explain how the modulator and demodulator when used in transmission of data across the Public Switched Telephone Network (PSTN). (4marks)

1. Modulator: The modulator's role in data transmission across the Public Switched Telephone Network (PSTN) is to convert digital signals into analog signals. This process is known as modulation. The modulator takes the binary data from the source device and converts it into an analog signal that can be transmitted over the PSTN. This is necessary because the PSTN was originally designed for voice communications, which are analog in nature. The modulator essentially translates the digital data into a format that the PSTN can handle.

2. Transmission: Once the digital data has been converted into an analog signal by the modulator, it is transmitted across the PSTN. The PSTN is a network of circuits that allows for voice and data communication. The analog signal travels over this network to its intended destination.

3. Demodulator: The demodulator's role is essentially the opposite of the modulator's. Once the analog signal reaches its destination, the demodulator converts it back into digital data. This process is known as demodulation. The demodulator takes the analog signal and translates it back into binary data that the receiving device can understand and process.

4. Reception: After the demodulator has converted the analog signal back into digital data, the data is received by the destination device. The device can then process the data as needed.

In summary, the modulator and demodulator play crucial roles in data transmission across the PSTN by converting digital data into analog signals and vice versa. This allows for the successful transmission and reception of data over a network that was originally designed for voice communications.