellular Technology
Week 13:Mobile Generations
Week 14:802.16
Week 15:802.15
Week 16:Miscellaneous
Introduction
Wireless Networks
Networking Basics
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Two or more connected devices
People can share files, peripherals such as
modems, printers and CD-ROM drives etc.
When networks at multiple locations are
connected, people can send e-mail,share links to
the global internet or conduct video conferences
in real time with other remote users.
Networking Components
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At least two computers
A network interface on each computer (a device
that lets the computer talk to the network) usually
an NIC or adapter.
A connection medium usually a wire or cable in
case of wired and atmosphere or air in case of
wireless communication.
Network operating system software, such as MS
Windows 95, NT, AppleShare.
Wireless Networks
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A wireless local area network (LAN) is a flexible
data communications system implemented as an
extension to or as an alternative for a wired LAN.
Using RF (Radio Frequency Technology) wireless
LANs transmit and receive data over the air
minimizing the need for wired LANs.
With WLANs, users access shared information
without looking for a place to plug in, and
network managers can setup or augment networks
without installing or moving wires.
Transmission
Fundamentals
Chapter 2
Electromagnetic Signal


Function of time
Can also be expressed as a function of frequency

Signal consists of components of different frequencies
Time-Domain Concepts
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Analog signal - signal intensity varies in a smooth fashion
over time
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No breaks or discontinuities in the signal
Digital signal - signal intensity maintains a constant level
for some period of time and then changes to another
constant level
Periodic signal - analog or digital signal pattern that
repeats over time
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
s(t +T ) = s(t )
- ∞< t < + ∞
where T is the period of the signal
Time-Domain Concepts
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Aperiodic signal - analog or digital signal pattern
that doesn't repeat over time
Peak amplitude (A) - maximum value or strength
of the signal over time; typically measured in
volts
Frequency (f )
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Rate, in cycles per second, or Hertz (Hz) at which the
signal repeats
Time-Domain Concepts

Period (T ) - amount of time it takes for one repetition of
the signal
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T = 1/f
Phase () - measure of the relative position in time within
a single period of a signal
Wavelength () - distance occupied by a single cycle of
the signal

Or, the distance between two points of corresponding phase of
two consecutive cycles
Sine Wave Parameters
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General sine wave
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Figure 2.3 shows the effect of varying each of the three
parameters
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s(t ) = A sin(2ft + )
(a) A = 1, f = 1 Hz,  = 0; thus T = 1s
(b) Reduced peak amplitude; A=0.5
(c) Increased frequency; f = 2, thus T = ½
(d) Phase shift;  = /4 radians (45 degrees)
note: 2 radians = 360° = 1 period
Sine Wave Parameters
Time vs. Distance
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When the horizontal axis is time, as in Figure 2.3, graphs
display the value of a signal at a given point in space as a
function of time
With the horizontal axis in space, graphs display the
value of a signal at a given point in time as a function of
distance

