Bo is engaged in a FPGA, has not really studied Ethernet-related technology, and now finally can calm down the heart to learn, I hope that they can more in-depth grasp the most basic communication interface technology. Here's the start.
I. OSI Reference ModelToday we first learn about Ethernet is the most basic and important knowledge--osi Reference model. 1, OSI source OSI (open System Interconnect), that is, open systems interconnection. Commonly called the OSI Reference Model, is the network interconnection model that the ISO (International Organization for Standardization) organization studied in the 1985. In order to make network application more popular, ISO has introduced the OSI Reference Model. The implication is that all companies are recommended to use this specification to control the network. So all companies have the same specifications, they can be connected. 2. OSI seven layer model the OSI defines a seven-layer framework for Network interconnection (physical layer, Data link layer, network layer, transport layer, Session layer, presentation layer, application layer), i.e. the ISO open Interconnect system Reference Model. Such as. Each layer implements its own functions and protocols, and communicates with the interfaces of the neighboring layers. The OSI service definition provides a detailed description of the services provided at each level. A layer of service is the ability of the layer and its lower layers, which are provided to a higher layer through the interface. The services provided by each tier are unrelated to how these services are implemented.
3, each layer function definition here we only have a general description of the functional aspects of the OSI layers, not in detail, because each layer is actually a complex layer. I will also follow the personal direction of the development of some layers of deep learning. Here we have a general look. Let's start with the top-level application layer.The entire process is explained by sending a commercial quote from company A and company B as an example.
The first layer of the OSI Reference Model in <1> application layer is the one that provides the application interface for computer users and provides various network services directly to users. Our Common Application Layer Network service protocols are: HTTP,HTTPS,FTP,POP3, SMTP and so on.The actual Company A's boss is the user we described, and he wants to send a business quotation, is the application layer to provide a network service, of course, the boss can also choose other services, for example, to send a business contract, send an inquiry form, and so on. The <2> presentation layer provides a variety of encoding and transformation functions for application layer data, ensuring that the data sent by the application layer of one system can be identified by the application layer of the other system. If necessary, this layer provides a standard representation for converting multiple data formats inside a computer into a standard representation used in communication. Data compression and encryption are also one of the transformations that the presentation layer can provide.since company A and Company B are companies of different countries, they agree to unify English as the language of communication, so at this point the presentation layer (company's secretary), is to translate the application layer transfer information into English. At the same time, in order to prevent other companies to see, company A's people will also do some encryption of this quotation processing. This is the function of representation, translating the data of the application layer into translation, etc. The session layer of the <3> session layer is responsible for establishing, managing, and terminating communication sessions between the presentation layer entities. This layer of communication consists of service requests and responses between applications in different devices. The conversation-level colleague gets the post-conversion data from the presentation layer (the conversation-level colleague resembles the company's outreach department), and the conversation-level colleague may have access to the company's contact with many other companies, where the company is the entity in the actual transfer process. They want to manage the contact conversation between the company and many other companies in the outside world. After receiving the data of the presentation layer, the session layer will establish and record this session, he first to find the address information of Company B, and then put the entire data into the envelope, and write the address and contact details. Ready to send out the information. After confirming that company B received the quotation, the session ended, and the colleague from the Outreach department terminated the session. The <4> Transport layer establishes a host end-to-end link that provides end-to-end, reliable, and transparent data transfer services for upper layer protocols, including handling error control and flow control issues. This layer shields the details of the lower data communication to the high level, so that the high-level users can see only a host-to-host, user-controlled and reliable data path between the two transport entities. As we usually say, TCP UDP is at this level. The port number is both "end" here.
The transport layer is equivalent to the company in charge of Courier Mail Transceiver, the company's own couriers, they are responsible for the previous layer to send the information sent to The courier company or post office. <5> Network Layer
This layer establishes the connection between two nodes through IP addressing, selects the appropriate routing and switching nodes for the packets sent from the transport layer at the source, and transmits them to the destination's transport layer correctly and without errors. is usually called the IP layer. This layer is what we often call the IP protocol layer. The IP protocol is the foundation of the Internet.
The network layer is equivalent to The courier company's huge express network, the country's different distribution centers, for example, from Shenzhen to Beijing, Shun Fung Express (for example, air transport seems to fly directly to Beijing), the first to shun Fung Shenzhen distribution Center, from the Shenzhen Distribution center and sent to the Wuhan distribution center, From Wuhan Distribution Center and then sent to Beijing Shunyi Distribution Center. This is the equivalent of an IP node in the network for each hub. The <6> Data link layer combines bits into bytes, then groups the bytes into frames, uses the link-layer address (Ethernet uses MAC address) to access the media, and makes error detection.
The data link layer is divided into 2 sub-tiers: A logical Link Control sublayer (LLC) and a media access control sublayer (MAC).
Mac sub-layer processing CSMA/CD algorithm, data error check, framing, etc. the LLC sublayer defines some fields that allow the last protocol to share the data link layer. In practical use, the LLC Sublayer is not required.
I didn't find the right example.
<7> Physical Layer
The transmission of the actual final signal is realized through the physical layer. Stream bitstream through physical media. The level, speed, and cable pins are specified. Common equipment has (a variety of physical equipment) hub, repeater, modem, network cable, twisted pair, coaxial cable. These are the transport media of the physical layer.The means of transportation in the courier delivery process is the equivalent of our physical layer, such as cars, trains, airplanes, and ships.
4, communication characteristics: Peer-to-peer communication, in order to make the data packet from the source to the destination, each layer of the source-side OSI model must communicate with the destination peer layer, which is called peer-level communication. During each layer of communication, use this layer's own protocol for communication.
Second, TCP/IP five layer modelthe TCP/IP five layer protocol and the OSI seven-layer protocol correspond to the following relationships.
in each layer of the work of different devices, such as our common switches work in the data link layer, the general router is working in the network layer.
The protocols that are implemented at each level are also different, that is, the services at each level are different. Lists the main protocols for each layer. Each layer of the specific protocol, I will be in the back one by one to learn.
OSI seven-layer model and TCP/IP five-layer model-Ethernet Base 01
