This article in addition to reference courseware, but also additional referenceAn article familiarizes you with the TCP/IP protocolandProtocol Forest 01. Thanks to the Internet

Well, here we go after all this time.

As mentioned earlier, the Internet is made up of various protocols, which are distributed at different levels to realize the functions of the network. We can also organize and manage the devices mentioned earlier according to the hierarchy.

Why stratification

In order to deal with the complexity of the situation (nonsense, to expand the word

  • Explicit structure helps us to identify the relationships between the parts of the system and clarify their logic
  • After layering, modularization is convenient, so it is easy to maintain, upgrade, and updating the system. It is possible to upgrade one part without affecting the other

So, when someone asks what are the benefits of doing this, it can be summed up like this:

  • Help with complexity: Break down complex design tasks into smaller tasks
  • Modularity simplifies maintenance and updates: change one part of the system, leave the rest unchanged)

There are two specific models

An overview of

TCP/IP model

TCP/IP does not refer to these two specific protocols. Specifically, IP or ICMP, TCP or UDP, TELNET or FTP, and HTTP are all TCP/IP protocols. They are closely related to TCP or IP and are a de facto integral part of the Internet

The term TCP/IP refers broadly to these protocols, and as a result, TCP/IP is sometimes referred to as the Internet Protocol Group

It is divided into:

  • Physical: “bits on the wire”. It refers to real physical media such as optical fibers, cables, or electromagnetic waves. How does this part spread by @telecommunication System
  • Connection layer, data link layer:It’s about point-to-point, the connection between two connected terminals, like WIFI, like Ethernet.
    • With the connection layer protocol, we can establish a local area and allow two computers in the same LAN to communicate.
    • Pay attention to the MAC address of a specific device
      • At the connection layer, information is transmitted in frames. We’ll talk more about that when we talk about the connection layer
      • The connection layer is like a postman in a community who knows everyone in the community. Each person in the community can hand him a letter (frame) for him to deliver to another family in the same community.
  • Network layer:Focus on how the data moves from start to finish and who is responsible for it.
    • Pay attention to the computer’s address and check for data corruption
      • Like the post office, in each neighborhood, you send something and it does the intermediate operation for you
      • The transmission unit is a datagram
  • Transport LayerConcentration is responsible forTo transmit data
    • Related to reliability, focusing on which program on the machine sends data
    • We need to write new information on the paper, such as the name of the recipient, to get the letter delivered. So the transport layer simply writes the new “addressee” message on the blank space of the paper. Each house will have an administrator (Transport layer protocol). The administrator takes the letter from the postman and gives it to someone in the house, according to the “recipient.”
    • The data transfer unit is package
  • Application layer:Network the APP
    • FTP (file), SMTP (mail), HTTP (WWW)

ISO/OSI reference model

ISO = International Standards Office OSI = Open Systems Interconnection

The OSI reference model focuses on “what are the necessary functions of the communication protocol”, while TCP/IP puts more emphasis on “what programs should be developed to implement the protocol on the computer”.

In other words, TCP/IP is practical and ISO/OSI is the ideal functional level

It has two more layers than TCP/IP

  • Session layer: responsible for synchronization, checking, data recovery, exchange, etc., related to the whole connection life cycle control
  • Presentation layer: Allows applications to interpret the meaning of data, such as encryption, compression, and machine-specific conventions. Related to data and character sets

Because the TCP/IP structure is already too large to be added, these functions should be implemented at the application layer as much as possible

Equipment at every level

It’s a repeater

Overview, salutations and exercises

The overview is just looking at the big picture again, surprise me

Common name: almost forget, look at the picture should be able to see, all in accordance with ISO/OSI representative number (Layer 1-7) to call

And then let’s see if we can separate them out

Identifier of layer — Headers

So what’s the head

Most layers of the TCP/IP model are associated with a specific type of “head,” and sometimes even “tail.” So, what is a head

  • They are separated from the data itself
  • Describe information about the data, such as:
    • Where will it be sent?
    • Which program will receive it?
    • How long is this string of data?

For example, layer 3 (the network) has a “Network Address” that identifies the host that should receive the data; Layer 4 (transport) has a port that identifies which program should receive it.

About the packaging

A new header is added each time it passes through a layer, so that more headers are included as it travels down the layer — a layer 2 packet has a layer 2 header, but includes headers from layer 3 and layer 4.

This picture is a schematic of this process

  • Everything in the source is pressed together and the physical plane propagates
  • Switch is unpacked to Link, modified and repackaged. In addition, each end of the link has to be decoded once, which means that it is responsible for each end
  • The router is unconnected to the network, and then the router is reencapsulated. Or the router is responsible for the Network layer; Network is about “finding your way”, which is really about IP
  • The transport header is only solved at the terminal to show the presence, focusing on the interface
  • The application layer, I’m sure you all know, but it’s data transmission, no head

After both arrive specific terminal just unpack knead

Example 1:

Including high-level

Example 2:

Shouldn’t be a problem

A little history of the Internet — CK Principles

  • Minimalism, automation — no need to say how much I want to send and how much you can change the structure of the Internet for me to send
  • B: Best effort service model
  • Stateless Routers routers are stateless and do not need to change
  • Decentralized Control Indicates the decentralized control