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Hello everyone,
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welcome back to the
computer networks course.
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And today we will see the various
components of a computer network.
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Upon the completion
of this session,
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we will be able to
understand nodes,
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we will also understand
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what are the different
media in computer network,
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and what are the various services
offered by computer network.
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Any computer network
has three components
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Nodes, Media and Services.
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Firstly we will deal with nodes.
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We have already seen nodes
in detail in the previous lectures.
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A node can send or receive or
both send and receive the data.
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And these nodes can be an end
node or an intermediary node.
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We can call end nodes as end devices
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and intermediary nodes
as intermediary devices.
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We will first see end nodes.
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End nodes are the nodes
that is going to be the
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starting point in
the communication
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or the end point
in the communication.
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If two devices wants to
communicate with each other,
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the device which initiates
this communication
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is an end device and the device
which accepts the communication
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at the final stage is an end device.
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And these two end devices
are going to communicate
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with each other with the help
of some intermediary devices.
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Let's first see some
examples for end devices.
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A computer is an end
device, network printers,
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voice-over IP Phones,
telepresence endpoint
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(this is mainly for video
conferencing), security cameras
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and many mobile
handheld devices like
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smart-phones, tablets,
personal digital assistants,
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wireless debit or credit card reader,
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bar-code scanner and many more.
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We are done with end nodes.
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Now we will see some
examples for intermediary nodes.
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Intermediary nodes are nodes
that just forwards the data
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from one node to another.
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In other words, they are going
to be placed in between end nodes.
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switches, wireless access points,
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routers, security devices like firewall,
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bridges, hubs, repeaters,
cell phone tower, etc.
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If you feel any of these
terms are new, no worries
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we are going to deal elaborately
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about all the terms in detail
in the upcoming lectures.
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There are lot of end devices
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and intermediary devices
involved in the scenario.
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These devices: smart phone,
Voice-over IP phone, printers,
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these desktop computers,
tablet and web servers --
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these are all end devices.
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Switches, cell phone towers,
this wireless router,
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these routers and this switch,
they are intermediary devices.
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We are done with nodes.
Now we will move on to the media.
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Media -- It is also called as the link.
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We know very well that,
link is going to carry
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the data from one side to the other.
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This link or this media can be
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a wired medium or a wireless medium.
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Some authors refer wired
medium as guided medium
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and wireless medium as unguided medium.
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In wired medium, there will be
a cable that connects two nodes
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whereas in a wireless medium,
cable will not be present.
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Since cables are used to
guide the data flow,
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we call wired medium
as guided medium
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whereas there is no cable
in a wireless medium
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and that is why we call wireless
medium to be unguided medium.
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We will see some examples for
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wired medium and wireless medium.
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The examples for wired
medium are ethernet cables,
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fiber optic cable, coaxial
cable and USB cable.
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We will see each of
these cables in detail now.
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Firstly, ethernet cable.
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This is an example
of an ethernet cable.
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Ethernet cable is an example
of a twisted-pair cable.
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I will talk about twisted-pair
cable in the upcoming lectures.
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For time bring, you just
know this is an ethernet cable
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and this ethernet cable
comes in two variations:
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one is ethernet straight-through cable
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and ethernet crossover table.
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We will see the difference between this
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ethernet straight-through cable
and ethernet crossover cable.
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If we want to connect
different devices,
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we have to go for ethernet
straight-through cable.
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In case if we want to connect
two devices of same kind,
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say two switches or two routers,
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or two computers wants to
be connected to each other,
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then we have to go
for ethernet cross-over.
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In ethernet cable the data
is going to be carried
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in terms of electrical signals.
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So far we have seen ethernet
straight-through cable
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and ethernet crossover cable.
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Now we will move onto
fiber optic cable.
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In fiber optic cable, the data is going
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to be carried in the
form of light waves.
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We know very well that light
is the fastest one in the world.
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Since this cable takes the data
in the form of light waves,
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this is the fastest mode
of wired communication.
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Now we will see coaxial cable.
