Cisco Certified Network Associate
Day One. Welcome back everybody.
I am Imran Rafai, your trainer for this entire series.
Today we would be starting with network fundamentals
and when I say fundamentals we would deal with the
very very basic of the networking
industry. So this video ideally is not
only for the people who are going for the CCNA certification but
anybody who's interested to, OR looking to start a career
in networking feel free to watch this because you
are going to learn as lot. But CCNA as a certification, is a very valuable
certification and I urge everybody to go ahead and
take that certification because it is gonna add a lot of value.
Before I go any further I would ask
everybody to concentrate on the first three days
of our video because we will be covering
the very basic concepts
which, if I can dare, I would say
is going to be the base
of your entire networking career, maybe even twenty years from now.
So please concentrate and
be clear with every concept we cover here.
And in case you still have doubts please feel free to email me
at imran.rafai@NWKING.ORG
imran.rafai@NWKING.ORG
Alright, without further ado, let
us get into the video. Let's start with the
very basic question, "What is a network"
well when I asked this question to my students
more often than not I get answers like Facebook
Twitter Picasa whatever whatever you see on the screen but
well that is social network, that's not the network we are here to learn
and that definitely is not the network I am going to talk about
what I am intrested in is it
this network the network between computers
well this network is also the foundation or the base on which
applications like Twitter Facebook picassa
is built on. So we learn about
this network and maybe if we have time over the course of this
this series, we will talk a little bit about those
applications here and there. While preparing for this
video lecture
I was preparing this a image that you see on the screen and I was thinking
okay let me see how to explain this concept
to students who are starting
on at the networking industry so
how do I explain this concept without actually using a lot of technical terms
Or saying - 'okay this thing communicates with that
thing over this thing' - I mean it was difficult
and then I thought okay I need a better way to explain this and I i remember the
story that a teacher of mine told me when she taught me
networking. It is about
the olden days of how Kings exchanged messages with
the ally, they would pass the message
to a messenger who used to ride on horse backs
and they used to go through all these paved paths
along the road and then they used to go through the city gate and then
this go to other King and deliver the message.
So if you compare that to computer network
the the messenger sending the message
so the 'message' is like the data that you send and the data could be anything
it could be a
doc file - a Word document or it could be an excel file it could be an image
could be a Video.... it could be anythng... the DATA.
And the road on which the the messenger travelled
that basically is the network. Of course
computer network is much more interesting than just paving
roads, but
if you see that is the very reason why computer network is
invented..... to communicate between computers!
If you see this image you would see.... let me just take a
highlighter..... you will see that we have the Windows PC,
we have Linux systems, an iMac
and we have laptop, mobile phone, palm top
you have web servers, maybe it's running on CentOS, you have database server
file servers but
in spite of them all running on different operating systems,
they all can communicate absolutely perfectly with each other!!!
This is the magic of computer networks
the computer network runs on
a global standard called the OSI Models
and things like that which defines clearly what
when any manufacturer manufactures a networking device
what and how they should communicate with each other!
So they all know the language of networking
and that enables them to communicate with each other.
Let's try to break this a little more further and see
how Internet works!
So if you look at the picture on your screens
this is the very basic network!
TWO computers connected with a wire... in this case we will use
a cat5 cable, a cat 5 cable looks something like this!
And they come in different colors, you have
blue colour ones, red color ones and this is obviously another color.
And this outer cover is just a protective layer.
Inside you have eight tiny cables
these cables go into a connector called RJ45
that looks something like this that you see on the screen. And on the back of your
computer
and most the computer that you have today
you have a port a port like this
that is your interface, your network interface card.
So your network interface card is where this RJ45 connects
and using this you can communicate
these two computers can communicate with each other.
This is the very basic form of networking and this is called as
ETHERNET!
Let me just
write it down. Its E sorry about my handwriting.
It's very difficult to write on screen
especially with my mouse but lemme
just......ETHERNET!
Maybe for my next video I will buy a stylus so that I can just
write it with a more legible
handwriting. Alright but for now...
Yeah.... this cable connects between these two computers
and you can have a very basic network.
But what happens if you have more than two computers so
lets say you have five computers. You obviously .... I mean there is one way
obviously you can go on adding more
network interface cards on your computer then you can have
but a better of connecting is by making use of a networking device
maybe a switch or hub - of course switch and hub are two different devices
they have totally different functions...we will obviously learn about them in
future video episodes
but for now you know we have a networking device.... in this case it is a
switch
and these computers can communicate with each other.
