Form of information. Information is represented as an analog or digital signal. It is transmitted as an analog or digital signal according to transmission media. For telecommunications, analog or digital data should be converted to an analog signal, especially in an analog channel. Transmission types include in Digital to digital signal, Analog to digital signal, Digital to analog signal, Analog to analog signal. There are two kinds of signals, and therefore, there are two kinds of channels. The channels are analog and digital. To transmit the signals without large loss, the signals should be converted to match the channel. The conversion process is called modulation. Furthermore, there are four types of transmissions. The digital signal is converted to a corresponding digital signal that is transmitted through a digital channel. In an analog to digital signal environment, an input signal is analog and the transmitting signal is digital, and the channel is also digital. Please click the “next” button. In the figure, the transmitting signals are analog. The telephone plays the role of converting an analog signal to other analog signals. In the second figure, the modem converts digital signals to analog signals. This case is for transmission through a digital channel. Codec and media play the roles of converting signals.