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 a 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
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 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 Picasa is built on.
So we learn about this network and maybe if we have time over the course of 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 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 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 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. Sorry about my handwriting. It’s very difficult to write on screen especially with my mouse but let me 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…. of course 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 types ‘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.
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