So for instance this guy has got a word document that he wants to send across
the network to this guy, all he has to do is send it across
to his IP address! 'What is an IP address?'
you would ask. IP addresses is how
computers recognize each other on the network!
We will learn about IP addresses in the next
video series but for now just know they are identifiers
for computers!
Another critical reason why people use networking is
because of devices like this. Maybe, let's assume, that this was a very
expensive
printer or scanner that the company invested in.
If networking was not available the way this device would be connected is
to this .... let me just change the colour to show that it is....
okay lets use BLACK. This is how
it would have had to be connected directly to the computer.
Now let's assume that this user maybe prints one
page a day and maybe all the
users in this company has similar requirement that they have
to print one or two pages
every day! So the company will have to invest on more
printer, so you will have one more print here. This guy will have one more printer
so company will have to unnecessarily
invest on a lot of printers when the usage on them...
in all the printers are gonna be very very minimal!
Better way for companies to invest money on IT infrastructures is to
have one printer
very expensive good quality printer. Plug it onto the network and everybody can
print to it!
That's a lot of money saved and that's very efficient way of using
IT Budget!
So that is the very basic
requirement and the reason why we have computer network!
So a computer network in a local office you know maybe one
home office, in a room...in a single company.... that's called as a LAN or
Local Area Network and 'local' signify that is very local
to a geographical area!
If this same local LANs, now these are
LANs and you have another LAN here
and let's assume that your company has two offices, one in New York and then you
have another office in Boston!
One way you could communicate or create a network between the
the two offices of your company is.... ofcourse if you had
the kind of money that is required to cable from New York to Boston
and of course if you can get the permissions you could run your own
private cable from your Boston office to New York office.... no problem at all!
But not too many companies have that kind of money
and not many companies would like to waste that kind of money.
We have a better way of doing it!
You could connect your office to a local ISP
ISP is nothing but Internet Service Provider.
and the similar thing happens on the other end...Boston connects
their office to an ISP ...Internet Service Provider
and ISP's already have their backbone, very massive, high bandwidth connections
between their offices!
So your data that you sent from here goes through the network to the ISP
from ISP to the ISP in Boston and then through that
they go back to the Boston office and a computer. So this computer
can communicate with this computer absolutely fine
using the ISP. Now this
forms the Wide Area Network where
LANs are inter-connected with each other to form a
Wide Area Network and 'wide' here signifies
a wide geographical area! It could be across the country
it could be in different cities in the the same country or
maybe in different countries.... basically it's a WAN.
So that is how it works...now how do you connect from ISP
to your Local Area Network... how do you connect?
Well.... in normal situation... what happens is
you get a a jack on the wall
you might have a small jack on the wall and your LAN
....you just connect it to the jack! So from the switch... or from the router
of your company
you connect it to the jack! On the backend this ISP, they would
lay cable.... maybe they would lay it under the
ground .....they lay a cable to their office
and from their office they go here from From their office again maybe underground
they lay a cable to
the Boston office. Again there will be a wall socket
that is provided and you just plug a cable from the wall to your
Router.... and that is how
your WAN link works. Well this is also
INTERNET because we are using the ISP.
Internet is nothing but a very massive
WAN which covers the entire world,
where you have a lot of public resources! So
if you google this is the definition of what an
internet is! "A global computer network providing
a variety of information and communication facilities
consisting of interconnected networks using standardized communication
protocols!". WOW... that is big definition...
Well that's exactly what it is ...you know.... Internet
is nothing but you have a lot of WANs. So you have a WAN here you have a WAN here
you have a WAN here
you have a WAN here and then just WANs are connected with each other.
So you have another WAN here and you have another WAN here
another one here another one here maybe few
more here....I know in India there are quite a lot...
you have all these things and they are connected .....let's say for instance you are connected
from here its
connected here, from here connected here and this is connected..... this is connected
this is connected....this is connected ....this is connected......
so this is nothing but how an internet works! So for instance if from
India somebody has to communicate
to New York this is how the data will transfer.... they will go..
if this thing disconnects you will have
the data going through a longer path! So this is what
internet is .....it is just nothing but interconnections of a lot of WANs!
Let's find out more about the applications we were talking about earlier.
There are lot of usage of the Internet or
networking as a whole.... we have YouTube, CNN
EBay, Skype.... this is just very,
very very few examples that use the Internet!
But they're lots of sites and applications which use the internet as
you already know!
