2024-07-11
한어Русский языкEnglishFrançaisIndonesianSanskrit日本語DeutschPortuguêsΕλληνικάespañolItalianoSuomalainenLatina
The Open Systems Interconnection (OSI) model is a conceptual model that represents how network communications work.
The Open Systems Interconnection (OSI) model is a conceptual model created by the International Organization for Standardization that supports the use of standards by various communication systems.protocolTo communicate. In simple terms,OSI provides standards for ensuring that different computer systems can communicate with each other.
One can think of the OSI model as a universal computer network language. According to this concept, the communication system is divided into seven abstract layers, which are stacked one on top of the other.
OSI ModelEach layer is responsible for handling specific tasks and communicating with the layers above and below it.DDoS attacksThe target is a specific network connection layer;Application layer attacksThe goalLevel 7, protocol layer attacks target layers 3 and 4.
While the modern Internet does not strictly follow the OSI model (it more strictly follows the simpler Internet Protocol Suite), the OSI model is still very helpful for troubleshooting network problems. Whether it's a single user who can't get online on their laptop, or a website that's down for thousands of users, the OSI model can help break down the problem and find its source. If you can narrow down the problem to a specific layer of the model, you can avoid a lot of unnecessary work.
The seven abstraction layers of the OSI model are defined as follows (from top to bottom):
This isThe only layer that directly contacts user dataSoftware applications, such as web browsers and email clients, rely on the application layer to initiate communications. However, it is important to be clear that client software applications are not part of the application layer; instead, the application layer is responsible for the protocols and data manipulation that the software relies on to present valid data to the user.
Application layer protocols include HTTP andSMTP(Simple Mail Transfer Protocol is a protocol that supportse-mailOne of the protocols for communication).
This layer is mainly responsible forPrepare the data, so that the application layer can use it; in other words, layer 6 is usedEnsure data is available to applicationsThe presentation layer is responsible for completingData conversion,encryptionand compression.
Two devices communicating with each other may use different encoding methods, soLayer 6 is responsible for converting incoming data into a syntax that can be understood by the receiving device's application layer.
If the devices are communicating over an encrypted connection, then Layer 6Responsible for encryption at the sender and decryption at the receiver, in order to present non-encrypted readable data to the application layer.
Finally, the presentation layer alsoResponsible for compressing data received from the application layer, and then passes the data to Layer 5. This helps minimize the amount of data to be transmitted, thereby increasing communication speed and efficiency.
This layer is responsible forTurns communication between two devices on and offThe time between the opening and closing of a communication is called a session. The session layer is responsible for ensuring that the session remains open long enough to transfer all exchanged data and then closes the session immediately to avoid wasting resources.
The session layer alsoResponsible for synchronizing data transfer and checkpointing.For example, if you are transferring a 100MB file, the session layer can set a checkpoint every 5MB. If the connection is lost or crashes after 52MB has been transferred, the session can be restored from the last checkpoint, which means that only 50MB of data needs to be transferred. Without checkpoints, the entire file must be transferred from the beginning.
Layer 4 is responsible for the communication between two devices.End-to-end communicationIt involves taking data from the session layer and breaking it into chunks (called segments) before sending it to layer 3.The receiving device's transport layer is responsible for reassembling the data segments to ensure that the data is usable by the session layer.
The transport layer is also responsible for flow control and error control. Flow control is used to determine the optimal transmission speed to prevent senders on fast connections from overwhelming receivers on slow connections. The transport layer provides error control on the receiving end by ensuring the integrity of the received data (or requesting a retransmission if it is incomplete).
Transport layer protocols include Transmission Control Protocol (TCP) andUser Datagram Protocol (UDP)。
Network layerResponsible for facilitating the transfer of data between two different networks. If the two communicating devices are on the same network, the network layer is not needed. The network layer breaks down the data segments sent by the transport layer into smaller units (calleddata pack), and then reassembles the packets on the receiving device. The network layer also determines the best physical path for the data to reach its destination; this is calledrouting。
Network layer protocols include IP, Internet Control Message Protocol (ICMP)， Internet Group Message Protocol (IGMP),as well as IPsec Kit.
The data link layer is very similar to the network layer, but the data link layer is used to facilitatesameThe transmission of data between two devices on a network. The data link layer extracts packets from the network layer and breaks them into smaller parts (called frames). Like the network layer, the data link layer is also responsible for flow control and error control of intra-network communications (the transport layer is only responsible for flow control and error control of inter-network communications).
This layer includes the physical equipment involved in data transmission, such as cables andswitchIt is also responsible for converting data into a bit stream, which is a string of 1s and 0s. In addition, the physical layers of the two devices must agree on a signaling convention to distinguish between the strings of 1s and 0s of the two devices.
In order to transmit human-readable information from one device to another over a network, the data must be transmitted down the seven layers of the OSI model at the sending device and then transmitted up the seven layers at the receiving end.
Mr. Cooper wants to send an email to Ms. Palme. Mr. Cooper composes the message in the email application on his laptop and clicks "Send."The email application passes the email to the application layer，Application layer mail protocol (SMTP)，Then pass the data to the presentation layer.then,Presentation layer compressed data，Then pass the data to the session layer，The communication session is initiated by the session layer。
The data will then reach the sender's transport layer.Segmentation at the transport layer,AgainBreak these segments into packets at the network layer,ThenAt the data link layer, it is further broken down into framesThe data link layer then passes these frames to the physical layer.The physical layer converts data into a bit stream of 1s and 0s,at lastSending data over a physical medium such as a cable。
Once Ms. Palme's computer receives the bit stream over a physical medium, such as her WiFi, the data flows through the same series of layers on her device, but in reverse order. First, the physical layer converts the bit stream from 1s and 0s into frames, which are passed to the data link layer. The data link layer then reassembles the frames into packets for the network layer. The network layer then reassembles the packets into segments for the transport layer, which reassembles the segments into fragments.
The data then flows to the recipient's session layer, which passes the data to the presentation layer and ends the communication session. The presentation layer decompresses the data and passes the raw data to the application layer. The application layer passes the human-readable data to Ms. Palme's email software so she can read Mr. Cooper's email on her laptop screen.
refer to:What is the OSI model? | Cloudflare (cloudflare-cn.com)
I have devoted myself to the research of technology for more than 30 years. I am proficient in various languages such as Java, Linux, JavaScript, PHP, CSS, etc. I have made many contributions in the field of open source. I have established a developer documentation site to share some problems in technology development for everyone to read.
