Pertemuan 4
Bandwidth
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Discussion Topics
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Importance of bandwidth
The desktop
Measurement
Limitations
Throughput
Data transfer calculation
Digital versus analog
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Importance of bandwidth
• Bandwidth is defined as the amount of information that
can flow through a network connection in a given period
of time.
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Banwidth Analogies
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Measurement
• In digital systems, the basic unit of bandwidth is
bits per second (bps).
• Bandwidth is the measure of how much
information, or bits, can flow from one place to
another in a given amount of time, or seconds.
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Limitations
• Bandwidth varies depending upon the type of media as well as the
LAN and WAN technologies used.
• The physics of the media account for some of the difference.
• Signals travel through twisted-pair copper wire, coaxial cable, optical
fiber, and air.
• The actual bandwidth of a network is determined by a combination
of the physical media and the technologies chosen for signaling and
detecting network signals.
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Throughput
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Throughput refers to actual measured bandwidth, at a specific time of day, using
specific Internet routes, and while a specific set of data is transmitted on the network.
• Throughput is often far less than the maximum possible digital bandwidth of the
medium that is being used. Internetworking devices
The following are some of the factors that determine throughput:
• Type of data being transferred
• Network topology
• Number of users on the network
• User computer
• Server computer
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• Power conditions
Data transfer calculation
• Using the formula transfer time = size of file / bandwidth
(T=S/BW) allows a network administrator to estimate
several of the important components of network
performance.
• If the typical file size for a given application is known,
dividing the file size by the network bandwidth yields an
estimate of the fastest time that the file can be
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transferred.
Digital versus analog
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Analog bandwidth is measured by how much of the electromagnetic
spectrum is occupied by each signal.
The basic unit of analog bandwidth is hertz (Hz), or cycles per second.
While analog signals are capable of carrying a variety of information, they
have some significant disadvantages in comparison to digital transmissions.
The analog video signal that requires a wide frequency range for
transmission cannot be squeezed into a smaller band.
Therefore, if the necessary analog bandwidth is not available, the signal
cannot be sent.
In digital signaling all information is sent as bits, regardless of the kind of
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information it is.
Digital and Analog Bandwidth
Bandwidth = The width or carrying capacity of a communications circuit.
Digital bandwidth = the number of bits per second (bps) the circuit can
carry
• used in digital communications such as T-1 or DDS
• measure in bps
• T-1 -> 1.544 Mbps
Analog bandwidth = the range of frequencies the circuit can carry
• used in analog communications such as voice (telephones)
• measured in Hertz (Hz), cycles per second
• voice-grade telephone lines have a 3,100 Hz bandwidth
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Digital and Analog Bandwidth
DTE
DCE
digital
analog
PSTN
Dial-up network
Modulation
DTE
DCE
digital
analog
PSTN
Dial-up network
Demodulation
Digital Signals
• digital signal = a signal whose state consists of discrete elements such
as high or low, on or off
GOLDMAN: DATACOMM
FIG.02-14
Analog Signals
• analog signal = a signal which is “analogous” to sound waves
• telephone lines are designed to carry analog signals
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Sound Waves
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Analog Signals, Modulation and
Modem Standards
• A perfect or steady tone makes a wave with consistent
height (amplitude) and pitch (frequency) which looks like
a sine wave. (Figure 4-15)
• A cycle or one complete cycle of the wave
• The frequency (the number of cycles) of the wave is
measured in Hertz
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• Hertz (Hz) = the number of cycles per second