During communication, there are two causes of terminal resistance signal reflection: impedance discontinuity and impedance mismatch.
Impedance discontinuity, the signal at the end of the transmission line suddenly meets the cable impedance is very little or no, the signal will cause reflection at this point. The principle of signal reflection is similar to the way light is reflected from one medium to another. To eliminate this reflection, a terminal resistance of the same size as the characteristic impedance of the cable must be spanded at the end of the cable, so that the impedance of the cable is continuous. Because the signal is transmitted bidirectionally ON the cable, A terminal resistor of the same size can be spanked at the other end of the communication cable.
Another cause of signal reflection is the impedance mismatch between the data transceiver and the transmission cable. The reflection caused by this reason is mainly manifested in the confusion of the whole network data when the communication line is in idle mode. To reduce the influence of reflected signal on the communication line, noise suppression and bias resistance are usually used. In practice, for small reflected signals, the method of adding bias resistance is often used for simplicity and convenience.