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Network BANDWIDTH Explained | Bandwidth measurement Calculation examples | frequency modulation, BPS - YouTube
Channel: ISO Training Institute
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I'll begin by discussing electric magnetic聽
waves define what I mean by the term bandwidth聽聽
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distinguished the definition of bandwidth that聽
I'm using from another common use of the word聽聽
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bandwidth performs some example calculations and聽
then gives some band widths of common network聽聽
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media the way that I'm going to define bandwidth聽
is that it is a physical layer property this is聽聽
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a property that exists at layer 1 of the OSI聽
model in order to begin discussing bandwidth聽聽
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the first need to discuss electromagnetic waves聽
the electromagnetic waves are common throughout聽聽
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the universe these include waves such as radio聽
waves invisible and infrared light in humans for聽聽
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a number of years have been using these types聽
of electromagnetic waves certainly whenever聽聽
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we look at something we are seeing visible light聽
reflected off that object our eyes are sensitive聽聽
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to electromagnetic radiation and the so called聽
visible spectrum we're able to see that radio we聽聽
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use for radio and television broadcasting聽
we've used that for quite some time these聽聽
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electromagnetic waves in general propagate through聽
space at the speed of light in other words they聽聽
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travel speed of light through a vacuum in other聽
materials they travel slightly slower than the聽聽
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speed of light but for our purposes they travel聽
near enough to the speed of light that that slight聽聽
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slowdown caused by the material is irrelevant聽
we can characterize waves by their amplitude聽聽
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and by their frequency now the amplitude of an聽
electromagnetic wave measures the height of the聽聽
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wave whenever we plot a representation of that聽
wave on a graph here I'm measuring the height聽聽
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from the center line and I can see that this wave聽
has a height that goes up to one from the center聽聽
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line which is a zero in communications this wave聽
height this amplitude directly corresponds to the聽聽
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strength or power of the transmitted signal so if聽
I'm transmitting a signal of let's say of mine a聽聽
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lot of power then this wave having an amplitude聽
of one could be said to have one watt of power
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if I were to transmit with two watts of power I聽
would have a higher amplitude signal so this thin聽聽
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blue line here or this taller wave is an example聽
of a higher amplitude signal it's a taller wave聽聽
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when it's plotted the red line is the original聽
lead which alternates between minus 1 and plus 1
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now in addition to varying the amplitude of a聽
wave I can also look at the frequency of a wave聽聽
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and the frequency of a wave measures how many聽
full cycles of a wave of her per unit time so聽聽
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a full cycle of a wave is how long it takes to聽
get back to the same part of the waveform so if聽聽
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I start here at the end of my blue arrow and聽
I go up and then I come back down and then I聽聽
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come back up until I reach the center line聽
again that is one cycle or one period of a聽聽
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wave and however many of these cycles occur聽
per unit time gives me the frequency of the聽聽
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wave and the standard time unit that we use聽
for measuring frequency is one second and the聽聽
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standard unit that we use for frequency is聽
one cycle of a wave per second or one Hertz
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now if we have a wave that goes up down and comes聽
back more frequently within the same time span聽聽
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then we say that wave is a higher frequency wave聽
more cycles free at a time it's a higher frequency聽聽
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so a 100 Hertz wave for example is a higher聽
frequency than a 1 Hertz wave in my example聽聽
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the wave in blue is a higher frequency wave than聽
the wave in red because in the time span of this聽聽
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plot the blue line representing blue wave goes聽
up and down and completes more cycles in that聽聽
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same amount of time than those the red wave now聽
different physical materials at the physical layer聽聽
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can carry different frequencies at limited power聽
levels not every type of material that we have聽聽
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can carry every frequency of electromagnetic聽
wave and not every material that we have is聽聽
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compatible with every amplitude or every power聽
of electromagnetic wave for example if I take an聽聽
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optical fiber cable this is a cable made of glass聽
or plastic which does not conduct electricity very聽聽
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well an optical fiber cable would not transmit聽
an electrical signal very well unless I sent an聽聽
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extremely high amplitude electrical signal enough聽
