Physical Layer of Computer Network

The physical layer of computer network I. Introduction The Physical Layer considers how to transmit data bit streams over the transmission media connected to various computers, instead of specific transmission media (such as twisted pair wires, coaxial cables, optical cables, and wireless channels ). Transmission media can be viewed as "Layer 3 ". 2. transmission rate of the channel's extreme information signal after modulation. There are two formulas for the maximum capacity of the channel: (1) in the formula, C indicates the transmission rate (B/s), W indicates the bandwidth (Hz), and M indicates the signal encoding level. It provides the upper limit of the transmission rate of the code element to avoid inter-code crosstalk under the assumption ideal conditions. In the real environment, there is another important factor to consider: noise. Based on this, Shannon gives the following formula. (2) Shannon formula: In formula, S/N is the signal-to-noise ratio, that is, the ratio of the average signal power to the average noise power. The significance of this formula is that as long as the information transmission rate is lower than the extreme information transmission rate of the channel, a certain method can be found to achieve error-free transmission.