OSI seven-layer model and TCP/IP four-layer model

1) OSI seven-layer model and TCP/IP four-layer model

OSI layer Seven model: a standard system developed by the International Organization for Standardization (ISO) for interconnection between computers or communication systems. It is a seven-layer, abstract model that includes not only a series of abstract terms or concepts, but also specific protocols.

TCP/IP four-layer model: It is a reference model for the computer network's grandfather ARPANET and its subsequent internet use.

Comparison of 1.1.1:osi seven-layer model and TCP/IP model

A physical layer: contains a variety of physical media-related protocols, which are used to support TCP/IP communications.

• Electronic/Optical Protocol: Describes the various characteristics of the signal. For example: voltage, light intensity, bit timing, coding, signal waveform, etc.;
• Mechanical Agreement: Specifies the size of the connector or the metal component of the wire;
• Functional protocol: Describes what to do. For example: The function description on the 4th pin of the eia-232-d connector is "signal sending";
• Procedural protocol: Describes how to do it. For example: On the eia-232-d wire, the binary 1 indicates that the voltage is less than -3v;

B Data Link Layer: Contains the protocol to control the physical layer, is based on the data Link flow control and error control mechanism. For example: How to access and share media, how to identify the device on the media, data on the media before the completion of the data frame, etc.

C Network layer: It is mainly responsible for defining the format and address form of the packet, and routing the data through the logical network path;

D Transport Layer: Contains the protocol to control the network layer, is based on the logic link flow control and error control;

Note: The physical link (data link) refers to the connection relationship between two adjacent physical devices, and the logical link is the end-to-end connection of two devices, which may be separated by many network devices;

A brief introduction to the 1.1.2:osi seven-layer model

The application layer of the TCP/IP model corresponds to the session layer, presentation layer, and application layer of the OSI model. Some routing protocols use this layer, such as Border Gateway Protocol (BGP), routing Protocol (RIP), and so on, but the most common service for the application layer is to provide the interface to the user application to access the network.

1.1.3: Data encapsulation process

TCP Head: The TCP datagram, which contains the port number of the source and destination, is used to find the application process of the originating and receiving end;

IP head : Used to find the location of the destination host in the network in the logical network;

LLC Header : Responsible for identifying the network layer protocols and then encapsulating them. The LLC header tells the data link layer what to do with the packet once the frame is received. It works like this: the host receives the frame and views its LLC header to find the destination of the packet, for example, the IP protocol at the network layer.

MAC head : Used to find the location of the host in the network equipment;

OSI seven-layer model and TCP/IP four-layer model