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Material Type: Notes; Class: Introduction to Computer Networks; Subject: Electrical And Computer Engr; University: University of Tennessee - Knoxville; Term: Unknown 1989;
Typology: Study notes
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application transport network link physical
application transport network link physical (^) application transport network link physical
application transport network link physical
network link physical
data
data
data
application
application
ack
Open a brower
Type in web address (send in a request)
wait for peer to ack receipt and return result
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application transport network link physical
application transport network link physical application transport network link physical
application transport network link physical
network link physical
data
data
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http://setiathome.berkeley.edu/
Scenario 1: Assume each user is active 10% of their time. When active, they generate data at a constant rate of 100Kbps. The whole bandwidth is 1Mbps How many users if we use circuit switching? (10) How many if we use packet switching? Scenario 2: Assume there are 10 users and one user suddenly generates one thousand 1,000-bit packets, while others remain inactive. How long does it take to transmit the 1M bits if using circuit switching? How long if using packet switching?
Statistical Multiplexing
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ECE 453 – Introduction to
Computer Networks
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Reconstruction: Sampling rate = 2H
Nyquist theorem:
SNR (signal-to-noise ratio)
S/N in decibel (dB) (10log 10 S/N)
maximum datarate= 2 H log 2 V bits/sec
maximum datarate= H log 2 ( 1 + S / N ) bits/sec
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What is the maximum data rate for a channel of 3000-Hz bandwidth with a signal to thermal noise ratio of 30dB?
According to a report, during the 1998 Tennessee-Florida game, the crowd noise measured at Neyland stadium peaked at 117dB, twice as high as the one measured at Tiger stadium during the 2000 LSU-Alabama game (111dB). In order to transmit a voice signal over this crowd at a rate of 1000bps at Neyland stadium, what kind of minimum bandwidth is required?
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Frequency vs. Wavelength vs.
Data rate
In vacuum
Given the width of a wavelength band, how
to calculate the corresponding frequency?
λ f = c
∆ = 2 ∆
c f
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Transmission Media and EM
Spectrum
Twisted pair, coax, fiber
Radio, microwave, infrared
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1 mm thick, run several km
Bandwidth: several Mb/s for a few km
Category 3 UTP (16MHz).
Category 5 UTP (100MHz).
Category 6 UTP (250MHz)
Category 7 UTP (600MHz)
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Single-mode vs. Multimode Fiber
Fiber diameter: a few wavelengths of light
Light propagate in a straight line
More expensive
Longer distance
50Gbps for 100km
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Uses infrared frequency (850-1500nm)
Electromagnetically isolated
8~10μm in diameter
50Gbps for 100km
Inexpensive to build
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Transmission of Light through
Fiber
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Digital transmission (50-ohm cable) Analog and cable TV (75-ohm cable) Telephone for long dist.
Analog and digital Telephone line
Application
Several Mbps 1 GHz 30THz Category 3: 16 MHz Category 5: 100 MHz 6: 250 MHz, 7: 600 MHz
Bandwidth
Longest distance, highest speed
Longer distance, higher speed
Length Several km
Thickness 1mm Ultra thin, few microns
Better shielding Core glass Copper core
two insulated copper wires
Construction
Twisted pair Coax Fiber optics
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Who Gets to Use Which Frequency?
Beauty contest
Hold a lottery
Not allocate freq. at all
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Remote controller
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Convection currents can interfere with laser communication systems.
A bidirectional system with two lasers is pictured here.
Does not need license
