What is the role and significance of the OSI seven layer model in the development of computer networ

In a computer network, a computer can be seen as a layer of equipment in the OSI reference model.

Including physical networking media such as cavity front twisted pair, coaxial cable, cable connector, etc., the foundation of computer networking, at this layer, the data has not been organized. (1) Repeater: Its function is to amplify the signal, compensate for the signal attenuation, and support long-distance communication.

2) Hub: provide the function of signal amplification and relay, and have signal broadcasting. The difference between a repeater and a hub is the number of cables that connect the device.

A repeater usually has only two ports, while a hub usually has 4 to 20 or more ports. 2. Layer 2 data link layer: It controls the communication between the network layer and the physical layer.

1) Switches: physical addressing, network topology, error checking, frame sequence, and flow control. (2) Network card:

There are the functions of sending and receiving frames, encapsulating and unpacking frames, media access control, data encoding and decoding, and data caching 3, and the main function of the third layer network layer is to translate the network ground brigade clearance address into the corresponding physical address. (1) Router (gateway): connect different networks and select the line of information transmission.

2) The Layer 3 switch has a routing function, one route, multiple times.

The Open Systems Interconnection Model (OSI) is a reference model proposed by the International Organization for Standardization (ISO) in 1984. As a conceptual framework, it is a standard for devices and application software from different manufacturers to communicate in a network. Now this model has become the main structural model of Mt. Yama for communication between computers and networks.

The structure of most of the network communication protocols currently in use is based on the OSI model. OSI defines the communication process as seven layers, that is, the task of transferring information between networked computers into seven smaller, more manageable task groups. Each task or task group is assigned to each OSI layer.

Each layer exists independently, so the tasks assigned to each layer can be executed independently. This makes it possible to change the scheme provided by one of the layers without affecting the others.

Each layer of the OSI seven-layer model has clear features. Basically, Layers 7 to 4 handle end-to-end communication between the data source and the data destination, while Layers 3 to 1 handle communication between network devices. In addition, the seven layers of the OSI model can also be divided into two groups:

Upper (Layer 7, Layer 6, and Layer 5) and Lower Layers (Layer 4, Layer 3, Layer 2, and Layer 1). The upper layer of the OSI model deals with application problems and is usually applied only to software. The layer, i.e., the application layer, is the closest to the end user.

The lower layer of the OSI model is to handle data transfer. The physical layer and the data link layer are applied on both hardware and software. The lowest layer, the physical layer, is the closest to the physical network medium (e.g., wires) and is responsible for sending data on the medium.

The specific descriptions of each layer are as follows:

Layer 7: Application Layer defines the interface for communication and data transmission in the network - user programs;

Provision of standard services, such as the transfer and processing of virtual terminals, files and tasks;

Layer 6: Presentation Layer masks the differences in data formats between different systems;

Specify the data transmission format of the independent structure;

encoding and decoding of data; encryption and decryption; Compression and decompression Layer 5: Session Layer manages user sessions and conversations;

control the establishment and hanging up of logical connections between users;

Report an error that occurred in the previous layer.

Layer 4: Transport Layer manages end-to-end information transmission in the middle of the network;

Provide reliable and orderly packet delivery through error correction and flow control mechanisms;

Provide connection-free packet delivery;

Layer 3: Network Layer defines how data is transferred between network devices.

route packets based on the address of the network device;

Provides flow and congestion control to prevent loss of network resources.

Layer 2: Data Link Layer defines the program that operates the communication connection;

Encapsulating packets as data frames;

Monitor and correct packet transmission errors.

Layer 1: Physical Layer defines the physical way in which data is sent through network devices;

as an interface between network media and devices;

Define optical, electrical, and mechanical properties.

Summary. Application layer: provides an interface for communication between network service applications; Representation layer:

formatting data, processing encryption, compression, etc.; Session layer: realize the control of the session between two applications and support data flow; Transport layer: provides end-to-end reliable message transmission services; Network Layer:

Packets are transmitted to the correct network, and the routing algorithm determines the path of the data; Data Link Layer: Transmits a bitstream on a physical medium, which defines the method of accessing the physical medium; Physical Layer: Defines the encoding method and physical connection method between the transmission bitstreams on a physical medium.

There are 7 layers in the OSI hierarchical model, and the functions of each layer are briefly explained.

Application layer: provides an interface for communication between network service applications; Presentation layer: format data, handle encryption, compression, etc.; Session Layer:

Implement the session between two applications and support coarse and pure control of data flow; Transport layer: provides end-to-end reliable message transmission services; Network layer: Transmit data packets to the correct network, and the routing algorithm determines the path of the data; Data Link Layer:

Transmits a bitstream on a physical medium, which defines the method of accessing the physical medium; Physical Layer: Defines the encoding method and physical connection method between the transmission bitstreams on a physical medium.

Oh. 1. Suppose that Zao Shichang A sends a data block with a length of 200MB to the bench work leaseback station B with a bandwidth of 2MB s, the channel is optical fiber, and the two stations are 1000km apart, calculate the transmission delay and propagation delay?

Trouble directly look at the last question Trouble a little faster.

Good. There are several problems.

1. Suppose that Zao Shichang A sends a data block with a length of 200MB to the bench work leaseback station B with a bandwidth of 2MB s, the channel is optical fiber, and the two stations are 1000km apart, calculate the transmission delay and propagation delay?

The propagation delay is 1000km 2MB s, that is, 500s; The delay is 200MB 2MB s, which is 100s. Therefore, the total time without grip is 600s