Finally someone explained the role of OSI and TCP clearly

I have mentioned the OSI reference model and the TCP reference model before. These two models can be said to be the cornerstones of the Internet. Today we will expand on this part.

The era of fighting for each other

Send an email on your computer, and your friends who are chatting on QQ on their mobile phones can receive it immediately. A long time ago... not too long ago, before 1974, devices produced by different manufacturers could not interconnect and communicate with each other, which caused a lot of trouble.

Imagine sending a message to a desktop computer with an iPhone, but the desktop computer cannot receive it...

The reason for this is that each manufacturer uses a different communication protocol, just like the British speak English and the Chinese speak Chinese, and one day they meet and say hello.

One said: "hello."

One said "Hello."

No one could understand what the other was saying and there was no way to communicate at all.

People realized that if everyone did not unify the protocol, the development of the Internet would be greatly restricted.

OSI Reference Model

In 1974, ISO (International Organization for Standardization) stepped forward and said to everyone: "I will be the leader, and everyone will work according to one standard." Thus the OSI model was born.

As long as everyone complies with this protocol, all devices can interconnect and communicate.

Just like Esperanto invented by Zamenhof in 1887, everyone speaks Esperanto, and people from the British, Chinese, and other countries can communicate with each other.

British: "Sa."

Chinese: “Sa.”

Oh! It turns out that the other party was saying hello to me.

The OSI reference model divides the computer network architecture into seven layers. If everyone follows the standards, devices can communicate with each other and transmit information.

Comparing computer network architecture to a post office, then:

• Physical layer: It is equivalent to the porters in the post office. It converts data into electronic signals that can be transmitted through physical media.
• Data link layer: responsible for communication transmission between two adjacent hosts, that is, the generation and reception of data frames.
• Network layer: Equivalent to the sorting workers at the post office. Routes data through large networks.
• Transport layer: It is equivalent to the courier running from the company to the post office. It provides reliable connection from end to end.
• Session layer: It is equivalent to the secretary who receives, writes and opens letters in the company. It allows users to establish connections using easy-to-remember names.
• Presentation layer: It is equivalent to the assistant who briefs the boss and writes letters for the boss. It negotiates the data exchange format.
• Application layer: The interface between the user's application and the network.

The OSI reference model was proposed, which was of epoch-making significance. However, OSI was only a conceptual model, which did not explain how to implement it. Moreover, the model was too rigorous and complex, resulting in low communication efficiency.

TCP/IP Model

The OSI model is too idealistic. It defines the reference model first and then the protocol, which makes it difficult to implement. Therefore, TCP/IP, which defines the protocol first and then the reference model, quickly became the actual mainstream network protocol standard.

OSI is like Esperanto, which is too idealistic and not popularized, while TCP/IP is like English, which has become the most widely used language in the world.

As long as you want to communicate with other computers and exchange information through the Internet, you must comply with the TCP/IP protocol.

Compared with OSI, TCP/IP simplifies the high-level protocols and integrates the session layer and presentation layer, which provide similar services, into the application layer, reducing the communication levels and greatly improving communication efficiency.

The four layers of TCP/IP are:

• Network Access Layer: The OSI physical layer and data link layer are combined into the network access layer, which defines how to use the network to transmit data.
• Network layer: Uses the IP protocol to send data packets from the source address to the destination address.
• Transport layer: enables applications to communicate with each other.
• Application layer: A layer that directly provides services to application processes. Different types of applications can use different protocols of the application layer according to their needs.

OSI and TCP/IP are two very important models. Without them, the Internet exists today.