To put it simply, the delay is the

To put it simply, the delay is the time required from the first byte of data received by the sending end to the first byte of data output from the serial port of the receiving end. The delay in communication refers to the general term of transmission delay, equipment delay and propagation delay, that is, total delay = transmission delay + equipment delay + propagation delay. Transmission delay is the delay caused by the signal passing through the transmission medium. For example, the delay of an optical fiber is generally 5 μs / km. The device delay generally refers to the delay generated when the device processes the signal, which has a great relationship with the performance of the device and the selected devices. Such devices include repeaters, BTS amplifiers, tower-top amplifiers, etc. Propagation delay is the time delay that an electrical signal transmits from the sending end to the receiving end and the data is received in the air due to multipath or Doppler effects.