At a particular instant of time, the intensity of the signal varies as
a function of distance from the source
Frequency-Domain Concepts
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Fundamental frequency - when all frequency components
of a signal are integer multiples of one frequency, it’s
referred to as the fundamental frequency
Spectrum - range of frequencies that a signal contains
Absolute bandwidth - width of the spectrum of a signal
Effective bandwidth (or just bandwidth) - narrow band of
frequencies that most of the signal’s energy is contained
in
Frequency-Domain Concepts
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
Any electromagnetic signal can be shown to
consist of a collection of periodic analog signals
(sine waves) at different amplitudes, frequencies,
and phases
The period of the total signal is equal to the
period of the fundamental frequency
Relationship between Data Rate
and Bandwidth
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The greater the bandwidth, the higher the informationcarrying capacity
Conclusions
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Any digital waveform will have infinite bandwidth
BUT the transmission system will limit the bandwidth that can be
transmitted
AND, for any given medium, the greater the bandwidth
transmitted, the greater the cost
HOWEVER, limiting the bandwidth creates distortions
Data Communication Terms
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Data - entities that convey meaning, or
information
Signals - electric or electromagnetic
representations of data
Transmission - communication of data by the
propagation and processing of signals
Examples of Analog and Digital
Data
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Analog
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Video
Audio
Digital
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Text
Integers
Analog Signals
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A continuously varying electromagnetic wave that may be
propagated over a variety of media, depending on
frequency
Examples of media:
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Copper wire media (twisted pair and coaxial cable)
Fiber optic cable
Atmosphere or space propagation
Analog signals can propagate analog and digital data
Digital Signals
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A sequence of voltage pulses that may be
transmitted over a copper wire medium
Generally cheaper than analog signaling
Less susceptible to noise interference
Suffer more from attenuation
Digital signals can propagate analog and digital
data
Analog Signaling
Digital Signaling
Reasons for Choosing Data and
Signal Combinations
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Digital data, digital signal
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Analog data, digital signal
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Conversion permits use of modern digital transmission and
switching equipment
Digital data, analog signal
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Equipment for encoding is less expensive than digital-toanalog equipment
Some transmission media will only propagate analog signals
Examples include optical fiber and satellite
Analog data, analog signal
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Analog data easily converted to analog signal
Analog Transmission
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Transmit analog signals without regard to content
Attenuation limits length of transmission link
Cascaded amplifiers boost signal’s energy for
longer distances but cause distortion
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Analog data can tolerate distortion
Introduces errors in digital data
Digital Transmission
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Concerned with the content of the signal
Attenuation endangers integrity of data
Digital Signal
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Repeaters achieve greater distance
Repeaters recover the signal and retransmit
Analog signal carrying digital data
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Retransmission device recovers the digital data from analog
signal
Generates new, clean analog signal
About Channel Capacity
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Impairments, such as noise, limit data rate that
can be achieved
For digital data, to what extent do impairments
limit data rate?
Channel Capacity – the maximum rate at which
data can be transmitted over a given
communication path, or channel, under given
conditions
Concepts Related to Channel
Capacity
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Data rate - rate at which data can be communicated (bps)
Bandwidth - the bandwidth of the transmitted signal as
constrained by the transmitter and the nature of the
transmission medium (Hertz)
Noise - average level of noise over the communications
path
Error rate - rate at which errors occur

Error = transmit 1 and receive 0; transmit 0 and receive 1
Nyquist Bandwidth
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For binary signals (two voltage levels)
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C = 2B
With multilevel signaling
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C = 2B log2 M
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M = number of discrete signal or voltage levels
Signal-to-Noise Ratio
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Ratio of the power in a signal to the power contained in
the noise that’s present at a particular point in the
transmission
Typically measured at a receiver
Signal-to-noise ratio (SNR, or S/N)
signal power
( SNR) dB  10 log 10
noise power
A high SNR means a high-quality signal, low number of
required intermediate repeaters
SNR sets upper bound on achievable data rate
Shannon Capacity Formula
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Equation:
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Represents theoretical maximum that can be achieved
In practice, only much lower rates achieved
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C  B log 2 1  SNR
Formula assumes white noise (thermal noise)
Impulse noise is not accounted for
Attenuation distortion or delay distortion not accounted for
Example of Nyquist and Shannon
Formulations
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Spectrum of a channel between 3 MHz and 4
MHz ; SNRdB = 24 dB
B  4 MHz  3 MHz  1 MHz
SNR dB  24 dB  10 log 10 SNR 
SNR  251
Using Shannon’s formula
C  10  log 2 1  251  10  8  8Mbps
6
6
Example of Nyquist and Shannon
Formulations
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How many signaling levels are required?
C  2 B log 2 M
 
