TCP/IP protocol Overview

Public Internet is a world-wide computer network. It is a network that connects millions of computing devices (such as desktop PCs, servers, and workstations) across the world. All these devices are called the host or end system ). The end system is connected by a communication link and a packet switch. When one end system sends data to another end system, the sending end system segments the data and adds the first byte to each segment. The resulting information package is called a group. The group switch receives a packet from one of its inbound communication links and forwards the packet from one of its outbound communication links. In today's Internet, the two most famous switches are routers and link layer switches. Both devices are forwarded to the destination. End Systems, group switches, and other Internet components all need to run a series of protocols that control information receiving and sending over the Internet. TCP (Transmission Control Protocol) and IP (Internet
Protocol) is the two most important protocols on the Internet.

What is a protocol? To understand network protocols and compare some human activities, we can easily understand the abstraction of protocols, because we humans use protocols to communicate with each other all the time. Such as the process of human interaction. A human protocol (or a polite behavior) requires one party to greet (the "hello" indicated by the first blue arrow in the figure) first to begin communication with another person. A typical response to "hello" is to return a "hello" message. This person responds with a warm "hello", which implies continuing to ask the person about the time. Different Responses to the original "hello", such as "don't bother me", "I don't understand English, can only speak Chinese", etc., all think that they cannot communicate. If people execute different protocols (for example, one person is polite while the other person is not polite, or one person understands the concept of time, and the other person simply does not know what time is), the agreement cannot interact, therefore, it is impossible to complete useful work. In the network, this principle is also true. To complete a job, two or more communication entities are required to run the same protocol.

To provide a structure for the design of network protocols, network designers organize protocols and network hardware and software to implement these protocols in a hierarchical manner. Each Protocol belongs to one layer. A protocol stack is a combination of protocols at different layers. For example, it is the layer 5 of the TCP/IP protocol cluster.

The layered architecture of the Internet can be analogous to an example in a human society. It is assumed that a series of actions taken by a certain flight of a route system are described. The entire flight process: buy a ticket, check your luggage, find the boarding gate, and finally boarding the flight. The plane took off and flew to its destination. When the plane lands, it leaves the plane from the boarding gate and claim the luggage. If this trip is not ideal, you can complain to the ticket agency about the flight. The entire process is as follows:

Similar to a computer network: airlines send passengers from the source to the destination, and are grouped by source hosts from the Internet to the destination host. We can see that each layer has a ticket function, a baggage function for checked passengers, and a boarding gate function for checked passengers; passengers who have passed the boarding gate can fly and land, while passengers can fly by planned routes during flight. This reminds us that we can look at these functions horizontally,

It can be seen that each layer is combined with the following layers to achieve certain functions and tickets. On the ticket layer and below, a person is transferred from the route counter to the route counter. At and below the baggage level, complete a person's luggage check to claim the luggage and transfer the hand luggage. Note that the luggage layer only applies to people who have completed the ticket. On the boarding gate layer, the transfer of hand luggage from the boarding gate to the boarding gate is completed. On the departure/landing layer, a person and his luggage are transferred to the terminal. Each layer improves its services through the following methods: 1) some actions are performed on this layer (such as boarding and departure of passengers on a certain route layer) 2) use lower-level services (for example, at the boarding gate layer, use the departure/landing layer runway to the passenger transfer service on the runway ).

This article is a reading note of "Computer Network-top-down method". I would like to thank the author for using the abstract content in the network to compare it with some phenomena in my life, describe some concepts that are easy to understand.