The TCP/IP Model Explained

CertBrosCisco CCNA

What is the TCP/IP model? It’s a model to standardise computer networking.

Sound familiar? It should because it’s the same description as the OSI model. The OSI model, while widely referenced isn’t used in the real world. The TCP/IP model, however, is the real deal. Thankfully, it’s not that different.

The TCP/IP model has four simple layers, Application, Transport, Internet, and Link. Just like the OSI model, it’s numbered from the bottom up but the direction depends on if you’re sending or receiving data.

Original and Updated Model

So this is the original model, but, it has been updated. Here is the brand new, freshly designed model! One extra layer, and one renamed layer. That’s it!

The Link layer has been split into Data link and Physical and the Internet layer has been renamed the Network layer. Simple right?

TCP/IP Model vs OSI Model

It gets even better when we compare the TCP/IP model to the OSI model

If you remember, the OSI model has 7 layers compared to our 5 layers here. But when you look at it, you’ll notice that the application, presentation and session layers are just shown as the application layer in the TCP/IP model.

All other layers line up nicely, which is great because we should already know the concepts of how this works.

The Layers

So let’s remind ourselves about the protocols and devices at each layer.

Application layer: Here we have application protocols such as HTTP, FTP, and SMTP.

Transport Layer: The two most common transport protocols are TCP and UDP. Port numbers are also added here.

Network layer: Here we have the Internet Protocol or IP. Routers also commonly operate at this layer.

Data Link layer: This layer contains some Ethernet standards. Switches usually operate at this layer. Although you can get layer 3 switches that have routing capabilities.

Physical layer: Think of everything you can touch and feel here. Things like cables, hubs and Network interface cards.

Encapsulation

OK, so as we send data, each layer will add its own bit of information. This process is called encapsulation.

When we hit the physical layer, the data is transmitted over to the receiving device. The receiving device then starts to decapsulate the data.

Each time a header is added, this will contain specific information.

For example, a TCP header will contain things like source and destination port numbers, sequence number and a few more bits of information.

It’s important to note that at each step, the data has a specific name.

At layer 5, the data is called, well, it’s just called data at this stage.

Once the transport information has been added, it’s now called a segment.

Adding the network layer information makes our segments a packet.

And finally, once we add our data link layer information to our packet, it becomes a frame.

So that’s it for the TCP/ IP model.

After looking at the OSI model, thankfully there is not much else to learn.

Follow us