8 10  2  10  log 2 M
6
4  log 2 M
M  16
6
Classifications of Transmission
Media
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Transmission Medium
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Guided Media
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Physical path between transmitter and receiver
Waves are guided along a solid medium
E.g., copper twisted pair, copper coaxial cable, optical fiber
Unguided Media
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Provides means of transmission but does not guide
electromagnetic signals
Usually referred to as wireless transmission
E.g., atmosphere, outer space
Unguided Media
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Transmission and reception are achieved by
means of an antenna
Configurations for wireless transmission
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Directional
Omnidirectional
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
Terrestrial Microwave
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Description of common microwave antenna
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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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Long haul telecommunications service
Short point-to-point links between buildings
Satellite Microwave
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Description of communication satellite
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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)
Applications
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Television distribution
Long-distance telephone transmission
Private business networks
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
 VHF and part of the UHF band; 30 MHZ to 1GHz
 Covers FM radio and UHF and VHF television
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
Multiplexing
Multiple Access
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Multiple Access schemes are used to allow many
mobile users to share a finite amount of radio
spectrum.
The sharing of spectrum is required to achieve
high capacity by simultaneous allocating the
bandwidth.
Constraint: there should not be severe
performance degradation.
Reasons for Widespread Use of
Multiplexing
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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
Multiplexing Techniques
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Frequency-division multiplexing (FDM)
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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
Frequency-division Multiplexing
Time-division Multiplexing
Communication
Networks
Chapter 3
Types of Communication
Networks
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Traditional
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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)
Speed and Distance of
Communications Networks
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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10s and 100s of Mbps common
Characteristics of LANs
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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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Provide data rates of 1 to 20 Mbps
High-speed LANS
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Provide data rates of 100 Mbps to 1 Gbps
Differences between LANs and
WANs
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Scope of a LAN is smaller
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LAN usually owned by organization that owns the
attached devices
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LAN interconnects devices within a single building or
cluster of buildings
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
Switching Terms
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Switching Nodes:
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Stations:
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Intermediate switching device that moves data
Not concerned with content of data
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
Switched Network
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
Techniques Used in Switched
Networks
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Circuit switching
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Dedicated communications path between two stations
E.g., public telephone network
Packet switching
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Message is broken into a series of packets
Each node determines next leg of transmission for each
packet
Phases of Circuit Switching
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Circuit establishment
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Information Transfer
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An end to end circuit is established through switching nodes
Information transmitted through the network
Data may be analog voice, digitized voice, or binary data
Circuit disconnect
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Circuit is terminated
Each node deallocates dedicated resources
Characteristics of Circuit
Switching
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Can be inefficient
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Channel capacity dedicated for duration of connection
Utilization not 100%
Delay prior to signal transfer for establishment
Once established, network is transparent to users
Information transmitted at fixed data rate with only
propagation delay
Components of Public
Telecommunications Network
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Subscribers - devices that attach to the network; mostly
telephones
Subscriber line - link between subscriber and network
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Exchanges - switching centers in the network
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Also called subscriber loop or local loop
A switching centers that support subscribers is an end office
Trunks - branches between exchanges
How Packet Switching Works
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Data is transmitted in blocks, called packets
Before sending, the message is broken into a
series of packets
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Typical packet length is 1000 octets (bytes)
Packets consists of a portion of data plus a packet
header that includes control information
At each node en route, packet is received, stored
briefly and passed to the next node
Packet Switching
Packet Switching
Packet Switching Advantages
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Line efficiency is greater
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Packet-switching networks can carry out data-rate
conversion
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Many packets over time can dynamically share the same
node to node link
Two stations with different data rates can exchange
information
Unlike circuit-switching networks that block calls
when traffic is heavy, packet-switching still accepts
packets, but with increased delivery delay
Priorities can be used
Disadvantages of Packet
Switching
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Each packet switching node introduces a delay
Overall packet delay can vary substantially
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Each packet requires overhead information
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This is referred to as jitter
Caused by differing packet sizes, routes taken and varying delay
in the switches
Includes destination and sequencing information
Reduces communication capacity
More processing required at each node
Packet Switching Networks Datagram
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Each packet treated independently, without reference to
previous packets
Each node chooses next node on packet’s path
Packets don’t necessarily follow same route and may
arrive out of sequence
Exit node restores packets to original order
Responsibility of exit node or destination to detect loss of
packet and how to recover
Packet Switching Networks –
Datagram
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Advantages:
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Call setup phase is avoided
Because it’s more primitive, it’s more flexible
Datagram delivery is more reliable
Packet Switching Networks –
Virtual Circuit
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Preplanned route established before packets sent
All packets between source and destination follow this
route
Routing decision not required by nodes for each packet
Emulates a circuit in a circuit switching network but is
not a dedicated path

Packets still buffered at each node and queued for output over a
line
Packet Switching Networks –
Virtual Circuit
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Advantages:
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Packets arrive in original order
Packets arrive correctly
Packets transmitted more rapidly without routing
decisions made at each node
Effect of Packet Size on
Transmission
Effect of Packet Size on
Transmission
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Breaking up packets decreases transmission time because
transmission is allowed to overlap
Figure 3.9a
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Entire message (40 octets) + header information (3 octets) sent at
once
Transmission time: 129 octet-times
Figure 3.9b
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Message broken into 2 packets (20 octets) + header (3 octets)
Transmission time: 92 octet-times
Effect of Packet Size on
Transmission
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Figure 3.9c
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Message broken into 5 packets (8 octets) + header (3 octets)
Transmission time: 77 octet-times
Figure 3.9d
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Making the packets too small, transmission time starts increases
Each packet requires a fixed header; the more packets, the more
headers
Questions?