physical layer
Physical layer: is the medium in which information is transmitted
Examples of physical layers: overhead wires, cables, fiber optics, wireless channels
What the physical layer transmits: high and low levels, 0s and 1s Example: 0110100010010010010
link layer
Three basic problems of the link layer
Encapsulation into a frame : It is to add a header and a trailer before and after a piece of data. Receiver to identify the start and end of the frame from the received bitstream
Description: For example, the data you want to send is 010, then add the first 100 and the tail 001, then all the data becomes 100010001
Transparent transmission: avoid confusion between message symbols and frame delimiter symbols;
Explanation: When the bit combination in the transmitted data happens to be exactly the same as a certain control information, appropriate measures must be taken so that the receiver will not mistake such data as some kind of control information. For example, the header is 1,000,000, and if the data you want to send is also 1,000,000, how can the other party not misjudge? It is stipulated that every 5 0s are filled with a 1, then the data you want to send will be changed to 10000010
Error detection: Prevents invalid data frames from errors and wastes network resources.
The link layer can no longer see 0 and 1, and directly manipulate bytes, such as FA, BE