to overcome the resistance of the non conductive聽聽
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plastic or glass and if I sent a signal with that聽
much power that signal would actually probably be聽聽
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transferred through the air around the conductor聽
and it would probably damage the cable in the聽聽
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process so I can't use an optical fiber to send聽
an electrical signal conversely I can't take a聽聽
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copper wire and send an optical signal down in聽
other words I can't take a laser light attach it聽聽
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to the end of a copper wire and expect the light聽
to come out the other end of the wire that won't聽聽
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happen because the copper wire while it carries聽
electrical signal as well cannot carry an ultra聽聽
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magnetic signal and within the visible light聽
range because it's too high frequency a signal
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so the way that we measure bandwidth depends聽
upon whether we're talking about a cable or聽聽
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wired connection or a wireless connection the聽
bandwidth of a cable or non wireless connection聽聽
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is the difference between the highest frequency聽
signal and the lowest frequency signal that the聽聽
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material can carry reliably and this difference聽
is expressed in hertz we can use SI prefixes聽聽
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as shorthand to abbreviate say a thousand聽
Hertz as one kilohertz with wireless it's聽聽
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slightly more complicated because wireless聽
transmitting devices use part of the radio聽聽
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spectrum and governments around the world聽
regulate this radio spectrum and say who聽聽
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can use what pieces of it or what frequencies聽
in it for what purpose so the bandwidth of a聽聽
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wireless physical connection is the difference聽
between the upper and lower frequency that a聽聽
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single channel can use in the legally allocated聽
radio frequency range for the wireless device so聽聽
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a wireless device cannot operate outside of聽
its legally allocated radio frequency range聽聽
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whereas legally allocated band without violating聽
the laws of the country that it's operating in聽聽
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the United States for example the Federal聽
Communications Commission regulates radio聽聽
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frequency spectrum and there are substantial聽
fines and even possible federal prison time聽聽
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for transmitting on frequencies that have聽
not been properly assigned to you therefore聽聽
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with wireless our limitations actually wind up聽
being more legal limitations than technical ones聽聽
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again this bandwidth is expressed in Hertz and聽
we may have SI prefixes in front of the Hertz
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now I've defined bandwidth as a physical property聽
measured in Hertz this is the so-called analog聽聽
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bandwidth that signal processing folks use聽
in networking the term bandwidth often gets聽聽
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casually used to mean so-called digital聽
bandwidth and this digital bandwidth term聽聽
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refers to the maximum data speed or the maximum聽
data rate that a given connection can carry and聽聽
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this can be measured at any layer of the OSI聽
model and is expressed in bits per second the聽聽
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problem with this term is that nobody says analog聽
bandwidth or digital bandwidth and when we're聽聽
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being precise about the entire networking system聽
it can get confusing which type of bandwidth is聽聽
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under discussion sometimes it's obvious from the聽
context sometimes it isn't so to avoid confusion聽聽
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I'm going to be calling this quantity or the so聽
called digital bandwidth quantity in bits per聽聽
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second the maximum throughput of the connection聽
and I'll be reserving the term bandwidth for its聽聽
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analog signal processing definition with units and聽
Hertz there is a relationship between these two聽聽
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quantities however because the maximum throughput聽
is related to the bandwidth as a rule of thumb聽聽
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the higher the bandwidth of a physical medium the聽
more data it can carry per unit time however that聽聽
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maximum throughput is still limited by some other聽
factors such as the noise and the capability of聽聽
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the transmitters and receivers and so bandwidth聽
alone does not determine the maximum through play聽聽
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so let's do some bandwidth calculations here's a聽
simple calculation suppose that a physical medium聽聽
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can reliably carry signals between one kilohertz聽
and 10 kilohertz well to get the bandwidth I聽聽
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simply subtract the upper frequency 10 kilohertz聽
and I subtract the lower frequency 1 kilohertz聽聽
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from that upper frequency so I take 10 kilohertz聽
subtract 1 kilohertz I get 9 kilohertz now the 1聽聽
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kilohertz reported value has one significant聽
figure because there's only one digit the 10聽聽
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kilohertz reported value only has one significant聽
figure because there's only one digit to the left聽聽
