TCP/IP protocol stack and OSI Reference Model detailed

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OSI Reference Model

OSI RM: Open Systems Interconnect Reference Model (open Systeminterconnection Reference Model)

The OSI Reference model has the following advantages:

• Simplifies the related network operation;
• Provide compatibility and standard interface between devices;
• promote standardization work;
• The structure can be separated;
• Easy to implement and maintain.

Since the 1960s, the computer network has been growing rapidly. In order to dominate in the field of data communication networks, major manufacturers have launched their own network architecture and standards, such as IBM's Sna,novell ipx/spx agreement, Apple's AppleTalk agreement, Dec DECnet, and the widely popular TCP /IP protocol. At the same time, the major manufacturers for their own agreement to produce different hardware and software. The joint efforts of various manufacturers have promoted the rapid development of network technology and the rapid growth of the types of network equipment. However, due to the coexistence of multiple protocols, the network becomes more and more complex, and the network devices between the manufacturers are mostly incompatible and difficult to communicate.

In order to solve the network compatibility problems, to help manufacturers to produce compatible network equipment, ISO in 1984, the OSI RM (Opensystem interconnection Reference model, open System Interconnect Reference Model). The OSI reference model quickly becomes the basic model of computer network communication. In designing the OSI Reference Model, the following principles are followed: there is a clear boundary between the layers to achieve a specific function, the division of the hierarchy is conducive to the development of international standards Agreement; The number of layers should be sufficient to avoid duplication of functionality across layers.

OSI layering

The OSI reference model is usually the first layer to the third layer called the underlying (lower layer), also known as the media layer (media layers), the bottom is responsible for data transmission in the network, network interconnection devices are often located in the next three layers, hardware and software to achieve the way. The fifth to seventh layers of the OSI reference model are called high-level (upper layer) and several layers (host layer), which are used to ensure the correct transmission of data and are implemented in software mode.

OSI Layer Seven features:

TCP/IP protocol stack

Because the OSI model and protocol are complex, they are not widely used.

TCP/IP (Transfer Control Protocol/internet protocol, Transmission Protocol/Internet Protocol) model has been widely used in practice because of its openness and ease of use, and the TCP/IP protocol stack has become the mainstream protocol of the Internet.

Each level of the TCP/IP model corresponds to a different protocol. The TCP/IP protocol stack is a collection of data communication protocols that contain many protocols. Its protocol stack name comes from the two most important protocols TCP (Transmission Control Protocol) and IP (Internet Protocol). The TCP/IP protocol stack is responsible for ensuring communication between network devices. It is a set of rules that specify how information is transmitted over the network.

Inter-layer communication and data encapsulation of TCP/IP model

Each layer of TCP/IP allows data to be transmitted over the network, and these tiers use PDUs (Protocol data units) to exchange information with each other to ensure communication between network devices.

A. When A TCP header is added to the transport layer data, the PDU is called segment (data segment);
B. The data segment is passed to the network layer, and the PDU obtained by adding IP header to the network layer is called packet (packet);
C. Packets are passed to the data link layer, and the PDU that encapsulates the data link layer header is called FRAME (data frame);
D. Frames are converted to bits and transmitted over the network media.

This protocol stack passes data down, and the process of adding headers and tails is called encapsulation, and after the data is encapsulated and transmitted over the network, the receiving device deletes the added information and determines how the data is passed along the protocol stack to the appropriate application based on the information in the header, a process known as unpacking. The peer layer of different devices relies on encapsulation and encapsulation to achieve mutual communication.

Physical Layer

Physical Layer Features:

• Specify the type of media, interface type, signaling type;
• Specification of electrical, mechanical, process and functional requirements for activating, maintaining and shutting down physical links between end systems;
• Specifications for levels, data rates, maximum transmission distances, and physical connectors.

TCP/IP protocol stack and OSI Reference Model detailed