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This is an example coaxial cable.
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This cable is mainly used for
audio or video communication.
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We can see this cable in our home.
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If you have a set-top box,
just go and see this coaxial cable
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which connects the dish antenna
and the set-top box.
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This cable also carries the data
in the form of electrical signals.
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And coming to USB cable,
USB stands for Universal Serial Bus.
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This cable is used to connect
a computer and a smart phone.
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We know very well if we want
to connect our computer
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to a smart phone, most of us
will prefer this cable only.
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And we are done with wired medium.
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Now we will move onto wireless media.
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In wireless media, two or more
devices are going to communicate
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with each other but without
the help of a cable.
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Here, air is the medium that carries
the data from one node to other.
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In wired networks, the data
are converted into signals,
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maybe electrical signals
or light signals.
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Whereas in wireless network
data are converted into waves.
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Coming to the wireless media,
we have infrared waves,
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radio waves, microwaves
and Satellite waves.
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Infrared waves are mainly used
for short range of communication.
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Example: TV remote control.
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The wave between the remote control
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and the television is
an infrared wave.
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And if the distance between the TV
and the remote control increases,
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this communication cannot happen.
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Because infrared are used
for short range communication.
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Coming to the radio wave,
the range of this radio wave
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is higher than infrared.
Bluetooth and Wi-Fi uses radio waves.
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The next one is the microwaves.
Example: Cellular system.
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Our cell phone technology uses microwaves.
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Microwaves are used for
long distance communication
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when compared to radio
waves or infrared waves.
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And finally, the satellite communication.
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And this is ultimately
the long distance communication.
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Our GPS enabled cell phone
gives signal to the satellite
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and the location of this device is
identified with the help of this signal.
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So far we have seen,
nodes and media.
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Two types of media
are addressed:
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wired media and wireless media.
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This scenario involves both
wired media and wireless media.
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This straight lines represents
ethernet straight-through.
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Just recall what are
ethernet straight-through cables.
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Say a computer with a switch,
a switch with a printer,
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a switch with a router or wireless router.
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But ethernet crossover cables are used
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to connect devices of similar type.
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Between routers we use only
straight-through cables.
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Straight lines are ethernet
straight-through cables,
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and dashed lines are crossover cables.
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So this is an example for a wired media.
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At the same time our example
also uses wireless media.
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In this case, between smart phone
and cell phone tower
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wireless technology is used,
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between smart phone
and wireless router,
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between tablet and wireless router
we have wireless technologies.
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To be specific, here
microwaves are used
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because this is a long
distance communication.
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And here radio waves are used,
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because this is a Wi-Fi
router and smart device.
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So this is a longer
distance communication
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when compared to this communication.
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We will now see the third component
of a computer network, services.
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We use computer network for
sending mails or receiving mails,
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storing our data in
a remote computer.
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Google Drive is an example for storage.
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We can share files using computer network,
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we can send instant messages like
whats-app using computer network,
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we can play online games
using computer networks,
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we can make voice calls
using voice-over IP,
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we can also do video calls or video
conferencing using video telephony,
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and we can also use computer
network for surfing internet
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that is accessing
websites.
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We have already seen
about nodes and media
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and the last part here
is the services.
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This scenario involves
many kinds of services.
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Suppose if this guy is
sending some message
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to his friend through whatsapp.
So it uses instant messaging.
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And two people are talking
over voice-over phone,
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so here voice communication is happening.
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So,voice communication is one of
the services of computer network.
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If somebody is accessing amazon.com,
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so he using www that is the
world wide web services.
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And there is a file here,
if this computer wants this file,
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it uses this computer network
for getting that file.
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So, file sharing is another
service depicted in this scenario.
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And that's it guys.
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We have seen nodes,
media and services.
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I hope now you are clear with nodes,
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different media -- wired media and wireless media
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and various services
like E-mail, instant messaging,
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file sharing, world wide web,
voice-over IP etc.
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I hope the session is informative.
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Thank you for watching.