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of the decimal point that isn't zero so any聽
zeros between the last non-zero digit and聽聽
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the decimal point are not significant values not聽
significant figures unless the decimal point is聽聽
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actually their decimal point is not here in this聽
particular example so I only have one sitting to聽聽
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configure here no matter though because I only had聽
one significant figure here and my final result聽聽
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needs to use the lower of the significant figures聽
that I've been given in this case it's going to be聽聽
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one significant figure so 9 kilohertz is perfectly聽
OK as my final answer in the second example I have聽聽
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a different physical medium that can carry signals聽
between 100 Hertz and 1.2 gigahertz 1.20 gigahertz聽聽
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to be specific I have three significant figures聽
in this value so 1.20 gigahertz is equal to 1聽聽
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billion two hundred million Hertz or in British聽
English one thousand two hundred million Hertz if聽聽
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I subtract one Hertz from the 1.2 gigahertz value聽
I get one billion one hundred ninety nine thousand聽聽
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nine hundred I'm sorry one billion one hundred聽
ninety nine million nine hundred ninety nine聽聽
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thousand nine hundred Hertz or one thousand one聽
hundred ninety nine million nine hundred ninety聽聽
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nine thousand nine hundred Hertz I can't use this聽
answer though as my final answer because my given聽聽
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quantities I had three significant figures here聽
but I only had one significant figure here what聽聽
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this means is that the person who said that oh聽
yeah this this medium can support one hundred聽聽
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Hertz might have been saying that it can support聽
99.9 seven Hertz or might have been saying that聽聽
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it can support one hundred five Hertz or one聽
hundred and ten Hertz and they simply round it聽聽
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down so what I need to do is I need to round this聽
final answer to one significant figure which means聽聽
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I can only have one digit left of the decimal聽
point that isn't zero so I'm going to first聽聽
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truncate all these nines because I'm only going聽
to look to the digit immediately right of this聽聽
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first digit in order to do my rounding and I can聽
see I have one here that rounds down and so I'm聽聽
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going to report my bandwidth is only one gigahertz聽
now here are some common bandwidths of some actual聽聽
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technologies a voice only line with the plain old聽
telephone system has a nominal bandwidth of about聽聽
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three kilohertz a telephone digital subscriber聽
line using the adsl2 plus standard increases that聽聽
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nominal bandwidth the 2.2 megahertz if I'm using a聽
single wireless channel following the 802 dot 11g聽聽
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specification I could have a 20 megahertz nominal聽
bandwidth in video DSL 2 which is an extension of聽聽
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the digital subscriber line technology supports聽
30 megahertz bandwidth the 802 dot 11 in standard聽聽
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provides an optional way to use a single channel聽
of 40 megahertz bandwidth that's still less than聽聽
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a category-5 Ethernet cable however which has a聽
hundred megahertz nominal bandwidth the newest聽聽
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standard or newest at the time that I recorded聽
this lecture and this should give you an idea聽聽
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of the age of this lecture by the time you watch聽
it the newest 802 dat 11 AC standard optionally聽聽
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spanning the 2.4 and 5 gigahertz bands can support聽
a single channel with a nominal bandwidth of 160聽聽
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megahertz but that's still less than the聽
equivalent new form of wired Ethernet with聽聽
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category 6 Ethernet cable at 250 megahertz or聽
double to 500 megahertz for category 6a cable聽聽
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that's still far less than an RG 400 coaxial聽
cable which can carry a nominal bandwidth of聽聽
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30 1.5 gigahertz and this is all significantly聽
less than what we can do with fiber-optics a聽聽
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short length of optical fiber for example has聽
a nominal bandwidth point-9 patterns so we get聽聽
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a lot more bandwidth using optical technologies聽
at the moment with our current technology than聽聽
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we can with the radiofrequency technologies so聽
to summarize the bandwidth is a physical layer聽聽
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property that measures the difference between the聽
highest and lowest frequencies that a medium can聽聽
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carry this is a distinct value from the maximum聽
throughput even though the word bandwidth is聽聽
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thrown around in networking all the time to mean聽
maximum throughput but there is a relationship a聽聽
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higher bandwidth physical layer tends to support聽
a higher data throughput at the physical layer and聽聽
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a lower bandwidth physical layer will have the聽
effect of reducing the speed of the connection
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