Characteristics of OSI Physical Layer
The physical layer is at the bottom of the OSI model, and its main function is to use the physical transmission medium to provide a physical connection for the data link layer to transmit bit streams. The physical layer defines how the cable is connected to the network card, and what transmission technology needs to be used to send data on the cable, and defines the access method of the upper layer (data link layer).
Usually, the equipment with certain data processing and sending and receiving capabilities is called data terminal equipment (DTE), and the equipment between the DTE and the transmission medium is called data circuit terminating equipment (DCE). DCE provides signal conversion and encoding functions between DTE and transmission medium, and is responsible for establishing, maintaining and releasing physical connections. Because the DCE is between the DTE and the transmission medium, during the communication process, the DCE transmits the data of the DTE to the transmission medium on the one hand, and on the other hand, it needs to transmit the bit stream received from the transmission medium to the DTE sequentially. , DCE needs the transmission of data information and control information, and needs to work in a high degree of coordination, so it is necessary to formulate the interface standards for DTE and DCE, these standards are physical interface standards.
And this standard defines four characteristics of the physical layer:
1. Mechanical characteristics: Define the characteristics of the physical connection, specify the specifications, interface shape, number of leads, number and arrangement of pins used in the physical connection, etc.
2. Electrical characteristics: When specifying the transmission of binary bits, the voltage range, impedance matching, transmission rate and distance limit of the signal on the line, etc.
3. Functional characteristics: indicate what the meaning of a certain level on a certain line means, and the purpose of the signal line whose interface is not visible
4. Procedure characteristics (process characteristics): define the working procedures and timing relationships of each physical circuit
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