Understand the OSI model in less than 5 minutes

3 min readJul 31, 2022

The Open Systems Interconnection (OSI) model describes seven layers that computer systems use to communicate over a network. It was the first standard model for network communications, adopted by all major computer and telecommunication companies in the early 1980s. In this simple tutorial, we will understand the OSI model with its seven layers in simple words, let’s go!

The best way to view the OSI model is to view it from top to bottom, so we will start with the higher layers and go beneath.

Layer 7: Application Layer

Let’s say that you are a user and want to go to medium.com The website here represents a chunk of data. But, the data can be very big so we split it into multiple chunks. We Assume we took one chunk of it to send it to the requesting user.

N.B. We don’t really care about the 6th and 5th layers

Layer 4: Transport Layer

This layer is much more like an envelope we add headers to the data chucks. The website chunk is added to the payload section as well as some headers like (Source port, Dest Port, Flags, #Seq, # ACK, PayLoad)
We call this envelop a Sgement. The Segment is a chunk of data with transport layer headers.

Layer 3: Network Layer

The data in this layer is much more like a packet we add headers to the data chucks where the website chunk is added to the payload section as well as some headers like (Source IP, Dest IP, TTL, Other, PayLoad) called Network layer headers.

Layer 2: Data Link Layer

This layer is much more like a frame we add headers to the data chucks and the website chunk is added to the payload section.
It has some headers like (Source MAC, Dest MAC, PayLoad) AKA. Data Link layer headers. The Frame is a chunk of data with data link layer headers.