TCP/ IP Model

Tcp/ ip model, application layer, transport layer, internet layer, network access layer, osi vs tcp/ ip model

TCP/ IP MODEL

In this blog, we will see the basic understanding of the TCP/ IP model and the difference between OSI and TCP/ IP. First, understand the difference between model and standard. The model describes how devices communicate in the computer network. On another side, some different standards and specifications describe actual communication. That's why the TCP/ IP model is used for understanding and explaining how different devices communicate with each other.

TCP model contains four different layers. These are the application layer, transport layer, internet layer, and network access layer. The name of this model was constructed using two different major protocols that are used in computer networking. Such protocols are TCP that stands for transmission control protocol and IP that stands for internet protocol. TCP belongs to the transport layer. IP belongs to the internet layer.

Application Layer

The application layer is about different applications and different protocols that are utilized by different applications. Some examples of applications like HTTP, FTP, DNS, or DHCP. These protocols are used at the top level of the TCP/ IP model and that's why we need computer networking we need to transfer or receive some data using specific protocols and use resulting data in some applications. But underneath the application layer, there are three other layers called transport, internet, and network access.

Transport Layer

What is the purpose of the transport layer? It establishes end-to-end communication and delivers data between two different endpoints in the computer network. Two different protocols are used on the transport layer. They are TCP that stands for transmission control protocol and UDP user datagram protocol. The difference between these two protocols is that TCP establishes end-to-end sessions between two different endpoints reliably sense data. What does it mean reliably? It means that if some data was lost on the way from one endpoint to another then TCP will attempt to retransmit such data. This process will be fully transparent for the application layer. Also, TCP has torn down the process of the connection when data was sent then there is no need to have the TCP session alive and it is terminated.

UDP does not establish a session. It sends data from one endpoint to another. There is no connection setup or connection tear down. That's why we can't say that UDP sends data reliably. TCP is a reliable protocol UDP is unreliable.

Internet Layer

The responsibility of this layer is to connect different networks, find the optimal paths between different networks, and send packets from one network to another. Several protocols work on this layer of the TCP/ IP model. They are IP version 4, IP version 6, or ICMP. Also, accept these protocols there are other protocols called routing protocols that are responsible for the discovery of different networks, finding the optimal path, and afterward routing of the packets from one network to another.

Network Access Layer

This one is the lowest layer in the TCP/ IP model. This layer handles the transmission of the data over the physical media. Some protocols are used on this network access layer.

An example of such a protocol is Ethernet. Also, different technologies are used on the network access layers like Bluetooth, Wi-Fi, or CDMA. But main responsibility of the network access layer is to send actual data over the physical media and there could be different types of media between different endpoints that are connected to the computer network. For example packet from my computer to some remote server on another side of the ocean goes first via wireless connection from my computer to the wireless router. Afterward using Ethernet cable goes from the wireless router to devices on the internet provider side. Afterward, there are fiber cables that interconnect different internet providers and connect different continents. That's how different media could be used on the network access layer.

The main idea here is that layers in the TCP model are fully independent. It means that the application layer doesn't care about what happens on the transport layer. The transport layer is independent of the internet layer same internet layer is independent of the network access layer and so on. Layers are fully independent.

Now we mapped some protocols to different layers of the OSI and TCP/ IP model. These models under no means specify exactly how devices communicate with each other. For example, some protocols could not be mapped to one specific layer instead they work on many layers. An example of such protocol is the IP security protocol it works on session transport and network layers simultaneously. It uses a set of other different technologies and standards. That's why again OSI and TCP are reference models that could be used for a better understanding of what is happening between devices in a computer network.

OSI vs TCP/ IP Model

Now compare the OSI and TCP/ IP model and map layers of the TCP/ IP model to the OSI model. So layer 4 application layer of the TCP model is a combined layer. It combines application, presentation, and session layers of the OSI model. Because application itself for example web browser is responsible for all operations that happen on these three layers like presentation, session, and application.

The next layer transport is called the same in both models OSI and TCP. The purpose of this layer is the same in both cases. TCP and UDP protocols are examples of the protocols that are used on this transport layer.

The next layer is different in both. But the purpose of this layer is the same in both models. It is responsible for the delivery of the packets from source to destination and for that we need first somehow discover routes and afterward find the optimal path to destination routes. That is also the responsibility of the internet layer in the TCP/ IP model or network layer in the OSI model.

Finally, the network access layer in the TCP/ IP model combines two layers of OSI model data link and physical layer. Sometimes that TCP/ IP model consists of five different layers and those two layers instead of one network access.

Conclusion

There are four layers in the TCP model application, transport, internet, and network access. Computers communicate using different protocols on different layers. Also, we have seen the difference between OSI and TCP/ IP models relating to the naming of different layers. The only difference is application layer in the TCP model combines three different layers of the OSI model.