Now how it works is YouTube for instance is owned by Google ...So Google
has put a
public server somewhere on the Internet that is accessible
to anybody on internet!
So if I want to watch a video on youtube
I go to my web browser and type 'www.youtube.com'
The process that takes place in the background
is much more complicated ....I'm simplifying this whole process.... we will look into
exactly how it works
in future video.....but for now when somebody times
'youtube.com' and hit enter
my computer sends an HTTP request
to YouTube's public server!
When the server gets that information it says 'Ah fine that is an HTTP request ...so I
will send an HTMLfile back'
and it creates and sends that HTML file back to me.
My web browser takes that and says..'Ah that's an HTML file and I know how to
process it'.
So it processes that and your YouTube website come to life and you see that
it shows a lot of videos and you click on one of those videos this process
repeats...
they send you back the Video and that's how that works.
Similarly it happens to eBay.... you go to CNN, Skype
that's how it works! So this is how internet
works.... basically they have a public server... they put all the files there
your computer request that....they send the file back to you and this
is how internet helps you
run this globalized world!
When we talk about internet, very critically we need to talk about the
speed of Internet!
Before we get to the speed of internet lets get to
'What is the difference between bit and byte?'
Bit is the smallest
information computer can understand.... it's either 0 or 1
Whereas byte is nothing but.... its formed by 8
bits.... so 8 bits together form one byte!
It could be some thing like
11011101.... whatever ....something!
So that is a BYTE. So eight BITs form one BYTE.
Now a lot of people get confused - DATA is
always denoted by 'bytes'... so when I say I have 1gb of
RAM it is one gigaBYTE of
RAM but when I tell I have a 10 Mbps connection
it is 10 mbps... connection 'bits' per second mega'BITS' per second
connection.
If you confuse these two.... it's going to be very very difficult
at one mBps.... 'byte' per second connection
is 8 mbps connection ....eight times
the speed of what it is supposed to be! So
speed is always denoted by the small 'b' data size is always
in big 'B'.
In computer world kilo is always '1024' so....
one kilo bit is 1024 bits.... similarly
one kilobyte is 1024 bytes!
Right so for instance let me see I have 1 Mbps connection
and I have a file of 128 KBytes.
So lets say for instance you have WORD and in word you type
the alphabet 'A'.... now with one
.... to produce that one alphabet ....that
takes about one BYTE.... capital
'B' of space.... so one
BYTE is how much it needs to store this
alphabet A..... one BYTE is
is 8 BITs.... right?.....
according the convertion.... so to type A... it takes eight bits or one
BYTE of data. Alright having known that let's look at this example.... so
you have 128 KB.... that is BYTE
a file of 128 KB
now it needs to go across a network with speeds of
1 Mbps.... one megabits per second!
How much time will it take? It is a very simple question .... let's try to convert
128 kilobyte if we convert it to
bits it is...... 128 into 8 bits... this conversion if you know!
bit to byte..... its 8 right?
So 128 BYTE
is..... if you convert it into
bits .....it is 1024
kilobits of data
right? so 1024 kilobits
where is that .... its 1024 kilobits is nothing but
1 megabit..... right? One Megabit!
What is the speed .....it is 1 megabit per second is
the speed of our connection..... so on a connection of 1mbps
a 1mb file will take
exactly one second!!!
So that's what speed is..... so understand this...... the difference between speed
and data....... the difference between bit and byte.
So if you can understand different between bit and byte..... the whole process
of understanding further videos can be very very easy!!!
When we talk about speed we need to want to talk about three other critical
factors that is..... Speed
Delay and Availability....the three of them always go hand in hand!
Like for instance now ....when you connect a cable from your router to your
PC it tells you that it is connected at 100 Mbps
that's because today with our LAN cards...the maximum they can do is a 100 Mbps!
but then don't forget that speed that they're telling is the speed between
your computer
and the router! Your internet connection maybe is a 1mbps connection!
so if you send 100MB/s data
100 MB per second data it will not go through your
internet because your internet can only do 1 Mbps!
Similarly you go.....
lets say from your bangalore office to New York office... you are sending a file.
So from bangalore office it goes through our gateway.... from gateway we have a 1mbps
slow connection.
It then comes to our bangalore ISP. Bangalore ISP to Mumbai ISP
they have a 100 Mbps line..... very fast
and then from Mumbai to Dubai they have a 10mbps line...
a little slower connection.... from Dubai again to Cairo
they have a 100 bps line and then Cairo to Madrid, let us say
you have a 100 mbps line. So similarly they have
a slower and faster.... different speed connections.
