Network Programming basics OSI/RM

When talking about the network, we can't go without talking about the OSI reference model. Although the actual application of the OSI reference model is not significant, it is indeed helpful to understand the internal operation of the network protocol, it also provides a good reference for us to learn network protocols. In the real world, TCP/IP protocol stacks have been widely used. I have seen many times in the above section, that is, I recently think this is indeed the case. During an interview, I was asked to talk about the OSI reference model, because I was expected to be asked this question before, so I prepared it. Now I think it's just like an idiot. My answer is to talk about the functions of each layer from the bottom up. It is obviously not a good method to describe the OSI reference model in a dialog mode. I thought about it and I should follow the following ideas. OSI/RM, a reference model for Open System Interconnection, is an Open System Interconnection model defined by ISO in Network Communication in 1978. It is a model describing network hierarchies and ensures the compatibility and interoperability of various network technologies. In the OSI reference model, information transmission between computers is divided into seven smaller and easier to manage problems. Each small problem is solved by a layer of the model. Layer 3 to Layer 3 belongs to the lower layer of the OSI network model and is responsible for creating network communication links. Layer 3 to Layer 3 is the high-level layer of the OSI communication model, and is responsible for end-to-end data communication. Each layer provides certain functions, and each layer directly provides services for the upper layer. The following is a brief overview of each Layer: 1. How does a Physical Layer use Physical media? The physical layer specifies the mechanical, electrical, functional, and process characteristics between activation, maintenance, and closure of the Communication endpoint. This layer provides a physical media for the upper-layer protocol to transmit data. At this layer, the unit of data is bit ). Representative of typical specifications defined by the physical layer include: EIA/TIA RS-232, EIA/TIA RS-449, V.35, RJ-45, etc. 2. How do I perform each step of the Data Link Layer? The data link layer provides reliable transmission on unreliable physical media. The role of this layer includes physical address addressing, data frame formation, traffic control, data error detection, and re-transmission. At this layer, the unit of data is frame ). Data link layer protocols include SDLC, HDLC, PPP, STP, and frame relay. 3. Which path does the Network Layer take? The network layer is responsible for routing and selection of packets between sub-networks. In addition, the network layer can implement congestion control, Internet interconnection, and other functions. At this layer, the unit of data is called packet ). Network Layer Protocols include IP, IPX, RIP, and OSPF. 4. Where is the Transport Layer? The transport layer is the first end-to-end, that is, the layer from the host to the host. The Transport Layer segments upper-layer data and provides end-to-end, reliable, or unreliable transmission. In addition, the transport layer also handles end-to-end Error Control and traffic control issues. At this layer, the unit of data is called a segment ). The Transport Layer Protocol includes TCP, UDP, and SPX. Who should talk to the Session Layer? Where can I start? The Session Layer manages session processes between hosts, that is, sessions between processes are established, managed, and terminated. The Session Layer also inserts verification points into the data to synchronize data. Session-layer protocols include NetBIOS and ZIP. 6. What does the Presentation Layer look like? The presentation layer changes the upper layer data or information to ensure that the application layer information of one host can be understood by applications of another host. Data conversion in the presentation layer includes data encryption, compression, and format conversion. Representatives of presentation layer protocols include ASCII, ASN.1, JPEG, and MPEG. 7. What does the Application Layer do? The application layer provides interfaces for operating systems or network applications to access network services. Application layer protocols include Telnet, FTP, HTTP, and SNMP. Post-reading: this is the content of the University's network course, but the examples here are more profound and easier to understand, laying the foundation for learning the current TCP/IP