ISO OSI network architecture for computer network architecture

Physical layer. physical layer)

Function: Provides a way to establish, maintain, and release physical connections to enable bitstreaming on physical channels.

Transmission. Data link layer.

data link layer)

Function: It is a network layer that implements reliable data transmission on less reliable physical links. network layer)

Function: Implement packets between source and destination nodes on different networks.

Transmission (Data Link Layer.

It is only responsible for link management and frame transmission between two adjacent nodes in the same network), that is, to complete the communication sub.

Control of the normal operation of the network.

Transport layer. transport layer)

Function: Realize the end-to-end reliable transmission of communication subnet (to ensure the quality of communication) session layer

Function: Provides a user-facing connectivity service and is necessary to provide effective organization and synchronization of session activity.

means to provide control and management for data transfer.

Presentation layer functions: data encoding, data compression, data encryption, etc.

Application layer.

Physical layer bit streaming.

The data link layer provides media access, link control, and more.

Network layer addressing and routing.

Transport Layer establishes end-to-end connectivity to the host.

Session layer establishes, maintains, and manages sessions.

The presentation layer deals with data formats, data encryption, and more.

The application layer provides inter-program communication.

The architecture of a LAN is very different from that of an OSI. Its architecture has only the lower three layers of the OSI and no layers above the fourth layer. Even in the lower three layers, there are obvious differences between the two because the LAN is a shared broadcast channel, and there are many types of products, involving a variety of first-class access methods.

In a local area network, the physical layer is responsible for the physical connection and the transmission of bitstreams on the subject, and its main task is to describe some of the characteristics of the transport interface. This is the same as the physical layer of the OSI reference model.

However, due to the fact that the LAN can adopt a variety of transmissions, the processing process of the physical layer in the LAN is more complex. In general, the physical layer of most LANs is divided into two sublayers: one that describes the physical characteristics related to the transmission, and the other that describes the physical characteristics that are not related to the transmission.

In the local area network, the main function of the data link layer is to achieve reliable data transmission on the less reliable transmission channel through some data link layer protocols, and is responsible for the transmission and control of frames.

This is the same as the data link layer of the OSI reference model. However, in the local area network, because each station shares the common channel of the network, it is necessary to solve how to allocate the channel and how to avoid or solve the channel contention, that is, the data link layer must have the best access control function. Due to the variety of topologies and transmissions used in the local area network, and the corresponding access control methods, the parts related to transmission and the irrelevant parts should be separated in the data link function.

There is no network layer in the IEEE802 LAN reference model. This is because the topology of the LAN is very simple, and each site shares the transmission channel, and there is only one link between any two nodes, and there is no need for routing and flow control, so the network layer is not set separately in the LAN. This is different from the OSI reference model.

However, from an OSI point of view, the network device should be connected to the service access point SAP at the network layer. Therefore, although the network layer is not set in the LAN, the service access point SAP of the network layer is set at the interface between the LLC sublayer and the higher-layer protocol.

From the above analysis, it can be seen that the reference model of the LAN is only equivalent to the lowest two layers of the OSI reference model, and there is a big difference between the physical layer and the data link layer of the two. In the IEEE802 series of standards, there is a difference between the physical layer of each sub-standard and the access control MAC sub-layer, while the logical link control LLC sub-layer is the same, that is, the LLC sub-layer is actually a standard interface between the high-level protocol and any kind of MAC sub-layer.