What is the difference and connection between osi and tcp/ip

Difference: 1. TCP/IP is a protocol cluster, while OSI is a model; 2. TCP/IP is a five-layer structure, while OSI is a seven-layer structure; 3. The third layer of TCP/IP Only IP protocol is supported, OSI supports all network layer protocols. Connection: 1. OSI introduces the concepts of services, interfaces, protocols, and layers, while TCP/IP draws on the concepts of OSI; 2. OSI has models first, then protocols, standards first, and then practices, while TCP/IP IP first has protocols and applications and then proposes a model, which is the reference OSI model.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

OSI definition:

OSI (Open system interconnect), that is, open system interconnection. Generally called the OSI reference model, it is a network interconnection model studied by ISO (International Organization for Standardization) in 1985. In order to make the Internet more popular, ISO launched the OSI model. The implication is that all companies are recommended to use this specification to control their networks. In this way, all companies will have the same specifications and can interconnect.

OSI defines a seven-layer framework for network interconnection (physical layer, data link layer, network layer, transport layer, session layer, presentation layer, application layer)

Each layer Function:

• #Application layer: The application layer is the highest layer of the OSI reference model and is the interface between the user and the network.

• Presentation layer: The presentation layer handles the representation of data encoding flowing through nodes to ensure that the information sent by the application layer of one system can be read by the application layer of another system. Data formatting, data encryption

• Session layer: The main function of the session layer is to manage and coordinate the communication (dialogue) between various processes on different hosts, that is, it is responsible for establishing, managing and terminating Session establishment, management and maintenance between applications

• Transport layer: The role of the transport layer is to provide end-to-end reliable and transparent data transmission services for upper layer protocols, including error handling issues such as control and flow control.

• Network layer: The network layer provides services for the transport layer. The protocol data units transmitted are called packets or packets.

• Data link layer: The data link layer provides services for the network layer and solves communication problems between two adjacent nodes.

• Physical layer: The physical layer is the lowest layer of the OSI reference model, which uses the transmission medium to provide physical connections for the data link layer.

Each layer implements its own functions and protocols, and completes interface communication with adjacent layers. OSI service definitions detail the services provided by each layer. The service of a certain layer is a capability of that layer and the layers below it, which is provided to the higher layer through the interface. The services provided by each layer have nothing to do with how these services are implemented.

As we all know, the OSI reference model is an international academic and legal standard and a complete and authoritative network reference model. The TCP/IP reference model is the de facto international standard, that is, the network reference model that is widely used in real life.

The relationship between OSI and TCP/IP

OSI introduces the concepts of services, interfaces, protocols, and layers, and TCP/IP draws on them These concepts of OSI establish the TCP/IP model.

OSI has models first, protocols later, standards first, and practices later; TCP/IP, on the contrary, has protocols and applications first and then proposes a model, and it is a reference OSI model.

OSI is a theoretical model, while TCP/IP has been widely used and has become the de facto standard for network interconnection.

• TCP：transmission control protocol Transmission Control Protocol

• UDP：user data protocol User Datagram Protocol

The difference between OSI seven layers and TCP/IP:

1. TCP/IP is a protocol cluster; while OSI (Open Systems Interconnection) It is a model, and TCP/IP was developed before OSI.

2. TCP/IP is a hierarchical protocol made of some interactive modules, each of which provides specific functions; OSi specifies which function belongs to which layer.

3. The number of layers is different—TCP/IP is a five-layer structure, while OSI is a seven-layer structure. The highest three layers of OSI are represented by the application layer in TCP.

• Classic diagram

4. The third part of the TCP/IP model The TCP/IP model only supports IP protocols, and OSI supports all network layer protocols

5. The TCP/IP model supports cross-layer encapsulation; the OSI model does not support it; Cross-layer encapsulation is mainly used between non-terminal devices (PC...) Traffic communicating with each other, not long distance;

• When there is no transport layer, the IPV4 header will fragment the application layer traffic, and then fill the fragmentation information in the IPV4 header;

• Use protocol number to mark application layer traffic, protocol number 0-255;

• Protocol 6 marks the transport layer as TCP, protocol number 17 Indicates that the transport layer is UDP; all other numbers correspond to cross-layer encapsulation traffic; the ICMP protocol number is 1, OSPF is 89, and EIGRP88;

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