8. Network addressing

Let us now clarify a very important question, namely addressing in the network. You may have noticed that this question comes up 3 times when discussing the communication process, because information related to addresses or numbers is added to as many as three layers.

But this time, let's start at the bottom of the stack and see that the TCP/IP model network access layer and the ISO/OSI model data link layer have come up with the concept of physical addresses. A physical address, also known as a MAC address, is a 48-bit hexadecimal encoded number on the network card of the end device, or computer. This address can be of the form: 28-81-34-C6-EB-12, given at the card creation stage. It consists of two equal parts, the first being the manufacturer's identifier and the second being the card's identifier.

All of these hexadecimal codes are used to find a host on the local network, the LAN, is this address, the physical address of the source host and the router on the local network, the gateway connecting our local network and the WAN.

Moving upwards, we have the Internet layer of the TCP/IP model and the network layer of the ISO/OSI model. In these layers, IP addresses, also called logical addresses, are added during the encapsulation process. These addresses are the IP address of the sender computer and the IP address of the receiver computer.

Finally, we have the transport layer, which does not use addressing to detect hosts like the previously discussed layers, but instead uses port numbers to assign data to specific applications in the operating system. Today's computers allow multiple applications to run simultaneously. At the same time, we can use the browser to surf the Internet, listen to Internet radio, send and receive e-mail and even play online games. If applications are not partitioned, if port numbers are not assigned at the transport layer to allow specific network services to be identified, we may experience e.g. that incoming e-mails will appear on the screen during gameplay.