What is OSI Model | Real World Examples — Transcript

Full transcript

1. 0:07How is data sent over the internet?
2. 0:09What does that have to do with the OSI model?
3. 0:11How does TCP/IP fit into this?
4. 0:14Let’s take a look.
5. 0:16The OSI model, or the Open  Systems Interconnect model,
6. 0:19is a theoretical framework that provides  one way of thinking about networking.
7. 0:24It splits the network communication between two
8. 0:27devices on a network into  seven abstraction layers.
9. 0:31The physical layer is the bottom-most layer.
10. 0:34It is responsible for transmitting raw  bits of data across a physical connection.
11. 0:39The data link layer is the second  layer. It takes the raw bits from
12. 0:43the physical layer and organizes them into frames.
13. 0:47It ensures that the frames are  delivered to the correct destination.
14. 0:50The Ethernet primarily lives in this layer.
15. 0:55The network layer is the third layer.
16. 0:57It is responsible for routing data  frames across different networks.
17. 1:01The IP part of TCP/IP is a  well-known example of this layer.
18. 1:06The transport layer is the fourth layer.
19. 1:09It handles end-to-end  communication between two nodes.
20. 1:12This is the layer where TCP and UDP live.
21. 1:16TCP provides reliable, end-to-end  communication between devices.
22. 1:21It does this by dividing the data into small,
23. 1:23manageable segments and sending  each segment individually.
24. 1:28Each segment has a sequence number attached to it.
25. 1:30The receiving end uses the sequence numbers  to reassemble the data in the correct order.
26. 1:36TCP also provides error checking to make sure that  the data was not corrupted during transmission.
27. 1:43UDP is another popular protocol  in the transport layer.
28. 1:46It is similar to TCP, but  it is simpler and faster.
29. 1:51Unlike TCP, UDP does not provide the same  level of error-checking and reliability.
30. 1:57It simply sends packets of data  from one device to another.
31. 2:00The receiving end is responsible for determining  whether the packets were received correctly.
32. 2:05If an error is detected, the receiving  end simply discards the packet.
33. 2:10The remaining layers are the session,  presentation, and application layers.
34. 2:15This is where the OSI model  loses its usefulness in practice.
35. 2:18They are too fine-grained and  do not really reflect reality.
36. 2:23In general, it is sufficient  to collapse them into a single
37. 2:27layer and consider application protocols  like HTTP as simply layer 7 protocols.
38. 2:34Let’s go through an example and examine how data
39. 2:36moves through the layers when  transmitting over the network.
40. 2:40When a user sends an HTTP request  to a web server over the network,
41. 2:44the HTTP header is added to the  data at the application layer.
42. 2:50Then, a TCP header is added to the data.
43. 2:53It is encapsulated into TCP  segments at the transport layer.
44. 2:57The header contains the source port,  destination port, and sequence number.
45. 3:02The segments are then encapsulated  with an IP header at the network layer.
46. 3:07The IP header contains the source  and destination IP addresses.
47. 3:11A MAC header is added at the data link layer,  with the source and destination MAC addresses.
48. 3:17It is worth noting that in the  real world this is a bit nuanced.
49. 3:20The MAC addresses are usually not the MAC  address of the sending and receiving ends.
50. 3:26They are the MAC address of the routing devices in
51. 3:29the next hop of a usually long  journey across the internet.
52. 3:35The encapsulated frames are sent over the  network in raw bits in the physical layer.
53. 3:39When the web server receives the raw bits  from the network, it reverses the process.
54. 3:44The headers are removed layer by layer,
55. 3:46and eventually, the web server  processes the HTTP request.
56. 3:51To conclude, the OSI model is one  way of thinking about networks.
57. 3:55Its primary purpose is educational.
58. 3:57Even though the layers don’t fit  the real-world use cases perfectly,
59. 4:01they are still widely used by networking  vendors and cloud providers as a shorthand
60. 4:07to describe where their networking  products sit in the OSI model.
61. 4:11For example, cloud load balancers are broadly  divided into two categories - L4 or L7.
62. 4:18An L7 load balancer is a shorthand to  mean that the load balancer operates at
63. 4:23the application protocol layer like HTTP or HTTPS.
64. 4:27An L4 load balancer, on the other  hand, operates at the TCP level.
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66. 4:38Please subscribe if you learned something new.
67. 4:40Thank you so much, and we’ll see you next time.