What attribute layer and nominal layer?

The term property layer is rare. Generally, it is the difference between physical layer and nominal layer. Physical layer means that all floors in the building are counted from the first floor to the top floor from bottom to top. Nominal floors are divided into floor numbers according to the developer's distinction between floor uses. Generally, the first floor of a nominal floor is the first floor of an above-ground building.

Extended data:

Main problems to be solved in physical layer:

(1) The physical layer should shield physical devices, transmission media and communication means as much as possible, so that the data link layer will not feel these differences, and only consider completing the protocols and services of this layer.

(2) Give its service users (data link layer) the ability to transmit and receive bit streams (usually serial bit streams transmitted sequentially) on physical transmission media. Therefore, the physical layer should solve the problems of establishing, maintaining and releasing physical connections. ?

(3) The data circuit is uniquely identified between two adjacent systems.

The main function of physical layer is to provide data transmission path and data transmission for data terminal equipment.

1. provides data transmission path for data terminal equipment. The data path can be a physical medium or a combination of multiple physical media. A complete data transmission, including activating physical connection, transmitting data and terminating physical connection. Activation means that no matter how many physical media are involved, two data terminal devices need to be connected for communication to form a path.

2. In order to transmit data, the physical layer should form an entity suitable for data transmission and serve for data transmission.

The first is to ensure that the data can pass correctly.

The second is to provide enough bandwidth (bandwidth refers to the number of bits that can pass per second) to reduce the congestion on the channel. The data transmission mode can meet the needs of point-to-point, point-to-multipoint, serial or parallel, half-duplex or full-duplex, synchronous or asynchronous transmission.

3. Complete some management work of the physical layer. ?

Baidu encyclopedia-physical layer