What is TCP/IP?

TCP/IP is a term that describes a set of network protocols that allow communication between computers. The largest TCP/IP based network is the Internet. In this blog, we explain what TCP/IP is, which TCP IP layers the model consists of, and what role the different TCP IP layers play.

IP stands for Internet Protocol, the primary way of establishing connections over networks and the Internet. An IP address can be compared with a residential address; it tells in detail where data should be requested or delivered. Every IP address on the internet is therefore unique.

Send Packets

When you send data over the internet, you send this data unnoticed in several so-called packets. The division of data into these packets takes place automatically behind the scenes. IP ensures that all these packets eventually reach the correct destination (the correct IP address).

However, the route packets take may differ. This also means that the order in which the packets arrive may vary. The Transmission Control Protocol (TCP) reorders the packets. Is one of the packets not arriving properly? Then TCP requests it again so that the receiver receives all the data sent.

History of the TCP/IP model

The basis for the TCP/IP model was laid in the 1970s by Vinton Cerf and Robert Kahn. In 1974, as RFC (Request for Comments), they published the first paper ever on the Internet under the title ‘A Protocol for Packet Network Intercommunication.’ This paper describes the TCP model for the first time. IP did not yet exist as a model at that time and was part of the TCP model.

The testing and further development of the TCP model eventually led to the TCP/IP model. After several revisions, version 4 of the Internet Protocol (IPv4) was published in 1981. This version is still in use today – alongside its successor IPv6.

Five TCP IP layers

The TCP IP model consists of five different TCP IP layers, each of which has its own functions. This concerns the:

  • Application layer
  • Transport layer
  • Network layer
  • Data Link Layer
  • Physical layer

The application layer is the top layer of the TCP/IP model. In this layer, applications and processes create and transport data to other applications and processes on the same or a different host. These processes are addressed via ports, which are assigned to specific services. For example, some ports are reserved for common protocols. Think of port 80 for HTTP and port 23 for Telnet.

The transport layer handles communication between processes that take place on the hosts. In the TCP/IP model, the transport layer determines where, when and how much data is sent. Applications use TCP or the User Datagram Protocol (UDP) for the transport layer. TCP is aimed at completely error-free transfer of data, whereby TCP monitors the order of packets and requests missing packets. UDP is focused on speed and minimizing overhead.

The network layer defines protocols responsible for transmitting data over the entire network. This layer packs data into datagrams. A datagram is a data packet that contains information with which it can independently find its way to its intended destination. This without having to set up a connection between the sender and receiver in advance. The network layer is, among other things, responsible for forwarding packets and determining the route that packets take. The layer includes several protocols. Think of IP for delivering packets to the right recipient,

The data link layer ensures, among other things, the translation of IP addresses into physical addresses and converts datagrams from the network layer into so-called frames. A frame is a fragment of data that is sent over a network connection. The data link layer then sends these frames to the receiver via the physical layer. The data link layer defines how a data stream is divided into manageable blocks of data.

The physical layer is responsible for sending bits from one device to another. Binary data in digital form travels from the sending device to the receiving device, over wired or wireless networks. The physical layer is aimed at sending and receiving the data stream over a physical medium.

In older versions, the TCP/IP model is limited to four TCP/IP layers. Here, the data link layer and physical layer are combined to form the network access layer, also known as the link layer.

OSI Model

The TCP/IP model differs from the OSI model, where OSI stands for Open Systems Interconnection. The TCP/IP model defines how a computer is connected to the Internet and can communicate with other systems over the Internet. The OSI model is a logical and conceptual model that manages network communication between systems that communicate with each other. The OSI model consists of seven layers:

  • Application layer
  • Presentation layer
  • Session Layer
  • Transport layer
  • Network layer
  • Data Link Layer
  • Physical layer

The OSI model was developed by the International Standard Organization.

What principles lie behind TCP/IP?

A number of principles play an important role in TCP/IP. This concerns the end-to-end principle, the robustness principle, and encapsulation.

End-to-end principle

The end-to-end principle states that networks should only include functions to provide efficient routing of traffic between endpoints. All application-specific functions and intelligence remain at the edge of the network, in the applications themselves. This is necessary to achieve the desired efficiency and performance when sending data. Ensuring the reliability and correctness of transmitted data is handled by endpoints, which are applications in practice.

Robustness principle

The robustness principle helps to ensure – as the name suggests – robust communication. This means that an application must send correctly prepared datagrams. At the same time, the application must accept any kind of datagram it can interpret. For example, an application should also accept datagrams with errors, provided the meaning is clear.

Encapsulation

When an application sends data, this data moves across the different TCP/IP layers of the TCP/IP model. A new translation takes place between each layer so that the next layer can handle the data. This process is also known as encapsulation, where data is further encapsulated at each layer. Each layer builds a so-called protocol data unit (PDU), which contains the control information associated with the data. This information is stored in the header of the data field (the header) or at the end of the data field (the trailer).

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