So basically when I say Internet this what happens.... internet...
if you pull off the cloud
it is nothing but a lot of routers... jumping here and there!
Now even if I have a very high speed connection
your data-throughput between your bangalore and New York office will depend on
slower connections in between. So even if I had a
very high speed connection... a 100 Mbps line in Bangalore...
It can only travel at the slowest link in between.
So our slowest link is the 10 Mbps line that we have here.
So from New York office to Bangalore office,
the maximum it can do is the 1 mbps line that we have
in New York. So this is how it works.
This is not the exact data flow from Bangalore to New York.
I have just given you an example... it need not obviously go via Dubai and Cairo...
Maybe it goes through some other location but basically it
actually....the data packet flows through one location to another
location to another location.
So like I said the speed always depends on
different factors..... of the link speed that you have in between.
Another critical factor is of dealey.
Now when I send a data from New York to Banglore
it has to....like we have already discussed... it has to pass through a lot of nodes
in between.
But let's assume that we have another office in Boston
I love Boston, dont I? So lets say we have
Boston office and we send data from New York to Boston office....
it has to pass through less number of nodes and hence
it would reach much more quicker. So
that's another factor. If the distance between the two devices
is long you will
have delay in the communication.
And that's why today, if you see, if you go to Google... even 'Google.com'
for instance... or you go to
'YouTube.com'... they redirect you to a content delivery network
closer to your place. So if you are in Singapore and you say
'google.com' or you go to 'youtube.com'
YouTube would not connect you to the Google Server or YouTube server
in United States. It will connect your to
a content delivery network close to Singapore, may be in Singapore.
So there is not much delay or
there is in-significant delay in the communication and the
the whole process is much much more fast. So that
is the delay part of it. And availability, again for instance
the link between Cairo and Dubai is down.
Communication between New York and Banglore would
not happen or it would happen but then it has to take maybe a longer path.
You might have another path
which goes via russia and then it comes via...
... it goes via China and comes to India and it is a long long
long
process. So thats another thing about availablility. Availability
is if all the links in between are up and running!
Another thing we need to discuss in today video
is network topology. Network topology
...there are three fundamental network topology....The STAR topology, the RING
topology and the BUS topology.
They are very very olden ways of how computers were
connected but even in today's world
they are in use. I will show you how.
Now for instance STAR. How does STAR work? STAR is where all the computers or
devices are connected to a central
switch or a connecting device.
Now if this line goes down it doesn't affect everybody else.... only
this guy goes off the network.
So in RING for instance every
computer is connected to each other. So if this guy goes down
the communication between these 2 devices can still happen through
this way. Right? So that's how
this works. Now in bus
topology .... let's say for instance.... this is again like that....you have a
device here... this is connected to this device... you have another device here that is connected
to that.
So every computer is connected to their own little device.
Right... now if the link goes down here
this part of the network can communicate the each other but not with
another device from the other segment of the network.
That's how a bus network works! Let's see how
it is implemented in today's world. We go back to our old
example that we saw earlier in this video
and if you see this switch
and these systems or PCs are connected
in a star formation - everybody is connected to this central switch!
Here the server also similar thing happens. Everybody is connected to the
switch!
These devices are connected to the access point in STAR formation
or.... so to say!
And if you look at the switch, the switch is connected in
a bus formation. Now if the link goes down here,
this part of the network can communicate with each other but it cannot communicate
with anybody else from this part of the network.
Sometimes you might even have networks where this is connected like
this
and this is connected like this.... so even if this goes down
this switch can still access this network around
this path and they can get access to these
these windows.... I mean... these systems here!
So in real-world the network topology
that we use is called HYBRID - which makes use of the STAR and
RING.... maybe even the BUS.
So it's a combination of all the three or either of them!
And that's how it is...So it is a hybrid network that we use in today's world.
I think that is about all the information that I wanted
to speak about in this first video.
We will further get into a lot of other topics
in our second video. This is the review of what we did
today....Go through all the
topics that is mentioned here and see if you understood.
If you din't you can always go back and try to learn little bit more.
And even after that if you have conclusion if you want more clarity on
any topic...please feel free to write into
'imran.rafai@nwking.org'
and I will look into it and I will answer your queries.
And of-course subscribe to our YouTube channel
and you can keep getting all our videos LIVE
on YouTube. Thank you for watching and
please visit our WEBSITE! BYE.