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What is the Network of computer Network (1)

What is the Internet?

Implementation of Network Communication: tcp/ip Protocol

Using Wireshark to grab packets and analyze tcp/ip protocol stack

What is the Internet?

The so-called network, is through a certain form of connected objects, objects and objects can achieve communication.

For example, it is called a computer network. It can realize the communication between computers.

Or so, it is called a neural network. It can communicate signals through biological synapses. Recently, in-depth learning, artificial intelligence has made extensive use of the working mechanism of neural networks.

Or so, it is called the Internet of things. It can achieve the Internet of everything, think about it is still a little excited, I do not know whether it is a blessing or curse.

As long as you can think of, can be connected in a certain form, can be called the network. Cats and dogs can also form a network, we may be able to connect cats and dogs through magical bionic technology, so that they can achieve barrier-free communication, this is the Internet of everything language. I'm looking forward to this day.

Magical computer Network 1.1 the three ways of communication of computer network what is a computer network, as you probably know, is the communication between computer and computing. Here are some of the three communication methods commonly used by computers, which you should know. 1. Unicast, that is, two computers communicate through a unique channel. two。 Broadcast, that is, multiple computers communicate within a certain range (local subnet). When one computer sends a message, all other computers will receive information. 3. Multicast, that is, sender and receiver can achieve a variety of communication modes, which exist in groups, which can be either the same physical network or different physical networks. In this way, the rate of communication can be greatly increased.

1.2 computer communication protocol have you ever thought about how computers communicate? Isn't it amazing that computers can communicate all over the world through electricity, network cards and networks? Human communication depends on language, and computers naturally communicate through language. What is the language of computing? In fact, computers communicate through binary language. The so-called language naturally obeys certain rules, which is the same as human language. China speaks Chinese, the United States speaks English, animals speak animal language, and computers naturally speak computer language. Every language has certain rules and languages, and so does computing. In the early days, there was a very powerful organization, full of ambition, ready to make a communication rule for computer network communication. This rule is called the OSI seven-tier model, and this organization is called the International Organization for Standardization (ISO). Later, through continuous practice and exploration, the great sages constantly fell into the pit, and then climbed out of the pit. After several great struggles, they finally worked out the computer communication TCP/IP model that has been used so far. For these wise men, what else can we do but marvel and worship? Yes, that is to learn the TCP/IP model well and live up to the wisdom of the wise men. 1.3 OSI and TCP/IP models are shown in the following figure, comparing the TCP/ IP five-layer model with the OSI model. It is not difficult to find that there is an one-to-one correspondence between the lower four layers, while the upper three layers of OSI are included in the application layer. TCP/IP five-layer model (others think it is a four-layer model, which combines the physical layer with the data link layer into one layer.) There is no doubt that it has become an international standard, and although the OSI model is more reliable, it is difficult to implement and does not accord with the actual situation, so it has come to an end now.

The corresponding functions of each level are shown below. Note that the following figure shows the corresponding relationship of the OSI seven-tier model, while the TCP/ IP five-tier model only needs to include the upper three layers of the following figure. I'm sure you know.

2. Brief introduction of TCP/IP five-tier model

Computer communication begins at the underlying physical layer and ends at the top application layer. The lower the level, the closer to the hardware, the higher the top, the closer to the user, dealing with the user. So how does the computer climb up layer by layer, through what medium or protocol to reach the pinnacle of life (network interconnection)? Next I will come one by one.

1. Physical layer

What does physics do? It's too complicated to implement binary data transfer. In fact, it is connected by cable, twisted pair, radio waves and so on. Like this.

two。 Data link layer

The bit stream data is framed, and the computer communication of the local network segment can be realized by the way of MAC address. How does the MAC address realize the communication of the local network segment computer? An ARP protocol is involved here, which I will explain in the next section. The MAC address is unique in the world and is embedded on each network card, representing the unique status of each computer. The computer communication of the local network segment is identified by the MAC address of the network card, which is like this.

3. Network layer

The most important thing in the network layer is, of course, IP. Let's just say that MAC addresses only allow you to communicate on local network segments, but with IP, you can communicate across network segments. Cross-segment communication involves routing devices, switches and so on. The network layer also involves ARP protocol, RARP protocol, IP protocol and ICMP protocol. All of this will be explained in the next section.

4. Transport layer

The function of the transport layer is to establish port-to-port communication. With the MAC address (for local communication), the IP address (for cross-segment communication), and the port, you can communicate with the application layer applications. You can also understand that a port is an interface to the application layer. There are TCP,UDP protocols in the transport layer, which determine the reliability of communication and the way to communicate with the application layer. Both have their own advantages. TCP is more reliable and UDP is faster.

5. Application layer

The function of the "application layer" is to specify the data format of the application. For example, FTP has the packet format of FTP, which also defines the format of the service by protocol. FTP has FTP protocol, e-mail has SMTP protocol, remote connection has SSH protocol, and domain name resolution has DNS protocol. The application layer is the protocol that defines the application.

So far, over. This paper introduces what the network is and the TCP/ IP five-layer model. Thank you for your time to watch.

Author Michael

April 30, 2017

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