The OSI Model - Explained by Example

OSI is a model that standardized the communication in computer system, its what the internet runs on. In this video we will try to learn about the OSI model by example! Stands for Open Systems Interconnection model.

In this video we will make a HTTP GET request to a web server and explain how the data flow through the OSI model layers from the application layer, presentation layer, session layer, transport layer, network layer, data link layer and finally physical layer. we will also explain why people tell you not to connect to public WIFIs.

0:00 Intro
2:15 public vs private ip address
4:00 Application Layer
5:30 Presentation Layer
6:20 Session Layer
7:20 Transport Layer
9:20 Network Layer
11:20 Data Link
13:00 ARP protocol
14:00 Physical Layer
19:00 Why you shouldn’t connect to public WIFI

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Stay Awesome,
Hussein

Stay Awesome!
Hussein

[hnasr]

Hey guys in minute 16:00 I forgot to mention this is a WIFI configuration not wired .

so all devices within range will receive the those packets since they are in radio vicinity and drop them if they are not intended for them.

if that was wired than the router (acting like a switch) will be smart enough to only forward to required device by identifying which port it is connected to.

[Ryfibi]

I feel like I want to quit my job and spend a few weeks just studying your backend topic videos. Really interesting stuff. I was even able to explain to my wife why she can't access homebanking in a starbucks.

[hnasr]

Guys here are some jump codes to help you navigate, 2:15 public vs private ip address, 4:00 Application Layer, 5:30 Presentation Layer, 6:20 Session Layer, 7:20 Transport Layer, 9:20 Network Layer, 11:20 Data Link, 13:00 ARP protocol, 14:00 Physical Layer, 19:00 Why you shouldn’t connect to public WIFI
I enjoyed making this video!

[cppdog]

Hi Hussein, thank you for making this video. I just want to clarify one thing. At 16:20, you say that the stream of bits that are being sent from the client will go into server 1, 2, 3, 4..etc essentially to all servers. This is not correct. I'm a software engineer working in networking domain, and in networking the direction of packets is either "unicast" (meaning it's directed to one client only), multicast (meaning it's directed to two or more known clients), or broadcast (meaning the traffic is directed to any machine that's on that network). In your case, since the server is hosted on machine C, the data is directed to that machine and it will only go to the router first and then to that machine regardless of the medium used to transfer the packet (Ethernet or WiFi). If the stream of bytes were transferred using WiFi, you are right in that the data will be broadcasted all over the place using radio waves but only the router will be able to interpret those packets, because that's how WiFi works, and the other machines (even if they have a WiFi receiver) will not be able to decode the packet and see the bit streams. Just wanted to point this out to clear any confusion. Thanks for making these video. They're very useful and informative.

[palaniappanrm]

"Intended for you as a device, but not as an application" - Perfect way to explain the way the router works when you make a request to external network 👌

[andrescastillo]

Summary of:
OSI (Open Systems Interconnect) model, from a software Engineer's view (Please correct me if I'm wrong):

Layer 1 Physical
This is the physical layer, in which 1 and 0 data bytes can be sent as electric signals, wifi, or light via "the wire"

Layer 2 Data Link
These are the separation of the data bytes into frames.
Notably, the frames will identify the source and destination MAC addresses of the devices' network card.
Since electrical signals travel in all directions in a network, the data frames reach all devices in the network.
Once the data frame is able to identify that the device is not the intended destination, the frames drop.
In an unsecured network, this is where a malicious application can choose to not drop the frames, and steal the data.

Layer 3 Network
Once layer 2 is done, it generalizes the frames from MAC addresses to IP addresses.

Layer 4 Transport
This tranport layer further generalizes the network layer IP address into source and destination ports.

Layer 5 Session
Since there may be several TCP connections to one server at a time, with identical packet information from layers 1 through 4, we need a way to distinguish the session by ID to tag it.

Layer 6 Presentation
This is where the resource might be secured/encrypted with HTTPS/TLS by scrambling the HTTP request string.
I didn't know HTTPS encrypted anything. I thought it was only a way to identify the true identity of a website.
Also, encryption might be accomplished via VPN.
At this step, if the data is encrypted, the model decrypts the information to reach step 7.
It might be possible that a malicious attack to steal data can be avoided by encrypting.
"This is where you can get screwed if you are on public wifi...people can sniff your data."

Layer 7 Application
This is where a client device makes a request to a server device, such as a GET request.
This request contains a whole bunch of information, such as headers, cookies, content-type headers, etc, which is summarized into a string, so the string can participate with the rest of the OSI models as byte data.

[AbandonedVoid]

It is a dry topic, but somehow even with your thick accent and minimalist presentation style, your charisma makes this video a joy to watch. Seriously.

[jeffreypham]

I have watched many youtube videos on the OSI layers, and this is my favorite one. This really gave me a good understanding of the OSI layers in a real world scenario. Explained simply and gets the points across. Just great!

[Deepakkumar]

Your Channel is a gem. I landed on this channel searching about the difference between proxy vs reverse proxy, ended up watching at least 10 videos as of now. Though I am a frontend engineer, still I feel everyone should have this basic networking knowledge.

[saahilnayyer]

First ever I came across the concept of OSI was in 3rd year bachelors and it's been 4 years since. Today is the first time I can say that I understand the whole damn thing and what each layer does. You are a legend Hussein.😁

[shubhamchandramishra]

I wish i could understood the Beauty of OSI model a year before. Really awesome video ...

[ebymathew]

At last i laughed when the web server got the GET explanation

[pratikgaur]

Your humour lines in between your awesome teachings are really nice and engaging.
Thanks for a refresher and keep it up!

[hulksmash]

Omggg where was Nasser in 2015 when I was pursuing my undergrad?! Computer Networks made me cry as a subject just because I could not digest the huge amount of information bombarded at us during the coursework. This info along with the diagrams, is gold 💯. Really helped me understand the OSI model - something I thought would never be possible (coz I tend to get lazy when things stop making sense or when I'm unable to visualize what is happening)!!! Thank you Nasser 💯❤

[vishalvatsalya]

I am binge watching the backend engineering playlists. Awesome content. Keep up the good work! :)

[LLDG]

I have been listening to your videos for days. I can finally understand this stuff. Thank you so much!

[shreyasmali]

I don't think I've ever heard any explanation of any topic to be this much interesting and fun ever! Thanks a lot! I wish I could learn every other subject from you...

[lakshayasood]

thank you sir.. you just explained something in a great and easy way that i couldn't understand though out my computer networks class. Now i am less scared of the subject

[felipemartinezalbeche]

Hey Hussein!
You really rocks!! It's amazing how clearly your explanations are about complex stuff!
Congrats!

[IktaSol]

" OSI is Open Systems Interconnect, I don't expect you to remember it"
Me: "meh I think I will"
*midway through the video*
"what's OSI again"